碰撞造山过程中流体向前陆盆地大规模迁移汇聚:来自长江中下游三叠纪膏盐建造和区域蚀变的证据

Large-scale Migration of Fluids towards Foreland Basins During Collisional Orogeny: Evidence from Triassic Anhydrock Sequences and Regional Alteration in Middle-Lower Yangtze Area

文章通过对长江中下游的地质调查 ,提出了大规模流体迁移汇聚的 3个地质证据 :①穿切寒武系_三叠系的大面积白云石化和硅化蚀变域 ,整体上发育在沿江成矿带与大别造山带的夹持地带 ,蚀变域内强弱相间的蚀变带呈NW向展布 ,受垂直于大别造山带的断裂系统控制 ,可能记录了长距离迁移的流体活动轨迹 ;②沿江局限盆地内大量发育的中下三叠统巨厚的膏盐建造 ,其结构构造特征揭示了区域热卤水在局限盆地内的排泄汇聚与化学沉积对其形成有重要的贡献 ;③早中三叠世同生沉积的铁碳酸盐建造和块状硫化物铁铜铅锌矿床 ,与膏盐建造或呈互层 ,或者分离 ,但均具有相同的产出层位和密切的伴生关系 ,是高盐度热卤水同生沉积的产物。根据调查结果 ,结合前人资料 ,提出了大别碰撞造山过程中流体迁移汇聚与成矿的概念性模式。

The middle_lower Yangtze area has undergone a series of complex tectonic evolution processes, such as Hercynian extensional rifting, Indosinian foreland basining, and Yanshanian transpression_transtension, forming a large distinctive Cu, Fe, and Au metallogenic belt. In the tectonic evolution, large_scale migration and convergence of fluids towards foreland basins during collisional orogeny of the Yangtze and North China continental blocks were of vital importance in the formation of the metallogenic belt. Through geological survey of the middle_lower Yangtze area, three pieces of evidence for large_scale fluid migration are recognized. (1) The extensive dolomitic and silicic alteration penetrating Cambrian_Triassic strata generally occurs in a region sandwiched between the metallogenic belt along the Yangtze River and the Dabie orogenic belt, and the alternate strong and weak alteration zones extending in a NW direction are controlled by the fault system of the Dabie orogenic belt, which might record the locus of the activities of long_distance migrating fluids. (2) The textures and structures of very thick Middle_Lower Triassic anhydrock sequences in confined basins along the river reveal the important contribution made by the convergence and chemical deposition of regional hot brine within confined basins in the formation of these sequences. (3) Although Early_Middle Triassic syndepositional iron carbonate sequences and Fe_Cu_Pb_Zn massive sulfide deposits are alternated with or separated from anhydrock sequences, they all occur in the same stratigraphic horizon and are intimately associated with each other, suggesting they are syndepositional products of high_salinity hot brines. According to the geological survey combined with the data available, the authors propose in this paper a conceptual model for fluid migration_convergence and mineralization in the Dabie collisional orogeny.