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U -Pb geochronology of zircons from river sediments in Sri Lanka:
Implications on early Archean to late Cambrian magmatism and episodic
crustal growth
Article · September 2018
DOI: 10.1016/j.jseaes.2018.08.029
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Full length article
U-Pb geochronology of zircons from river sediments in Sri Lanka:
Implications on early Archean to late Cambrian magmatism and episodic
crustal growth
Sanjeewa P.K. Malaviarachchia,b,1,⁎, Subhashani Bindusaraa, Prasanna Lakshitha Dharmapriyaa,
Ben-Can Suc, Li Sud, Ben-Xun Sue, Hong Zhangf, Chengli Zhangf, Krishnan Sajeevg,
Patrick Asamoah Sakyih, Melesse Alemayehui,j
a Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya 20400, Sri Lanka
bDepartment of Geology, Faculty of Science, Niigata University, Ikarashi 950-2181, Japan
c PetroChina Co Ltd of Changqing Oilfield Company Eighth Oil Production Plant, Xi’an 710000, China
dGeological Lab Center, China University of Geosciences, Beijing 100083, China
e Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
f Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, China
g Centre for Earth Science, Indian Institute of Science, Bangalore, India
hDepartment of Earth Science, School of Physical and Mathematical Sciences, University of Ghana, P.O. Box LG 58, Legon-Accra, Ghana
i School of Applied Natural Science, Applied Geology Department, Adama Science and Technology University, P.O. Box 1888, Adama, Ethiopia
j State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
A R T I C L E I N F O A B S T R A C T
Keywords: Geochronology of zircons from river-sediments in Sri Lanka has never been attempted. Here we present Rare
U–Pb geochronology Earth Elements (REE) and U-Pb isotopes of ∼700 zircon grains by laser ablation ICP-MS technique, from se-
Gondwana diments of the major rivers in the Sri Lankan basement (rivers of Mahaweli, Kelani, Kalu, Walawe, Maduru Oya
River sediment and Maha Oya). Most of the studied zircons display oscillatory zoning and Th/U > 0.1, confirming their igneous
Zircon origin. U-Pb age distribution of these river-sand zircons exhibits two major populations depicting
Sri Lanka
Mesoproterozoic to Archean (∼30%;> 1100–3100Ma) and Neoproterozoic to late Cambrian
(∼70%;> 430–1000Ma) magmatism. The two populations could be further resolved into intensive and epi-
sodic magmatic peaks at 480–680Ma, 680–1000Ma, 1100–1300Ma, 1300–1700Ma, 1700–1900Ma,
2100–2300Ma, 2300–2600Ma and 2600–3100Ma. These river-sediment-zircon data are consistent with the
principal episodes of global continental crustal growth and the recognized U-Pb ages of magmatism are mostly
correlative with those obtained from basement rocks by previous studies of Sri Lanka. The older zircons found in
this study may have mainly originated from reworked/recycled ancient (Palaoproterozoic to Archean) crust. A
younger zircon group of 450–700Ma with homogenous core-rim zoning texture and Th/U ratios< 0.1 were
inferred to be of metamorphic origin, indicating their possible crystallization at late Neoproterozoic meta-
morphic events, associated with the final assembly of the Gondwana Supercontinent. Thus, our data imply that
the present-day continental crust of Sri Lanka may have predominantly formed and grown in the Neoproterozoic,
while there is evidence that crustal growth began at least in the Paleoproterozoic. Further, the Mesoproterozoic
peaks of the frequency distribution of U-Pb ages of river-sand zircons at ∼1.6 Ga and ∼1.1 Ga might reflect
triggering of subduction in a paleo tectonic setting forming the Wanni and Vijayan dual arc systems, respec-
tively.
1. Introduction growth periods of the continental crust in the history of the Earth.
However, the continental crust may have experienced long-term ero-
Accurate dating of rocks is very essential for unravelling major sion and weathering whenever unroofed to the surface, so that most of
⁎ Corresponding author at: Department of Geology, Faculty of Science, Niigata University, Ikarashi 950-2181, Japan.
E-mail addresses: malavi@pdn.ac.lk, sanjeewa@geo.sci.niigata-u.ac.jp (S.P.K. Malaviarachchi).
1 Permanent address: Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya 20400, Sri Lanka.
https://doi.org/10.1016/j.jseaes.2018.08.029
Received 12 March 2018; Received in revised form 28 August 2018; Accepted 28 August 2018
1367-9120/ © 2018 Elsevier Ltd. All rights reserved.
Please cite this article as: Malaviarachchi, S.P.K., Journal of Asian Earth Sciences, https://doi.org/10.1016/j.jseaes.2018.08.029
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
the time all rock units were not well preserved. This perhaps, limits the 2.1. Lithological characteristics
opportunity for the entire rock succession to be successfully dated (e.g.
Iizuka et al., 2005; Kemp et al., 2006; Rino et al., 2008; Hawkesworth The HC is made up of granulitic meta-quartzites, marbles, calcsili-
et al., 2010, 2013; Condie et al., 2009, 2011). Thus, surveying of ages cates and metapelitic gneisses, intimately associated with charnockites
for all the rock units of a terrain is cumbersome and sometimes is very (Cooray, 1962, 1984; Mathavan and Fernando, 2001). Meta-sedimen-
difficult in practice (Xu et al., 2016). However, zircon geochronology or tary rocks such as marble and quartzite could be traced for more than
‘zirconology’, has been widely used to investigate provenance of ter- 40 km in the central and northeastern parts of the HC, while marble and
rains worldwide mainly due to the fact that zircon is a highly resistant quartzite in the southwestern parts of the HC are scarce (Mathavan
mineral to weathering, produced by magmatic crystallization or as a et al., 1999). Bands of wollastonite, diopside- and scapolite-bearing
result of metamorphic reactions. Thus, often zircons are entrapped in granulites and cordierite-bearing gneisses mainly occur in the south and
sedimentary rocks as ‘detrital zircons’, and commonly reworked in south western parts of the HC (Cooray, 1962, 1984; Hapuarachchi,
crust-mantle environments through multiple cycles. However, the U–Pb 1968; Mathavan et al., 1999; Perera, 1984; Prame, 1991). Typical high
age would represent the formation of the original source rocks from temperature (granulite facies) metamorphic conditions are well estab-
which the zircon grains were derived (e.g. Amidon et al., 2005; Alizai lished for the HC from meta-basaltic and gabbroic to intermediate rocks
et al., 2011; Su et al., 2011; Zheng et al., 2013; Deng et al., 2017). (Sandiford et al., 1988; Schumacher et al., 1990), charnockites and
Therefore, in addition to routine dating of zircons in rocks, those se- metamorphosed pelitic rocks (Perera, 1984, 1987; Prame, 1991, Hiroi
parated from river sands are also utilized in several studies (e.g. Iizuka et al., 1994, Raase and Schenk, 1994; Dharmapriya et al., 2016, 2017;
et al., 2005, 2013a,b; Rino et al., 2008; Yang et al., 2009; Wang et al., Fernando et al., 2017).
2009, 2011a,b; Xu et al., 2016; Sakyi et al., 2018), since they may have The HC granulites have been subjected to a folding and thrusting
preserved useful information for the age spectrum of the continental event after the peak metamorphic conditions (Berger and Jayasinghe,
crust throughout the Earth’s history. 1976; Kriegsman, 1995; Kleinschrodt, 1994). The large folds with wa-
The geology of the Sri Lankan basement is important to understand velengths of about 7–10 km and an exposed length parallel to their axes
the tectonics of the Proterozoic to Cambrian Earth due to its close up to 50 km in the central Highlands were formed at slightly lower
proximity to India, Madagascar and East Antarctica in the assembly of temperatures (700–750 °C) than the peak metamorphism (800–850 °C,
the Gondwana continent (e.g. Meert, 2003). Calc-silicate, Mg- and Al- 8–9 kbar) and hence the deformation has ended at granulite facies
rich meta-sedimentary, mafic to felsic meta-igneous and high- to ultra conditions (Kleinschrodt, 1994). Hiroi et al. (2014) reported evidence
high-temperature granulites together with amphibolites, migmatites, for fast exhumation of lower-crustal rocks to andalusite-stable upper-
minor gabbroic, granitic, pegmatitic and aplitic igneous intrusions crustal conditions by channel flow in a continental collision orogeny,
characterize the Sri Lankan basement (Cooray, 1994 and references based on felsic inclusions (granitic inclusions) within high grade or-
therein). Therefore, this tectonic amalgamation of amphibolite to dinary granulites and UHT granulites of the HC.
granulite-facies terrains with igneous intercalations consisting of di- The WC occurs northwest and west of the HC and is consists pre-
verse geochemical signatures in a small area within the Sri Lankan dominantly of upper amphibolite to granulite facies meta-igneous
terrain attracts great interest in the fields of petrology, geochronology gneisses and minor meta-sediments. The predominant meta-igneous
and structural geology. rocks show a vast range of protolith-chemistry from granitic, grano-
Despite many previous studies on zirconology of the basement rocks dioritic, monzonitic, tonalitic, charnockitic and enderbitic compositions
of Sri Lanka, the provenance, evolutionary history and the U–Pb isotope (e.g., Pohl and Emmermann, 1991). Garnet sillimanite gneisses, cor-
systematics of individual detrital zircon grains from the Sri Lankan river dierite gneisses, quartzites and calc-silicate rocks occur as minor meta-
systems have never been attempted. Therefore, we present a synthesis sediments, close to the inferred boundary with the HC. The western part
of U-Pb age data on various zircons sampled from major rivers in the Sri of the WC is mainly composed of less-deformed granites.
Lankan Precambrian basement (rivers of Mahaweli, Kelani, Kalu, The KC is a set of doubly plunging synforms, cropping out in the
Walawe, Maduru Oya and Maha Oya). These zircons show two major northwestern part of Kandy. It comprises upper amphibolite to granu-
populations depicting wide-spread magmatism dated as lite facies basement rocks (Kröner et al., 1991; Cooray, 1994). Relics of
Mesoproterozoic to Archean and Neoproterozoic to late Cambrian, primary magmatic layering are preserved in these synforms mainly
evidencing episodic crustal growth in the Sri Lankan basement. composed of hornblende gneisses, amphibolites and minor pyroxenites
(Kröner et al., 1991). Hornblende- and biotite-bearing ortho gneissic
2. Geological outline rocks are of calc-alkaline origin with gabbroic, dioritic and trondhje-
mitic compositions, interlayered with granodioritic to granitic gneisses,
The Sri Lankan Precambrian basement has been subdivided into four charnockites, enderbites and minor meta-sediments (Kröner et al.,
major terrains (e.g. Cooray, 1994), namely: the Highland (HC), Wanni 2003).
(WC), Vijayan (VC) and Kadugannawa (KC) complexes (Fig. 1), based on The VC is exposed in eastern Sri Lanka and consists predominantly
Nd isotope model age mapping and zircon geochronology (Milisenda of meta-igneous rocks, which are upper amphibolite-facies calc-alkaline
et al., 1988, 1994; Kröner et al., 1987, 1991). The WC occupies a higher granitoid gneisses including augen-gneisses, with minor amphibolite
crustal level than the HC although there is no clear structural break be- layers possibly derived from mafic dykes. This granitoid suite was in-
tween the rocks of the two complexes; probably the contact has been terpreted as a product of subduction-related magmatism (Pohl and
obliterated by later events (Voll and Kleinschrodt, 1991). The boundary Emmermann, 1991). The granitoid gneisses show TTG-dominated I-
between the VC and the HC is well defined as a thrust/shear contact type signatures (Milisenda, 1991; Pohl and Emmermann, 1991), while
(Hatherton et al., 1975; Vitanage, 1985; Voll and Kleinschrodt, 1991; the hornblende gneisses display compositions between diorite and
Kriegsman, 1995). Three tectonic klippens with petrological and structural leucogranite with the dominant compositions being granodiorite and
features similar to the HC are exposed in the southeastern part of Sri Lanka granite (Kröner et al., 1991; Milisenda, 1991; Kleinschrodt, 1994;
as inliers, namely Kataragama Klippe, Buttala Klippe and Kuda Oya Milisenda et al., 1994).
Klippe. The HC domain is interpreted to be a part of a supracrustal basin
developed in a suture zone with Lützow-Holm Complex in East Antarctica 2.2. Previous geochronology
at the last phase of Gondwana assembly (Shiraishi et al., 1994). The KC is
in contact with the WC and the HC. The WC, KC and VC domains were Ion microprobe U-Pb study on zircons by Kröner et al. (1987)
originated in Grenville-age arc-related settings (Kröner et al., 2003; documented late Archean to Paleoproterozoic ages (3.2–2.4 Ga) for
Willbold et al., 2004; Kröner et al., 2013). detrital grains from the HC meta-sediments. Also, they reported an
2
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 1. Simplified geologic map of Sri Lanka (after Cooray, 1994), showing river-sand sample localities of the major river basins of Sri Lanka, namely: Mahaweli,
Kelani, Kalu, Walawe, Maha Oya and Maduru Oya Rivers. Sample numbers are: Mahaweli (MHL2, RV-2b), Kelani (KEL2), Kalu (KLL1), Walawe (WAL1), Maha Oya
(MOL1, RV-3c) and Maduru Oya (MDL2).
intrusion age of 1.1 Ga and new zircon growth at about 550Ma in meta- metamorphism. Malaviarachchi and Takasu (2011) obtained ages of
igneous rocks. Milisenda et al. (1988) found Nd isotope model ages for ∼728–460Ma from monazite.
the HC at 3.0–2.2 Ga, indicating the HC was derived from late Archean The WC has Nd isotope modal ages of ca. 700–1.1 Ga and shows a
sources. Köhler et al. (1991) and Baur et al. (1991) reported U-Pb zircon wide spectrum of magmatic events as documented by zircon ages of
crystallization ages of 1940Ma and a Pb loss event at 560–550Ma, 1100–530Ma (Burton and O’Nions, 1990; Kröner et al., 1991, 2003).
indicating that high grade metamorphism. Kröner and Williams (1993) Massive charnockites from north of the WC have protolith emplacement
reported SHRIMP zircon ages for granitic gneiss from the HC as 1.9 Ga ages of ∼1 GaMa determined from zircon evaporation method (Kröner
for the crystallization of the igneous protolith and 531Ma as the age of et al., 1994). Deposition of detrital zircons in meta-pelites and the
3
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Table 1 zircon 91,500 (Wiedenbeck et al., 1995) as external standard. Zircon
Sample locations of zircons in Sri Lankan river sands. standard TEMORA (417Ma) from Australia (Black et al., 2003) is also
River Sample no. Location Coordinates used as a secondary standard to supervise the deviation of age mea-
surement/calculation.
Mahaweli MHL2 (n= 72) Manampitiya 7.9121° N, 81.0899° E Samples RV-2b and RV-3c were mounted in epoxy resins and po-
RV-2b (n= 88) Mahiyangana 7.3312° N, 80.9880° E lished down to near half sections to expose internal structures, and then
Kelani KEL2 (n=88) Sedawatta 6.9540° N, 79.8827° E
Kalu KLL1 (n= 112) Kaluthara 6.5922° N, 79.9657° E analyzed at Key Laboratory of Continental Dynamics, Northwest
Walawe WAL1 (n= 88) Ambalantota 6.1063° N, 81.0158° E University in Xi’an, using a Geolas 193 nm laser ablation system cou-
Maduru Oya MDL2 (n= 85) Aralaganwila 7.7577° N, 81.1776° E pled with an Agilent 7700x mass spectrometer using analytical proce-
Maha Oya MOL1 (n= 50) Kochchikade 7.2710° N, 79.8654° E dures of Yuan et al. (2004). Using a combination of cathodolumines-
RV3c (n= 75) Alawwa 7.2942° N, 80.2420° E cence (CL) and optical microscopy, the zircon crystals with the internal
structure were selected as suitable targets for laser ablation analyses.
emplacement of magmatic zircons of charnockitic and enderbitic rocks Laser ablation was operated at a constant energy 60mJ and a repetition
yielded ion microprobe U-Pb concordia upper intercept ages of∼1.1 Ga rate of 6 Hz, with a spot diameter of 30 μm, using external standards of
as their precursor protolith timings. The respective lower intercept ages 91,500 and NIST 612 for U-Pb age and trace elements, respectively.
range between 540 and 590Ma, re ecting high-grade metamorphism. Isotopic ratios and element concentrations of zircons were calcu-fl
Nd-model ages of the rocks from the KC range between ∼900Ma lated using GLITTER (ver. 4.4, Macquarie University). Concordia ages
and 1.6 Ga (Milisenda et al., 1988, 1994). Pb-Pb zircon evaporation and diagrams were obtained using Isoplot/Ex (3.0) (Ludwig, 2003). The
ages for the KC yielded ∼770Ma – 1.1 Ga, indicating multiple calc- common Pb was corrected using LA-ICP-MS Common Lead Correction
alkaline magmatic activities, covering a period of approx. 300Ma (ver. 3.15), followed the method of Andersen (2002). All the quoted age
(Kröner et al., 2003; Willbold et al., 2004). Most of the dioritic to uncertainties are at 2 sigma level.
granodioritic rocks of the KC display ca. 900Ma ages. Xenomorphic
zircons of gabbroic gneisses yielded relatively younger ages of 4. Samples
∼700Ma while idiomorphic zircons from the same sample gave ages of
∼900Ma (Kröner et al., 2003; Willbold et al., 2004). In the present work, we contribute new data on Rare Earth Elements
Milisenda et al. (1988, 1994) reported whole-rock Nd isotope ana- (REE) and U–Pb ages of zircons in sand from the major rivers of Sri
lyses of the VC rocks and found a mean crustal residence ages of Lanka. The data included in this paper come from the Mahaweli (MHL2,
1.0–1.8 Ga. These authors also found that their Sr isotope data are in RV-2b), Kelani (KEL2), Kalu (KLL1), Walawe (WAL1), Maha Oya
line with the Nd isotope results, suggesting that the majority of the VC (MOL1, RV-3c) and Maduru Oya (MDL2) rivers in Sri Lanka (Table 1;
rocks were juvenile and derived from a typical LREE-depleted, mantle- Fig. 1). These rivers drain a large area covering more than half of the Sri
derived precursor and not from anatexis of older crustal lithologies Lankan continental block. Also, the large catchment area of these rivers
(Milisenda et al., 1988, 1994; Kröner et al., 1991). Rb–Sr whole-rock located in the core portions of all the litho-tectonic units of Sri Lanka is
isochron ages of ∼800Ma by De Maesschalck et al. (1990) were as- composed of high-grade metamorphic rocks. The zircon grains from six
cribed to metamorphic resetting. Magmatic zircons re ect emplace- rivers were investigated for morphology, REE analysis and U-Pb dating.fl
ment of the protoliths of the Vijayan gneisses at 1000–1100Ma (Kröner Most of the analyzed zircons are euhedral to subhedral in shape, col-
et al., 2013). orless to dark, and range in size from 25 to 400 µm, where most zircons
(∼80–85%) display oscillatory zoning patterns implying their mag-
matic origin (Fig. 2). Metamorphic zircons appear in CL images as
3. Methodology more-or-less homogeneous and/or have overgrowth rims on detrital
cores, constituting up to ca. 15–20% of total grains studied.
