Diamonds recovered from peridotite of the Purang ophiolite in the Yarlung-Zangbo suture of Tibet: A proposal for a new type of diamond occurrence.
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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。Abstract: 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.
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Key words:
- Diamond /
- Ophiolite /
- Peridotite /
- Purang /
- Yarlung-Zangbo suture zone
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[1] 白文吉,杨经绥,方青松,颜秉刚,张仲明.2002.西藏蛇绿岩的超高压矿物:FeO、Fe、FeSi、Si和SiO2组合及其地球动力学意义.地球学报,23(5):395-402
[2] 白文吉,杨经绥,施倪承,方青松,代明泉,熊明,颜秉刚.2004.西藏罗布莎蛇绿岩地幔岩中首次发现超高压矿物方铁矿和自然铁.地质论评,50(2):184-187
[3] 白文吉,施倪承,方青松,李国武,杨经绥,熊明,戎合.2006. 新矿物:罗布莎矿.地质学报,80(10):1487-1490
[4] 白文吉,施倪承,杨经绥,方青松,任玉峰,戎合,李国武,马喆生.2007.西藏蛇绿岩豆荚状铬铁矿中简单氧化物矿物组合及其超高压成因.地质学报,81(11):1538-1549
[5] 李建峰,夏斌,刘立文,徐力峰,何观生,王洪,张玉泉,杨之青. 2008. 西藏普兰地区拉昂错蛇绿岩中辉绿岩的锆石SHRIMP U-Pb年龄及其地质意义. 地质通报,27(10):1739-1743
[6] 刘钊,李源,熊发挥,吴迪,刘飞.2011.西藏普兰拉昂错的MOR型辉长岩:岩石学和年代学. 岩石学报,27(11):3269-3279
[7] 施倪承,白文吉,李国武,熊明,方青松,杨经绥,马喆生,戎合.2009. 雅鲁矿:一种金属碳化物新矿物.地质学报,83(1):25-30
[8] 王希斌,鲍佩声,邓万明,王方国.1987.西藏蛇绿岩.北京:地质出版社,1-336
[9] 吴新国,贾建称,崔邢涛.2006. 雅鲁藏布江缝合带开合演化模式的探讨.现代地质,19(4):488-494
[10] 肖序常,王方国.1984.中国蛇绿岩概论.中国地质科学院院报,9:19-30
[11] 徐向珍,杨经绥,巴登珠,陈松永,方青松,白文吉.2008.雅鲁藏布江蛇绿岩带的康金拉铬铁矿中发现金刚石.岩石学报,24(7):1453-1462
[12] 徐向珍,杨经绥,郭国林,李金阳.2011. 雅鲁藏布江缝合带西段普兰蛇绿岩中地幔橄榄岩的岩石学研究. 岩石学报,27(11):3179-3196
[13] 杨经绥,白文吉,戎合,张仲明,许志琴,方青松,颜秉刚,李天福,任玉峰,陈松永.2005.中国大陆科学钻(CCSD)主孔石榴石橄榄岩中发现Fe2P合金矿物.岩石学报,21(2):271-276
[14] 杨经绥,白文吉,方青松,孟繁聪,陈松永,张仲明,戎合.2007.极地乌拉尔豆荚状铬铁矿中发现金刚石和一个异常矿物群.中国地质,34(5):950-952
[15] 杨经绥,白文吉,方青松,戎合.2008a.西藏罗布莎蛇绿岩铬铁矿中的超高压矿物和新矿物(综述).地球学报,29(3):263-274
[16] 杨经绥,张仲明,李天福,任玉峰,徐向珍,巴登珠,白文吉,方青松,陈松永,戎合.2008 b.西藏罗布莎铬铁矿体围岩方辉橄榄岩中的异常矿物.岩石学报,24(7):1545-1552
[17] 中国地质科学院地质研究所金刚石组.1981.西藏阿尔卑斯型超基性岩中发现金刚石.地质论评,22:455-457
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