Multiple migmatite events and cooling from granulite facies metamorphism within the Famatina arc margin of northwest Argentina

SEAN R. MULCAHY; SARAH M. ROESKE; WILLIAM C. MCCLELLAND; JOSHUA R. ELLIS; FRED JOURDAN; PAUL R. RENNE; JEFFREY D. VERVOOR; GRACIELA I. VUJOVICH

TECTONICS

AMER GEOPHYSICAL UNION

Lugar: XX; Año: 2014 vol. 33 p. 1 - 21

0278-7407

The Famatina margin records an orogenic cycle of convergence, metamorphism,magmatism, and extension related to the accretion of the allochthonous Precordilleraterrane. New structural, petrologic, and geochronologic data from the Loma de LasChacras region demonstrate two distinct episodes of lower crustal migmatization. Thefirst event preserves a counterclockwise pressure-temperature path in kyanite-K-feldsparpelitic migmatites that resulted in lower crustal migmatization via muscovite dehydrationmelting at 12 kbar and 868ıC at 461 ˙1.7 Ma. The shape of the pressure temperaturepath and timing of metamorphism are similar to those of regional midcrustal granulitesand suggest pervasive Ordovician migmatization throughout the Famatina margin.One-dimensional thermal modeling coupled with regional isotopic data suggestsOrdovician melts remained at temperatures above their solidus for 20?30 Ma followingpeak granulite facies metamorphism, throughout a time period marked by regionaloblique convergence. The onset of synconvergent extension occurred only after regionalmigmatites cooled beneath their solidus and was synchronous with the cessation ofPrecordillera terrane accretion at 436 Ma. The second migmatite event was regionallylocalized and occurred at 700ıC and 12 kbar between 411 and 407 Ma via vaporsaturated melting of muscovite. Migmatization was synchronous with extension,exhumation, and strike-slip deformation that likely resulted from a change in the plateboundary configuration related to the convergence and collision of the Chilenia terrane.