皖南新元古代双峰式岩墙群的年龄、地球化学特征及地质意义  

Age and geochemistry of the Neoproterozoic series of bimodal dikes in the Southern Anhui Province and their geological significance

作　　者：黄文成[1] 叶海敏[1] 孟庆秀[1] 

机构地区：[1]中国地质调查局南京地质调查中心,南京210016

出　　处：《资源调查与环境》2014年第3期192-201,共10页Resources Survey & Environment

基　　金：中国地质调查局地质调查项目<晋宁期-加里东期构造-岩浆活动及构造格局演变对区域成矿作用的制约>(项目编号:1212011121097)资助

摘　　要：皖南许村镇附近发育一套岩墙群，主要由辉长岩和花岗闪长斑岩组成，它们在时空上紧密伴生，成因上密切相关。岩石的SiO2含量集中分布在酸性和基性成分之间，缺乏中性及中酸性成分，构成一套双峰式侵入岩组合。对花岗闪长斑岩进行锆石LA-ICP-MS U-Pb年代学研究，表明双峰式岩墙侵入时间为822．1＆#177;6．6Ma。辉长岩具有正εHf （t）值（2．1～4．4）、大离子亲石元素和LREE富集，显示大陆拉斑质玄武岩地球化学和同位素组成特征；花岗闪长斑岩富含Zr、Hf和稀土元素，较高的Ga/A1比值，较低Ba、Sr、P、Ti含量，总体上地球化学特征类似A2-型花岗岩，εHf （t ）值范围（1．8～4．6）与辉长岩基本相同。许村双峰式岩墙群的基性端员辉长岩是拉张环境下华南弱亏损岩石圈地幔部分熔融产生玄武质岩浆的产物，而酸性端员花岗闪长斑岩是玄武质岩浆在上升途中受地壳混染，并发生底侵作用和由玄武岩浆提供的热源导致地壳重熔的结果。A series of dikes composed of gabbros and granodiorite porphyries are developed near the Xucun town in the Southern Anhui Province .The dikes are inseparably associated in time-space and closely related in genesis .The SiO2 contents in the rocks from the dikes are concentratedly a lack of SiO 2 contents between 56% -63% consistent with the intermediate and intermediate-acidic composition ranges ,constitu-ting an assemblage of bimodal intrusive rocks .The high-precision LA-ICP-MS U-Pb zircon dating of 822 ± 6 .6Ma obtained by the present study may indicate The intrusion age of the bimodal dikes .The gabbros have positiveεHf （t） values of 2 .1~4 .4 ,enriched large ion lithophile elements and LREE ,showing charac-teristies of petrochemical and isotopic compositions of the continental tholeiite basalts .The granodiorite porphyries have enriched Zr ,Hf and REE ,relativity higher Ga/Al values ,and relatively lower Ba ,Sr ,P ,Ti , being overall analogous to the geochemical characteristics of A 2-type granites ,withεHf （t） values of 1 .8~4 .6 basically similar to those of gabbros .Therefore ,in the Xucun series of bimodal dikes ,the basic and member gabbros may have produced from the basaltic magma originated by the partial melting of the de-plated lithospheric mantle in South China in a tensional settling ,whereas the acidic end member granodior-ite porphyries are likely resulted from the remelting of the crust caused by the heat source provided by the basaltic magma during its upwelling and underplating accompanied by hybridism of the crust .

关 键 词：双峰式岩墙 新元古代 锆石U-PB定年 地球化学 皖南 

分 类 号：P588.12[天文地球—岩石学]