蛇绿岩地幔橄榄岩中的深部矿物:发现与研究进展

Deep Minerals in Ophiolitic Mantle Peridotites: Discovery and Progress

经典的板块构造理论认为,蛇绿岩地幔橄榄岩(大洋地幔橄榄岩)通常来自浅部地幔。近些年在雅鲁藏布江中生代蛇绿岩的多个不同地幔橄榄岩体和俄罗斯极地乌拉尔早古生代的蛇绿岩型铬铁矿中均发现了金刚石等深部矿物,尤其发现了作为矿物包裹体原位产出的金刚石,认为蛇绿岩地幔橄榄岩中含有金刚石可能是普遍现象。这些金刚石在碳同位素和矿物包裹体等方面特征相同,而不同于金伯利岩型金刚石和超高压变质带中产出的变质成因金刚石类型,被认为是一种新的金刚石产出类型,命名为蛇绿岩型金刚石。金刚石等深部矿物的发现和确定,表明这些蛇绿岩地幔橄榄岩和铬铁矿可能来自深部,需要重新思考上地幔的性质和蛇绿岩的形成条件及板块构造的一些经典理论。

In the classic theory of plate tectonics, ophiolitic mantle peridotites （i. e. , abyssal peridotite） are thought to originate in the shallow mantle beneath ocean spreading centers. Diamonds and other UHP minerals have been found in opholitic mantle peridotites and chromitites along the Neo-Tethyan Yarlung Zangbo suture of southern Ti- bet, and in a Paleozoic ophiolite in the Polar Urals of Russia,suggesting that UHP minerals may be widespread in ophiolitic peridotites. Diamonds from these different localities all have very similar features in C isotope and mineral inclusions,and are distinct from the other two well known types, i.e. kimberlitic diamonds and UHP metamorphic diamonds. The occurrence of diamond in ophiolite indicate a completely new environment for diamond formation, which can be regarded as ophiolite-type diamond. These new findings indicate a need to reconsider the nature of the upper mantle and the conditions under which ophiolites form.