Tectonic versus magmatic extension in the presence of core complexes at slow-spreading ridges from a visualization of faulted seafloor topography

Abstract

We develop a forward model of the generation of faulted seafloor topography (visualization) to estimate the relative roles of tectonic and magmatic extension in the presence of core complexes at slow-spreading ridges. The visualization assumes flexural rotation of 60° normal faults, a constant effective elastic thickness, Te , of young lithosphere, and a continuous infill of the depressed hanging wall by lava flowing from the spreading axis. We obtain a new estimate of Te = 0.5–1 km from the shapes of the toes of 6 well-documented oceanic core complexes. We model an 80-km-long bathymetric profile in the equatorial Atlantic across a core complex and the ridge axis at 13°20′N and estimate the variation in tectonic extension, which yields the variation in the fraction of upper crust extension, M , by magmatic diking at the ridge axis. Core complex formation appears to be stable for all values of M < 0.5. The visualization shows how gabbro emplaced at the base of the lithosphere during extension by magmatic diking is partitioned to each side of the spreading axis, and predicts a high probability of finding gabbros in the domes of core complexes.