Cooling history of Atlantis Bank oceanic core complex; evidence for hydrothermal activity 2.6 Ma off axis

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doi: 10.1029/2009GC002466
Author(s): Schwartz, Joshua J.; John, Barbara E.; Cheadle, Michael J.; Reiners, Peter W.; Baines, A. Graham
Author Affiliation(s): Primary:
University of Wyoming, Department of Geology and Geophysics, Laramie, WY, United States
University of Arizona, United States
University of Adelaide, Australia
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 10(8). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. Includes appendices. 96 refs.; illus., incl. 3 tables
Summary: We report 26 (U-Th)/He zircon ages from Atlantis Bank, Southwest Indian Ridge, which constrain time scales and rates of lower crustal cooling in ultraslow spreading oceanic crust in this setting. Samples from the detachment fault surface indicate that denuded oceanic crust cooled rapidly (<1 Ma), yielding cooling rates >1200°C/Ma, consistent with existing models for the cooling of oceanic crust. (U-Th)/He zircon ages from samples collected along N-S and E-W trending faults scarps record young ages inconsistent with standard cooling models for lower oceanic crust. These samples have a mean (U-Th)/He zircon age 2.6 Ma younger than their corresponding igneous crystallization ages and record cooling through 200°C well outside the rift valley. Similar anomalously young ages are recorded by zircon, sphene, and apatite fission track data from ODP Hole 735B. We interpret these young ages as recording an off-axis thermal/heating event associated with localized high-temperature (>300°C) hydrothermal fluid flow resulting from underplated mafic magmas.
Year of Publication: 2009
Research Program: ODP Ocean Drilling Program
Key Words: (U-Th)/He; 07 Marine Geology and Oceanography; Apatite; Atlantis; Atlantis Bank; Atlantis II fracture zone; Cenozoic; Cooling; Crust; Fission-track dating; Fluid phase; Geochronology; Hydrothermal conditions; Indian Ocean; Leg 118; Lower crust; Mafic magmas; Magma chambers; Magmas; Neogene; Nesosilicates; ODP Site 735; Ocean Drilling Program; Ocean floors; Oceanic core complexes; Oceanic crust; Orthosilicates; Phosphates; Silicates; Southwest Indian Ridge; Tertiary; Thermochronology; Titanite; Titanite group; Zircon; Zircon group
Coordinates: S325500 S323500 E0572500 E0571000
Record ID: 2010043483
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