Evolution of Large-Scale Topography and River Drainage Direction From Mantle Flow Models

Abstract

Flow within the mantle imposes a deformation of the Earth's surface called dynamic topography. However, quantifying this topography in space and time remains a challenge. Over the last few years, we have developed dynamic Earth models that progressively assimilate cutting-edge tectonic reconstructions with continuously closing plates and plate deformation. These models read in plate velocities and subduction zone location and geometry defined in million-year increment for the last 230 Myr. The approach allows us to simultaneously model global mantle flow and large-scale lithospheric deformation, and in turn estimate the evolution of both dynamic and isostatic topography back to the Jurassic. In the South Atlantic domain, we show that long-wavelength topographic features, including the anomalously high elevations of southern Africa and East Brazil, could result from whole mantle flow, rather than asthenospheric flow, as previously suggested. Comparing model tectonic subsidence along the South American passive margin with that estimated from boreholes, we attribute the post-rift subsidence of the East Brazil Rift System since the Eocene to the motion of South America over ancient subducted slabs. This interplay between plate motion and mantle flow, combined with the development of flat slab subduction in Peru, also explains the reversal of the drainage direction of the Amazon River and the drying of the Pebas System since the Miocene. On a smaller scale, we show that deformation within the central Andes imposes an inboard migration of the subduction zone relative to the South American plate that could have resulted in the migration of the depocenter of the Bolivian Chaco foreland basin, and associated drainage reorganization. In South East Asia, we use simpler models without lithospheric deformation to attribute missing sedimentary sections of latest Cretaceous to Paleocene age across Sundaland to dynamic uplift resulting from a ~10 Myr subduction hiatus along the Sunda active margin. In the Arctic, we show that subduction-driven dynamic topography can explain the rapid Middle to Late Jurassic subsidence of the Slave Craton and North Slope of Alaska and the vertical motions of the Barents Sea region, characterized by subsidence between ~170–50 Ma followed by uplift since 50 Ma. Together, these results illustrate the important role of mantle flow on the evolution of large-scale topography, making dynamic Earth models powerful for frontier hydrocarbon exploration.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015