秦岭造山带内高压榴辉岩变质带与元古宙碰撞作用

在北秦岭造山带的秦岭群中发现两个高压变质（岩）带，分别出露于秦岭群的北部和南部边界线之内侧。其中北带内以榴辉岩为主，并伴生有石榴角闪岩、含石榴斜长角闪岩、含多硅白云母及石榴石的长英质片岩；南带中由石榴单辉岩和石榴角闪岩组成。变质作用可分为三个阶段，依次为榴辉岩或石榴单辉岩阶段、石榴角闪岩阶段、斜长角闪岩阶段，前二者是元古宙时期华北和华南板块碰撞中地壳发生了强烈增厚作用的产物，后秆是晚期抬升作用下出现降压过程的结果。在板块碰撞作用的早一中期（榴辉岩），压力为１～１．２Ｐａ，温度在６００～７００℃；晚期（斜长角闪岩）的压力为０．４～０．５Ｐａ，温度在５５０～６００℃。现有压力和温度数据还显示出，南带均稍高于北带。

HIGH PRESSURE ECLOGITE METAMORPHIC ZONES AND PROTEROZOIC COLLISION IN THE QINLING OROGEN

Recently two high-pressure metamorphic zones have been found in the Qinling Group inthe North Qinling orogen. They are exposed along the inner sides of the northern and southernboundaries of the Qinling Group respectively. The northern zone consists mainly of eclogiteswith garnet amphibolite, garnet-bearing amphibolites, garnet-and phengite-bearing felsicschists. The southern zone is composed of garnet clinopyroxenite and garnet amphibolite.Metamorphism involved three stages : the eclogite or garnet clinopyroxenite stage, garnet am-phibolite stage and amphibolitite stage. The first two stages are related to the intense crustalthickening caused by the collision between the North China plate and South China plate in theProterozoic. The last stage resulted from the decompression following the crustal uplift in thelate stage. In the early and middle（eclogite） stages of the plate collision the pressure was 1-1. 2 GPa and the temperature was in the range of 600-700℃. In the late （amphibolite） stage,the pressure dropped to 0.4-0. 5 tJPa and the temperature was 550-600℃.