Spasmodic deformation in the Southwest of the Gondwana boundary, Upper Paleozoic of Ventana ranges in Argentina

RENATA N. TOMEZZOLLI; GUADALUPE ARZADÚN; NATALIA FORTUNATTI; NORA N. CESARETTI; MARÍA BELÉN FEBBO; JUAN M. CALVAGNO; GISELLE CHOQUE

Viena

Otro; EGU General Assembly 2022; 2022

European Geosciences Union

At the east of the Ventana Ranges, Buenos Aires, Argentina, outcrops the Carboniferous-Permian Pillahuincó Group (Sauce Grande, Piedra Azul, Bonete and Tunas Formation). Wecarried out an Anisotropy of Magnetic Susceptibility (AMS) study on Sauce Grande, Piedra Azul and Bonete Formation that displays ellipsoids with constant Kmax axes trending NW-SE,parallel to the fold axes. The Kmin axes are orientated in the NE-SW quadrants, oscillating from horizontal (base of the sequence-western) to vertical (top of the sequence-eastern)positions, showing a change from tectonic to almost sedimentary fabric. This is in concordance with the type and direction of foliation measured in petrographic thin sections which iscontinuous and penetrative to the base and spaced and less developed to the top. We integrated this study with previous Tunas Formation results (Permian). Similar changes in theAMS pattern (tectonic to sedimentary fabric), as well as other characteristics such as the paleo-environmental and sharp curvature in the apparent polar wander path of Gondwanamarks a new threshold in the evolution of the basin. Those changes along the Pillahuincó deposition indicate two different spasms in the tectonic deformation that according to theages of the rocks are 300-290 Ma (Sauce Grande to Bonete Formation deposition) and 290-276 Ma (Tunas Formation deposition). This Carboniferous-Permian deformation is locallyassigned to the San Rafael (Hercinian) orogenic phase, interpreted as the result of rearrangements of the microplates that collided previously with Gondwana, and latitudinalmovements of Gondwana toward north and Laurentia toward south to reach the Triassic Pangea.