巴基斯坦北部科希斯坦弧奇拉斯杂岩体的地质及地球化学特征(英文)  

GEOLOGY AND GEOCHEMISTRY OF THE CHILAS COMPLEX IN THE KOHISTAN ISLAND ARC, NORTHERN PAKISTAN

作　　者：高桥浩 御子柴真澄 高桥裕平 ABKausa TKhan 

机构地区：[1]日本经济产业省地质调查所 [2]巴基斯坦地质调查局地球科学实验室

出　　处：《新疆地质》2003年第1期63-64,共2页Xinjiang Geology

基　　金：日本经济产业省ITIT项目资助

摘　　要：位于巴基斯坦北部西喜马拉雅的科希斯坦地体为夹持于亚洲板块与印度板块之间的倾斜的岛弧型壳体.科希斯坦岛弧北界为主地幔逆冲断层(MMT),北界为北部缝合带(或喀啦昆仑主逆冲断层,MKT),可将其划分为几个地质单元.奇拉斯(Chilas)杂岩体为一长约300 km、宽50 km的巨型基性侵入岩体与MMT和MKT近平行展布.它被认为是科希斯坦岛弧的岩浆房根区.奇拉斯杂岩体主要由辉长苏长岩和几个超镁铁质岩.镁铁质岩(简称UMA)岩体组成.前者侵入后者之中.奇拉斯杂岩体 岩石普遍发生轻微变形,出现叶理化和韧性剪切带.UMA主要由橄榄石(含或不含单斜辉石)堆积岩 (纯橄岩,异剥橄岩)和斜长石.单斜辉石-斜方辉石堆积岩(二辉辉长岩)组成,含有少量单斜辉石-斜方 辉石堆积岩(辉石岩)。辉长苏长岩的地球化学特征表明其为岛弧环境下形成的非堆积岩,而UMA的 地球化学特征表明其为岛弧环境下的堆积岩.辉长苏长岩和UMA的主元素地球化学特征在AFM图 解上可用堆积和非堆积的模式来解释.辉长苏长岩的稀土和微量元素地球化学特征在100 MgO/(MgO+TFeO)图解上显示岛弧型特点,且UMA表明其堆积特性.The Kohistan Terrane in the western Himalaya, northern Pakistan, is regarded as a tilted island arc type crust sandwiched between the Asian and Indian continental crusts. The Kohistan Island Arc is bounded along the south by Main Mantle Thrust (MMT), and along the north by Northern Suture (or Main Karakoram Thrust, MKT), which can be divided into some geological units. The Chilas complex is a huge basic intrusion about 50 km wide and elongates 300 km almost parallel to the MMT and the MKT. It has been interpreted as the magma chamber root zone of the Kohistan Island Arc . The Chilas complex is composed mainly of gabbronorite and several masses of ultraniafic-mafic association (UMA). The UMA is composed mainly of olivine (with or without clinopyroxene) cumulate (dunite, wehlrite) and plagioclase-clinopyroxene-orthopyroxene cumulate (two pyroxene gabbro), with minor amount of clinopyroxene-orthopyroxene cumulate (pyroxenite). Bulk chemical compositions of major elements for the gabbronorite plotted on the ternary AFM diagram are suitable to island arc non-cumulate, and those for the UMA are suitable to island arc cumulate. Major element geochemistry of the gabbronorite and the UMA, plotted on the variation diagram of 100 MgO/(MgO+TFeO) versus oxides, is explained by cumulate and non-cumulate model.

关 键 词：巴基斯坦 科希斯坦弧 奇拉斯杂岩体 地球化学特征 超镁铁质岩-镁铁质岩组合 辉长苏长岩 

分 类 号：P588.125[天文地球—岩石学]