Ordovician metamorphism and plutonism in the Sierra de Quilmes metamorphic complex: Implications for the tectonic setting of the northern Sierras Pampeanas (NW Argentina)

The massive Early Ordovician heat transfer, the absence of major prograde deformation, and subsequent, prolonged phases of non-penetrative deformation in the high-grade metamorphic zones during slow near-isobaric cooling contradict crustal thickening and continent collision models, as have been proposed for the southern Sierras Pampeanas. We suggest continuous or stepwise extensional tectonics in a back-arc or a mobile belt tectonic environment for the Ordovician Sierra de Quilmes, and the northern Sierras Pampeanas in general. An extensional setting of the northern Sierras Pampeanas in the Ordovician is in agreement with the coeval formation of marine extensional sediment basins in vicinity of the Sierras Pampeanas in northwestern Argentina and southern Bolivia.