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摘要
This work presents evidence for early Paleozoic magmatism in the Baoshan block and Mesozoic magmatism in the Tengchong block and along the Gaoligong fault system in the Tethyan belt, western Yunnan Province, southwestern China, on the basis of SHRIMP dating of zircons from 12 granitoid samples. Deformed granitoids with gneissic textures contain zircons with magmatic oscillatory zoning that define weighted mean Pb-206/U-238 ages ranging from 481 +/- 3 to 493 +/- 3 Ma and are interpreted as the crystallization time of the host rocks. The granitoids are characterized by enriched light rare earth elements, high Th and U contents, and negative Nb anomalies on a primitive mantle-normalized spider diagram, which is indicative of crustal melting. The peraluminous, silica-rich compositions, high initial Sr-87/Sr-86 ratios, as well as negative epsilon(Nd(t)) and epsilon(Hf(t)) values also suggest that the granitoid rocks originated through crustal reworking. Zircons of 216-226 Ma, Late Triassic S-type granites of the Tengchong block also have negative epsilon(Hf(t)) values, suggesting that they are derived from Proterozoic crust and that they may have been generated in a postcollisional tectonic setting. A late Early Cretaceous 118 Ma S-type granite has a similar age to the Gaoligong granites and likewise likely formed through anatexis of Precambrian crust. Zircons of Late Cretaceous granites (84-70 Ma) of the Baoshan block have epsilon(Hf(t)) values of -3.7 to -2.1, indicating derivation from a Precambrian crustal source. Their emplacement may be related to closure of the Neotethys ocean.
- 出版日期2016-9
- 单位中国地质科学院; 中国地质科学院地质力学研究所
