Basement Structure of the Santos Basin from Gravity Data

Abstract

The ocean basement represents the tectonic situation of a specific area and its knowledge is crucial in studies aimed at exploring the seabed. Due to the high sedimentation rate, especially in ocean basins, the topography of the basement is masked and its structures can be buried, inaccessible to direct observation. This paper aims to estimate the depth of the basement in the region of the Santos Basin in Brazil from a combined analysis of gravity data obtained from satellite altimetry and marine gravimetry, bathymetric data and sediment thickness. In the first step of the work the gravity effect of sediments in Santos Basin was calculated and the Crustal Mantle Interface (CMI) was modeled from constrained gravity inversion. Next, the reliability of the models so obtained was tested by flexural analysis. The flexural and gravity CMI proved to be in agreement. The gravity effect of the CMI and the gravity effect of the sediments were then calculated and subtracted from the original Bouguer anomaly. The residual field thus obtained, which is assumed to represent the topographical features of the basement, was inverted in the last step of the work, providing information that shows a basement with features of up to 700 m that appear to be in agreement with tectonic features previously discussed, such as the Avedis volcanic chain. The depth of the basement estimated during this study showed values ranging from 1,500 to 10,500 m, and the deepest region is consistent with the Cabo Frio Fault.

Basement structures over Rio Grande Rise from gravity inversion

“…The ocean basement is presumed to be oceanic basaltic crust created at mid-ocean ridges and its knowledge is crucial in many applications of geosciences, as the basement, rather than the ocean bottom, is representative of the tectonic situation and history of a specific area (Braitenberg et al, 2006). Due to continuous sedimentation over oceanic areas, morphologic features of the basement can be buried and features of low amplitude will be the first ones to disappear, distorting the tectonic framework (Constantino and Molina, 2014). Therefore, a flat ocean bottom may hide a completely different tectonic situation of lineaments, tilted crustal blocks and ridges, which can only be observed directly on the basement.…”