Heavy mineral separation from river sand samples was performed at
the Department of Geology, Faculty of Science, University of 5. Results
Peradeniya. Zircons were further refined by gravimetric methods and
finally handpicked at Indian Institute of Science, Bangalore, India. The The zircon grains from the six rivers were analyzed for morphology,
separated zircons from six samples (MHL2, KEL2, KLL1, WAL1, MOL1 REE and U-Pb isotopes. U-Pb age data are tabulated in the Table 2 and
and MDL2) were then mounted in epoxy resins and polished down to REE are given in Supplementary Tables 1–6. The CL images of re-
near half sections at the Institute of Geology and Geophysics, Chinese presentative zircon grains are shown in Figs. 2 and 3. Approximately
Academy of Sciences (IGGCAS), Beijing, China. The internal structure 100 spots in zircon from each river were analyzed for U/Pb ages and
of zircons was studied with a NOVA NanoSEM scanning electron mi- only those with discordance<10% were considered for age data in-
croscope at IGGCAS. U-Pb dating of the above-mentioned six samples terpretations. The results are displayed graphically for each river in
was carried out using LA-ICPMS at the China University of Geoscience, concordia diagrams and U–Pb age histograms (Figs. 4–6). Th/U vs. age
Beijing, following analytical procedures described in Song et al. (2005, is plotted in the Fig. 7 and chondrite-normalized REE plots are shown in
2010). The laser ablation instrument couples a quadrupole ICP-MS Fig. 8. From the grains which plot off the U–Pb concordia curve, a true
(Agilient 7500a) and a UP-193 Solid-State laser (193 nm, New Wave discordant age was not obtained, because the zircons may be mutually
Research Inc.) with the automatic positioning system. For the present unrelated in their genesis. The results used for age interpretations here
work, laser spot size was set to ∼36 μm for most analyses and to 25 μm are only from grains with> 90% concordance. Further, we used
for metamorphic rims, laser energy density at 8.5 J/cm2 and repetition 207Pb/206Pb ages for the zircon grains with age>1.0 Ga and
rate at 10 Hz. The procedure of laser sampling is 5-s pre-ablation, 20-s 206Pb/238U ages for those< 1.0 Ga.
sample-chamber flushing and 40-s sampling ablation. The ablated ma- Most of the zircon grains from the Mahaweli River are rounded to
terial is carried into the ICP-MS by the high-purity Helium gas stream elongated and subhedral-anhedral in shape. These grains are big in size
with flux of 0.8 L/min. The whole laser path was fluxed with N2 (15 L/ and vary from 150 to 400 µm in length. They show oscillatory zoning,
min) and Ar (1.15 L/min) in order to increase energy stability. The core–rim texture and homogeneous appearance in CL images (Fig. 3a).
counting time for U, Th, 204Pb, 206Pb, 207Pb and 208Pb is 20ms, and is One hundred and eighty eight spots on 160 grains were analyzed.
15 ms for other elements. Calibrations for the zircon analyses were Grains younger than ∼700Ma closely plot on the concordia line
carried out using NIST 610 glass as an external standard and Si as in- (Fig. 4a). Zircon data from the Mahaweli River show a prominent peak
ternal standard. U–Pb isotope fractionation effects were corrected using at 560Ma and minor peaks from 730 to 2450Ma (Fig. 5a, g).
4
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 2. Cathodoluminescence (CL) images of the studied zircons from the major river basins of Sri Lanka. Representative age data (analytical spot is marked with a
circle) are also noted on the grains. Magmatic zircons are characterized by clear oscillatory zoning while, metamorphic grains are homogeneous and/or have core-rim
zones/overgrowths peculiar to different age populations. See text for details. Sample numbers are same as those in Fig. 1.
The zircon grains from the Kelani River are rounded to elongated homogeneous appearance in CL images (Fig. 3d). One hundred spots on
and subhedral-anhedral in shape. These grains vary from 50 to 250 µm 88 grains were analysed. Grains younger than ∼800Ma and as old as
in size. They show oscillatory zoning, core–rim texture and homo- ∼2 Ga closely plot on the Concordia line. Further, these grains define a
geneous appearance in CL images (Fig. 3b). Ninety-eight spots on 88 clear Discordia line as well, with a lower and upper intercept of
grains were analyzed. Grains younger than ∼1 Ga closely plot on the ∼600Ma and 1.8 Ga, respectively (Fig. 4d). Zircons from the Walawe
concordia line (Fig. 4b). Zircons from the Kelani River show two major River are characterized with a major peak shooting at 570–605Ma
peaks at 530 and 560Ma, together with significant multiple peaks from along with characteristic composite peaks from 1250 to 2100Ma and
660 to 2300Ma (Fig. 5b). subordinate peaks at 470, 700 and 870Ma (Fig. 5d).
From the Kalu River, most of the zircon grains are rounded to The Maduru Oya samples contain zircons rounded to elongated and
elongated and subhedral to anhedral in shape. These grains are rela- subhedral to anhedral in shape. These grains are relatively small and
tively small and vary from 25 to 200 µm in size. They show oscillatory vary from 100 to 400 µm in size. They show oscillatory zoning, cor-
zoning, core–rim texture and homogeneous appearance in CL images e–rim texture and homogeneous appearance in CL images (Fig. 3e). One
(Fig. 5c). One hundred and twenty spots on 112 grains were analyzed. hundred spots on 85 grains were analyzed. Grains younger than∼1 and
Grains younger than ∼700Ma closely plot on the concordia line ∼1.8 Ga closely plot on the concordia line (Fig. 4e). The Maduru Oya is
(Fig. 4c). Interestingly, zircons of Kalu River display five major peaks characterized by a clear peak at ∼550–580Ma, while having sub-
from 550 to 930Ma together with some minor peaks staring from ordinate peaks in the range of 460–2600Ma (Fig. 5e).
460Ma to 2200Ma. Obtained zircon grains from the Maha Oya are rounded to elongated
Rounded to elongated and subhedral to anhedral zircons were ob- and subhedral to anhedral in shape. These grains are relatively small
served in the Walawe River sample. These grains vary from 50- to and vary from 50 to 200 µm in size. They show oscillatory zoning,
200 µm in size. They show oscillatory zoning, core–rim texture and core–rim texture and homogeneous appearance in CL images (Fig. 3f).
5
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
6
Table 2
Measured U-Pb isotope ratios and age data of the river sand zircon from Sri Lanka.
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
Mahaweli MHL2-01 0.05491 0.00196 0.69040 0.02417 0.09117 0.00124 0.02703 0.00066 409 54 533 15 562 7 539 12 5.16% 0.44
MHL2-02 0.05857 0.00132 0.71575 0.01574 0.08861 0.00114 0.02653 0.00060 551 26 548 9 547 7 529 29 0.18% 0.36
MHL2-03 0.11466 0.00132 5.13048 0.05834 0.32445 0.00387 0.08989 0.00114 1875 10 1841 10 1811 19 1740 29 3.53% 0.71
MHL2-05 0.05870 0.00075 0.76740 0.00967 0.09480 0.00113 0.02708 0.00039 556 12 578 6 584 7 540 13 1.03% 0.28
MHL2-06 0.05860 0.00079 0.77394 0.01030 0.09577 0.00115 0.02756 0.00043 552 13 582 6 590 7 550 11 1.36% 0.24
MHL2-07 0.05919 0.00410 0.73326 0.05015 0.08983 0.00149 0.02591 0.00056 574 10 558 29 555 9 517 12 0.54% 1.78
MHL2-08 0.05801 0.00120 0.72913 0.01469 0.09114 0.00117 0.02668 0.00042 530 23 556 9 562 7 532 20 1.07% 0.80
MHL2-09 0.05852 0.00084 0.75587 0.01058 0.09367 0.00113 0.02714 0.00036 549 14 572 6 577 7 541 6 0.87% 0.93
MHL2-10 0.05805 0.00120 0.73644 0.01478 0.09200 0.00117 0.02718 0.00044 532 23 560 9 567 7 542 22 1.23% 0.69
MHL2-11 0.06039 0.00120 0.81702 0.01305 0.09812 0.00116 0.03028 0.00035 618 44 606 7 603 7 603 5 0.50% 0.17
MHL2-12 0.06025 0.00081 0.91132 0.01196 0.10967 0.00132 0.03128 0.00083 613 13 658 6 671 8 623 10 1.94% 0.05
MHL2-13 0.05830 0.00079 0.77355 0.01028 0.09621 0.00116 0.02735 0.00043 541 13 582 6 592 7 545 10 1.69% 0.23
MHL2-16 0.11361 0.00127 5.55319 0.06165 0.35443 0.00420 0.09144 0.00120 1858 10 1909 10 1956 20 1769 14 5.01% 0.26
MHL2-17 0.06032 0.00106 0.84259 0.01102 0.10131 0.00118 0.03127 0.00037 615 39 621 6 622 7 622 25 0.16% 0.07
MHL2-18 0.05982 0.00071 0.81574 0.00956 0.09888 0.00117 0.03080 0.00047 597 12 606 5 608 7 613 52 0.33% 0.11
MHL2-19 0.05861 0.01187 0.70889 0.14184 0.08771 0.00304 0.02816 0.00169 553 43 544 84 542 18 561 15 0.37% 1.03
MHL2-20 0.05946 0.01375 0.74330 0.17007 0.09065 0.00331 0.02672 0.00188 584 34 564 99 559 20 533 15 0.89% 1.01
MHL2-21 0.05917 0.01340 0.72649 0.16327 0.08902 0.00277 0.02908 0.00197 573 42 554 96 550 16 579 17 0.73% 0.95
MHL2-22 0.05899 0.00253 0.73260 0.03087 0.09005 0.00130 0.02715 0.00059 567 66 558 18 556 8 541 10 0.36% 0.89
MHL2-24 0.05769 0.00109 0.72358 0.01340 0.09095 0.00114 0.02719 0.00040 518 20 553 8 561 7 542 14 1.43% 0.91
MHL2-25 0.05825 0.00151 0.74630 0.01894 0.09291 0.00122 0.02768 0.00054 539 33 566 11 573 7 552 15 1.22% 0.54
MHL2-27 0.05883 0.00167 0.73771 0.02042 0.09092 0.00121 0.02869 0.00055 561 37 561 12 561 7 572 11 0.00% 0.63
MHL2-29 0.05937 0.00079 0.87391 0.01147 0.10674 0.00128 0.02978 0.00045 581 13 638 6 654 7 593 12 2.45% 0.26
MHL2-30 0.11652 0.00171 5.74205 0.08179 0.35734 0.00450 0.09768 0.00157 1904 11 1938 12 1970 21 1884 14 3.35% 0.67
MHL2-32 0.05771 0.00162 0.67227 0.01843 0.08446 0.00113 0.02734 0.00048 519 37 522 11 523 7 545 16 0.19% 0.77
MHL2-33 0.05824 0.00214 0.70477 0.02543 0.08775 0.00123 0.02672 0.00072 539 54 542 15 542 7 533 13 0.00% 0.55
MHL2-34 0.05823 0.00108 0.72509 0.01319 0.09029 0.00113 0.02820 0.00048 538 20 554 8 557 7 562 25 0.54% 0.45
MHL2-35 0.05790 0.00186 0.72457 0.02269 0.09074 0.00126 0.02511 0.00094 526 44 553 13 560 7 501 18 1.25% 0.37
MHL2-37 0.05881 0.00094 0.78841 0.01231 0.09721 0.00119 0.02770 0.00111 560 16 590 7 598 7 552 9 1.34% 0.07
MHL2-39 0.05834 0.00133 0.72541 0.01620 0.09016 0.00115 0.02710 0.00129 543 27 554 10 556 7 540 19 0.36% 0.11
MHL2-40 0.05962 0.00099 0.78731 0.01278 0.09575 0.00118 0.02792 0.00054 590 17 590 7 589 7 557 43 0.17% 0.27
MHL2-43 0.05902 0.00080 0.87299 0.01164 0.10726 0.00129 0.02999 0.00053 568 13 637 6 657 8 597 10 3.04% 0.15
MHL2-44 0.05777 0.00204 0.69242 0.02394 0.08691 0.00124 0.02718 0.00062 521 51 534 14 537 7 542 33 0.56% 0.64
MHL2-45 0.05789 0.00245 0.70314 0.02931 0.08807 0.00126 0.02732 0.00068 526 66 541 17 544 7 545 20 0.55% 0.61
MHL2-46 0.05915 0.00570 0.76338 0.07274 0.09358 0.00182 0.02845 0.00075 573 15 576 42 577 11 567 14 0.17% 2.02
MHL2-47 0.05559 0.00118 0.71519 0.01473 0.09328 0.00122 0.02746 0.00048 436 24 548 9 575 7 548 23 4.70% 0.81
MHL2-48 0.05828 0.00158 0.72230 0.01912 0.08986 0.00120 0.02651 0.00061 540 35 552 11 555 7 529 12 0.54% 0.49
MHL2-49 0.16040 0.00203 10.22051 0.12748 0.46203 0.00559 0.11652 0.00169 2460 10 2455 12 2449 25 2228 13 0.45% 0.57
MHL2-50 0.06216 0.00172 0.79730 0.02154 0.09301 0.00124 0.02576 0.00053 680 35 595 12 573 7 514 19 3.84% 0.61
MHL2-51 0.05934 0.00176 0.74546 0.02157 0.09110 0.00124 0.02671 0.00059 580 39 566 13 562 7 533 19 0.71% 0.64
MHL2-52 0.11072 0.00142 4.80724 0.06055 0.31484 0.00380 0.08381 0.00126 1811 10 1786 11 1764 19 1627 19 2.66% 0.27
MHL2-54 0.05822 0.00102 0.74054 0.01261 0.09224 0.00115 0.02658 0.00046 538 18 563 7 569 7 530 15 1.05% 0.47
MHL2-57 0.05894 0.00090 0.81571 0.01224 0.10035 0.00123 0.02855 0.00057 565 15 606 7 616 7 569 30 1.62% 0.15
MHL2-58 0.05896 0.00097 0.78328 0.01259 0.09633 0.00119 0.02808 0.00068 566 16 587 7 593 7 560 30 1.01% 0.13
MHL2-59 0.05937 0.00081 0.88009 0.01178 0.10749 0.00130 0.03030 0.00055 581 13 641 6 658 8 603 13 2.58% 0.09
MHL2-60 0.06181 0.00182 0.84404 0.02256 0.09905 0.00123 0.03048 0.00076 667 65 621 12 609 7 607 16 1.97% 0.12
MHL2-61 0.05855 0.00104 0.77112 0.01332 0.09550 0.00119 0.02790 0.00045 550 18 580 8 588 7 556 11 1.36% 0.79
MHL2-64 0.05852 0.00085 0.85308 0.01210 0.10571 0.00129 0.02922 0.00052 549 14 626 7 648 8 582 21 3.40% 0.15
MHL2-67 0.05992 0.00086 0.86559 0.01221 0.10475 0.00128 0.02942 0.00052 601 14 633 7 642 7 586 18 1.40% 0.14
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
7
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
MHL2-68 0.06534 0.00098 1.02132 0.01492 0.11335 0.00139 0.04404 0.00080 785 14 715 7 692 8 871 22 3.32% 0.13
MHL2-69 0.05956 0.00109 0.73180 0.01308 0.08910 0.00112 0.02629 0.00047 588 19 558 8 550 7 525 13 1.45% 0.53
MHL2-70 0.05870 0.00096 0.75002 0.01198 0.09265 0.00115 0.02553 0.00044 556 16 568 7 571 7 510 17 0.53% 0.41
MHL2-71 0.05814 0.00163 0.68826 0.01887 0.08584 0.00116 0.02572 0.00052 535 37 532 11 531 7 513 9 0.19% 0.78
MHL2-72 0.05779 0.00242 0.72469 0.02975 0.09093 0.00133 0.02790 0.00073 522 64 553 18 561 8 556 18 1.43% 0.63
MHL2-75 0.05884 0.00122 0.74627 0.01507 0.09197 0.00119 0.02712 0.00047 561 23 566 9 567 7 541 14 0.18% 1.07
MHL2-76 0.05881 0.00160 0.73619 0.01947 0.09077 0.00123 0.02646 0.00056 560 34 560 11 560 7 528 36 0.00% 0.67
MHL2-78 0.05794 0.00096 0.85321 0.01375 0.10678 0.00133 0.02815 0.00056 527 16 626 8 654 8 561 9 4.28% 0.22
MHL2-79 0.06029 0.00104 0.84448 0.01417 0.10157 0.00127 0.02810 0.00059 614 17 622 8 624 7 560 11 0.32% 0.22
MHL2-80 0.05868 0.00130 0.76666 0.01645 0.09474 0.00124 0.02741 0.00057 555 25 578 9 584 7 547 18 1.03% 0.51
