米易大槽层状超基性岩地质特征及成因探讨

四川大槽岩体由纯橄岩—辉橄岩组成,具层状构造,韵律结构发育。主要造岩矿物橄榄石普遍强烈塑性变形,具地幔岩结构特征。岩石化学成分既有阿尔卑斯型,又有层状型超基性岩特点;岩体内豆荚状、层状铬铁矿并存,岩体呈现特殊的二重性特征。现认为岩体是由地幔岩部分熔融分凝后的难熔残余物组成的“晶粥”,侵位于地壳内,形成“晶粥体”,经堆积作用成岩。大槽式超基性岩是含铬层状杂岩和铬铁矿的新成因类型。

GEOLOGICAL CHARACTERISTICS AND ORIGIN OF DACAO LAYERED ULTRABASIC ROCKS,MIYI COUNTY, SICHUAN PROVINCE

The Dacao ultrabasic body consists of dunite and peridotite and show' s conspicuous layer and rhythmic structures. The olivine,as the dominant rock-forming mineral, has been intensively deformed,displaying the feature of pyrolite. According to the petrochemical the rock body has the characteristics of both Alpine-type and layered ultrabasic rocks. Furthermore,there are podifor as well as layered chromite ores in it,also showing the dual nature. From the above mentioned, the authors suggest that the rock body was formed from a kind of "crystal mush"-the mixture of refractory iesidue and part of melt Irom partial melting of the uppei mantle. The mixture was emplaced in the earth' s crust,forming a "crystal mush chamber",and then the rock body formed in the chamber through accumulation. The Dacao ultrabasic rock is a new origin type of layered ultrabasic rocks and chromite deposit.