滇东南白垩纪高分异S型花岗岩研究进展

Research progress on the cretaceous highly fractionated S-type granite in the Southeastern Yunnan,China

滇东南地区广泛出露白垩纪花岗岩,面积超过500km2。在岩体周缘形成了众多金属矿床,如世界级的个旧Sn-Cu多金属矿床、都龙Zn-In-Sn多金属矿床、南秧田超大型W矿床等,使其成为国内地球科学研究的热点地区。本文系统收集了前人近年来公开发表的滇东南典型白垩纪花岗岩体(个旧、薄竹山和老君山)的地球化学数据,综合地质和地球化学分析表明滇东南白垩纪3个大型花岗岩体为高分异S型花岗岩,系统的年代学数据表明滇东南白垩纪岩浆活动与成矿主峰期发生在77～95 Ma。Sr、Nd、Hf同位素均显示该花岗岩岩浆主要来源于华夏板块元古代基底物质的部分熔融,综合分析后本研究初步认为滇东南地区晚白垩纪大规模的酸性岩浆活动是对晚三叠世华南板块与印支板块碰撞造山后伸展环境的响应。

Cretaceous granites are widely distributed in the Southeastern Yunnan,with an area of over 500 km2.Many metallic deposits,such as the world-class Gejiu Sn-Cu polymetallic deposit,Dulong Zn-In-Sn polymetallic deposit,and Nanyangtian superlarge W deposit,occurred in the peripheries of those granite bodies.Thus,the southeastern Yunnan Province has become a hot spot of domestic geoscientific researches.In this paper,we have systematically collected the geochemical,isotopic and chronological data,published by previous researchers recently,of typical Cretaceous granite bodies including the Gejiu,Bozhushan,and Laojunshan Cretaceous granite bodies in the Southeastern Yunnan.The comprehensive analysis of geologic and geochemical data shows that three large Cretaceous granite bodies in the southeastern Yunnan belong to the highly fractionated S-type granite.The systematical chronological data show that the Cretaceous magmatic movements and main metallogenic events occurred in the southeastern Yunnan with ages varying from 77 Ma to 95 Ma.The Sr and Nd isotopic values of whole rock samples and Hf isotopic values of zircon grains show that the granitic magma was mainly derived from the partial melting of the Proterozoic metasedimentary basement of the Cathaysia Block.After a comprehensive analysis,it is preliminarily considered that the large-scale late Cretaceous acid magmatism in the Southeastern Yunnan is a response to the post-collision extensional environment after the collision of the South China Block and the Indosinian Block in Late Triassic.