四川米仓山地区晋宁期基性超基性岩地球化学性质及其成因研究

RESEARCH ON THE GEOCHEMICAL PROPERTY AND GENESIS OF BASIC AND ULTRABAISC ROCKS OF JINNING PERIOD IN THE MICANGSHAN AREA, SICHUAN PROVINCE

米仓山西段南缘前震旦系结晶基底中多处产有小规模的晋宁期基性超基性岩体。这些岩体具层状侵入岩特点，有密切的同源演化关系。按岩石谱系单位等级体制划分原则，我们将其归为正源超单元，由四个单元组成。通过对其岩石化学、微量元素地球化学性质的研究，认为原始岩浆属拉斑玄武岩浆，源于地幔物质２９％的部分熔融；岩浆经深部岩浆房初步分异后多次脉动侵位，并再经原地结晶分异堆积形成韵律层状构造。成岩温度９２５℃～１２０４℃，岩体就位深度１８～２４ｋｍ；岩浆演化方向主要趋向于富铁，ＳｉＯ２的富集不明显，这种演化特点与低氧逸度条件下的还原环境有关。

In the southern margin of the western Micangshan ,There are a number of smallscale basic and ultrabasic rocks in the crystalline basement of Precambrian. These rocks ,which have been grouped into Zhengyuan superunit, are subdivided into 4 units. Based on their geochemical characteristics and trace elements it is revealed that the original magma belongs to tholeiitic magma derived from the partial melting of 29% mantle material. After the initial differentiation in the deep magma chamber, pulse intrusion took place for several times and crystalline differentiation occured in emplacing position, formed rhythmic layering structure. The rockforming temperature ranges from 925℃ to 1 204℃ at the depth of 18～24 km. The evolutionary direction of magma is characterized by the iron concentration and the unclear SiO2 concentration. This evolutionary character is related to the reduction environment of low oxygen fugacity.