CAMBRIAN STRIKE-SLIP EMPLACEMENT OF PAMPIA AND AREQUIPA ON CORDILLERAN MARGIN OF AMAZONIA: EVIDENCE FROM GEOCHRONOLOGY OF THE UMACHIRI FORMATION, PERU

Cambrian magmatism and deformation in the Cental Andes of SW South America have typically been attributed to the late stages of the Pampean orogeny (~540 Ma) or the early stages of the Famatanian orogeny (~470 Ma). Yet, critical to tectonic models of the Cordilleran margin of South America is an improved recognition of mid-Cambrian events associated with the emplacement and translation of exotic terranes. Here we present a new LA-ICPMS and CA-ID-TIMS geochronological constraints on the Umachiri Formation, which we suggest was deposited in a narrow strike-slip basin. Zircon from volcaniclaastic horizons within fine-grained siliciclastic strata yield ages as young as ~790 Ma that we correlate with the Gannakouriep dike swarm on the Kalahari carton. These data inspire a new tectonic model in which the Arequipa and Pampean terranes originated from the Kalahari carton, were dextrally translated in the mid-Cambrian, and were emplaned onto the Amazonian margin in the latest Cambrian.