滇西新街岩体LA-ICP-MS锆石U-Pb年龄、Hf同位素和地球化学及其构造意义
LA-ICP-MS zircon U-Pb chronology, Hf isotopes and geochemistry of the Xinjie granites in western Yunnan and their implications
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摘要: 新街岩体位于昌宁-孟连带北段，主要岩性为二长花岗岩。LA-ICP-MS锆石U-Pb定年结果表明，新街岩体侵位于约82Ma。岩体SiO2含量为74.28%~75.17%，富钾（K2O/Na2O=1.44~1.73）和较低钙CaO（0.37%~0.41%），铝饱和指数（A/CNK）为1.121~1.156，富集Rb、Th、K、LREE等元素，相对亏损Nb、Ta、Ti、Zr、Hf等高场强元素。这些特征表明，新街岩体属于强过铝质S型花岗岩。新街岩体负且变化范围大的锆石εHf(t)值(-16.9~-0.5)和古老的Hf同位素地壳模式年龄（1.19~2.28Ga），表明其主要来源于古老地壳物质的重熔，并有不同程度的幔源物质加入。由于喜马拉雅新特提斯洋封闭发生在65Ma左右，新街岩体很可能是在喜马拉雅新特提斯洋洋壳俯冲的地球动力学背景下形成的。Abstract: The Xinjie granite body is located in the north of the Changning-Menglian suture zone. The rock type is mainly monzogranite. LA-ICP-MS zircon U-Pb dating indicates that the Xinjie granite body was emplaced at about 82Ma of Late Cretaceous. The major element chemical data of the Xinjie granites show that SiO2 values vary from 74.28% to 75.17%, with high K2O (K2O/Na2O=1.44~1.73), low CaO (0.37%~0.41%) content, and A/CNK 1.10~1.22. The Xinjie granite body displays obvious enrichment of Rb, Th, K and LREE, and relatively negative anomalies of HFSE such as Nb, Ta, Ti, Zr and Hf. It is suggested that the Xinjie intrusion belongs to peraluminous S-type granite. The negative εHf(t) values are distributed in a wide range (-16.9~-0.5), which, together with ancient Hf-isotope crust model age (1.19~2.28Ga), indicates that the intrusion mainly originated from re-melted ancient crust materials with the addition of varying degrees of mantle materials. The partial melting was related to the subduction of Neo-Tethyan plate.
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Keywords:
- LA-ICP-MS zircon U-Pb ages /
- Hf isotope /
- geochemistry /
- petrogenesis /
- Xinjie granites /
- western Yunnan
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