Basement structures over Rio Grande Rise from gravity inversion

Abstract

The basement depth in the Rio Grande Rise (RGR), South Atlantic, is estimated from combining gravity data obtained from satellite altimetry, marine surveys, bathymetry, sediment thickness and crustal thickness information. We formulate a crustal model of the region by inverse gravity modeling. The effect of the sediment layer is evaluated using the global sediment thickness model of National Oceanic and Atmospheric Administration (NOAA) and fitting the sediment compaction model to observed density values from Deep Sea Drilling Project (DSDP) reports. The Global Relief Model ETOPO1 and constraining data from seismic interpretation on crustal thickness are integrated in the inversion process. The modeled Moho depth values vary between 6 and 27 km over the area, being thicker under the RGR and also in the direction of São Paulo Plateau. The inversion for the gravity-equivalent basement topography is applied to gravity residual data, which is free from the gravity effect of sediments and from the gravity effect of the estimated Moho interface. We find several short-wavelengths structures not present in the bathymetry data. Our model shows a rift crossing the entire Rio Grande Rise deeper than previously presented in literature, with depths up to 5 km in the East Rio Grande Rise (ERGR) and deeper in the West Rio Grande Rise (WRGR), reaching 6.4 km. An interesting NS structure that goes from 34°S and extends through de São Paulo Ridge may be related to the South Atlantic Opening and could reveal an extinct spreading center.