CRUSTAL STRUCTURE IN HIGH DEFORMATION ZONES: INSIGHTS FROM GRAVIMETRIC AND MAGNETOMETRIC STUDIES IN THE GUACHA CORRAL SHEAR ZONE (EASTERN SIERRAS PAMPEANAS, ARGENTINA)

RADICE, STEFANÍA; LINCE KLINGER, FEDERICO; MAFFINI, MARÍA NATALIA; PINOTTI, LUCIO PEDRO; DEMARTIS, MANUEL; D'ERAMO, FERNANDO JAVIER; GIMENEZ, MARIO ERNESTO; CONIGLIO, JORGE ENRIQUE

La Rioja

Otro; XVII REUNIÓN DE TECTÓNICA; 2018

ComPetro - Asociación Geológica Argentina

The Guacha Corral shear zone (GCSZ), is one of the most prominent shear zone in the Eastern Sierras Pampeanasand juxtaposes different metamorphic complexes of the Sierras de Córdoba and the Sierras de San Luis (Martino, 2003; Fagiano et al. 2002; Radice et al. 2017; Otamendi et al. 1996). Its extends for over 120 km in length and up to 20 km in width. This structure significantly deformed Pampean (Late Neoproterozoic-Early Cambrian) rocks that are principally represented by migmatites and amphibolites in the study area. From geophysical, structural and petrological data we determine the 3D geometry of the GCSZ. New gravimetric, magnetometric and structural studies, along an E-W profile in north of GCSZ were integrated with existing magnetotelluric and seismological data from a representative regional database of the Eastern Sierras Pampeanas. The zonation of different fabrics across the GCSZ suggests that the pre-existing heterogeneities of the protoliths played a key role in governing the degree of metamorphism of different regions. The low gravity anomalies observed in the GCSZ suggest a transitional boundary zone between the migmatitic and mylonitic domains, where highly deformed shear bands are interspersed with undeformed rocks, presenting gradual contacts. The mylonites in this shear zone show a considerably reduced density when compared to the migmatite protoliths. The density of the rocks gradually increases with depth until it reaches that of the protolith. These changes in the gravity values in response to density changes allowed us to infer the GCSZ reaches a ~20 km depth and present a listric geometry. Low gravity anomalies in the profiles, in regions where high density rocks (migmatites) outcrop at the surface, modelled as buried granitic plutons and could correspond either to the southern continuation of the Achala batholith or to a smaller, independent pluton of possible Devonian to Carboniferous age.