Sm-Nd isotopic constraints on the Neoproterozoic –Early Paleozoic evolution of the Eastern Sierras Pampeanas

LOPEZ DE LUCHI, M.G.; STEENKEN, A.; MARTÍNEZ DOPICO, C.; WEMMER, K.; SIEGESMUND, S.

BOLLETTINO DI GEOFISICA TEORICA ED APPLICATA

ISTITUTO NAZIONALE DI OCEANOGRAFIA E DI GEOFISICA

Año: 2010 vol. 51 p. 31 - 33

0006-6729

The Eastern Sierras Pampeanas were structured by three main events: the Ediacaran to early Cambrian (580–510 Ma) Pampean, the late Cambrian–Ordovician (500–440 Ma) Famatinian and the Devonian-Carboniferous (400–350 Ma) Achalian orogenies. The examination of reliable geochronological and Sm-Nd isotopic evidence with petrological observations and structural features in evaluating alternatives for a critical Early Paleozoic tectonic model for the Eastern Sierras Pampeanas might allow to speculate for Pre Pampean a major rift event and a subsequent closure and consumption of a ridge segment with an OIB signature input. This mafic input to the crust might have controlled the granulite facies metamorphism and led to a final collision (Pampean orogeny) with the western Mesoprotrozoic block. Ordovician re-activation of active margin along the western part of the block that collided in the Cambrian led to arc magmatism (Famatinian orogeny) and related ensialic back-arc basin in which high grade metamorphism is related with mid-crustal felsic plutonism and mafic magmatism which exhibit process of mixing/assimilation of depleted mantle signature melts and continental crust. In pre-Devonian times crustal reworking is dominant, whereas processes during Devonian times involved different geochemical and isotopic signatures that reflect a major input of juvenile magmatism, suggesting that a new subduction regime was installed west of the Eastern Sierras Pampeanas -the Achalian orogeny- .