The Pampean Orogen in the Eastern Sierras Pampeanas contains two paired magmatic belts, an eastern calc-alkaline magmatic belt and a western peraluminous granite/high-grade metasedimentary belt. The relationship between the two belts and their relative timing are constrained through new U-Pb zircon ages on granodiorites, monzogranites, and associated volcanic rocks from Sierra Norte and the easternmost Sierras de Córdoba. These ages indicate that calc-alkaline arc magmatism was active over at least a 30-m.yr. period from 555 to 525 Ma, terminating at the same time that peraluminous magmatism and associated high-grade metamorphism began in the adjoining metasedimentary belt (525–515 Ma). These temporal relationships and the metamorphic characteristics of the two belts appear to be in conflict with previously proposed models for the Pampean Orogeny as a continental-collision event, but they are consistent with models that propose eastward-dipping subduction of oceanic crust initiated at ca. 555 Ma, followed by ridge-trench collision at ca. 525 Ma. Similar-aged belts of arc-related and peraluminous magmatism occur elsewhere along the paleo-Pacific margin of Gondwana, suggesting that similar processes of subduction and noncollisional peraluminous magmatism occurred along much of the Gondwana margin in late Neoproterozoic to Cambrian time.

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