Browsing by Author "Wang, Z. M"
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Item The metasedimentary rocks from the eastern margin of the Tarim Craton: petrology, geochemistry, zircon U-Pb dating, Hf isotopes and tectonic implications.(Lithos, 179: 120-136 doi:10.1016/j.lithos.2013.08.010, 2013) Wang, Z. M; Han, C.M; Su, B.X; Sakyi, P.A; Malaviarachchi, P. K. S; Ao, S.J; Wang, L. J.The Dunhuang Block, located in the eastern Tarim Craton, widely exposes Precambrian TTG gneisses and metamorphosed supracrustal rocks. A suite of metasedimentary rocks of the Dunhuang Group in the Hongliuxia area on the easternmargin of the TarimCraton are characterized bymoderate contents of quartz, plagioclase, and biotite, with minor amounts of garnet or kyanite, most of which have experienced strong deformation, resulting in well-developed amphibolite-facies foliations. The examined samples are characterized by moderate Fe2O3+MgOand TiO2 contents, and Al2O3/SiO2 and K2O/Na2O ratios with low Chemical Index of Alteration (CIA) and high Index of Compositional Variability (ICV) values, suggesting that the protolith sediments originated from continental island arc environment. The U–Pb ages of magmatic-type detrital zircons from the Hongliuxia metasedimentary rocks range between 2476 Ma and 1950 Ma, with a peak at 2417 Ma. Detrital zircons of metamorphic origin yielded an age peak at 1832 Ma, which may represent a tectono-thermal event in the Paleoproterozoic. Considering that the main age populations of the analyzed samples are consistent with the tectono-thermal events in the Tarim Craton during the early Paleoproterozoic, we propose that the Tarim Craton was possibly the major source for the protolith sediments of the metasedimentary rocks in the Hongliuxia area. Zircon Hf isotopic compositions (εHf(t) =−5.8 to +2.9) suggest voluminous addition of juvenile materials to the crust and minor reworking of old materials in the eastern Tarim Craton during the Mesoarchean (TDM C = 2.8–2.9 Ga). The metasedimentary rocks of the Hongliuxia area provide clear constraints to the evolution of the Tarim Craton. A possible tectonic model is that multiple thermal events (~2.4 Ga, 2.2 Ga, 2.0 Ga and 1.8 Ga) occurred in the study area, and the time period of Mesoarchean was important for crustal growth in the eastern Tarim Craton, whereas the ~1.83 Ga metamorphism might represent a thermal event associated with the Tarim Craton within the supercontinent Columbia.Item The Petrogenesis and Tectonic Implications of the Granitoid Gneisses from Xingxingxia in the Eastern Segment of Central Tianshan.(J. Asian Earth Sciences, 88: 277-292, 2014) Wang, Z. M; Han, C.M; Xiao, W. M; Su, B.X; Sakyi, P.A; Song, D.F; Lin, L.NAs part of Central Asian Orogenic Belt (CAOB), the Central Tianshan zone plays a crucial role in the reconstruction of the tectonic evolution of the CAOB. Furthermore, it is bordered by the Tarim Craton to the south, and the comparable evolutionary history between them enables the Central Tianshan zone to provide essential information on the crustal evolution of the Tarim Craton. The eastern segment of the Central Tianshan tectonic zone is characterized by the presence of numerous Precambrian metamorphic rocks, among which the Xingxingxia Group is the most representative one. The granitoids gneisses, intruded into the Xingxingxia Group, consist of two major lithological assemblages: (1) biotite-monzonitic gneisses and (2) biotite-plagioclase gneisses. These metamorphosed granitoid rocks are characterized by enrichment in SiO2, Al2O3 and K2O and depletion in MgO and FeOT. The Rittmann index (r) spreads between 1.44 and 2.21 and ACNK (Al2O3/(CaO + Na2O + K2O)) ranges from 1.03 to 1.08, indicating that these granitoid gneisses are high-K calc-alkaline and peraluminous. Trace element data indicate that the studied samples are enriched in LREE with moderate REE fractionated patterns ((La/Yb)N = 10.5–75.3). The concentrations of HREE of the garnet-bearing gneisses are significantly higher than those of garnet-free gneisses. The former show pronounced negative Eu anomalies (Eu/Eu* = 0.32–0.57), while the latter are characterized by negligible negative Eu anomalies to moderate positive Eu anomalies (Eu/Eu* = 0.80–1.35). In addition, the enrichment of LILE (Rb, Th, K, Pb) and depletion of HFSE (Ta, Nb, P, Ti) of the examined granitoid gneisses are similar to typical volcanic-arc granites. Zircons U–Pb dating on the biotite monzonitic gneiss yields a weighted mean 206Pb/238U age of 942.4 ± 5.1 Ma, suggesting their protoliths were formed in the early Neoproterozoic, which is compatible with the time of the assembly of supercontinent Rodinia. The zircons have a large εHf(t) variation from -5.6 to +3.2, suggesting that both old crust-derived magmas and mantle-derived juvenile materials contributed to the formation of their protoliths. Based on field observation, and petrological, geochemical and geochronological investigations, we infer that the granitoid gneisses from Xingxingxia were probably formed on a continental arc that resulted from the interaction of Australia and the Tarim Craton during the assembly of the Rodinia supercontinent, and that the Central Tianshan zone was a part of the Tarim Craton during that time. Besides, the Grenvillian orogenic events may have developed better in the Tarim Craton than previously expected.