The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex

Nicole Schoolmeesters, Michael J. Cheadle, Barbara E. John, Peter W Reiners, Jeffrey Gee, Craig B. Grimes

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Oceanic core complexes (OCCs) are domal exposures of oceanic crust and mantle interpreted to be denuded to the seafloor by large slip oceanic detachment faults. We combine previously reported U-Pb zircon crystallization ages with (U-Th)/He zircon thermochronometry and multicomponent magnetic remanence data to determine the cooling history of the footwall to the Atlantis Massif OCC (30°N, MAR) and help establish cooling rates, as well as depths of detachment faulting and gabbro emplacement. We present nine new (U-Th)/He zircon ages for samples from IODP Hole U1309D ranging from 40 to 1415mbelow seafloor. These data paired with U-Pb zircon ages and magnetic remanence data constrain cooling rates of gabbroic rocks from the upper 800 m of the central dome at Atlantis Massif as 2895 (+1276/-1162) °C Myr -1 (from ∼780°C to ∼250°C); the lower 600 m of the borehole cooled more slowly at mean rates of ∼500 (+125/-102) °C Myr -1 (from ∼780°C to present-day temperatures). Rocks from the uppermost part of the hole also reveal a brief period of slow cooling at rates of ∼300°C Myr -1, possibly due to hydrothermal circulation to ∼4 km depth through the detachment fault zone. Assuming a fault slip rate of 20 mm/yr (from U-Pb zircon ages of surface samples) and a rolling hinge model for the sub-surface fault geometry, we predict that the 780°C isotherm lies at ∼7 km below the axial valley floor, likely corresponding both to the depth at which the semi-brittle detachment fault roots and the probable upper limit of significant gabbro emplacement.

Original languageEnglish (US)
Article numberQ0AG12
JournalGeochemistry, Geophysics, Geosystems
Volume13
Issue number1
DOIs
StatePublished - 2012

Fingerprint

Faulting
detachment
faulting
zircon
detachment fault
histories
Cooling
cooling
history
gabbro
Remanence
remanence
emplacement
slip
seafloor
Fault slips
Rocks
rocks
hydrothermal circulation
fault geometry

Keywords

  • Atlantis Massif
  • Oceanic core complex
  • Oceanic detachment fault
  • Zircon

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex. / Schoolmeesters, Nicole; Cheadle, Michael J.; John, Barbara E.; Reiners, Peter W; Gee, Jeffrey; Grimes, Craig B.

In: Geochemistry, Geophysics, Geosystems, Vol. 13, No. 1, Q0AG12, 2012.

Research output: Contribution to journalArticle

Schoolmeesters, Nicole ; Cheadle, Michael J. ; John, Barbara E. ; Reiners, Peter W ; Gee, Jeffrey ; Grimes, Craig B. / The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex. In: Geochemistry, Geophysics, Geosystems. 2012 ; Vol. 13, No. 1.
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AB - Oceanic core complexes (OCCs) are domal exposures of oceanic crust and mantle interpreted to be denuded to the seafloor by large slip oceanic detachment faults. We combine previously reported U-Pb zircon crystallization ages with (U-Th)/He zircon thermochronometry and multicomponent magnetic remanence data to determine the cooling history of the footwall to the Atlantis Massif OCC (30°N, MAR) and help establish cooling rates, as well as depths of detachment faulting and gabbro emplacement. We present nine new (U-Th)/He zircon ages for samples from IODP Hole U1309D ranging from 40 to 1415mbelow seafloor. These data paired with U-Pb zircon ages and magnetic remanence data constrain cooling rates of gabbroic rocks from the upper 800 m of the central dome at Atlantis Massif as 2895 (+1276/-1162) °C Myr -1 (from ∼780°C to ∼250°C); the lower 600 m of the borehole cooled more slowly at mean rates of ∼500 (+125/-102) °C Myr -1 (from ∼780°C to present-day temperatures). Rocks from the uppermost part of the hole also reveal a brief period of slow cooling at rates of ∼300°C Myr -1, possibly due to hydrothermal circulation to ∼4 km depth through the detachment fault zone. Assuming a fault slip rate of 20 mm/yr (from U-Pb zircon ages of surface samples) and a rolling hinge model for the sub-surface fault geometry, we predict that the 780°C isotherm lies at ∼7 km below the axial valley floor, likely corresponding both to the depth at which the semi-brittle detachment fault roots and the probable upper limit of significant gabbro emplacement.

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