Fluid and geochemical transport through oceanic crust; a transect across the eastern flank of the Juan de Fuca Ridge

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doi: 10.1016/S0012-821X(99)00191-0
Authors:Elderfield, H.; Wheat, C. G.; Mottl, M. J.; Monnin, C.; Spiro, B.
Author Affiliations:Primary:
University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom
Other:
West Coast and Polar Regions Undersea Research Center, Moss Landing, United States
University of Hawaii, United States
Université Paul Sabatier, France
NERC Isotope Geosciences Laboratory, United Kingdom
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 172(1-2), p.151-165. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1999
Note:In English. 30 refs.; illus., incl. sect., 4 tables, sketch map
Summary:The geochemical implications of thermally driven flow of seawater through oceanic crust on the mid-ocean ridge flank have been examined on a well-studied 80 km transect across the eastern flank of the Juan de Fuca Ridge at 48°N, using porewater and basement fluid samples obtained on ODP Leg 168. Fluid flow is recognised by near-basement reversals in porewater concentration gradients from altered values in the sediment section to seawater-like values in basaltic basement. In general, the basement fluids become more geochemically evolved with distance from the ridge and broadly follow basement temperature which ranges from ∼16° to 63°C. Although thermal effects of advective heat exchange are only seen within 20 km east of where basement is exposed near the ridge crest, chemical reactivity extends to all sites. Seawater passing through oceanic crust has reacted with basement rocks leading to increases in Ca2+ and decreases in alkalinity, Mg2+, Na+, K+, SO42- and δ18O. Sr isotope exchange between seawater and oceanic crust off axis is unequivocally demonstrated with endmember 87Sr/86Sr≈0.707. Evidence of more evolved fluids is seen at sites where rapid upwelling of fluids through sediments occurs. Chlorinities of the basement fluids are consistent with post-glacial seawater and thus a short residence time in the crust. Rates of lateral flow have been by estimated by modelling porewater sulphate gradients, using Cl as a glacial chronometer, and from radiocarbon dating of basal fluids. All three methods reveal fluid flow with 14C ages less than 10,000 yr and particle velocities of ∼1-5 m/yr, in agreement with thermally constrained volumetric flow rates through a ∼600 m thick permeable layer of ∼10% porosity. Δelementheat extraction ratios are similar to values for ridge-crest hydrothermal systems. Abstract Copyright (1999) Elsevier, B.V.
Sections:Geochemistry
Subsections:Igneous rocks
Subjects:Alkaline earth metals; Basement; Chemical composition; Crust; Enrichment; Fluid dynamics; Geochemistry; Heat flow; Heat transfer; Hydrochemistry; Hydrothermal alteration; Isotope ratios; Isotopes; Metals; Metasomatism; O-18/O-16; Ocean Drilling Program; Oceanic crust; Oxygen; Pore water; Sea water; Sr-87/Sr-86; Stable isotopes; Strontium; Transport; East Pacific; Juan de Fuca Ridge; Leg 168; North Pacific; Northeast Pacific; ODP Site 1026; Pacific Ocean
Coordinates:N474500 N480000 W1273000 W1290000
N474556 N474556 W1274526 W1274526
Abstract Numbers:00M/2940
Record ID:2000014030
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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