Abstract
At the east of the Ventana Ranges, Buenos Aires, Argentina, outcrops the Carboniferous-Permian Pillahuincó Group (Sauce Grande, Piedra Azul, Bonete and Tunas Formation). We carried 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 is continuous 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 the AMS 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 Gondwana, marks a new threshold in the evolution of the basin. Those changes along the Pillahuincó deposition indicate two different spasm in the tectonic deformation that according to the ages 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 locally assigned to the San Rafael (Hercinian) orogenic phase, interpreted as the result of rearrangements of the microplates that collided previously with Gondwana, and latitudinal movements of Gondwana toward north and Laurentia toward south to reach the Triassic Pangea.
Highlights
S0 Diagenetic or primary foliation plane S1 Secondary foliation plane Kmax Maximum axes of anisotropy of magnetic susceptibility ellipsoid Kmin Minimum axes of anisotropy of magnetic susceptibility ellipsoid T Shape parameter of anisotropy
The samples belong to the sites JS1 and JS4 classify as lithic diamictites while samples belong to JS3 classify as quarzitic diamictites (Fig. 2C)
As indicated by the anisotropy of magnetic susceptibility (AMS) ellipsoids, AMS parameters and micro-tectonic analyses, the intensity of the deformation decreases inside the Pillahuincó Group from the Sauce Grande to Bonete and the base of the Tunas Formations, and increases again in the Tunas Formation itself[30,31]
Summary
S0 Diagenetic or primary foliation plane S1 Secondary foliation plane Kmax Maximum axes of anisotropy of magnetic susceptibility ellipsoid Kmin Minimum axes of anisotropy of magnetic susceptibility ellipsoid T Shape parameter of anisotropy. The Ventana Ranges were part of a larger system interpreted as part of the Hesperides Basin (Pennsylvanian to Lower Triassic), which is in lateral continuity with the Kalahari, Karoo (Africa) and Chaco-Paraná basins (South America), with a depocenter of more than 3,000,000 km[] They are located in Buenos Aires Province, placed 37°–39° south latitude and 61°–63° west longitude and constitutes an exposed portion of the Claromecó Basin[4,5,6,7] (Fig. 1). For some authors, the deformation possibly began during the Devonian–Carboniferous[10,23,29] In this contribution, petrographic and AMS analysis were applied in samples from the Carboniferous-Permian sequence, belonging to the Pillahuincó Group, in order to get a better comprehension of the timing and intensity of the deformation in the area. Further results were compared with theoretical models of Saint-Bezar et al.[34], Parés and van der P luijm[35] and Weil and Yonkee[36]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
