Precambrian Research 321 (2019) 13–33
Contents lists available at ScienceDirect
Precambrian Research
journal homepage: www.elsevier.com/locate/precamres
Mineralogy, geochemistry, and zircon U-Pb-Hf isotopes of the T
Paleoproterozoic granulite-facies metamorphic rocks from the Aketashitage
area, southeastern Tarim Craton
Zhong-Mei Wanga,⁎, Chun-Ming Hanb,c, Wen-Jiao Xiaoa,c, Patrick Asamoah Sakyid, Lei Yanga,
Na Zhaob
a State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
b Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
c Xinjiang Research Center for Mineral Resources, Urumqi 830011, China
dDepartment of Earth Science, University of Ghana, P.O. Box LG 58, Legon-Accra, Ghana
A R T I C L E I N F O A B S T R A C T
Keywords: The key to understanding the generation of mantle-derived magma and the formation of new continental crust is
Garnet-biotite gneiss the recognition of the granulite-facies metamorphism, associated partial melting, and coeval magmatism that are
Mafic granulite documented in active continental margins. We firstly present a combined analysis of petrography, mineral
Zircon U-Pb ages and Hf isotopes chemistry, zircon U-Pb ages and hafnium (Hf) isotopes, in addition to whole-rock geochemistry on the garnet-
Dunhuang Block biotite gneisses (Grt-Bi gneisses) and mafic granulites from the Aketashitage area, southeastern Tarim Craton.
Active continental margins
The implications of this analysis are discussed with respect to the thermal and tectonic evolution of the Tarim
Craton. The Grt-Bi gneisses and mafic granulites are strongly peraluminous in composition and have flat REE
patterns with negative Eu anomalies that are identical to those from the middle crust but higher than lower
continental crust. Both the Grt-Bi gneisses and the mafic granulites have negative Nb-Ta anomalies, slightly
positive Zr-Hf anomalies, and pronounced positive spikes in U and Pb. The characteristics in whole-rock geo-
chemistry and mineral compositions indicate that the Grt-Bi gneisses and mafic granulites have the same source
locality, which is most likely the garnet-bearing middle crust. The retrograde metamorphic P-T estimates for the
Grt-Bi gneisses and mafic granulites are T=574 °C; P= 7.0 kbar and T=715 °C; P= 7.0 kbar, respectively.
SIMS zircon U-Pb dating results reveal a large spread in metamorphic ages (2036–1962Ma) for these granulite-
facies rocks, interpreted to be the consequence of a large amount of magmas being added to the crust in an
uninterrupted manner. Zircon Hf isotopes are characterized by variable but mostly negative εHf (t) values
(−18.2 to −0.6), reasonably uniform Hf isotopic compositions, and highly variable T CDM model ages between
2628 and 3599Ma, representing a long-lived reworking of the preexisting crust. Our data, along with available
geological evidences, lead us to propose a model for the evolution of the Dunhuang Block in the
Paleoproterozoic. That is, the southeastern margin of the Tarim Craton, the Dunhuang Block was possibly an
active continental margin during the Paleoproterozoic. The steep subduction of oceanic slab resulted in the
thickening of the continental crust, which in turn caused the crust anatexis. The increase in asthenosphere high
heat flow and the intrusion of mantle-derived magma induced extensive heating, which preceded the granulite-
facies metamorphism and coeval magmatism in the middle crust of the southern Tarim Craton.
1. Introduction margins, and potentially provide a window into understanding the
generation of mantle-derived magma and the formation of new con-
The typical accretionary orogeny is commonly characterized by tinental crust (Collins, 2002; Hyndman et al., 2005; Klepeis et al., 2007;
high heat flow, granulite-facies metamorphism and associated partial Zhang et al., 2013b). Accordingly, knowledge of the origin and petro-
melting, and coeval plutonism (Xiang et al., 2014). In general, these genesis of the deep-seated magmatism and metamorphism in active
geologic processes are the diagnostic features of active continental continental margins is essential to evaluate continental building
⁎ Corresponding author.
E-mail address: wangzm@mail.iggcas.ac.cn (Z.-M. Wang).
https://doi.org/10.1016/j.precamres.2018.11.003
Received 8 May 2018; Received in revised form 10 November 2018; Accepted 11 November 2018
Available online 13 November 2018
0301-9268/ © 2018 Elsevier B.V. All rights reserved.
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
processes (Debari, 1994; Jagoutz et al., 2007; Zhang et al., 2013b). The the Aketashitage area, Dunhuang Block, southern Tarim Craton (Fig. 2a
granulite-facies rocks exposed in high-grade regional metamorphic and b), with a view to better understanding the early evolutionary
belts and exhumed as xenoliths in basaltic pipes are considered to be a history of the Tarim Craton in addition to the reconstruction of the
window to decipher the properties of the lower crust, past and present tectonic framework prior to the onset of the orogeny. We present new
(Harley, 1989; Wei, 2016; Mao et al., 2017). Granulite-facies meta- petrographic evidence, as well as major and trace element mineral
morphic rocks are accessible either as large tracts of surface outcrop or chemistry that documents garnet growth to place some constraints on
as tiny fragments in deep volcanic conduits (Rudnick and Fountain, identifying the high-grade metamorphism. SIMS U-Pb in situ zircon
1995). These granulite-facies rocks can not only provide constraints on dating enables the timing of the metamorphic events that produced the
understanding the probable nature and composition of the lower crust garnet crystals to be defined. In addition, whole-rock geochemistry and
in the existing continents, but they also provide an insight into the zircon Hf isotopes are presented in order to explain the petrogenesis of
interpretation of formation and reworking of the continental crust, as their protoliths. All the presented data of these granulite-facies meta-
well as orogenic mechanisms. An exhaustive understanding of the tec- morphic rocks should be used to discuss their implications with respect
tonic settings, petrogenesis, and metamorphism of granulite-facies to the thermal and tectonic evolution of the Tarim Craton. Our new
rocks provide an ability to better recognize the evolutionary history of data provides direct information that the Grt-Bi gneisses and mafic
the continental crust. It is clear that granulite-facies metamorphism granulites in the Aketashitage area record a long-lived metamorphism.
may accompany, or very shortly follow, continental crust formation in Combined with previously reported coeval magmatism and crust ana-
some instances; whereas in other cases, it affects continental crust that taxis suggest that the Dunhuang Block, southeastern Tarim Craton, was
was formed much earlier and has possibly been affected by intervening possibly an active continental margin involved in the assembly of the
events (Bohlen and Mezger, 1989). Thus, a great number of systematic Columbia supercontinent. Our results contribute to a better under-
studies have been carried out to determine the formation environment standing of crustal growth and reworking in an active continental
and metamorphic evolution of these granulite-facies rocks (Bohlen and margin tectonic setting.
Mezger, 1989; Harley, 1989; Rudnick and Fountain, 1995; MÜNtener
et al., 2000). 2. Geological background and sampling
The Dunhuang Block, situated between the Tethyan domain, the
Tarim Craton, the North China Craton and the Central Asian Orogenic The Dunhuang Block lies to the east of the Tarim Craton, to the
Belt (CAOB) (Fig. 1), has been long considered to be part of the base- south of the Beishan Orogen (the southern margin of the CAOB), to the
ment of the Tarim Craton or the western part of the Alxa Block of the north of the Altyn Tagh Fault (Fig. 1). Previously, the Dunhuang Block
North China Craton (Lu et al., 2008; Zhang et al., 2012, 2013a; He had been widely accepted as a part of the Precambrian cratonic block or
et al., 2013; Xu et al., 2013; Long et al., 2014). However, some re- microcontinent dominated by Precambrian crystalline basement rocks,
searchers proposed that the Dunhuang Block was involved into the which are defined as the Milan Complex in the northeastern Altyn Tagh
early Paleozoic orogeny, representing the southernmost margin of the area, and the Dunhuang Complex in the Dunhuang area (BGMRG, 1989;
CAOB (Zhao et al., 2015a, 2016). New found high-grade metamorphic Mei et al., 1997, 1998; Xu et al., 1999; Lu et al., 2008; Zhang et al.,
rocks also reveal that the Dunhuang Block underwent Paleozoic sub- 2011). However, the latest studies propose that it is more reasonable to
duction and/or collision events (Zong et al., 2012; He et al., 2014; regard the Dunhuang Block as an orogenic belt (Zhao et al., 2016, 2017;
Wang et al., 2016, 2017a). The above research principally focused on Wang et al., 2017b), and the exposed rocks are considered to be pri-
the Paleozoic high-grade metamorphic rocks exposed in the northeast marily composed of Archean-early Mesoproterozoic crystalline base-
segment of the Dunhuang Block (Fig. 2a), thus, our understanding of ment rocks, Paleozoic high-grade metamorphic rocks and Paleozoic
the evolutionary history of the Dunhuang Block is hampered by the magmatic rocks (Zhao et al., 2017).
scarcity of data relating to high-grade metamorphic rocks of different The exposed Archean-early Mesoproterozoic rocks in the Dunhuang
ages or those are exposed in other regions. This knowledge gap is Block are mainly made up of extensive medium- to high-grade meta-
mainly the result of the extensive cover of the Gobi Desert. This study morphic supracrustal rocks and subordinate granitoid gneisses, having
focuses on the Paleoproterozoic Grt-Bi gneisses and mafic granulites in been named as Milan and Dunhuang Complexes (Lu et al., 2008; Liu
Fig. 1. Sketched tectonic and topographic map of the Tarim Craton and adjacent areas showing the distribution of the Precambrian basement outcrops (modified
after Lu et al., 2008; Xu et al., 2011). Inset Figure shows a simplified tectonic map of the Dunhuang Block (modified after Xiao et al., 2010). TC-Tarim Craton; NCC-
North China Craton; SCC-South China Craton; DB-Dunhuang Block.
14
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 2. (a) Simplified map of the Dunhuang Block showing locations of the Paleozoic magmatic and metamorphic rocks (modified after Wang et al., 2017e); (b)
Simplified geologic map of the Aketashitage area, southwest Dunhuang Block (modified after the geological map of Eboliang 1:200000).
et al., 2009). The Dunhuang Complex is primarily composed of a large discovered Eoarchean high-pressure TTGs with an age of∼ 3.7 Ga in
range of tonalite-trondhjemite-granodiorite (TTG) gneisses and supra- the same area. The supracrustal rocks of the Milan Complex exhibit
crustal rocks, with the latter being defined as the Dunhuang Group and complicated features of deformation and metamorphism (Che and Sun,
thought to be Archean-Paleoproterozoic in age (BGMRG, 1989; Mei 1996; Lu et al., 2008). The deposition ages of their protoliths have not
et al., 1997; Yu et al., 1998; Lu, 2002b; Lu et al., 2006a,b). The been well constrained, but they were intruded by 2.14–1.93 Ga pre- to
dominant rock types of the Dunhuang Group are metasedimentary syn-tectonic granitoids and carbonatites (Lu et al., 2008; Xin et al.,
rocks, amphibolites, and mafic granulites. Findings of Paleoproterozoic 2011, 2013).
amphibolite- to granulite-facies meta-mafic rocks in the Hongliuxia In this study, representative samples were collected from a single
area, lead to argue that the Dunhuang Block was possibly associated outcrop in the Aketashitage area, Dunhuang Block, southeastern Tarim
with the assembly of the Columbia supercontinent (Zhang et al., 2012, Craton. Sample locations are presented in Fig. 2b. The study area is
2013a; Wang et al., 2013; Zhao et al., 2013). Zircon U-Pb dating results dominated by Archean orthogneisses with variable degrees of partial
of the TTG gneisses revealed that they were crystallized at 2.7–2.5 Ga melting, including TTG rocks and monzogranitic gneisses, with tonalitic
and were modified by a Paleoproterozoic (2.0–1.8 Ga) high-grade me- melanosomes and granitic leucosomes (Lu, 2002a; Long et al., 2014).
tamorphic event (Zhang et al., 2013a; Zong et al., 2013). The Milan The remaining rocks exposed in the study area mainly consist of
Complex is mainly distributed along the NE Altyn Tagh area, dominated paragneisses, amphibolites, granulites, quartzites and marbles. Most of
by medium- to high-grade metamorphic rocks, including amphibolites, these supracrustal rocks underwent intense deformation and commonly
mafic granulites, felsic gneisses and marbles, as well as TTG-like occur as layers or boudins within the Archean orthogneisses (Che and
gneisses. Previous studies reveal that the TTG-like gneisses of the Milan Sun, 1996; Lu, 2002b; Lu and Yuan, 2003). Both the supracrustal rocks
Complex have crystallization ages of 2.8–2.5 Ga and metamorphic ages and Archean orthogneisses were intruded by Paleoproterozoic granitic
of 1.9–2.0 Ga, and were intruded by 1.78–1.87 Ga post-tectonic granitic veins and younger mafic dykes (Fig. 3a). Samples selected for analyses
and mafic dykes (Lu and Yuan, 2003; Xin et al., 2011, 2012, 2013; Long were relatively fresh and contain no veins. In the field, it is typical that
et al., 2014). However, Ge et al. (2018) report a suit of newly the analyzed mafic granulites occur as boudins or lenses within Grt-Bi
15
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 3. Field photographs and photomicrographs of the studied granulite-facies metamorphic rocks in the Aketashitage area. (a) and (b) Field occurrence and
relationship of garnet-biotite gneiss and mafic granulite; (c) Garnet-biotite gneiss is coarse-grained and weakly foliated; (d) and (e) Garnet-biotite gneiss have
abundant porphyroblastic garnets and euhedral matrix minerals; (f) Typical textrue of the matrix biotite; (g) and (h) Large garnet porphyroblasts in the typical mafic
granulite; (i) and (j) Garnet porphyroblasts are arounded by kelyphitic coronas in the mafic granulite; (k) and (l) Symplectitic plagioclase is extensively sericitized
and almost exclusively replaced by sericite. Abbreviations: Grt-garnet; Bi-biotite; Pl-plagioclase; Qz-quartz; Opx-orthopyroxene; Cpx-clinopyroxene; Ser-sericite; Rt-
rutile.
gneisses Fig. 3b. Occasionally, the contact is sharp but in most cases is Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) in
transitional. Beijing, China. Operating conditions were 15 kV and 10nA with a 3 μm
beam size. Counting times were 20 s for peaks and 10 s for each back-
ground. Natural and synthetic phases were used as standards. The data
3. Analytical methods were processed with an online ZAF correction.
3.1. Electron microprobe mineralogical analyses
3.2. Zircon U-Pb dating and Hf isotopic analyses
Compositional analyses of representative minerals were conducted
with a JEOL JXA-8100 electron microprobe (EMP) at the Institute of Zircons were separated using heavy liquid and magnetic techniques
16
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
and then handpicked under a binocular microscope. The selected zircon incorporated a background acquisition of approximately 20–30 s fol-
grains were mounted in epoxy mounts which were then polished to lowed by 50 s of data acquisition from the sample. An Excel-based
section for analysis. The structures and inclusions of zircon grains were software ICPMSDataCal was used to perform off-line selection and in-
documented with transmitted and reflected light micrographs. To ob- tegration of background and analyzed signals, time-drift correction and
serve the internal structure and select a potential target site for U-Pb quantitative calibration for trace element analysis (Liu et al., 2008).
and Hf isotopic analyses, high-resolution cathodoluminescence (CL)
imaging was conducted using a JXA8100 electron microprobe at 4. Petrography, microtextures and mineral compositions
IGGCAS.
