Tectono-Metamorphic Evolution of the Northern Dom Feliciano Belt Foreland, Santa Catarina, Brazil: Implications for Models of Subduction-Driven Orogenesis

Abstract

The Dom Feliciano Belt in southern Brazil and Uruguay represents the western half of a Neoproterozoic orogenic belt located in the southern portion of the South Atlantic Neoproterozoic Orogenic System. Current interpretations are divided as to the nature of orogenesis in this belt, in part owing to lacking geochronological constraints. Metamorphosed and deformed supracrustal sequences of the Brusque Complex in the northern Dom Feliciano Belt, representing part of the orogenic foreland, record the onset and duration of crustal thickening. Structural analysis and pressure–temperature estimates indicate that the complex reached peak regional metamorphic conditions of 540–570°C and 5.5–6.7 kbar during thrusting and burial, consistent with orogenic metamorphism and early crustal thickening. Garnet–whole rock Lu–Hf and Sm–Nd isochron ages date this event to between circa 660–650 Ma. Ar–Ar dating of mica suggests thrust-controlled exhumation and partial cooling by circa 635 Ma, and that localised deformation occurred into the late Ediacaran. Our results show that the orogenic foreland reached metamorphic conditions typical for crustal thickening 20–30 million years prior to the onset of massive magmatic activity in the hinterland. Such a delay is typical of hot, internal parts of orogens, which supports interpretations that hinterland magmatism in the northern Dom Feliciano Belt represents post-collisional magmatism and not arc magmatism above a subduction zone. Instead, we suggest that orogenesis in the northern Dom Feliciano Belt was initiated by rift-basin inversion driven by far-field forces transmitted through the crust in an intracontinental rift or back-arc rift setting.