Crustal growth during Western Gondwana amalgamation and onset of the Brasiliano orogeny: Insights from geochemistry and Pb–Sr–Nd–O isotopes from granites in northeastern Brazil

Abstract

The lithological units of the eastern Pernambuco–Alagoas superterrane of the Borborema Province, northeastern Brazil, includes the Santana do Ipanema (SI) batholith, whose framework is defined by a large multi-intrusive plutonic complex. The results from field, petrologic, geochemical, whole-rock Sr–Nd–O isotopes, and zircon U-Pb geochronological studies on a suite of three porphyritic granites from this batholith are reported here. The studied granites carry biotite, amphibole, titanite, and ± magmatic epidote as major mafic phases. These rocks have high Mg# (up to 52), and are metaluminous to slightly peraluminous, high-K calc-alkaline, and magnesian akin to Cordilleran granitic batholiths. All of the studied granitic rocks are enriched in LREE- and LILE-enriched (e.g., Rb, Ba, K, and Th), and HFSE-depleted (e.g., Nb, Ta, and Ti), typical of subduction-related volcanic arc rocks. Estimated intensive parameters suggest crystallization pressure from 3 to 4 kbar, temperature > 1000 °C (near-liquidus) to 640 ± 35 °C (near-solidus), and magmatic oxidizing conditions between ΔNNO+0 to ΔNNO+1. SHRIMP UPb zircon data point to crystallization ages from 643 to 625 Ma, while zircon xenocrysts are 800 to 1230 Ma old. Nd isotopes reveal depleted mantle model ages from 0.96 to 1.32 Ga, and εNd(t), initial 87Sr/86Sr, and δ18O[zircon] values from −3.35 to +0.73, 0.7054 to 0.7086, and 6.36 to 8.62‰, respectively. The geochemical and isotopic signatures of the studied granites, coupled with those from the Santana do Ipanema batholith available in the literature, suggest magma derivation from mixed juvenile Neoproterozoic (late Cryogenian to Early Ediacaran) high-K basalts and reworked Mesoproterozoic to late-Tonian components modified (metasomatized) by subduction-related processes during the amalgamation of the São Francisco Craton and Borborema Province. These data evidence crustal growth during Western Gondwana amalgamation, associated with the onset of the Brasiliano/Pan African orogeny.