This deep subsidence is a result of a tectonic concurrence between processes in the upper lithosphere that led to subsiding and a compensating upward flow of rocks in the deeper layers of the lithosphere.
This is a result presented by A. Petrunin and A. Sobolev from the GFZ - German Research Centre for Geosciences in the current issue of „PHYSICS OF THE EARTH AND PLANETARY INTERIORS“ (Vol. 171, S. 387 - 399).
In a series of thermomechanical numerical experiments they were able to show that the brittle layer of the Earth’s crust subsides when the African and the Arabian plate pass each other along a strike-slip fault. Due to the lateral displacement, the Earth’s crust gets thinner at this point and a pull-apart basin develops that in the course of roughly 15 million years has been filled with a layer of sediments that is up to ten kilometres thick.
In the upper part of the underlying Earth’s mantle, this basin development leads to a corresponding upward flow of hot and ductile rock material. These concurring tectonic processes thus determine the process of the basin development.
Petrunin and Sobolev demonstrate that the subsidence rate is controlled by four parameters: firstly the thickness of the brittle layer and the basin width, secondly the length of the strike-slip displacement, thirdly the rate of frictional softening of the crust and finally the viscosity of the ductile material in the upper mantle.
The detected mechanisms give insight into the formation and development of such pull-apart basins forming a natural rheology lab in which the history of the lithospheric deformation can be studied.
Franz Ossing | alfa
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