Pampean Orogen: An Intraplate Component of Early Paleozoic Deformation?

Abstract After accretion of the Pampean continental fragment to the western Rio de la Plata craton margin (530 Ma), subsequent deformation, crustal anatexis and plutonism may have been intraplate responses to Brasiliano-PanAfrican collisional tectonism on the eastern margin during the amalgamation of Gondwana. Investigations of intraplate orogens such as the Tien Shan and the Ancestral Rocky Mountains, as well as of analogue and numerical models, permit discrimination of two early Paleozoic tectonomagmatic phases in the Sierras Pampeanas. The first involved marginal trough subduction and calc-alkaline magmatism, culminating in accretion of the Pampean terrane to the western craton edge; the second was characterized by crustal anatexis and peraluminous plutonism, penetrative deformation and high-angle reverse faulting resulting from continental collision on the eastern craton margin. Field observations from modern (Tien Shan) and ancient (Ancestral Rocky Mountains) intraplate chains, deep seismic and borehole data, radiometric and fission-track data constitute control for analogue and numerical models of intraplate deformation resulting from continental collision. Near-simultaneous continent-wide deformation, regularly spaced ranges/buckles, reverse-fault initiation at fold hinges of buckles, and doubling of crustal thickness are replicated in structural arrays formed in four-layer analogue models of lithospheric buckling. These data have significant implications for the ductile deformation, crustral thickening and post-subduction plutonism that spanned central South America in Late Cambrian time.