HR: 10:20h
AN: T52B-01 INVITED    [Abstracts]
TI: Unexpected Widespread Detachment Faulting During Formation of Lithosphere at the Northern Mid-Atlantic Ridge
AU: * Smith, D K
EM: dsmith@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Geology and Geophysics, Woods Hole, MA 02540, United States
AU: Schouten, H
EM: hschouten@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Geology and Geophysics, Woods Hole, MA 02540, United States
AU: Escartin, J
EM: escartin@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Groupe de Geosciences Marines, Paris, 75252, France
AU: Cann, J R
EM: j.cann@see.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT, United Kingdom
AB: The region of the Mid-Atlantic Ridge (MAR) near 13N displays the topographic characteristics of prevalent and vigorous tectonic extension. Normal faults show large amounts of rotation, dome-shaped corrugated detachment surfaces (core complexes) intersect the seafloor within the inner valley floor, and dead core complexes cover the seafloor off-axis. Steep outward facing slopes indicate that the footwalls of many of the normal faults have rotated by more than 30 degrees suggesting at least 3 km of extension. The rotation occurs very close to the ridge axis and produces distinctive linear ridges with roughly symmetrical slopes. This morphology is very different from linear abyssal hill faults formed at magmatic sections of the ridge which display a smaller amount of backtilt (typically less than 15 degrees implying 1-1.5 km of extension). We suggest that the severe backtilt of faults is diagnostic of a region undergoing large amounts of tectonic extension on single faults. If faults are long-lived (more than 5 km extension) a dome-shaped corrugated surface develops in front of the ridges and lower crustal and upper mantle rocks are exposed. We have applied our understanding of the 13N region to the northern MAR between 15 and 35N and find up to15 ridge segments dominated by extreme fault rotation and core complex exhumation. Core complexes are not limited to inside corners of ridge-transform intersections but may occur anywhere along the length of a segment. A single ridge segment can have several active core complexes, some less than 25 km apart that are separated by swales. We present two models for multiple core complex formation: a continuous model in which a single detachment surface extends along axis to include all of the core complexes and swales, and a discontinuous model in which local detachment faults form the core complexes and magmatic spreading forms the intervening swales. Either model can explain the morphology that we observe. If there is a continuous detachment fault along axis then that suggests differential uplift of the footwall to explain the highs and lows of the domes and swales, perhaps indicating that relatively more gabbro is emplaced under the domes and less under the swales.
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3075 Submarine tectonics and volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting