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Título: Magnetic fabric of Araguainha complex impact structure (Central Brazil) : implications for deformation mechanisms and central uplift formation.
Autor(es): Yokoyama, Elder
Trindade, Ricardo Ivan Ferreira da
Lana, Cristiano de Carvalho
Souza Filho, Carlos Roberto de
Baratoux, D.
Marangoni, Yára Regina
Tohver, Eric
Palavras-chave: Microstructures
Magnetic anisotropy
Compleximpact crater
Weakening mechanism
Data do documento: 2012
Referência: YOKOYAMA, E. et al. Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation. Earth and Planetary Science Letters, v. 331-332, p.347-359, mai. 2012. Disponível em: <>. Acesso em: 22 out. 2012.
Resumo: 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 μm) 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, and its orientations revealed by magnetic studies indicate that acoustic fluidization likely operates at all scales, including the mineral scales. The cataclastic flow made possible by acoustic fluidization results in an apparent plastic deformation at the macroscopic scale in the core.
ISSN: 0012821X
Licença: O Periódico Earth and Planetary Science Letters concede permissão para depósito deste artigo no Repositório Institucional da UFOP. Número da licença: 3315440555391.
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