摘要
新疆柯坪地区玄武岩是塔里木盆地早二叠世大火成岩省北部重要的组成部分。通过对柯坪盖孜力克乡南部下二叠统巴立克立克组(P1b)中的玄武岩夹层进行锆石U-Pb定年及地球化学分析,获得年龄为(287.6±5.5)Ma,表明该玄武岩为塔里木盆地早二叠世岩浆活动的产物。地球化学特征表明,玄武岩w(SiO_2)为46.15%~48.64%,w(MgO)为2.87%~4.23%,w(Na_2O)-2%<w(K_2O),暗示其为钾质碱性玄武岩,岩石总体上亏损Rb、K、Sr等大离子亲石元素,而相对富集Th、U、Ti和LREE等高场强元素,但Nb-Ta显示弱的负异常,与峨眉山及区域上的四石厂、达木斯、其木干玄武岩具有相同或相近的图型特征。该玄武岩具有高的Ti和Nb含量及低的Zr/Nb比值,暗示其来自富集的地幔源区,Mg#和Cr、Ni等相容元素含量变化较大,表明其曾经历广泛的橄榄石、单斜辉石和斜长石的结晶分异作用,且Nb/U比值为19.27~21.44,指示成岩过程中受到一定程度的地壳混染。基于研究区玄武岩与区域上玄武岩相近的时代、地球化学特征及处于内陆稳定构造环境,认为该玄武岩与塔里木盆地广泛分布的玄武岩同属一个时代和构造背景下的产物。
Basalts in the Keping area make up a major part of Tarim Basin Permian Large igneous province.This study conducted U-Pb geochronology and geochemical analyses for zircons collected from basalts of Early Permian Balikelike Formation（P1b）in the south of Keping Gaizilikexiang village.Zircon U-Pb dating yields a crystallization age of（287.6±5.5）Ma.Geochemical analyses of basalts show that their SiO2 content varies from 46.15%to 48.64%and MgO content varies from 2.87%to 4.23%.The feature Na2O2-2%K2O indicates that they belong to potassium alkaline basalts.Generally,the rocks are depleted in LILE,such as Rb,K and Sr,and relatively enriched in HFSE,such as Th,U,Ti,and LREE.Nb-Ta shows slight negative anomalies,which is similar to patterns of basalts from Mountain Emei and Sishichang,Damusi and Qimugan.The basalts show high Ti and Nb value but low Zr/Nb ratio.This indicates an enriched mantle source.Big changes on Mg^#,and Cr and Ni contents imply that rocks should have experienced extended fractionation of olivine,clino-pyroxene and plagioclase.Their Nb/U values,changing from19.27 to 21.44,indicate that magma experienced certain crust contamination during their solidification.Based on these characteristics,we come to the conclusion that the Keping basalts and widely distributed regional basalts in Tarim Basin are originated from the same geological era and tectonic background.
出处
《地质科技情报》
CAS
CSCD
北大核心
2017年第1期1-13,共13页
Geological Science and Technology Information
基金
中国地质调查局项目"西南天山柯坪地区六幅地质矿产综合调查"(1212011504201)
关键词
玄武岩
早二叠世
年代学
地球化学
地质意义
柯坪
basalt
Early Permian
chronology
geochemistry
geological significance
Keping
