Accretion tectonics in Western Gondwana deduced from Sm-Nd isotope Mapping of Terranes in the Borborema Province, NE Brazil

Abstract

Whole rock Sm-Nd isotope mapping of metaplutonic and metasedimentary rocks in theTranversal Sub-province of the Borborema Province (central Western Gondwana) is used to verify the roleof crustal processes in the region. The region contains the Meso-Neoproterozoic Alto Pajeú andArchean-Paleoproterozoic Alto Moxotó terranes, which are separated by the Serra de Jabitacá thrust shearzone, the main terrane boundary. The distribution of TDMmodel ages on histograms and gridded mapsreveals contrasting isotopic sources. The older terrane shows model ages ranging from Paleoarchean toPaleoproterozoic, whereas the younger presents ages ranging from late Paleoproterozoic toMesoproterozoic. Contrasting ages are even more evident away from the boundary. CalculatedεNd(t)usingwell-known U-Pb zircon ages reveals a complex tectonic scenario. First manifestations of crustal growthare evident in Neoarchean tonalite-trondhjemite-granodiorite rocks of the Alto Moxotó Terrane. This terranewas subjected to severe crustal reworking during the early to late Paleoproterozoic. The tectonic evolution ofthe Alto Pajeú Terrane is considerably younger, characterized by Neoproterozoic reworking of old crustduring the Cariris Velhos Orogeny (1,025–900 Ma). Our large Nd data set indicates that the Serra de JabitacáShear Zone separates two distinct crustal blocks exhibiting contrasting isotopic character, marking the onsetof the terrane assembly in this part of Western Gondwana.