Determinação de campos tensionais rúpteis em uma pedreira no município de Santana da Boa Vista – RS

Abstract

The Porongos Metamorphic Complex is located in the central portion of the SouthRiograndense Shield and is constituted by a metavulcanosedimentary sequence with intercalations of orthogneisses and metaultramafic rocks, which record a complex history of deformation related to at least five ductile and rusty tectonic events. In this work, a structural analysis was performed in a quarry with the integration of field structural data and information obtained through a Virtual Outcropping Model with the objective of elucidating the processes involved in the rump deformation events. Field data were obtained using traditional methods of structural geology such as acquisition of attitudes of planes and structural lines, descriptions of structures and kinematic analysis. The Outcrop Virtual Model was created from the image-based modeling method through the acquisition of photogrammetric data and orthorectification. The structural data were imported into WinTensor software to obtain the stressor orientation. This information revealed the superposition of three deformational events: i) Compressive; Ii) Transtrative, and iiii) Extensional. The compressive regime is related to a pure radiation compression with maximum horizontal compression vector of direction N-S, this tension regime corresponds mainly to the development of veins, reverse faults, contractional and undetermined motion. The transtrative regime has a sub-horizontal extension of NW-SE direction, horizontal NE-SW direction compression and subvertical intermediate vector, the structures that served as the basis for the determination of this paleotensor were normal faults, inverse, contractional and undetermined motion, beyond veins. The extensional regime has a transcurrent component and presents a sub-horizontal extension of NE-SW direction and a maximum subvertical compression vector of NW-SE direction, the related structures and this tensor consist of normal faults, pairs of conjugated fractures and veins. The cut-off relationships between the structures show that compression was followed by the transtration, and subsequently the extension was dominant. The method used proved to be efficient for structural analysis, as well as for the determination of tectonic regimes.