The closure of the Rocas Verdes Basin and early tectono-metamorphic evolution of the Magallanes Fold-and-Thrust Belt, southern Patagonian Andes (52–54°S)

The Western Domain of the Magallanes Fold-and-Thrust Belt (MFTB) between 52°-54°S is part a poorly studied hinterland region southernmost Andean Cordillera. This domain consists NNW-SSE trending tectonic slices pre-Jurassic basement units and Upper Jurassic-Lower Cretaceous ophiolitic complexes volcano-sedimentary successions Rocas Verdes Basin (RVB). New detrital zircon U–Pb ages metatuffs metapsammopelites constrain episodes Late Jurassic rift-related volcanism (ca. 160 Ma) followed by Early sedimentation 125 during opening RVB. Shear bands developed in RVB further record initial phases Orogeny. 30-km wide thrust stack located on top Eastern Tobífera Thrust mylonitic metatuffs, metapelites metabasalts with NE-verging brittle-ductile S1* foliation. Phengite-bearing commonly pressure-temperature (P-T) conditions ~3–6 kbar ~210–460 °C, consistent underthrusting beneath parautochthonous magmatic arc west. Peak metamorphic ~6 460 °C are derived from metapsammopelite textures contact metamorphism overprinting early structures (at least S1*). A back-arc quartz-diorite, intruded at ca. 83 Na, minimum age deformation deep crustal depths. Campanian-Maastrichtian 70–73 40Ar/39Ar phengite dates metapelite indicate timing thrusting backthrusting uplift underthrusted stack. These findings reveal ~400 km along-strike connection mylonite belts continent-verging structure that became active onset orogeny closure marginal basin.