Open-system magmatic evolution and crystallization conditions of the Ediacaran shoshonitic rocks from the São João do Sabugi Pluton, Borborema Province, NE Brazil

• Published in: Brazilian journal of geology Vol. 51; no. 2
• Main Authors: Paiva, Dayvison Bruno Cordeiro de, Vilalva, Frederico Castro Jobim, Souza, Zorano Sérgio de, Nascimento, Marcos Antônio Leite do
• Format: Journal Article
• Language: English
• Published: Sociedade Brasileira de Geologia 01.01.2021
• Subjects: Borborema Province; geochemical modeling; GEOLOGY; GEOSCIENCES, MULTIDISCIPLINARY; open-system processes; shoshonite; São João do Sabugi Pluton; geochemical modeling; open-system processes; shoshonite; Borborema Province; São João do Sabugi Pluton
• ISSN: 2317-4889; 2317-4692; 2317-4692
• DOI: 10.1590/2317-4889202120200040

Abstract The São João do Sabugi Pluton (SJSP) (∼579 Ma) is one of the most expressive occurrences of Ediacaran, syn- to post-collisional shoshonitic rocks in the Rio Piranhas-Seridó Domain, Borborema Province, NE Brazil. The petrography, whole rock and mineral composition of this pluton were investigated to characterize its open-system magmatic differentiation processes. The pluton is composed of three rock groups: gabbro-diorite, with clinopyroxene ± orthopyroxene ± amphibole ± biotite; monzodiorite, with amphibole and biotite (± pyroxenes); and granodiorite, with biotite as the main mafic mineral. Evidences of open-system processes, including partially resorbed metasediment xenoliths, are widespread. These rocks are metaluminous, alkali-calcic and magnesian, and have shoshonitic affinity. They show relative LILE and LREE enrichment and pronounced negative Nb-Ta anomalies. Major and trace element geochemical modeling favors magma differentiation by fractional crystallization (56–62%) after crustal assimilation of ∼30% of local paragneisses and schists from the Seridó Group in a relatively stationary magma chamber at crustal depth, under pressures of 5–6 kbar, temperatures of ∼800–1,000°C and relatively oxidizing conditions. The less evolved gabbro-diorite was generated by ∼18% modal dynamic partial melting of a metasomatized mantle source.