The petrogenesis and tectonic implications of the granitoid gneisses from Xingxingxia in the eastern segment of Central Tianshan
作者单位：State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of Sciences Xinjiang Research Center for Mineral Resources University of Chinese Academy of Sciences Department of Earth ScienceUniversity of Ghana
会议名称：《中国科学院地质与地球物理研究所2014年度（第14届）学术年会》
会议日期：2015年
学科分类：070904[理学-构造地质学] 0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学]
基 金：financially supported by National Natural Science Foundation Projects (41272107,41230207,41190072,41390441,41202150 and 41102132) the National 305 Projects (2011BAB06B04-1)
关 键 词：Central Tianshan Tarim Craton Grenvillian Granitoid gneisses Zircon U–Pb dating and Hf isotopes
摘 要：As 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 Si O2, Al2O3 and K2O and depletion in Mg O and Fe O T. The Rittmann index(r) spreads between 1.44 and2.21 and ACNK(Al2O3/(Ca O + Na2 O + 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 mean206Pb/238 U 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 e Hf(t) variation f