Multiple sources and multi-stage emplacement of the Esperança Granitic Complex and its relationship with the Patos – Campina Grande shear zone system, Borborema Province - NE Brazil

Abstract

Expressive granitic magmatism and a complex system of transcurrent shear zones are the main features associated with the Ediacaran evolution of the Borborema Province (northeastern Brazil). Their petrogenesis and relationships with tectonic structures can provide important insights into lithospheric processes during the collisional to post-collisional stages of the Brasiliano Orogeny. The Esperança Complex is a NE-trending elongated granitic batholith with ca. 650 km2 comprising five plutons emplaced between the Patos and Campina Grande dextral shear zones in the central–eastern part of the Borborema Province. An integrated study of the complex was carried out using UPb zircon SHRIMP and LA-ICPMS geochronology, mineral and whole-rock geochemistry, and NdHf isotope geochemistry (whole-rock and zircon). The plutons are metaluminous to slightly peraluminous with geochemical and isotopic signature reflecting different sources. The Remigio and Areial plutons have Paleoproterozoic to Neoarchean Nd and Hf TDM model ages and strong negative εNd(t) (−15.29 to −16.71) and εHf (−12.20 to −21.03) values. Their geochemistry is compatible with derivation through partial melting of mafic to intermediate metaigneous sources like the Paleoproterozoic basement (Areial pluton) and metasedimentary sources (Remígio pluton). The Puxinanã, Serrote da Cobra and Pocinhos plutons show higher ɛNd (−5.90 to −7.35) and ɛHf (−2.83 to −6.91) values, and Statherian to Calymmian Nd and Hf TDM model ages, ranging from 1.4 to 1.7 Ga and from 1.6 to 1.8 Ga, respectively. They have geochemical affinity with A-type ferroan granites. The geochemical and isotopic signature are similar to those of Tonian orthogneiss that constitute part of the plutons' host rocks, suggesting derivation from Tonian crustal sources. Evidence of magma mixing and the presence of inherited zircon grains with ages like those of metasedimentary host rocks suggest contribution of the lithospheric mantle and sedimentary sources in different proportions in their petrogenesis. The reported data are compatible with building of the Esperança Complex by multiple intrusive events. The Pocinhos and Serrote da Cobra plutons are the oldest (~600 Ma) and their genesis is probably associated with heat input resulting from crustal thickening at the end of a long contractional period (ca. 630–600 Ma). The genesis of the Puxinanã and Areial plutons (~585 to 565 Ma) involved interactions of crustal and mantle mafic melts, with magma transport and emplacement controlled by the Campina Grande shear zone at the beginning of the transcurrent regime. The Remígio pluton is the youngest intrusion (~565 Ma) and its genesis can be related to a high geothermal gradient resulting from emplacement of the older plutons, possibly enhanced by strain heating related to displacement along the Patos shear zone.