阿尔金淡水泉花岗质高压麻粒岩P-T演化及年代学研究

P-T path and geochronology of high pressure granitic granulite from Danshuiquan area in Altyn Tagh

岩相学研究表明阿尔金南缘淡水泉一带出露的花岗质片麻岩的峰期矿物组合为Grt＋Kfs＋Ky＋Rt＋Qz,为典型的高压麻粒岩相矿物组合。利用Thermocalc3.33程序计算的P-T视剖面图和矿物温压计,确定其峰期变质温压条件为T=875~925℃,P=14.5~15.9kbar,该岩石后期还经历了以矿物组合Grt＋Kfs＋Bt＋Pl＋Sill＋Ilm＋Qz为代表的麻粒岩相和以Sill＋Bt＋Pl＋Mu＋Qz±Ilm为代表的角闪岩相的退变质作用,具有一个早期快速等温降压,后期近等压降温的顺时针型的退变质P-T演化轨迹。锆石的U-Pb同位素定年结果显示其原岩的时代为866±5Ma,峰期变质时代为505±5Ma。其中该岩石原岩的形成时代与阿尔金及其周缘地区广泛发育的由Rodinia超大陆裂解事件导致的岩浆活动时代一致,而峰期变质时代则与南阿尔金高压/超高压变质岩的峰期变质时代（486~509Ma）一致,说明花岗片麻岩原岩的形成与罗迪尼亚超大陆裂解有关,并在早古生代卷入了陆壳深俯冲事件,构成了南阿尔金高压/超高压变质带的一部分。

A microstructural study of the granitic gneiss from Danshuiquan area in Altyn Tagh shows the peak metamorphic mineral assemblage of Grt ＋ Kfs ＋ Ky ＋ Rt ＋ Qz, which is the typical high pressure granulite facies mineral assemblage. Based on the THERMOCALC 3.33 and geothermobarometer, the peak P-T condition of the granulite is estimated to be T = 875 - 925℃ and P = 14. 5 - 15.9kbar and the post -peak metamorphic mineral assemblages in granulite and amphibolite facies charactericticed by the mineral assemblages of Grt ＋ Kfs ＋ Bt ＋ P1 ＋ Sill ＋ Ilm ＋ Qz and Sill ＋ Bt ＋ P1 ＋ Mu ＋ Qz ＋ Ilm, respectively, showing a clockwise retrograde metamorphic P-T path with early decompression and late isobaric cooling. The U-Pb zircon ages reveal that the protolith age of granulite is 866 ＋ 5Ma and the peak metamorphism occurred at 505 ＋ 5Ma. Combining with previous researches, the formation of the protolith of granulite could be related with the breakup of Rodinia, which had become involved in continental deep subduction-collision process during Early Paleozoic, and become part of the South Altyn Tagh HP/UHP metamorphic belt.