MHL2-81 0.05864 0.00090 0.75503 0.01130 0.09336 0.00115 0.02715 0.00044 554 15 571 7 575 7 541 2 0.70% 0.70
MHL2-84 0.05877 0.00138 0.78425 0.01796 0.09676 0.00127 0.02839 0.00055 559 28 588 10 595 7 566 14 1.18% 0.74
MHL2-85 0.06135 0.00128 0.90176 0.01528 0.10660 0.00130 0.03284 0.00039 652 46 653 8 653 8 653 5 0.00% 0.11
MHL2-88 0.06179 0.00118 0.92103 0.01363 0.10811 0.00130 0.03327 0.00087 667 42 663 7 662 8 662 8 0.15% 0.01
MHL2-89 0.06132 0.00125 0.89002 0.01454 0.10527 0.00127 0.03243 0.00039 650 45 646 8 645 7 645 12 0.16% 0.08
MHL2-90 0.05813 0.00743 0.72321 0.09151 0.09022 0.00207 0.02634 0.00148 535 14 553 54 557 12 525 9 0.72% 0.77
MHL2-92 0.05989 0.00213 0.70010 0.02324 0.08478 0.00110 0.02619 0.00038 600 79 539 14 525 7 522 7 2.67% 0.27
MHL2-94 0.06050 0.00097 0.80224 0.01255 0.09615 0.00119 0.02813 0.00053 622 16 598 7 592 7 561 7 1.01% 0.14
MHL2-95 0.05887 0.00140 0.72074 0.01671 0.08878 0.00116 0.02748 0.00062 562 28 551 10 548 7 548 9 0.55% 0.32
MHL2-96 0.05911 0.00096 0.76749 0.01213 0.09415 0.00117 0.02406 0.00045 571 16 578 7 580 7 481 10 0.34% 0.18
RV-2b-92 0.07055 0.00098 1.09690 0.01268 0.11274 0.00080 0.04184 0.00041 945 28 752 6 689 5 829 8 9.18% 0.29
RV-2b-93 0.06840 0.00130 0.97435 0.01672 0.10330 0.00082 0.05437 0.00117 881 39 691 9 634 5 1070 22 8.99% 0.08
RV-2b-64 0.06724 0.00223 0.93512 0.02949 0.10084 0.00110 0.02722 0.00110 845 67 670 15 619 6 543 22 8.24% 0.16
RV-2b-79 0.06640 0.00104 0.90702 0.01238 0.09906 0.00073 0.06045 0.00091 819 33 656 7 609 4 1186 17 7.65% 0.09
RV-2b-39 0.07489 0.00170 1.46548 0.03083 0.14188 0.00127 0.04925 0.00082 1066 45 916 13 855 7 972 16 7.13% 0.36
RV-2b-54 0.06895 0.00241 1.09280 0.03658 0.11494 0.00132 0.04120 0.00085 897 71 750 18 701 8 816 17 6.93% 0.56
RV-2b-36 0.06374 0.00344 0.78696 0.04110 0.08953 0.00140 0.02923 0.00189 733 27 589 23 553 8 582 37 6.64% 0.16
RV-2b-84 0.06255 0.00090 0.72150 0.00878 0.08365 0.00059 0.02916 0.00033 693 30 552 5 518 4 581 7 6.51% 0.20
RV-2b-94 0.07494 0.00210 1.55273 0.04120 0.15026 0.00154 0.04402 0.00073 1067 55 952 16 902 9 871 14 5.45% 0.72
RV-2b-24 0.06477 0.00176 0.89564 0.02291 0.10027 0.00095 0.04479 0.00103 767 56 649 12 616 6 886 20 5.42% 0.19
RV-2b-56 0.07544 0.00281 1.60095 0.05731 0.15390 0.00192 0.04774 0.00106 1080 73 971 22 923 11 943 20 5.18% 0.67
RV-2b-57 0.06379 0.00181 0.85243 0.02281 0.09691 0.00094 0.03610 0.00083 735 59 626 13 596 6 717 16 4.98% 0.25
RV-2b-35 0.06630 0.00102 1.02364 0.01364 0.11195 0.00083 0.04840 0.00082 816 32 716 7 684 5 955 16 4.62% 0.09
RV-2b-04 0.06160 0.00383 0.74429 0.04496 0.08761 0.00152 0.02712 0.00136 660 23 565 26 541 9 541 27 4.34% 0.31
RV-2b-34 0.06117 0.00317 0.72111 0.03620 0.08548 0.00125 0.02706 0.00084 645 22 551 21 529 7 540 16 4.27% 0.53
RV-2b-30 0.06182 0.00229 0.76372 0.02712 0.08957 0.00100 0.02677 0.00051 668 11 576 16 553 6 534 10 4.20% 0.75
RV-2b-72 0.07377 0.00226 1.53880 0.04479 0.15127 0.00165 0.04758 0.00074 1035 61 946 18 908 9 940 14 4.17% 0.98
RV-2b-52 0.06928 0.00107 1.23694 0.01660 0.12947 0.00096 0.04449 0.00043 907 32 818 8 785 5 880 8 4.15% 0.49
RV-2b-32 0.16787 0.00221 10.23509 0.11269 0.44210 0.00358 0.11946 0.00168 2537 22 2456 10 2360 16 2281 30 7.48% 0.31
RV-2b-107 0.06622 0.00242 1.04290 0.03655 0.11421 0.00133 0.03364 0.00082 813 75 725 18 697 8 669 16 4.06% 0.48
RV-2b-104 0.06135 0.00288 0.74110 0.03369 0.08760 0.00117 0.02724 0.00068 651 46 563 20 541 7 543 13 4.01% 0.65
RV-2b-77 0.07044 0.00275 1.33380 0.05009 0.13730 0.00176 0.04143 0.00075 941 78 861 22 829 10 821 15 3.75% 1.14
RV-2b-09 0.06080 0.00091 0.73390 0.00949 0.08753 0.00064 0.03307 0.00056 632 32 559 6 541 4 658 11 3.31% 0.08
RV-2b-13 0.11104 0.00172 4.62326 0.06268 0.30190 0.00251 0.09066 0.00100 1817 28 1754 11 1701 12 1754 19 6.81% 0.64
RV-2b-110 0.07147 0.00197 1.43672 0.03754 0.14578 0.00147 0.04184 0.00068 971 55 904 16 877 8 828 13 3.09% 0.70
RV-2b-66 0.11267 0.00189 4.81343 0.07191 0.30979 0.00268 0.09164 0.00100 1843 30 1787 13 1740 13 1772 18 5.93% 0.92
RV-2b-71 0.10923 0.00184 4.50761 0.06727 0.29923 0.00256 0.08515 0.00109 1787 30 1732 12 1688 13 1652 20 5.87% 0.60
RV-2b-82 0.11331 0.00161 4.89158 0.05881 0.31304 0.00244 0.08815 0.00084 1853 25 1801 10 1756 12 1708 16 5.55% 0.77
RV-2b-51 0.06048 0.00140 0.74425 0.01607 0.08924 0.00076 0.02846 0.00094 621 49 565 9 551 5 567 18 2.50% 0.08
RV-2b-83 0.11261 0.00189 4.83775 0.07233 0.31153 0.00269 0.08969 0.00114 1842 30 1792 13 1748 13 1736 21 5.37% 0.60
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
8
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
RV-2b-101 0.07225 0.00307 1.52629 0.06257 0.15319 0.00212 0.04819 0.00150 993 84 941 25 919 12 951 29 2.42% 0.43
RV-2b-95 0.07368 0.00223 1.62795 0.04694 0.16022 0.00172 0.04773 0.00109 1033 60 981 18 958 10 942 21 2.41% 0.42
RV-2b-67 0.07259 0.00149 1.56094 0.02938 0.15592 0.00133 0.04830 0.00049 1003 41 955 12 934 7 953 10 2.22% 1.13
RV-2b-05 0.10737 0.00130 4.39322 0.04272 0.29671 0.00217 0.08344 0.00073 1755 22 1711 8 1675 11 1620 14 4.79% 0.48
RV-2b-108 0.11175 0.00215 4.81995 0.08481 0.31276 0.00295 0.08869 0.00123 1828 34 1788 15 1754 14 1717 23 4.21% 0.71
RV-2b-78 0.06731 0.00119 1.22273 0.01936 0.13174 0.00102 0.04085 0.00049 847 36 811 9 798 6 809 10 1.65% 0.43
RV-2b-43 0.06231 0.00231 0.89506 0.03182 0.10416 0.00118 0.03152 0.00106 685 77 649 17 639 7 627 21 1.63% 0.25
RV-2b-58 0.05977 0.00133 0.73600 0.01523 0.08931 0.00074 0.02661 0.00109 595 48 560 9 551 4 531 21 1.58% 0.06
RV-2b-109 0.05994 0.00332 0.74927 0.04036 0.09065 0.00138 0.02655 0.00105 601 56 568 23 559 8 530 21 1.50% 0.39
RV-2b-81 0.05917 0.00146 0.70293 0.01618 0.08615 0.00075 0.02775 0.00066 573 53 541 10 533 4 553 13 1.46% 0.18
RV-2b-99 0.05828 0.00156 0.64918 0.01643 0.08077 0.00074 0.02588 0.00061 540 58 508 10 501 4 516 12 1.46% 0.22
RV-2b-85 0.06414 0.00130 1.02677 0.01910 0.11608 0.00095 0.03545 0.00051 746 42 717 10 708 5 704 10 1.31% 0.38
RV-2b-41 0.07022 0.00303 1.44819 0.06027 0.14955 0.00205 0.04263 0.00083 935 86 909 25 899 11 844 16 1.18% 1.22
RV-2b-29 0.05942 0.00193 0.73027 0.02261 0.08911 0.00091 0.02601 0.00033 583 69 557 13 550 5 519 6 1.16% 1.40
RV-2b-75 0.06787 0.00178 1.28590 0.03178 0.13740 0.00131 0.04302 0.00046 865 54 840 14 830 7 851 9 1.16% 1.64
RV-2b-86 0.07119 0.00163 1.52850 0.03242 0.15569 0.00140 0.04598 0.00065 963 46 942 13 933 8 909 12 0.98% 0.63
RV-2b-73 0.07143 0.00212 1.54742 0.04368 0.15710 0.00166 0.04705 0.00124 970 59 950 17 941 9 929 24 0.95% 0.30
RV-2b-74 0.06386 0.00214 1.03360 0.03313 0.11737 0.00127 0.03821 0.00107 737 69 721 17 715 7 758 21 0.74% 0.29
RV-2b-40 0.07160 0.00142 1.57225 0.02852 0.15923 0.00133 0.04875 0.00091 975 40 959 11 953 7 962 18 0.71% 0.23
RV-2b-91 0.07477 0.00249 1.82033 0.05797 0.17656 0.00207 0.05101 0.00091 1062 66 1053 21 1048 11 1006 17 1.35% 0.92
RV-2b-80 0.06020 0.00215 0.80953 0.02769 0.09752 0.00106 0.04221 0.00884 611 75 602 16 600 6 836 15 0.38% 0.01
RV-2b-76 0.06988 0.00177 1.46665 0.03496 0.15219 0.00144 0.04364 0.00054 925 51 917 14 913 8 863 11 0.38% 1.10
RV-2b-33 0.06901 0.00132 1.40783 0.02453 0.14793 0.00121 0.04280 0.00048 899 39 892 10 889 7 847 9 0.33% 0.72
RV-2b-06 0.05949 0.00239 0.76766 0.02964 0.09357 0.00113 0.02785 0.00074 585 85 578 17 577 7 555 14 0.31% 0.45
RV-2b-08 0.11022 0.00166 4.87027 0.06413 0.32042 0.00264 0.10692 0.00106 1803 27 1797 11 1792 13 2053 19 0.63% 0.74
RV-2b-105 0.05943 0.00158 0.77931 0.01954 0.09509 0.00086 0.02878 0.00055 583 57 585 11 586 5 574 11 0.07% 0.34
RV-2b-23 0.11284 0.00141 5.19813 0.05253 0.33403 0.00247 0.09116 0.00078 1846 22 1852 9 1858 12 1763 15 0.66% 0.65
RV-2b-27 0.11232 0.00180 5.15059 0.07302 0.33250 0.00283 0.09454 0.00107 1837 29 1845 12 1851 14 1826 20 0.71% 0.73
RV-2b-12 0.05814 0.00251 0.70726 0.02947 0.08821 0.00109 0.03192 0.00128 534 92 543 18 545 6 635 25 0.35% 0.19
RV-2b-88 0.06604 0.00256 1.24359 0.04629 0.13656 0.00170 0.03935 0.00779 808 79 821 21 825 10 780 4 0.57% 0.02
RV-2b-02 0.05813 0.00119 0.71641 0.01347 0.08937 0.00073 0.02652 0.00027 534 45 549 8 552 4 529 5 0.60% 0.82
RV-2b-11 0.06159 0.00117 0.94438 0.01627 0.11118 0.00089 0.03480 0.00058 660 40 675 9 680 5 692 11 0.65% 0.21
RV-2b-100 0.05684 0.00182 0.63804 0.01946 0.08140 0.00080 0.02461 0.00058 485 70 501 12 505 5 491 11 0.67% 0.32
RV-2b-62 0.05885 0.00108 0.77068 0.01265 0.09496 0.00073 0.02963 0.00052 562 39 580 7 585 4 590 10 0.79% 0.17
RV-2b-17 0.06678 0.00237 1.32319 0.04502 0.14366 0.00166 0.04340 0.00108 831 72 856 20 865 9 859 21 1.09% 0.44
RV-2b-25 0.05727 0.00713 0.69061 0.08472 0.08744 0.00221 0.03198 0.00557 501 56 533 51 540 13 636 9 1.33% 0.13
RV-2b-55 0.06885 0.00294 1.49274 0.06157 0.15724 0.00217 0.04565 0.00143 894 86 927 25 941 12 902 28 1.49% 0.44
RV-2b-96 0.05710 0.00528 0.68816 0.06247 0.08739 0.00181 0.02525 0.00101 495 12 532 38 540 11 504 20 1.56% 0.86
RV-2b-59 0.05720 0.00172 0.69464 0.01986 0.08807 0.00085 0.04407 0.00232 499 65 536 12 544 5 872 45 1.56% 0.04
RV-2b-45 0.05712 0.00166 0.69680 0.01927 0.08845 0.00084 0.02671 0.00076 496 64 537 12 546 5 533 15 1.74% 0.19
RV-2b-03 0.05710 0.00126 0.70133 0.01442 0.08907 0.00075 0.02660 0.00040 495 49 540 9 550 4 531 8 1.89% 0.38
RV-2b-16 0.05698 0.00227 0.70054 0.02695 0.08915 0.00103 0.02618 0.00077 490 86 539 16 551 6 522 15 2.07% 0.35
RV-2b-10 0.05651 0.00192 0.69685 0.02266 0.08942 0.00094 0.02880 0.00163 472 74 537 14 552 6 574 32 2.75% 0.07
RV-2b-60 0.05616 0.00301 0.70163 0.03670 0.09060 0.00121 0.02561 0.00087 459 45 540 22 559 7 511 17 3.45% 0.41
RV-2b-49 0.06521 0.00538 1.43239 0.11595 0.15928 0.00346 0.03893 0.00275 781 65 903 48 953 19 772 53 5.28% 0.37
Kelani KEL2-01 0.05987 0.00108 0.74731 0.01345 0.09051 0.00104 0.02679 0.00046 599 20 567 8 559 6 534 9 1.43% 0.22
KEL2-02 0.07023 0.00163 1.09705 0.02206 0.11330 0.00131 0.03437 0.00038 935 49 752 11 692 8 683 7 8.67% 0.11
KEL2-03 0.06036 0.00110 0.83132 0.01509 0.09987 0.00115 0.03718 0.00064 617 20 614 8 614 7 738 12 0.00% 0.19
KEL2-04 0.05790 0.00131 0.68698 0.01535 0.08603 0.00104 0.02581 0.00058 526 28 531 9 532 6 515 11 0.19% 0.30
KEL2-05 0.06175 0.00203 0.79125 0.02413 0.09293 0.00115 0.02860 0.00037 666 72 592 14 573 7 570 7 3.32% 0.10
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
9
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
KEL2-06 0.16392 0.00318 9.81822 0.18791 0.43432 0.00537 0.12298 0.00218 2497 17 2418 18 2325 24 2344 39 7.40% 1.07
KEL2-10 0.06703 0.00129 1.17569 0.02249 0.12720 0.00149 0.03825 0.00065 839 21 789 10 772 9 759 13 2.20% 0.67
KEL2-100 0.06661 0.00179 1.21647 0.03242 0.13242 0.00174 0.03923 0.00108 826 34 808 15 802 10 778 21 0.75% 0.68
KEL2-11 0.05850 0.00134 0.70788 0.01608 0.08775 0.00106 0.02857 0.00053 549 29 543 10 542 6 569 10 0.18% 0.49
KEL2-12 0.05915 0.00125 0.67911 0.01415 0.08325 0.00099 0.02609 0.00046 573 25 526 9 515 6 521 9 2.14% 0.59
KEL2-14 0.06154 0.00175 0.90125 0.02314 0.10622 0.00128 0.03271 0.00050 658 62 652 12 651 7 650 10 0.15% 0.08
KEL2-15 0.05982 0.00147 0.70525 0.01530 0.08550 0.00099 0.02641 0.00029 597 55 542 9 529 6 527 6 2.46% 0.11
KEL2-16 0.05972 0.00133 0.74253 0.01632 0.09016 0.00109 -0.00085 0.04733 593 27 564 10 556 6 -17 17 1.44% 0.00
KEL2-18 0.07021 0.00197 1.22024 0.03093 0.12605 0.00151 0.03823 0.00060 935 59 810 14 765 9 758 12 5.88% 0.11
KEL2-19 0.07209 0.00337 1.49636 0.06879 0.15052 0.00226 0.04738 0.00148 988 69 929 28 904 13 936 29 2.77% 0.60
KEL2-20 0.11848 0.00216 5.20670 0.09490 0.31867 0.00371 0.09293 0.00156 1933 17 1854 16 1783 18 1796 29 8.41% 0.72
KEL2-21 0.06155 0.00164 0.87075 0.02277 0.10258 0.00130 0.03248 0.00065 659 35 636 12 630 8 646 13 0.95% 0.83
KEL2-23 0.05893 0.00194 0.67701 0.02191 0.08331 0.00110 0.02591 0.00055 565 47 525 13 516 7 517 11 1.74% 0.90
KEL2-24 0.05870 0.00124 0.69005 0.01445 0.08525 0.00102 0.02501 0.00060 556 26 533 9 527 6 499 12 1.14% 0.15
KEL2-25 0.06291 0.00138 0.83813 0.01813 0.09661 0.00117 0.04039 0.00105 705 26 618 10 595 7 800 20 3.87% 0.13
KEL2-26 0.05867 0.00157 0.66266 0.01590 0.08192 0.00098 0.02536 0.00029 555 60 516 10 508 6 506 6 1.57% 0.06
KEL2-27 0.06586 0.00253 1.07243 0.04058 0.11808 0.00160 0.04081 0.00113 802 56 740 20 720 9 808 22 2.78% 0.44
KEL2-29 0.07420 0.00970 1.74728 0.22502 0.17076 0.00476 0.06129 0.00552 1047 25 1026 83 1016 26 1202 15 3.05% 0.44
KEL2-31 0.05837 0.00159 0.66302 0.01773 0.08237 0.00105 0.02570 0.00053 544 36 516 11 510 6 513 10 1.18% 0.76
KEL2-32 0.05972 0.00120 0.75107 0.01502 0.09120 0.00108 0.02758 0.00051 593 24 569 9 563 6 550 10 1.07% 0.46
KEL2-34 0.05923 0.00152 0.72595 0.01847 0.08887 0.00110 0.02857 0.00069 576 34 554 11 549 7 569 14 0.91% 0.25
KEL2-36 0.06045 0.00122 0.81516 0.01639 0.09778 0.00116 0.03740 0.00133 620 24 605 9 601 7 742 26 0.67% 0.03
KEL2-37 0.05818 0.00128 0.67860 0.01478 0.08458 0.00103 0.02763 0.00058 537 27 526 9 523 6 551 11 0.57% 0.26
KEL2-40 0.06013 0.00143 0.78636 0.01842 0.09483 0.00117 0.02949 0.00078 608 30 589 10 584 7 587 15 0.86% 0.19
KEL2-41 0.05972 0.00152 0.75104 0.01884 0.09119 0.00114 0.02856 0.00074 593 33 569 11 563 7 569 15 1.07% 0.27
KEL2-42 0.05884 0.00153 0.66259 0.01697 0.08166 0.00103 0.02537 0.00058 561 34 516 10 506 6 506 11 1.98% 0.44
