蛇绿岩的分类

文中把蛇绿岩分为三类:科迪勒拉型、东地中海型和西地中海型。科迪勒拉型蛇。绿岩通常构成构造地层地体的基底,岩石序列中有相当数量的富Si质岩石出现,大多与岛弧或弧间盆地环境有关。东地中海型蛇绿岩以产出较强烈亏损的地幔岩和低Ti玄武岩以及玻安岩为特征,产于洋内消减带之上的岛弧和弧后盆地环境。西地中海型以阿尔卑斯蛇绿岩和横断山区古特提斯蛇绿岩为代表,地幔岩亏损较弱,玄武岩则是MORB型的,形成于小洋盆或转换断层环境。

CLASSIFICATION OF OPHJOLITES

The author divided ophiolites in the world into three types, they are: Cordillera type ophiolite, west Mediterranean type and east Miditerranean type ophiolite. The Cordillera type ophiolite is situated in western North America and Circum Pacific area. These Cordilleran ophiolite associations are often incomplete, metamorphosed, or dismembered and are invariably the basement rock for individual terraines and usually mark the boundary between these terraines. It is known that these ophiolites have formed in some sort of inter-arc settings rather than representing fragments of abyssai oceanic crust. The Cordilleran ophiolites are distinctive because of the(?)volume of silicic plutonic and volcanic rocks, ultramafic cumulate of clinopyroxene-type, the lack of dike complexes, and the presence of sill complexes.The east Mediterranean type ophiolite is characterized by strongly depleted mantle sources, clinopyroxene- and/or orthopyroxene type cumulates, low-Ti basalts and boninites. It is speculated that the ophiolites formed in island arc or back-arc settings above subducted zone, so Pearce et al.(1984)called them as supra-subduction zone ophiolites.The west Mediterranean type ophiolite mainly occurred in both Alps and Hengduan Mountain Regions of southwest China. The ophiolites are composed of pl-or sp-lherzolite, gabbro and basalt, and lack or few of cumulate and dike. It is characterized by MORB-type volcanic rocks comparing with other two type ophiolites.The author disccuses the diversity of ophiolites and indicates that if you have found the MORB in investigations for some ophiolites, you should be careful since they are not likely from mid oceanic ridge, and could be from small ocean basin, back-arc basin, transform fault, or rift settings. Because abyssal oceanic crust has been mainly consumed by subduction and only in extremely rare instance it become accreted into continental crust.