The North Atlantic Transect seismic reflection data, collected southwest of Bermuda, have been reinterpreted following post-stack migration and reveal two major intracrustal reflections. The shallower of these two events, located ~1 s below the igneous basement, is a subhorizontal, undulating surface that in some places is continuous for as much as 10 km. This upper crustal reflection corresponds to the intermittently sharp contact between the sheeted dikes and the underlying isotropic gabbro. A second set of lower crustal reflections, dipping ~20??-40?? eastward, is also prominent on the migrated profile and terminates downdip against the subhorizontal reflection Moho. Their presence may be ascribed to mafic-ultramafic cumulate layers frozen into the oceanic crust at the time of formation at the paleo-spreading center. The gradual thinning in the crust approaching the fracture zones is shown to be more complex than was originally inferred. An intepretation advocating crustal thickening in this narrow zone is proposed as an alternative to the crustal-thinning model of Mutter and others. -from Authors
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Relic magma chamber structures preserved within the Mesozoic North Atlantic crust?