大陆碰撞造山带的两类橄榄岩——以柴北缘超高压变质带为例

Two types of peridotite in continental orogenic belts—a case study from the North Qaidam UHP metamorphic belt

论述了大陆俯冲碰撞带中地幔橄榄岩的基本特征和成岩类型,并重点讨论柴北缘超高压变质带中不同性质的橄榄岩及其成因。根据岩石学特征,我们确定柴北缘超高压带中发育有两种类型的橄榄岩:(1)石榴橄榄岩,岩石类型包括石榴二辉橄榄岩、石榴方辉橄榄岩、纯橄岩和石榴辉石岩,是大陆型俯冲带的标志性岩石。金刚石包裹体、石榴石和橄榄石的出溶结构、温压计算等均反映其来源深度大于200km。地球化学特征表明该橄榄岩的原岩是岛弧环境下高镁岩浆在地幔环境下堆晶的产物。(2)大洋蛇绿岩型地幔橄榄岩,与变质的堆晶杂岩(包括石榴辉石岩、蓝晶石榴辉岩)和具有大洋玄武岩特征的榴辉岩构成典型的蛇绿岩剖面,代表大洋岩石圈残片。这两类橄榄岩的确定对了解柴北缘超高压变质带的性质和构造演化过程有重要意义。

This paper gives a brief review of the characteristics and petrogenesis of mantle peridotite in continental subduction and collision belts, and then discusses in more detail the petrogenesis of peridotites in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. There are two types of peridotites within this UHP belt. (1) Garnet peridotite consists of garnet lherzolite, garnet-bearing dunite, garnet-free dunite and garnet pyroxenite, which could be considered as one of the critical rock types in a con...