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

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doi: 10.1029/2012GC004314
Author(s): Schoolmeesters, Nicole; Cheadle, Michael J.; John, Barbara E.; Reiners, Peter W.; Gee, Jeffrey; Grimes, Craig B.
Author Affiliation(s): Primary:
University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
Other:
University of Arizona, United States
University of California at San Diego, United States
Ohio University, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 13(10). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 103 refs.; illus., incl. 2 tables
Summary: 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 1415 m below 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.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Absolute age; Atlantic Ocean; Atlantis Massif; Cooling; Crust; Dates; Depth; Detachment faults; Expeditions 304/305; Faults; Gabbros; Hydrothermal conditions; IODP Site U1309; Igneous rocks; Integrated Ocean Drilling Program; Magnetization; Mantle; Mid-Atlantic Ridge; Nesosilicates; North Atlantic; Ocean floors; Oceanic core complexes; Oceanic crust; Orthosilicates; Paleomagnetism; Plutonic rocks; Precambrian; Remanent magnetization; Silicates; Thermochronology; U/Pb; Zircon; Zircon group
Coordinates: N301000 N301100 W0420600 W0420700
N300200 N302000 W0420000 W0421500
Record ID: 2013088586
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