Oxygen isotope evidence for short-lived high-temperature fluid flow in the lower oceanic crust at fast-spreading ridges

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doi: 10.1016/j.epsl.2007.06.013
Author(s): Coogan, Laurence A.; Manning, Craig E.; Wilson, Robert N.
Edinburgh Ion Microprobe Facility, Edinburgh
Author Affiliation(s): Primary:
University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada
University of California, Los Angeles, United States
University of Leicester, Canada
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 260(3-4), p.524-536. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplemental information/data is available in the online version of this article. 46 refs.; illus., incl. 1 table
Summary: Millimeter-scale amphibole veins in the lower oceanic crust record fracture-controlled fluid flow at high-temperatures but the importance of this fluid flow for the thermal and chemical evolution of the lower oceanic crust is unclear. In the section of lower oceanic crust recovered at Hess Deep from ODP Hole 894G, which formed at the fast-spreading East Pacific Rise, these veins are randomly distributed with an average spacing of ∼1 m. We unravel the history of fluid flow through one of these veins by combining in situ O-isotope analyses of wall-rock plagioclase with major element analyses, geothermometry and diffusion modeling. Thermometry indicates vein sealing by amphibole at ∼720 °C over a narrow temperature interval (20 °C). In situ O-isotope analyses by ion microprobe, with a precision of <0.5ppm, reveal zoning of O-isotopes in plagioclase adjacent to the vein. The zoning profiles can be reproduced using a diffusion model if the duration of O-isotope exchange was ≤100 yr. A similar interval of fluid-rock exchange is suggested by modeling potassium depletion in plagioclase adjacent to the vein. If representative of fracture controlled fluid flow in the lower oceanic crust the limited duration of fluid flow, and its occurrence over a narrow temperature interval, suggest that high-temperature fluid flow in this porosity network does not transport significant heat. Abstract Copyright (2007) Elsevier, B.V.
Year of Publication: 2007
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 18 Geophysics, Solid-Earth; Amphibole group; Amphibolite facies; Chain silicates; Circulation; Crust; Diffusion; East Pacific; East Pacific Rise; Equatorial Pacific; Facies; Feldspar group; Fractures; Framework silicates; Gabbros; Geologic thermometry; Hess Deep; High temperature; Hydrothermal conditions; Igneous rocks; Isotope ratios; Isotopes; Leg 147; Mid-ocean ridges; North Pacific; Northeast Pacific; Numerical models; O-18/O-16; ODP Site 894; Ocean Drilling Program; Ocean floors; Oceanic crust; Oxygen; Pacific Ocean; Plagioclase; Plutonic rocks; Silicates; Spatial distribution; Spreading centers; Stable isotopes; Temperature; Thermal history; Veins; Water-rock interaction; Zoning
Coordinates: N021757 N021806 W1013129 W1013136
Record ID: 2008044505
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands