滇西地区腾冲地块东侧混合岩锆石年龄和Sr—Nd-Hf同位素组成  

Zircon age and Sr-Nd-Hf isotopic composition of migmatite in the eastern Tengchong block,western Yunnan.

作　　者：陈福坤[1] 李秋立[1] 王秀丽[1] 李向辉[1] 

机构地区：[1]中国科学院地质与地球物理研究所固体同位素地球化学实验室,北京100029

出　　处：《岩石学报》2006年第2期439-448,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金委员会资助(批准号:40372106;40525007;40421202)

摘　　要：滇西地区特提斯构造带,是东特提斯构造带的重要组成部分之一,由多个微陆块和陆块相间的造山带组成。陆块内部基底出露局限并经历多期构造作用的叠加,因而其基底属性和演化历史难于恢复。本文报道腾冲地块东侧混合岩的锆石年龄、地球化学组成和锶-钕-铪同位素特征,探讨原岩的形成时代和背景。混合岩原岩可能源自中元古代花岗闪长岩-花岗岩质地壳岩石,晚中生代重熔再造,可能经历后期混合岩化。亏损地幔钕模式年龄为1．9～1．5Ga,锆石铪模式年龄集中于1．8～1．5Ga,与出露于保山地块的早古生代和晚中生代花岗岩存在明显差别。原岩主要表现轻稀土富集、轻度的中/重稀土分馏、显著的负铕、铌、钛、钡和锶异常。初始ε_(Md)值(1．0Ga,-1．7～3．5)和锆石ε_(Hf)值(1．0Ga,平均值10．5～13．1)及地球化学特征可能暗示腾冲地块基底东侧在中元古代发育与岛弧有关的岩浆作用。The Tethyan belt in western Yunnan, being one of the important parts of the eastern Tethyan belt, is made up of several micro-continental blocks and orogenic belts in between. Provenance and evolution of basements within these blocks are rarely known due to limited exposure of the basements that were subjected to imprint of tectonic events. This study presents zircon age, geochemical composition and Sr-Nd-Hf isotopic characteristic of migmatite from the eastern part of the Tengchong block, to discussion the formation age and tectonic setting of the protolith. Protoliths of migmatite originated from Middle Proterozoic granodioritic to granitic material that was subjected to re-melting in late Mesozoic and probably later migmatitization. The analyzed rocks have depleted-mantle Nd modal ages of 1.9 to 1.5Ga and zircon Hf modal ages of 1.8 to 1.5Ga, different from those of the early Paleozoic and late Mesozoic granites exposed in the Baoshan block. Geochemically, they exhibit enrichment in light REEs, light-degree fractionation between middle and heavy REEs, significantly negative Eu-, Nb-, Ti-, Ba-, and Sr-anomaly. Initial εNd values （ - 1.7 to 3.5 at 1.0Ga） of whole-rocks and zircon initial εNd values （ mean values 10.5 to 13.1 at 1.0Ga）, combined within chemical feature, can imply that there was probably arc-related magmatism in the eastern part of the Tengchong block in middle Proterozoic.

关 键 词：滇西地区 基底 混合岩 锆石年龄 锶-钕-锶同位素组成 

分 类 号：P597.3[天文地球—地球化学]