Geological and isotopic characteristics of granites from the Western Pernambuco-Alagoas Domain: implications for the crustal evolution of the Neoproterozoic Borborema Province

Ana Cláudia De Aguiar Accioly,Rodrigo Fabiano Da Cruz,Joseneusa Brilhant Rodrigues,Márcio Martins Pimentel

doi:10.5327/z23174889201400040008

Ana Cláudia De Aguiar Accioly, Rodrigo Fabiano Da Cruz + Show 2 more

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https://doi.org/10.5327/z23174889201400040008

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Abstract

The Western Pernambuco-Alagoas Domain is a complex tectonic domain of the Southern part of the Neoproterozoic Borborema Province. It borders the Northern margin of São Francisco Craton. U-Pb and Sm-Nd data discussed in this work show that, in the Western Pernambuco-Alagoas Domain, large volumes of granitic rocks of various ages related to different tectonic events are recognized. The Cariris Velhos Event is represented by Lobo (974 ± 8 Ma) and Rocinha (956 ± 2 Ma) orthogneisses; whereas Paleoproterozoic and Archean basement rocks are represented by Fulgêncio Orthogneiss (1,996 ± 8 Ma), Riacho Seco Gneissic-migmatitic Complex (1,992 ± 27 Ma), and orthogneisses of Entremontes Complex (2,734 ± 11 Ma). Six groups of granitoids are recognized: Brasiliano granitoids (Ediacaran-Cryogenian), with Meso- to Paleoproterozoic model ages; Cariris Velhos granitoids (Tonian) yielding Mesoproterozoic model ages; Paleoproterozoic granitoids from Pernambuco-Alagoas Domain, with Neoarchean to Paleoproterozoic Nd model ages; Paleoproterozoic granitoids from Riacho Seco Nucleus, represented by Riacho Seco Gneissic-migmatitic Complex, with Archean model ages; Archean granitoids represented by the rocks of Entremontes Complex; and granitoids emplaced in the São Francisco Craton displaying Paleoproterozoic to Archean model ages. Prominent among the new data obtained is the Paleoproterozoic age of Riacho Seco Gneissic-migmatitic Complex, which is formed by Archean basement reworking. The new data reveal the presence of Paleoproterozoic and Archean basement inliers and a large volume of Cariris Velhos granitoids in the Western Pernambuco-Alagoas Domain. The orogen, therefore, involved extensive reworking of older blocks, possibly including parts of São Francisco-Congo Craton.

Highlights

The Borborema Province (Almeida et al 1977), in Northeastern Brazil, underlies an area of approximately 450,000 km2, corresponding to the Western portion of the extensive Brasiliano-Pan African orogenic system formed by a convergence of the West Africa/São Luis and San Francisco-Congo Cratons (Fig. 1)
Based on U-Pb and Sm-Nd isotopic data gathered in this study, it was possible to divide the granitoids of the study area into six main groups: ■■ Brasiliano granites (Cryogenian-Ediacaran), with model ages ranging from Paleoproterozoic to Mesoproterozoic and chemical features similar to those of the high-K calc-alkaline series; ■■ Cariris Velhos granites ( Tonian), presenting Mesoproterozoic model ages and chemical characteristics ranging from alkali-rich to calc-alkaline
This group includes Lobo (974 ± 8 Ma) and Rocinha (956 ± 2 Ma) orthogneisses; ■■ Paleoproterozoic granites from Pernambuco-Alagoas Domain (PEAL), with model ages ranging between Neoarchean and Paleoproterozoic and high-K calc-alkaline chemical nature, including Fulgêncio Orthogneiss (1,996 ± 8 Ma); ■■ Paleoproterozoic granites from Riacho Seco Nucleus (RSN), with Archean model ages, mainly represented by Riacho Seco Gneissic-migmatitic Complex (1,992 ± 27 Ma); ■■ Archean granites from PEAL, represented by rocks of the Entremontes Complex with U-Pb age of 2,734 ± 11 Ma and model age of 3.2.60 Ga and eNd (2 Ga); ■■ São Francisco Craton granites with model ages ranging from Mesoarchean to Paleoproterozoic periods

Summary

INTRODUCTION

The Borborema Province (Almeida et al 1977), in Northeastern Brazil, underlies an area of approximately 450,000 km, corresponding to the Western portion of the extensive Brasiliano-Pan African orogenic system formed by a convergence of the West Africa/São Luis and San Francisco-Congo Cratons (Fig. 1). The study area is located in the Pernambuco-Alagoas Domain (PEAL) and its subdomain, the Riacho Seco Nucleus (RSN) in the Southern Borborema Province. The PEAL is located between the E-W Pernambuco Lineament to the North and the Sergipano Belt, and São Francisco Craton to the South. This is one of the crustal blocks comprising the Southern Subprovince of Van Schmus et al (2011) or the Southern Domain of Brito Neves et al (2000), which are part of the Neoproterozoic orogenic system along the Northern margin of São Francisco Craton.

ANALYTICAL PROCEDURES

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