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在青藏高原安多微陆块中发现了高压基性麻粒岩,其峰期矿物组合为石榴子石+单斜辉石+石英+金红石.该高压麻粒岩经历了两期退变质作用,退变质矿物呈后成合晶产状,早期退变质矿物组合是Opx+Pl±Spl,晚期退变质矿物组成是Hbl+Pl.温度与压力计算表明,高压麻粒岩相峰期变质温度为860~920℃,压力为14.6~15.6kbar;早期退变质的形成温压为820~890℃和8.8~11.5kbar;晚期退变质条件为550~670℃和5.2~6.5kbar.其退变质作用P-T轨迹为顺时针型近等温降压到降温降压的过程,指示该麻粒岩经历了俯冲至深部地壳层位(~50km),之后又快速抬升到浅部地壳(~20km)的变质过程.该高压麻粒岩的形成可能与安多微陆块和羌塘地体中生代时期的弧-陆碰撞作用有关,这对探讨青藏高原的构造演化具有重要的意义.
High-pressure basic granulites have been found in the Ando micro-block of the Qinghai-Tibetan Plateau, and their peak mineral assemblages are garnet + clinopyroxene + quartz + rutile. The high-pressure granulite experienced two retrogressive metamorphism, The retrograded metamorphic minerals are in the form of postcrystallization. The early retrogressive mineral assemblages are Opx + Pl ± Spl and the late retrograded metamorphic minerals are Hbl + Pl. The calculation of temperature and pressure shows that the peak metamorphic temperature of high-pressure granulite facies is 860 ~ 920 ℃, and the pressure is 14.6 ~ 15.6kbar. The formation temperature of early degenerated matter is 820 ~ 890 ℃ and 8.8 ~ 11.5kbar, while the late degenerated conditions are 550 ~ 670 ℃ and 5.2 ~ 6.5kbar. The degenerated PT trajectory is The clockwise isothermal depressurization to temperature-depressurization process indicates that the granulite experienced subduction to deep crust (~ 50km) and then rapidly uplifted into the metamorphic process of the shallow crust (~ 20km) The formation of granulite may be related to the Arc-Continent collision during the Mesozoic in the Ando micro-block and the Qiangtang terrane, which is of great significance to the study of the tectonic evolution of the Qinghai-Tibet Plateau.