Resumo

TIBALDI, Alina M et al. Infernal structure of the migmatites of the northern portion of the Sierra de Valle Fértil, San Juan. Rev. Asoc. Geol. Argent. [online]. 2012, vol.69, n.2, pp.252-262. ISSN 0004-4822.

In the northern portion of the sierra de Valle Fértil, there are migmatitic rocks which have been classifed as metatexites and diatexites according to their fabric, and as metapelitic and metasemipelitic-metagreywacke in function of their protoliths. Field relationships and a detailed structural analysis of the migmatites and the resisters associated to them, allow recognizing the presence of pre-migmatitic structures (S-SR) interpreted as sedimentary bedding and relictic metamorphic foliation, this last one related to the buried processes. The generation of anatectic granites related to migmatites with foliations (S1abc) and (P ,b), are associated to a deformational phase (D ) developed at high temperature conditions (granulite facies) and contemporary with the magmatism. Lastly, postmigmatic fabrics (S and S 2b) related to a deformational event (D ), show an evolution under ductile-brittle conditions related to the cióse and exhumation stage of the Famatinian are. This fabric is superimposed by a planar structure of brittle character (S ). Thus, we establish that the Famatinian magmatic are is developed in a thick sedimentary sequence, deposited and consolidated since the mid-Cambrian. This sequence does not record a previous deformational history to the emplacement of Ordovician magmatism. In contrast, all the preserved structural features are related to metamorphism (migmatization) and exhumation during the are development.

Palavras-chave : Migmatites; Deformation; Sierra de Valle Fértil; Pampean Ranges; Famatinian orogen.

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