Dynamic topography and anomalously negative residual depth of the Argentine Basin

Abstract

A substantial portion of Earth's topography is known to be caused by the viscous coupling of mantle flow to the lithosphere but the relative contributions of shallow asthenospheric flow versus deeper flow remains controversial. The Argentine Basin, located offshore of the Atlantic margin of southern South America, is one of the most anomalously deep ocean regions as it is significantly deeper than its age would suggest. Previously, the anomalous depth has been attributed to asthenospheric flow and the coupling of the South American plate's westward motion to the shallow mantle. Using a combination of geophysical observations and geodynamic modeling we propose that subducted slab-driven dynamic topography has primarily driven the long-wavelength anomalous residual basin depth since the opening of the South Atlantic. Using an inverse mantle convection model with plate motions since the early Cretaceous, we suggest that the median of present-day dynamic topography of the basin is -400. m. When the residual basement depth is low-pass filtered the depth anomaly is -730. m, suggesting that more than half of the residual basement depth can be attributed to deep-seated mantle dynamics. We conclude that coupled plate tectonic-mantle convection models tied to seismic tomography, bathymetry and sediment thickness data can help to elucidate the driving forces behind Earth's topography, one of the most fundamental characteristics of this planet. Show more