新疆坡北镁铁-超镁铁质岩体地球动力学背景探讨  

Geodynamic setting of the Pobei mafic-ultramafic intrusion in Xinjiang

作　　者：王亚磊[1] 张照伟[1] 张铭杰[2] 张江伟[1] 高永宝[1] 

机构地区：[1]西安地质矿产研究所国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054 [2]兰州大学地质科学与矿产资源学院,西部矿产资源甘肃省重点实验室,甘肃兰州730000

出　　处：《岩石矿物学杂志》2013年第5期693-707,共15页Acta Petrologica et Mineralogica

基　　金：中国地质调查局地质科研项目(121201112092,1212011220897,1212011120183);国家自然科学基金项目(41372095);高等学校博士学科点专项科研基金(20120211110023)

摘　　要：坡北镁铁-超镁铁质岩体位于塔里木板块东北缘的北山地区，主要由坡一、坡三、坡七和坡十等十几个侵入体组成，已发现坡一和坡十岩体赋存大型Cu—Ni硫化物矿床，目前对坡北含矿岩体成岩成矿构造背景存在不同认识。本文对坡一岩体各类岩石的矿物、主量和微量元素组成进行了系统分析，坡北岩体橄榄石FO值范围为83．17～90．2，斜方辉石主要为古铜辉石，单斜辉石主要为普通辉石和透辉石；铬尖晶石D#和Mg#值变化范围分别为0．45--0．69和0．11--0．41，具有由富铝、富镁向富铬、富铁方向演化的趋势。微量元素具有明显的Nb、Ta和Ti负异常，Pb正异常。岩体主量元素变化特征主要受橄榄石、辉石和斜长石分离结晶／堆晶作用控制。模拟计算表明，岩体母岩浆MgO含量为16．09％，FeO含量为10．38％，岩浆结晶温度为1331～1411℃，为高温苦橄质岩浆。坡北岩体是早期受俯冲流体交代的岩石圈地幔在塔里木地幔柱作用下发生较高程度部分熔融的产物。Located in the northeastern margin of Tarim Plate, the Pobei mafic-ultramafic intrusion consists of several intrusive bodies, such as Poyi, Posan, Poqi, and Poshi, in which the Poyi and Poshi intrusive bodies show the better metallogenic potential. In the past, the Pobei intrusion was considered to have been geodynami- cally formed in the post-collisional setting or the mantle plume setting. In this paper, systematic mineralogical and geochemical data of the Poyi intrusive body were used to reveal the geodynamic setting. The results show that the Fo values of the olivine range from 83.17 to 90.2, the orthopyroxene minerals are mainly bronzite, whereas the clinopyroxene minerals are mainly augite and endiopside; the Cr# and Mg# of chrome spinel range from 0.45 to 0.69 and from 0.11 to 0.41, respectively, and show the evolution trend from A1 and Mg richness to Cr and Fe richness. The trace elements display obvious Nb, Ta, Ti negative anomalies and Pb positive anomalies. The variations of major elements are mainly controlled by fractional crystallization/cumulate action of olivine, pyroxene and plagioclase The MgO content and FeO content of parent magma are estimated to be 16.09 % and 10.38 %, respectively. The initial crystallization temperature of parent mamma is estimated from 13311℃ to 1 411℃, indicating that the parental magma is picritic magma. The Pobei intrusion might have been derived from a high degree of partial melting of matasomatized lithospheric mantle during the activity of Tarim mantle plume.

关 键 词：构造背景 母岩浆成分 矿物岩石化学 坡北镁铁-超镁铁质岩体 塔里木地幔柱 

分 类 号：P541[天文地球—构造地质学] P588.112[天文地球—地质学]