KEL2-44 0.06482 0.00149 0.81420 0.01857 0.09108 0.00112 0.04010 0.00092 768 28 605 10 562 7 795 18 7.65% 0.22
KEL2-45 0.06240 0.00136 0.90294 0.01943 0.10492 0.00128 0.03016 0.00077 688 26 653 10 643 7 601 15 1.56% 0.13
KEL2-48 0.05809 0.00125 0.75935 0.01625 0.09478 0.00115 0.02835 0.00094 533 26 574 9 584 7 565 18 1.71% 0.06
KEL2-49 0.05782 0.00204 0.65685 0.02283 0.08238 0.00112 0.02437 0.00061 523 52 513 14 510 7 487 12 0.59% 0.77
KEL2-50 0.05732 0.00143 0.64117 0.01580 0.08111 0.00102 0.02508 0.00053 504 32 503 10 503 6 501 10 0.00% 0.91
KEL2-53 0.06444 0.00389 1.17277 0.06982 0.13197 0.00211 0.03821 0.00160 756 99 788 33 799 12 758 31 1.38% 0.65
KEL2-56 0.05835 0.00143 0.68817 0.01667 0.08552 0.00107 0.02573 0.00116 543 31 532 10 529 6 513 23 0.57% 0.07
KEL2-58 0.06062 0.00130 0.74801 0.01593 0.08947 0.00108 0.03035 0.00071 626 26 567 9 552 6 604 14 2.72% 0.06
KEL2-60 0.06382 0.00159 0.90788 0.02231 0.10315 0.00131 0.04868 0.00125 736 31 656 12 633 8 961 24 3.63% 0.18
KEL2-61 0.07321 0.00214 1.54801 0.04440 0.15333 0.00206 0.04317 0.00107 1020 36 950 18 920 12 854 21 3.26% 0.77
KEL2-63 0.05854 0.00155 0.67455 0.01767 0.08356 0.00107 0.02550 0.00066 550 35 523 11 517 6 509 13 1.16% 0.36
KEL2-64 0.06789 0.00214 1.00751 0.03121 0.10762 0.00146 0.03401 0.00077 865 42 708 16 659 8 676 15 7.44% 2.03
KEL2-65 0.05827 0.00151 0.70064 0.01798 0.08719 0.00112 0.02601 0.00072 540 34 539 11 539 7 519 14 0.00% 0.25
KEL2-66 0.06360 0.00430 1.02263 0.06741 0.11661 0.00175 0.03577 0.00040 728 17 715 34 711 10 710 8 0.56% 0.87
KEL2-67 0.06470 0.00314 1.11884 0.05355 0.12540 0.00185 0.04019 0.00106 765 76 762 26 762 11 796 21 0.00% 1.17
KEL2-68 0.11501 0.00270 5.02507 0.11668 0.31683 0.00404 0.09006 0.00210 1880 24 1824 20 1774 20 1743 39 5.98% 0.60
KEL2-69 0.05815 0.00153 0.69595 0.01804 0.08678 0.00111 0.02706 0.00075 535 35 536 11 536 7 540 15 0.00% 0.19
KEL2-71 0.05973 0.00143 0.75107 0.01778 0.09118 0.00114 0.02672 0.00065 594 30 569 10 563 7 533 13 1.07% 0.23
KEL2-73 0.06846 0.00161 1.21002 0.02819 0.12816 0.00160 0.04706 0.00110 883 28 805 13 777 9 929 21 3.60% 0.35
KEL2-74 0.06679 0.00160 1.07860 0.02564 0.11709 0.00148 0.03793 0.00087 831 29 743 13 714 9 752 17 4.06% 1.11
KEL2-78 0.05834 0.00149 0.68114 0.01722 0.08466 0.00109 0.02581 0.00067 543 33 527 10 524 6 515 13 0.57% 0.27
KEL2-80 0.06335 0.00165 0.97770 0.02524 0.11192 0.00145 0.03658 0.00092 720 33 692 13 684 8 726 18 1.17% 0.48
KEL2-83 0.06131 0.00150 0.79097 0.01927 0.09355 0.00119 0.02970 0.00076 650 31 592 11 576 7 592 15 2.78% 0.12
KEL2-86 0.06042 0.00158 0.76896 0.01990 0.09228 0.00120 0.02722 0.00070 619 34 579 11 569 7 543 14 1.76% 0.70
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S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
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Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
KEL2-87 0.07202 0.00206 1.67358 0.04708 0.16849 0.00229 0.04865 0.00134 987 35 999 18 1004 13 960 26 1.69% 0.60
KEL2-88 0.11480 0.00294 5.02351 0.12737 0.31731 0.00415 0.09146 0.00238 1877 27 1823 21 1777 20 1769 44 5.63% 0.64
KEL2-89 0.07230 0.00220 1.48655 0.04459 0.14909 0.00205 0.04216 0.00117 994 39 925 18 896 12 835 23 3.24% 0.87
KEL2-93 0.06485 0.07327 1.04954 1.18010 0.11735 0.01349 0.05502 0.01855 769 16 729 585 715 78 1083 35 1.96% 0.11
KEL2-95 0.05835 0.00307 0.73259 0.03810 0.09104 0.00141 0.02344 0.00210 543 87 558 22 562 8 468 41 0.71% 0.84
KEL2-96 0.11631 0.00370 4.95676 0.15447 0.30901 0.00462 0.07301 0.00715 1900 35 1812 26 1736 23 1424 15 9.45% 0.18
Kalu KLL1-001 0.06823 0.00705 1.22496 0.12425 0.13022 0.00253 0.03963 0.00053 875 23 812 57 789 14 785 10 2.92% 0.49
KLL1-002 0.06883 0.03564 1.36898 0.70542 0.14423 0.00808 0.05436 0.01463 894 21 876 302 869 46 1070 20 0.81% 0.55
KLL1-005 0.07019 0.00584 1.56547 0.12867 0.16173 0.00306 0.04750 0.00201 934 23 957 51 966 17 938 39 0.93% 0.73
KLL1-006 0.12418 0.00178 6.25013 0.09196 0.36497 0.00434 0.09549 0.00134 2017 12 2011 13 2006 20 1843 25 0.55% 0.63
KLL1-008 0.06012 0.00092 0.76890 0.01201 0.09274 0.00109 0.02736 0.00054 608 16 579 7 572 6 546 11 1.22% 0.11
KLL1-009 0.06469 0.00151 1.10719 0.02234 0.12413 0.00146 0.03800 0.00044 764 50 757 11 754 8 754 9 0.40% 0.22
KLL1-010 0.07152 0.00143 1.57647 0.03150 0.15983 0.00200 0.04571 0.00068 972 21 961 12 956 11 903 13 0.52% 1.26
KLL1-011 0.06818 0.00162 1.36036 0.03192 0.14467 0.00187 0.04298 0.00087 874 28 872 14 871 11 851 17 0.11% 0.56
KLL1-012 0.05806 0.00095 0.69126 0.01148 0.08633 0.00103 0.02603 0.00046 532 18 534 7 534 6 519 9 0.00% 0.23
KLL1-013 0.05869 0.00207 0.71044 0.02472 0.08778 0.00122 0.02650 0.00056 556 52 545 15 542 7 529 11 0.55% 0.71
KLL1-014 0.05937 0.00111 0.78532 0.01476 0.09591 0.00116 0.04311 0.00130 581 21 589 8 590 7 853 25 0.17% 0.09
KLL1-015 0.05778 0.00141 0.66332 0.01607 0.08325 0.00106 0.02416 0.00165 521 31 517 10 515 6 483 33 0.39% 0.07
KLL1-016 0.05949 0.00150 0.82875 0.02084 0.10101 0.00127 0.02980 0.00112 585 33 613 12 620 7 594 22 1.13% 0.15
KLL1-017 0.06105 0.00780 0.86758 0.10987 0.10304 0.00224 0.03083 0.00102 641 24 634 60 632 13 614 20 0.32% 1.54
KLL1-018 0.07455 0.00300 1.73856 0.06885 0.16910 0.00254 0.05038 0.00143 1056 55 1023 26 1007 14 993 28 4.87% 0.60
KLL1-019 0.06775 0.00443 1.35218 0.08742 0.14471 0.00240 0.04010 0.00137 861 10 869 38 871 14 795 27 0.23% 0.84
KLL1-020 0.05658 0.00081 0.78040 0.01155 0.10001 0.00117 0.02599 0.00042 475 15 586 7 614 7 519 8 4.56% 0.10
KLL1-021 0.06417 0.00103 1.13260 0.01852 0.12797 0.00152 0.04155 0.00068 747 17 769 9 776 9 823 13 0.90% 0.28
KLL1-022 0.07143 0.00147 1.23135 0.02520 0.12500 0.00157 0.04723 0.00090 970 22 815 11 759 9 933 17 7.38% 0.37
KLL1-025 0.06851 0.00107 1.27391 0.02029 0.13483 0.00160 0.03906 0.00053 884 16 834 9 815 9 774 10 2.33% 2.04
KLL1-029 0.06042 0.00105 0.82449 0.01443 0.09895 0.00119 0.03203 0.00087 619 19 611 8 608 7 637 17 0.49% 0.09
KLL1-031 0.05985 0.00272 0.79389 0.03566 0.09617 0.00140 0.02624 0.00075 598 72 593 20 592 8 524 15 0.17% 0.73
KLL1-032 0.05873 0.00302 0.72968 0.03699 0.09008 0.00137 0.02565 0.00065 557 84 556 22 556 8 512 13 0.00% 0.89
KLL1-034 0.07461 0.00165 1.39515 0.03066 0.13559 0.00173 0.03004 0.00048 1058 24 887 13 820 10 598 9 8.17% 1.75
KLL1-035 0.06297 0.00266 0.87515 0.03650 0.10077 0.00145 0.03063 0.00089 707 64 638 20 619 8 610 17 3.07% 0.58
KLL1-036 0.05733 0.00163 0.68071 0.01919 0.08609 0.00113 0.02508 0.00070 504 39 527 12 532 7 501 14 0.94% 0.28
KLL1-037 0.06122 0.00145 0.77535 0.01584 0.09186 0.00110 0.02830 0.00032 647 52 583 9 567 6 564 6 2.82% 0.10
KLL1-039 0.12593 0.00195 6.03954 0.09515 0.34774 0.00415 0.09461 0.00153 2042 13 1982 14 1924 20 1827 28 6.13% 0.37
KLL1-040 0.06158 0.00122 0.61784 0.01215 0.07275 0.00090 0.01659 0.00024 660 22 488 8 453 5 333 5 7.73% 0.23
KLL1-041 0.06474 0.00151 1.08459 0.02183 0.12150 0.00144 0.03720 0.00042 766 50 746 11 739 8 738 8 0.95% 0.19
KLL1-042 0.05780 0.00096 0.71425 0.01201 0.08960 0.00107 0.02623 0.00065 522 18 547 7 553 6 523 13 1.08% 0.06
KLL1-043 0.06939 0.00111 1.49321 0.02430 0.15602 0.00186 0.04164 0.00062 910 16 928 10 935 10 825 12 0.75% 1.45
KLL1-046 0.05906 0.00293 0.73450 0.03602 0.09018 0.00132 0.02643 0.00055 569 81 559 21 557 8 527 11 0.36% 1.34
KLL1-047 0.06652 0.00106 0.92068 0.01485 0.10035 0.00119 0.01082 0.00016 823 16 663 8 616 7 218 3 7.63% 2.82
KLL1-048 0.07219 0.00380 1.41632 0.07157 0.14230 0.00213 0.04303 0.00053 991 11 896 30 858 12 852 10 4.43% 0.89
KLL1-050 0.07328 0.00134 1.55881 0.02858 0.15424 0.00189 0.04538 0.00076 1022 19 954 11 925 11 897 15 3.14% 0.78
KLL1-051 0.06019 0.00131 0.76228 0.01649 0.09182 0.00116 0.02607 0.00066 610 26 575 10 566 7 520 13 1.59% 0.26
KLL1-052 0.06756 0.00212 1.24500 0.03864 0.13361 0.00179 0.03873 0.00079 855 42 821 17 808 10 768 15 1.61% 0.90
KLL1-055 0.06008 0.00131 0.72814 0.01345 0.08790 0.00103 0.02714 0.00032 606 48 555 8 543 6 541 6 2.21% 0.10
KLL1-056 0.06684 0.00327 1.32751 0.06228 0.14405 0.00200 0.04394 0.00050 833 10 858 27 868 11 869 10 1.15% 0.89
KLL1-057 0.07530 0.00128 1.66533 0.02850 0.16035 0.00193 0.04860 0.00081 1077 17 995 11 959 11 959 16 3.75% 0.48
KLL1-058 0.07472 0.00201 1.57780 0.04184 0.15312 0.00204 0.04734 0.00129 1061 32 962 16 918 11 935 25 4.79% 0.38
KLL1-059 0.06025 0.00108 0.78285 0.01403 0.09421 0.00114 0.06830 0.00275 613 19 587 8 580 7 1335 52 1.21% 0.01
KLL1-060 0.06518 0.00118 1.11623 0.02023 0.12418 0.00151 0.03736 0.00076 780 19 761 10 755 9 741 15 0.79% 0.18
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
11
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
KLL1-061 0.06707 0.00125 1.07108 0.02000 0.11579 0.00142 0.04591 0.00079 840 20 739 10 706 8 907 15 4.67% 0.72
KLL1-063 0.06656 0.00150 1.27849 0.02843 0.13927 0.00177 0.04079 0.00085 824 26 836 13 841 10 808 17 0.59% 0.47
KLL1-064 0.06417 0.00122 0.94138 0.01780 0.10638 0.00131 0.02704 0.00051 747 21 674 9 652 8 539 10 3.37% 0.44
KLL1-065 0.06537 0.00203 1.11729 0.03405 0.12394 0.00171 0.03947 0.00073 786 41 762 16 753 10 782 14 1.20% 2.06
KLL1-066 0.05881 0.00169 0.67844 0.01924 0.08365 0.00109 0.02541 0.00077 560 39 526 12 518 6 507 15 1.54% 0.27
KLL1-067 0.07431 0.00130 1.59487 0.02805 0.15562 0.00188 0.03200 0.00055 1050 18 968 11 932 10 637 11 3.86% 1.18
KLL1-068 0.06542 0.00183 0.88436 0.02437 0.09802 0.00131 0.03159 0.00062 788 36 643 13 603 8 629 12 6.63% 1.14
KLL1-069 0.06284 0.00110 0.86265 0.01519 0.09953 0.00120 0.03901 0.00070 703 19 632 8 612 7 773 14 3.27% 0.17
KLL1-070 0.07175 0.00129 1.63176 0.02932 0.16490 0.00201 0.04620 0.00082 979 18 983 11 984 11 913 16 0.10% 0.59
KLL1-071 0.05883 0.00289 0.70477 0.03412 0.08686 0.00129 0.02658 0.00068 561 80 542 20 537 8 530 13 0.93% 0.88
KLL1-072 0.07271 0.00243 1.67641 0.05512 0.16718 0.00236 0.05090 0.00132 1006 44 1000 21 997 13 1003 25 0.30% 0.61
KLL1-073 0.10421 0.00292 4.03446 0.10067 0.28077 0.00356 0.08164 0.00097 1701 53 1641 20 1595 18 1586 18 6.65% 0.48
KLL1-074 0.06989 0.00135 1.23653 0.02372 0.12829 0.00159 0.02248 0.00043 925 20 817 11 778 9 449 9 5.01% 0.81
KLL1-076 0.05991 0.00124 0.82630 0.01692 0.10001 0.00125 0.02699 0.00095 600 24 612 9 614 7 538 19 0.33% 0.11
KLL1-078 0.05891 0.00149 0.74904 0.01865 0.09219 0.00119 0.03543 0.00219 564 32 568 11 568 7 704 43 0.00% 0.05
KLL1-079 0.05974 0.00109 0.76404 0.01395 0.09274 0.00113 0.02750 0.00052 594 20 576 8 572 7 548 10 0.70% 0.20
KLL1-080 0.06258 0.00122 0.79886 0.01550 0.09256 0.00114 0.03097 0.00168 694 22 596 9 571 7 616 33 4.38% 0.02
KLL1-081 0.07156 0.00244 1.39529 0.04655 0.14139 0.00206 0.04208 0.00102 973 44 887 20 853 12 833 20 3.99% 0.95
KLL1-082 0.06482 0.00132 1.12980 0.02277 0.12639 0.00158 0.03827 0.00074 768 22 768 11 767 9 759 14 0.13% 0.79
KLL1-083 0.07822 0.00202 1.99098 0.05039 0.18458 0.00248 0.05525 0.00120 1152 29 1112 17 1092 13 1087 23 5.49% 0.85
KLL1-084 0.06286 0.00170 0.78330 0.01884 0.09038 0.00113 0.02776 0.00061 703 59 587 11 558 7 553 12 5.20% 0.03
KLL1-085 0.06537 0.00154 1.13165 0.02626 0.12554 0.00162 0.03619 0.00069 786 28 769 13 762 9 719 13 0.92% 3.92
KLL1-086 0.07329 0.00170 1.56666 0.03573 0.15500 0.00201 0.04357 0.00098 1022 26 957 14 929 11 862 19 3.01% 0.56
KLL1-087 0.07376 0.00170 1.53243 0.03479 0.15066 0.00194 0.04609 0.00099 1035 26 943 14 905 11 911 19 4.20% 0.67
KLL1-088 0.07004 0.00143 1.43732 0.02897 0.14881 0.00186 0.04644 0.00096 930 22 905 12 894 10 918 19 1.23% 0.40
KLL1-091 0.06509 0.00181 1.09585 0.03000 0.12209 0.00162 0.03755 0.00079 777 35 751 15 743 9 745 15 1.08% 1.23
KLL1-092 0.06815 0.00430 1.20240 0.07485 0.12794 0.00215 0.03806 0.00152 873 11 802 35 776 12 755 30 3.35% 0.70
KLL1-093 0.07345 0.00321 1.52341 0.06544 0.15041 0.00229 0.04767 0.00155 1026 62 940 26 903 13 941 30 4.10% 0.58
KLL1-094 0.05804 0.00157 0.70134 0.01862 0.08763 0.00116 0.02691 0.00067 531 35 540 11 542 7 537 13 0.37% 0.44
KLL1-095 0.06732 0.00278 1.07081 0.04333 0.11536 0.00176 0.03639 0.00083 848 59 739 21 704 10 722 16 4.97% 2.03
KLL1-096 0.07540 0.00179 1.36578 0.03181 0.13136 0.00170 0.02535 0.00056 1079 27 874 14 796 10 506 11 9.80% 0.97
KLL1-097 0.07848 0.00183 1.76279 0.04046 0.16289 0.00212 0.04887 0.00107 1159 26 1032 15 973 12 964 21 6.06% 0.79
KLL1-098 0.06760 0.00187 1.25366 0.03392 0.13449 0.00181 0.03974 0.00093 856 34 825 15 813 10 788 18 1.48% 0.88
KLL1-099 0.05974 0.00167 0.73499 0.02016 0.08922 0.00118 0.02259 0.00112 594 37 559 12 551 7 452 22 1.45% 0.12
KLL1-100 0.05841 0.00141 0.70920 0.01685 0.08805 0.00114 0.02732 0.00064 545 30 544 10 544 7 545 13 0.00% 0.43
KLL1-101 0.06781 0.00178 1.17362 0.03013 0.12551 0.00168 0.03887 0.00088 863 31 788 14 762 10 771 17 3.41% 0.98
KLL1-103 0.07220 0.00257 1.33873 0.04431 0.13448 0.00176 0.04067 0.00047 992 74 863 19 813 10 806 9 6.15% 0.50
KLL1-104 0.06688 0.00158 1.29719 0.03000 0.14066 0.00183 0.04358 0.00094 834 27 844 13 848 10 862 18 0.47% 1.30
KLL1-105 0.05957 0.00162 0.72329 0.01933 0.08805 0.00117 0.02599 0.00072 588 35 553 11 544 7 519 14 1.65% 0.29
KLL1-106 0.07033 0.00249 1.15067 0.03986 0.11865 0.00173 0.07322 0.00189 938 47 778 19 723 10 1428 36 7.61% 0.51
KLL1-107 0.07352 0.00169 1.25355 0.02825 0.12365 0.00160 0.03315 0.00080 1028 25 825 13 752 9 659 16 9.71% 0.40
KLL1-108 0.07228 0.00156 1.43886 0.03054 0.14437 0.00183 0.04360 0.00094 994 23 905 13 869 10 863 18 4.14% 0.87
KLL1-109 0.07332 0.00333 1.57909 0.06803 0.15620 0.00225 0.04715 0.00058 1023 94 962 27 936 13 931 11 2.78% 0.53
KLL1-110 0.05948 0.00139 0.73030 0.01673 0.08904 0.00115 0.02744 0.00065 585 28 557 10 550 7 547 13 1.27% 0.31
KLL1-111 0.06464 0.00243 1.08013 0.03979 0.12119 0.00174 0.05033 0.00365 763 53 744 19 737 10 993 70 0.95% 0.11
KLL1-112 0.06707 0.00196 1.24050 0.03542 0.13415 0.00184 0.04102 0.00130 840 37 819 16 811 10 813 25 0.99% 0.26
KLL1-114 0.07060 0.00256 1.36490 0.04856 0.14021 0.00202 0.04350 0.00118 946 49 874 21 846 11 861 23 3.31% 0.67
KLL1-116 0.06824 0.00339 1.28333 0.06088 0.13639 0.00199 0.04150 0.00050 876 15 838 27 824 11 822 10 1.70% 0.54
KLL1-117 0.06539 0.00164 1.02668 0.02512 0.11387 0.00150 0.03837 0.00092 787 30 717 13 695 9 761 18 3.17% 0.61
KLL1-118 0.07095 0.00162 1.35655 0.03038 0.13867 0.00179 0.04253 0.00098 956 25 870 13 837 10 842 19 3.94% 0.56
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S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
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Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
KLL1-119 0.06583 0.00151 0.99386 0.02236 0.10950 0.00141 0.03372 0.00080 801 26 701 11 670 8 670 16 4.63% 0.32
KLL1-120 0.07281 0.00163 1.69558 0.03732 0.16889 0.00216 0.04934 0.00113 1009 25 1007 14 1006 12 973 22 0.30% 0.59
Walawe WAL1-03 0.11179 0.00292 5.10478 0.13165 0.33107 0.00444 0.07261 0.00198 1829 28 1837 22 1844 22 1417 37 0.81% 0.60
WAL1-05 0.06879 0.00161 1.35190 0.03159 0.14249 0.00178 0.03446 0.00178 892 28 868 14 859 10 685 35 1.05% 0.04
WAL1-06 0.06502 0.00188 0.81670 0.02337 0.09107 0.00118 0.02607 0.00065 775 38 606 13 562 7 520 13 7.83% 0.49
WAL1-11 0.06316 0.00139 0.90209 0.01991 0.10355 0.00126 0.03281 0.00081 714 27 653 11 635 7 653 16 2.83% 0.07
WAL1-13 0.07588 0.00181 1.53027 0.03623 0.14622 0.00185 0.04425 0.00108 1092 28 943 15 880 10 875 21 7.16% 0.31
WAL1-15 0.06278 0.00159 0.80395 0.02015 0.09285 0.00117 0.02581 0.00057 701 32 599 11 572 7 515 11 4.72% 0.79
WAL1-16 0.06301 0.00154 0.84642 0.01814 0.09743 0.00116 0.02992 0.00034 709 53 623 10 599 7 596 7 4.01% 0.02
WAL1-18 0.06035 0.00136 0.79216 0.01778 0.09517 0.00117 0.02746 0.00067 616 28 592 10 586 7 548 13 1.02% 0.08
WAL1-25 0.06103 0.00151 0.74486 0.01824 0.08850 0.00112 0.04183 0.00126 640 31 565 11 547 7 828 24 3.29% 0.07
WAL1-26 0.06981 0.00166 1.38172 0.03261 0.14350 0.00179 0.04854 0.00114 923 28 881 14 864 10 958 22 1.97% 0.30
WAL1-32 0.06041 0.00182 0.62989 0.01738 0.07562 0.00092 0.02333 0.00028 618 67 496 11 470 6 466 6 5.53% 0.12
WAL1-34 0.06003 0.00144 0.81645 0.01955 0.09861 0.00123 0.06261 0.00342 605 31 606 11 606 7 1227 65 0.00% 0.01
WAL1-36 0.06542 0.00207 1.02994 0.02997 0.11418 0.00143 0.03491 0.00063 788 68 719 15 697 8 694 12 3.16% 0.07
WAL1-37 0.06145 0.00151 0.76330 0.01862 0.09007 0.00113 0.02860 0.00071 655 31 576 11 556 7 570 14 3.60% 0.21
WAL1-40 0.06014 0.00147 0.75570 0.01837 0.09110 0.00114 0.02882 0.00074 609 31 572 11 562 7 574 15 1.78% 0.09
WAL1-42 0.11673 0.00288 5.02392 0.12305 0.31207 0.00393 0.08924 0.00220 1907 26 1823 21 1751 19 1728 41 8.91% 0.49
WAL1-44 0.13581 0.00340 6.85916 0.17041 0.36620 0.00467 0.10018 0.00252 2174 26 2093 22 2011 22 1930 46 8.11% 0.70
WAL1-46 0.06616 0.00190 0.83392 0.02364 0.09139 0.00121 0.02864 0.00078 811 37 616 13 564 7 571 15 9.22% 0.65
WAL1-47 0.07078 0.00202 1.48601 0.04187 0.15224 0.00203 0.04551 0.00127 951 36 925 17 914 11 900 25 1.20% 0.51
WAL1-52 0.11572 0.00310 5.31927 0.14080 0.33329 0.00435 0.09377 0.00255 1891 29 1872 23 1854 21 1812 47 2.00% 0.64
WAL1-53 0.06063 0.00163 0.81844 0.02173 0.09788 0.00126 0.02907 0.00080 626 35 607 12 602 7 579 16 0.83% 0.31
WAL1-55 0.06162 0.00169 0.78733 0.02133 0.09265 0.00120 0.02842 0.00090 661 36 590 12 571 7 566 18 3.33% 0.09
WAL1-59 0.11617 0.00319 5.33326 0.14469 0.33288 0.00436 0.09486 0.00268 1898 30 1874 23 1852 21 1832 49 2.48% 0.54
WAL1-60 0.05959 0.00174 0.73638 0.02118 0.08960 0.00119 0.02724 0.00078 589 39 560 12 553 7 543 15 1.27% 0.85
WAL1-61 0.06190 0.00181 0.84031 0.02423 0.09843 0.00131 0.02980 0.00092 671 39 619 13 605 8 594 18 2.31% 0.25
WAL1-64 0.21786 0.00657 18.65612 0.55322 0.62094 0.00908 0.17149 0.00571 2965 29 3024 29 3114 36 3199 99 4.78% 0.74
WAL1-70 0.06105 0.00190 0.79053 0.02421 0.09389 0.00128 0.03959 0.00381 641 42 591 14 579 8 785 74 2.07% 0.02
WAL1-74 0.06123 0.00201 0.84113 0.02535 0.09964 0.00131 0.03070 0.00042 647 72 620 14 612 8 611 8 1.31% 0.03
WAL1-75 0.06274 0.00218 0.87859 0.03000 0.10153 0.00144 0.03385 0.01304 699 49 640 16 623 8 673 25 2.73% 0.01
WAL1-77 0.06434 0.00244 0.88759 0.03307 0.10003 0.00147 0.02991 0.00111 753 54 645 18 615 9 596 22 4.88% 0.49
WAL1-81 0.06130 0.00195 0.77830 0.02432 0.09207 0.00126 0.02926 0.00110 650 44 585 14 568 7 583 22 2.99% 0.03
WAL1-82 0.06108 0.00272 0.74313 0.03247 0.08823 0.00137 0.02815 0.00106 642 67 564 19 545 8 561 21 3.49% 0.79
WAL1-83 0.06014 0.00193 0.79749 0.02512 0.09616 0.00132 0.03038 0.00118 609 44 595 14 592 8 605 23 0.51% 0.02
WAL1-88 0.06271 0.00216 0.87740 0.02780 0.10147 0.00139 0.03118 0.00056 699 75 640 15 623 8 621 11 2.73% 0.01
WAL1-91 0.06097 0.00209 0.77113 0.02589 0.09171 0.00130 0.02983 0.00110 638 48 580 15 566 8 594 22 2.47% 0.22
WAL1-92 0.06502 0.00270 0.97708 0.03826 0.10899 0.00153 0.03335 0.00063 775 90 692 20 667 9 663 12 3.75% 0.07
WAL1-93 0.14166 0.00495 7.55088 0.25836 0.38652 0.00567 0.11637 0.00440 2248 39 2179 31 2107 26 2225 80 6.69% 0.60
WAL1-95 0.07161 0.00255 1.12697 0.03930 0.11412 0.00165 0.05033 0.00193 975 47 766 19 697 10 993 37 9.90% 0.25
Maduru Oya MDL2-01 0.11537 0.00097 5.24963 0.04419 0.32994 0.00372 0.07951 0.00104 1886 10 1861 7 1838 18 1546 19 2.61% 0.14
MDL2-02 0.06557 0.00063 1.14710 0.01099 0.12685 0.00144 0.03649 0.00035 793 11 776 5 770 8 724 7 0.78% 0.88
MDL2-03 0.05820 0.00095 0.69966 0.01116 0.08718 0.00104 0.02588 0.00036 537 16 539 7 539 6 516 7 0.00% 0.57
MDL2-04 0.06539 0.00219 1.09390 0.03597 0.12130 0.00160 0.03928 0.00098 787 47 750 17 738 9 779 19 1.63% 0.37
MDL2-05 0.06115 0.00057 0.77143 0.00713 0.09148 0.00103 0.02414 0.00027 645 11 581 4 564 6 482 5 3.01% 0.27
MDL2-06 0.11100 0.00094 4.50754 0.03822 0.29446 0.00332 0.08104 0.00081 1816 10 1732 7 1664 17 1575 15 9.13% 0.43
MDL2-07 0.06329 0.00063 1.05117 0.01048 0.12043 0.00136 0.03289 0.00051 718 11 729 5 733 8 654 10 0.55% 0.08
MDL2-08 0.06575 0.00084 1.18744 0.01480 0.13097 0.00152 0.03932 0.00041 798 12 795 7 793 9 780 8 0.25% 1.01
MDL2-09 0.05820 0.00075 0.74148 0.00938 0.09239 0.00107 0.02611 0.00038 537 12 563 5 570 6 521 7 1.23% 0.33
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S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
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Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
MDL2-10 0.05816 0.00066 0.70586 0.00788 0.08800 0.00101 0.02677 0.00029 536 11 542 5 544 6 534 6 0.37% 0.59
MDL2-100 0.06460 0.00950 0.95827 0.13946 0.10756 0.00277 0.05241 0.00574 761 45 682 72 659 16 1032 23 3.49% 0.25
MDL2-11 0.05898 0.00060 0.78240 0.00783 0.09620 0.00109 0.02633 0.00039 566 11 587 4 592 6 525 8 0.84% 0.13
MDL2-12 0.06901 0.00124 0.99223 0.01387 0.10429 0.00118 0.03170 0.00041 899 38 700 7 639 7 631 8 9.55% 0.14
MDL2-13 0.06195 0.00055 0.86182 0.00771 0.10089 0.00114 0.04705 0.00049 672 11 631 4 620 7 929 9 1.77% 0.16
MDL2-15 0.06473 0.00149 1.07623 0.02401 0.12057 0.00155 0.03642 0.00052 766 26 742 12 734 9 723 10 1.09% 1.16
MDL2-16 0.05978 0.00059 0.78215 0.00773 0.09487 0.00108 0.02696 0.00039 596 11 587 4 584 6 538 8 0.51% 0.12
MDL2-18 0.06438 0.00118 0.94069 0.01341 0.10598 0.00122 0.03246 0.00039 754 40 673 7 649 7 646 8 3.70% 0.08
MDL2-19 0.07136 0.00111 1.57543 0.02384 0.16009 0.00194 0.04821 0.00067 968 14 961 9 957 11 952 13 0.42% 0.65
MDL2-20 0.06056 0.00055 0.62102 0.00562 0.07436 0.00084 0.01414 0.00023 624 11 490 4 462 5 284 5 6.06% 0.06
MDL2-21 0.05955 0.00088 0.77639 0.01122 0.09454 0.00111 0.02778 0.00053 587 14 583 6 582 7 554 10 0.17% 0.17
MDL2-22 0.05819 0.00125 0.70276 0.01478 0.08758 0.00108 0.02611 0.00061 537 25 540 9 541 6 521 12 0.18% 0.26
MDL2-23 0.07367 0.00132 1.27809 0.01749 0.12583 0.00145 0.03797 0.00055 1032 37 836 8 764 8 753 11 9.42% 0.08
MDL2-25 0.05715 0.00067 0.69728 0.00800 0.08848 0.00102 0.02510 0.00038 497 12 537 5 547 6 501 7 1.83% 0.20
MDL2-26 0.05828 0.00129 0.72970 0.01376 0.09081 0.00106 0.02814 0.00032 540 50 556 8 560 6 561 6 0.71% 0.12
MDL2-27 0.06538 0.00095 1.14256 0.01631 0.12672 0.00150 0.03932 0.00045 787 14 774 8 769 9 780 9 0.65% 1.18
MDL2-28 0.05924 0.00076 0.76358 0.00965 0.09347 0.00109 0.02780 0.00039 576 12 576 6 576 6 554 8 0.00% 0.30
MDL2-29 0.06797 0.00080 1.34196 0.01546 0.14317 0.00166 0.04119 0.00049 868 11 864 7 863 9 816 10 0.12% 0.54
MDL2-31 0.06304 0.00316 1.00447 0.04962 0.11554 0.00173 0.03646 0.00067 710 23 706 25 705 10 724 13 0.14% 1.50
MDL2-32 0.07562 0.00183 1.41377 0.02950 0.13560 0.00167 0.04079 0.00064 1085 50 895 12 820 10 808 12 9.15% 0.10
MDL2-33 0.05947 0.00066 0.73124 0.00800 0.08917 0.00103 0.02431 0.00037 584 11 557 5 551 6 485 7 1.09% 0.14
MDL2-34 0.05995 0.00066 0.77005 0.00839 0.09314 0.00107 0.02326 0.00035 602 11 580 5 574 6 465 7 1.05% 0.15
MDL2-35 0.05910 0.00061 0.78171 0.00800 0.09592 0.00110 0.02745 0.00037 571 11 586 5 590 6 547 7 0.68% 0.13
MDL2-36 0.05855 0.00091 0.72556 0.01105 0.08987 0.00107 0.02753 0.00056 550 15 554 7 555 6 549 11 0.18% 0.15
MDL2-37 0.05890 0.00064 0.80078 0.00863 0.09860 0.00114 0.02898 0.00041 563 11 597 5 606 7 577 8 1.49% 0.15
MDL2-38 0.05919 0.00130 0.73189 0.01566 0.08967 0.00111 0.02678 0.00046 574 26 558 9 554 7 534 9 0.72% 0.64
MDL2-39 0.06069 0.00102 0.80594 0.01318 0.09630 0.00117 0.02920 0.00062 628 17 600 7 593 7 582 12 1.18% 0.19
MDL2-41 0.05958 0.00090 0.77725 0.01152 0.09460 0.00113 0.02705 0.00042 588 15 584 7 583 7 539 8 0.17% 0.36
MDL2-42 0.05873 0.00120 0.73216 0.01462 0.09040 0.00111 0.02778 0.00052 557 23 558 9 558 7 554 10 0.00% 0.39
MDL2-45 0.06003 0.00104 0.77911 0.01318 0.09412 0.00114 0.02856 0.00040 605 18 585 8 580 7 569 8 0.86% 0.65
MDL2-46 0.06002 0.00114 0.75980 0.01398 0.09180 0.00114 0.02796 0.00046 604 20 574 8 566 7 557 9 1.41% 0.57
MDL2-47 0.05832 0.00343 0.67216 0.03908 0.08357 0.00125 0.02595 0.00046 542 10 522 24 517 7 518 9 0.97% 1.76
MDL2-49 0.05854 0.00108 0.72367 0.01311 0.08964 0.00109 0.02670 0.00045 550 20 553 8 553 6 533 9 0.00% 0.44
MDL2-51 0.05912 0.00082 0.76719 0.01046 0.09410 0.00111 0.02691 0.00035 572 13 578 6 580 7 537 7 0.34% 0.76
MDL2-52 0.10962 0.00150 4.62465 0.06159 0.30594 0.00375 0.08747 0.00136 1793 11 1754 11 1721 19 1695 25 4.18% 0.55
MDL2-53 0.06544 0.00146 0.98753 0.02149 0.10944 0.00138 0.03673 0.00050 789 25 697 11 669 8 729 10 4.19% 1.52
MDL2-54 0.11483 0.00173 4.95146 0.07223 0.31269 0.00394 0.09362 0.00167 1877 12 1811 12 1754 19 1809 31 7.01% 0.46
MDL2-57 0.05900 0.00075 0.75248 0.00947 0.09249 0.00109 0.02428 0.00074 567 12 570 5 570 6 485 15 0.00% 0.05
MDL2-58 0.17877 0.00446 12.30161 0.25669 0.49909 0.00681 0.13758 0.00182 2641 42 2628 20 2610 29 2605 32 1.19% 0.98
MDL2-59 0.06048 0.00091 0.79952 0.01171 0.09586 0.00116 0.00838 0.00029 621 14 597 7 590 7 169 6 1.19% 0.16
MDL2-60 0.06230 0.00269 0.90892 0.03868 0.10580 0.00150 0.03860 0.00127 684 67 656 21 648 9 766 25 1.23% 0.32
MDL2-61 0.06606 0.00215 1.17252 0.03712 0.12872 0.00184 0.03922 0.00079 808 42 788 17 781 11 778 15 0.90% 0.86
MDL2-62 0.06060 0.00082 0.82343 0.01098 0.09854 0.00117 0.02819 0.00044 625 13 610 6 606 7 562 9 0.66% 0.28
MDL2-64 0.05816 0.00132 0.71147 0.01583 0.08872 0.00112 0.02700 0.00046 536 27 546 9 548 7 538 9 0.36% 0.72
MDL2-65 0.05760 0.00101 0.67761 0.01166 0.08530 0.00104 0.02509 0.00058 515 18 525 7 528 6 501 11 0.57% 0.17
MDL2-67 0.05912 0.00130 0.71543 0.01544 0.08776 0.00110 0.02464 0.00065 572 26 548 9 542 7 492 13 1.11% 0.26
MDL2-68 0.06221 0.00095 0.80096 0.01195 0.09337 0.00113 0.02758 0.00065 681 15 597 7 575 7 550 13 3.83% 0.12
MDL2-69 0.06579 0.00201 1.19774 0.03567 0.13201 0.00180 0.04060 0.00065 800 40 800 16 799 10 804 13 0.13% 1.79
MDL2-70 0.06252 0.00114 0.97433 0.01733 0.11302 0.00141 0.02207 0.00082 692 19 691 9 690 8 441 16 0.14% 0.13
MDL2-71 0.06059 0.00107 0.76531 0.01319 0.09159 0.00113 0.01539 0.00094 625 18 577 8 565 7 309 19 2.12% 0.08
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
14
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
MDL2-73 0.05785 0.00163 0.67324 0.01861 0.08438 0.00111 0.02512 0.00059 524 38 523 11 522 7 501 12 0.19% 0.43
MDL2-74 0.06055 0.00107 0.84326 0.01462 0.10098 0.00125 0.03237 0.00056 623 18 621 8 620 7 644 11 0.16% 0.40
MDL2-75 0.11313 0.00171 5.20192 0.07656 0.33343 0.00415 0.09453 0.00159 1850 12 1853 13 1855 20 1826 29 0.27% 0.55
MDL2-77 0.05885 0.00167 0.70961 0.01969 0.08743 0.00115 0.00791 0.00118 562 38 545 12 540 7 159 24 0.93% 0.13
MDL2-78 0.05939 0.00222 0.69399 0.02430 0.08475 0.00110 0.02620 0.00030 582 83 535 15 524 7 523 6 2.10% 0.50
MDL2-79 0.07060 0.00132 1.56689 0.02867 0.16094 0.00203 0.04650 0.00074 946 19 957 11 962 11 919 14 0.52% 0.94