Measurements of U, Th and Pb were conducted using the Cameca Representative major element compositions of garnet, orthopyr-
IMS-1280 SIMS at IGGCAS. The measurement procedures followed oxene, clinopyroxene, and mica are given in Supplementary Tables 1–3.
methods described by Li et al. (2009, 2010). U-Th-Pb ratios and abso- The trace element compositions of analyzed garnets are presented in
lute abundances were determined relative to the standard zircon Ple- Supplementary Table 4. Analyzed garnet grains are referred from now
sovice and 91500. The ellipsoidal spot is about 20× 30 μm in size. The on by their host rocks. Garnets 16AK22, 16AK26-A and -B, and 16AK27
mass resolution used to measure Pb/Pb and Pb/U isotopic ratios was are from the corresponding samples with the same name.
5400 during the analyses. A long-term uncertainty of 1.5% (1 RSD) for
206Pb/238U measurements of the standard zircons was propagated to 4.1. Garnet-biotite gneiss (samples 16AK22, 23, and 24)
the unknowns (Li et al., 2009, 2010). Measured compositions were
corrected for common Pb using non-radiogenic 204Pb. Corrections were The garnet-biotite gneiss is coarse-grained, porphyroblastic, and
sufficiently small to be insensitive to the choice of a common Pb weakly foliated, containing abundant garnet porphyroblasts (35–40%)
composition, and an average of present-day crustal compositions in a foliated matrix mainly composed of plagioclase, biotite, and quartz
(Stacey and Kramers, 1975) was used for the common Pb assuming that (Fig. 3c). Common accessary minerals are magnetite, and in lesser
the common Pb is largely surface contamination introduced during amounts, rutile. Large garnet porphyroblasts frequently contain various
sample preparation. Uncertainties of individual analyses in the tables inclusions, with lath-like plagioclase, sugar-like quartz and flake-like
are reported at a 1σ level; concordia U-Pb ages are quoted with a 95% biotite (Fig. 3d, e and f). Matrix-minerals are generally presented as
confidence interval. Data reduction was carried out using the Isoplot/Ex large and euhedral grains compared with those as inclusions within
3.0 program (Ludwig, 2003). garnets. Matrix biotite commonly occurs as clots of crystals fill in the
In situ Hf isotopic analyses were conducted by MC-ICP-MS at the interstitial spaces of garnet porphyroblasts and align with the regional
IGGCAS, using the same Geolas-193 laser ablation system. Lu-Hf iso- foliation (Fig. 3f). Quartz in the matrix occurs mainly as lobate or
topic compositions were analyzed near the same spots where U-Pb rounded megacryst and is unevenly distribute (Fig. 3d and e). Com-
analyses were carried out. A beam diameter of 44 μm was used for all positional transects in garnet 16AK24 show Alm69Prp23Grs5Sps1 as the
the samples. The repetition rate was 8 Hz and the laser energy was core composition, with a progressive outward decrease in almandine
15mJ/cm2. Detailed analytical procedure and isobaric interference and spessartine to the rim, although there is a slight increase at the
correction are reported in Wu et al. (2006) and Xie et al. (2008). During outmost rim (Fig. 4a). The increase in XFe from the inner rim to outmost
the analyses, the 176Hf/177Hf and 176Lu/177Hf ratios of the standard rim is most likely related to retrograde exchange reactions between
zircon (91500) were 0.282294 ± 15 (2σn, n=20) and 0.00031 (Yang garnet and biotite. The minor increase in Xsps at the outmost rim is
et al., 2006). probably the result of the retrograde kick-up effect (Kohn and Spear,
2000). Pyrope and grossular contents are essentially unzoned from core
3.3. Whole-rock geochemical analyses to rim (Fig. 4b). Chondrite-normalized REE patterns have no obvious
variation in REE concentrations between core and rim (Fig. 5a). Both
Samples were grounded in an agate mill to 200 mesh. Major oxides the core and rim are characterized by remarkable negative Eu anoma-
were determined by wavelength-dispersive X-ray fluorescence (XRF) lies and flat HREE patterns. As shown by Fig. 6a, the zoning profiles of
spectrometry on fused glass at IGGCAS. The analytical precision was Y, Ti, Cr, V, and Co are continuous from core to rim, suggesting that an
estimated to be better than 1% for elements with concentrations higher equilibrium was maintained during garnet growth (Hickmott and
than 0.5 wt%. Trace element concentrations were analyzed by in- Shimizu, 1990).
ductively coupled plasma mass spectrometry (ICP-MS) Ⅱ at IGGCAS. We
used pure elemental standards for external calibration and granite as a 4.2. Mafic granulite (samples 16AK25, 26, and 27)
reference material. The accuracy of the analyses was better than 2.5%.
The mafic granulites are coarse-grained and dark in color. They
3.4. In situ trace element analyses of garnets have mineral assemblages typical of mafic granulites, with abundant
garnet, orthopyroxene, clinopyroxene and quartz, and some plagioclase
Trace element analyses of garnets were conducted by LA-ICP-MS at as well as accessory ilmenite, zircon, monazite and rutile. Large garnet
the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, porphyroblasts are commonly euhedral in morphology and typically
China. Detailed operating conditions for the laser ablation system and contain abundant inclusions of rounded quartz (Fig. 3g and h); whereas,
the ICP-MS instrument and data reduction are the same as those de- fine-grained garnet crystals are hypidioblastic with varying degrees of
scribed by Zong et al. (2017). Laser sampling was performed using a resorption associated with coronal or symplectitic reaction texture
GeolasPro laser ablation system that consists of a COMPexPro 102 ArF microdomains (Fig. 3i and j). In some localized domains, the develop-
excimer laser (wavelength of 193 nm and maximum energy of 200mJ) ment of the kelyphitic coronas around garnet replaces most of the
and a MicroLas optical system. An Agilent 7700e ICP-MS instrument garnet crystal. The coronas are represented by the intergrowth of or-
was used to acquire ion-signal intensities. Helium was applied as a thopyroxene and plagioclase, with the symplectitic plagioclase is ex-
carrier gas. Argon was used as the make-up gas and mixed with the tensively sericitized and almost exclusively replaced by sericite (Fig. 3k
carrier gas via a T-connector before entering the ICP. A “wire” signal and l). Matrix quartz generally occurs as interstitial phases in ag-
smoothing device is included in this laser ablation system (Hu et al., gregates, shows evidence for high temperature intracrystalline re-
2014). The spot size and frequency of the laser were set to 44 µm and crystallization, such as undulatory extinction and subgrains (Fig. 3h).
5 Hz, respectively. Trace element compositions of garnets were cali- Subhedral orthopyroxene with inclusions of quartz is commonly related
brated against various reference materials (BHVO-2G, BCR-2G and BIR- to the metamorphic peak conditions.
1G) without using an internal standard (Liu et al., 2008). Each analysis Garnets from sample 16AK26 vary considerably in composition
17
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 4. The compositional profiles and BES images of the garnet porphyroblasts. Alm-almandine; Sps-spessartine; Prp-pyrope; Grs-grossular.
between different grains. Major element profile of garnet 16AK26-A characterized by striking depletion in LREE, minor variation in HREE
shows a pronounced variation from core (Alm55Prp23Grs19Sps3) to rim and strongly negative Eu anomalies. In contrast, the rims have more
(Alm59Prp17Grs19Sps5), with a marked increase in almandine and complicated REE patterns, which show variable concentrations in LREE
spessartine (Fig. 4c), and a sharp decrease in pyrope contents. Grossular and flat patterns in HREE. These two garnet grains have asymmetrical
contents are essentially unzoned (Fig. 4d). Whereas, the compositional compositional zoning in terms of Y, Ti, Cr, V and Co, which display a
transects of garnet 16AK26-B differ clearly from those of garnet homogeneous composition in the core, and decrease continuously to-
16AK26-A by exhibiting a wide plateau of homogeneous contents from ward the rims, with uniform contents in the outmost rims (Fig. 6b and
core (Alm56Prp21Grs19Sps4) to rim (Alm58Prp18Grs19Sps4), suggesting c). The slight increases in Co, V and Cr in the outermost rim of garnet
limited modification during garnet growth (Fig. 4e and f). The slight 16AK26-A may be caused by the involvement of magnetite and/or il-
variation of the outmost rim is related to retrograde reactions. How- menite in garnet growth. The decreases in Y and HREE for garnet
ever, the two aforementioned garnet grains have analogous chondrite- 16AK26-B appear to be caused by clinozoisite growth coupled with
normalized REE patterns (Fig. 5b and c). Both of them display sig- variations in temperature and pressure (Hickmott and Spear, 1992).
nificant distinction between core and rim. Garnet cores are The low Y concentration in the garnet rim is might be controlled by
18
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 5. Chondrite-normalized rare earth element diagrams of garnets in the granet-biotite gneiss and granulite. Chondrite-normalized values are from Sun and
McDonough (1989).
growth of competing phases such as monazite. Mostly, the analyzed 5. Metamorphic P-T conditions
pyroxene in sample 16AK26 is orthopyroxene, and is chemically
homogeneous (Supplementary Table 2). They have low jadeite Pressure-temperature (P-T) results are reported in Tables 1–3. The
(Na2O=0.05–0.18wt%) and CaO (0.70–3.76wt%) contents, although most serious drawback for a quantitative P-T determination of peak
some variations exist in Al2O3 (17.4–18.1 wt%) and FeO metamorphism is the lack of compositions relating to the complete
(23.76–28.49 wt%) contents of different grains. Mica is sporadically equilibration between minerals. Thus, in the following discussion, only
developed in the matrix, and is homogeneous in composition. the retrograde P-T conditions are presented. The P-T estimates for the
Chemical composition profile across garnet 16AK27 (Fig. 4g and h) studied samples were obtained by combining relevant mineral chem-
is characterized by an increase in almandine and spessartine, and a istry information with conventional thermobarometers.
decrease in pyrope from core (Alm58Prp20Grs19Sps3) to rim The texture and composition of the analyzed Grt-Bi gneiss reveal
(Alm51Prp15Grs19Sps5). Grossular displays slightly decreased zoning three-stage mineral assemblage: that is, the mineral inclusions enclosed
towards the outermost rim, interpreted as the consequence of decom- in garnet porphyroblasts formed an earlier assemblage of
pression. The chondrite-normalized REE patterns (Fig. 5d) are char- Bi+ Pl+Qz+ Ilm, the garnet cores and matrix minerals form a peak
acterized by progressive LREE- and HREE-depletion from core to rim. mineral assemblage of Grt+Bi+Pl+Qz+ Ilm ± Rt, and the retro-
Garnet cores display steep chondrite-normalized REE patterns and grade assemblage is represented by the biotite those rimming the garnet
strong negative Eu anomalies. Rims have flat REE patterns, with a or replacing garnet around the cracks. Unfortunately, in the absence of
slightly depletion in HREE and more pronounced negative Eu anoma- available barometers, the metamorphic pressure conditions are esti-
lies. With respect to the contents of Y, Ti, Cr, V and Co, they exhibit a mated roughly by the observed mineral assemblages. The rim compo-
homogeneous distribution in cores and a sharp decrease in rims sitions of the garnet porphyroblast and the rim compositions of the
(Fig. 6d). Pyroxene from sample 16AK27 is dominated by clinopyr- surrounding biotite were used to estimate the temperature conditions
oxene in composition, and is chemically homogeneous (Supplementary during retrograde metamorphism using a garnet-biotite Fe-Mg ex-
Table 2). They have low contents in Na2O (0.09–0.25wt%) and Al2O3 change thermometer. The average P-T conditions were determined to
(0.45–1.56 wt%), relatively high contents in CaO (21.82–22.74 wt%). be 574 °C and 7.0 kbar, taken to represent the retrograde metamorphic
P-T conditions of the Grt-Bi gneiss.
19
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 6. Representative trace-element zoning in garnets from the granet-biotite gneiss and granulite.
Table 1 estimated temperatures are considerably higher than that calculated for
Retrograde P-T estimates for the analyzed samples. the Grt-Bi gneiss. However, both the Grt-Bi gneiss and mafic granulite
Sample Method (T&P) T (°C) P (kbar) have similar pressure estimations.
16AK24 Grt-Bi (Holdaway, 2000) 574 7.0
16AK26 Grt-Opx (Glebovitsky et al., 2004) 700 7.4 6. Zircon U-Pb ages and Hf isotopes
16AK27 Grt-Cpx (Berman et al., 1995) 715 7.0
Cathodoluminescence (CL) images of representative zircon grains
are shown in Fig. 7. Zircon U-Pb dating results and Hf isotopic com-
For the mafic granulites, three episodes of metamorphic mineral positions are reported in Tables 2 and 3. Analyses spots that are highly
assemblages are also preserved. The prograde assemblages are inclusion discordant with high errors are not shown and are excluded from cal-
minerals (Pl+Qz+ Ilm) enclosed in garnet porphyroblasts. The peak culations. Dated zircon crystals in both the Grt-Bi gneiss and mafic
assemblages are formed by garnet porphyroblasts and matrix minerals granulite samples were handpicked from the whole rock, that is, were
(Grt+Cpx+Opx+Pl+Qz ± Ilm ± Rt), and the retrograde as- found in the matrix, implying that these zircon grains were formed at
semblages are represented by the symplectitic intergrowth of Cpx+ Pl peak metamorphism. They mostly preserve well-developed sector,
around the garnet. The garnet-orthopyroxene thermobarometry and the patchy, fir-tree and planar zoning, which are common features in high-
garnet-clinopyroxene thermometer are combined to estimate the P-T temperature metamorphic zircons produced through new zircon growth
conditions during retrograde metamorphism. For sample 16AK26, or by recrystallization (Vavra et al., 1999; Hoskin and Black, 2000;
compositions of garnet rim and orthopyroxene rim are used to calculate Hoskin and Schaltegger, 2003; Kelly and Harley, 2005; Harley et al.,
the retrograde P-T conditions, which gave averages of 700 °C and 7.4 2007).
kbar. For sample 16AK27, similar retrograde P-T conditions Zircon grains from sample 16AK22 are rounded-ovoid or “soccer
(T= 715 °C; P=7.0 kbar) were given by garnet rim and associated ball” in shape and variable in size, with crystal lengths of 50 to 100 μm.
clinopyroxene using the garnet-clinopyroxene thermometer. These Most crystals are characterized by sector zoning, patchy and/or fir-tree
20
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 2
U-Pb data for zircons from the analyzed garnet-biotite gneisses and mafic granulites.
