3D magnetic characterization of the Aimorés structure (Brazil) aiming to identify interpretation elements under cover: Impact crater or circular intrusion?

Abstract

The Aimorés intrusive complex (AIC), located in the Araçuaí belt (Brazil), has been characterized for many years as the Aimorés Impact Crater due to its topographic features, such as the circular morphology and the ring-shaped rim. Detailed geologic mapping finds a zoned igneous intrusion composed of granite and charnockite rocks in the outer rims, whereas the central part of the structure is covered by overburden. In the absence of direct evidence under the center of the structure, uncertainty remains and there is ambiguity about the geologic interpretation of the area. For this reason, we have used magnetic data to investigate the AIC structure in the subsurface. We explore the different possibilities of geologic scenarios for this region, namely, a pluton with eroded center, a zoned intrusion, a simple impact crater, and a complex impact crater through a synthetic study. Our synthetic tests revealed zoned intrusion and simple impact crater as possible geologic scenarios. Then, in the next stage, we characterize the AIC in three dimensions to unveil the subsurface geometry of the magnetic rocks. The inverted model found the geometry of a high susceptibility ring-shaped body that extends at 4 km depth, pointing to a circular zoned intrusion as the more likely interpretation. Our study has revealed two new geologic features in the study area: (1) the presence of two distinct zones under the central depression cover of the AIC and (2) a new zoned body at southeast of the AIC, which has not been mapped previously because of the overburden. We find the efficacy of using magnetic data for mapping postcollisional intrusions potentially associated with lithium mineralization in subsurface.