辽西义县四合屯义县组中部湖相沉积岩地球化学及物源特征  

Geochemistry and Provenance of the Early Cretaceous Lacustrine Clastic Sedimentary Rocks of Yixian Formation from the Sihetun Section,West Liaoning

作　　者：柯霖[1] 高山[1] 潘永信[2] 胡兆初[1] 

机构地区：[1]中国地质大学地球科学学院 [2]中国科学院地质与地球物理研究所,北京100029

出　　处：《地球科学（中国地质大学学报）》2008年第4期504-514,共11页Earth Science-Journal of China University of Geosciences

基　　金：教育部创新团队研究计划项目(IRT0441);国家自然科学基金委创新研究群体科学基金项目(No.40521001);高等学校学科创新引智计划项目(B07039)

摘　　要：辽西北票上园镇四合屯地区义县组沉积层是热河生物群珍稀化石的重要产出层位之一,其中蕴含丰富的地壳演化和古地理环境演化信息.分析了四合屯剖面上12m厚的含鸟化石沉积岩层的50件样品的微量元素组成和其中10件样品的主量元素组成.结合前人已发表数据,得出以下认识:(1)该套沉积岩具有与下伏火山岩类似的地球化学特征:Mg#值较高,大离子亲石元素含量较高.稀土元素的分异程度较高,在微量元素分布蛛网图中表现为明显的Nb负异常和Pb正异常等.因此我们认为义县组高镁火山岩构成了该沉积岩的主要源区之一;(2)样品的Eu/Eu*=0.48～1.81,其中大部分样品具负Eu异常.正的Eu异常(7件样品)主要由于含有长石造成;(3)通过微量元素Th-Co-Zr/10沉积构造环境判别图解对区域构造环境进行分析,结果表明该沉积岩物源区具有大陆岛弧和活动大陆边缘物源特征.A wide range of well-preserved Jehol biota fossils have been found in the sedimentary rocks of the Yixian Formation from the Sihetun area in West Liaoning Provinc. We have analyzed major and trace element compositions of fifty sampies of clastic sedimentary rocks from this section. Combined with data previously publicized by others, the conclusions are as follows, firstly, this set of sedimentary rocks share similar chemical characteristics to the associated volcanic rocks, with LREE enrichment, flat HREE, high-Mg^#, high contents of large ion lithophile element （LILE） and variable REE anomalies. Their spider diagrams show significant negative Nb and positive Pb anomalies. It is deducted that the sedimentary rocks were mainly derived from the high-Mg^# volcanic rocks from the Yixian Formation. Secondly, these sedimentary rocks show variable Eu anomalies （Eu/Eu^＊ =0. 48--1.81） with the average value being 0. 75. The positive anomaly is due to presence of plagioclase. Moreover, tectonic discrimination diagram of Th-Co-Zr/10 suggests that these sedimentary rocks were formed in a tectonic setting similar to the continental island arc and active continental margin.

关 键 词：四合屯 中生代 沉积岩 微量元素组成 

分 类 号：P595[天文地球—地球化学]