Isotopic and geochemical constraints for a Paleoproterozoic accretionary orogen in the Borborema Province, NE Brazil: implications for reconstructing Nuna/Columbia

Abstract

The Alto Moxotó Terrane of the Borborema Province presents a wide exposure of Paleoproterozoic crust, but unlike other continental blocks of South America, its orogenic history is strongly obliterated by late Neoproterozoic deformation. New isotopic and geochemical studies were conducted in mafic-ultramafic (Fazenda Carmo Suite) and granitic-gneissic rocks (Riacho do Navio Suite) within the terrane. The former present zircon U-Pb crystallization ages at ca. 2.13 Ga, whereas Sm-Nd data suggests a juvenile origin via melting of early Paleoproterozoic to Archean peridotitic sources. Geochemical data for these rocks are compatible with tholeiitic magmas with some degree of crustal contamination and trace element distribution points to a continental-arc related setting interpreted as remnants of the early stages of subduction. In contrast, the Riacho do Navio Suite was emplaced at ca. 2.08 Ga and has highly negative εNd(t) values indicating crustal reworking. The suite displays calc-alkali to alkali-calcic and ferroan geochemical signatures compatible with Cordilleran magmas. In addition, traceelement distribution as well as discriminant diagrams suggest that the precursor magmas were generated during the later stages of a continental arc or in a syn-collisional setting. Based on our results, we suggest that the studied units might represent missing pieces of a Paleoproterozoic accretionary orogen that formed the crustal framework of the Alto Moxotó Terrane, and that this represents a block associated with assembly of the Nuna/Columbia supercontinent, which is now largely hidden within the Neoproterozoic orogenic belts of West Gondwana.