摘要
东昆仑古特提斯域镁铁—超镁铁质岩石的研究极为薄弱,对青海东昆仑东段加当橄榄辉长岩进行岩相学、年代学和地球化学分析,以期为东昆仑晚古生代—早中生代构造岩浆演化提供新的约束。利用LA-ICPMS锆石U-Pb定年技术,获得橄榄辉长岩加权平均年龄为249.7±3.0Ma(n=21,MSWD=0.105),表明岩体形成时代为早三叠世。岩石地球化学研究表明,加当橄榄辉长岩具有高Al_2O_3(14.71%~18.60%)、低TiO_2(0.07%~0.19%)、贫P2O5(0.02%)、低碱(K_2O+Na_2O=1.65%~2.01%)及Na_2O>K_2O的特征,属亚碱性辉长岩。岩石微量元素总体上富集大离子亲石元素(LILE:Rb、Sr、Ba、Th、K)和Pb,相对亏损高场强元素(HFSE:Nb、Ta、P、Zr、Ti),稀土元素总量较低,ΣREE=9.79×10^(-6)~12.55×10^(-6),(La/Yb)N为5.61~28.51,平均11.43,显示轻稀土富集的特征,δEu=1.64~2.48,具有明显的Eu正异常。根据地球化学特征和微量元素判别图解,橄榄辉长岩源区为被俯冲改造的岩石圈幔源岩浆,岩浆在演化过程中遭受了上地壳物质的同化混染,并经历了一定程度的结晶分异作用。结合东昆仑区域构造演化,认为加当橄榄辉长岩是早三叠世阿尼玛卿古特提斯洋北向俯冲阶段岩浆活动的产物。
The mafic-ultramafic rocks in Paleo-Tethys domain of East Kunlun are poorly documented.Study of petrography,geochronology and geochemistry of the Jiadang olivine gabbro from the Eastern Section of East Kunlun,Qinghai Province can provide new constraints for the Late Paleozoic-Early Mesozoic tectonomagmatic evolution in East Kunlun.LA-ICP-MS zircon U-Pb dating yielded a weighted mean age of 249.7±3.0 Ma(n=21,MSWD=0.105)for olivine gabbro,indicating that the rock formed in the Early Triassic.Detailed lithogeochemical studies show that the olivine gabbro is characterized by high content of Al2O3(14.71%-18.60%),low content of TiO2(0.07%-0.19%),P2O5(0.02%),alkali(K2O+Na2O=1.65%-2.01%),and Na2OK2O,suggesting that the olivine gabbro belongs to sub-alkaline gabbro series.This suite of rocks is enriched in LILE(such as Rb,Sr,Ba,Th,K)and Pb,relatively depleted in HFSE(such as Nb,Ta,P,Zr,Ti),low REE contents,slightly enriched in LREE with obviously positive Eu anomaly(ΣREE=9.79×10-6-12.55×10-6,(La/Yb)N=5.61-28.51,δEu=1.64-2.48).The geochemical characteristics and trace element discrimination diagrams show that the parental magma of olivine gabbro derived probably from the mantle influenced by the subducton,with the parental magma experiencing assimilation contamination by the upper crustal material and a certain extent of crystallization differentiation during the magma evolution.In combination with evolutionary characteristics of regional structures in East Kunlun,the authors consider that the olivine gabbro was formed during AnyemaqenPaleo-Tethys ocean subduction in Early Triassic.
作者
孔会磊
李金超
栗亚芝
贾群子
国显正
张斌
KONG Huilei, LI Jinchao, LI Yazhi, JIA Qunzi, GUO Xianzheng, ZHANG Bin(Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Xi'an Center of Geological Survey, CGS, Xi' an, 71005)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2018年第5期964-978,共15页
Acta Geologica Sinica
基金
中国地质调查局地质大调查项目(编号DD20160013
12120115022101
12120113029000)资助的成果