--> --> Abstract: Tectonic Subsidence History and Thermal Evolution of the Orange Basin, by Katja K. Hirsch, Magdalena Scheck-Wenderoth, Douglas A. Paton, Gesa Kuhlmann, Jan-Diederick van Wees, and Sierd Cloetingh; #90082 (2008)

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Tectonic Subsidence History and Thermal Evolution of the Orange Basin

Katja K. Hirsch1, Magdalena Scheck-Wenderoth1, Douglas A. Paton2, Gesa Kuhlmann1, Jan-Diederick van Wees3, and Sierd Cloetingh4
1GFZ, Potsdam, Germany
2School of Earth and Environment, Leeds, United Kingdom
3TNO, Utrecht, Netherlands
4Vrije Universiteit, Amsterdam, Netherlands

The Orange Basin is an optimal location to study the interplay of lithospheric extension and tectonic rifting as it contains a fully evolved stratigraphic record from the onset of continental rifting until present day.

Seismic data were used to create a 3D volume of the uppermost 14km of the margin and with the help of isostatic and gravity modelling we investigated the deeper structure of the margin. We found a high density body in the lower crust close to the COT and mapped it throughout the southern Orange Basin. These underplated, mafic bodies are commonly found in volcanic, passive margin settings and presumably emplaced during the process of rifting.

With these models we can describe the present day structure of the margin. But to unravel the basin history and the parameters which defined the rifting and the subsequent subsidence of the basin, methods of subsidence analysis such as backstripping were applied. The backstripping approach yields the basement subsidence of the basin and the assessment of the tectonic driven subsidence gives us indications on tectonic events or thermal perturbations during the basin evolution. The results of the backstripping procedure were used in turn as input data for forward models of the basin subsidence, which are calibrated to temperatures and measured vitrinite reflectance data. From these models we can reconstruct the rifting parameters as initial crustal thickness or stretching factors. Furthermore we can evaluate the heat flow history for each well and linked to that the maturity of the organic matter. We apply this approach in 1D for individual (real) wells but also in 2D for an equidistant grid of synthetic wells constructed from the lithological 3D volume. We discuss the geodynamic implications of the modelled basin evolution scenarios with special focus on temperature and heat flow variations in space and time.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery