西藏雅鲁藏布江缝合带的普兰地幔橄榄岩中发现金刚石：蛇绿岩型金刚石分类的提出  

Diamonds recovered from peridotite of the Purang ophiolite in the Yarlung-Zangbo suture of Tibet:A proposal for a new type of diamond occurrence

作　　者：杨经绥[1] 徐向珍[1] 李源[1] 李金阳[1] 巴登珠[1] 戎合[1] 张仲明[1] 

机构地区：[1]大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2011年第11期3171-3178,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目(40930313);国家行业专项(SinoProbe-05-02);中国地质调查局工作项目(1212011121263、1212011121272);创新研究群体科学基金项目(40921001)联合资助

摘　　要：西藏罗布莎蛇绿岩的地幔橄榄岩和铬铁矿中发现金刚石和特殊矿物群引发了新的问题,罗布莎地幔橄榄岩含特殊地幔矿物是不是一个孤立的特殊现象,或这是一个普遍存在的规律?显然,这是一个至关重要的问题。本文报道在雅鲁藏布江缝合带西段,距离罗布莎1000km以远的普兰蛇绿岩的地幔橄榄岩中发现与罗布莎类似的金刚石和特殊地幔矿物群。普兰的地幔橄榄岩体主体为方辉橄榄岩,含少量的纯橄岩和二辉橄榄岩,研究表明,属典型MOR型亏损地幔橄榄岩。通过分选,在657kg的地幔橄榄岩大样中发现了金刚石和碳硅石等30余种矿物的特殊矿物群,包括自然铬、自然铁和自然锌等强还原条件下形成的单质元素矿物。该矿物群与罗布莎地幔橄榄岩和铬铁矿中发现的特殊矿物群十分相似,表明罗布莎的地幔橄榄岩不是雅鲁藏布江缝合带中的一个特例。结合在俄罗斯乌拉尔Ray-Iz铬铁矿中发现类似的矿物群,以及世界其他地区的有关阿尔卑斯型地幔橄榄岩中金刚石的报道,认为蛇绿岩地幔橄榄岩中可能普遍含有金刚石,并将蛇绿岩地幔橄榄岩中产出的金刚石归为一种新的金刚石产出类型,即蛇绿岩型金刚石,不同于金伯利岩型金刚石和超高压变质带中产出的变质金刚石类型。After the discovery of diamonds and other unusual minerals in peridotites and chromitites of the Luobusa ophiolite,Tibet,it became important to determine if this was an isolated occurrence or if the same minerals occur in other ophiolites of the Yarlung-Zangbo suture zone.Here,we report the discovery of a similar collection of minerals in mantle peridotites of the Purang ophiolite,which lies in the westernmost part of the Yarlung-Zangbo suture,more than 1000km from the Luobusa massif.The Purang ophiolite consists mainly of harzburgite,lherzolite and dunite,probably of MOR type,which were modified in a SSZ environment.Many grains of diamond and some unusual minerals,such as moissanite,were recovered by standard mineral separation techniques from a 657kg sample of harzburgite.The presence of native Cr,Fe and Zn,together with the moissanite,indicates a strongly reducing environment.This discovery confirms that the Luobusa massif is not unique in the Yarlung-Zangbo suture.Based on the presence of similar minerals in the Ray-Iz ophiolite of the Polar Urals,and reports of diamonds in Alpine-type mantle peridotites,we suggest that diamonds and highly reduced minerals may be common in ophiolitic peridotites.These occurrences indicate a completely new environment for diamond formation,which can be regarded as ophiolite-type diamond,distinct from the other two well known types,i.e.kimberlitic diamonds and ultrahigh pressure metamorphic diamonds.

关 键 词：金刚石 蛇绿岩 橄榄岩 普兰 雅鲁藏布江缝合带 

分 类 号：P548.2[天文地球—构造地质学]