The Ordovician of Sierra de San Luis: Famatinian magmatic arc and low to high-grade metamorphism

SATO ANA MARÍA; GONZÁLEZ, PABLO D.; LLAMBÍAS EDUARDO

Aspects of the Ordovician System in Argentina

Ediciones MAGNA-INSUGEO

Lugar: San Miguel de Tucumán; Año: 2002; p. 327 - 346

The main features of the Sierra de San Luis basement were delineated during the Ordovician Famatinian orogeny, that involved the active SW Gondwana margin. The metamorphic and sedimentary rocks formed during previous processes (Pampean orogeny?) were affected by arc magmatism, NNE-SSW penetrative deformation, and low to high-grade regional metamorphism. Available isotopic data constrain the arc magmatism (pre- and synorogenic granitoids) between Middle Cambrian and late Ordovician. Regional metamorphism occurred at variable crustal levels, associated with compressive deformation. The highgrade metamorphism was of Barrovian-type, with P-T conditions mostly in the range 5 - 7.5 Kb and 518° - 770°C. The duration of metamorphism was apparently longer for the high-grade (early to late Ordovician) than for the low-grade rocks (Middle to late Ordovician). After the main Ordovician events, the outlasting compression produced ductile shear zones and a thickened crust, that favored the production of postorogenic granitoids. Along the collision-related Famatinian orogen of Sierras Pampeanas, the analysis of metamorphic conditions suggests that the compressive regime associated with terrane accretion was variable.