TY - JOUR
T1 - Discovery of coesite from Indus Suture Zone (ISZ), Ladakh, India
T2 - Evidence for deep subduction
AU - Sachani, Himanshu K.
AU - Mukherjee, Barun K.
AU - Ogasawara, Yoshihide
AU - Maruyama, Shigenori
AU - Ishida, Haruhito
AU - Muko, Atsumi
AU - Yoshioka, Nobuhiro
PY - 2004/3
Y1 - 2004/3
N2 - 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 polycrystalline 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.
AB - 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 polycrystalline 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.
KW - Coesite
KW - Garnet
KW - Raman spectroscopy
KW - Tso-Morari
KW - UHP eclogite
KW - Western Himalaya
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U2 - 10.1127/0935-1221/2004/0016-0235
DO - 10.1127/0935-1221/2004/0016-0235
M3 - Article
AN - SCOPUS:2142829560
SN - 0935-1221
VL - 16
SP - 235
EP - 240
JO - European Journal of Mineralogy
JF - European Journal of Mineralogy
IS - 2
ER -