Structure, inferred mechanical properties, and implications for fluid transport in the décollement zone, Costa Rica convergent margin

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doi: 10.1130/0091-7613(2001)029<0907:SIMPAI>2.0.CO;2
Author(s): Tobin, Harold; Vannucchi, Paola; Meschede, Martin
Author Affiliation(s): Primary:
New Mexico Institute of Mining and Technology, Department of Earth and Environmental Science, Socorro, NM, United States
Università di Modena, Italy
University of Tübingen, Federal Republic of Germany
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 29(10), p.907-910. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. 17 refs.; illus., incl. sects., sketch map
Summary: Faults in a variety of tectonic settings can act as both conduits for and barriers to fluid flow, sometimes simultaneously. Documenting the interaction between hydrologic and tectonic processes in active faults in situ is the key to understanding their mechanical behavior and large-scale fluid transport properties. We present observations of the plate boundary décollement zone at the Middle America Trench off Costa Rica, showing that it is structurally divisible into an upper brittle-fracture-dominated domain overlying a lower, ductile domain. Pore-water geochemical evidence shows that along-fault flow is occurring specifically in the upper brittle domain, but is hydrologically isolated from fluids in the underlying footwall sediments. We propose a model for the mechanics of these contrasting domains in which differing stress paths coexist in the upper and lower parts of the décollement zone. The data suggest a mechanically controlled permeability anisotropy at a scale of several meters to ∼10 m across the décollement zone. This documentation of separate yet simultaneously active mechanical and hydrologic subregimes within a décollement provides a relatively simple explanation for enhanced along-fault permeability coexisting with reduced cross-fault permeability, without requiring matrix-scale permeability anisotropy.
Year of Publication: 2001
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Active faults; Anisotropy; Central America; Cocos Plate; Continental margin; Costa Rica; Decollement; East Pacific; Fault zones; Faults; Fluid dynamics; Geochemistry; Hydrochemistry; Leg 170; Marine sediments; Mechanical properties; Middle America Trench; North Pacific; Northeast Pacific; ODP Site 1039; ODP Site 1040; ODP Site 1043; Ocean Drilling Program; Pacific Ocean; Permeability; Plate convergence; Plate tectonics; Pore water; Sediments; Stress; Subduction zones; Well logs
Coordinates: N093943 N093943 W0861045 W0861045
N093916 N093916 W0861109 W0861109
N093823 N093823 W0861200 W0861200
Record ID: 2001073328
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States