MDL2-80 0.05777 0.00128 0.67073 0.01456 0.08419 0.00106 0.02614 0.00044 521 26 521 9 521 6 522 9 0.00% 0.73
MDL2-81 0.10390 0.00294 4.20373 0.11572 0.29337 0.00423 0.06544 0.00174 1695 30 1675 23 1658 21 1281 33 2.23% 0.69
MDL2-82 0.11850 0.00169 5.62815 0.07865 0.34439 0.00424 0.09150 0.00191 1934 11 1920 12 1908 20 1770 35 1.36% 0.18
MDL2-83 0.05924 0.00087 0.77010 0.01109 0.09427 0.00114 0.02521 0.00041 576 14 580 6 581 7 503 8 0.17% 0.34
MDL2-85 0.06008 0.00084 0.82813 0.01137 0.09995 0.00120 0.02990 0.00057 606 13 613 6 614 7 595 11 0.16% 0.09
MDL2-89 0.06980 0.00107 1.05305 0.01589 0.10940 0.00134 0.02876 0.00061 922 14 730 8 669 8 573 12 9.12% 0.16
MDL2-90 0.05980 0.00116 0.72794 0.01125 0.08829 0.00104 0.02728 0.00044 596 43 555 7 545 6 544 9 1.83% 0.05
MDL2-91 0.06753 0.00097 1.15238 0.01638 0.12375 0.00150 0.03741 0.00057 854 13 778 8 752 9 742 11 3.46% 0.69
MDL2-93 0.07013 0.00115 1.40692 0.02255 0.14548 0.00181 0.04444 0.00074 932 15 892 10 876 10 879 14 1.83% 0.59
MDL2-94 0.11466 0.00166 5.33717 0.07611 0.33754 0.00415 0.09457 0.00153 1875 12 1875 12 1875 20 1826 28 0.00% 0.58
MDL2-98 0.06233 0.00629 0.93634 0.09312 0.10893 0.00237 0.03722 0.00171 685 56 671 49 667 14 739 33 0.60% 0.63
MDL2-99 0.05969 0.01168 0.76986 0.14918 0.09352 0.00291 0.02648 0.00104 592 56 580 86 576 17 528 20 0.69% 2.31
Maha Oya MOL1-02 0.05980 0.00140 0.73551 0.01487 0.08921 0.00105 0.02756 0.00033 596 52 560 9 551 6 550 7 1.63% 0.11
MOL1-03 0.07685 0.00327 1.51728 0.06135 0.14320 0.00191 0.04300 0.00051 1117 87 937 25 863 11 851 10 8.57% 0.65
MOL1-04 0.06525 0.00151 1.01275 0.02016 0.11256 0.00133 0.03443 0.00040 783 50 710 10 688 8 684 8 3.20% 0.13
MOL1-05 0.07632 0.00323 1.72166 0.06909 0.16360 0.00219 0.04917 0.00057 1104 87 1017 26 977 12 970 11 4.09% 0.71
MOL1-06 0.06894 0.00116 1.26936 0.02158 0.13353 0.00159 0.02192 0.00036 897 17 832 10 808 9 438 7 2.97% 0.24
MOL1-07 0.05797 0.00105 0.73246 0.01340 0.09162 0.00111 0.02604 0.00050 529 20 558 8 565 7 520 10 1.24% 0.20
MOL1-08 0.05935 0.00108 0.74883 0.01370 0.09149 0.00110 0.02441 0.00055 580 20 568 8 564 6 487 11 0.71% 0.10
MOL1-09 0.06377 0.00136 0.98853 0.02102 0.11241 0.00141 0.03385 0.00059 734 25 698 11 687 8 673 12 1.60% 1.23
MOL1-10 0.06689 0.00115 1.18975 0.02069 0.12898 0.00154 0.03812 0.00062 834 18 796 10 782 9 756 12 1.79% 0.84
MOL1-11 0.06560 0.00115 1.14131 0.02023 0.12616 0.00151 0.03261 0.00055 794 19 773 10 766 9 649 11 0.91% 0.55
MOL1-12 0.06159 0.00107 0.84315 0.01485 0.09927 0.00119 0.02117 0.00042 660 19 621 8 610 7 423 8 1.80% 0.10
MOL1-14 0.06970 0.00227 1.50641 0.04520 0.15675 0.00196 0.04759 0.00054 920 68 933 18 939 11 940 10 0.64% 0.46
MOL1-15 0.05911 0.00125 0.75570 0.01338 0.09272 0.00108 0.02869 0.00034 571 47 572 8 572 6 572 7 0.00% 0.04
MOL1-16 0.07215 0.00130 1.61594 0.02935 0.16242 0.00196 0.04763 0.00080 990 19 976 11 970 11 940 15 0.62% 1.09
MOL1-17 0.07093 0.00127 1.38304 0.02493 0.14141 0.00170 0.04424 0.00076 955 19 882 11 853 10 875 15 3.40% 0.52
MOL1-18 0.07178 0.00134 1.71783 0.03215 0.17355 0.00212 0.05540 0.00098 980 20 1015 12 1032 12 1090 19 5.04% 0.57
MOL1-19 0.07726 0.00149 1.68768 0.03253 0.15841 0.00195 0.04839 0.00090 1128 20 1004 12 948 11 955 17 5.91% 0.43
MOL1-20 0.07386 0.00156 1.77337 0.03718 0.17412 0.00219 0.05108 0.00095 1038 23 1036 14 1035 12 1007 18 0.29% 0.79
MOL1-21 0.05936 0.00105 0.74046 0.01325 0.09046 0.00109 0.02691 0.00048 580 20 563 8 558 6 537 9 0.90% 0.18
MOL1-22 0.06341 0.00131 0.85986 0.01765 0.09833 0.00122 0.06526 0.00218 722 23 630 10 605 7 1278 41 4.13% 0.04
MOL1-23 0.05926 0.00108 0.73199 0.01336 0.08957 0.00108 0.03327 0.00064 577 20 558 8 553 6 662 13 0.90% 0.12
MOL1-24 0.06025 0.00111 0.78393 0.01445 0.09436 0.00114 0.02713 0.00056 613 20 588 8 581 7 541 11 1.20% 0.11
MOL1-25 0.06098 0.00121 0.81246 0.01605 0.09661 0.00119 0.02909 0.00052 639 22 604 9 595 7 580 10 1.51% 0.64
MOL1-26 0.06065 0.00195 0.69007 0.02053 0.08252 0.00100 0.02545 0.00091 627 71 533 12 511 6 508 18 4.31% 0.07
MOL1-27 0.06852 0.00122 1.27811 0.02299 0.13527 0.00162 0.04461 0.00077 884 19 836 10 818 9 882 15 2.20% 0.44
MOL1-28 0.06200 0.00112 0.85807 0.01564 0.10037 0.00121 0.03116 0.00072 674 20 629 9 617 7 620 14 1.94% 0.05
MOL1-29 0.06809 0.00120 1.08128 0.01923 0.11516 0.00138 0.03468 0.00065 871 19 744 9 703 8 689 13 5.83% 0.04
MOL1-30 0.06657 0.00127 0.93742 0.01795 0.10212 0.00125 0.02664 0.00075 824 21 672 9 627 7 531 15 7.18% 0.07
MOL1-31 0.05863 0.00133 0.70586 0.01591 0.08730 0.00110 0.02636 0.00051 553 28 542 9 540 7 526 10 0.37% 0.75
MOL1-32 0.06020 0.00136 0.71163 0.01597 0.08572 0.00109 0.02556 0.00051 611 27 546 9 530 6 510 10 3.02% 0.62
MOL1-33 0.06342 0.00115 0.86015 0.01570 0.09835 0.00118 0.02225 0.00042 722 20 630 9 605 7 445 8 4.13% 0.13
MOL1-34 0.06915 0.00146 1.39992 0.02932 0.14681 0.00184 0.04447 0.00103 903 23 889 12 883 10 879 20 0.68% 0.26
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S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
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Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
MOL1-36 0.07003 0.00129 1.17720 0.02174 0.12189 0.00147 0.03749 0.00067 929 19 790 10 741 8 744 13 6.61% 0.44
MOL1-37 0.07542 0.00147 1.65485 0.03230 0.15912 0.00196 0.04235 0.00078 1080 21 991 12 952 11 838 15 4.10% 0.86
MOL1-39 0.07199 0.00141 1.41304 0.02767 0.14234 0.00175 0.04109 0.00078 986 21 894 12 858 10 814 15 4.20% 0.59
MOL1-40 0.06599 0.00143 1.09156 0.02347 0.11996 0.00150 0.03708 0.00069 806 25 749 11 730 9 736 13 2.60% 1.28
MOL1-41 0.05857 0.00123 0.72432 0.01510 0.08968 0.00111 0.02948 0.00102 551 25 553 9 554 7 587 20 0.18% 0.06
MOL1-42 0.05879 0.00111 0.74648 0.01414 0.09207 0.00112 0.02672 0.00056 559 21 566 8 568 7 533 11 0.35% 0.08
MOL1-44 0.05924 0.00111 0.72391 0.01366 0.08862 0.00107 0.02599 0.00049 576 21 553 8 547 6 519 10 1.10% 0.17
MOL1-45 0.05932 0.00114 0.74408 0.01427 0.09097 0.00111 0.02642 0.00051 579 22 565 8 561 7 527 10 0.71% 0.21
MOL1-46 0.05915 0.00114 0.70464 0.01357 0.08638 0.00105 0.02661 0.00051 573 22 542 8 534 6 531 10 1.50% 0.22
MOL1-47 0.06124 0.00167 0.70291 0.01710 0.08324 0.00101 0.02565 0.00029 648 60 541 10 515 6 512 6 5.05% 0.19
MOL1-48 0.06053 0.00154 0.70360 0.01763 0.08429 0.00110 0.02627 0.00060 623 32 541 11 522 7 524 12 3.64% 0.49
MOL1-49 0.06188 0.00126 0.74848 0.01523 0.08772 0.00108 0.02699 0.00055 670 23 567 9 542 6 538 11 4.61% 0.35
MOL1-50 0.06678 0.00298 1.14982 0.04897 0.12487 0.00167 0.03809 0.00043 831 95 777 23 759 10 756 8 2.37% 0.77
MOL1-51 0.06564 0.00154 1.11867 0.02589 0.12358 0.00158 0.03741 0.00074 795 28 762 12 751 9 742 14 1.46% 1.60
MOL1-53 0.06900 0.00139 1.22285 0.02456 0.12852 0.00159 0.03996 0.00078 899 22 811 11 779 9 792 15 4.11% 0.95
MOL1-55 0.05924 0.00128 0.71853 0.01547 0.08795 0.00110 0.02685 0.00055 576 26 550 9 543 7 536 11 1.29% 0.48
MOL1-56 0.06974 0.00141 1.23684 0.02485 0.12860 0.00159 0.04023 0.00079 921 22 817 11 780 9 797 15 4.74% 0.99
MOL1-57 0.06684 0.00170 0.90265 0.02015 0.09794 0.00120 0.02987 0.00034 833 54 653 11 602 7 595 7 8.47% 0.13
MOL1-58 0.06120 0.00149 0.72700 0.01748 0.08615 0.00111 0.02635 0.00066 646 30 555 10 533 7 526 13 4.13% 0.31
MOL1-59 0.07133 0.00144 1.37243 0.02764 0.13952 0.00172 0.03016 0.00061 967 22 877 12 842 10 601 12 4.16% 0.42
MOL1-60 0.17104 0.00345 10.66728 0.21451 0.45227 0.00561 0.12132 0.00250 2568 18 2495 19 2405 25 2314 45 6.78% 0.36
MOL1-61 0.06918 0.00164 1.32224 0.03093 0.13860 0.00178 0.04216 0.00095 904 28 855 14 837 10 835 18 2.15% 0.47
MOL1-62 0.05924 0.00150 0.76411 0.01910 0.09353 0.00122 0.00903 0.00054 576 32 576 11 576 7 182 11 0.00% 0.18
MOL1-63 0.06934 0.00166 1.21729 0.02870 0.12731 0.00164 0.03892 0.00087 909 28 809 13 773 9 772 17 4.66% 0.54
MOL1-64 0.06666 0.00181 1.18459 0.03162 0.12887 0.00174 0.03977 0.00105 827 33 793 15 781 10 788 20 1.54% 0.41
MOL1-65 0.06703 0.00167 1.13792 0.02802 0.12311 0.00160 0.05183 0.00125 839 30 772 13 748 9 1021 24 3.21% 0.56
MOL1-66 0.06437 0.00160 1.04065 0.02558 0.11723 0.00152 0.03566 0.00082 754 30 724 13 715 9 708 16 1.26% 0.52
MOL1-67 0.06648 0.00162 1.23545 0.02961 0.13477 0.00175 0.03973 0.00090 822 29 817 13 815 10 787 17 0.25% 0.65
MOL1-70 0.07048 0.00295 1.58121 0.06271 0.16271 0.00221 0.04934 0.00058 942 88 963 25 972 12 973 11 0.93% 0.56
MOL1-71 0.07478 0.00165 1.40181 0.03072 0.13594 0.00172 0.04289 0.00094 1063 24 890 13 822 10 849 18 8.27% 0.55
MOL1-72 0.06318 0.00279 0.95109 0.03982 0.10918 0.00152 0.03352 0.00041 714 96 679 21 668 9 666 8 1.65% 0.36
MOL1-73 0.07193 0.00177 1.48786 0.03605 0.15000 0.00195 0.04753 0.00108 984 29 925 15 901 11 939 21 2.66% 0.71
MOL1-74 0.07299 0.00162 1.72342 0.03797 0.17123 0.00217 0.04933 0.00109 1014 25 1017 14 1019 12 973 21 0.49% 0.50
MOL1-76 0.07055 0.00198 1.17517 0.03239 0.12080 0.00164 0.03796 0.00099 944 34 789 15 735 9 753 19 7.35% 0.55
MOL1-77 0.06108 0.00151 0.77418 0.01886 0.09192 0.00120 0.03004 0.00071 642 30 582 11 567 7 598 14 2.65% 0.53
MOL1-78 0.06124 0.00151 0.73542 0.01786 0.08708 0.00113 0.02630 0.00071 648 30 560 10 538 7 525 14 4.09% 0.19
MOL1-80 0.06060 0.00717 0.70777 0.08298 0.08470 0.00175 0.02571 0.00094 625 32 543 49 524 10 513 19 3.63% 1.72
RV3C-01 0.06089 0.00095 0.58186 0.00806 0.06933 0.00049 0.02201 0.00018 636 33 466 5 432 3 440 4 7.78% 25.10
RV3C-72 0.06458 0.00103 0.80484 0.01124 0.09038 0.00067 0.05180 0.00119 761 33 600 6 558 4 1021 23 7.49% 0.04
RV3C-89 0.07669 0.00429 1.57802 0.08575 0.14923 0.00259 0.04786 0.00154 1113 57 962 34 897 15 945 30 7.24% 0.70
RV3C-104 0.06704 0.00606 0.96445 0.08521 0.10434 0.00242 0.03122 0.00141 839 45 686 44 640 14 621 28 7.16% 0.73
RV3C-02 0.06154 0.00215 0.65407 0.02199 0.07711 0.00077 0.02272 0.00018 658 73 511 14 479 5 454 4 6.73% 153.86
RV3C-78 0.06364 0.00144 0.80152 0.01686 0.09134 0.00078 0.06150 0.01005 730 47 598 10 563 5 1206 12 6.09% 0.00
RV3C-10 0.06739 0.00200 1.04908 0.02962 0.11292 0.00109 0.03490 0.00975 850 60 728 15 690 6 694 11 5.61% 0.01
RV3C-73 0.06262 0.00693 0.76164 0.08245 0.08821 0.00238 0.02810 0.00154 695 78 575 48 545 14 560 30 5.50% 0.68
RV3C-11 0.05944 0.00089 0.57795 0.00765 0.07051 0.00050 0.02262 0.00019 583 32 463 5 439 3 452 4 5.42% 22.17
RV3C-09 0.06007 0.00183 0.61793 0.01798 0.07462 0.00070 0.02036 0.00017 606 64 489 11 464 4 407 3 5.30% 54.28
RV3C-06 0.06186 0.00384 0.73120 0.04440 0.08574 0.00122 0.02681 0.00317 669 44 557 26 530 7 535 62 5.09% 0.11
RV3C-67 0.06181 0.00236 0.73029 0.02677 0.08568 0.00099 0.02657 0.00088 668 80 557 16 530 6 530 17 5.06% 0.25
RV3C-79 0.12048 0.00197 5.31035 0.07683 0.31965 0.00276 0.09318 0.00131 1963 29 1871 12 1788 13 1801 24 9.80% 0.44
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S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
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Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
RV3C-27 0.07475 0.00223 1.59245 0.04560 0.15446 0.00160 0.05524 0.00136 1062 59 967 18 926 9 1087 26 4.47% 0.31
RV3C-76 0.06941 0.00711 1.23043 0.12322 0.12857 0.00355 0.03617 0.00295 911 69 815 56 780 20 718 58 4.46% 0.40
RV3C-109 0.07018 0.00495 1.29555 0.08906 0.13389 0.00270 0.03932 0.00164 934 56 844 39 810 15 780 32 4.17% 0.66
RV3C-60 0.10873 0.00306 4.33917 0.11592 0.28939 0.00359 0.09141 0.00215 1778 50 1701 22 1639 18 1768 40 8.53% 0.49
RV3C-12 0.11618 0.00292 5.05995 0.12028 0.31587 0.00342 0.09017 0.00197 1898 45 1829 20 1770 17 1745 36 7.27% 0.54
RV3C-64 0.06102 0.00123 0.75673 0.01392 0.08994 0.00072 0.02872 0.00312 640 43 572 8 555 4 572 61 3.04% 0.01
RV3C-22 0.07317 0.00237 1.55909 0.04847 0.15451 0.00167 0.04676 0.00100 1019 64 954 19 926 9 924 19 3.01% 0.58
RV3C-04 0.05997 0.00208 0.69721 0.02324 0.08435 0.00087 0.02508 0.00143 602 73 537 14 522 5 501 28 2.89% 0.09
RV3C-34 0.05734 0.00084 0.54524 0.00744 0.06894 0.00049 0.02261 0.00024 504 32 442 5 430 3 452 5 2.82% 18.28
RV3C-107 0.06065 0.00166 0.74629 0.01926 0.08924 0.00083 0.02572 0.00054 627 58 566 11 551 5 513 11 2.72% 0.31
RV3C-07 0.06027 0.00312 0.72415 0.03657 0.08715 0.00110 0.02815 0.00278 613 21 553 22 539 7 561 55 2.67% 0.10
RV3C-41 0.15265 0.00468 8.84874 0.26286 0.42036 0.00624 0.11697 0.00260 2376 51 2323 27 2262 28 2236 47 5.03% 1.27
RV3C-97 0.07397 0.00240 1.63768 0.05068 0.16058 0.00181 0.04541 0.00116 1041 64 985 20 960 10 898 22 2.58% 0.39
RV3C-23 0.06595 0.00176 1.09136 0.02774 0.11998 0.00111 0.03471 0.00343 805 55 749 13 731 6 690 67 2.56% 0.03
RV3C-94 0.16009 0.00510 9.68649 0.30013 0.43883 0.00747 0.10483 0.00285 2457 53 2405 29 2345 33 2015 52 4.74% 0.89
RV3C-18 0.06071 0.00309 0.75717 0.03757 0.09045 0.00118 0.04302 0.00555 629 32 572 22 558 7 851 5 2.54% 0.05
RV3C-54 0.07285 0.00183 1.56181 0.03669 0.15547 0.00149 0.04629 0.00065 1010 50 955 15 932 8 915 12 2.53% 0.80
RV3C-39 0.05982 0.01261 0.70336 0.14522 0.08526 0.00414 0.02521 0.00299 597 34 541 87 528 25 503 59 2.52% 0.57
RV3C-74 0.18135 0.00330 12.15026 0.20367 0.48587 0.00527 0.12861 0.00279 2665 30 2616 16 2553 23 2445 50 4.41% 0.39
RV3C-83 0.06707 0.00248 1.16851 0.04155 0.12635 0.00150 0.03740 0.00124 840 75 786 19 767 9 742 24 2.46% 0.27
RV3C-59 0.11001 0.00176 4.62844 0.06498 0.30510 0.00255 0.08908 0.00115 1800 29 1754 12 1717 13 1725 21 4.84% 0.46
