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Revista de la Asociación Geológica Argentina
Print version ISSN 0004-4822
Abstract
CRISTOFOLINI, Eber et al. Geology of the western portion of the Sierra de Valle Fértil, San Juan, from observations in the Quebrada de Otarola. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.4, pp.521-535. ISSN 0004-4822.
This work presents field relationships, petrography and structural features of the crystalline complex that form the central-western portion of the Valle Fértil range, San Juan. The crystalline complex comprises five main lithologic associations: gabbroic rocks, dioritic rocks, metasedimentary migmatites, pegmatitic granites and mylonite series rocks. The fabric igneous preserved in the gabbroic association is which manifest as either layering of cumulate origin (S0a) and magmatic flow bands (S0b). In most places, the primary fabrics occur reworked and/or cross-cut by the submagmatic foliation (S1). However, S1 is associated with low differential stress and the only changes in the primary igneous and metamorphic mineral assemblages are growth of hornblende in mafic rocks and biotite + sillimanite in the metasedimentary rocks. This suggests that (D1) deformation acted under high temperature and synchronously with the igneous activity. Subsequent deformation (D2) is related to high-strain shearing and formed the fabrics S2a and S2b associated a typical mylonite series rocks. Kinematic analysis in mylonites indicates top-to-west reverse sense of shear during D 2 deformation. All structures are locally truncated by brittle planar features (S3). The u-Pb zircon age of 474 ± 4.7 Ma for a metasedimentary migmatite dates the time of the metamorphic peak. This also proves that the metasedimentary rocks reached granulite-facies conditions at the same time that igneous activity was active.
Keywords : Famatinian orogen; Valle Fértil range; Gabbro; Shear zone; Structural evolution.