Subduction-induced pore fluid venting and the formation of authigenic carbonates along the cascadia continental margin: Implications for the global Ca-cycle.

Han, M. W. and Suess, Erwin (1989) Subduction-induced pore fluid venting and the formation of authigenic carbonates along the cascadia continental margin: Implications for the global Ca-cycle. Open Access Palaeogeography, Palaeoclimatology, Palaeoecology, 71 (1-2). pp. 97-118. DOI 10.1016/0031-0182(89)90032-1.

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Abstract

Pore fluid venting associated with subduction-induced sediment deformation causes precipitation of calcium carbonate as prominent carbonate chimneys or cement in the accreted sediments across the active continental margin off Oregon and Washington. A depletion of interstitial Ca2+ with a maximum decrease of 50% relative to seawater Ca2+ over only 1.5m depth and reduction in porosity in the deformed sediments suggest that interstitial Ca2+ is removed to form calcium carbonate cement. In contrast, the pore waters of the undeformed abyssal plain sediments show no depletion in dissolved Ca2+. They are either enriched to a maximum of 5% or show no change in dissolved Ca2+. Here the background level of CaCO3 content in the sediment is only 0.1 to 1%.

Calcium carbonate precipitation in the deformed sediments probably occurs as the result of upward migration and oxidation of biogenic methane and of the increase in carbonate saturation due to release of excess pore pressure during fluid venting. Upward advection of fluids at rates of 1–28 cm y−1 is predicted from diffusion-advection-reaction models applied to the downcore concentration profiles of dissolved Ca2+ and NH4+ in the tectonically-deformed sediments. The range of predicted flow rates is related to the type of calcium carbonate lithification; i.e. slow rates generate cement and fast rates generate chimneys.

Carbonate mineral precipitation associated with pore fluid venting requires direct transfer of Ca2+ from the oceanic basement to the accretionary complex. Such a mechanism leads us to propose that the accretionary complexes of the global plate subduction zones are a major sink for crustal Ca2+. A global flux of crustal Ca2+ that is removed by carbonate mineral precipitation may be as muc3 as the hydrothermal Ca-input. This significant Ca-flux, not previously considered in the global geochemical budget, implies that pore fluid venting in subduction zones may also act as a global sink or source for other elements.

Document Type: Article
Keywords: carbonates, Cascadia Continental Margin
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/0031-0182(89)90032-1
ISSN: 0031-0182
Date Deposited: 06 May 2019 08:18
Last Modified: 06 May 2019 08:38
URI: http://oceanrep.geomar.de/id/eprint/46582

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