Spot no. Contnets Ratios Age(Ma)
Th U Th/U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
16AK-22
1 18 212 0.085 0.1174 0.6473 5.3685 1.6344 0.3318 1.5008 1916 12 1880 14 1847 24
2 30 214 0.140 0.1217 0.5834 6.3216 1.7101 0.3767 1.6075 1982 10 2021 15 2061 28
3 2 449 0.004 0.1177 0.7028 5.5198 1.6875 0.3403 1.5341 1921 13 1904 15 1888 25
4 24 342 0.071 0.1213 0.3082 5.9885 1.5871 0.3582 1.5569 1975 5 1974 14 1973 27
5 23 225 0.101 0.1174 0.7514 5.5580 1.7818 0.3433 1.6156 1917 13 1910 15 1903 27
6 10 260 0.038 0.1193 0.6838 5.4356 1.7415 0.3304 1.6016 1946 12 1890 15 1840 26
7 14 449 0.030 0.1209 0.7977 5.7892 1.7028 0.3473 1.5044 1970 14 1945 15 1922 25
8 13 443 0.029 0.1236 1.1132 5.9740 2.0765 0.3506 1.7528 2008 20 1972 18 1938 29
9 41 396 0.103 0.1194 0.6317 5.5579 1.7629 0.3375 1.6458 1948 11 1910 15 1875 27
10 7 227 0.032 0.1201 0.5197 5.9397 1.6001 0.3587 1.5133 1958 9 1967 14 1976 26
11 29 195 0.149 0.1181 0.9760 5.4675 1.8386 0.3359 1.5581 1927 17 1896 16 1867 25
12 17 279 0.060 0.1220 0.5666 5.9952 1.6052 0.3563 1.5019 1986 10 1975 14 1965 25
13 10 258 0.037 0.1188 0.5634 5.5615 1.6067 0.3396 1.5047 1938 10 1910 14 1885 25
14 5 489 0.010 0.1185 0.6040 5.7142 1.6170 0.3498 1.5000 1933 11 1934 14 1934 25
15 7 254 0.027 0.1266 0.4923 8.2052 4.7768 0.4700 4.7514 2052 9 2254 44 2483 99
16 29 244 0.119 0.1209 0.7127 5.9451 1.6670 0.3565 1.5069 1970 13 1968 15 1966 26
17 0 359 0.001 0.1175 0.4403 5.5686 1.5991 0.3438 1.5372 1918 8 1911 14 1905 25
18 35 258 0.137 0.1201 0.6427 5.3455 4.9163 0.3228 4.8741 1958 11 1876 43 1803 77
19 9 330 0.028 0.1203 0.7501 5.8250 1.6886 0.3512 1.5129 1960 13 1950 15 1940 25
20 52 369 0.141 0.1175 0.6392 5.5659 1.6499 0.3435 1.5211 1919 11 1911 14 1903 25
21 11 276 0.040 0.1207 0.8664 5.7699 1.8125 0.3468 1.5921 1966 15 1942 16 1919 26
22 10 287 0.034 0.1162 0.6567 5.5060 1.7363 0.3435 1.6073 1899 12 1902 15 1904 27
23 18 328 0.054 0.1192 0.8095 5.6560 1.7070 0.3442 1.5029 1944 14 1925 15 1907 25
24 11 473 0.024 0.1178 0.4628 5.6672 1.5991 0.3489 1.5307 1923 8 1926 14 1929 26
25 21 652 0.033 0.1189 0.3634 5.8917 1.5435 0.3595 1.5001 1939 6 1960 13 1980 26
16AK23
1 20 579 0.035 0.1155 1.8648 4.1932 3.3738 0.2634 2.8116 1887 33 1673 28 1507 38
2 20 170 0.119 0.1189 0.6618 5.4884 1.6523 0.3349 1.5139 1939 12 1899 14 1862 25
3 11 371 0.030 0.1211 0.4023 5.6838 1.5651 0.3403 1.5125 1973 7 1929 14 1888 25
4 11 232 0.046 0.1221 0.6394 5.8899 1.6491 0.3498 1.5201 1987 11 1960 14 1934 25
5 11 214 0.053 0.1182 0.5352 5.4312 1.6025 0.3333 1.5105 1929 10 1890 14 1855 24
6 11 305 0.037 0.1248 0.9468 5.9694 1.7801 0.3470 1.5074 2026 17 1971 16 1920 25
7 18 314 0.056 0.1185 0.4536 5.6119 1.5683 0.3434 1.5013 1934 8 1918 14 1903 25
8 10 269 0.036 0.1192 0.8898 5.2119 1.7512 0.3171 1.5083 1945 16 1855 15 1775 23
9 31 427 0.072 0.1201 0.3466 5.7794 1.5448 0.3490 1.5054 1958 6 1943 13 1930 25
10 14 416 0.033 0.1232 1.0234 5.8990 1.8305 0.3474 1.5177 2002 18 1961 16 1922 25
11 13 386 0.033 0.1231 0.4976 5.9404 1.6196 0.3499 1.5413 2002 9 1967 14 1934 26
12 24 208 0.115 0.1214 0.8596 5.8590 1.7314 0.3499 1.5029 1978 15 1955 15 1934 25
13 10 284 0.036 0.1218 0.4632 5.7067 1.5923 0.3397 1.5235 1983 8 1932 14 1885 25
14 12 309 0.040 0.1175 0.5053 5.4735 1.6072 0.3378 1.5256 1919 9 1896 14 1876 25
15 16 590 0.028 0.1220 0.4482 5.5298 1.5933 0.3286 1.5290 1986 8 1905 14 1832 24
16 23 178 0.128 0.1176 0.8271 5.5132 1.7147 0.3399 1.5021 1921 15 1903 15 1886 25
17 11 403 0.026 0.1191 0.5001 5.6773 1.5893 0.3457 1.5086 1943 9 1928 14 1914 25
18 14 259 0.054 0.1169 3.5529 5.1560 3.8569 0.3199 1.5009 1909 62 1845 33 1789 23
19 8 342 0.023 0.1178 0.4808 5.4963 1.5779 0.3384 1.5028 1923 9 1900 14 1879 25
20 18 317 0.056 0.1166 0.4457 5.2639 1.6664 0.3275 1.6057 1904 8 1863 14 1826 26
21 11 292 0.037 0.1229 0.9800 6.1131 1.8065 0.3607 1.5175 1999 17 1992 16 1986 26
22 32 325 0.098 0.1201 0.4064 5.8100 1.5631 0.3509 1.5093 1957 7 1948 14 1939 25
23 11 278 0.040 0.1181 0.7365 5.6201 1.9694 0.3452 1.8265 1927 13 1919 17 1912 30
24 29 224 0.130 0.1168 0.5590 5.3799 1.6093 0.3342 1.5091 1907 10 1882 14 1859 24
25 14 306 0.045 0.1190 0.4579 5.7057 1.5702 0.3477 1.5019 1941 8 1932 14 1924 25
16AK24
1 10 190 0.055 0.1217 0.4213 5.7557 1.5612 0.3431 1.5032 1981 7 1940 14 1902 25
2 12 195 0.061 0.1179 0.4095 5.6887 1.5638 0.3500 1.5092 1925 7 1930 14 1934 25
3 9 244 0.038 0.1173 0.4170 5.5238 1.5841 0.3416 1.5282 1915 7 1904 14 1894 25
4 238 648 0.367 0.1268 0.5632 5.6740 1.6040 0.3245 1.5018 2054 10 1927 14 1812 24
5 13 389 0.033 0.1206 0.4156 5.7281 1.5699 0.3446 1.5139 1964 7 1936 14 1909 25
6 11 324 0.034 0.1179 0.3770 5.6280 1.5795 0.3463 1.5339 1924 7 1920 14 1917 25
7 26 367 0.071 0.1213 0.4208 6.0117 1.5754 0.3594 1.5182 1976 7 1978 14 1979 26
8 21 336 0.063 0.1226 0.4557 5.9329 1.5691 0.3509 1.5015 1995 8 1966 14 1939 25
9 10 443 0.023 0.1202 0.4588 5.3959 1.5918 0.3256 1.5242 1959 8 1884 14 1817 24
10 284 377 0.753 0.1741 0.5589 11.1605 1.6069 0.4650 1.5066 2597 9 2537 15 2462 31
11 50 341 0.146 0.1194 0.3243 5.6397 1.5413 0.3426 1.5068 1947 6 1922 13 1899 25
12 100 596 0.168 0.1208 0.3279 5.8127 1.5389 0.3490 1.5035 1968 6 1948 13 1930 25
13 53 322 0.163 0.1213 0.4310 5.9051 1.5633 0.3531 1.5027 1975 8 1962 14 1950 25
14 12 320 0.039 0.1205 0.3179 5.9092 1.5448 0.3557 1.5117 1963 6 1963 14 1962 26
15 62 422 0.146 0.1210 0.4151 5.8370 1.5615 0.3498 1.5053 1971 7 1952 14 1934 25
16 56 339 0.164 0.1195 0.4172 5.8042 1.5846 0.3522 1.5287 1949 7 1947 14 1945 26
17 24 431 0.055 0.1225 0.5889 5.7993 1.6260 0.3433 1.5156 1993 10 1946 14 1903 25
18 15 431 0.034 0.1268 0.4110 6.3331 1.5611 0.3622 1.5060 2054 7 2023 14 1992 26
(continued on next page)
21
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 2 (continued)
Spot no. Contnets Ratios Age(Ma)
Th U Th/U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
19 15 464 0.033 0.1252 0.3681 6.2520 1.5511 0.3622 1.5068 2031 7 2012 14 1993 26
20 19 431 0.044 0.1221 0.4408 5.9148 1.5667 0.3513 1.5034 1987 8 1963 14 1941 25
21 14 434 0.033 0.1219 0.3482 5.9627 1.5509 0.3549 1.5113 1984 6 1970 14 1958 26
22 11 176 0.060 0.1210 0.4686 5.8663 1.5854 0.3517 1.5145 1970 8 1956 14 1943 25
23 25 240 0.105 0.1215 0.5583 6.0697 1.6389 0.3622 1.5409 1979 10 1986 14 1993 26
24 51 367 0.139 0.1209 0.3516 5.9643 1.5463 0.3578 1.5058 1970 6 1971 14 1972 26
25 6 292 0.022 0.1205 0.4734 5.9941 1.5916 0.3609 1.5195 1963 8 1975 14 1986 26
1 291 2971 0.098 0.0916 0.3301 2.0276 1.5610 0.1606 1.5257 1459 6 1125 11 960 14
2 366 3281 0.111 0.1089 0.4218 3.0877 1.6245 0.2056 1.5688 1781 8 1430 13 1205 17
3 220 2241 0.098 0.1111 0.3451 3.7022 1.5516 0.2416 1.5127 1818 6 1572 12 1395 19
4 394 2064 0.191 0.0984 0.4788 2.5198 1.5814 0.1857 1.5072 1594 9 1278 12 1098 15
5 250 2072 0.121 0.1023 0.4176 2.7060 1.5648 0.1918 1.5080 1667 8 1330 12 1131 16
6 243 1856 0.131 0.1101 0.4769 3.5272 1.5740 0.2323 1.5000 1801 9 1533 13 1347 18
7 262 2515 0.104 0.0965 1.2646 2.5637 1.9627 0.1926 1.5010 1558 24 1290 14 1136 16
8 231 1981 0.117 0.1026 1.0615 2.9740 1.8480 0.2103 1.5127 1671 19 1401 14 1230 17
9 293 2035 0.144 0.1014 1.0916 2.8027 1.8899 0.2005 1.5427 1650 20 1356 14 1178 17
10 399 2285 0.175 0.1099 0.6347 3.2125 1.6373 0.2119 1.5093 1798 12 1460 13 1239 17
11 732 4095 0.179 0.1018 0.4286 2.9127 1.6113 0.2076 1.5533 1656 8 1385 12 1216 17
12 265 1993 0.133 0.1058 0.8511 3.2062 1.7283 0.2197 1.5042 1729 16 1459 13 1280 17
13 226 1490 0.151 0.1102 0.9325 3.6599 1.7936 0.2408 1.5321 1803 17 1563 14 1391 19
14 435 2513 0.173 0.0940 0.5094 1.7609 1.6615 0.1359 1.5815 1508 10 1031 11 821 12
15 40 2922 0.014 0.0991 0.4532 2.7462 1.6316 0.2009 1.5673 1608 8 1341 12 1180 17
16 192 1783 0.108 0.1063 0.6349 3.4757 1.9202 0.2371 1.8122 1737 12 1522 15 1371 22
17 267 3099 0.086 0.0961 0.7008 2.5409 1.6580 0.1917 1.5026 1550 13 1284 12 1131 16
18 243 2197 0.110 0.1011 1.8477 2.3471 2.3871 0.1684 1.5115 1645 34 1227 17 1003 14
19 293 3120 0.094 0.0829 2.3307 1.5936 2.7893 0.1394 1.5324 1267 45 968 18 841 12
20 468 4536 0.103 0.0954 0.4461 2.5486 1.5883 0.1937 1.5244 1537 8 1286 12 1141 16
21 226 2288 0.099 0.1127 0.3397 3.6689 1.5635 0.2360 1.5261 1844 6 1565 13 1366 19
22 81 872 0.093 0.1224 0.3615 5.0441 1.5709 0.2989 1.5287 1991 6 1827 13 1686 23
23 44 1021 0.043 0.1169 0.3787 4.2302 1.7259 0.2624 1.6839 1910 7 1680 14 1502 23
16AK26
1 147 1388 0.106 0.1080 0.4392 3.3257 1.5949 0.2233 1.5332 1766 8 1487 13 1299 18
2 15 401 0.037 0.1189 1.2143 5.0396 1.9383 0.3073 1.5108 1940 22 1826 17 1728 23
3 252 1932 0.130 0.1014 0.3184 2.8564 1.5487 0.2044 1.5156 1649 6 1370 12 1199 17
4 293 2276 0.129 0.1001 0.6108 2.8365 1.6659 0.2055 1.5499 1626 11 1365 13 1205 17
5 230 2480 0.093 0.0939 0.9300 2.2782 1.7705 0.1760 1.5065 1506 17 1206 13 1045 15
6 99 2409 0.041 0.1050 0.8387 3.1836 2.3185 0.2200 2.1615 1714 15 1453 18 1282 25
7 269 2385 0.113 0.0997 1.2164 3.0927 1.9492 0.2250 1.5230 1618 22 1431 15 1308 18
8 265 2399 0.111 0.0894 0.3772 2.0723 1.5512 0.1681 1.5046 1413 7 1140 11 1002 14
9 134 1460 0.092 0.1076 0.3917 3.2377 1.5633 0.2182 1.5134 1759 7 1466 12 1273 18
10 212 1597 0.133 0.1080 0.3273 3.3341 1.5357 0.2239 1.5004 1766 6 1489 12 1303 18
11 299 2995 0.100 0.0987 0.7684 2.7976 1.6884 0.2056 1.5035 1600 14 1355 13 1205 17
12 243 1856 0.131 0.1018 1.3854 2.9996 3.5266 0.2136 3.2431 1658 25 1408 27 1248 37
13 264 2576 0.102 0.0889 0.3967 1.9780 1.5521 0.1613 1.5005 1402 8 1108 11 964 13
14 79 2276 0.035 0.1007 0.3930 2.8238 1.5866 0.2034 1.5371 1637 7 1362 12 1193 17
15 244 2499 0.098 0.1033 0.4412 2.9614 1.5642 0.2079 1.5007 1685 8 1398 12 1217 17
16 145 2382 0.061 0.0993 0.5308 2.8056 1.6042 0.2049 1.5139 1611 10 1357 12 1202 17
17 216 2038 0.106 0.1054 0.5188 3.0576 1.5961 0.2104 1.5094 1721 10 1422 12 1231 17
18 208 2361 0.088 0.1040 0.5475 3.1817 1.6351 0.2218 1.5407 1697 10 1453 13 1291 18
19 265 2474 0.107 0.1011 0.3393 2.9557 1.6648 0.2119 1.6298 1645 6 1396 13 1239 18
20 120 1499 0.080 0.1071 0.3570 3.3526 1.5453 0.2271 1.5035 1750 7 1493 12 1319 18
21 249 2478 0.101 0.1020 2.6944 2.9104 3.0842 0.2070 1.5010 1660 49 1385 24 1213 17
22 85 2650 0.032 0.1028 1.2338 3.2319 2.2082 0.2279 1.8314 1676 23 1465 17 1324 22
16AK27
1 92 2461 0.037 0.1005 0.5831 3.0218 1.6112 0.2182 1.5020 1633 11 1413 12 1272 17
2 417 3775 0.110 0.0983 0.4905 2.7830 1.5965 0.2053 1.5193 1592 9 1351 12 1204 17
3 154 1478 0.104 0.1242 0.3474 6.4837 1.5966 0.3786 1.5583 2017 6 2044 14 2070 28
4 250 1864 0.134 0.1075 0.5133 3.4438 1.5961 0.2324 1.5113 1757 9 1514 13 1347 18
5 213 2227 0.095 0.1041 0.3503 2.9920 1.5411 0.2085 1.5008 1698 6 1406 12 1221 17
6 220 1696 0.130 0.1107 0.2462 3.2805 1.5222 0.2148 1.5021 1812 4 1476 12 1255 17
7 365 2270 0.161 0.1018 0.3817 2.8582 1.5478 0.2035 1.5000 1658 7 1371 12 1194 16
8 187 1345 0.139 0.1053 0.3544 3.0305 1.5573 0.2088 1.5164 1719 6 1415 12 1222 17
9 339 3265 0.104 0.0971 0.7261 2.8483 1.7678 0.2128 1.6118 1569 14 1368 13 1244 18
10 360 3683 0.098 0.1121 0.3093 3.2010 1.5415 0.2071 1.5101 1834 6 1457 12 1213 17
11 353 3305 0.107 0.1089 0.3811 3.1461 1.5512 0.2094 1.5037 1782 7 1444 12 1226 17
12 176 1497 0.117 0.1069 0.7237 3.2037 1.8323 0.2174 1.6834 1747 13 1458 14 1268 19
13 437 2910 0.150 0.0942 0.4136 2.2896 1.6140 0.1762 1.5601 1513 8 1209 11 1046 15
14 366 3708 0.099 0.0962 0.7426 2.8185 1.6742 0.2126 1.5005 1551 14 1360 13 1242 17
15 207 2150 0.096 0.1017 1.4205 2.9290 3.5778 0.2089 3.2837 1655 26 1389 27 1223 37
16 715 3194 0.224 0.0991 0.9319 3.0814 1.8113 0.2254 1.5532 1608 17 1428 14 1310 18
17 261 2766 0.094 0.1022 1.1608 2.9840 2.1501 0.2119 1.8098 1664 21 1404 16 1239 20
18 356 3552 0.100 0.0971 0.7833 2.4381 1.7137 0.1821 1.5241 1569 15 1254 12 1079 15
(continued on next page)
22
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 2 (continued)
Spot no. Contnets Ratios Age(Ma)
Th U Th/U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
19 242 2014 0.120 0.1110 0.3830 3.3951 1.5687 0.2217 1.5213 1817 7 1503 12 1291 18
20 275 2810 0.098 0.0937 0.6109 2.0882 1.7936 0.1617 1.6864 1501 12 1145 12 966 15
zoning, while a few grains are unzoned with homogeneous internal blurred zoning, typically diagnostic of metamorphic zircons. They have
structure (Fig. 7a). A total of 25 analyses recorded Th/U ratios ranging relatively low Th/U ratios between 0.03 and 0.13. A total of twenty-two
from 0.01 to 0.15 (mostly< 0.1) by SIMS, suggesting a metamorphic analyses were conducted by SIMS. All the age data define a discordant
origin (Rubatto, 2002). Twenty-five analysis results fall on a discordant line with an upper intercept age of age of 2016 ± 27Ma
line with an upper intercept age of 1962 ± 18Ma (MSWD=1.13), (MSWD=2.9) (Fig. 8e), taken to record the metamorphic age of the
which is similar, within analytical error, to the weighted mean granulite. The dated zircon grains have relatively uniform initial
207Pb/206Pb age of 1952 ± 78Ma (MSWD=0.03) (Fig. 8a). Given the 176Hf/177Hf ratios of 0.281450–0.281543, corresponding to highly
diagnostic characteristics of metamorphic zircons, this upper intercept variable εHf (t) values between −14.4 and −1.8 (Fig. 9), resulting in
age is taken to represent the metamorphic age of the Grt-Bi gneiss. T CDM model ages spread between 2706 and 3086Ma.
Twenty-four dated zircons were performed for Hf isotopic analyses Zircon grains from sample 16AK27 are mostly rounded crystals,
later. The obtained results are characterized by variable initial Hf with highly variable sizes between 80 and 150 μm. Their internal
compositions (176Hf/177Hf (i) = 0.280755–0.281497) and negative εHf growth structure is characterized by convolute or planar zoning
(t) values (from −4.6 to −0.6), with T CDM model ages ranging from (Fig. 7f), a zoning pattern typically resulting from high-grade meta-
2709 to 2889Ma (Fig. 9). morphism (Vavra et al., 1999). They have Th/U ratios range between
Zircons from sample 16AK23 are predominantly rounded and 0.04 and 0.22, predominantly< 0.1, suggesting a metamorphic origin.
equant crystals, small in size with sector or planar zoning (Fig. 7b), A total of twenty analytical spots defined a discordant line with an
indicative of a metamorphic origin. Meanwhile, they mostly exhibit low upper intercept age of 2003 ± 93Ma (MSWD=13.0) (Fig. 8f), which
Th/U ratios (< 0.1). Twenty-five zircon grains were analyzed by SIMS is taken to represent the metamorphic age of the granulite. All the dated
for U-Pb ages. The obtained ages are concordant to variably discordant zircons were selected for Hf isotopic analyses. They yielded relatively
(Fig. 8b), falling on a discordia with an upper intercept age of variable initial Hf ratios (176Hf/177Hf (i)) of 0.281471–0.281620 and
1977 ± 24Ma (MSWD=2.6), which is, within analytical un- negative εHf(t) values between −3.0 and −12.7 (Fig. 9), except one
certainties, consistent with the weighted mean 207Pb/206Pb age of zircon grain (εHf (t)=+1.1). The zircons with negative εHf (t) values
1951 ± 75Ma (MSWD=0.03). This age more likely represents the have T CDM model ages of 2655–3056Ma.
metamorphic age of the Grt-Bi gneiss. Twenty-five dated spots were
analyzed for Hf isotopic compositions. They show a narrow range in
initial Hf compositions (176Hf/177Hf (i) = 0.281191–0.281494) and
7. Whole-rock major and trace element geochemistry
large range in ε (t) values (from −11.7 to −1.5), with T CHf DM model
ages scatter from 2704 to 3368Ma (Fig. 9). The analytical results of major and trace elements for samples are
Zircon grains contained in sample 16AK24 have length-to-width listed in Table 4. The least altered samples were selected for chemical
ratios near to 1:1 and are predominantly rounded crystals with patchy analyses, and the major and trace element compositions can be used to
zoning (Fig. 7c), indicative of metamorphic zircons. A total of twenty- identify the original geochemical characteristics of these metamorphic
five analyses were performed on these zircons, with majority of the data rocks.
plotting on, or near, the concordant line (Fig. 8c), defining an upper The Grt-Bi gneisses show low contents in SiO2 (52.0–53.2 wt%) and
intercept age of 1984 ± 26Ma (MSWD=3.5). Within analytical error, CaO (1.94–1.97 wt%), relatively high contents in Al2O3 (17.4–18.1 wtT
this age is consistent with the weighted mean 207Pb/206Pb age of %) and total Fe2O3 (18.9–19.0 wt%), and moderate concentrations of
1971 ± 57Ma (MSWD=0.05), interpreted as best representing the MgO (4.92–4.96 wt%) and Na2O (1.40–1.48 wt%). As the total alkali
metamorphic age of the Grt-Bi gneiss. All the dated zircons were se- silica (TAS) diagram shows (Fig. 10), they have a basaltic-andesite af-
lected for Hf isotopic analyses. Except for one grain with a positive ε finity. With respect to trace element concentrations, the Grt-Bi gneissesHf
(t) value (+2.5), the other zircons have highly variable negative εHf (t)
have total REE contents ranging from 66 to 76 ppm. They have low and
values between −1.0 and −15.0 (Fig. 9). Accordingly, they have re- nearly flat chondrite-normalized REE patterns (Fig. 11a), with slightly
latively variable initial Hf ratios (176Hf/177Hf = 0.281137–0.281508) negative Eu anomalies (Eu/Eu
*= 0.82–0.85). On the spider plots nor-
(i)
and corresponding to T C model ages of 2672–3526Ma. malized to primitive mantle (Fig. 11b), the samples are relatively uni-DM
Most zircons from sample 16AK25 are subrounded and small in size, form and show moderately negative Nb-Ta and slightly positive Zr-Hf
with patchy zoning or are unzoned (Fig. 7d). Twenty-three zircon anomalies, and pronounced positive spikes in U and Pb. Generally, the
grains were analyzed for U-Pb compositions. Th/U ratios of these zir- analyzed samples exhibit low Nb/Ta and Zr/Hf ratios.
cons vary from 0.01 to 0.19, indicative of metamorphic origin. The Mafic granulites have similar SiO2 (49.3–54.7 wt%) content with
analytical results define a normal discordant line with an upper inter- Grt-Bi gneisses, higher concentrations of MgO (5.03–6.33 wt%), and
cept age of 2036 ± 79Ma (MSWD=11) (Fig. 8d), representing the relatively low total Fe2O
T
3 (16.7–18.6 wt%), Al2O3 (13.7–14.8 wt%)
metamorphic age of the mafic granulite. Twenty-three dated spots were and Na2O (0.21–0.25) contents. The granulite samples have higher
analyzed for Hf compositions. They have initial Hf compositions contents of some transition metals and HREE compared with Grt-Bi
changing between 0.281113 and 0.281606. Their corresponding ε (t) gneisses, reflecting their higher garnet and rutile contents. In theHf
values and T C model ages range from −18.2 to −3.0 and 2772 to chondrite-normalized REE patterns (Fig. 11a), the granulite samplesDM
3648Ma (Fig. 9), respectively. exhibit almost identical LREE and HREE normalized values, and thus,
Zircon grains in sample 16AK26 have crystal lengths range from 60 display a relatively flat pattern with insignificant negative Eu anomalies
to 100 μm, and aspect ratios from 1:1 to 2:1. Ovoid morphology dom- (Eu/Eu
*= 0.69–0.93). They have similar patterns with Grt-Bi gneisses
inates most zircon crystals, although some grains display rounded ter- on the primitive mantle-normalized spider diagram (Fig. 11a), except
minations (Fig. 7e). Most crystals are essentially unzoned or have the less marked positive spike in Pb.
All the analyzed samples are strongly peraluminous in composition,
23
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 3
Lu-Hf isotopic data of zircons from the analyzed garnet-biotite gneisses and mafic granulites.
