Synkinematic emplacement of the magmatic epidote bearing Major Isidoro tonalite-granite batholith: Relicts of an Ediacaran continental arc in the Pernambuco–Alagoas domain, Borborema Province, NE Brazil

Abstract

The Neoproterozoic Major Isidoro batholith (∼100 km2), composed of metaluminous to slightly peraluminous magmatic epidote-bearing tonalite to granite, is part of the Águas Belas–Canindé composite batholith, which intruded the Pernambuco–Alagoas Domain of the Borborema Province, northeastern Brazil. These rocks contain biotite, amphibole, titanite and epidote that often shows an allanite core as key mafic mineral phases. K-diorite mafic enclaves are abundant in this pluton as well as are amphibole-rich clots. The plutonic rocks are medium-to high-K calc-alkaline, with SiO2 varying from 59.1 to 71.6%, Fe# from 0.6 to 0.9 and total alkalis from 6.1 to 8.5%. Chondrite-normalized REE patterns are moderately fractionated, show (La/Lu)N ratios from 13.6 to 31.8 and discrete negative Eu anomalies (0.48–0.85). Incompatible-element spidergrams exhibit negative Nb–Ta and Ti anomalies.This batholith was emplaced around 627 Ma (U–Pb SHRIMP zircon age) coevally with an amphibolite-facies metamorphic event in the region. It shows Nd-model age varying from 1.1 to 1.4 Ga, average εNd(627Ma) of −1.60 and back-calculated (627 Ma) initial 87Sr/86Sr ratios from 0.7069 to 0.7086. Inherited zircon cores that yielded 206Pb/238U ages from 800 to 1000 Ma are likely derived from rocks formed during the Cariris Velhos (1.1–0.9 Ga) orogenic event. These isotopic data coupled with calculated δ18O(w.r.) value of +8.75‰ VSMOW indicate an I-type source and suggest a reworked lower continental crust as source rock. A granodioritic orthogneiss next to the Major Isidoro pluton, emplaced along the Jacaré dos Homens transpressional shear zone, yielded a U–Pb SHRIMP zircon age of 642 Ma, recording early tectonic movements along this shear zone that separates the Pernambuco–Alagoas Domain to the north, from the Sergipano Domain to the south. The emplacement of the Major Isidoro pluton was synkinematic, coeval with the development of a regional flat-lying foliation, probably during the peak of metamorphism related to the convergence/contractional deformation of the São Francisco craton and Pernambuco–Alagoas block during the Brasiliano Orogeny.