青藏高原羌塘高压变质带的特征及其构造意义
High-pressure metamorphic belt in Qiangtang, Qinghai-Tibet Plateau, and its tectonic significance.
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摘要: 羌塘高压变质带分布于龙木错－双湖板块缝合带的南侧，西起红脊山，经片石山、蓝岭、角木查尕日、纳若,到双湖以东的才多茶卡,长约500km。向东已经延伸到巴青以北和昌都的吉塘地区，再向南进入滇西与澜沧江蓝片岩带共同构成一条断续延伸近2000km的高压变质带。羌塘高压变质带主要由蓝片岩和榴辉岩构成，蓝闪石片岩中蓝闪石和多硅白云母同位素定年结果为223～215Ma，榴辉岩的变质年龄为243～217Ma。估算蓝片岩的变质温度为410～460℃，变质压力为0.67～0.75GPa；榴辉岩相的变质作用温度不超过500℃，压力为1.56～2.35GPa。羌塘高压变质岩定年研究结果确定龙木错－双湖板块缝合带最终碰撞闭合发生在晚三叠世早期。羌塘高压变质带是冈瓦纳与欧亚大陆汇聚事件的重要记录。Abstract: The Qiangtang high-pressure (HP) metamorphic belt is distributed for ~500 km from Hongjishan eastward through Pianshishan, Lanling, Jiaomuchagari and Naruo to Caiduo Caka east of Shuanghu, tectonically on the southern side of the Lungmu Co-Shuanghu suture zone. Eastward the belt extends to north of Baqên and in the Gyitang area of Qamdo and connects with the Lancangjiang blueschist belt to form a HP metamorphic belt extending discontinuously nearly 2000 km. The Qiangtang HP metamorphic belt is composed mainly of blueschist and eclogite. Isotopic dating of glaucophane and phengite from blueschist yielded ages of 223 to 215 Ma and the metamorphic ages of eclogite range from 243 to 217 Ma. The metamorphic temperatures and pressures of blueschist are 410-460℃ and 0.67-0.75 GPa and those of eclogite are less than 500℃ and 1.56-2.35 GPa. The dating results of HP metamorphic rocks suggest that the final collision of the Lungmu Co-Shuanghu suture zone occurred in the early stage of the Late Triassic, and this HP belt is an important record of the convergence between Gondwana and Eurasia.
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