赣南大富足岩体岩石地球化学特征及其构造环境判别

PETROGEOCHEMISTRY AND TECTONIC ENVIRONMENT OF DAFUZU ROCK MASS IN SOUTHERN JIANGXI PROVINCE

大富足岩体位于武夷山隆起带南段,为一多期复式花岗岩侵入体,岩体由当风凹、泮塘、春坑、荷树岽、土桥凹、水隘背、新村、沙告、先坑、石教坪共10个单元所组成,固结指数、Rb/Sr和K/Rb比值以及稀土配分型式反映侏罗纪的石教坪、先坑、沙告单元和二叠纪的泮塘、当风凹单元均为相对独立的没有分异演化关系的单元,而由新村、水隘背、土桥凹、荷树岽、春坑单元组成的三叠纪富城超单元则为同源岩浆房岩浆过程的产物。根据矿物成分和化学成分和微量元素特征判别,岩体属CCG或同碰撞花岗岩类型,形成于大陆碰撞的构造环境,扬子板块与华夏板块在二叠-侏罗纪的大致沿着杭州-诸广山-花山这条缝合带发生的陆内A型俯冲与这种构造环境相呼应。

Dafuzu terrane, occurring in the southern section of Wuyishan uplift belt, is a composite granite intrusive made up of ten units, namely Dangfengao, Pantang, Chunkeng, Heshudong, Tuqiaoao, Shuiaibei, Xincun, Shagao, Xiankeng, and Shijiaoping. These granites show 71.70% -76.70% of SiO2 , 12.32% - 14. 19% of Al2O3 , 1. 41 - 2.45 for composite index （σ） , and demonstrate the enrichment of Rb, U and Th and the dilution of Cu, Zn, Co, Cr, Ni, Sr, Ba, Zr and Hf. Their solidification index （SI）, Rb/Sr and K/Rb radio, and the REE pattern show that the units in Jurassic and Permian are all unrelated to one another, demonstrating no differentiation and evolution interrelationships, but the Triassic Fucheng superunit, comprised of Chunkeng, Heshudong, Tuqiao＇ ao, Shui＇ aibei, Xincun units, is a result of the magmatic process in a single magma reservoir. The distinction based on the mineral and chemical compositions and the trace element characteristics indicates that the Dafuzu terrane belongs to the CCG or syn-eollision granite type that occurs in the tectonic setting of contient collision and is associated with the A-type continental subduction between Yiangtze and Cathay plates along the Huangzhu -Zhuguangshan -Huashan suture belt in Permian -Jurassic.