Abstract
Abstract The northeastern part of the Borborema Province is dominated by Paleoproterozoic migmatitic tonalitic to granitic orthogneisses (Caico Complex) that are the basement for younger, metavolcanosedimentary rock assemblages. Within this complex gneissified, porphyritic metagranitoid rocks (the G2-type augen gneisses) are fairly common and supposed to define a synorogenic magmatism at c . 2.0 Ga. New U–Pb (SHRIMP) on zircons and Sm–Nd data shows that these augen gneisses do not differ significantly from the metaplutonic rocks of the basement complex regarding their nature and emplacement age of the primary magmas. U–Pb ages cluster in a time interval between 2.17 and 2.25 Ga and are correlated with Nd parameters (older t DM model ages and negative initial eNd values) indicating an origin from recycling of an older, probably Neoarchean crust. The regional host rocks that accommodate the augen gneiss could be c . 2.4–2.3 Ga supracrustal sequences presently preserved as small remnants in the Caico Complex. The Paleoproterozoic magmatic activity extends to the Late Paleoproterozoic with the intrusion of the Serra Negra pluton (now a coarse augen gneiss) which yielded a (semi) concordant U–Pb age of c . 1.75 Ga. This magmatic activity, until now unsuspected in the Caico Complex, was probably related to crustal extension and rifting over large areas that include the NE Brazil and the Nigerian shield in Africa.
Published Version
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