东秦岭松树沟高压变质基性岩石及其退变质作用的PTt演化轨迹

High Pressure Metabasites and Their Retrograde Metamorphic P-T-t Path from Songshugou Area,Eastern Qinling Mountain

在北秦岭商南松树沟出露的高压变质基性岩石，包括高压基性麻粒岩和石榴单斜辉石岩，遭受了从中压麻粒岩相、高角闪岩相到绿帘角闪岩相的连续的退变质作用的改造。这些岩石形成的温度为８２６℃～８８７℃，压力约为１．４０～１．５８ＧＰａ，其不同退变质阶段的温压条件依次分别是７６５℃～８２５℃和约１．０３～１．１４ＧＰａ、６５０℃～７５０℃和约０．９ＧＰａ以及４００℃～５００℃和约０．５～０．６ＧＰａ。它们共同构成一个早期近等温降压（ＩＴＤ）和晚期降温降压的顺时针ＰＴｔ演化轨迹。结合高压岩石９８３±１４０Ｍａ的退变质年龄和松树沟残存的蛇绿岩片考虑，这些高压岩石的形成和抬升与秦岭造山带中、晚元古宙时期洋壳的俯冲、消减和陆块碰撞伴随的快速构造上升作用有关。

The high pressure metabasites, including basic high--pressure granulite and garnetclinopyroxenite. having undergone successive complicated retrograde metamorphism from median pressure granulite facies through amphibolite facies to epidote-amphibolite factes in Shangnan Songshugou area of the northern Qinling mountain have been recognized with the study results of petrography, mineral chemistry and metamorphic P-T condition. The high pressure metabasites were estimated to form at temperature 826℃~ 887℃ and pressure 1. 40~ 1. 58GPa and its P-T conditions of different retrograde metamorphic stages are 765℃ ~825℃ at 1. 03~ 1.14GPa, 650℃ ~ 750℃ at approximately 0. 90GPa and 400℃ ~ 500℃ at 0. 5~ 0.6GPa, respectively, all of which reconstruct a former stage of near-isothermal decompression (ITD) and a later stage of clockwise P-T-t path. The facts mentioned above connecting with the retrograde metamorphic dating of 983± 140Ma from the high pressure rocks and the remains of ophiolite sheet in Songshugou area suggest that the formation and uplift of these high pressure metabasites are related to subduction of ocean crust and collision between continental segment as well as associated with rapid uplift especially in Middle to Late Proterozoic in the Qinling orogenic zone.