Detecting subduction-related metamorphic events during the early Brasiliano Orogeny in southern Borborema Province using detrital rutile 

The ubiquity of detrital zircon in clastic sediments and their typical high U and low common Pb contents, resulting in relatively high precision U-Pb age determination, made zircon one of the primary minerals for provenance studies. Yet, its high closure temperature (>900oC), limited growth of new zircon under upper amphibolite-eclogite facies, inherited bias towards zircon-rich sources (e.g., felsic plutonic rocks), and the refractory behavior in sedimentary deposits rarely representing first-cycle sedimentation, can hamper the ability to detect some key tectonomagmatic events. In this sense, other mineral assemblages, like detrital rutile, that is formed in medium- to high-grade metapelite and metabasite mainly during high-pressure and low-temperature subduction metamorphism, can be used to provide a more complete record of orogenesis with polyphase evolution. Herein, we present U-Pb detrital rutile ages from the Cambrian-Ordovician Tacaratu Formation (lowermost unit of the late Jurassic to Cretaceous Tucano-Jatobá Basin, that directly overlies the Borborema Province in its southern region) to track the complete polyphase evolution of southern Borborema Province in the northeastern Brazil. The geodynamic evolution of this structural province is still a matter of debate, with interpretations varying from reworking of Paleoproterozoic continental crust with sedimentation and metamorphism in intracontinental setting, to oceanic closure during a complete Wilson Cycle with or without terrane accretion. Considering the southern Borborema Province Sergipano Belt, subduction started ca. 740 Ma ending with collisional processes (ca. 590-570 Ma) associated with the closure of the Sergipano-Oubanguides oceanic basin. The Neoproterozoic Pernambuco-Alagoas Domain and Sergipano Belt, both formed due to the collision between São Francisco-Congo Craton and the Pernambuco-Alagoas superterrane, are the main source of detritus of the Tacaratu Formation. Coupled U-Pb detrital zircon and rutile analysis revealed that detrital zircon ages lags (i.e., are younger) detrital rutile ages by around 100 Ma. Detrital rutile and zircon present main young peaks at ca. 650 Ma and 545 Ma, respectively. Recently, Neoproterozoic arc-back-arc amphibolite (ca. 743 ± 3 Ma), a rare setting for the early phases of Brasiliano Orogeny, and Cordilleran-type medium- to high-K granites (ca. 645-610 Ma), were recognized in southern Borborema Province, in agreement with our detrital rutile U-Pb ages. Thus, our detrital rutile ages record earlier phases of Brasiliano Orogeny in the southern Borborema Province (subduction-related metamorphism; closure of Sergipano-Oubanguides ocean), since the Brasiliano Orogeny culminated in the collision of blocks that were followed by high-temperature metamorphism (hampering the formation of younger rutile?). Notwithstanding, detrital rutile ages interesting marks around late Tonian to Cryogenian subduction-related metamorphism, perhaps in a magma-poor orogenic phase.