铜陵矿集区构造-流体-成矿系统演化格架

THE EVOLUTIONARY FRAME OF TECTONIC-FLUID-METALLOGENIC SYSTEM IN TONGLING ORE DEPOSIT CONCENTRATED DISTRICT

铜陵矿集区的成矿作用与印支—燕山期特定构造背景控制下的岩浆活动密切相关 ,地壳浅部成矿岩浆运移侵位过程和主成矿期构造变形机制是建立区域构造流体成矿系统演化格架的两个关键问题。通过对区域重磁异常、遥感影像的线性解译结果和区域变形变质作用的分析 ,确定了在区域中部存在一浅层隐伏岩体 ,从而进一步查清了浅部成矿岩浆运移侵位过程 ;引入复杂性科学的思维 ,对基础地质资料进行了重新分析 ,提出铜陵矿集区在印支—燕山期经历了“先剪后压”的递进变形这一新认识。在此基础上 ,结合区域构造演化背景 ,总结了铜陵构造流体成矿系统演化格架 ,即 :(1 )印支期初始 ,在华北、华夏板块的挤压下 ,下扬子地块内部发育了系列岩石圈断裂与地壳断裂 ,使其裂解为很多与铜陵矿集区类似的次级地质单元 ;同时断裂的深切割作用引发了下地壳—上地幔的岩浆活动 ,岩浆沿深断裂上侵 ,分别在 2 0km和 1 0km左右形成深部和中部的岩浆房 ;(2 )印支中期开始 ,相对独立的铜陵矿集区在周围地质单元的夹持和围限下 ,经历了挤压 -剪切的递进变形 ,形成了 3套主要构造形迹 (包括北东向“S”型褶皱、北东向顺层滑脱断层和北西向左型走滑断裂 ) ,其组成了盖层的导流控矿网络 ;同时由于剪切作用导致的区域中部拉伸减薄 。

A distinct and definitive evolutionary frame of tectonic-fluid-metallogenic system in Tongling ore deposit concentrated district, which has been studied for years, is still difficult to be established, because the key problems relating directly to metallogeny in the surface have not been solved, including the problem of the transport process of magma in the upper crust and the problem of the tectonic deformation mechanism in main metallogenic phase. The former problem is induced by the shortage of related materials concerning the concealed magmatic body, while the latter is resulted from the complexity of tectonic phenomena and the limitation of analysis. The authors took the following steps to overcome the difficulties. First, the gravity-aeromagnetism anomaly, the special structure assemblage showed in TM images and the deformation and metamorphism phenomena were utilized to ascertain the existence of the shallow concealed magma chamber in the center of Tongling area. Secondly, by adopting the thought of complexity science, we reexamined the basic geological documents and proposed that Tongling block experienced the “compression-shear” deformation process caused by the enclosing and confinement of surrounding geological blocks in Indo sinian and Yanshanian epochs. Finally, integrating with the regional tectonic background, the evolutionary frame was generalized. The frame is mainly divided into three stages: (1)From the beginning of Indo-China movement, owing to the soft collision between the lower-Yangtze block and the Cathaysian and north China block, the lower-Yangtze block was disintegrated into many secondary geologic units with the development of lithospheric and crustal faults. Contemporarily, the deep-cut function of the faults initiated the magma activity in the domain of lower crust and upper mantle. The magma transported along the deep faults, formed the deep magma chamber in about 20 km and successively aggregated at about 10 km level. (2) From the middle stage of Indo-China movement, the Tongling ore deposit concentrated district experienced the progressive deformation process of “compression-shear” owing to the confinement and grip of the surrounding tectonic units, and three types of fundamental structures, including the northeastward S-shape folds, the northwestward detachment faults and the northwestward sinistral strike-slip faults, were developed, which composed the main conduit net for the metallogenic fluid in the caprock. As shearing instead of compression became dominant in the regional stress field, the stress field in the center of Tongling area transformed from compressional to extensional state. Subsequently the magma in the middle magma chamber transported into the upper crust forming the upper magma chamber in the center. (3) From the middle stage of Yanshan movement, the magma in the upper chamber moved to the surface along the northwestward faults,and aggregated in the core of folds and in the detachment faults,and ultimately resulted in the regional metallogeny.