HR: 0800h
AN: V41C-0714    [Abstracts]
TI: On the Microstructure of Omphacite in Eclogite from Dabie Mountains, China
AU: * Liu, X
EM: xwliu@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China
AU: Jin, Z
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China
AU: Jin, Z
AF: Faculty of Earth Sciences, China University of Geosciences, Wuhan, 430074, China
AU: Wang, L
AF: Dept. of Marine Geology, Ocean University of China, Qingdao, 266100, China
AU: Zhang, J
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China
AU: Zhang, J
AF: Faculty of Earth Sciences, China University of Geosciences, Wuhan, 430074, China
AB: Observations of omphacite in eclogite from Shuanghe massif of Dabie Mountains, Eastern China by transmission electron microscope show banded subgrains of omphacite with C2/c space group and high dislocation densities exist in the matrix of omphacite with P2/n space group and low dislocation density. Barrosites and albites are distributed along with the banded omphacite subgrains defined by dislocation walls. Based on the P-T path of eclogite and jadeite-quartzite from Shuanghe, we studied the relationship of barrosites, albites, and omphacites. Our results suggest that the banded C2/c omphacite subgrains were formed by dynamic recrystallization under high pressure and temperature during the UHP metamorphic peak stage and/or early exhumation stage. The barrosite and albite should form within the C2/c omphacite before it transforms to P2/n structure at T > 700 °C during exhumation. The omphacite preserves its C2/c structure because of the loss of Na component to the albite. This evolution processes suggest that the P-T path of retrogression of eclogite and jadeite-quartzite from Shuanghe should move toward the high temperature side comparing to previous studies. Barrosites formed under high-pressure before the C2/c to P2/n transformation in omphacite indicates that nominally anhydrous omphacite can preserve considerable amounts of water at great depth. Barrosites and albites distributed along with the high dislocation zones of omphacite suggest that dislocation tubes may act as channels and reservoirs that transport active components including the hydroxyls.
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3625 Petrography, microstructures, and textures
DE: 3652 Pressure-temperature-time paths
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting