Seawater recharge into oceanic crust: IODP Exp 327 Site U1363 Grizzly Bare outcrop

C. Geoffrey Wheat, Samuel M. Hulme, Andrew T. Fisher, Beth N. Orcutt, Keir Becker

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Systematic differences in sediment thermal and pore water chemical profiles from Integrated Ocean Drilling Program Site U1363 document mixing and reaction within the basaltic crust adjacent to Grizzly Bare outcrop, a site of hydrothermal recharge into 3.6 My-old basaltic crust. A transect of seven holes was drilled ∼50 m to ∼750 m away from the base of the outcrop. Temperatures at the sediment-basement interface increase from ∼6°C to >30°C with increasing distance from the outcrop, and heat flow is suppressed within several hundred meters from the outcrop. Calculated fluid compositions at the sediment-basement interface are generally explained by mixing between bottom seawater and altered crustal basement fluids, with a composition similar but not identical to fluids from seeps at Baby Bare outcrop, located ∼45 km to the northeast. Reactions within upper basement and overlying sediment affect a variety of ions (Mn, Fe, Mo, Si, PO4 3-, V, and U) and δ13DIC, indicating a diagenetic influence and diffusive exchange with overlying sediment pore waters. The apparent 14C age of basal pore fluids is much older than bottom seawater. Collectively, these results are consistent with seawater recharge at Grizzly Bare outcrop; however, there are strong gradients in fluid composition within 50 m of the outcrop, providing evidence for complex flow paths and vigorous mixing of young, recently recharged seawater with much older, more reacted basement fluid. The proximity of these altered fluids to the edge of the outcrop raises the possibility for fluid seepage from the outcrop in addition to seawater recharge.

Original languageEnglish (US)
Pages (from-to)1957-1972
Number of pages16
JournalGeochemistry, Geophysics, Geosystems
Volume14
Issue number6
DOIs
StatePublished - 2013

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outcrops
Seawater
oceanic crust
recharge
crusts
outcrop
seawater
Fluids
basements
Sediments
fluids
sediments
fluid
fluid composition
sediment
porosity
Chemical analysis
porewater
crust
Water

Keywords

  • chemical exchange
  • hydrothermal
  • low temperature
  • outcrop
  • pore water
  • ridge flank

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Seawater recharge into oceanic crust : IODP Exp 327 Site U1363 Grizzly Bare outcrop. / Wheat, C. Geoffrey; Hulme, Samuel M.; Fisher, Andrew T.; Orcutt, Beth N.; Becker, Keir.

In: Geochemistry, Geophysics, Geosystems, Vol. 14, No. 6, 2013, p. 1957-1972.

Research output: Contribution to journalArticle

Wheat, C. Geoffrey ; Hulme, Samuel M. ; Fisher, Andrew T. ; Orcutt, Beth N. ; Becker, Keir. / Seawater recharge into oceanic crust : IODP Exp 327 Site U1363 Grizzly Bare outcrop. In: Geochemistry, Geophysics, Geosystems. 2013 ; Vol. 14, No. 6. pp. 1957-1972.
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