浙西南松阳地区石榴辉石岩变质作用演化与地质意义  

Metamorphism evolution and geological significance of garnet pyroxenite in Songyang area of southwestern Zhejiang Province

作　　者：郭腾达 郑常青[1,2] 周喜文 董云峰[1,2] 周枭 王照元[1,2] 宋旸 石磊 GUOTengDa;ZHENGChangQing;ZHOUXiWen;DONGYunFeng;ZHOUXiao;WANGZhaoYuan;SONGYang(Collage of Earth Sciences,Jilin University,Changchun 130051,China;MLR Key Laboratory of Mineral Resources Evaluation in Northeast,Changehun 130061,China;Institute of Geology,Chinese Academy of Geological Sciences,Belling 100037,China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]国土资源部东北亚矿产资源评价重点实验室,长春130061 [3]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2018年第12期3627-3642,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41472164);中国地质调查局地质调查项目(D1434-3)联合资助

摘　　要：浙西南松阳地区的八都群中分布有一套基性变质岩:石榴辉石岩与石榴角闪岩,其变质作用演化特点目前尚不明确。根据岩相学和矿物微区化学系统研究,发现石榴角闪岩是由石榴辉石岩退变而来,而非由榴辉岩退变而来,并经历了三个变质演化阶段,分别为峰期高压麻粒岩相阶段(M1),其矿物组合为石榴石+次透辉石±钛铁矿±石英;峰后近等温减压中压麻粒岩相退变质阶段(M2),以出现典型的减压反应结构和斜方辉石+斜长石(An_(90-92))为标志;角闪岩相退变质阶段(M3),以角闪石+斜长石(An_(33-53))+钛铁矿±次透辉石±石英等退变矿物组合为特征。相平衡模拟与传统地质温压计结合限定M1期温压条件为P=11. 6～12. 5kbar,T=780～840℃,M2期温压条件为P=7. 4～8. 2kbar,T=800～880℃,M3期温压条件为P=6. 6～7. 5kbar,T=500～560℃,三个变质阶段的温压条件具有典型的顺时针近等温减压型ITD型特征,这种演化轨迹通常代表加厚下地壳快速折返地表的动力学过程,因此,该项研究对华夏地块构造作用演化的动力学过程具有重要意义。There is a set of mafic metamorphic rock: garnet pyroxenite and garnet amphibolite in the Badu Group of Songyang area,southwestern Zhejiang Province,metamorphism evolution of which is still unclear. In this study,on the basis of the investigation of petrography and mineral chemistry,it was found that garnet amphibolite was degenerated from garnet pyroxenite rather than eclogite,and has experienced three stages of metamorphic evolution. Peak high-pressure granulite facies stage( M1) consists of garnet + sahlite± ilmenite ± quartz. Post-peak near isothermal decompression medium granulite facies stage( M2) is characterized by typical decompression reaction textures and mineral assemblages of orthopyroxene + plagioclase( An = 90 ~ 92),and amphibolite-facies retrograde metamorphic stage( M3) is characterized by the assemblage of amphibole + plagioclase( An = 33 ~ 53) + ilmenite ± sahlite± quartz. By means of phase equilibrium simulation and traditional thermobarometer,P-T conditions of 11. 6 ~ 12. 5 kbar and 780 ~840℃ for M1,7. 4 ~ 8. 2 kbar and 800 ~ 880℃ for M2,and 6. 6 ~ 7. 5 kbar and 500 ~ 560℃ for M3 were obtained. These temperature and pressure conditions confined a typical clockwise P-T path dominated by near isothermal decompression characteristic( ITD). This evolutionary trajectory usually represents the dynamic process of thickening the lower crustal and subsequently rapid exhumation to the surface,which has significant implication for the tectonic evolution of the Cathaysia block.

关 键 词：石榴辉石岩 石榴角闪岩 变质作用演化 八都群 浙西南 

分 类 号：P588.34[天文地球—岩石学]