Magnetometric and seismic investigation of the Nova Colinas impact structure, Parnaíba Basin, Brazil

Abstract

Nova Colinas (NC) is a complex-type impact structure located in the northeast region of Brazil. It was formed in the volcano-sedimentary strata of the Parnaíba Basin, in the northern part of Western Gondwana. With an apparent diameter of approximately 6.5–7 km, its rim exhibits a distinctive magnetic signal, likely associated to basic volcanic rocks from the Mosquito Formation. These rocks present shock deformation, bracketing the maximum age of the impact event to 197 Ma. We use the magnetometric and seismic methods to establish the geophysical signature of NC and it is the structural framework in subsurface, as well as for characterizing the occurrence and extent of the volcanics. The magnetometric maps present two distinct magnetic domains in the region of NC: (i) the northern area is characterized by short-wavelength magnetic anomalies related to the basaltic flows of the Mosquito Formation; and (ii) the southern region, where sedimentary rocks from the Sambaiba Formation occur, which lacks significant magnetic anomalies, a typical pattern of siliciclastic sedimentary strata. The magnetic sources at the structure's rim reach an estimated depth of ∼250 m, and the position of the rim itself has been effectively established by the total horizontal derivative of the tilt derivative (THDR_TDR) technique. The regional magnetic anomaly suggests a deeper source at the center of the structure, possibly caused by strata with high magnetic susceptibility uplifted in the modification stage of crater formation. Magnetometric modeling using the magnetization vector inversion (MVI) method allowed detailed mapping of the volcanic rocks that form NC's rim. Additionally, analysis of the seismic data allowed the identification of two well-marked horizons, interpreted as diabase sills, located at depths of 600 m and 1200 m, respectively. Impact-related deformation represented by structures such as fractures, a central uplift, and reflector discontinuities associated with faulting, fracturing, and brecciation, were also unveiled by the seismic data, as well as the establishment of the depth of the crystalline basement at ca. 2200 m.