北秦岭老湾金矿带变质岩原岩恢复及其形成过程

老湾金矿带位于桐柏-大别造山带北缘，是一个由前寒武系绿帘角闪岩相、角闪岩相和麻粒岩相组成的中-低P/T变质带。通过对老湾金矿带变质岩产状、岩石组合特征、岩相学、岩石地球化学特征等进行综合研究，探讨了该区的变质岩原岩及其形成过程。研究结果表明：1）老湾金矿带龟山岩组斜长角闪岩类原岩为大陆拉斑玄武岩（玄武质熔岩）、火山碎屑岩及少量基性岩脉；云母石英片岩类原岩为中性泥质岩、砂岩等沉积岩；大理岩原岩为纯净的白云岩。2）龟山岩组形成于中-新元古代（920 Ma±），经历了志留纪（410 Ma±）、石炭纪（314 Ma±）、白垩纪（130 Ma±）三期变质作用，龟山岩组变质岩是其先就位于地壳中的原岩后来发生陆壳俯冲再折返抬升退变质的产物。

Restoration and formation process of metamorphic rocks in the Laowan gold ore belt, North Qinling

The Laowan gold ore belt located in the northern edge of the Tongbai-Dabie orogenic belt is a medium-low P/T metamorphic belt composed of Precambrian epoch-amphibolite facies, amphibolite facies and granulite facies. The metamorphic rock occurrence, lithological assemblage, petrography and lithochemistry in the Laowan gold ore belt are comprehensively studied and the metamorphic rock''s protolith and formation process are discussed. The results show that:1. The protoliths of the plagioclase amphibolite of the Guishanyan formation in the Laowan gold ore belt are continental tholeiite (basaltic lava), volcaniclastic rocks and a few basic dykes. The protoliths of mica quartz schist are neutral sedimentary rocks such as neutral argillaceous rocks and sandstones. The protoliths of marble is pure dolomite. 2. The Guishanyan formation was formed during the Meso-Neoproterozoic (about 920 Ma) and exposed to three stages of metamorphissm respectively in Silurian (about 410 Ma), Carboniferous (about 314 Ma), and the Cretaceous (about 130 Ma) period. The metamorphic rocks of the Guishanyan Formation are the products of the protoliths that emplaced in the crust then exhumed to shallow part by subduction of the continental crust and retogressively metamorphosed.