To what degree does mantle convection drive sea-level change and subsequently coastline change around South America in the Tertiary? The westward movement of the South American plate implies the overriding of the Phoenix and Farallon slabs. Temperature and density anomalies of subducted slabs are preserved in the mantle and can be inferred from seismic tomography images. The currently subducting Nazca Plate, is expected to generate a dynamic surface topography effect, leading to variable surface tilting and vertical motions over time. We use numerical models to discern the contribution to subsidence or uplift due to mantle convection and slab subduction. Geodynamic modelling software, CitcomS combined with the GPlates software facilitates the modelling of linked plate kinematic and mantle convection processes. The quality of model output for the surface dynamic topography can be assessed by comparison with observations. These include geological data constraining surface uplift or subsidence, mantle tomography models, as well as regional versus global estimates of sea-level and palaeoshoreline analysis. Initial results show an encouraging connection between palaeogeography reconstructed from geological data and modelled dynamic topography. Modelled vertical motions suggest changes of up to ±1500m amplitude, or ~±150m/10Ma. A South American digital elevation model that is corrected for time-dependent dynamic topography effects, and inundated using a eustatic sea level model, shows a substantially improved agreement with mapped paleo-coastlines from geological data compared with an uncorrected elevation model. This supports the notion that mantle convection effects through time have played a profound role in driving shifts in coastlines and river drainage in South America. The uplift of the Andes has previously been suggested as attributing to the reversal in flow of the Amazon river. However, our results suggest an alternative mechanism for major Miocene changes in paleo-Amazon river drainage. An eastward-sweeping negative dynamic topography signal since ~26Ma may have, in-part, contributed to major changes of paleogeography and basin evolution. Our results may also hold clues for accounting for the anomalously negative residual depth of the Argentine Basin. Our models also suggest that the elevation of the Andes themselves has been modulated by time-dependent dynamic topography.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8158 TECTONOPHYSICS / Plate motions: present and recent;
- 8170 TECTONOPHYSICS / Subduction zone processes;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution