The impact of splay faults on fluid flow, solute transport, and pore pressure distribution in subduction zones; a case study offshore the Nicoya Peninsula, Costa Rica

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doi: 10.1002/2014GC005638
Author(s): Lauer, Rachel M.; Saffer, Demian M.
Author Affiliation(s): Primary:
University of California, Department of Earth and Planetary Sciences, Santa Cruz, CA, United States
Other:
Pennsylvania State University, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 16(4), p.1089-1104. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 96 refs.; illus., incl. 1 table
Summary: Observations of seafloor seeps on the continental slope of many subduction zones illustrate that splay faults represent a primary hydraulic connection to the plate boundary at depth, carry deeply sourced fluids to the seafloor, and are in some cases associated with mud volcanoes. However, the role of these structures in forearc hydrogeology remains poorly quantified. We use a 2-D numerical model that simulates coupled fluid flow and solute transport driven by fluid sources from tectonically driven compaction and smectite transformation to investigate the effects of permeable splay faults on solute transport and pore pressure distribution. We focus on the Nicoya margin of Costa Rica as a case study, where previous modeling and field studies constrain flow rates, thermal structure, and margin geology. In our simulations, splay faults accommodate up to 33% of the total dewatering flux, primarily along faults that outcrop within 25 km of the trench. The distribution and fate of dehydration-derived fluids is strongly dependent on thermal structure, which determines the locus of smectite transformation. In simulations of a cold end-member margin, smectite transformation initiates 30 km from the trench, and 64% of the dehydration-derived fluids are intercepted by splay faults and carried to the middle and upper slope, rather than exiting at the trench. For a warm end-member, smectite transformation initiates 7 km from the trench, and the associated fluids are primarily transmitted to the trench via the decollement (50%), and faults intercept only 21% of these fluids. For a wide range of splay fault permeabilities, simulated fluid pressures are near lithostatic where the faults intersect overlying slope sediments, providing a viable mechanism for the formation of mud volcanoes. Abstract Copyright (2015), American Geophysical Union. All Rights Reserved.
Year of Publication: 2015
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Active margins; Case studies; Central America; Clay minerals; Cocos Plate; Costa Rica; Dehydration; East Pacific; Faults; Fluid flow; Ground water; Heat flow; Leg 170; Leg 205; Mud volcanoes; Nicoya Peninsula; North Pacific; Northeast Pacific; Numerical models; ODP Site 1039; ODP Site 1040; ODP Site 1043; ODP Site 1254; Ocean Drilling Program; Ocean floors; Offshore; Pacific Ocean; Permeability; Plate boundaries; Plate tectonics; Pore pressure; Sheet silicates; Silicates; Smectite; Solute transport; Splay faults; Subduction zones; Tectonics; Thermal regime; Transport; Two-dimensional models
Coordinates: N090000 N110000 W0850000 W0863000
Record ID: 2016072008
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom, Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union