RV3C-25 0.05894 0.00353 0.66609 0.03890 0.08194 0.00120 0.02513 0.00096 565 45 518 24 508 7 502 19 2.09% 0.45
RV3C-106 0.06784 0.00232 1.24025 0.04064 0.13260 0.00150 0.04289 0.00087 864 69 819 18 803 9 849 17 2.03% 0.58
RV3C-58 0.05999 0.00234 0.74104 0.02786 0.08958 0.00102 0.03283 0.00070 603 82 563 16 553 6 653 14 1.81% 0.51
RV3C-85 0.06629 0.00360 1.14657 0.06050 0.12545 0.00189 0.03737 0.00077 815 10 776 29 762 11 742 15 1.80% 1.35
RV3C-87 0.05990 0.00300 0.73733 0.03580 0.08928 0.00124 0.02521 0.00079 600 34 561 21 551 7 503 16 1.72% 0.49
RV3C-81 0.06395 0.00447 0.99642 0.06794 0.11301 0.00215 0.03445 0.00090 740 43 702 35 690 12 685 18 1.71% 1.32
RV3C-66 0.11349 0.00223 5.01326 0.09023 0.32033 0.00309 0.09301 0.00138 1856 35 1822 15 1791 15 1798 25 3.62% 0.63
RV3C-08 0.07017 0.00583 1.41696 0.11548 0.14648 0.00280 0.04417 0.00262 933 45 896 49 881 16 874 51 1.69% 0.47
RV3C-96 0.07325 0.00181 1.63756 0.03792 0.16214 0.00153 0.04682 0.00064 1021 49 985 15 969 8 925 12 1.67% 0.79
RV3C-92 0.05863 0.00178 0.66580 0.01923 0.08235 0.00081 0.02565 0.00282 554 65 518 12 510 5 512 56 1.57% 0.02
RV3C-43 0.05920 0.00381 0.70257 0.04425 0.08606 0.00139 0.02713 0.00091 575 34 540 26 532 8 541 18 1.52% 0.68
RV3C-77 0.06769 0.00233 1.26094 0.04154 0.13510 0.00154 0.04647 0.01199 859 70 828 19 817 9 918 34 1.40% 0.01
RV3C-98 0.06571 0.00225 1.12814 0.03693 0.12452 0.00137 0.02219 0.00134 797 70 767 18 757 8 444 26 1.36% 0.29
RV3C-38 0.06859 0.00374 1.32911 0.07068 0.14051 0.00221 0.04708 0.00149 886 34 859 31 848 12 930 29 1.29% 0.63
RV3C-16 0.05955 0.00970 0.74092 0.11923 0.09023 0.00256 0.02380 0.00369 587 45 563 70 557 15 475 73 1.08% 0.33
RV3C-13 0.05861 0.00241 0.68369 0.02718 0.08459 0.00100 0.02916 0.00150 553 87 529 16 524 6 581 29 1.05% 0.11
RV3C-52 0.05918 0.00277 0.72766 0.03294 0.08917 0.00114 0.02753 0.00076 574 99 555 19 551 7 549 15 0.84% 0.51
RV3C-110 0.07081 0.00359 1.50955 0.07421 0.15463 0.00246 0.04255 0.00126 952 12 934 30 927 14 842 24 0.81% 0.73
RV3C-21 0.11664 0.00382 5.42749 0.17052 0.33740 0.00461 0.09570 0.00278 1905 58 1889 27 1874 22 1847 51 1.66% 0.53
RV3C-56 0.05854 0.00209 0.69554 0.02384 0.08616 0.00092 0.02990 0.00226 550 76 536 14 533 5 596 44 0.62% 0.05
RV3C-71 0.07102 0.00185 1.54243 0.03770 0.15750 0.00152 0.04716 0.00076 958 52 948 15 943 8 931 15 0.49% 0.58
RV3C-75 0.06713 0.00337 1.27206 0.06196 0.13742 0.00201 0.04386 0.00144 842 23 833 28 830 11 868 28 0.39% 0.46
RV3C-26 0.06995 0.00410 1.47827 0.08422 0.15323 0.00261 0.04743 0.00143 927 23 922 35 919 15 937 28 0.27% 0.86
RV3C-84 0.05850 0.00176 0.70621 0.02025 0.08756 0.00086 0.03079 0.00128 548 65 543 12 541 5 613 25 0.26% 0.09
RV3C-49 0.05887 0.00167 0.73116 0.02024 0.09008 0.00085 0.03144 0.00193 562 61 557 12 556 5 626 38 0.22% 0.04
RV3C-88 0.06965 0.00164 1.46535 0.03223 0.15258 0.00139 0.04464 0.00083 918 48 916 13 915 8 883 16 0.09% 0.34
RV3C-62 0.05847 0.00347 0.71796 0.04137 0.08904 0.00142 0.02905 0.00213 548 34 550 24 550 8 579 42 0.05% 0.12
RV3C-05 0.06353 0.00272 1.04706 0.04343 0.11957 0.00143 0.04828 0.00203 726 88 727 22 728 8 953 39 0.10% 0.18
RV3C-46 0.05586 0.00318 0.55749 0.03102 0.07238 0.00108 0.01999 0.00025 446 33 450 20 451 6 400 5 0.13% 207.80
(continued on next page)
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
17
Table 2 (continued)
CORRECTED RATIOS CORRECTED AGES
(Ma)
River Analysis 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Degree of Th/U
(Sample No. and 1σ 1σ 1σ 1σ 1σ 1σ 1σ 1σ Discordance
Spot No.)
RV3C-102 0.07069 0.00271 1.55586 0.05755 0.15964 0.00196 0.04478 0.00144 948 77 953 23 955 11 885 28 0.21% 0.33
RV3C-19 0.05845 0.00336 0.72323 0.04044 0.08972 0.00135 0.06864 0.01605 547 23 553 24 554 8 1342 45 0.23% 0.01
RV3C-55 0.05789 0.00154 0.68926 0.01721 0.08634 0.00078 0.02642 0.00057 525 57 532 10 534 5 527 11 0.26% 0.25
RV3C-30 0.05855 0.00728 0.73339 0.08979 0.09081 0.00228 0.02798 0.00302 551 45 559 53 560 13 558 59 0.32% 0.27
RV3C-63 0.05722 0.00202 0.65232 0.02214 0.08268 0.00087 0.02367 0.00408 499 77 510 14 512 5 473 81 0.43% 0.02
RV3C-28 0.05825 0.00225 0.71820 0.02690 0.08940 0.00099 0.02930 0.00254 539 83 550 16 552 6 584 50 0.43% 0.05
RV3C-37 0.06672 0.00261 1.28645 0.04878 0.13980 0.00171 0.04300 0.00101 829 79 840 22 844 10 851 20 0.45% 0.68
RV3C-93 0.06347 0.00231 1.06243 0.03708 0.12139 0.00139 0.03568 0.00048 724 75 735 18 739 8 709 9 0.49% 1.64
RV3C-35 0.06298 0.00295 1.03339 0.04706 0.11896 0.00159 0.03455 0.00256 708 97 721 24 725 9 687 50 0.55% 0.11
RV3C-42 0.05796 0.00300 0.70944 0.03584 0.08876 0.00126 -0.00299 0.00397 528 56 544 21 548 7 -61 81 0.69% 0.05
RV3C-32 0.05803 0.00538 0.72032 0.06544 0.09000 0.00195 0.02646 0.00229 531 34 551 39 556 12 528 45 0.83% 0.28
RV3C-61 0.06675 0.00228 1.30722 0.04273 0.14201 0.00160 0.03872 0.00306 830 70 849 19 856 9 768 60 0.83% 0.07
RV3C-48 0.05806 0.00210 0.72633 0.02559 0.09073 0.00099 0.02836 0.00127 532 78 554 15 560 6 565 25 0.96% 0.13
RV3C-47 0.05788 0.00146 0.71615 0.01763 0.08973 0.00079 0.02069 0.00158 525 55 548 10 554 5 414 31 0.99% 0.03
RV3C-100 0.05699 0.00149 0.67097 0.01658 0.08539 0.00076 0.02534 0.00064 491 57 521 10 528 5 506 13 1.31% 0.19
RV3C-86 0.06962 0.00333 1.54129 0.07162 0.16057 0.00237 0.04630 0.00164 917 96 947 29 960 13 915 32 1.34% 0.42
RV3C-99 0.05672 0.00349 0.65961 0.03955 0.08435 0.00133 0.02446 0.00079 480 34 514 24 522 8 488 16 1.46% 0.62
RV3C-103 0.06216 0.00303 1.02028 0.04817 0.11904 0.00169 0.03582 0.00179 680 23 714 24 725 10 711 35 1.50% 0.19
RV3C-57 0.06348 0.00140 1.11401 0.02281 0.12725 0.00109 0.03968 0.00042 725 46 760 11 772 6 787 8 1.57% 0.95
RV3C-44 0.07122 0.00450 1.67912 0.10352 0.17096 0.00315 0.05287 0.00234 964 21 1001 39 1017 17 1041 45 5.27% 0.50
RV3C-40 0.06425 0.00393 1.18329 0.07060 0.13355 0.00228 0.03906 0.00088 750 24 793 33 808 13 774 17 1.89% 1.94
RV3C-70 0.06748 0.00367 1.42900 0.07584 0.15357 0.00233 0.04576 0.00125 853 12 901 32 921 13 904 24 2.15% 0.77
RV3C-90 0.05504 0.00245 0.60418 0.02601 0.07960 0.00098 0.02325 0.00079 414 23 480 16 494 6 465 16 2.81% 0.31
RV3C-82 0.05624 0.00183 0.69732 0.02176 0.08992 0.00090 0.02639 0.00046 461 71 537 13 555 5 526 9 3.22% 0.62
RV3C-105 0.05605 0.00217 0.68919 0.02576 0.08918 0.00099 0.02662 0.00073 454 84 532 15 551 6 531 14 3.34% 0.33
RV3C-50 0.06820 0.00302 0.96219 0.04156 0.10232 0.00135 0.02810 0.00170 875 89 684 22 628 8 560 34 8.98% 0.18
RV3C-31 0.05552 0.00273 0.68147 0.03270 0.08900 0.00116 0.02710 0.00090 433 34 528 20 550 7 541 18 3.98% 0.40
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 3. Representative older grains of Mesoproterozoic to Archean zircons found in this study, from each river basin. The grain point number and the respective age
are also given (analytical spot marked with a circle). Sample numbers are same as those in Fig. 1.
One hundred and sixty spots on 125 grains were analyzed. Grains rivers display moderately enriched light REE patterns without a sig-
younger than ∼1.1 Ga closely plot on the concordia line (Fig. 4a). nificant Ce anomaly (Fig. 8). The Neoproterozoic to late Cambrian
Zircons from Maha Oya are characterized by giving a majority of con- zircons show slightly elevated overall REE abundances compared to the
cordant ages. Major peaks at 560, 610, 780, 820 and 970Ma are ob- Mesoproterozoic to Archean zircon population. The metamorphic
served along with subordinate peaks between 1020 and 2400Ma grains and rims/overgrowths display slightly flat REE (particularly
(Fig. 5f, h). heavy REE, though variable) patterns (Fig. 8).
Most zircons have Th/U values> 0.1 (Fig. 7) consistent with their
igneous origin. Also, the zircons which could have been derived from
6. Discussion
felsic sources are plotted above those from other igneous sources
(Fig. 7a). Several different trends can be distinguished from the Th/U
6.1. Detrital zircons as provenance indicators
vs. U-Pb age diagram, and it could be attributed to different growth
mechanisms as magmatic events prolonged in the Sri Lankan basement.
In a single river sediment sample, the zircons may represent a
Hence, clearly distinct zircon populations are visible: an older popula-
variety of sources, such as mafic, felsic, intermediate or metamorphic
tion with ages from Mesoproterozoic to Archean, and a younger po-
rocks. In addition, once formed, the zircons may be reworked and re-
pulation with ages of early Neoproterozoic to late Cambrian (Fig. 6).
cycled within the crust through various geological processes. In geo-
The younger population is also characterized by a group of zircons with
chronology, the provenance of detrital zircons is interpreted based on
homogenous and/or core-rim zoning texture in CL images and Th/U
the population distributions of U–Pb ages. The presence of particular
ratios< 0.1, indicating metamorphic origin (Figs. 3 and 7b). These
age groups is a powerful indicator of the source area within the drai-
grains characteristically plot in the range of∼500–650Ma (Fig. 6). The
nage system during or prior to the deposition of the sample (Rubatto,
early Neoproterozoic to late Cambrian zircons are characterized by
2002). However, detrital zircons can be recycled from older sedimen-
variable Th/U ratios> 0.1 reaching values of ∼3, whereas the Meso-
tary rocks, and potential source areas may contain several groups of
proterozoic to Archean zircons could be distinguished by their rela-
different ages. Therefore, it is not simply possible to assign individual
tively homogeneous Th/U ratios compared to the former (Fig. 7).
age groups to a specific source area. Hence, provenance analysis re-
In general, on chondrite-normalized REE diagrams, most of the
quires a thorough understanding of the distribution of primary bed-
zircons have slightly fractionated, depleted light REE and enriched
rocks and sedimentary sources for the zircon grains in the target sam-
heavy REE patterns with variable positive Ce anomalies and negative
ples (e.g. Xiang et al., 2011; Iizuka et al., 2013b).
Eu anomalies, although some zircons from Kalu Ganga and Maha Oya
In elucidating zircon provenances, Th/U plays an important role.
18
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 4. Concordia diagrams of dated zircons from each of the major river basins of Sri Lanka. Sample numbers are same as those in Fig. 1.
The U and Th contents and Th/U ratios of magmatic zircon should The Th/U ratios of our zircon samples are plotted in the Fig. 7. It is
promote higher Th contents relative to U contents at their crystal- clear from this figure that majority of the zircons have Th/U > 0.1 and
lization, resulting in higher Th/U ratios for zircons in mafic to inter- span in an age range from late Cambrian to late Proterozoic. Out of this
mediate rocks than in felsic rocks (Kemp et al. 2006; Xiang et al., 2011; group, more younger zircons (e.g. ca.< 1000Ma old) are characterized
Iizuka et al., 2013a). However, when zircon crystallizes in dis- with a variable Th/U ratio from 0.1 to 2.9 whereas the older grains
equilibrium with melt, U and Th are more easily able to enter the zircon have Th/U < ∼1. The metamorphic zircons have Th/U ratio below
lattice, and their contents and Th/U values depend mainly on the de- 0.1, reaching very low values. Accordingly, distinct origins of sources as
gree of disequilibrium (e.g. Wang et al., 2011a,b). On the other hand, mafic to intermediate and felsic and metamorphic could be identified
Th/U values in metamorphic zircons is usually very low (typically from the studied zircon population.
below 0.1) due to availability of other common phases with differential
geochemical affinities for U and Th (e.g. Rubatto, 2002). Hence, based 6.2. Zircon growth episodes displayed by Sri Lankan rivers
on observations and experimental data (e.g. Wang et al., 2011a,b,
Rubatto, 2002), the Th/U value of zircons is generally fixed as follows; Out of the total population of zircons of each river, nearly 30% of
felsic magmatic sources (> 1), mafic-intermediate magmatic sources the grains are represented by Mesoproterozoic to Archean zircons
(< 1,> 0.1) and metamorphic sources (< 0.1). Thus, the behavior of U (>∼1100–3100Ma). Most of these older grains are transparent in CL
and Th in zircon can be used as a geochemical indicator to determine images and with rounded edges, having clear magmatic textures with
their origins and crystallization environments (Rubatto, 2002; Xiang oscillatory zoning (Figs. 2 and 3). These grain morphologies and tex-
et al., 2011). tural patterns are consistent with Archean detrital zircons found
19
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 5. Relative probability against U-Pb age for analyzed zircons of each river in this study, showing distribution of age peaks. Sample numbers are same as those in
Fig. 1. See text for details.
elsewhere in the world (e.g. Su et al., 2011; Li et al., 2014; Chen et al., in terms of Th/U values (Fig. 7). Some of the grains were overgrown
2017; Sakyi et al., 2018), probably subjected to repeated crustal re- during the Neoproterozoic metamorphic activity by generating a clear
cycling, before they were trapped in the precursor rocks of the Sri mantle-rim domain over the early igneous core domain (Fig. 2).
