Oblique megashear zones in the Precordillera (Central Andes, Argentina): the Rodeo?Talacasto Transpressional Belt

JAPAS, MARÍA SILVIA; RÉ, GUILLERMO HÉCTOR; VILAS, JUAN FRANCISCO; ORIOLO, SEBASTIÁN

Conferencia; Deformation mechanisms, Rheology and Tectonics Conference; 2011

The Andean segment located between 28° and 33° S shows a strong anisotropic character as it is composed of tectono-stratigraphic units with different previous geological stories. They also show up major planar anisotropies that resulted from the accretion and amalgamation of different terranes (Ramos 1999). Therefore the deformation as a whole is strongly inhomogeneous. Tectonic Fabric Analysis focused on the Central Andes from Argentina revealed two systems of conjugated megashear zones. The first system comprises left-lateral NNW and right-lateral NNE transpressional sets while the second one involves left-lateral WNW and right-lateral ENE transtensional sets (Japas 1998, Ré et al. 2001, Japas et al. 2002a and b, Ré and Japas 2004). One of these left-lateral NNW transpressional structures (Mendoza Norte, Ré et al. 2001) was lately confirmed as a NNW sinistral transpressional belt (Barreal-Las Peñas Belt, Cortés and Cegarra 2004, Cortés et al. 2005). The Andean Precordillera is a North-trending, thin-skinned (Western and Central Precordillera) and thick-skinned (Eastern Precordillera) fold and thrust belt developed at the foreland of the Pampean flat slab. Between Rodeo and Talacasto towns, a set of thrust-controlled exposures of synorogenic Tertiary rocks are arranged in an en-échèlon pattern following a NNW trend. Along this NNW belt, trends of Andean regional thrusts and folds change from NNE to NS/NNW as well as NNE-oriented outcrops of Palaeozoic sedimentary rocks are deflected counterclockwise. Furthermore, a NNW brachianticline (Loma Negra) developed at the eastern border of this Rodeo-Talacasto belt. Preliminary structural fabric, kinematic and paleomagnetic data (work in progress) allow to define the Rodeo-Talacasto belt as the consequence of NNW sinistral transpression. According to both previous proposals (Cortés et al. 2005) and recent analogue models (Yagupsky et al. 2007), the structure of pre-Tertiary rocks would have controlled the development of this oblique belt.