HR: 10:50h
AN: T12B-03    [Abstracts]
TI: Dynamic interaction between pore fluids and faulting along the Costa Rica D‚collement (ODP Legs 170 and 205)
AU: * Vannucchi, P
EM: paolav@geo.unifi.it
AF: Dip. Scienze della Terra, Universita' di Firenze Via La Pira, 4, Firenze, 50121 Italy
AU: Leoni, L
EM: lorenzoleoni@aliceposta.it
AF: Dip. Scienze della Terra, Universita' di Firenze Via La Pira, 4, Firenze, 50121 Italy
AU: Tobin, H
EM: tobin@nmt.edu
AF: Dept. Earth and Environmental Sciences, New Mexico Tech, Socorro, NM 87801 United States
AU: Saffer, D
EM: dsaffer@geosc.psu.edu
AF: Dept. Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AB: The long-term, accretionary or erosive, tectonic regime of subduction zones controls the sedimentary budget, affecting the dewatering condition of the material within the d‚collement zone. The d‚collement at the erosive Costa Rica margin, drilled in 1996 and 2001 by ODP Legs 170 and 205, cuts through the sediment of the frontal prism, formed by material transferred from the slope. To understand how fragment size distribution along the brecciated fault zone influences fluid distribution along the plate boundary and the mechanical behavior of the d‚collement we analyzed the fault at 4 sites. The analysis allows to estimate the processes linked to fragmentation and shear zones localization describing the evolution of frictional and permeability properties of the fault zone. Borehole observations have been supported by thin section analysis across the entire thickness of the fault. The d‚collement is formed by an upper thick brecciated horizon (10 to 50 m) and a lower thin (1 to 10 cm) shear zone. The analysis suggests that the brecciated horizon has produced by : a) cataclasis triggered by increasing effective confining stress which inhibits grain boundary sliding (stress concentration exceeds sediment strength) and b) hydrofracturing. The basal shear zone accommodated the slip. Since fluids contributed to shape the fault zone and influenced its hydrogeological and mechanical properties, the understanding of these processes require the knowledge of fluid composition and the architecture of the porous network.
DE: 3036 Ocean drilling
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8030 Microstructures
SC: Tectonophysics [T]
MN: Fall Meeting 2005