Geometric analysis and timing of structures on mafic-ultramafic bodies andhigh grade metamorphic rocks in the Sierras Grandes of San Luis Province, Argentina

The study area comprises a portion of the Sierras Grandes of San Luis Provi nce in west-central Argentina. This sector is composed of high-grade granul ite facies metamorphic rocks, mainly gneisses and migmatites, with intercal ated igneous mafic-ultramafic bodies. These bodies occur as discontinuous l enses along a narrow central belt concordant with the general NE-SW structu ral trend. The granulite facies metamorphism reached by this central area h as been ascribed to the intrusion of the mafic-ultramafic bodies into an am phibolite facies metamorphic sequence. On both sides of the mafic-ultramafi c bodies, a decrease of metamorphic grade to amphibolite facies is apparent . Numerous pegmatitic bodies intruding the metamorphic complex can be found elsewhere and, towards the western limit of the study area, La Escalerilla metagranite constitutes one of the larger granitic exposures of the Sierra s. The results of the structural analysis, done along cross-sections transv erse to the mafic-ultramafic brit, allow us to establish a structural evolu tion for this large geological feature. The described deformational events can be correlated with the tectonic framework postulated for the southern P ampean Ranges. (C) 2001 Elsevier Science Ltd. All rights reserved.