青藏高原东南缘哀牢山构造带泥质高压麻粒岩的发现及其构造意义

哀牢山构造带泥质高压麻粒岩主要由石榴石、夕线石、钾长石和斜长石变斑晶及尖晶石、铁假蓝宝石、蓝晶石、石英、金红石和钛铁矿包裹体组成,为确定印支地块和华南地块的边界提供了关键性标志。石榴石-黑云母-斜长石-石英地质温压计(GBPQ)计算结果及标志性高温矿物组合(Spl+Qz)表明泥质高压麻粒岩的形成和演化经历了高压/高温进变质到中温/低压退变质的顺时针P-T演化过程。其中:1)高压/高温进变质阶段的矿物组合为Ky+Sil+Grt1+Kf1+Pl1+Spr+Ter(Kf+Pl)+Bt1+Spl+Qtz+Ilm1+Rut1,形成于850～919℃,≥10.4kbar;2)中温/低压退变质阶段的矿物组合为Grt2+Bt2+Pl2+Ms+Qtz+Ilm2+Rut2,早期和晚期的温压条件分别为664～754℃,4.9～6.5kbar和572～576℃,3.5～3.9kbar。反映陆壳物质在碰撞过程中俯冲到地下深处(≥30km)经高压高温变质后快速折返到中上地壳的动力学演变轨迹。

Discovery of high-pressure pelitic granulite in Ailaoshan orogenic belt, southeastern Tibet, and its tectonic implications

High-pressure pelitic granulite containing porphyroblasts of garnet(Grt),sillimanite(Sil),K-feldspar(Kf) and plagioclase(Pl),and inclusions of spinel(Spl),kyanite(Ky),sapphirine(Spr) and rutile(Rut) have been found from the Ailaoshan orogenic belt,southeastern Tibet,regarded as a key indicator for identification of the boundary between the Indochina and South China blocks.The temperatures and pressures calculated by garnet-biotite-plagioclase-quartz geothermobarometery and hightemperature equilibrium spinel + quartz assemblage show the formation and evolution of the graunlite had experienced clockwise P-T path from high-pressure/-temperature to mid-temperature and low-pressure metamorphism.That are:1) the high-pressure/-temperature metamorphism(HP/HT) is characterized by an assemblage of Ky + Sil + Grt1 + Kf1 + Pl1 + Spr + Ter(Kf + Pl) + Bt1 + Spl + Qtz + Ilm1 + Rut1,and the peak P-T conditions of ≥ 10.4kbar at 850 ～ 919℃;2) the mid-temperature and low-pressure retrogressive metamorphism characterized by an assemblage of Grt2 + Bt2 + Pl2 + Ms + Qtz + Ilm2 + Rut2,and two stage P-T conditions of 4.9 ～ 6.5kbar at 664 ～ 754℃ and 3.5 ～ 3.9kbar at 572 ～ 576℃ respectively.The dynamic metamorphic path was that the metapelitic rock experienced high-pressure/-temperature granulite-facies metamorphism in lower continental crust(≥30km) exhumated to mid-upper crust rapidly,it might be related to the continental collision and underthrusting between the Indochina and South China blocks,and exhumation and slip shearing lately.