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
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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