华北克拉通南缘后大陆碰撞背景下的岩石圈演化及金、钼成矿规律探讨

摘要

Many studies show that the ore mineralization in the southern margin of the North China Craton is closely associated with the Yanshanian magmatism. After the collision and amalgamation between the Yangtze Block and the North China Craton in Late Triassic, the southern margin of the North China Craton evolved into post-collisional regime in Jurassic to Cretaceous. On the other hand, the subduction of the Pacific Plate in Jurassic to Cretaceous may also have affected the East Qinling orogen, the western Henan province in particular. The resulted lithosphere thinning in the eastern North China Craton is coincident with the extensive magmatism in the East Qinling orogen. The Yanshanian granites in the study area were likely derived from remelting of the thickened lower crust with input of juvenile mantle. It is evidenced that the granites are the decisive factor controlling the ore mineralization. We argue that the pooling and ascending of the granitic magmas might have also created the channel ways for the uprising ore fluids; moreover, the granitic intrusions may provide heat which is very important for the convection of hydrothermal fluids.%通过对华北克拉通南缘大量的岩浆岩和矿床研究表明，矿床的形成与燕山期岩浆岩具有非常密切的关系，豫西矿集区是华北克拉通南缘岩石圈剧烈演化的结果。岩石圈的这种剧烈演化是在两件重大地质事件的共同作用下进行的：一方面，扬子板块与华北板块在印支期拼合，并发生了广泛的陆-陆碰撞造山活动，此后，克拉通边缘转入了后造山演化阶段；另一方面，燕山晚期的J-K之交，太平洋板块向欧亚板块俯冲，导致地幔大规模活动。中国东部大规模的地壳减薄和壳幔作用，使本来就处于造山后演化阶段的华北陆块南缘发生了广泛的岩浆活动。正因为这两大地质作用叠加效应，区域岩浆演化剧烈而复杂，大批重融花岗岩的地球化学特征往往既显示造山带的特点，又具有大规模壳幔作用的特征。这两大地质作用为豫西矿集区的形成提供了良好的成矿地质背景，大量的研究表明，各种矿床与燕山期岩浆岩在形成时间上高度吻合，空间上密切相关，同位素指标极为相近，显示它们在成因上的密切关系。岩浆一方面作为深部赋矿流体的上升通道，另一方面提供持续的高温环境，保证了元素迁移和成矿作用的进行。因此，华北克拉通南缘后大陆碰撞背景下的壳幔演化、大规模岩浆活动是豫西矿集区形成的决定性因素。