HR: 1340h
AN: T33C-1496    [Abstracts]
TI: Preferential Acceleration of Pressure Solution Creep of Shear Zones in Shale of Subduction Zone
AU: * KAWABATA, K
EM: kuniyo@eps.s.u-tokyo.ac.jp
AF: The University of Tokyo, Graduate school of Science Hongo 7 - 3 - 1, Bunkyo-ku, Tokyo, 1130033, Japan
AU: TANAKA, H
EM: tanaka@eps.s.u-tokyo.ac.jp
AF: The University of Tokyo, Graduate school of Science Hongo 7 - 3 - 1, Bunkyo-ku, Tokyo, 1130033, Japan
AB: We have estimated activation energy of natural pressure solution deformation in shales of the Shimanto accretionary complex in southwestern Shikoku Island, Japan. Pressure solution deformation affected two types of shales: shear-dominated (type S) and compaction-dominated (type C) shales. Additionally, within each type of shale, pressure solution seams (PSS) density, indicative of the intensity of the deformation, is highly variable in relation with a relatively wide range of paleotemperature [Kawabata et al., 2007]. Correlating the PSS density and the paleotemperature with an Arrhenius expression, we extracted low activation energies of 18 kJ/mol for type S and 45 kJ/mol for type C. The good agreement between these values and the activation energy of diffusion controlled pressure solution creep (approximately 35kJ/mol), which is sum of activation energy of diffusion coefficient through grain boundary fluid (15kJ/mol) [Nakashima, 1995] and equilibrium constant of silica (20kJ/mol) [Rimstidt and Barnes, 1980], as well as our microstructural observations, show that diffusion is indeed the controlling process of pressure solution deformation. Difference in activation energy between Type S and Type C is probably caused by grain boundary structure, which can be either wetted (connected) or non-wetted (non-connected) [Nakashima, 1995]. Shear deformation, active in type S shales, creates more wetted (connected) grain boundary than compaction in type C shales, resulting in smaller activation energy. Such interplay between shear deformation and the fluid phase structure promotes the localization of deformation within shear zones deforming by pressure solution.
DE: 3902 Creep and deformation
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8036 Paleoseismology (7221)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting