Heat flow, sediment and pore fluid chemistry, and hydrothermal circulation on the east flank of Alarcon Ridge, Gulf of California

A. T. Fisher, E. Giambalvo, J. Sclater, M. Kastner, B. Ransom, Y. Weinstein, P. Lonsdale

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

New seismic, heat flow, sediment and pore fluid geochemistry data from the east flank of Alarcon Ridge, at the mouth of the Gulf of California, provide evidence for vigorous hydrothermal circulation within young oceanic crust formed at a moderate-rate spreading center. Data and samples were collected 9-20 km from the ridge axis to assess the hydrologic state of 0.30-0.65 Ma seafloor. Conductive heat flow values are 15-55% of that input at the base of the lithosphere. Heat flow is highest near the center of a sediment-covered trough, and lowest along the trough margins, suggesting that trough-bounding faults and basement exposures may help to focus hydrothermal recharge. Sediment and pore fluid geochemistry data, in combination with reactive transport modeling, indicate that conditions within the shallow sediments are dominantly diffusive and reactive in two locations, but that bottom seawater recharges through the thin sediment layer with velocities on the order of 2-10 mm/yr at other sites. Seafloor heat flow appears to be entirely conductive, which is consistent with the slow rate of seepage inferred from pore fluid observations and modeling. Fluid recharge through sediments requires that basement is underpressured relative to hydrostatic conditions. We interpret these observations and inferences to indicate vigorous fluid flow in basement, and secondary seepage through overlying sediments. The heat flow deficit along the 11-km Alarcon Basin transect averages 440 mW/ m2, equivalent to heat output of 5 MW per kilometer of spreading axis. This heat output is similar to the combined focused and diffusive heat output of a single basement outcrop on the east flank of Juan de Fuca Ridge, and suggests that sites of concentrated heat and fluid outflow may exist on the east flank of Alarcon Ridge.

Original languageEnglish
Pages (from-to)521-534
Number of pages14
JournalEarth and Planetary Science Letters
Volume188
Issue number3-4
DOIs
StatePublished - 2001
Externally publishedYes

Bibliographical note

Funding Information:
We are grateful for the advice and cooperation of colleagues from the Department of Geology at CICESE, Ensenada, Mexico, without whom the Alarcon Basin expedition would not have been possible. Gretchen Robertson and Holger Michaelis provided analytical assistance. We also thank SIO ship operations, and the officers and crew of the R/V Roger Revelle, particularly Capt. Chris Curl and Marine Technicians Seth Mogt and Bob Wilson. Funding in support of this project was provided by the UCSC Committee on Research, the CULAR/UCSC program (STB-UC 98-181), and NSF/OCE-9819242. [EB]

Keywords

  • Crust
  • Geochemistry
  • Gulf of California
  • Heat flow
  • Hydrothermal conditions
  • Pore water

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