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; GIMÉNEZ, MARIO; CONIGLIO, JORGE E.

La Rioja

Congreso; XVII REUNIÓN DE TE C T ÓNICA; 2018

Comisión de Tectónica de la Asociación Geológica Argentina

The Guacha Corralshear zone (GCSZ), is one of the most prominent shear zone in the EasternSierras Pampeanasand juxtaposes different metamorphic complexes of the Sierrasde 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 inlength and up to 20 km in width. This structure significantly deformed Pampean(Late Neoproterozoic-Early Cambrian) rocks that are principally represented bymigmatites and amphibolites in the study area. From geophysical, structural andpetrological data we determine the 3D geometry of the GCSZ. New gravimetric,magnetometric and structural studies, along an E-W profile in north of GCSZwere integrated with existing magnetotelluric and seismological data from arepresentative regional database of the Eastern Sierras Pampeanas. The zonationof different fabrics across the GCSZ suggests that the pre-existingheterogeneities of the protoliths played a key role in governing the degree ofmetamorphism of different regions. The low gravity anomalies observed in theGCSZ suggest a transitional boundary zone between the migmatitic and myloniticdomains, where highly deformed shear bands are interspersed with undeformedrocks, presenting gradual contacts. The mylonites in this shear zone show aconsiderably reduced density when compared to the migmatite protoliths. Thedensity of the rocks gradually increases with depth until it reaches that ofthe protolith. These changes in the gravity values in response to densitychanges allowed us to infer the GCSZ reaches a ~20 km depth and present alistric geometry. Low gravity anomalies in the profiles, in regions where highdensity rocks (migmatites) outcrop at the surface, modelled as buried graniticplutons and could correspond either to the southern continuation of the Achalabatholith or to a smaller, independent pluton of possible Devonian toCarboniferous age.