Spot. No Age (Ma) 176Yb/177Hf 1σ 176Lu/177Hf 1σ 176Hf/177Hf 1σ 176Hf/177Hfi e (t) T (Hf) T (Hf) T CHf DM1 DM2 DM fLu/Hf
16AK22
1 1916 0.00079 0.00002 0.00003 0.00000 0.28144 0.00001 0.281438 −4.5 2473 2829 2859 −1.00
2 1982 0.00052 0.00001 0.00002 0.00000 0.28147 0.00001 0.281468 −1.9 2432 2721 2746 −1.00
3 1921 0.00039 0.00001 0.00001 0.00000 0.28149 0.00001 0.281484 −2.7 2411 2725 2751 −1.00
4 1975 0.00040 0.00000 0.00001 0.00000 0.28146 0.00001 0.281453 −2.6 2453 2759 2786 −1.00
5 1917 0.00197 0.00014 0.00009 0.00001 0.28147 0.00001 0.281461 −3.6 2443 2778 2807 −1.00
6 1946 0.00305 0.00017 0.00012 0.00001 0.28142 0.00001 0.281416 −4.6 2504 2858 2889 −1.00
7 1970 0.00213 0.00015 0.00009 0.00001 0.28144 0.00001 0.281430 −3.5 2484 2811 2840 −1.00
8 2008 0.00627 0.00037 0.00029 0.00002 0.28145 0.00001 0.281434 −2.5 2481 2778 2805 −0.99
9 1948 0.00126 0.00004 0.00005 0.00000 0.28143 0.00001 0.281424 −4.2 2492 2839 2869 −1.00
10 1958 0.00094 0.00002 0.00003 0.00000 0.28143 0.00001 0.281430 −3.8 2484 2820 2849 −1.00
11 1927 0.00105 0.00004 0.00004 0.00000 0.28144 0.00001 0.281435 −4.3 2476 2828 2857 −1.00
12 1986 0.00052 0.00002 0.00002 0.00000 0.28144 0.00001 0.281440 −2.8 2470 2779 2807 −1.00
13 1938 0.00250 0.00025 0.00011 0.00001 0.28145 0.00001 0.281448 −3.6 2460 2793 2821 −1.00
14 1933 0.00170 0.00022 0.00007 0.00001 0.28144 0.00001 0.281435 −4.2 2477 2824 2853 −1.00
15 2052 0.00071 0.00001 0.00002 0.00000 0.28146 0.00001 0.281460 −0.6 2443 2693 2717 −1.00
16 1970 0.00060 0.00001 0.00002 0.00000 0.28148 0.00001 0.281479 −1.8 2417 2704 2729 −1.00
17 1918 0.00077 0.00003 0.00003 0.00000 0.28148 0.00001 0.281475 −3.1 2423 2747 2774 −1.00
18 1958 0.00104 0.00015 0.00004 0.00001 0.28146 0.00001 0.281452 −3.0 2455 2772 2800 −1.00
19 1960 0.00168 0.00031 0.00007 0.00002 0.28146 0.00001 0.281453 −3.0 2454 2768 2796 −1.00
20 1919 0.00062 0.00001 0.00002 0.00000 0.28145 0.00001 0.281451 −4.0 2455 2798 2827 −1.00
21 1966 0.00207 0.00035 0.00009 0.00002 0.28143 0.00001 0.281424 −3.8 2492 2826 2856 −1.00
22 1899 0.00166 0.00016 0.00007 0.00001 0.28145 0.00001 0.281445 −4.6 2464 2825 2855 −1.00
23 1944 0.00070 0.00001 0.00002 0.00000 0.28146 0.00001 0.281453 −3.3 2452 2777 2805 −1.00
25 1939 0.00049 0.00001 0.00002 0.00000 0.28150 0.00001 0.281497 −1.9 2393 2684 2709 −1.00
16AK23
1 1887 0.01291 0.00050 0.00066 0.00003 0.28141 0.00001 0.281389 −6.9 2549 2955 2989 −0.98
2 1939 0.00137 0.00020 0.00006 0.00001 0.28146 0.00001 0.281452 −3.5 2455 2784 2812 −1.00
3 1973 0.00116 0.00007 0.00004 0.00000 0.28145 0.00001 0.281446 −2.9 2462 2775 2802 −1.00
4 1987 0.00355 0.00045 0.00017 0.00002 0.28144 0.00001 0.281431 −3.1 2483 2797 2825 −0.99
5 1929 0.00084 0.00002 0.00003 0.00000 0.28146 0.00001 0.281461 −3.4 2442 2771 2799 −1.00
6 2026 0.00062 0.00002 0.00002 0.00000 0.28139 0.00001 0.281390 −3.7 2537 2865 2894 −1.00
7 1934 0.00123 0.00001 0.00004 0.00000 0.28142 0.00001 0.281416 −4.9 2503 2866 2897 −1.00
8 1945 0.00548 0.00023 0.00026 0.00001 0.28145 0.00001 0.281441 −3.7 2472 2804 2833 −0.99
9 1958 0.00216 0.00019 0.00008 0.00001 0.28143 0.00001 0.281429 −3.9 2486 2822 2851 −1.00
10 2002 0.00530 0.00035 0.00026 0.00002 0.28146 0.00001 0.281448 −2.2 2462 2751 2778 −0.99
11 2002 0.00126 0.00014 0.00005 0.00001 0.28144 0.00001 0.281438 −2.5 2473 2774 2801 −1.00
12 1978 0.00068 0.00006 0.00002 0.00000 0.28145 0.00001 0.281444 −2.8 2464 2775 2803 −1.00
13 1983 0.00438 0.00036 0.00021 0.00002 0.28120 0.00002 0.281191 −11.7 2805 3325 3368 −0.99
14 1919 0.00047 0.00003 0.00002 0.00000 0.28148 0.00001 0.281476 −3.1 2422 2745 2772 −1.00
15 1986 0.00096 0.00001 0.00003 0.00000 0.28143 0.00001 0.281430 −3.2 2484 2801 2830 −1.00
16 1921 0.00113 0.00014 0.00004 0.00001 0.28144 0.00001 0.281436 −4.4 2475 2829 2859 −1.00
17 1943 0.00180 0.00009 0.00007 0.00000 0.28145 0.00001 0.281446 −3.6 2462 2793 2821 −1.00
18 1909 0.00754 0.00045 0.00038 0.00002 0.28146 0.00001 0.281445 −4.4 2468 2818 2847 −0.99
19 1923 0.00066 0.00013 0.00003 0.00001 0.28147 0.00001 0.281469 −3.2 2431 2757 2784 −1.00
20 1904 0.00055 0.00001 0.00002 0.00000 0.28146 0.00001 0.281459 −4.0 2444 2790 2818 −1.00
21 1999 0.00069 0.00001 0.00003 0.00000 0.28146 0.00001 0.281461 −1.8 2441 2724 2750 −1.00
22 1957 0.00430 0.00076 0.00021 0.00004 0.28150 0.00001 0.281494 −1.5 2400 2679 2704 −0.99
23 1927 0.00214 0.00017 0.00009 0.00001 0.28147 0.00001 0.281469 −3.1 2432 2754 2782 −1.00
24 1907 0.01408 0.00067 0.00063 0.00003 0.28138 0.00001 0.281357 −7.6 2592 3013 3048 −0.98
25 1941 0.00077 0.00001 0.00003 0.00000 0.28146 0.00001 0.281458 −3.2 2446 2769 2796 −1.00
16AK24
1 1981 0.00101 0.00002 0.00004 0.00000 0.28147 0.00001 0.281467 −2.0 2434 2724 2750 −1.00
2 1925 0.00906 0.00086 0.00038 0.00003 0.28115 0.00003 0.281137 −15.0 2881 3479 3526 −0.99
3 1915 0.00244 0.00012 0.00010 0.00001 0.28140 0.00001 0.281390 −6.2 2538 2935 2968 −1.00
4 2054 0.01434 0.00034 0.00063 0.00002 0.28124 0.00001 0.281211 −9.4 2786 3235 3276 −0.98
5 1964 0.00791 0.00082 0.00039 0.00004 0.28149 0.00001 0.281477 −2.0 2425 2712 2738 −0.99
6 1924 0.00098 0.00001 0.00003 0.00000 0.28147 0.00001 0.281463 −3.4 2439 2768 2796 −1.00
7 1976 0.00073 0.00003 0.00002 0.00000 0.28148 0.00001 0.281480 −1.6 2417 2699 2724 −1.00
8 1995 0.00975 0.00088 0.00049 0.00004 0.28148 0.00001 0.281462 −1.8 2446 2726 2752 −0.99
9 1959 0.01127 0.00094 0.00054 0.00005 0.28153 0.00001 0.281508 −1.0 2385 2648 2672 −0.98
10 2597 0.02161 0.00065 0.00095 0.00003 0.28124 0.00001 0.281195 2.5 2800 2922 2937 −0.97
11 1947 0.00082 0.00001 0.00003 0.00000 0.28148 0.00001 0.281475 −2.5 2423 2728 2755 −1.00
12 1968 0.00087 0.00002 0.00003 0.00000 0.28142 0.00001 0.281418 −4.0 2500 2840 2870 −1.00
13 1975 0.00070 0.00003 0.00002 0.00000 0.28141 0.00001 0.281407 −4.2 2514 2860 2890 −1.00
14 1963 0.00045 0.00001 0.00001 0.00000 0.28143 0.00001 0.281423 −3.9 2493 2832 2861 −1.00
15 1971 0.00058 0.00001 0.00002 0.00000 0.28142 0.00001 0.281416 −4.0 2501 2841 2870 −1.00
16 1949 0.00056 0.00002 0.00002 0.00000 0.28140 0.00001 0.281400 −5.1 2523 2890 2921 −1.00
17 1993 0.00085 0.00001 0.00003 0.00000 0.28146 0.00001 0.281453 −2.2 2453 2747 2773 −1.00
18 2054 0.00076 0.00001 0.00002 0.00000 0.28143 0.00001 0.281431 −1.6 2482 2756 2782 −1.00
19 2031 0.00051 0.00002 0.00002 0.00000 0.28143 0.00001 0.281430 −2.1 2484 2773 2799 −1.00
(continued on next page)
24
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 3 (continued)
Spot. No Age (Ma) 176Yb/177Hf 1σ 176Lu/177Hf 1σ 176Hf/177Hf 1σ 176Hf/177Hfi eHf(t) TDM1(Hf) TDM2(Hf) T CDM fLu/Hf
20 1987 0.00114 0.00003 0.00004 0.00000 0.28144 0.00001 0.281435 −3.0 2477 2791 2819 −1.00
21 1984 0.00094 0.00001 0.00003 0.00000 0.28145 0.00001 0.281447 −2.6 2461 2766 2793 −1.00
22 1970 0.00439 0.00050 0.00020 0.00002 0.28142 0.00001 0.281414 −4.1 2506 2845 2875 −0.99
23 1979 0.00054 0.00005 0.00002 0.00000 0.28146 0.00001 0.281461 −2.2 2441 2738 2764 −1.00
24 1970 0.00065 0.00001 0.00002 0.00000 0.28145 0.00001 0.281447 −2.9 2461 2775 2803 −1.00
25 1963 0.00616 0.00047 0.00027 0.00002 0.28147 0.00001 0.281461 −2.6 2444 2747 2774 −0.99
16AK25
1 1459 0.00044 0.00003 0.00002 0.00000 0.28144 0.00001 0.281436 −14.9 2475 3126 3161 −1.00
2 1781 0.00038 0.00001 0.00002 0.00000 0.28142 0.00001 0.281419 −8.2 2498 2956 2990 −1.00
3 1818 0.00546 0.00035 0.00023 0.00001 0.28112 0.00001 0.281113 −18.2 2910 3599 3648 −0.99
4 1594 0.00042 0.00001 0.00002 0.00000 0.28137 0.00001 0.281371 −14.2 2563 3182 3220 −1.00
5 1667 0.00056 0.00001 0.00002 0.00000 0.28144 0.00001 0.281441 −10.0 2469 2983 3017 −1.00
6 1801 0.00058 0.00001 0.00002 0.00000 0.28142 0.00001 0.281415 −7.9 2504 2954 2988 −1.00
7 1558 0.00209 0.00049 0.00009 0.00002 0.28145 0.00001 0.281442 −12.5 2469 3050 3085 −1.00
8 1671 0.00192 0.00017 0.00009 0.00001 0.28141 0.00001 0.281404 −11.2 2519 3060 3096 −1.00
9 1650 0.00052 0.00002 0.00002 0.00000 0.28141 0.00001 0.281409 −11.6 2511 3063 3099 −1.00
10 1798 0.00243 0.00029 0.00011 0.00001 0.28139 0.00001 0.281389 −8.9 2540 3011 3047 −1.00
11 1656 0.00244 0.00003 0.00010 0.00000 0.28148 0.00001 0.281475 −9.1 2424 2913 2946 −1.00
12 1729 0.00209 0.00009 0.00009 0.00000 0.28154 0.00001 0.281532 −5.4 2349 2744 2773 −1.00
13 1803 0.00032 0.00001 0.00001 0.00000 0.28149 0.00001 0.281485 −5.4 2410 2799 2829 −1.00
14 1508 0.00054 0.00001 0.00002 0.00000 0.28152 0.00001 0.281518 −10.9 2367 2916 2949 −1.00
15 1608 0.00025 0.00002 0.00001 0.00000 0.28152 0.00001 0.281518 −8.6 2366 2851 2883 −1.00
16 1737 0.01227 0.00066 0.00052 0.00003 0.28132 0.00001 0.281299 −13.5 2670 3247 3288 −0.98
17 1550 0.00306 0.00056 0.00014 0.00003 0.28142 0.00001 0.281411 −13.7 2511 3122 3158 −1.00
18 1645 0.00037 0.00001 0.00002 0.00000 0.28147 0.00001 0.281463 −9.8 2439 2948 2982 −1.00
19 1267 0.00072 0.00002 0.00003 0.00000 0.28161 0.00001 0.281606 −13.2 2248 2876 2905 −1.00
20 1537 0.00130 0.00015 0.00005 0.00001 0.28143 0.00001 0.281428 −13.4 2487 3094 3130 −1.00
21 1844 0.00028 0.00002 0.00001 0.00000 0.28140 0.00001 0.281402 −7.4 2520 2953 2987 −1.00
22 1991 0.00268 0.00022 0.00012 0.00001 0.28144 0.00001 0.281432 −3.0 2482 2793 2821 −1.00
23 1910 0.00142 0.00008 0.00006 0.00000 0.28148 0.00001 0.281478 −3.2 2419 2744 2772 −1.00
16AK26
1 1766 0.00232 0.00019 0.00011 0.00001 0.28149 0.00001 0.281485 −6.2 2411 2822 2853 −1.00
2 1940 0.00062 0.00002 0.00003 0.00000 0.28150 0.00001 0.281498 −1.8 2392 2681 2706 −1.00
3 1649 0.00039 0.00004 0.00002 0.00000 0.28150 0.00001 0.281498 −8.4 2393 2870 2902 −1.00
4 1626 0.00150 0.00018 0.00006 0.00001 0.28151 0.00001 0.281508 −8.6 2380 2860 2892 −1.00
5 1506 0.00068 0.00006 0.00003 0.00000 0.28151 0.00001 0.281508 −11.3 2380 2939 2972 −1.00
6 1714 0.00007 0.00001 0.00000 0.00000 0.28153 0.00001 0.281525 −6.0 2356 2768 2798 −1.00
7 1618 0.00039 0.00001 0.00001 0.00000 0.28152 0.00001 0.281514 −8.6 2372 2854 2886 −1.00
8 1413 0.00041 0.00001 0.00002 0.00000 0.28152 0.00001 0.281522 −12.9 2361 2967 2999 −1.00
9 1759 0.00022 0.00001 0.00001 0.00000 0.28152 0.00001 0.281522 −5.1 2361 2746 2775 −1.00
10 1766 0.00033 0.00001 0.00001 0.00000 0.28152 0.00001 0.281522 −4.9 2360 2741 2770 −1.00
11 1600 0.00038 0.00002 0.00001 0.00000 0.28152 0.00001 0.281521 −8.7 2361 2849 2881 −1.00
12 1658 0.00036 0.00002 0.00001 0.00000 0.28152 0.00001 0.281522 −7.4 2360 2810 2841 −1.00
13 1402 0.00009 0.00000 0.00000 0.00000 0.28149 0.00001 0.281486 −14.4 2408 3053 3086 −1.00
14 1637 0.00034 0.00005 0.00002 0.00000 0.28155 0.00001 0.281543 −7.1 2332 2777 2807 −−1.00
15 1685 0.00034 0.00001 0.00001 0.00000 0.28151 0.00001 0.281507 −7.3 2381 2826 2857 −1.00
16 1611 0.00018 0.00000 0.00001 0.00000 0.28150 0.00001 0.281503 −9.1 2386 2882 2915 −1.00
17 1721 0.00045 0.00002 0.00002 0.00000 0.28152 0.00001 0.281514 −6.2 2372 2788 2818 −1.00
18 1697 0.00140 0.00029 0.00006 0.00001 0.28147 0.00001 0.281469 −8.3 2432 2901 2934 −1.00
19 1645 0.00043 0.00001 0.00002 0.00000 0.28149 0.00001 0.281483 −9.0 2412 2904 2936 −1.00
20 1750 0.00057 0.00007 0.00002 0.00000 0.28149 0.00001 0.281488 −6.5 2406 2826 2857 −1.00
21 1660 0.00552 0.00065 0.00026 0.00003 0.28146 0.00001 0.281450 −9.9 2462 2967 3001 −0.99
22 1676 0.00006 0.00000 0.00000 0.00000 0.28150 0.00001 0.281494 −7.9 2397 2859 2891 −1.00
16AK27
1 1633 0.00091 0.00005 0.00003 0.00000 0.28149 0.00001 0.281490 −9.1 2403 2896 2929 −1.00
2 1592 0.00059 0.00003 0.00002 0.00000 0.28154 0.00001 0.281539 −8.2 2337 2814 2845 −1.00
3 2017 0.00052 0.00001 0.00002 0.00000 0.28153 0.00001 0.281529 1.1 2351 2564 2584 −1.00
4 1757 0.00039 0.00002 0.00002 0.00000 0.28151 0.00002 0.281512 −5.5 2374 2769 2799 −1.00
5 1698 0.00042 0.00002 0.00002 0.00000 0.28150 0.00001 0.281501 −7.2 2388 2830 2862 −1.00
6 1812 0.00064 0.00003 0.00003 0.00000 0.28152 0.00001 0.281516 −4.1 2368 2724 2752 −1.00
7 1658 0.00098 0.00001 0.00004 0.00000 0.28156 0.00001 0.281552 −6.3 2321 2744 2774 −1.00
8 1719 0.00036 0.00000 0.00001 0.00000 0.28150 0.00002 0.281499 −6.8 2391 2821 2852 −1.00
9 1569 0.00115 0.00008 0.00004 0.00000 0.28154 0.00002 0.281533 −9.0 2346 2842 2874 −1.00
10 1834 0.00061 0.00001 0.00002 0.00000 0.28154 0.00001 0.281533 −3.0 2346 2674 2700 −1.00
11 1782 0.00053 0.00001 0.00002 0.00000 0.28154 0.00001 0.281537 −4.0 2340 2698 2725 −1.00
12 1747 0.00049 0.00002 0.00002 0.00000 0.28155 0.00001 0.281546 −4.5 2328 2700 2728 −1.00
13 1513 0.00079 0.00001 0.00003 0.00000 0.28154 0.00001 0.281536 −10.2 2343 2874 2905 −1.00
14 1551 0.00121 0.00005 0.00004 0.00000 0.28153 0.00001 0.281532 −9.4 2348 2858 2889 −1.00
15 1655 0.00104 0.00011 0.00004 0.00000 0.28148 0.00001 0.281473 −9.2 2427 2920 2953 −1.00
16 1608 0.00441 0.00007 0.00016 0.00000 0.28163 0.00002 0.281620 −5.0 2232 2628 2655 −1.00
17 1664 0.00078 0.00002 0.00003 0.00000 0.28152 0.00001 0.281520 −7.3 2363 2811 2842 −1.00
(continued on next page)
25
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 3 (continued)
Spot. No Age (Ma) 176Yb/177Hf 1σ 176Lu/177Hf 1σ 176Hf/177Hf 1σ 176Hf/177Hfi eHf(t) TDM1(Hf) TDM2(Hf) T CDM fLu/Hf
