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Exposed sections of accretionary orogens allow reconstruction of their tectonic evolution. Most commonly, orogens are characterized by two-dimensional shortening perpendicular to the orogenic front. We describe the midcrustal section of the backarc of the early Paleozoic Famatinian accretionary orogen, exposed in the Sierra de Quilmes. Here crustal deformation evolved from a typical two-dimensional shortening with tectonic transport toward the west, to a noncoaxial constrictional strain with a southward tectonic transport parallel to the orogen. During the early phase of deformation, high-temperature and low-pressure (HT-LP) metamorphic complexes were juxtaposed by west directed thrusting on remarkably thick shear zones forming a thrust duplex. Deformation of the buried footwall complex continued after the exhumed hanging wall ceased to deform. We suggest that the thermally weakened footwall complex responded by initiating a phase of south verging thrusting, parallel to the orogen, associated with strong constriction, associated with L-tectonites, and sheath folds. This late phase of deformation defines a noncoaxial constrictional regime characterized by simultaneous east-west and vertical shortening and strong north-south, orogen-parallel stretching. Titanite ages and Zr-in-titanite thermometry demonstrate that this backarc remained above 700°C for 120 Myr between 500 and 380 Ma. Combined with regional geology, the new data suggest that west verging thrusting interrupted an early, back-arc extensional phase, and lasted from~470 to 440 Ma and that footwall constriction and south verging thrusting continued for another 40 to 60 Ma. The Famatinian backarc exposed in Sierra de Quilmes thus is an example of how shortening and orogenic growth in a hot orogen was counterbalanced by lateral flow.

U‐Pb dates of zircon, monazite, and titanite combined with trace element composition, allows characterization of the thermal evolution of the migmatitic Agua del Sapo complex. This complex comprises Al‐rich and Ca‐rich metasedimentary rocks with a detrital zircon maximum depositional age of 550 Ma. The rocks record two consecutive early Paleozoic orogenies. During subduction associated with the 550–510 Ma Pampean orogeny, the complex was in the fore‐arc region and was intruded by 550–520 Ma granites indicative of anomalous heating possibly related to ridge subduction. During the subsequent 500–440 Ma Famatinian orogeny, the arc migrated trenchwards and the region became part of a retro‐arc that underwent melting at upper‐amphibolite facies. This event was recorded differently by each of the accessory phases. Detrital zircon cores were overgrown by rare Famatinian rims that range from 500 to 420 Ma, while monazite records only Famatinian dates with a growth peak at ∼457 Ma that extends to 410 Ma, possibly due to coupled dissolution‐precipitation. Published titanite dates define a 120 Myr thermal history, starting at ∼500 Ma with temperatures of ∼750°C ± 25°C, ending at 380 Ma and ∼700°C ± 25°C. Cooling was accompanied by a decrease in titanite light rare earth element contents in response to increased abundance of allanite/epidote. Thus, the complementary time‐compositional record of the accessory phases reveals continued high heat flow, associated with deformation, to 380 Ma. This prolonged event blurs the boundary between the Famatinian and the subsequent Achalian/Chanic orogenies and extends the Silurian Rinconada tectonic phase of the Famatinian orogeny to the east into the Eastern Sierras Pampeanas.

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