西藏雅鲁藏布江缝合带东波地幔橄榄岩中金刚石的发现及地质意义

本文报道了雅鲁藏布江缝合带西段的东波蛇绿岩地幔橄榄岩中发现与罗布莎和普兰岩体相似的金刚石和特殊地幔矿物群。东波地幔橄榄岩体以方辉橄榄岩为主,含少量二辉橄榄岩和纯橄岩,辉石岩和辉长岩呈脉状产在方辉橄榄岩中。岩石地球化学特征表明东波岩体形成于MOR环境后受到SSZ环境的改造。通过重砂分选实验,在693 kg的地幔橄榄岩大样中发现了金刚石和碳硅石等30余种特殊矿物群,包括金刚石、自然铬、自然金、自然铁、自然硅、自然铜等自然元素矿物类;碳硅石等碳化物;铬尖晶石、金红石、铬铁矿、刚玉、黑钨矿、铌钽铁矿、磁铁矿、赤铁矿、方铁矿、锡石等氧化物;铁铬镍合金、镍铁合金、铜锌合金等合金互化物;辉钼矿、方铅矿、辉铋矿、黄铁矿、黄铜矿、毒砂和闪锌矿等硫化物;橄榄石、辉石、锆石、蓝晶石、白云母、蛇纹石、绿帘石等硅酸岩;萤石等氟化物。该矿物群与雅鲁藏布江缝合带的罗布莎和普兰两个岩体中发现的特殊矿物群非常类似,同时也为蛇绿岩型金刚石这一新类型提供了佐证。

Diamond discovered from the Dongbo mantle peridotite in the Yarlung Zangbo suture zone, Tibet

Abstract: This paper reports the discovery of unusual mantle mineral group in the mantle peridotites of Dongbo ophiolite, which lies in the western part of the Yarlung Zangbo suture zone. The Dongbo ophiolite consists mainly of harzburgite, with a small amount of lherzolite and dunite, pyroxenite and gabbro dikes cutting across the harzburgite. Geochemical characteristics suggest that the Dongbo mantle peridotite was derived from mid-ocean ridge (MOR) but modified in a suprasubduction zone (SSZ) environment. Some grains of diamond and other unusual minerals, such as moissanite, were recovered by standard mineral separation techniques from a 693 kg sample of harzburgite. The presence of diamond, native Cr, Au, Fe, Si and Cu, together with the moissanite, indicates a strong reducing environment. The authors also found a lot of alloys, oxides, sulfides, silicates, fluoride and some other materials. These mineral assemblages recovered from the Dongbo harzburgite are very similar to those of Luobusa and Purang harzburgite, which gives evidence to the ophiolite-type diamond.