川西丹巴穹状变质体的P－T－t－d演化

P-T-t-d EVOLUTION OF DOMAL METAMORPHIC BODIES IN DANBA,WEST SICHUAN

在扬子地台西缘松潘－甘孜复合造山带东部的丹巴地区，发育一系列穹状变质体。据近年的研究，这些变质体至少经历了四期变形及相伴随的三期变质作用。利用变质反应、角闪石和二云母的矿物化学，矿物地质温压计及相关的同位素年龄资料，建立了丹巴变质体演化的Ｐ－Ｔ－ｔ－ｄ轨迹。此轨迹呈顺时针形式，反映了变质分带属于叠加复合型，黑云母带－蓝晶石带属于中压型。矽线石带则属低压高温型，即变质作用曾经历了增温增压，增温降压和恒压降温三个演化阶段，表明变质体具陆－陆碰撞的地壳加厚和随后花岗岩浆活化上侵的回返上隆的演化特点，这和区域大地构造背景相吻合。

A series of domal metamorphic bodies occur in Danba in the east ofSongpan -Garze orogenic belt in the western margin of the Yangtze platform.Recent study shows that these metamorphic bodies experienced at least four deformation events and relevant three singes of metamorphism.Clockwise P-T-t-d path for the metamorphic bodies is constructed by use of metamorhpic reactions,mineral chemisty of hornblende and mica,geothermobarometer and related isotopic dating data, indicating a typical superimposed metamorphic zonation.Barrovian type biotite-kyanite zones were overprinted by low-p/high-T type sillimanite-cordierite zone.In other words,metamorphism went through three stages: increase in T and P,increase in T and decrease in P,constant P and decrease in T,reflecting crustal thickening during continent-continent collision followed by uplift induced by granitoid intrusion.This is consistent with regional geotectonic setting.