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Post-rift seaward downwarping at passive margins: New insights from southern Oman using stratigraphy to constrain apatite fission-track and (U-Th)/He dating

¹ Laboratoire de Géographie Physique, Université Paris 7, 2 place Jussieu, 75251 Paris Cedex 5, France
² School of Earth Science, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
³ Laboratoire de Tectonique, Université Paris 6, 4 place Jussieu, 75252 Paris Cedex 5, France

The plateau edge of southern Oman is used as a natural laboratory to independently test apatite fission-track analysis, (U-Th)/He dating, and stratigraphy as methods for quantifying post-rift erosion depths and lithospheric response at passive margins. A mappable unconformity between the Proterozoic basement and the low-conductivity, pre-rift sediment cover links residual buttes preserved at the coast to the escarpment, and therefore imposes tight limitations on parameter choices for modeling the Cenozoic topographic evolution. A mean geothermal gradient of 33 °C km^–1 ensures the best fit between the thermochronologic data and the stratigraphically defined coast-to-scarp maximum denudation depth of 1.75 km. With a lithospheric elastic thickness of 7 km, the resulting flexural response generates a retreat and uplift of the escarpment associated with a seaward downwarp of the unconformity, made possible because denudation minima are inboard of the escarpment and sediment loading occurs offshore. This closed experiment confirms the value of low-temperature thermochronology as a tool for quantifying long-term erosion, but also highlights the benefits of including independent stratigraphic information in terms of obtaining more plausible solutions. This study suggests that post-rift downwarping of eroded rift shoulders can occur, and may have not been commonly detected because low-temperature thermochronology data sets lack both suitable geologic data and intrinsic sensitivity.

Key Words: thermochronology • rifted margin • denudation • flexure • Oman

This article has been cited by other articles:

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