Lithospheric instability beneath the Transverse Ranges of California

摘要: Recent high-resolution seismic experiments reveal that the crust beneath San Gabriel Mountains portion of Transverse Ranges thickens by 10–15 km (contrary to earlier studies). Associated with Ranges, there is an anomalous ridge seismically fast upper mantle material extending at least 200 into mantle. This high-velocity anomaly has previously been interpreted as a lithospheric downwelling. Both downwelling and crustal thickening are associated oblique convergence Pacific North America plates across Andreas Fault, though it seems likely driven partly gravitational instability cold We show means numerical experiment balance between buoyancy forces drive deformation viscous stresses resist determines geometry use simple two-layered model in which dense overlies relatively inviscid less asthenosphere overlain buoyant crust. External plate motion drives convergence, constrained boundary conditions occur within central convergent zone specified width. A fundamental transition revealed our experiments. For slow or low viscosity, occurs multiple sheets on margins zone. stronger than lithosphere single center complexity evolution system attributed interaction evolving instability. In order for narrow slab have formed last 5 Myr, effective viscosity region most about 10^20 Pa s.