科研之友
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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%, K2O 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 similar to 31. 3, (La/Yb)(N) = 16. 82 similar to 50. 41) and depleted in HREE. They also demonstrate flat HREE patterns for elements from Ho to Lu with (Ho/Yb)(N) = 0.93 similar to 1. 42, positive or slightly negative Eu anomalies (0.78 similar to 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 epsilon(Hf)(t) values (-11. 22 similar to 4. 87), and have relatively younger zircon Hf crustal modal ages of 552 similar to 1179Ma. Both zircon Hf isotopic data and bulk-rock zircon saturation temperature (746 similar to 791 degrees C) 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.
- 出版日期2013-6
- 单位中国地质科学院; 中国地质大学（北京）
