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Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation

Yokoyama, Elder; Trindade, Ricardo Ivan Ferreira da; Lana, Cristiano de Carvalho; Souza Filho, Carlos Roberto de; Baratoux, D.; Marangoni, Y?ra Regina; Tohver, Eric
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
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The weakening mechanisms involved in the collapse of compleximpact craters are controversial. The Araguainhaimpact crater, in Brazil, exposes a complexstructure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (< 10 ?m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magneticfabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of compleximpactstructures. The widespread occurrence of cataclasis in the central peak...