Metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet-staurolitemuscovite schists in central Qiangtang, Tibet
Metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet-staurolitemuscovite schists in central Qiangtang, Tibet
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西藏羌塘中部石榴石-十字石白云母片岩揭示的俯冲侵蚀和随后的底侵过程的变质记录
DOI：
10.1002/2016gc006576
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Ming-Liang Huang
中科院分区：
文献类型：
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作者：
Xiu-Zheng Zhang;Yong-Sheng Dong;Qiang Wang;Wei Dan;Chunfu Zhang;Wang Xu;Ming-Liang Huang
通过对现代辐合板块边缘的地质、地球化学和地球物理观测，证实了俯冲侵蚀是地壳再循环的一个重要地球动力学过程。到目前为止，还没有一个单一的变质记录被用来约束俯冲侵蚀的一般构造演化。物源分析表明，石榴石-小辉石-白云母片岩原岩具有北强塘亲和性，形成于活动大陆边缘环境。矿物包裹体资料显示，早变质期（M1）录得0.8 ~ 1.1 GPa、402 ~ 4418c的蓝片岩相压力-温度（P-T）条件，表明上覆板块部分物质被磨入俯冲通道，经历了高压/低温变质作用。峰变质期（M2）记录角闪岩相P-T条件为0.3 ~ 0.5 GPa, 470 ~ 5208c。白云母的40Ar/39Ar冷却年龄（263 ~ 259 Ma）表明角闪岩相变质作用（> ~ 263 Ma）发生在大洋俯冲阶段。阶段分明的变质作用确定了一条顺时针和升温的P-T-t减压路径，揭示了早期俯冲侵蚀后的下覆过程。在构造过程中，受侵蚀的低密度物质从冷俯冲通道中逸出，向上进入温暖的上板块中下地壳，发生角闪岩相变质作用。我们的新结果揭示了古特提斯洋北俯冲过程中从早期俯冲侵蚀到随后的海底沉积的完整演化过程。
Subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological, geochemical, and geophysical observations at modern convergent plate margins. So far, not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion. Here we first revealed metamorphic records for a subduction erosion process based on our study of the Late Paleozoic garnet-staurolite-muscovite schists in the central Qiangtang block, Tibet. Provenance analyses suggest that the protoliths of garnet-staurolite-muscovite schists have the Northern Qiangtangaffinity and were deposited in an active continental margin setting. Mineral inclusion data show that the early metamorphic stage (M1) recorded blueschist facies pressure-temperature (P-T) conditions of 0.8–1.1 GPa and 402–4418C, indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high-pressure/low-temperature metamorphism. The peak metamorphic stage (M2) recorded amphibolite facies P-T conditions of 0.3–0.5 GPa and 470–5208C. The 40Ar/39Ar cooling ages (263–259 Ma) yielded from muscovite suggest the amphibolite facies metamorphism (>263 Ma) occurred at oceanic subduction stage. The distinctly staged metamorphism defines a clockwise and warming decompression P-T-t path which reveals an underplating process following the early subduction erosion. During the tectonic process, the eroded low-density material escaped from the cold subduction channel and rise upward into the warm middle-lower crust of the upper plate, undergoing amphibolite facies metamorphism. Our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the Paleo-Tethys Ocean.