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Episodic and constant flow models for the origin of low‐chloride waters in a modern accretionary complex
Author(s) -
Bekins Barbara A.,
McCaffrey Anne M.,
Dreiss Shirley J.
Publication year - 1995
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/95wr02569
Subject(s) - geology , seafloor spreading , décollement , fault (geology) , permeability (electromagnetism) , petrology , accretionary wedge , consolidation (business) , chloride , dehydration , pore water pressure , mineralogy , geomorphology , geotechnical engineering , seismology , subduction , geophysics , tectonics , materials science , chemistry , biochemistry , accounting , membrane , metallurgy , business
Some low‐chloride pore waters observed in accretionary complexes are thought to result from clay dehydration and subsequent migration of the released water along faults or sand layers. We test this hypothesis with a two‐dimensional flow and transport model for a cross section of the northern Barbados accretionary complex. The model flow system is driven by consolidation of the accreted sediments and by fluids from smectite clay dehydration. Steady state simulations result in concentrations that are too high along the décollement fault and too low near the seafloor. In a transient model we simulate buildup and release of fluids by assuming that strain or hydrofracture along the fault causes an instantaneous increase in décollement permeability of 2–3 orders of magnitude. With such an increase, the observed concentrations can be achieved in 100–1000 years. Also pressures along the fault rise to near lithostatic values in 10–100 years and remain high for 1000–10,000 years. This pressure rise may represent a mechanism for sustaining high fault permeabilities long after the initial increase.