Neoproterozoic high magmatic addition rate episode building a composite batholith in northeastern Brazil, and implications for the western Gondwana assembly

Abstract

The composite Santana do Ipanema batholith is made up of several Cryogenian-Ediacaran granitic plutons in the Pernambuco-Alagoas (PEAL) Domain of the Borborema province, northeastern Brazil. The individual plutons in this batholith are high-K calc-alkalic to shoshonitic, metaluminous to peraluminous quartz syenites to granites that belong to magnetite-series and magnesian Cordilleran-type granitoids. They carry comagmatic microgranular mafic enclaves with evidence of magma mixing. Their chemical compositions overlap, and they exhibit enrichment in some incompatible and depletion in HFS elements, with variable initial 87Sr/86Sr ratios that range from 0.70511 to 0.71071. The εNd(0.6Ga) values cluster into two groups, in which plutons with ages ≥ 625 Ma exhibit slightly negative to slightly positive εNd values (average −1.6), in contrast with the younger plutons that have more negative ones (average −8.7), pointing out that mantle contribution to the source decreased with time, while recycled ancient crust augmented. Geochronological data from the literature indicate that the batholith has been constructed by continuous amalgamations of successive magma pulses via diking for ~30 m.y., with no large crystallization age gap among the plutons. A magma supply rate of 0.003 m3/year is estimated considering this batholith together with two other nearby composite batholiths of similar age in the PEAL Domain, and low volcanic-plutonic ratio. This rather high magmatic addition rate episode has been probably triggered by extensive and repeated basaltic underplating stalled in the lower crust in the magmatic arc formed during the convergence of the São Francisco craton and the Pernambuco-Alagoas block in the course of the western Gondwana amalgamation.