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The Famatina margin records an orogenic cycle of convergence, metamorphism, magmatism, and extension related to the accretion of the allochthonous Precordillera terrane. New structural, petrologic, and geochronologic data from the Loma de Las Chacras region demonstrate two distinct episodes of lower crustal migmatization. The first event preserves a counterclockwise pressure-temperature path in kyanite-K-feldspar pelitic migmatites that resulted in lower crustal migmatization via muscovite dehydration melting at ∼12 kbar and 868°C at 461 ±1.7 Ma. The shape of the pressure temperature path and timing of metamorphism are similar to those of regional midcrustal granulites and suggest pervasive Ordovician migmatization throughout the Famatina margin. One-dimensional thermal modeling coupled with regional isotopic data suggests Ordovician melts remained at temperatures above their solidus for 20–30 Ma following peak granulite facies metamorphism, throughout a time period marked by regional oblique convergence. The onset of synconvergent extension occurred only after regional migmatites cooled beneath their solidus and was synchronous with the cessation of Precordillera terrane accretion at ∼436 Ma. The second migmatite event was regionally localized and occurred at ∼700°C and 12 kbar between 411 and 407 Ma via vapor saturated melting of muscovite. Migmatization was synchronous with extension, exhumation, and strike-slip deformation that likely resulted from a change in the plate boundary configuration related to the convergence and collision of the Chilenia terrane. Fil: Mulcahy, Sean R.. University of California at Berkeley; Estados Unidos Fil: Roeske, Sarah M.. University of California at Davis; Estados Unidos Fil: McClelland, William C.. University of Iowa; Estados Unidos Fil: Ellis, Joshua R.. Kinross Gold Corporation; Canadá Fil: Jourdan, Fred. Curtin University; Australia Fil: Renne, Paul R.. University of California at Berkeley; Estados Unidos Fil: Vervoort, Jeffrey D.. Washington State University; Estados Unidos Fil: Vujovich, Graciela Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Mulcahy, S.R., Roekse, S.M., McClelland, W.C., 2014, The link between collisional tectonics and arc magmatism in the Paleozoic Famatina arc,Argentina, AGU Fall Meeting. Studies of the Famatina margin of northwest Argentina highlight the challenges in understanding the links between Cordilleran arc processes, terrane accretion, and lower crustal deformation, metamorphism, and magmatism. The evolution of the Famatina arc suggests that regional convergence and lower crustal shortening drove voluminous arc magmatism during terrane accretion, pervasive melting of the middle and lower crust did not result in regional extension, and the cessation in arc magmatism and late syn­convergent extension coincided with the end of terrane accretion and a change in the plate margin. The Famatina arc extends more than 1800 km along strike and records the transition from a Cambrian convergent margin to an Ordovician collisional orogen with the accretion of the allochthonous Precordillera terrane. The Famatina arc was established on mid­Proterozoic basement following the onset of regional convergence and east­dipping subduction by ~515-­495 Ma. The peak in arc magmatism in the central portion of the Famatina arc occurred from ~485-­465 Ma and is coincident initial collision of the Precordillera terrane, major crustal shortening accommodated along a series of oblique lower­Studies of the Famatina margin of northwest Argentina highlight the challenges in understanding the links between Cordilleran arc processes, terrane accretion, and lower crustal deformation, metamorphism, and magmatism. The evolution of the Famatina arc suggests that regionalconvergence and lower crustal shortening drove voluminous arc magmatism during terrane accretion, pervasive melting of the middle and lower crust did not result in regional extension, and the cessation in arc magmatism and late syn­convergent extension coincided with the end of terrane accretion and a change in the plate margin. The Famatina arc extends more than 1800 km along strike and records the transition from a Cambrian convergent margin to an Ordovician collisional orogen with the accretion of the allochthonous Precordillera terrane. The Famatina arc was established on mid­-Proterozoic basement following the onset of regional convergence and east­dipping subduction by ~515-495 Ma. The peak in arc magmatism in the central portion of the Famatina arc occurred from ~485-­465 Ma and is coincident initial collision of the Precordillera terrane, major crustal shortening accommodated along a series of oblique lower crustal shear zones, and deformation within the back arc. Steeply dipping reverse­sense ductile fabrics within the arc have hornblende cooling ages of >445 Ma and suggest that voluminous arc magmatism was concurrent with intra­arc shortening. Intrusion of mafic and intermediate magmas during the peak in arc magmatism lead to widespread granulite facies metamorphism of the middle and lower arc crust from ~470­-465 Ma. Pelitic rocks melted in this event remained above the solidus for ~20-­30 Ma concurrent with peak convergence. Pressure-temperature paths from middle and lower crustal migmatites suggest that cooling from peak conditions was near isothermal. Decreased convergence associated with the end of Precordillera terrane accretion at ~436 Ma facilitated the onset of syn­convergent extension, cooling and exhumation from granulite facies conditions, and the termination of Famatina arc magmatism crustal shear zones, and deformation within the back arc. Steeply dipping reverse­sense ductile fabrics within the arc have hornblende cooling ages of >445 Ma and suggest that voluminous arc magmatism was concurrent with intra-­arc shortening. Intrusion of mafic and intermediate magmas during the peak in arc magmatism lead to widespread granulite facies metamorphism of the middle and lower arc crust from ~470­-465 Ma. Pelitic rocks melted in this event remained above the solidus for ~20-­30 Ma concurrent with peak convergence. Pressure-temperature paths from middle and lower crustal migmatites suggest that cooling from peak conditions was near isothermal. Decreased convergence associated with the end of Precordillera terrane accretion at ~436 Ma facilitated the onset of syn­convergent extension, cooling and exhumation from granulite facies conditions, and the termination of Famatina arc magmatism.