Evidence and models for lower crustal flow beneath the G alápagos platform

The volcanic Galápagos Islands are constructed upon a broad platform, with their active westernmost islands marking the current position of the hotspot. Built upon young oceanic lithosphere (<15 Ma), this platform exhibits unique morphologic features including a system of stepped terraces on the southwestern escarpment with 3 km relief, contrasting with gentle slopes off the eastern platform toward the Carnegie Ridge. Considering horizontal lithostatic pressure differences associated with this relief, along with high temperatures within the young, hotspot‐affected lithosphere, it is likely that lower crustal flow contributes significantly to crustal deformation within the Galápagos platform. Using a 2‐D, isostatic, thin‐sheet approximation for the Stokes flow equation with (Newtonian) space‐time‐dependent viscosity, we suggest that the bathymetric rim along the eastern platform region (where gravimetry indicates Airy isostasy) near Española Island may be the expression of a mature lower crustal flow front developed over the last ∼3 Myr; horizontal mass displacements (∼50 km) associated with this crustal flow episode may have advected mantle plume geochemical signatures toward the southeast, and in directions not necessarily parallel to the hotspot track. Also, the stepped terraces along the southwestern platform may be explained by lower crustal flow‐associated backward tilting of the bathymetric surface that, although resulting in small angular changes (∼0.1°), effectively hinders the horizontal flow of lava sheets. This backward‐tilting process was likely restricted to the last ∼1 Ma or less, and may be a unique event involving extrusion of lavas from within the southwestward‐marching lower‐crustal flow front.