准噶尔盆地中拐地区石炭—二叠纪火山岩特征及构造环境分析  

Geochemical characteristics and tectonic setting of the Carboniferous-Permian volcanic rocks in Zhongguai area northwestern Junggar Basin

作　　者：孙国强[1] 史基安[1] 张顺存[1] 陈吉[1,2] 贾艳艳[1,2] 

机构地区：[1]中国科学院油气资源研究重点实验室,兰州730000 [2]中国科学院研究生院,北京100049

出　　处：《地质科学》2012年第4期993-1004,共12页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家重大专项“准噶尔盆地深层火山岩储集体形成演化与分布预测”(编号:2011ZX05008-003-40)资助

摘　　要：中拐地区位于准噶尔盆地西北缘,是在石炭纪—早二叠世挤压应力场作用下形成的宽缓鼻状古隆起。石炭—二叠纪火山岩是主要的含油层系之一,到目前为止已发现了多个油气藏和出油气点,显示出良好的勘探前景。根据系统、精细的地震资料解释,中拐地区在石炭—二叠纪时期主要存在4期构造运动,分别对应4个不整合面:1)石炭系与二叠系之间;2)二叠系佳木河组与下乌尔禾组之间;3)二叠系下乌尔禾组与上乌尔禾组之间;4)二叠系上乌尔禾组与三叠系百口泉组之间。通过对中拐地区石炭—二叠纪火山岩的全岩元素分析表明,该区域主要为中-酸性的安山岩、英安岩和流纹岩及火山角砾岩和凝灰岩为主,其中SiO_2的含量普遍较高,平均含量达到了67%,判定中拐地区的石炭—二叠纪火山岩喷发环境应位于岛弧体系的大陆内侧,在喷发过程中经历过陆壳的熔融作用。结合前人对周缘火山岩的研究,认为石炭—二叠纪时期中拐地区由岛弧环境逐渐进入陆内演化阶段,三叠纪开始进入稳定的沉积演化时期。Territorial volcanic formation developed in Late Carboniferous-Early Permian period in northwestern margin of Junggar Basin.The volcanic rocks mainly composed of acidic dacite and rhyolites,including a few intermediate basalts and basaltic andesites.They belong to calc-alkalic series of low-medium potassium.Volcanic rock samples have relatively high alkali（Na2O＋K2O=0.99%～8.12%）,low rare earth element contents and relatively low K2O（3.01%～0.05%）contents.Chondrite normalized REE patterns shows the characteristic of LREE enrichment（（La/Yb）N=0.76～5.18）and differentiation,with weak Eu anomalies（δEu=0.533～1.148）and positive Ce anomalies（δCe=0.979～1.224）.These samples are enriched in LILE but relatively depleted in HFSE（Nb,Ta）,These characteristics indicate that the Late Carboniferous-Early Permian period volcanic rocks in study area are certain differential production of primitive magma,mainly generated in island arc environments,with in infra-plate continental setting partially.These volcanic rocks are from extensional setting of fore-arc basin nearby the intra-oceanic.

关 键 词：全岩元素分析石炭-二叠系火山岩 中拐地区 准噶尔盆地西北缘 

分 类 号：P542[天文地球—构造地质学] P618[天文地球—地质学]