18 1569 0.00101 0.00003 0.00004 0.00000 0.28152 0.00001 0.281519 −9.5 2365 2874 2906 −1.00
19 1817 0.00043 0.00001 0.00002 0.00000 0.28148 0.00001 0.281474 −5.5 2424 2813 2843 −1.00
20 1501 0.00029 0.00000 0.00001 0.00000 0.28147 0.00001 0.281471 −12.7 2428 3022 3056 −1.00
Note: ε (t)= (((176Hf/177Hf) − (176Lu/177Hf) × (eλt− 1))/((176Hf S S Hf/177Hf) 176 177CHUR,0− ( Lu/ Hf) λtCHUR× (e −1))− 1)× 10000; TDM1(Hf)= 1/λ× ln
(1+ ((176Hf/177Hf) − (176Hf/177Hf) )/((176Lu/177Hf) − (176Lu/177S DM S Hf)DM)); TDM2(Hf)=TDM1(Hf)− (TDM1(Hf)− t)((fcc− fs)/(fcc− f cDM)); TDM = (1/k)− ln
[1+ (176Hf/177Hf − 176Hf/177DM HfS)/(176Lu/177Hf − 176Lu/177Hf )]; f 176 177 176 177DM S Lu/Hf= ( Lu/ Hf)S/( Hf/ Hf)CHUR−1; where fCC, fS and fDM are the fLu/Hf values of
the continental crust, sample and the depleted mantle; t= crystallization age of zircon; subscript S= analyzed sample, CHUR=chondritic uniform reservoir,
DM=depleted mantle.
with the Grt-Bi gneisses showing higher A/CNK values (2.33–2.34) than Analytical results of zircon Hf isotopes from both the Grt-Bi gneisses
mafic granulites (A/CNK=1.22–1.25). Both the Grt-Bi gneiss and and mafic granulites reveal that they have variable but mostly negative
mafic granulite have flat REE patterns with negative Eu anomalies, εHf (t) values (from −18.2 to −0.6), fairly uniform Hf isotopic com-
resembling the REE patterns of mid-crust level garnets. These garnets positions, and highly variable T CDM model ages ranging from 2628 to
tend to lose their negative fractionation pattern compared with garnets 3599Ma. Notably, the large variation in Hf crustal model ages was
of more epizonal levels, thus acquiring a flatter pattern (Bea, 1996; mirrored exactly by the long time span of zircon ages. These distinctive
Villaseca et al., 1999). All analyzed samples are characterized by higher negative εHf (t) values, initial Hf isotopic compositions, and Hf crustal
LREE and HREE contents in comparison with estimated lower con- model ages are generally consistent with those from a Hf-in-zircon
tinental crust of Rudnick and Gao (2003). study for orthogneisses reported in the Lapeiquan area (Long et al.,
2014). These data suggest a long-lived reworking of Archean crust in
8. Discussion southern Tarim Craton during the Paleoproterozoic.
8.1. Interpretation and significance of zircon data 8.2. Granulite-facies metamorphism and recrystallization
Processes of zircon-forming, zircon-consuming and zircon-mod- The retrograde metamorphic reactions recorded by the Grt-Bi
ifying are generally controlled by rock composition, pressure and fluid- gneisses occur under P-T conditions of 574 °C and 7.0 kbar, and the
melt-rock interaction (Harley et al., 2007). calculated retrograde P-T conditions for the mafic granulites are
SIMS zircon U-Pb dating results from six samples indicate the pre- roughly at 700 °C and 7.4 kbar, suggesting much higher metamorphic
sence of a well-defined age group, which covers a long time interval up peak pressures and temperatures. Zircon grains from three Grt-Bi gneiss
to 70 Myr (from ca. 2036 to 1962Ma). Hoskin and Black (2000) pionted samples provide metamorphic ages covering a range of 1962–1984Ma.
out that the large spread in ages is likely to represent incomplete re- The external morphology and internal structure, as well as Th/U ratios
setting of U-Pb isotopic compositions due to varying degrees of partial of zircons from Grt-Bi gneisses suggest that they have a metamorphic
recrystallization. Therefore, the youngest ages represent more complete origin, and were probably produced by extensive melt recrystallization.
recrystallization and probably provide the best approximation to the The metamorphic-origin zircons from the mafic granulites give an age
timing of the recrystallization-including events (Hoskin and Black, range of 2003–2036Ma, which is consistent with the previously re-
2000). Alternative, this kind of noticeable scatter in ages is probably ported magmatism and metamorphism in the study area (Long et al.,
resulted from pre- and post-peak high-temperature reactions, de- 2014; Wang et al., 2017c). Considering the dating uncertainty, it re-
formation and/or fluid ingress (Harley et al., 2007). Zircon formed by mains unclear whether the older age cluster records an earlier meta-
complete recrystallization of protolith zircon displays no internal morphic event and the younger one records another, or both of them
structures, except for possible weak sector zonation (Hoskin and Black, record different stages of the same event. Based on their field occur-
2000). When the recrystallization of protolith zircon is incomplete, rences, mineral assemblages and compositions, as well as the typical
zircon crystals may display internal textural characteristics including diagnostic of zircon crystals, it is reasonable to be concluded that the
areas where oscillatory zoning is preserved and unzoned areas where age clusters given by the Grt-Bi gneisses and mafic granulites represent
zoning has been destroyed (Hoskin and Black, 2000). In our study, it is a long-lasting recrystallization-included granulite-facies meta-
noteworthy that some zircon crystals in sample 16AK22 are shaped in morphism.
“soccer ball”, typical of growth from a melt (Harley et al., 2007). Thus,
the age of 1962 ± 18Ma given by sample 16AK22 provides a prefer- 8.3. Regional implications
able constraint on the timing of melt crystallization. Dating results re-
cord a large age span from 2036 to 1962Ma given by mafic granulite The late Paleoproterozoic magmatic and metamorphic activities
(sample 16AK25) and Grt-Bi gneiss (sample 16AK22), respectively. As with ages of 2.1–1.8 Ga are well-documented in the Tarim Craton (Lu
already mentioned, the large spread in ages is likely to be resulted from et al., 2008; Ge et al., 2013a, 2013b, 2015; Wang et al., 2013, 2014,
varying degrees of partial recrystallization, and the youngest ages 2017c, 2017d; Long et al., 2014, 2015; Zhao et al., 2015b), and as they
possibly provide the best approximation to the timing of melt re- are in other continents, have been considered to be probably related to
crystallization. Given the above, age data of the Grt-Bi gneiss and mafic the assembly of the Columbia supercontinent (Condie, 2002; Rogers
granulite samples indicate a main stage of melt recrystallization at ca. and Santosh, 2002; 2003; Zhao et al., 2002, 2004; Michael, 2007; Zhao
1962Ma recorded by the Grt-Bi gneiss (sample 16AK22). Moreover, the and Cawood, 2012). Globally, the assembly of detached continental
long duration of high-grade metamorphic ages indicate that these rocks blocks generates collisional orogens along the colliding margins and is
were metamorphosed in a tectonic setting that prevailed for long per- usually marked by high-grade regional metamorphism. For the Tarim
iods and where large amounts of magmas were added to the crust un- Craton, the Paleoproterozoic high-grade metamorphism associated with
interruptedly. In summary, zircon U-Pb data of the Grt-Bi gneisses and the assembly of the Columbia supercontinent was mostly reported
mafic granulites reveal that the study area experienced Paleoproter- along its northern margin (Lu et al., 2006a,b; Long et al., 2011; Ge
ozoic granulite-facies metamorphism, which appears to have been a et al., 2013a; He et al., 2013; Xu et al., 2013). Whereas, the well-de-
long-lived process, being sustained for over 70Myr. veloped high-grade metamorphism in the southeastern margin of the
26
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
(caption on next page)
27
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 7. Representative Cathodoluminescence (CL) images and corresponding ages for zircons from the studied samples. The red circles show the locations of U-Pb
dating. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 8. Zircon U-Pb concordia diagrams and weighted mean 206Pb/238U ages of the analyzed samples.
28
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Table 4
Major and trace element compositions for the garnet-biotite gneisses and mafic
granulites.
Sample 16AK23 16AK24 16AK26 16AK27
SiO2 53.2 52.0 54.7 49.3
TiO2 1.25 1.28 1.1 1.15
Al2O3 17.4 18.1 13.7 14.8
Fe T2O3 18.9 19.0 16.7 18.6
MnO 0.20 0.21 0.74 0.71
MgO 4.92 4.96 5.03 6.33
CaO 1.97 1.94 5.22 5.54
Na2O 1.40 1.48 0.21 0.25
K2O 1.44 1.66 1.06 1.47
P2O5 0.04 0.03 0.33 0.20
Total 99.9 100.0 101.9 101.4
Mg# 37.8 37.8 41.2 44.3
Sc 62 55 45 53
V 310 308 278 342
Cr 237 238 127 132
Co 69 71 58 79
Ni 102 101 81 154
Cu 72 107 18 33
Zn 159 164 173 239
Ga 20 20 20 30
Rb 53.2 59.2 33 45.9
Sr 136 142 118 182
Y 30.2 29.3 36.4 23.7
Fig. 9. Diagram of εHf (t) values versus ages for zircons in the the granet-biotite Zr 96 130 105 99
gneiss and granulite. Nb 6.1 6.6 5.4 5.4
Cs 0.67 0.71 0.49 0.56
Ba 400 500 310 410
Tarim Craton (Dunhuang Block) is mostly dated as Paleozoic (Zong La 10 <10 10 10
et al., 2012; He et al., 2014; Wang et al., 2016, 2017a, 217b, 2018), and Ce 24.7 19.7 30.8 25.8
the Paleoproterozoic metamorphic ages are limited. The available Pa- Pr 3.05 2.35 4.17 3.4
leoproterozoic metamorphic age (1.98 Ga) was given by a garnet-silli- Nd 12.2 9.2 18 14.3
Sm 3.68 3.06 5.22 3.81
manite-quartz schist and a granite gneiss from the Aketashitage area, Eu 1.16 1.09 1.36 1.33
Dunhuang Block (Lu et al., 2008). Synchronous anatexis events have Gd 5.07 5 7 5.05
been reported for the monzonitic granite and igneous carbonate rocks Tb 0.92 0.91 1.23 0.91
in the same area, which yielded zircon SHRIMP U-Pb anatexic ages of Dy 5.93 5.76 7.57 5.33
1.97 Ga and 1.93 Ga, respectively (Xin et al., 2011). Moreover, a si- Ho 1.2 1.13 1.46 0.96Er 3.56 3.52 4.12 2.79
multaneous migmatization event at 2.0 Ga has been recorded by a Tm 0.52 0.49 0.58 0.41
migmatitic biotite-plagioclase gneiss in the Lapeiquan area (Liu and Yb 3.4 3.37 3.96 2.63
Wang, 2012). Some other Paleoproterozoic metamorphic ages were Lu 0.53 0.49 0.6 0.4
reported in the Hongliuxia area, Dunhuang Block (Zhang et al; 2012, Hf 2.7 3.5 2.9 2.9
Ta 0.4 0.4 0.4 0.4
2013a; Zong et al., 2013). In this study, our detailed report about the Pb 8 10 2 2
granulites in the Aketashitage area reveals the existence of Paleopro- Th <20 <20 <20 <20
terozoic high-grade metamorphism in the Dunhuang Block, south- U <10 <10 <10 <10
eastern margin of the Tarim Craton. A/CNK 2.34 2.33 1.25 1.22
In terms of whole-rock geochemistry characteristics, the Grt-Bi ΣREE 75.9 66.1 96.1 77.1LREE 54.8 45.4 69.6 58.6
gneisses and mafic granulites display uniform major and trace element HREE 21.1 20.7 26.5 18.5
compositions. They are strongly peraluminous in composition and have LREE/HREE 2.59 2.20 2.62 3.17
REE patterns that are identical to those from the middle crust but higher LaN/YbN 2.11 2.13 1.81 2.73
than lower continental crust. These data suggest that the Grt-Bi gneisses δEu 0.82 0.85 0.69 0.93
δCe 1.10 1.00 1.17 1.08
and mafic granulites share the same source, which is probably the
middle continental crust. Although the REE patterns of the garnets from Note: δEu= (Eusample/Euchondrite)/[(Smsample/Smchondrite+Gdsample/Gdchondrite)/2];
different samples differ considerably, all of them have similarly flat δCe=(Cesample/Cechondrite)/[(Lasample/Lachondrite+Prsample/Prchondrite)/2].
patterns in HREE. Overall, the HREE and Y are relatively low in con-
centrations, suggesting a garnet-rich source (Otamendi et al., 2002;
Carlson, 2012). magmatism and metamorphism. Our new data combined with pre-
Our previous study on the lower-grade meta-felsic and mafic rocks viously published data (Xin et al., 2011, 2012; Long et al., 2014; Wang
from the Aketashitage area revealed two comparable emplaced ages of et al., 2017c) reveal that the southeastern Tarim Craton (Dunhuang
1.96 and 2.06 Ga, and a significant contribution of juvenile materials in Block) is characterized by Paleoproterozoic granulite-facies meta-
the Paleoproterozoic (Wang et al., 2017c). Zircon Hf isotopes of the Grt- morphism, anatexis and coeval plutonism, which are diagnostic fea-
Bi gneisses and mafic granulites suggest a long-lived reworking of Ar- tures of active continental margins. In this study, the whole-rock geo-
chean crust during the Paleoproterozoic. These data demonstrate that chemistry and mineral compositions of the analyzed samples suggest
the southeastern Tarim Craton simultaneously experienced addition of that they were possibly formed in the garnet-bearing middle crust, and
juvenile material and reworking of preexisting crust in the Paleopro- their granulite-facies metamorphism is probably the consequence of
terozoic. The crystallization ages of the meta-felsic and mafic rocks steep subduction. The coeval magmatism and anatexis can be inter-
exactly coincide with the metamorphic ages of the Grt-Bi gneisses and preted as a result of the partial melting of the thickening crust related to
mafic granulites, probably indicating a close temporal association of the collision.
