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. In this paper, we present and discuss some geological characteristics and implications of a 3D subsurface mass density model of the Vargeao impact structure, constructed based on forward gravity modeling constrained by geological information. Vargeao is a complex structure formed by a meteorite impact in basalts of the Serra Geral Formation, with a central uplift exposing sandstones of Piramboia/Botucatu Formations and impact breccias. There are only a few known examples of impact structures formed in basalts on the surface of the Earth, but they are common on other terrestrial planets and their satellites. Therefore, the geophysical modeling of these impact structures on Earth may also provide insights into planetary geology studies. The selected density model encompasses six geological layers that are consistent with the known regional stratigraphy. Densities were measured from rock samples from each geological unit and used as constraints in the modeling process. The model shows a large sedimentary block with the shape of a vertical truncated cone and a thickness of ∼650 m in the center of the structure. This block corresponds to the Piramboia/Botucatu formations and it cuts the upper basalt layers. The model is consistent with sandstones outcrops located in the central uplift area of Vargeao, suggesting that the cratering process was responsible for positioning these rocks in a higher level than the surrounding basalts. Keywords: gravity modeling, impact crater, central uplift, Serra Geral Formation. RESUMO. Neste artigo, apresentamos e discutimos algumas caracteristicas e implicacoes geologicas de um modelo 3D de densidade de massa da subsuperficie da estrutura de impacto Vargeao, elaborado com base em modelagem gravimetrica direta controlada por informacoes geologicas. Vargeao e uma estrutura complexa formada por impacto meteoritico em basaltos da Formacao Serra Geral, com um nucleo central soerguido expondo arenitos das Formacoes Piramboia/Botucatu, alem de brechas de impacto. Existem apenas alguns poucos exemplos de estruturas de impacto formadas sobre basaltos na superficie da Terra, mas elas sao comuns em outros planetas terrestres e em seus satelites. Portanto, a modelagem geofisica de estruturas de impacto na Terra pode fornecer novas perspectivas em estudos de geologia planetaria. O modelo selecionado engloba seis camadas geologicas que sao consistentes com a estratigrafia regional previamente conhecida. Densidades de massa foram obtidas a partir de amostras de rocha de cada camada e utilizadas como controle no processo de modelagem. O modelo apresenta um grande bloco sedimentar na forma de um cone vertical truncado com∼650 m de espessura no centro da estrutura. Este bloco corresponde as Formacoes Piramboia/Botucatu e corta as camadas superiores de basalto. O modelo e consistente com afloramentos de arenitos dessas formacoes, localizados na regiao do nucleo soerguido de Vargeao, mostrando que o processo de formacao da cratera foi respons´avel por posicionar essas rochas em niveis superiores aqueles dos basaltos adjacentes. Palavras-chave: modelagem gravimetrica, cratera de impacto, nucleo soerguido, Formacao Serra Geral.

3D GRAVITY MODELING OF IMPACT STRUCTURES IN BASALTIC FORMATIONS IN BRAZIL: PART I – VARGEÃO, SANTA CATARINA