中文摘要：

青藏高原班公湖-怒江结合带内中东段八宿、安多、蓬错西等地已有高压-超高压变质岩的报道,然而西段至今尚没有发现类似岩石出露。在班公湖-怒江西段改则洞错地区舍拉玛沟中发现高压麻粒岩（可能是退变榴辉岩）,岩石呈透镜状、似层状或块状产于斜长角闪岩及变质辉长岩中,详细的岩相学及矿物化学研究确认,早期矿物组合主要为石榴子石、单斜辉石及斜长石（大部分钠黝帘石化）,后期发生了较强烈的退变质作用,矿物组合为角闪石和斜长石,发育典型的＂白眼圈＂结构。利用LA-ICP-MS锆石U-Pb方法获得高压麻粒岩的原岩时代为254±2Ma,指示班公湖-怒江洋盆打开的时限可以追溯到晚二叠世。地质温压计估算结果表明,高压麻粒岩相变质作用发生的温度和压力条件为780-900℃和13-16k Pa,角闪岩相变质作用发生的温度和压力条件为430-480℃和4.5-5.2k Pa,极有可能是班公湖-怒江特提斯洋壳发生高压麻粒岩相（甚至达到榴辉岩相）变质作用的产物。它的发现说明在班公湖-怒江结合带内部存在高压变质带,可能是大洋深俯冲的产物,这对研究青藏高原特提斯洋的形成演化具有重要意义。

英文摘要：

A high pressure metamorphic （HP） and ultrahigh pressure metamorphic （UHP） belt is exposed in Baxoi, Amdo and Pengco areas along the middle-eastern Bangongco-Nujiang suture zone （BNSZ）. However, the similar HP-UHP metamorphic rocks have not discovered in the western section of BNSZ. In this paper, the authors first report the high-pressure granulite （probably retrograde eclogite） at Dongco area in the western section of the BNSZ. Dongco high-pressure granulite occurs in lenticular, stratoid and massive forms in plagioclase amphibolites and metamorphic gabbros. Based on the intensive study of petrology and mineralogical geochemistry, the authors hold that the HP granulite was made up of the early mineral assemblage of garnet （Grt）＋clinopyroxene （Cpx） ＋ plagioclase （PI） （mostly saussuritized） and the late massive retrograde mineral assemblages amphibole （Hb）＋plagioclase （Pl）. Garnets in high-pres- sure granulites are surrounded by plagioclase which forms the corona. LA-ICP-MS zircon U Pb dating yielded the age of original rock from the high-pressure granulite of 254±2Ma, indicating that the opening time ofBangong Co-Nujiang River oceanic basin can be traced to the Late Permian. Geological temperature pressure indicator shows that the temperature-pressure conditions ofhigh-pressure granulite phase are 780-900℃, 13 16kPa, while those of retrogressive metamorphic amphibolite phase are 430-480℃, 4.5- 5.2kPa, respectively, suggesting that the high-pressure granulites were most likely the product of granulite facies （even eclogite facies） high pressure metamorphism of the Bangong Co-Nujiang River Tethyan oceanic crust. The discovery of Dongco high pressure granulites shows that a high-pressure metamorphic belt might exist within the BNSZ, and might have been formed by the deep subduction of the Bangong Co-Nujiang River Tethyan Ocean. Further study of the high-pressure granulites is of great significance for recognizing the deep subduction process, continent continent