Geology, gravity, and numerical modeling of the Nova Colinas impact structure, Parnaíba Basin, Brazil

Abstract

Nova Colinas, centered at 07°09′33″ S/46°06′30″ W, is the ninth confirmed complex impact structure in Brazil and the fifth in the Parnaíba Basin, with a diameter of ~6.5–7 km and a nearly circular shape. Impactites include shocked siltstones from the Pedra de Fogo Fm. found at the central peak, brecciated sandstone from the Sambaíba Fm. bearing microscopic shock features, and brecciated basalt from the Mosquito Fm. bearing shatter cones. The impact event's age has been constrained to the interval from ~130 to ~199 Ma based on the local stratigraphy. Due to its moderate to advanced stage of erosion, geophysical modeling combined with geological field data were employed for its characterization. A new geological map was produced through field observations and remote sensing image interpretation, as well as a 3-D model based on ground gravity data and numerical modeling. iSALE2D shock physics code was employed to simulate the formation of Nova Colinas crater. The results revealed its main structural zones: the central uplift, annular basin, and outer rim, each associated with specific lithostratigraphic units from the Parnaíba Basin. Bouguer residual anomalies ranged from −3.6 to 1.2 mGal, with a nearly circular positive anomaly at the center of the structure, surrounded by a negative anomaly. 3-D gravity data inversion indicated a buried high-density body, likely due to the uplift of a diabase sill. Results of the numerical modeling point out that the final crater reached gravitational stability with a diameter of ~7 km and a depth of ~240 m, suggesting that a narrow outcrop strip of the Motuca Fm. was uplifted to a higher level compared to the Sambaíba Fm. strata, forming an antiform-like “arch” that creates an inner ring that exposes rocks of the Motuca Formation.