THE QUATERNARY EVOLUTION OF THE GULF OF CORINTH, CENTRAL GREECE: COUPLING BETWEEN EROSION, SEDIMENTATION, AND FLOW IN THE LOWER CONTINENTAL CRUST

The Gulf of Corinth in Greece is an active normal-fault-zone, with clear evidence of isostatic footwall uplift, constrained by Quaternary marine terraces, and hanging-wall subsidence and sedimentation. It is bounded by a Plio-Early-Pleistocene sedimentary basin which is now eroding into the Gulf. The local relief has increased dramatically since the Early Pleistocene, as the isostatic response to increased rates of footwall erosion and hanging-wall sedimentation: incision accompanying the draw-down of global sea-level at ~0.9Ma, during the first major Pleistocene glaciation, initiated the erosion of this basin and so increased the sedimentation rate in the Gulf. An estimated typical layer thickness of ~200m has since been eroded from this basin. The resulting transient thermal and isostatic response to these changes is modelled, with the depocentre and sediment-source coupled by flow in the lower crust. Rates of flow are determined from lateral pressure gradients at the base of the upper-crustal brittle layer, which are recalculated for each time step taking account of the depth variations of the base of this layer that result from the heat-flow perturbations induced by the surface processes. The subsequent enhancement of relief, involving an increase in bathymetry from near zero to ~900m and ~500m of uplift of the eroding land surface in the sediment-source, is a direct consequence of this change. The model is sensitive to the effective viscosity of the lower crust, and can thus resolve it to ~5x10^19Pa s, suggesting a Moho viscosity no greater than ~10^18Pa s. This study indicates that such low viscosities are entirely reasonable in regions of normal crustal thickness and geothermal gradient, and indicates that lower-crustal flow is thus of widespread importance. The calculations also indicate that isostatic responses can be very different from simple Airy predictions. In the present study region, ~200m of denudation has accompanied a ~500m increase in altitude of an eroding land surface and thus ~700m of uplift of marine terraces that have not eroded.