Inversion of geoid anomaly from the Borborema Province: new constraints on its thermal and compositional state from density models

• Grant number: 21/07047-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): September 01, 2021
• Effective date (End): August 31, 2022
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geophysics
• Principal Investigator: Carlos Alberto Moreno Chaves
• Grantee: Alexandre Andreucetti de Matos
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

In this project, we aim to obtain a new density model for the upper mantle beneath the Borborema Province from the inversion of residual geoid anomalies. The Borborema Province has positive geoid anomalies with an amplitude of approximately 10 meters, which are obtained after the removal of the long-wavelength components associated with sources in the lower mantle. To obtain geoid anomalies relate to the density variations in the upper mantle, we will estimate the anomalies caused by the topography masses, sediments, and the density contrast due to Moho and lithosphere depth variations using steroids, so that the spherical shape of the Earth is taken into account. The estimated effects will be removed from the geoid anomalies of the EGM2008 model by truncating it to its maximum degree (2159), with the very long-wavelength component removed (degree 10). Previous results indicate that there is a residual geoid anomaly caused by a decrease in density whose source is probably located in the upper mantle. The geodynamic processes responsible for such a decrease in density are still unknown, but it is speculated that it is caused either by lithospheric delamination or stretching due to the post-rift process and the subsequent rise of the asthenospheric material at higher temperatures. In order to provide additional constraints on the current thermal and compositional status of the upper mantle underneath the Borborema Province, we will use the Lagrange multipliers method to invert residual geoid anomalies to obtain a density model that allows us to estimate the extent and the density contrast of the anomalous source and, with the integration of other results, to point out its most likely origin. (AU)