Using the 87Sr/86Sr of modern and paleoseep carbonates from northern Cascadia to link modern fluid flow to the past

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doi: 10.1016/j.chemgeo.2012.10.020
Author(s): Joseph, C.; Torres, M. E.; Martin, R. A.; Haley, B. A.; Pohlman, J. W.; Riedel, M.; Rose, K.
Author Affiliation(s): Primary:
Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, United States
Other:
Burke Museum, United States
U. S. Geological Survey, United States
Geological Survey of Canada, Canada
U. S. Department of Energy National Energy Technology Laboratory, United States
Volume Title: Chemical Geology
Source: Chemical Geology, Vol.334, p.122-130. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541 CODEN: CHGEAD
Note: In English. 57 refs.; illus., incl. 2 tables, sketch map
Summary: Most authigenic carbonates previously recovered from the Cascadia slope have 87Sr/86Sr signatures that reflect shallow precipitation in equilibrium with coeval seawater. There is also evidence for carbonate formation supported by fluids that have been modified by reactions with the incoming Juan de Fuca Plate (87Sr/86Sr=0.7071; Teichert et al., 2005) or with terrigenous turbidites (87Sr/86Sr=0.70975 to 0.71279; Sample et al., 1993). We report on the strontium isotopic composition of carbonates and fluids from IODP Site U1329 and nearby Barkley Canyon (offshore Vancouver Island), which have strontium isotope ratios as low as 0.70539. Whereas the strontium and oxygen isotopic compositions of carbonates from paleoseeps in the uplifted Coast Range forearc indicate formation in ambient bottom seawater, several samples from the Pysht/Sooke Fm. show a 87Sr-depleted signal (87Sr/86Sr=0.70494 and 0.70511) similar to that of the anomalous Site U1329 and Barkley Canyon carbonates. Our data, when analyzed in the context of published elemental and isotopic composition of these carbonates (Joseph et al., 2012), point to two formation mechanisms: 1) shallow precipitation driven by the anaerobic oxidation of methane (AOM) with δ13C values as low as -50 ppm and contemporaneous 87Sr/86Sr seawater ratios, and 2) carbonate precipitation driven by fluids that have circulated through the oceanic crust, which are depleted in 87Sr. Carbonates formed from the second mechanism precipitate both at depth and at sites of deep-sourced fluid seepage on the seafloor. The 87Sr-depleted carbonates and pore fluids found at Barkley Canyon represent migration of a deep, exotic fluid similar to that found in high permeability conglomerate layers at 188mbsf of Site U1329, and which may have fed paleoseeps in the Pysht/Sooke Fm. These exotic fluids likely reflect interaction with the 52-57Ma igneous Crescent Terrane, which supplies fluids with high calcium, manganese and strontium enriched in the non-radiogenic nucleide. Tectonic compression and dehydration reactions then force these fluids updip, where they pick up the thermogenic hydrocarbons and 13C-enriched dissolved inorganic carbon that are manifested in fluids and carbonates sampled at Barkley Canyon and at Site U1329. The Crescent Terrane may have sourced cold seeps in this margin since at least the late Oligocene. Abstract Copyright (2012) Elsevier, B.V.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; Aliphatic hydrocarbons; Alkaline earth metals; Alkanes; Authigenic minerals; Barkley Canyon; C-13/C-12; Carbon; Carbonates; Cascadia subduction zone; Cenozoic; Chemical composition; Crescent Terrane; Crystal chemistry; East Pacific; Expedition 311; Hydrocarbons; ICP mass spectra; IODP Site U1329; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Juan de Fuca Plate; Marine sediments; Mass spectra; Metals; Methane; North Pacific; Northeast Pacific; Oligocene; Organic compounds; Pacific Ocean; Paleogene; Pysth Formation; Sea water; Sediments; Seepage; Sooke Formation; Spectra; Sr-87/Sr-86; Stable isotopes; Strontium; Tertiary; Water-rock interaction
Coordinates: N484700 N484700 W1264100 W1264100
Record ID: 2013018071
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands