北大别山肖畈岩体地球化学特征和锆石LA-ICP-MSU-Pb同位素定年  

Geochemical Characteristics and Zircon LA-ICP-MS U-Pb Isotopic Dating of the Xiaofan Rock Bodies in North Dabieshan

作　　者：杨泽强[1] 唐相伟[1] 

机构地区：[1]河南省地质矿产勘查开发局第三地质矿产调查院,河南信阳464000

出　　处：《地质学报》2015年第4期692-700,共9页Acta Geologica Sinica

基　　金：河南省地勘基金科研攻关项目资助成果

摘　　要：本文对肖畈岩体进行了系统的锆石U-Pb定年、岩石全分析测试,认为该岩体化学成分具超酸、富碱、弱过铝和贫钠富钾等特点,属超酸性富碱钾玄岩系列岩浆岩。岩石轻稀土明显富集,重稀土亏损,（La/Yb）N在10.65-20.53之间,δEu负异常中等,稀土元素分布曲线为左高右平倾斜的＂U＂字型,属后碰撞花岗岩类,与东秦岭—大别钼多金属成矿带中富钼中酸性小岩体地球化学特征一致。利用LA-ICP-MS锆石U-Pb定年测得肖畈岩体似斑状花岗岩体的加权平均年龄值为139.30±0.64 Ma（2σ,n=12,MSWD=1.3）,代表岩体的结晶年龄。研究认为肖畈岩体不是灵山花岗岩基同源岩浆演化的产物,它们分属两期岩浆活动,依据如下：1肖畈岩体成岩年龄早于灵山岩体近10 Ma;2肖畈岩体来源于下地壳相对高温高压岩浆源区,不可能由灵山岩体（低温岩浆）分异而成。肖畈岩体形成的地球动力学背景为中生代构造体制转换及其后伸展机制下岩石圈大规模拆沉减薄而引起的岩浆活动。地壳拆沉,幔源物质上侵,含斜长石一角闪石-石榴子石-辉石的高压麻粒岩下地壳部分熔融,形成肖畈深源浅成型富钼（铜）花岗岩体。In this article, the author conducted systematical zircon U-Pb dating and rock analysis. The study shows that that those rock bodies have characteristics of superacid, alkali-rich, weak peraluminous, poor sodium and rich potassium, suggesting that they belong to magmatic rocks of shoshonite series with superacid, alkali-rich. Those rocks are rich in light rare earth and poor in heavy rare earth, with （La/ Yb）N of 10.65-20.53 and medium negative Eu anomaly. U-type REE distribution diagram suggests they belongs to post-collision granitoid rocks, which is in accordance with geochemical characteristics of rich molybdenum, intermediate-acid rock bodies in east Qinling-Dabie molybdenum polymetallic metallogenic belt. LA-ICP-MS zircon U-Pb dating yields a weighted average age of 139. 30 ±0. 64 Ma （2σ, n= 12, MSWD=1. 3） for porphyry-like granite body of Xiaofan rock bodies, which represents the crystallization age of rock bodies. The research suggests that Xiaofan rock bodies are not the evolution product of Lingshan granite batholiths homologous magma. Xiaofan and Lingshan rock bodies belong to two different magma activities. The main evidence is listed as follows. （1） The Xiaofan rock bodies formed 10 Ma earlier than Lingshan rock bodies. （2） Xiaofan rock bodies originated from magma source region with relatively high temperature and high pressure in lower crust, but not from differentiation of the Lingshan rock bodies （low temperature magma）. The geodynamics background of Xiaofan rock bodies is magma activities which resulted from Mesozoic tectonic regimes changes and large-scale lithosphere delaminating thinning under post stretching mechanism. Crust delaminating and mantle material intruding resulted in partial melting of the lower crust high pressure granulites consisting of plagioclase-hornblende-garnet-pyroxene, thus forming the Xiaofan deep-sourced and hypabyssal type rich molybdenum （copper） granite rock bodies.

关 键 词：矿床地球化学 LA-ICP-MS定年 后碰撞花岗岩 斑岩型钼矿 肖畈岩体 

分 类 号：P597[天文地球—地球化学] P584[天文地球—地质学]