Dynamic topography and lithospheric stresses since 400 Ma
Résumé
We present a global model of dynamic topography and lithospheric stresses for the last 400 Ma. Our starting point is a simple geodynamic model combining both contributions of subducted lithosphere and long-wavelength upwellings in a reference frame linked to the fixed African plate. A dominant feature of plate tectonics is the quasi permanence of a girdle of subductions around the Pacific Ocean (or its ancestor), which creates large-wavelength positive topography anomaly within the ring they form. The superimposition of the resultant extension with the one induced by the dome leads to a permanent extensional regime over Africa and the future Indian ocean which creates faults with azimuth directions depending on the direction of the most active part of the ring of subductions. We thus obtain fractures with NW-SE azimuth during the period 275-165 Ma parallel to the strike of the subduction zone of the West South American active margin, which appears to be very active during this period. Between 155 and 95 Ma, subduction became more active along the Eastern Australian coast involving a change in the direction of the faults toward an E-W direction, in agreement with the observed fault systems between Africa and India, Antartica and Australia. During the Mesozoic and the Cenozoic, we correlate the permanent extensional regime over Africa and Indian Ocean with the observed rift systems. Finally we emphasize the role of three primary hotspots as local additional contributors to the stress field imposed by our proposed subduction-doming system, which help in the opening of Indian and South Atlantic Oceans.
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Geochem Geophys Geosyst - 2017 - Greff%u2010Lefftz - Dynamic topography and lithospheric stresses since 400 Ma.pdf (5.49 Mo)
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