Geochemical Features and Tectonic Significance of Granitic Gneiss of Laguigangri Metamorphic Core Complexes in Southern Tibet
详细信息
- 责任者：Gu Pingyang (Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits ; MLR ; Xi’an Geological Survey Center ; Xi’an 710054 ; China ) ; He Shiping
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(3)
- 关键词：花岗质片麻岩 ; granitic gneiss ; 岩石地球化学 ; lithogeochemistry ; 西藏 ; Tibet
- 页码：p.756-768
- 图表：illus., 5 tables, 88 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The granitic gneiss of Laguigangri metamorphic core complexes in southern Tibet is characterized by high SiO2 and K2O, low Fe2O3, MgO and MnO, with alumina saturation index (A/CNK) of 1.07～1.19 and peraluminous minerals (such as muscovite and garnet). These features suggest that the granitic gneiss belongs to the high-K calci-alkaline peraluminous rocks. It is obvious that the chondrite-normalized REE shows right inclined patterns with obvious negative Eu abnormity, simultaneously, the primitive mantle normalized trace element spidergrams are characterized by enriched LILE (such as Rb, Th and U) and depleted HFSE (such as Sr and Nb), as well as evidently low contents of Ba and Hf, which are compatible with the characteristics of crustal derived S-type granites. The initial values of 87Sr/86Sr(ISr) are in a range of 0.709～0.7306, the εSr(t) in a range of 80.65～379 and εNd(t=514Ma) values of -7.13～-8.97, without significant correlation between εNd(t) and ISr. The ratios of (206Pb/204Pb)t(=18.1062～18.8085), (207Pb/204Pb)t(=15.7～15.8) and (208Pb/204Pb)t(=37.5～38.2) also reveal crustal Pb isotopic features. Therefore, the granitic magma is originated from partially melting of clay and sandstone sedimentary rocks. With the U-Pb isotopic age of 514Ma, we believe that these rocks in Laguigangri formed during the transition period from syncollision (compressional) to post collision (extensional environment) in Pan African orogenic events in the north Himalayan. This magmatic activity may play an important role in formation of the Laguigangri metamorphic core complex.
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