Involvement of the Argentine Precordillera terrane in the Famatinian mobile belt: U-PbSHRIMP and metamorphic evidence from the Sierra de Pie de Palo

New data suggest that the eastern margin of the Argentine Precordillera ter rane comprises Grenvillian basement and a sedimentary cover derived from it that were together affected by Middle Ordovician deformation and metamorph ism during accretion to the Gondwana margin. The basement first underwent l ow pressure/temperature (P/T) type metamorphism, reaching high-grade migmat itic conditions in places (686 +/- 40 MPa, 790 +/- 17 degreesC), comparable to the Grenvillian M-2 metamorphism of the supposed Laurentian counterpart of the terrane. The second metamorphism, recognized in the cover sequence, is of Famatinian age and took place under higher P/T conditions, following a clockwise P-T path (baric peak: 1300 +/- 100 Mpa, 600 +/- 50 degreesC). Low-U zircon overgrew detrital Grenvillian cores as pressure fell from its peak, and yields U-Pb SHRIMP ages of ca. 460 Ma. This is Interpreted as the age of ductile thrusting coincident with early uplift; initial accretion t o Gondwana must have occurred before this. The absence of late Neoproterozo ic detrital zircons is consistent with a Laurentian origin of the Argentine Precordillera terrane.