Long-Term Erosional Development of Rifted Continental Margins: Toward a Quantitative Understanding

Two independent sets of observations from rifted con-tinental margins suggest a way to reach a quantitative under-standing of how the topography of rifted margins erodes. First, a prominent erosional escarpment, which demarcates an elevated, inland region of low relief from rugged, deeply-incised terrain on the seaward side, is the main feature of the geomorphology of many rifted continental margins. Second, apatite fission track ages from the southeast Australian and southwest Saudi Arabian margins scatter about constant Paleozoic ages over the higher elevations inland from the escarpment, but decrease systematically seaward of the escarpment to near-rifting ages approaching the coastlines. We have developed erosion models based on conservation of mass principles to explain these observations. These models seek to explain the "rejuvenation" of erosion at the time of rifting, initiation of the observed erosional escarpment, and its migration inland with time at a rate on the order of 1 km/10 yr. We find from the modeling that erosion at rift flanks and passive margins is fundamentally a non-linear pro-cess. The erosional development of passive margin topogra-phy has much is common with travelling wave solutions to non-linear diffusion-type problems, and to self-similar sto-chastic processes, such as diffusion-limited aggregation. We suggest that the fission track data record the thermal effects of erosional unroofing at rift flanks and passive continental margins. Models intended to explain the erosional develop-ment of continental margins must explain both the geomor-phology and the fission track observations as well.