Permo-Triassic Subducted Slabs Return from the Grave

Douwe G. Van der Meer¹ and Douwe J.J. Van Hinsbergen^2
1Utrecht University / Shell Exploration and Production, Rijswijk, Netherlands
²Utrecht University, Utrecht, Netherlands

In this presentation we test a scenario in which subducted plates (slabs) penetrate the D”-layer at the base of the mantle and generate mantle plumes, completing a whole mantle convection cycle. At crustal level, parts of a subducting plate can be accreted to the overriding plate to form orogens. We use the duration of orogenesis to date the onset and end of a subduction event and apply seismic tomography to image slabs in the mantle. Slabs at the base of the mantle, detectable as high seismic velocity anomalies, underneath the northern America-Atlantic-European realm correspond to the Permo-Triassic active margins of western Pangea. The D”-layer forms both the final sink ('slab graveyard') and a possible source region for mantle plumes. Surrounding the projected position of these slabs at the earth surface, a large number of upper Mesozoic and Cenozoic mantle-plume related Large Igneous Provinces and hotspots have been identified, suggesting a causal link between slabs and mantle upwelling. In this presentation we link four orogenies to mantle plume events and show a slab mantle transit time of 230-250 Myr between onset of orogeny and onset of mantle plume volcanism, coupled through a whole mantle convection cycle. Comparison of paleogeographic reconstructions with tomographic images provides a novel tool to constrain paleolongitude of former subduction zones. Our analyses suggests that western Pangea and edge of the Tethys Ocean had a 45 degree more westerly paleolongitude (~5000 km at the equator) than currently assumed.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece