皖南浅变质岩区的构造演化及矿产分布规律

THE TECTONIC EVOLUTION OF LOWER-METAMORPHIC ROCKS AND THE DISTRIBUTION DISTRICT OF MINERAL IN SOUTH ANHUI

皖南浅变质岩地区由四个不同构造单元拼合而成。中元古早期皖南为一古岛弧;约1000Ma前,华南板块沿江山-绍兴一带俯冲,是岛弧向扬子板块增生;约900Ma前左右,皖南沿祁门-三阳坑一带产生弧后扩张盆地;而850Ma前,华夏古陆沿江山-绍兴一带与扬子板块对接拼合,弧后盆地被动俯冲结束,标志增生的完成,同时深部发生重熔,形成初生陆壳改造型(S型)花岗岩类侵入体,如休宁、许村、歙县等岩体;约780Ma,华南洋壳的俯冲使洋盆逐渐缩小,华南板块和扬子板块发生碰撞,以至祁门-三阳海盆关闭,形成祁门-三阳坑陆壳碰撞地缝合线。这时期的碰撞挤压,使初生陆壳重熔形成板内改造型灵山、莲花山和白际山侵入岩体,最终形成白际岭火山岩推覆席,标志皖南构造格局形成。这些构造演化既奠定了本区的构造格局,又控制着该区的矿产分布。本区主要矿种的成矿期为晋宁期和燕山期,中生代的成矿作用是在晋宁期变质基底上局部演化的结果,即中生代的矿产分布仍反映了基底格局对区域成矿的控制。

The low degree of metamorphic rock units in South Anhui were formed by the assemblage of four tectonic units around the region. Before the early Meso-Proterozoic, it was ancient island arc around South Anhui. 1000Ma ago, South China Block subducted along the Jiangshan-Shaoxing zone and made the island arc accret onto the Yangtze Block. 900Ma, the spreading of back-arc basin took place along Qimen-Sanyangkeng. Around 850Ma, the cathysian Block collided with the Yangtze Block along the Jiangshan-Shaoxing zone, which marked the completion of subduction and accretion. The continental crust remelted to form the S-type granitoid intrusions, such as Xiuning, Xucun and Shexian intrusions. At about 780Ma, the gradual subduction of South China Sea led to the collision between South China and Yangtze blocks, and the final closing of Qimen-Sanyang sea, such as the Qimen-Sanyangkeng suture. This collision also induced the primary continental crust to remelt and then the magma emplaced within the plate to form the Lingshan, Lianhna and Baiji intrusions. Eventually it formed the volcanic rock nappe of Baiji Ridge, and marked the formation of tectonic framework in the South Anhui. The tectonic evolution not only resulted in the structural pattern of the district, but also controlled the distribution of regional mineral. The Jinning and Yangshan Periods are the main time of mineralization in South Anhui. The Mesozoic mineralization was resulted from the evolution of partly metamorphic basement aged in the Jinning. The mineral distribution in Mesozoic time still indicates that the pattern of basement can control the regional mineralization.