LAUSR

Abstract A Silurian regional tectonometamorphic event has been widely recorded by different geochronological methods in the Sierras Pampeanas, NW Argentina and the Precordillera. It took place between ca. 445 and 420 Ma after the regional Hirnantian (late Ordovician) glaciogenic sedimentation. Three domains are recognized. 1) The eastern Sierras Pampeanas and the Puna mainly record focused westward ductile thrusting and heating. 2) In the westernmost Sierras Pampeanas (Maz, Espinal, and Umango) garnet-amphibolite facies metamorphism, penetrative foliation development and westward ductile thrusting (nappes) took place. 3) In the Precordillera, the Rinconada formation of Silurian age consisting of chaotic olistoliths of Ordovician and Cambrian age correlates with this event. The three domains correspond to the hinterland, the internal hot and thickened metamorphic core, and the foreland respectively of an orogenic belt. Remarkably no Cordilleran-type magmatism of this age has been recorded. The regional importance of this event was overlooked so far.