Open AccessCooling history of Atlantis Bank oceanic core complex: Evidence for hydrothermal activity 2.6 Ma off axis
Author(s) -
Schwartz Joshua J.,
John Barbara E.,
Cheadle Michael J.,
Reiners Peter W.,
Baines A. Graham
Publication year - 2009
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2009gc002466
Subject(s) - zircon , geology , oceanic crust , hydrothermal circulation , crust , geochemistry , fission track dating , rift , mafic , igneous rock , petrology , seismology , subduction , tectonics
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.