Intracrustal reflections from a Cretaceous inside corner are interpreted as
a detachment fault that dips gently within the basement and can be followe
d up the flank of a domed high. The fault heave is sufficient for ridge-nor
mal extension to have exhumed deep-crustal and probably mantle rocks, as sa
mpled at some inside corner domed massifs. The morphology of these massifs
closely resembles that of the Cretaceous high, implying that the structures
are analogous and supporting the notion that modern inside corner massifs
are oceanic core complexes formed by unroofing the footwalls of similar det
achment faults, partially exposed as corrugated slip surfaces. This is the
first demonstration of the overall geometry of an oceanic core complex deta
chment fault.