摘要
长江中下游成矿带是我国最重要的矿产资源生产基地之一。为了深入理解和认识此成矿带形成的深部构造背景及其岩浆活动与成矿作用过程,本文利用NW-SE向利辛-宜兴地球物理探测剖面的重力场资料构建了跨越长江中下游成矿带地域的二维深部地壳密度结构模型。并在结合其他已有研究成果的基础上,从Moho界面的展布形态、密度分布特征与壳内低密度区的存在等方面探讨了该区的深部构造格局与成矿作用过程。研究结果表明:长江中下游成矿带地域下方的地壳密度结构与其两侧地域存在显著差异;在宁芜矿集区下方的Moho界面呈上隆形态,矿集区存在密度值略低于两侧地域的低密度异常区。幔源岩浆的上涌底侵与MASH成矿作用可较好地解释该区的结构与构造形态以及在地表所见到的岩浆广泛存在和矿产资源富集的特征。岩石圈地幔物质在宁芜矿集区下方的上涌导致了Moho界面的抬升,而脆性上地壳中的伸展断裂则为岩浆的向上运移与矿产资源的形成提供了有利场所与环境。
To further understand the deep tectonic background and the magma activities as well as the deep mineralization processes in the Middle-Lower Yangtze metallogenic belt,we construct the 2D crustal density structure model based on the gravity data collected along the Lixin-Yixing geophysical profile in direction of NW-SE. We discuss the deep tectonic framework and mineralization processes on the view points of Moho undulation,characteristics of densities distribution and exist of low-density zones in crust based on the density model we got. The research results show that: the density structure varies strongly beneath the Lixin-Yixing profile; the Moho interface shallows by 3km beneath the Ningwu ore concentration area and shows an uplift form; there exists low-density zone beneath Ningwu ore concentration area. The underplating of magma from upper mantle and MASH( melting,assimilation,storage and homogenisation) process can provide reasonable explanation for such structure and tectonic framework and the existence of magma and minerals on ground surface. Upwelling of the materials from the lithospheric mantle results not only in the uplift of the Moho interface,but also in the formation of low density zone beneath the Ningwu ore concentration area. Meanwhile,the extensional faults in the brittle upper crust have provided theoretical environment for the upward movement of magmas and the formation of mineral resources.