Lankan lithotectonic units. In addition, they may have experienced Considering the overall age distribution data, the total zircon po-
multiphase reworking with exotic Archean sources. pulations could be further subdivided into several narrow sub-groups,
The vast majority of the zircon population (∼70%) from all rivers such as 480–680Ma, 680–1000Ma, 1100–1300Ma, 1300–1700Ma,
could be classified as Neoproterozoic to late Cambrian zircons 1700–1900Ma, 2100–2300Ma, 2300–2600Ma. This could be seen in
(>∼430–1000Ma). Of course, there is a minor population of zircons Fig. 6 and indicate that the crustal growth of Sri Lanka was not con-
which falls in to the Silurian times as well (Fig. 6a). In this category, tinuous and has been episodic since the Archean.
zircon grains belong to both igneous and metamorphic origin. In gen-
eral, these ‘younger’ zircons are highly variable in shape compared to
the older counterparts (Mesoproterozoic to Archean zircons). The 6.3. Regional provenance controls on the detrital zircons
magmatic zircons are clearly distinguished from those of metamorphic
origin with respect to their morphology and internal textures, and also 6.3.1. Provenance implications of older zircon population
As mentioned above, Mesoproterozoic- to Archean-aged Zircons
20
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 6. Relative probability against U-Pb age for the entire zircon population dated in the present study, showing overall distribution of age peaks at different
geological times. The total zircon ages could be distributed into several narrow groups, such as 480–680Ma, 680–1000Ma, 1100–1300Ma, 1300–1700Ma,
1700–1900Ma, 2100–2300Ma, 2300–2600Ma, showing discontinuous crustal growth in Sri Lanka from Archean to late Cambrian. See text for details.
(>∼1100–3100Ma) make up approximately 30% of the total age (Fig. 5f). Hence, the older population of detrital zircons from the four
population with a prominent peak at 1.6–2 Ga (Fig. 6), which may be rivers (Mahaweli, Kalu, Kelani and Maha Oya) probably indicates the
related to Meso to Paleoproterozoic HC, WC and KC rocks in the same provenance. On the other hand, the Walawe and Maduru Oya
catchment of most of the rivers. The detrital zircons from the HC rocks Rivers flow over a wider area of the VC and their older zircons show
indicate a widespread igneous intrusion event at 1.9 Ga, while Sm-Nd more or less similar distribution pattern with a wider peak from 1.1 to
crustal residence ages of the HC and WC rocks are in the range of 2.1 Ga. This could be a characteristic provenance indication with re-
∼1.6–2 Ga (Milisenda et al. 1988, 1994; Hölzl et al., 1994). The zircon spect to the VC, although a minor fraction of the older zircons could be
εHf values in metamorphosed rocks of the HC show variation from derived from the HC sources as well, probably as a result of tectonic
−20.5 to 1.6, with crustal model ages in the range of 1.5–2.8 Ga mixture at the boundary between the HC and VC (Fig. 1).
(Santosh et al., 2014; He et al., 2015). Zircons in charnockitic rocks also
display a predominantly large negative εHf values ranging from −33.3 6.3.2. Provenance implications of younger zircon population
to −6.7, and older crustal model ages from 2 to 3.6 Ga (Santosh et al., As discussed above, ∼70% of Neoproterozoic- to late Cambrian-
2014; He et al., 2015). These authors have suggested a mixed source aged zircon grains (∼430–1000Ma) accumulate with prominent peak
comprising juvenile Neoproterozoic and reworked Mesoproterozoic – ages at 530–670Ma, 700–870Ma and ∼910–1030Ma from all the
Archean components in the HC. In the Wanni Complex rocks, Sm–Nd rivers. This spectrum of ages is remarkably similar in all the rivers,
crustal residence age peak at ∼1.6 Ga is prominent, and markedly displaying a pervasive zircon growth history related to Neoproterozoic
positive εHf values of the WC (from +5 to +15) suggest juvenile magmatic events in the Sri Lankan terrane. This age distribution is
components as the source of the protoliths. The εHf values of samples particularly analogous to the trends found in lithologies in the Sri
from the KC range from slightly negative to positive, with crustal model Lankan basement (e.g. Kröner and Williams, 1993; Kröner et al., 1991;
ages mainly from 1.5 Ga to 1.8 Ga. This trend suggests its protoliths Shiraishi et al. 1994; Hölzl et al., 1994; Kröner et al., 2013; Santosh
were derived from mantle sources with the input of minor reworked et al., 2014; Dharmapriya et al., 2015; Takamura et al., 2016; He et al.,
Neoarchean-Paleoproterozoic deep crustal sources. Particularly the 2016a,b). Hence, these magmatic pulses could be directly linked to the
Mahaweli and Kalu Rivers flow over a large part of the HC (Fig. 1) and orogenic events of collision of the Wanni and Vijayan arcs, closing the
the Mesoproterozoic and Archean zircons from these rivers have wider HC paleo-ocean during the assembly of the Gondwana supercontinent
peaks at 1.2–2.5 Ga. Although both Kelani River and Maha Oya origi- (e.g. Shiraishi et al., 1994; Santosh et al., 2014).
nate from the HC, they flow largely on the WC and KC. However, wide
age peaks of Mesoproterozoic to Archean zircons in the Kelani River
almost overlap with those shown by Mahaweli and Kalu Rivers which 6.3.3. Metamorphic and metasomatic impacts on younger zircons
flow entirely over the HC (Fig. 1), despite the fact that the abundance of Older populations (Mesoproterozoic to Archean) of zircons show
older zircon population in the Maha Oya river is less prominent unchanged Th/U evolution through time (Fig. 7), which we interpret to
reflect a closed system behavior. One younger population shows a trend
Fig. 7. Plot of Th/U vs. U/Pb age of the entire zircon population showing zircons derived from felsic, pure magmatic and metamorphic sources. See text for details.
21
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Fig. 8. Chondrite-normalized rare earth element (REE) patterns of dated zircons showing geochemical differences of Mesoproterozoic to Archean and Neoproterozoic
to late Cambrian zircons. Note the slightly high overall REE levels of the younger age population and more-or-less flat heavy REE patterns of metamorphic zircons.
of lowering of the Th/U values, especially in overgrowths, which could their formation (e.g. Hoskin and Schaltegger, 2003; Grimes et al.,
indicate competition for Th with high Th minerals (monazite, allanite 2007).
etc.) during their evolution. Late Neoproterozoic metamorphism may
have affected these grains, lowering the Th/U values and paving the 6.3.4. Comparison with zircon data from various lithologies from Sri Lanka
way for crystallization of a zircon population with typically low Th/U Previous studies reported Mesoarchean to Paleoproterozoic ages for
values (< 0.1). Thus, latest Neoproterozoic-Cambrian zircon popula- detrital zircon cores (3200–1800Ma with peaks at 3200, 2900, 2400,
tion with distinctly low Th/U values (< 0.1) observed in all the river 2000Ma) from the HC (Hölzl et al., 1994; Kröner et al., 1987, 1994;
sand samples clearly represent high-grade metamorphism in the three Dharmapriya et al., 2016). Kitano et al. (2018) reported predominant
lithologic complexes of Sri Lanka. In some of the Neoproterozoic grains, Paleoproterozoic to Early Mesoproterozoic detrital zircon ages (ca.
higher Th/U and could be interpreted to reflect open system behavior 2000–1500Ma) from the eastern HC, and predominant Early to Mid-
such as breakdown of minerals with high Th/U competition with high U Neoproterozoic ages (ca. 1000–700Ma) from the western part.
minerals (e.g. xenotime), sedimentary components or metasomatic ef- Dharmapriya et al. (2016) and Takamura et al. (2016) reported
fects. Further, a negative Eu anomaly is usually attributed to the pre-
2+ 2+ Neoarchean to Paleoproterozoic (ca. 2800–1800Ma) and Neoproter-sence of Eu in the melt since Eu partitions less readily into zircon
3+ ozoic (ca. 1000–700Ma) ages of detrital zircons from the central HC. Inthan Eu . Many zircons exhibit both positive Ce and negative Eu the WC, the 916–980Ma ages represent arc magmatism during early
anomalies, indicating both oxidised and reduced conditions during Neoproterozoic (Hölzl et al., 1994; Santosh et al., 2014). This was
22
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
followed by the 805Ma tonalitic magma emplacement in the WC. forming the Vijayan and Wanni arcs against a ‘Highland Complex paleo-
TheKC also bears more-or-less similar age spectrum. The 924–966Ma ocean’ (Shiraishi et al., 1994; Santosh et al., 2014). This inference is
ages from zircons of granitic gneisses and 617–770Ma zircon ages from also supported by previous geochronological studies which revealed
mafic rocks have records of magmatism in the VC. The metamorphic derivation of higher amount of arc-related calc-alkaline and mafic
zircons from all the complexes mark ∼550Ma as a wide-spread over- lithologies in the Wanni (from 1.6 to 1.1 Ga) and Vijayan Complexes
printed event (Kröner et al., 1987, 1994; Hölzl et al., 1994; Santosh (from 1.1 to 0.9 Ga), particularly with close proximity to their bound-
et al., 2014; He et al., 2016a,b). aries with the HC (Kröner et al., 2002, 2013; Braun and Kriegsman,
Based on magmatic zircons in meta-igneous and meta-sedimentary 2003; Willbold et al., 2004; Santosh et al., 2014, Takamura et al., 2016;
rocks, several workers suggested that the Sri Lankan crustal basement He et al., 2016a,b; Wijeratne and Malaviarachchi, 2017).
likely contains considerable amounts of recycled Paleoproterozoic to The magmatic episodes ranging from the 1.1–1.6 Ga and
Archean rocks (e.g. Santosh et al., 2014; Kröner et al., 2013; Takamura 870–1000Ma could be considered as Grenvillian (e.g. Kröner et al.,
et al., 2016; Dharmapriya et al., 2015; Osanai et al., 2016; 2003, Willbold et al., 2004; Li et al., 2014) and related to mark the
Malaviarachchi, 2016, 2018). Furthermore, the basement rocks in the beginning of the breakup of the Rodinia supercontinent. The wide-
Highland, Wanni and Vijayan complexes of Sri Lanka have whole-rock spread breakup of Rodinia occurred during 830–800Ma (Li et al., 2014)
Nd and Hf model ages spanning from 2.65 to 2.87 Ga with an average of and therefore it is evident that near-continuous magmatic pulses ob-
ca. 2.8 Ga (see review in Malaviarachchi, 2018). In this study, ap- served in this study at 820–870, 700–780Ma could have a connection
proximately 3–5% of zircons from each river were found to be between to the dispersal of Rodinia. Subsequently, collisions and metamorphism
∼2.5 and ∼3 Ga (Fig. 6). Detrital zircons with similar Archean ages are associated with the assembly of Gondwana during the late Neoproter-
ubiquitous in all litho tectonic units of Sri Lanka, which are in the ozoic (Meert, 2003) are well reflected in the continuous age peaks of
upstream of the studied rivers (Santosh et al., 2014; Kröner et al., 1987, 605–610, 530–580 and 430–500Ma. Thus, a regional provenance
1991, 2003, 2013; He et al., 2015, 2016a,b; Takamura et al., 2016; contribution from sources of Grenvillian and Gondwanan is evident in
Dharmapriya et al., 2015; Osanai et al., 2016). Therefore, we infer that the entire Sri Lankan basement. Similar records of magmatic events
the 2.8 Ga may be an important episode for the growth of juvenile crust have been found in the East Africa (e.g. Kröner et al., 2000) and in
and existence of an Archean basement in Sri Lanka. South India (Santosh et al., 1989; Braun and Kriegsman, 2003), im-
Majority of zircons from these crustal units are of Neoproterozoic to plying Sri Lankan terranes were probably a part of the East Africa.
Cambrian origin and formed during the magmatic and collisional
events related to the Gondwana assembly (e.g. Santosh et al., 2014; 7. Conclusions
Kröner et al., 1987, 1991, 2003, 2013; He et al., 2015, 2016a,b;
Takamura et al., 2016; Dharmapriya et al., 2015; Osanai et al., 2016). We draw the following conclusions from the geochronology of
Among the studied river sands, Neoproterozoic- to Cambrian-aged detrital zircons from the major rivers in the Sri Lankan basement.
zircon grains constitute up to ∼70% of the total age population with a
peak at ∼550Ma (Fig. 6a). Rivers Mahaweli, Kelani Kalu and Maha (1) Two main zircon populations are distinguishable depicting a wide-
Oya flow over the Highland and Wanni crustal blocks of Sri Lanka spread magmatism: Mesoproterozoic to Archean
(Fig. 1), and the Walawe River mainly touches the Vijayan Complex (∼30%;> 1100–3100Ma) and Neoproterozoic to late Cambrian
crustal unit. Therefore, approximately similar age peak among the (∼70%;>∼430–1000Ma), adding substantial amount of juvenile
Neoproterozoic- to Cambrian-aged zircon grains could be related to the crust to the Sri Lankan basement from Palaeoproterozoic to late
pervasive Neoproterozoic magmatic events in connection with the Cambrian.
amalgamation of the Gondwana Supercontinent. (2) The studied zircons provide evidence for intensive and episodic
Zircons of river sands in this study showing distribution from (both short-spanned and long-spanned) magmatic activities re-
Archean to Paleoproterozoic and Neoproterozoic to late Cambrian age solvable into fine groups at 480–680Ma, 680–1000Ma,
peaks are consistent with zircons from of basement rocks known from 1100–1300Ma, 1300–1700Ma, 1700–1900Ma, 2100–2300Ma,
petrological studies of Sri Lanka (Kröner et al., 1987, 1994; Hölzl et al., 2300–2600Ma and 2600–3100Ma. These periods of magmatism
1994; Santosh et al., 2014; Dharmapriya et al., 2015; Kitano et al., are correspondent with principal episodes of global continental
2018; Takamura et al., 2016; He et al., 2016a,b; Osanai et al., 2016). crustal growth, indicating most of the continental crust of Sri Lanka
However, late Mesoproterozoic to early Neoproterozoic age populations have formed in the Neoproterozoic. The older zircons may have
(ca. 1100–1000Ma) reported in previous studies (Kröner et al., 2003; mainly originated from the recycled ancient (Palaoproterozoic to
Willbold et al., 2004; Kitano et al., 2018; Dharmapriya et al., 2016), Archean) crust.
were not recorded as a prominent peak in our zircons (e.g. Figs. 5 and (3) The change of the frequency of age peaks at ∼1.1 Ga and ∼1.6 Ga,
6). giving rise to significant peaks in the Mesoproterozoic might reflect
In summary, the zircon geochronological data from this study triggering of subduction in a paleo tectonic setting, forming the
generally indicate that multiple phases of magmatic pulses with epi- Wanni and Vijayan dual arc system, respectively.
sodic addition of new crust and reworking of older crust in the Sri
Lankan basement throughout the history. This is clearly seen as age Acknowledgements
peaks at 480–680Ma, 680–1000Ma, 1100–1300Ma, 1300–1700Ma,
1700–1900Ma, 2100–2300Ma, 2300–2600Ma (Fig. 6). The older U-Pb dating was financially supported by the National Key R & D
model ages from previous studies from Sri Lanka could be correlated to Program of China (2017YFC0601306) and National Natural Science
crustal components ubiquitously found in subducted sediments in the Foundation of China (41522203). Financial support from National
Wanni-Vijayan dual arc system. We therefore suggest that the overall Research Council of Sri Lanka Grant No. NRC-15-089 for field work is
age peaks at ∼1800Ma and 550Ma date the major crust formation gratefully acknowledged. Preleminary analytical preparations of zir-
events in the Sri Lankan basement. cons in Sri Lanka and laboratory work in India were generously sup-
ported by Indo-Sri Lanka bilateral research project under Ministry of
6.4. Tectonic implications Science, Technology and Research, Sri Lanka (Grant No. MTR/TRD/
AGR/3/2/20) and Department of Science and Technology, India (Grant
The transitional age span (between ∼1.1 Ga and ∼1.6 Ga) showing No. DSTO/CEAS/SJK/1802). Ms. P.G. Athira of the Indian Institute of
a quick increase of zircon population observed in our study could be Science, Bangalore, Ms. Chen Chen, IGGCAS of the Chinese Academy of
interpreted as correspondent with the timing of the onset of subduction Science, Beijing and Mr. Wang Yu of the China University of
23
S.P.K. Malaviarachchi et al. Journal of Asian Earth Sciences xxx (xxxx) xxx–xxx
Geoscience, Beijing are especially thanked for helps in zircon sepera- Hatherton, T., Pattiarachchi, D.B., Ranasinghe, V.V.C., 1975. Gravity map of Sri Lanka
tion, making zircon grain mounts and LA-ICPMS analytical assistance, 1:1,000,000. Geological Survey Department, Sri Lanka, Professional Paper 3, pp. 39.
Hawkesworth, C.J., Dhuime, B., Pietranik, A.B., Cawood, P.A., Kemp, A.I.S., Storey, C.D.,
respectively. Prof. M. Satish-Kumar is thanked for providing necessary 2010. The generation and evolution of the continental crust. J. Geol. Soc. 167 (2),
facilities at Niigata University, Japan for the first author to finalyse the 229–248.
manuscript during a collaborative stay. Authors are also thankful for Hawkesworth, C.J., Cawood, P.A., Dhuime, B., 2013. Continental growth and the crustal
positive comments by Prof. Guochun Zhao on a previous version of the record. Tectonophysics 609, 651–660.He, X.-F., Santosh, M., Tsunogae, T., Malaviarachchi, S.P.K., 2015. Early to late
manuscript, two anonymous reviewers and the handling Editor Dr. Neoproterozoic magmatism and magma mixing–mingling in Sri Lanka: implications
Manoj Pandit for improving the manuscript. for convergent margin processes. Gondwana Res. https://doi.org/10.1016/j.gr.2015.
02.013.
He, X.F., Santosh, M., Tsunogae, T., Malaviarachchi, S.P.K., Dharmapriya, P.L., 2016a.
Appendix A. Supplementary material Neoproterozoic arc accretion along the ‘eastern suture’ in Sri Lanka during Gondwana
assembly. Precambr. Res. 279, 57–80.
Supplementary data associated with this article can be found, in the He, X.F., Santosh, M., Tsunogae, T., Malaviarachchi, S.P.K., 2016b. Early to late
Neoproterozoic magmatism and magma mixing–mingling in Sri Lanka: Implications
online version, at https://doi.org/10.1016/j.jseaes.2018.08.029. for convergent margin processes during Gondwana assembly. Gondwana Res. 32,
151–180.
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