Discovery of coesite from Indus Suture Zone (ISZ), Ladakh, India: Evidence for deep subduction
Discovery of coesite from Indus Suture Zone (ISZ), Ladakh, India: Evidence for deep subduction
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DOI：
10.1127/0935-1221/2004/0016-0235
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发表时间：
2004-03
影响因子：
2.1
通讯作者：
H. Sachan;B. Mukherjee;Y. Ogasawara;S. Maruyama;H. Ishida;A. Muko;Nobuhiro Yoshioka
中科院分区：
文献类型：
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作者：
H. Sachan;B. Mukherjee;Y. Ogasawara;S. Maruyama;H. Ishida;A. Muko;Nobuhiro Yoshioka
柯石英，石英的高压多晶型物，首次在喜马拉雅带拉达克（印度）的Tso-Morari结晶杂岩中被发现。柯石英以包裹体形式保存在榴辉岩石香肠中的石榴石中，表明在大陆碰撞背景下存在超高压变质作用。柯石英经光学鉴定，其存在由其特征拉曼谱带证实。柯石英和多晶石英包裹体在其寄主石榴石中均表现出明显的放射状裂隙。硅质包裹体（单矿物柯石英、单矿物石英和双矿物石英+柯石英）与石榴子石内部的各种结构特征和发育的化学分带有关，显示了超高压变质作用的侵入性。初步的P-T估计表明柯石英生长发生在压力> 28 kbar（> 90 km深度）和温度> 640°C的条件下。值得注意的是，柯石英包裹体被解释为在折返过程中经历了减压而没有变成石英，这很可能是由于快速隆起。这一发现也表明印度板块在亚洲大陆之下的深度俯冲。柯石英的出现和印度板块的俯冲基本上是由一个低的地热梯度，发生在快速折返。这对于形成超高压岩石的变质作用和暴露的连贯图像至关重要。
Coesite, the high-pressure polymorph of quartz has been identified for the first time in the Tso-Morari Crystalline Complex, Ladakh (India) in the Himalayan belt. The preservation of coesite grains as inclusions in garnet within eclogite boudins indicates the existence of UHP metamorphism in this continental collision setting. The coesite was identified optically and its presence confirmed by its characteristic Raman bands. Both coesite and polycrys-talline quartz inclusions exhibit prominent radial fractures in their host garnet. The silica inclusions (monomineralic coesite, monomineralic quartz and bimineralic quartz+coesite) are associated with various textural features and well-developed chemical zonation within the garnet, which show the prograde nature of the UHP metamorphism. Preliminary P-T estimates suggest that the coesite growth took place at pressure > 28 kbar (> 90 km depth) and temperatures > 640°C. Significantly, the coesite inclusions are interpreted as having suffered decompression during exhumation without changing to quartz, most likely due to the rapid uplift. This finding also indicates deep subduction of the Indian plate beneath the Asian continent. The occurrence of coesite and subduction of the Indian plate was essentially governed by a low geothermal gradient which occurred prior to rapid exhumation. This was vital for generating the coherent picture of metamorphism and exposure of UHP rocks.