| The oceanic lithosphere is observed to have sufficient intrinsic strength to support the weight of large seamounts, undersea volcanoes, and oceanic islands for long periods of time. The support of these features appears to be accommodated by regional isostatic compensation related to flexure of the lithosphere. While the evidence for the flexure of the lithosphere can be successfully analyzed using a simple elastic plate model, rheological considerations and observations of flexure at some trenches indicate that anelastic processes play an important role in the response of the plate. Observations of the bending of the oceanic lithosphere may be compared to flexure predicted by a model of the lithosphere in which the rheology is determined from the results of experimental rock mechanics. Results using an elastic-plastic model based on empirical rock flow laws show that the thickness of the long-term mechanically strong part of the lithosphere is governed mainly by temperature structure and is smaller by a factor of two or three than the seismic and thermal thicknesses. The long-term mechanical response of the oceanic lithosphere changes very little for load durations greater than 1 to 10 m.y. and is relatively insensitive to load size. The simple elastic model is shown to be an adequate approximation for the lithosphere for intraplate loads (e.g. seamounts). Model results for flexure seaward of trenches are consistent with earthquake and reflection seismology data and show that horizontal forces at convergent plate boundaries exert a strong influence on the shape of the Outer Rise. These model results relate the mechanical properties of the oceanic lithosphere to the thermal structure of the lithosphere. This information provides a means of relating geologic data associated with flexure such as subsidence of seamounts, sedimentary loading of subsiding basins, and the historical pattern of marine volcanism, to thermal processes in the lower lithosphere and asthenosphere. |
