Diorites of the High-K Calc-Alkalic Association: Geochemistry and Sm-Nd Data and Implications for the Evolution of the Borborema Province,Northeast Brazil

Accretion of exotic terranes during the Cariris Velhos (late Mesoproterozoic to early Neoproterozoic) and Brasiliano (late Neoproterozoic) events has been proposed as an important process of continental growth in Borborema province, northeastern Brazil. If this hypothesis holds true, it is reasonable to assume that the roots of these accreted blocks have variable chemical and isotopic compositions. Here, we investigate this possibility using lithospheric-derived high-K calc-alkalic diorites. These rocks are widespread throughout the province and occur in areas proposed to represent distinct tectonic terranes. The similar geochemical and Sm-Nd isotopic signatures of the diorites (T _DM from 1.7 to 2.0 Ga), except for one pluton, impose serious limitations to the terrane accretion model in Borborema province. On the contrary, these data strongly suggest that a large portion of the province is underlain by a LILE-enriched metasomatized lithospheric mantle formed around 2.0 Ga.