造山橄榄岩及其意义

造山橄榄岩和蛇绿岩的橄榄岩主要由地幔岩组成，造山橄榄岩代表陆壳下的地幔，蛇绿岩的橄榄岩代表洋壳下的地幔。洋壳下的地幔与陆壳下的地幔在物质组成上大体接近，但产出的构造背景明显不同。介绍了造山橄榄岩的组成、与造山橄榄岩有关的高压-超高压变质作用、地幔流体作用、成矿作用、造山橄榄岩侵位的机制等，以及中国几个可能的造山橄榄岩的基本情况，讨论了造山橄榄岩的演变过程及其与蛇绿岩的橄榄岩的区别。造山橄榄岩的形成大体经历了初期的陆壳减薄和裂谷阶段、晚期的挤压造山2个构造演化阶段。有些地区只发育裂谷阶段，构造演化在裂谷后即夭折了，也称为造山橄榄岩。
蛇绿岩与造山橄榄岩之间的区别不在物质组成和地球化学方面，而是在构造背景上。如有没有深海沉积、混杂堆积，有，是蛇绿岩；没有，则是造山橄榄岩。有没有超高压变质作用、地幔交代作用或地幔交代作用是否强烈，有且很强，可能是造山橄榄岩；没有，则可能是蛇绿岩。岩体是冷侵位还是热侵位，冷侵位是蛇绿岩，热侵位是造山橄榄岩。蛇绿岩出现在造山带，代表已经消失的洋盆；造山橄榄岩一般也出现在造山带，但代表的是减薄和撕裂的陆壳下的地幔。

Orogenic peridotite and its significance

Orogenic peridotite and peridotite of ophiolite are mainly composed of mantlerock.Orogenic peridotite represents the mantle beneath the continental crust, and peridotite of ophiolite represents the mantle beneath the oceanic crust.The mantle beneath the oceanic crust is generally close to the mantle beneath the continental crust in terms of material composition, but the tectonic setting is different.This paper briefly introduces the composition of orogenic peridotites, high-pressure and ultrahigh-pressure metamorphism related to orogenic peridotites, mantle fluids, mineralization, and mechanisms of orogenic peridotite emplacement, and also briefly introduces several possible orogenic peridotites in China such as the Songshugou peridotite in the Qinling Mountain, the Raobazhai rock mass in Anhui, several rock masses in the Yidun-type area in western Sichuan, Santai rock mass in western Yunnan, and Dadaoerji rock mass in Gansu.The evolution process of orogenic peridotite and its difference from ophiolite peridotite are discussed.It is pointed out that the difference between ophiolite and orogenic peridotite is not mainly in material composition and geochemistry, but in tectonic setting.Is there no abyssal sediment? Is it mixed up? Yes, it is peridotite of ophiolite; no, it is orogenic peridotite.
Is there any UHP metamorphic effect? Is there mantle metasomatism or strong mantle metasomatism? Some are very strong and may be orogenic peridotites; no, they may be peridotites of ophiolite.Cold emplacement is peridotite of ophiolite, and thermal emplacement is orogenic peridotite.It is pointed out in this paper that the formation of orogenic peridotite has generally experienced two stages of tectonic evolution:the initial thinning of the continental crust, the rifting stage, and the late extruding orogenic belt.In some areas, only the rift stage is developed, and the tectonic evolution finished after the rift, also known as orogenic peridotites, such as Zabargad in the Red Sea, Ronda in Spain, Beni Bousera in Morocco, and Yidun peridotite in China.The peridotite of ophiolite appears in the orogenic belt, representing the ocean basin that has disappeared; the orogenic peridotite generally appears in the orogenic belt, but it represents the thinned and torn continental crust.It is necessary to study and demonstrate whether the peridotite that appears in the orogenic belt is ophiolite because their tectonic meanings are different.