29
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 10. TAS diagram for the analyzed samples (after Middlemost, 1994).
Based on the aforementioned analysis, we proposed a model 9. Conclusions
(Fig. 12) that the steep subduction of an oceanic lithosphere resulted in
the thickening of the continental crust, which in turn caused the crust 1. The Grt-Bi gneisses and mafic granulites from the Aketashitage area
anatexis. The increase in asthenosphere high heat flow and the intru- of the southwest Dunhuang Block yielded metamorphic ages be-
sion of mantle-derived magma induced extensive heating, which pre- tween 1962 and 2036Ma, which are coeval with the extensive
ceded the granulite-facies metamorphism and coeval magmatism in the magmatism and anatexis in the same region, indicative of an active
middle crust of the Dunhuang Block. The long-lived metamorphic continental margin.
processes, revealed by our new data, are possibly the result of con- 2. The Grt-Bi gneisses and mafic granulites have variable but mostly
tinuous subduction. Thus, the Dunhuang Block, located on the south- negative εHf (t) values of −18.2 to −0.6, fairly uniform Hf isotopic
eastern margin of the Tarim Craton, was probably an active continental compositions, and highly variable T CDM model ages of 2628 to
margin in the Paleoproterozoic, and is considered to be associated with 3599Ma, suggesting a long-lived reworking of preexisting crust.
the assembly of the Columbia supercontinent. 3. The Grt-Bi gneisses and mafic granulites are formed in the garnet-
bearing middle crust, and the steep subduction of oceanic slab is
probably responsible for their granulite-facies metamorphism.
Fig. 11. (a) Chondrite-normalized rare earth element diagrams and (b) primitive mantle-normalized spider diagrams for the analyzed samples. Chondrite- and
primitive mantle-normalized values are from Sun and McDonough (1989).
30
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Fig. 12. Schematic model illustrating the tectonic setting of the Dunhuang Block during the Paleoproterozoic.
4. We tentatively proposed that the Dunhuang Block, located on the reworking recorded in late Paleoproterozoic granitoids in the northern Tarim craton:
southeastern margin of the Tarim Craton, was possibly an active in situ zircon U-Pb-Hf-O isotopic and geochemical constraints and tectonic implica-
continental margin in the Paleoproterozoic, and can be considered tions. Geol. Soc. Am. Bull. 127 (5–6), 781–803.Ge, R., Zhu, W., Wilde, S.A., Wu, H., 2018. Remnants of Eoarchean continental crust
to be associated with the assembly of the Columbia supercontinent. derived from a subducted proto-arc. Sci. Adv. 4 (2).
Glebovitsky, V.A., Nikitina, L.P., Khiltova, V.Ya., Ovchinnikov, N.O., 2004. The thermal
Acknowledgements regimes of the upper mantle beneath Precambrian and Phanerozoic structures up tothe thermobarometry data of mantle xenoliths. Lithos 74, 1–20.
Harley, S., 1989. The origins of granulites: a metamorphic perspective. Geol. Mag. 126
This work was financially supported by the National Key R&D (3), 215–247.
Program of China (2017YFC0601205), 973 Program (2014CB440801), Harley, S.L., Kelly, N.M., Möller, A., 2007. Zircon behaviour and the thermal histories ofmountain chains. Elements 3 (1), 25–30.
National Natural Science Foundation Projects (41702236) and the He, Z.Y., Zhang, Z.M., Zong, K.Q., Dong, X., 2013. Paleoproterozoic crustal evolution of
China Postdoctoral Foundation Fund Project (2015M580133). This the Tarim Craton: constrained by zircon U-Pb and Hf isotopes of meta-igneous rocks
paper is a contribution to IGCP 592. from Korla and Dunhuang. J. Asian Earth Sci. 78, 54–70.
He, Z., Zhang, Z., Zong, K., Xiang, H., Klemd, R., 2014. Metamorphic P-T-t evolution of
mafic HP granulites in the northeastern segment of the Tarim Craton (Dunhuang
Appendix A. Supplementary data block): evidence for early Paleozoic continental subduction. Lithos 196–197, 1–13.
Hickmott, D.D., Shimizu, N., 1990. Trace element zoning in garnet from the Kwoiek Area,
British Columbia: disequilibrium partitioning during garnet growth? Contrib. Miner.
Supplementary data to this article can be found online at https:// Petrol. 104 (6), 619–630.
doi.org/10.1016/j.precamres.2018.11.003. Hickmott, D., Spear, F.S., 1992. Major-and trace-element zoning in garnets from calcar-
eous pelites in the NW Shelburne Falls Quadrangle, Massachusetts: garnet growth
References histories in retrograded rocks. J. Petrol. 33 (5), 965–1005.Holdaway, M.J., 2000. Application of new experimental and garnet Margules data to the
garnet-biotite geothermometer. Am. Mineral. 85, 881–892.
Bea, F., 1996. Controls on the trace element composition of crustal melts. In: Brown, M., Hoskin, P.W.O., Black, L.P., 2000. Metamorphic zircon formation by solid-state re-
Candela, P.A., Peck, D.L., Stephens, W.E., Walker, R.J., Zen, E.A. (Eds.), The Third crystallization of protolith igneous zircon. J. Metamorph. Geol. 18 (4), 423–439.
Hutton Symposium on the Origin of Granites and Related Rocks. Geological Society Hoskin, P.W., Schaltegger, U., 2003. The composition of zircon and igneous and meta-
of America. morphic petrogenesis. Rev. Mineral. Geochem. 53 (1), 27–62.
Berman, R.G., Aranovich, L.Ya., Pattison, D.R.M., 1995. Reassessment of the garnet- Hu, Z., Zhang, W., Liu, Y., Gao, S., Li, M., Zong, K., Chen, H., Hu, S., 2014. “Wave” signal-
clinopyroxene Fe-Mg exchange thermometer: II. thermodynamic analysis. Contrib. smoothing and mercury-removing device for laser ablation quadrupole and multiple
Miner. Petrol. 119, 30–42. collector ICPMS analysis: application to lead isotope analysis. Anal. Chem. 87 (2),
BGMRG, 1989. Regional geology of Gansu Province, People's Republic of China, Ministry 1152–1157.
of geology and mineral resources. Geological memoirs, Series 1, No. 19. Geological Hyndman, R.D., Currie, C.A., Mazzotti, S.P., 2005. Subduction zone backarcs, mobile
Publishing House, Beijing (in Chinese). belts, and orogenic heat. GSA Today 15 (2), 4–10.
Bohlen, S., Mezger, K., 1989. Origin of granulite terranes and the formation of the low- Jagoutz, O., Müntener, O., Ulmer, P., Pettke, T., Burg, J.P., Dawood, H., Hussain, S., 2007.
ermost continental crust. Science 244 (4902), 326. Petrology and mineral chemistry of lower crustal intrusions: the Chilas Complex,
Carlson, W.D., 2012. Rates and mechanism of Y, REE, and Cr diffusion in garnet. Am. Kohistan (NW Pakistan). J. Petrol. 48 (10), 1895–1953.
Mineral. 97 (10), 1598–1618. Kelly, N.M., Harley, S.L., 2005. An integrated microtextural and chemical approach to
Che, Z.C., Sun, Y., 1996. The age of the Altun granulite facies complex and the basement zircon geochronology: refining the Archaean history of the Napier Complex, east
of the Tarim basin. Regional Geology of China 56, 51–57 in Chinese with English Antarctica. Contrib. Miner. Petrol. 149 (1), 57–84.
abstract. Klepeis, K.A., King, D.M., Paoli, De, Clarke, G.L., Gehrels, G., 2007. Interaction of strong
Collins, W.J., 2002. Nature of extensional accretionary orogens. Tectonics 21 (4), 6-1- lower and weak middle crust during lithospheric extension in western New Zealand.
6-12. Tectonics 26, (4).
Condie, K.C., 2002. Breakup of a Paleoproterozoic Supercontinent. Gondwana Res. 5 (1), Kohn, M.J., Spear, F., 2000. Retrograde net transfer reaction insurance for pressure-
41–43. temperature estimates. Geology 28 (12), 1127–1130.
Debari, S.M., 1994. Petrogenesis of the Fiambalá Gabbroic Intrusion, Northwestern Li, Q.L., Li, X.H., Liu, Y., Tang, G.Q., Yang, J.H., Zhu, W.G., 2010. Precise U-Pb and Pb-Pb
Argentina, a Deep Crustal Syntectonic Pluton in a Continental Magmatic Arc. J. dating of Phanerozoic baddeleyite by SIMS with oxygen flooding technique. J. Anal.
Petrol. 35 (3), 679–713. At. Spectrom. 25 (7), 1107–1113.
Ge, R., Zhu, W., Wu, H., Zheng, B., He, J., 2013b. Timing and mechanisms of multiple Li, X.H., Liu, Y., Li, Q.L., Guo, C.H., Chamberlain, K.R., 2009. Precise determination of
episodes of migmatization in the Korla Complex, northern Tarim Craton, NW China: Phanerozoic zircon Pb/Pb age by multicollector SIMS without external standardiza-
Constraints from zircon U-Pb-Lu-Hf isotopes and implications for crustal growth. tion. Geochem. Geophys. Geosyst. 10 (4), 1–21.
Precambr. Res. 231, 136–156. Liu, Y., Hu, Z., Gao, S., Günther, D., Xu, J., Gao, C., Chen, H., 2008. In situ analysis of
Ge, R., Zhu, W., Wu, H., He, J., Zheng, B., 2013a. Zircon U-Pb ages and Lu-Hf isotopes of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an
Paleoproterozoic metasedimentary rocks in the Korla Complex, NW China: internal standard. Chem. Geol. 257 (1), 34–43.
Implications for metamorphic zircon formation and geological evolution of the Tarim Liu, H., Wang, G.C., 2012. LA-ICP-MS zircon U-Pb dating of gneiss of Milan Group and
Craton. Precambr. Res. 231, 1–18. mafic dyke swarms from Lapeiquan in northern Altun and its tectonic significance.
Ge, R., Zhu, W., Wilde, S.A., He, J., Cui, X., 2015. Synchronous crustal growth and Geological Bulletin of China 31, 1461–1468 in Chinese with English abstract.
Liu, Y.S., Yu, H.F., Xin, H.T., Lu, S.N., Xiu, Q.Y., Li, Q., 2009. Tectonic units division and
31
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
Precambrian significant geological events in Altyn Tagh Mountain, China. Geol. Bull. from the Dunhuang Block, Eastern Tarim Craton. Precambr. Res. 255 163–180.
China 28, 1430–1438 in Chinese with English abstract. Wang, Z.M., Han, C.M., Xiao, W.J., Su, B.X., Ding, J.X., 2017c. Paleoproterozoic sub-
Long, X., Yuan, C., Sun, M., Xiao, W., Zhao, G., Zhou, K., Wang, Y., Hu, A., 2011. The duction-related magmatism and crustal evolution of the Dunhuang Block, NW China.
discovery of the oldest rocks in the Kuluketage area and its geological implications. J. Asian Earth Sci. 134, 13–28.
Sci. China Earth Sci. 54 (3), 342–348. Wang, Z.M., Han, C.M., Xiao, W.J., Su, B.X., Ding, J.X., Song, S.H., 2017d. Geochemical
Long, X., Yuan, C., Sun, M., Kröner, A., Zhao, G., 2014. New geochemical and combined and zircon U-Pb and Lu-Hf isotopic constraints on the origin of supracrustal rocks
zircon U-Pb and Lu-Hf isotopic data of orthogneisses in the northern Altyn Tagh, from the mid-Qilian terrane: a comparison between supracrustal rocks on the two
northern margin of the Tibetan plateau: implication for Archean evolution of the sides of the eastern segment of the Altyn Tagh Fault. Precambr. Res. 294, 284–306.
Dunhuang Block and crust formation in NW China. Lithos 200–201, 418–431. Wang, Z.M., Han, C.M., Xiao, W.J., Wan, B., Sakyi, P.A., 2017e. Paleozoic subduction-
Long, X., Wilde, S.A., Yuan, C., Hu, A., Sun, M., 2015. Provenance and depositional age of related magmatism in the Duobagou area, Dunhuang block: constrained by zircon U-
Paleoproterozoic metasedimentary rocks in the Kuluketage Block, northern Tarim Pb geochronology and Lu-Hf isotopes and whole-rock geochemistry of metaigneous
Craton: implications for tectonic setting and crustal growth. Precambr. Res. 260, rocks. Lithosphere 9 (6), 1012–1032.
76–90. Wang, H.Y.C., Wang, J., Wang, G.D., Lu, J.S., Chen, H.X., Peng, T., Zhang, H.C.G., Zhang,
Lu, S.N., 2002b. A review of major problems of Precambrian research. Prog. Precambr. Q.W.L., Xiao, W.J., Hou, Q.L., Yan, Q.R., Zhang, Q., Wu, C.M., 2017b. Metamorphic
Res. 25, 65–72 in Chinese with English abstract. evolution and geochronology of the Dunhuang orogenic belt in the Hongliuxia area,
Lu, S.N., 2002a. In: Preliminary study of Precambrian geology in Tibet-Qinghai plateau. northwestern China. J. Asian Earth Sci. 135, 51–69.
