辽西早白垩世义县组火山岩的地质特征及其构造背景  

Geological characteristics and its setting for volcanic rocks of early Cretaceous Yixian Formation in western Liaoning province, eastern China

作　　者：李伍平[1] 李献华[2] 路凤香[3] 周瑶琪[4] 章大港[4] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]长安大学地球科学学院,西安710054 [3]中国地质大学地球科学学院,武汉430074 [4]石油大学油气资源与环境地质研究所,东营257062

出　　处：《岩石学报》2002年第2期193-204,共12页Acta Petrologica Sinica

基　　金：国家杰出青年科学基金项目(批号:49725309);国家自然科学基金项目(批号49733110);国土资源部"九五"重大基础研究项目(批号9501111)资助

摘　　要：早白垩世义县组火山岩是辽西地区分布最为广泛的中生代火山岩。岩石学、元素-同位素地球化学研究表明,义县组火山岩主要为高钾钙碱性系列,相容元素(Cr、Co、Ni、V等)和大离子亲石元素(如Rb、Sr、Ba等)相对富集,高场强元素(如Nb、Ta、Ti、Zr、Hf等)和放射性元素(U、Th)相对亏损,轻重稀土元素分馏明显,δEu弱负异常,放射成因的Nd、Sr、Pb同位素较低,具有板内和活动大陆边缘弧地球化学特点。作者认为辽西早白垩世义县组火山岩起源于富集的岩石圈地幔的部分熔融,岩浆在演化过程中以结晶分异作用为主,伴有少量的地壳混染作用,即AFC过程。结合区域构造,作者认为义县组火山岩形成于权内岩石圈的不均匀拉伸环境,是燕山板内造山作用的产物,与中生代古太平洋板块向欧亚板块俯冲没有直接关系。Volcanic rocks of early Cretaceous Yixian Formation were widely distributed in western Liaoning province. Based on the studies of petrology, element- isotopic geochemistry, volcanic rocks of Yixian Formation have the characteristics of continental intraplate and continent margin arc which were mainly high-K calc-alkaline series and enriched relatively in large ion lithophile elements (e.g. Rb, Sr, Ba etc.) and relatively low radio-active elements (U, Th) and high field strength elements (e. g. Nb, Ta, Ti, Zr, Hf etc.) and unconspicuous Eu-negative abnormity, lower radio-origin isotopes of Nd, Sr and Pb. The authors think the volcanic rocks of Yixian Formation in western Liaoning province derived from partial melting of enriched lithosphere mantle and suffered from the dominant evolution by crystal-liquild fractionation with the small degrees of lower crust assimilation (AFC-type processes). Combined to the prevenient study of regional structures and geochemisty of volcanic rocks, the volcanic rocks of Yixian Formation were generated in response to lithosphere inhomogeneous extension in the continental intraplate orogenic belt, which were not directly associated with the subduction of the Pacific plate beneath the Eurasian plate during the Mesozoic.

关 键 词：钙碱性火山岩 岩石圈地幔 岩石圈 伸展作用 早白垩世 板内造山带 义县组 辽西地区 

分 类 号：P588.14[天文地球—岩石学] P59[天文地球—地质学]