Lower crustal variability and the crust/mantle transition at the Atlantis Massif oceanic core complex

Details Lower crustal variability and the crust/mantle transition at the Atlantis Massif oceanic core complex Lower crustal variability and the crust/mantle transition at the Atlantis Massif oceanic core complex

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010georl..3724303b&link_type=abstract

Geophysical Research Letters, Volume 37, Issue 24, CiteID L24303

Physics

Geophysics

1

Marine Geology And Geophysics: Midocean Ridge Processes, Seismology: Oceanic Crust, Marine Geology And Geophysics: Marine Seismics (0935, 7294)

Scientific paper

Seismic refraction data provide new constraints on the structure of the lower oceanic crust and its variability across the Atlantis Massif oceanic core complex, ˜30°N on the Mid-Atlantic Ridge. A 40 km-long spreading-parallel profile constrains P-wave velocities to depths of up to ˜7 km beneath the seafloor. Two shorter spreading-perpendicular lines provide coverage to ˜2 km depth. The anomalous character of the massif's central dome crust is clear compared to the neighboring rift valley and similar-age crust on the opposite ridge flank. The domal core of the massif, unroofed via detachment faulting, has velocities >7.0 km/s at depths below ˜2.5 km sub-seafloor, increasing to 7.5-7.8 km/s over the depth range 4.8-6.8 km. Within the core complex, the Moho does not appear to be sharp as no PmP arrivals are observed. Within the axial valley, velocities do not reach mantle-transition zone values in the uppermost 6 km. We infer that crust there is of normal thickness but that a thinner than average mafic section is present in the central massif. Near IODP Hole U1309D, located on the central dome, there is a low velocity gradient interval at 1-3 km depth with velocities of 6.6-6.8 km/s, that coincides with a 3-5 km wide region where shallower velocities are highest. Given the predominantly gabbroic section recovered from the 1.4 km deep drillhole, this seismic structure suggests that the mafic body extends a few km both laterally and vertically.

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