Petrogenesis of High Sr/Y Granite in Motuo Area of Namche Barwa Syntaxis: Constraints from Geochemistry, Zircon U-Pb Geochronology and Hf Isotopic Compositions
详细信息
- 责任者：Dong Hanwen (State Key Laboratory of Continental Tectonics and Dynamics ; Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Xu Zhiqin
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(6)
- 关键词：花岗岩 ; granite ; 铀—铅计时 ; U-Pb dating ; 铪同位素 ; hafnium isotopes ; 冈底斯山 ; Gangdise Range
- 页码：p.2013-2023
- 图表：illus., 3 tables, 53 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Motuo granite belt,which can be regard as the southeastern extension of Gangdese granite belt,locates in the east of Namche Barwa Syntaxis. This paper reports a systematic study of geochemical,LA-MC-ICP-MS U-Pb zircon dating and Hf isotopes data of both Beibeng and Damu granites. The dating indicates that these two granitic blocks emplaced at 62Ma and 64. 5Ma, respectively. The chemical analyses show that: ( 1) the granites are high-K calc-alkaline peraluminous,with SiO2 from 71. 09% to 74.37% ,K20 from 1.38% to 5. 93% and A/CNK from 1. 01 to 1. 02. (2) The Motuo granites are highly enriched in LREE ( ( La/Dy) N = 13. 55 ～31.3,( La/Yb) N = 16. 82～50.41) and depleted in HREE. They also demonstrate flat HREE patterns for elements from Ho to Luwith ( Ho/Yb) N = 0. 93～1.42,positive or slightly negative Eu anomalies ( 0. 78～1. 09) ,relatively high Ba,Sr/Y and La/Yb,low Y and Mg # ( <45) ,as well as depleted HFSE( Nb,Ti,Zr) . The Motuo granites are heterogeneous in zircon ε Hf ( t) values ( -11.22 ～4. 87) ,and have relatively younger zircon Hf crustal modal ages of 552 ～1179Ma. Both zircon Hf isotopicdata and bulk- rock zircon saturation temperature ( 746～791℃ ) indicate that mantle-derived materials may have played an important role in the generation of Motuo granites. We propose that,with the underplating of mantle-derived magma during India-Asia continental collision, the Motuo high Sr/Y granites were most likely generated from the magma mixing between mantle source and crust source.
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