摘要
川西拉拉含矿镁铁质层状岩体位于扬子地块西缘,构造环境复杂,关于其成因机制及岩浆源区的问题至今仍缺乏系统的研究。文章针对该岩体七个岩相带,进行了主、微量元素和Sr-Nd同位素分析,结果表明,七个岩相带(YWS-1—YWS-7)是岩浆经历不同的演化过程而形成的。其中,第五相带SiO2含量高(42. 95%～44. 07%),MgO含量低(1. 62%～1. 89%),稀土总量明显偏低(295. 32×10^(-6)～366. 36×10^(-6)),Cr、Ni含量偏低,87Sr/86Sr为0. 7391～0. 7812,是受到地壳混染所致;其它相带Mg#值高(0. 54～0. 74),稀土总量偏高(672. 53×10^(-6)～986. 66×10^(-6)),87Sr/86Sr为0. 7087～0. 7097,显示岩石圈地幔源区特征。结合区域地质背景分析,认为该层状岩体产生于大陆裂谷构造环境,岩浆来源于岩石圈地幔源区,演化过程中结晶分异和多次脉动作用相伴。这一活动过程与新元古时期扬子板块西缘的超级地幔柱活动有关。
The ore-bearing mafic layered intrusions in Lala District,Western Sichuan Province,is located on the west margin of the Yangzi platform with complex tectonic environment,and there is still a lack of systematic research on its genesis mechanism and magmatic source.The main,trace elements and Sr-Nd isotopes of the seven lithofacies belts are analyzed in this article,and the results show that the seven lithofacies belts(YWS-1-YWS-7)were formed by different evolution processes of magma.The fifth lithofacies(YWS-5)represents the magma derived from mantle contaminated by earth crust,with high SiO2 content(42.95%~44.07%),low MgO content(1.62%~1.89%),obviously low total amount of rare earth elements(295.32×10^-6~366.36×10^-6),low content of Cr,Ni,87 Sr/86 Sr 0.7391~0.7812;other lithofacies represent the magma derived from lithospheric mantle source area,with high Mg^#content(0.54~0.74),high content of rare earth elements(672.53×10^-6~986.66×10^-6),87Sr/86Sr 0.7087~0.7097.Based on the analysis of regional geological background,it is concluded that the layered intrusions were produced in continental rift tectonic environment and the magma originated from lithospheric mantle source area,with crystallization differentiation and multiple pulsations associated in the evolution process.This process is related to the Neoproterozoic super mantle plume activities on the western margin of the Yangtze plate.
作者
孙君一
于文佳
崔加伟
李重
罗照华
SUN Junyi;YU Wenjia;CUI Jiawei;LI Zhong;LUO Zhaohua(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China)
出处
《地质力学学报》
CSCD
2019年第1期139-150,共12页
Journal of Geomechanics
基金
中国地质调查局地质调查项目(1212011220921
1221011121266
12120113094100
1212011121075)
关键词
拉拉矿区
层状岩体
主、微量元素
岩石圈地幔
岩石成因
Lala mining area
layered intrusions
major and trace elements
lithospheric mantle
petrogenesis
