Geology and structure of the area around Paso de las Nubes, North-Patagonian Andes, Argentina

OLAIZOLA, E.; BECHIS, F.; YAGUPSKY, D.L.; BRAN, D.; ORIOLO, S.

Montgenevre

Conferencia; Young Researchers in Structural Geology and Tectonics; 2018

The present study constitutes a lithological and structural analysis located in the centralsector of the North-Patagonian Andes, between 41°06?00?? and 41°11?00??S, and 71°50?00??and 71°33?40??W, east of the Tronador Mount. Currently there are two non-exclusive theoriesthat explain the mechanism through which the North-Patagonian Andes at these latitudeswere formed from Neogene times: the first of them proposes a compressive regime, whilethe second one considers a transpressive structural style.The objectives of this study consisted in the mapping and analysis of the outcroppinglithological units, the kinematic and chronological characterization of the observedstructures, and the understanding of the deformation evolution and the structural style of theregion.The lithological characterization of the exposed units consisted in a petrographical analysisof all the units, a stratigraphic section and an Ar-Ar dating of the Tronador I unit. In order todevelop the structural analysis, the methodology employed was constituted by: theidentification of lineaments along with statistical and spatial analysis of the obtained data; theclassification of the interpreted lineaments according to the unit they affected and theirlongitude; the measurement of fault slip data in 34 mesoscopic faults; the determination ofthe slip direction and the sense of fault-slip in each fault measuring the orientation of striae infault planes and of associated secondary Riedel fractures.The outcropping units mapped are: the Colohuincul Complex (Devonian-Permian), aJurassic Volcano-Sedimentary Complex, the Miocene Coluco Formation and the volcanicTronador Complex (Pleistocene), represented by the Tronador I and Tronador III units. Anobtained age of 1.178 ± 0.057 My constitutes a high resolution dating for the Tronador I unitand helped refining the stratigraphy of the homonym complex, whose eruptive activity islimited between 1.2 ? 0.3 My. The kinematic results from the structural analysis allowed todetermine two fault systems: a transtensive population and a right-lateral strike-slip one.Taking into account the obtained data and the regional tectonic context, the followinginferences were made: i) the reactivation of former structures of the basement would haveplayed a fundamental role in the Mesozoic-Cenozoic tectonic evolution of the region; ii) asthe measurements reveal the presence of a strike-slip deformation component in the region,the mechanism of construction of the Andean orogeny at this latitude is more consistent withthe transpressive regime, than to the purely compressive one; iii) a coupled structuralevolution is proposed between the studied region and the Liquiñe-Ofqui Fault Zone in Chile.