3D gravimetric investigation of the Cerro do Jarau structure, Rio Grande do Sul, Brazil

Abstract

The Cerro do Jarau structure is possibly the third Brazilian basaltic crater formed in continental flood basalt of the Serra Geral Formation, Paraná Basin, a large igneous province (LIP) in southern Brazil. It is a nearly circular landform with a diameter of approximately 13 km that rises 200 m above the plains of the “pampas” in southern Brazil. In this work, Bouguer anomalies were calculated from gravity accelerations measured on the area of this structure. The residual Bouguer map shows a strong positive anomaly trending NE‐SW, located in the northeastern part of the structure, a feature not commonly associated with impact structures. However, the negative anomaly present in its center and the circular positive anomaly surrounding the central portion are typical of impact structures. The residual Bouguer anomaly varies from −2 mGal to 8 mGal. The positive circular anomaly is not spatially coincident with the rim of the structure. Based on the interpretation of our gravimetric data, the estimated diameter of the structure is 12 km and the central portion has a diameter of approximately 5 km, both slightly smaller than previously suggested. The Bouguer anomaly map was inverted into a 3D density model using a constrained inversion method with a maximum density contrast of 0.5 g cm−3. This model was interpreted to associate densities with rock types, resulting in a geological model. This geological model is in accordance with the meteorite impact nature of Cerro do Jarau.

Shock deformation confirms the impact origin for the Cerro do Jarau, Rio Grande do Sul, Brazil, structure

“…; Giacomini et al. ). Although the current knowledge clearly favors an impact origin, conclusive evidence in the form of truly diagnostic shock indicators has not been fully demonstrated to date.…”

“…A geological explanation for this anomalous feature has been sought for decades, with postulations ranging from endogenous (magmatic intrusion or structural uplift- Grehs 1969) to exogenous (meteorite impact) processes (Lisboa et al 1987;Cr osta et al 2010;Philipp et al 2010;Sanchez, 2013;S anchez et al 2014;Giacomini et al 2017). Although the current knowledge clearly favors an impact origin, conclusive evidence in the form of truly diagnostic shock indicators has not been fully demonstrated to date.…”