Lower crustal flow and the role of shear in basin subsidence: an example from the Dead Sea basin

We interpret large-scale subsidence (5-6 km depth) with little attendant brittle deformation in the southern Dead Sea basin, a large pull-apart basin along the Dead Sea transform plate boundary, to indicate lower crustal thinning due to lower crustal flow. Along-axis flow within the lower crust could be induced by the reduction of overburden pressure in the central Dead Sea basin, where brittle extensional deformation is observed. Using a channel flow approximation, we estimate that lower crustal flow would occur within the time frame of basin subsidence if the viscosity is less than or equal to7 X 10(19) -1 X 10(21) Pa s, a value compatible with the normal heat flow in the region. Lower crustal viscosity due to the strain rate associated with basin extension is estimated to be similar to or smaller than the viscosity required for a channel flow. However, the viscosity under the basin may be reduced to 5 X 10(17) -5 X 10(19) Pa s by the enhanced strain rate due to lateral shear along the transform plate boundary, Thus, lower crustal flow facilitated by shear may be a viable mechanism to enlarge basins and modify other topographic features even in the absence of underlying thermal anomalies. (C) 2002 Elsevier Science B.V. All rights reserved.