Geology publishing house, pp. 135 in Chinese. Wang, H.Y., Zhang, Q.W.H., Chen, X., Liu, J.H., Zhang, H.C., Pham, V.T., Peng, T., Wu,
Lu, S., Li, H., Zhang, C., Niu, G., 2008. Geological and geochronological evidence for the C.M., 2018. Paleozoic subduction of the southern Dunhuang Orogenic Belt, northwest
Precambrian evolution of the Tarim Craton and surrounding continental fragments. China: metamorphism and geochronology of the Shuixiakou area. Geodin. Acta 30
Precambr. Res. 160 (1–2), 94–107. (1), 63–83.
Lu, S.N., Yu, H.F., Li, H.M., Guo, K.Y., Wang, H.K., Jin, W., Zhang, C.L., Liu, Y.S., 2006a. Wei, C.J., 2016. Granulite facies metamorphism and petrogenesis of granite (Ⅱ): quan-
In: Research on Precambrian Major Problems in China. Geological Publishing Press, titative modeling of the HT-UHT phase equilibria for metapelites and the petrogen-
Beijing, pp. 1–206 in Chinese. esis of S-type granite. Acta Petrol. Sin. 32 (6), 1625–1643 in Chinese with English
Lu, S., Yu, H., Li, H., Guo, K., Wang, H., Jin, W., Zhang, C., Liu, Y., 2006b. In: Research on abstract.
Precambrian Major Problems in China. Geological Publishing Press, Beijing, pp. 206 Wu, F.Y., Yang, Y.H., Xie, L.W., Yang, J.H., Xu, P., 2006. Hf isotopic compositions of the
in Chinese. standard zircons and baddeleyites used in U-Pb geochronology. Chem. Geol. 234
Lu, S.N., Yuan, G.B., 2003. Geochronology of early Precambrian magmatic activeties in (1–2), 105–126.
Aketashitage, East Altyn Tagh. Acta Geol. Sin. 77, 61–68 in Chinese with English Xiang, H., Zhang, Z.M., Lei, H.C., Qi, M., Dong, X., Wang, W., Lin, Y.H., 2014.
abstract. Paleoproterozoic ultrahigh-temperature pelitic granulites in the northern Sulu
Ludwig, K., 2003. In: Isoplot 3.0, a geochronological toolkit for Microsoft Excel. Berkeley orogen: constraints from petrology and geochronology. Precambr. Res. 254,
Geochronological Centre Special Publication No. 4, pp. 71 edited. 273–289.
Mao, X., Zhang, J., Yu, S., Li, Y., Yu, X., Lu, Z., 2017. Early Paleozoic granulite-facies Xiao, W.J., Mao, Q.G., Windley, B.F., Han, C.M., Qu, J.F., Zhang, J.E., Ao, S.J., Guo, Q.Q.,
metamorphism and anatexis in the northern West Qinling orogen: monazite and Cleven, N.R., Lin, S.F., Shan, Y.H., Li, J.L., 2010. Paleozoic multiple accretionary and
zircon U-Pb geochronological constraints. Sci. China Earth Sci. 60 (5), 943–957. collisional processes of the Beishan orogenic collage. Am. J. Sci. 310, 1553–1594.
Mei, H.L., Yu, H.F., Li, Q., Zuo, G.C., 1997. Preliminary litho-tectonic framework of early Xie, L., Zhang, Y., Zhang, H., Sun, J., Wu, F., 2008. In situ simultaneous determination of
precambrian rocks in Dunhuang-Beishan area, Gansu, West China. Prog. Precambr. trace elements, U-Pb and Lu-Hf isotopes in zircon and baddeleyite. Chin. Sci. Bull. 53
Res. 20, 47–54 in Chinese with English abstract. (10), 1565–1573.
Mei, H.L., Yu, H.F., Lu, S.N., Li, H.M., Li, Q., Lin, Y.X., Zuo, G.C., 1998. Archean tonalite Xin, H.T., Liu, Y.S., Luo, Z.H., Song, S.C., Wang, S.Q., 2013. The growth of Archean
in the Dunhuang, Gansu province: age from U-Pb single zircon and Nd isotope. Prog. continental crust in Aqtashtagh area of southeast Tarim, China: constraints from
Precambr. Res. 21, 41–45 in Chinese with English abstract. petrochemistry and chronology about Milan Group and TTG-gneiss. Earth Sci. Front.
Michael, B., 2007. Metamorphism, Plate Tectonics, and the Supercontinent Cycle. Earth 20, 240–259 in Chinese with English abstract.
Sci. Front. 14 (1), 1–18. Xin, H.Y., Luo, Z.H., Liu, Y.S., Wang, S.Q., Zhang, Z.L., 2012. Geological features and
Middlemost, E.A.K., 1994. Naming materials in the magma/igneous rock system. Earth significance of Paleoproterozoic carbonatite of crustal origin in Aqtashtagh area of
Sci. Rev. 37, 215–224. southeast Tarim Basin, China. Earth Sci. Front. 19, 167–178 in Chinese with English
MÜNtener, O., Hermann, J., Trommsdorff, V., 2000. Cooling history and exhumation of abstract.
lower-crustal granulite and upper mantle (Malenco, Eastern Central Alps). J. Petrol. Xin, H.T., Zhao, F.Q., Luo, Z.H., Liu, Y.S., Wan, Y.S., Wang, S.Q., 2011. Determination of
41 (2), 175–200. the Paleoproterozoic geochronological framework in Aqtashtagh area in southeastern
Otamendi, J.E., Jesús, D., Douce, A.E.P., Castro, A., 2002. Rayleigh fractionation of heavy Tarim, China. Acta Geol. Sin. 85, 1977–1993 in Chinese with English abstract.
rare earths and yttrium during metamorphic garnet growth. Geology 30 (2), Xu, Z.Q., Yang, J.S., Zhang, J.X., Jiang, M., Li, H.B., Cui, J.W., 1999. A comparison be-
159–162. tween the tectonic units on the two sides of the Altun sinistral strike-slip fault and the
Rogers, J.J.W., Santosh, M., 2002. Configuration of Columbia, a Mesoproterozoic mechanism of lithospheric shearing. Acta Geol. Sin. 73, 193–205 in Chinese with
Supercontinent. Gondwana Res. 5 (1), 5–22. English abstract.
Rogers, J.J.W., Santosh, M., 2003. Supercontinents in Earth History. Gondwana Res. 6 Xu, Z.Q., Li, S.T., Zhang, J.X., Yang, J.S., He, B.Z., Li, H.B., Lin, C.S., Cai, Z.H., 2011.
(3), 357–368. PaleoAsian and Tethyan tectonic systems with docking the Tarim block. Acta Petrol.
Rubatto, D., 2002. Zircon trace element geochemistry: partitioning with garnet and the Sin. 27, 1–22 in Chinese with English abstract.
link between U-Pb ages and metamorphism. Chem. Geol. 184 (1), 123–138. Xu, Z.Q., He, B.Z., Zhang, C.L., Zhang, J.X., Wang, Z.M., Cai, Z.H., 2013. Tectonic fra-
Rudnick, R.L., Fountain, D.M., 1995. Nature and composition of the continental crust: a mework and crustal evolution of the Precambrian basement of the Tarim Block in NW
lower crustal perspective. Rev. Geophys. 33 (3), 267–309. China: New geochronological evidence from deep drilling samples. Precambr. Res.
Rudnick, R.L., Gao, S., 2003. 3.01 – Composition of the Continental Crust A2 – Holland, 235, 150–162.
Heinrich D. In: Turekian, K.K. (Ed.), Treatise on Geochemistry. Pergamon, Oxford, Yang, J.H., Wu, F.Y., Shao, J.A., Wilde, S.A., Xie, L.W., Liu, X.M., 2006. Constraints on the
pp. 1–64. timing of uplift of the Yanshan Fold and Thrust Belt, North China. Earth Planet. Sci.
Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a Lett. 246 (3–4), 336–352.
two-stage model. Earth Planet. Sci. Lett. 26 (2), 207–221. Yu, H., Mei, H., Li, Q., 1998. The characteristics of Archean khondalite series in
Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: Dunhuang, Gansu province. Prog. Precambr. Res. 01, 19–25 in Chinese with English
implications for mantle composition and processes. Geol. Soc. London Spec. Publ. 42, abstract.
313–345. Zhang, Z., Dong, X., Xiang, H., Liou, J.G., Santosh, M., 2013b. Building of the Deep
Vavra, G., Schmid, R., Gebauer, D., 1999. Internal morphology, habit and U-Th-Pb mi- Gangdese Arc, South Tibet: paleocene Plutonism and Granulite-Facies meta-
croanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea morphism. J. Petrol. 54 (12), 2547–2580.
Zone (Southern Alps). Contrib. Miner. Petrol. 134 (4), 380–404. Zhang, J.X., Gong, J.H., Yu, S.Y., 2012. 1.85 Ga HP granulite-facies metamorphism in the
Villaseca, C., Downes, H., Pin, C., Barbero, L., 1999. Nature and composition of the lower Dunhuang block of the Tarim Craton, NW China: evidence from U-Pb zircon dating of
continental crust in Central Spain and the Granulite-Granite Linkage: inferences from mafic granulites. J. Geol. Soc. 169, 511–514.
Granulitic Xenoliths. J. Petrol. 40 (10), 1465–1496. Zhang, J., Li, H., Meng, F., Xiang, Z., Yu, S., Li, J., 2011. Polyphase tectonothermal events
Wang, H., Chen, H.X., Lu, J.S., Wang, G.D., Peng, T., Zhang, H., Yan, Q.R., Hou, Q.L., recorded in“metamorphic basement”from the Altyn Tagh, the southeastern margin of
Zhang, Q., Wu, C.M., 2016. Metamorphic evolution and SIMS U-Pb geochronology of the Tarim basin, western China: constraint from U-Pb zircon geochronology. Acta
the Qingshigou area, Dunhuang block, NW China: tectonic implications of the Petrol. Sin. 27 (1), 24 in Chinese with English abstract.
southernmost Central Asian orogenic belt. Lithosphere 8 (5), 463–479. Zhang, J., Yu, S., Gong, J., Li, H., Hou, K., 2013a. The latest Neoarchean-Paleoproterozoic
Wang, H.Y.C., Chen, H.X., Zhang, Q.W.L., Shi, M.Y., Yan, Q.R., Hou, Q.L., Zhang, Q., evolution of the Dunhuang block, eastern Tarim craton, northwestern China:
Kusky, T., Wu, C.M., 2017a. Tectonic mélange records the Silurian-Devonian sub- Evidence from zircon U-Pb dating and Hf isotopic analyses. Precambr. Res. 226,
duction-metamorphic process of the southern Dunhuang terrane, southernmost 21–42.
Central Asian Orogenic Belt. Geology 45 (5), 427–430. Zhao, G., Cawood, P.A., 2012. Precambrian geology of China. Precambr. Res. 222–223,
Wang, Z.M., Han, C.M., Su, B.X., Sakyi, P.A., Malaviarachchi, S.P.K., Ao, S.J., Wang, L.J., 13–54.
2013. The metasedimentary rocks from the eastern margin of the Tarim Craton: Zhao, G., Cawood, P.A., Wilde, S.A., Sun, M., 2002. Review of global 2.1-1.8 Ga orogens:
petrology, geochemistry, zircon U-Pb dating, Hf isotopes and tectonic implications. implications for a pre-Rodinia supercontinent. Earth Sci. Rev. 59 (1–4), 125–162.
Lithos 179, 120–136. Zhao, Y., Diwu, C., Sun, Y., Zhu, T., Wang, H., 2013. Zircon geochronology and Lu-Hf
Wang, Z.M., Han, C.M., Xiao, W.J., Wan, B., Sakyi, P.A., Ao, S.J., Zhang, J.E., Song, D.F., isotope compositions for Precambrian rocks of the Dunhuang complex in Shuixiakou
2014. Petrology and geochronology of Paleoproterozoic garnet-bearing amphibolites area, Gansu Province. Acta Petrol. Sin. 29 (5), 1698–1712 in Chinese with English
32
Z.-M. Wang et al. Precambrian Research 321 (2019) 13–33
abstract. evolution of the southernmost Central Asian Orogenic Belt. J. Asian Earth Sci. 138,
Zhao, Y., Diwu, C., Zhu, T., Wang, H., Sun, Y., 2015a. Discovery of the Late Devonian 562–587.
plagiogranite in Sanweishan area, Dunhuang, Gansu province and its geological Zong, K., Liu, Y., Zhang, Z., He, Z., Hu, Z., Guo, J., Chen, K., 2013. The generation and
implications. Acta Petrol. Sin. 31, 1855–1869 in Chinese with English abstract. evolution of Archean continental crust in the Dunhuang block, northeastern Tarim
Zhao, G., Sun, M., Wilde, S.A., Li, S., 2004. A Paleo-Mesoproterozoic supercontinent: craton, northwestern China. Precambr. Res. 235, 251–263.
assembly, growth and breakup. Earth Sci. Rev. 67 (1–2), 91–123. Zong, K., Klemd, R., Yuan, Y., He, Z., Guo, J., Shi, X., Liu, Y., Hu, Z., Zhang, Z., 2017. The
Zhao, Y., Sun, Y., Yan, J., Diwu, C., 2015b. The Archean-Paleoproterozoic crustal evo- assembly of Rodinia: The correlation of early Neoproterozoic (ca. 900Ma) high-grade
lution in the Dunhuang region, NW China: constraints from zircon U-Pb geochro- metamorphism and continental arc formation in the southern Beishan Orogen
nology and in situ Hf isotopes. Precambr. Res. 271, 83–97. southern Central Asian Orogenic Belt (CAOB). Precambr. Res. 290, 32–48.
Zhao, Y., Sun, Y., Diwu, C., Guo, A.L., Ao, W.H., Zhu, T., 2016. The Dunhuang block is a Zong, K.Q., Zhang, Z.M., He, Z.Y., Hu, Z.C., Santosh, M., Liu, Y.S., Wang, W., 2012. Early
Paleozoic orogenic belt and part of the Central Asian Orogenic Belt (CAOB), NW Palaeozoic high-pressure granulites from the Dunhuang block, northeastern Tarim
China. Gondwana Res. 30, 207–223. Craton: constraints on continental collision in the southern Central Asian Orogenic
Zhao, Y., Sun, Y., Diwu, C., Zhu, T., Ao, W., Zhang, H., Yan, J., 2017. Paleozoic intrusive Belt. J. Metamorph. Geol. 30 (8), 753–768.
rocks from the Dunhuang tectonic belt, NW China: constraints on the tectonic
33