Geology and Petrology of Metavolcanic Rocks in the Neoarchean Mundo Novo Greenstone Belt, Eastern São Francisco Craton, NE Brazil: Tectonic Setting Considerations Volume 1 - Issue 1

Ricardo Ramos Spreafico¹* ,Johildo Salomão Figueiredo Barbosa¹, Antônio Marcos Vitória de Moraes² and Francisco Dias de Souza Júnior²

• ¹Institute of Geosciences, Federal University of Bahia, Brazil
• ²Mining Company of Bahia State, Brazil

Received: October 29, 2019   Published: November 12, 2019

Corresponding author: Ricardo Ramos Spreafico, Mining Company of Bahia State and Institute of Geosciences, Federal University of Bahia, Brazil

 

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Abstract

Field and petrological data of metakomatiite, eastern and western metabasalts and metadacite were used to propose an intraoceanic or intracontinental provenance for the Neoarchean Mundo Novo Greenstone Belt (MNGB), eastern São Francisco Craton. Despite deformation, the metakomatiite preserves the spinifex texture and the eastern metabasalt’s pillow lava structure. The metavolcanics are recovered by an ocean floor lithological association composed of chemical metasedimentary rocks and the western metabasalt hosts ocean floor hydrothermal alteration zones. The eastern metabasalt plots in the IAT and MORB fields and western metabasalt is mainly in the MORB field in the Zr vs. Zr/Y diagram, suggesting nearby oceanic settings. Heterogeneous crustal assimilation and metamorphism during the Rhyacian-Orosirian explain the mineralogical differences between the two metabasalts. The metakomatiite and metabasalts feature a vector from the MORB-OIB array to the volcanic arc array in the Nb/Yb vs. Th/Yb diagram, similar to the intraoceanic arc-basin system of the Archean greenstone belts. The average (La/Yb) N ratio of 8.87 for the metadacite indicates a crustal contamination in subducting oceanic crust. An intraoceanic provenance in arc-basin settings and oceanic crust assimilations are proposed for the Neoarchean MNGB, which was posteriorly compressed between cratonic blocks during the Rhyacian-Orosirian and lies in the Contendas-Jacobina Lineament.

Keywords: Mundo Novo Greenstone Belt; metavolcanic rocks; Intraoceanic Setting; Petrology; São Francisco Craton

Abstract| Introduction| Materials and Methods| Results| Conclusions| Acknowledgements| References|