摘要
元古代末－寒武纪是北祁连山与海相火山岩有关的块状铜多金属硫化物矿床的主要成矿时期。台矿火山岩系产于大陆裂谷作用的初期阶段。这一时期陆壳拉张速度缓慢，碱性玄武岩浆可停滞于地壳中，导致地壳深熔，由此大量酸性岩浆产生。酸性岩浆上升、喷出并形成火山岩穹的中心。然后，基性岩浆喷溢，并覆盖在酸性火山岩之上，由此形成双层的火山岩穹．火山岩穹驱使海底热卤水对流和循环，同时火山喷出物提供了丰富的成矿元素，进而一系列受海底热卤水对流循环系统控制的矿体产生。笔者提出，大陆裂谷的初期阶段的海相火山作用提供了矿床形成的基本条件，即成矿元素及驱使成矿元素搬运和富集的海底热卤水对流循环系统。随着裂谷拉张强度加大，大量拉斑质岩浆形成并快速上升，深部地壳难于被熔融，只有少量或缺失酸性岩浆．因此，当大陆裂谷拉张速度快时，对成矿作用不利。
Abstract The period from the end of Late Proterozoic Era to Cambrian is an important metallogenic epoch of the massive sulfide copper-polymetallic deposits,which occurs in marine volcanic rocks.The ore-bearing volcanic rock series formed in initial stage of continental rifting.In this stage the velocity of extension of the continental crust is slow, alkali basaltic magma could stagnate wthin the crust,resulting in anatectic melting of the crust,therefore a large volume of acid magma was produced.The acid magma ascented, erupted and constituted the core of the volcanic dome.Then basic magma outpoured and covered on the acid volcanic rocks and so made up a two-storied volcanic done.The volcanic dome drived the hot brine to convecte and circulate on seafloor,simultaneously the volcanic eruptive materials supplied abundant ore-forming elements,furthermore a series of ore bodies,that were controlled by the hot brine convection-circulation system on seafloor,were produced. We suggest that the marine volcanism,which developed in the initial stage of continental rift,supplied the basic conditions for the formation of ore deposits,i.e.ore-forming elements and the hot brine convection-circulation system which drived the ore-forming elements to transport and enrich on seafloor.With the increase of the extension intensity of the continental rift,a large volume of tholeiitic magma was generated and ascented at a rapid speed so that the deep crust would be hard to melt and acid magma either was produced difficultly or absented.Therefore,when velocity of the extension intensity of continental rift speeded up,the conditions were infavorable for ore-forming process
出处
《西北地质科学》
1995年第1期29-37,共9页
Northwest Geoscience
