Gravity inversion for crustal thickness investigation of the continental and oceanic crusts of Brazil incorporating a lithosphere thermal gravity anomaly correction

Abstract

The application of potential field methods in regional geophysical studies with orbital data has proven helpful in identifying, modeling, and dimensioning structural features and geophysical signatures in regions of interest. Potential field data, particularly those from gravity satellites, are robust and have a high resolution for regional studies. Therefore, gravity data enable in-depth identification of information from low-frequency sources, interpreted as features with relevant geotectonic significance. Furthermore, by containing wavelengths from low-frequency sources, these data allow investigation of lithospheric depths. However, it is necessary to apply thermal correction because gravity data are affected by thermal anomalies present in the lithosphere. Thus, the greater precision/robustness is attributed to these extensive and heterogeneous areas onshore. In this context, data from the compilation World Gravity Map – 2012 were applied to evaluate the density variation of features in depth and obtain the crust-mantle limit. The three-dimensional (3D) gravity inversion with seismic and seismological constraints was applied to obtain the crust-mantle limit for the onshore and offshore regions of Brazil. Furthermore, our objective was to apply and evaluate a gravity inversion methodology with seismic data constraints for the onshore portion of Brazil, which has an exotic and rich geological setting. The onshore portion is covered by seismographic stations, but has sparse coverage areas, mainly in the Amazonian Craton. In addition, the scarcity of seismic refraction data in the national territory makes it impossible to detail the structure of the base of the crust or lithosphere in a spatialized manner. To obtain the crust-mantle limit, the inversion permits corrections, such as topographic effects, the gravity effect of sediments, and the thermal gravity anomaly correction, which interferes with the investigation of crustal thickness using gravity data. Thus, it was possible to observe shallow Moho depths (∼10 km) in the offshore portion and deep (∼50 km) in the cratonic regions onshore, equivalent to the depths provided by the deep refraction seismic and receiver function data. Therefore, from the gravity inversion, it was possible to obtain the 3D depth of the Moho, adding information to the seismic interpretations, with the possibility of observing 3D features and profiles that present a resolution compatible with the seismic data. Moreover, we interpreted areas with obliterated signatures owing to thermal anomalies in the heterogeneous continental lithosphere.