Long-term hydrogeochemical records in the oceanic basement and forearc prism at the Costa Rica subduction zone

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doi: 10.1016/j.epsl.2009.03.022
Author(s): Solomon, Evan A.; Kastner, Miriam; Wheat, C. Geoffrey; Jannasch, Hans; Robertson, Gretchen; Davis, Earl E.; Morris, Julie D.
Author Affiliation(s): Primary:
Scripps Institution of Oceanography, La Jolla, CA, United States
University of Alaska Fairbanks, United States
Monterey Bay Aquarium Research Institute, United States
Geological Survey of Canada, Canada
Washington University, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 282(1-4), p.240-251. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplemental information/data is available in the online version of this article. 62 refs.; illus., incl. sect., 1 table, geol. sketch map
Summary: Two sealed borehole hydrologic observatories (CORKs) were installed in two active hydrogeochemical systems at the Costa Rica subduction zone to investigate the relationship between tectonics, fluid flow, and fluid composition. The observatories were deployed during Ocean Drilling Program (ODP) Leg 205 at Site 1253, ∼0.2 km seaward of the trench, in the upper igneous basement, and at Site 1255, ∼0.5 km landward of the trench, in the decollement. Downhole instrumentation was designed to monitor formation fluid flow rates, composition, pressure, and temperature. The two-year records collected by this interdisciplinary effort constitute the first co-registered hydrological, chemical, and physical dataset from a subduction zone, providing critical information on the average and transient state of the subduction thrust and upper igneous basement. The continuous records at ODP Site 1253 show that the uppermost igneous basement is highly permeable hosting an average fluid flow rate of 0.3 m/yr, and indicate that the fluid sampled in the basement is a mixture between seawater (∼50%) and a subduction zone fluid originating within the forearc (∼50%). These results suggest that the uppermost basement serves as an efficient pathway for fluid expelled from the forearc that should be considered in models of subduction zone hydrogeology and deformation. Three transients in fluid flow rates were observed along the decollement at ODP Site 1255, two of which coincided with stepwise increases in formation pressure. These two transients are the result of aseismic slip dislocations that propagated up-dip from the seismogenic zone over the course of ∼2 weeks terminating before reaching ODP Site 1255 and the trench. The nature and temporal behavior of strain and the associated hydrological response during these slow slip events may be an analog for the response of the seaward part of the subduction prism during or soon after large subduction zone earthquakes. Abstract Copyright (2009) Elsevier, B.V.
Year of Publication: 2009
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Basement; Basins; Boreholes; Central America; Circulation Obviation Retrofit Kit; Costa Rica; Crust; Decollement; Downhole methods; Earthquakes; East Pacific; Fore-arc basins; Hydrochemistry; Instruments; Leg 205; Middle America Trench; North Pacific; Northeast Pacific; ODP Site 1253; ODP Site 1255; Observatories; Ocean Drilling Program; Ocean floors; Oceanic crust; Pacific Ocean; Permeability; Pore water; Sea water; Slow slip events; Subduction zones; Trenches
Coordinates: N093900 N093900 W0861100 W0861100
Record ID: 2009080749
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands