Evolution of the Famatinian orogen in the Sierra de San Luis: arc magmatism, deformation, and low to high-grade metamorphism

Abstract

In this geological review of the igneous-metamorphic basement of the Sierra de San Luis we recognize the following three-stage evolution: (1) Pre-Famatinian processes: Initial siliciclastic sedimentation of possible Precambrian age, with interbedded mafic to ultramafic lavas and banded iron formations. Only a few isotopic dates constrain the remnant northwest-trending deformation and associated metamorphism within the Pampean cycle. An additional sedimentary process is also identified within this cycle. (2) Famatinian orogenic cycle, main phase: this was responsible for delineating the most important features of the Sierra de San Luis basement. The Famatinian magmatic arc had already been active since Mid-Cambrian times (507 Ma), and the Ordovician was the climax of the magmatism, tectonism and metamorphism. The granitoids were deformed together with the country rock, and the entire Sierra de San Luis was affected by penetrative NNE-trending foliations. (3) Famatinian cycle, late- to post-orogenic phase: the orogenic activity decreased during Silurian to Early Carboniferous times. Final compression was concentrated through ductile shear zones that led to the juxtaposition and exhumation of metamorphic rock strips. The late- to postorogenic granitoids were also emplaced at this stage. From the regional viewpoint, the Ordovician deformation in Sierras Pampeanas was associated with terrane collision. The Sierra de San Luis was located at the proto-Andean margin of the Gondwana autochthon, where the magmatic arc was emplaced. The Ordovician deformation affected both the Gondwana margin and the Mesoproterozoic basement of the accreted Cuyania terrane, located to the west. To the east of Sierra de San Luis, the Sierra de Córdoba was not directly involved in the main famatinian orogenic axis, and therefore, all the Pampean processes were well preserved there.