东天山卡拉塔格地区镁铁质岩体年代学、岩石地球化学研究  

Geochronology and geochemistry of mafic intrusions in the Kalatag area,eastern Tianshan

作　　者：周国超 王玉往[2] 石煜[2] 解洪晶[2] 李德东[2] 郭博然 ZHOU GuoChao;WANG YuWang;SHI Yu;XIE HongJing;LI DeDong;GUO BoRan(School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;Beijing Institute of Geology for Mineral Resources,Deep Exploration Technic Center for Non-ferrous Mines,Beijing 100012,China)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]北京矿产地质研究院,有色金属矿山深部资源勘查工程技术研究中心,北京100012

出　　处：《岩石学报》2019年第10期3189-3212,共24页Acta Petrologica Sinica

基　　金：国家重点研发计划(2017YFC0601204)资助

摘　　要：东天山大南湖岛弧带北缘卡拉塔格地区发育一系列镁铁质岩体,出露面积<1km2。岩体岩相较为单一,主要岩性有辉长岩、橄榄辉长岩、橄长岩、淡色辉长岩和辉绿岩。本文利用LA-ICP-MS测得2个辉长岩的锆石U-Pb年龄分别为282. 2±0. 6Ma和278. 3±0. 6Ma;与吐哈盆地玄武岩及东天山地区铜镍硫化物矿床时代一致。岩石地球化学显示相对低Fe、高Al、Ca、碱、Ti,富集Rb、Ba、Sr、K,亏损Th、Nb、Ta的特征。岩石的(87Sr/86Sr)i=0. 70313~0. 70461,εNd(t)=+6. 22^+8. 64,(206Pb/204Pb)i=17. 68~18. 103,(207Pb/204Pb)i=15. 443~15. 536,(208Pb/204Pb)i=37. 423~37. 801,表现出高Nd、低Sr、低Pb,且变化范围较窄的特征。综合研究表明,该地区镁铁质岩体的岩浆动力学背景为后碰撞伸展环境;岩浆源区为俯冲板片交代的岩石圈地幔,并被软流圈物质混染;同位素和微量元素模拟显示母岩浆在源区遭受了5%~15%的板片流体交代,在上升过程中遭受了<5%的上地壳物质混染。卡拉塔格地区镁铁质岩体与东天山二叠纪镁铁-超镁铁质岩体和吐哈盆地玄武岩形成于同一构造岩浆系统,在剥蚀较浅的大南湖岛弧带具有形成铜镍硫化物矿床的潜力。A series of mafic intrusions are developed in the Kalatag area on the northern edge of the Dananhu arc in the eastern Tianshan,with an exposed area of < 1 km2. The lithofacies are relatively simple,and the main rock types include gabbro,olive gabbro,troctolite,pale gabbro and diabase. The LA-ICP-MS U-Pb ages of zircons from two gabbro samples were 282. 2 ± 0. 6 Ma and278. 3 ± 0. 6 Ma,respectively,which were consistent with the age of the Tuha basalt and Ni-Cu sulfide deposits in the eastern Tianshan. Geochemistry characteristic of the mafic intrusions shows relatively low of Fe and high of Al,Ca,alkali and Ti;enrichment of Rb,Ba,Sr,K and loss of Th,Nb,Ta. And the mafic intrusions are characterized by variable values of(87 Sr/86 Sr)i= 0. 70313 ~0. 70461,εNd( t) = + 6. 22 ~ + 8. 64,(206 Pb/204 Pb)i= 17. 68 ~ 18. 103,(207 Pb/204 Pb)i= 15. 443 ~ 15. 536,(208 Pb/204 Pb)i=37. 423 ~ 37. 801,indicating high of Nd,low of Sr and Pb,and a narrow range of variation. The comprehensive study shows that the magma dynamic background of the mafic intrusions in Kalatag is in the post-collision extension environment;the intrusions were the result of partial melting of a metasomatic mantle modified by the subducted slab-derived melt/fluid,as well contaminated by the asthenosphere material. Simulations with isotope and trace elements show that the primary magma suffered 5% ~ 15% of the slab fluid in the mantle source,and assimilated to < 5% of the upper crust material during the emplacement process. The mafic intrusions in the Kalatag area are formed in the same tectonic-magmatic system as the Permian Tuha basalts and mafic-ultramafic intrusions in the eastern Tianshan,and Dannanhu arc has a good potential for Ni-Cu sulfide deposits because of its shallow denudation thickness.

关 键 词：镁铁-超镁铁岩 二叠纪 地球化学 岩浆源区 卡拉塔格 东天山 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]