Accretion Tectonics in Western Gondwana Deduced From Sm-Nd Isotope Mapping of Terranes in the Borborema Province, NE Brazil

Whole rock Sm-Nd isotope mapping of metaplutonic and metasedimentary rocks in the Tranversal Sub-province of the Borborema Province (central Western Gondwana) is used to verify the role of crustal processes in the region. The region contains the Meso-Neoproterozoic Alto Pajeú and Archean-Paleoproterozoic Alto Moxotó terranes, which are separated by the Serra de Jabitacá thrust shear zone, the main terrane boundary. The distribution of T _DM model ages on histograms and gridded maps reveals contrasting isotopic sources. The older terrane shows model ages ranging from Paleoarchean to Paleoproterozoic, whereas the younger presents ages ranging from late Paleoproterozoic to Mesoproterozoic. Contrasting ages are even more evident away from the boundary. Calculated εNd _(t) using well-known U-Pb zircon ages reveals a complex tectonic scenario. First manifestations of crustal growth are evident in Neoarchean tonalite-trondhjemite-granodiorite rocks of the Alto Moxotó Terrane. This terrane was subjected to severe crustal reworking during the early to late Paleoproterozoic. The tectonic evolution of the Alto Pajeú Terrane is considerably younger, characterized by Neoproterozoic reworking of old crust during the Cariris Velhos Orogeny (1,025–900 Ma). Our large Nd data set indicates that the Serra de Jabitacá Shear Zone separates two distinct crustal blocks exhibiting contrasting isotopic character, marking the onset of the terrane assembly in this part of Western Gondwana.