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Evolution of the 3.65–2.58 Ga Mairi Gneiss Complex, Brazil: Implications for growth of the continental crust in the São Francisco Craton

2022; Elsevier BV; Volume: 13; Issue: 5 Linguagem: Inglês

10.1016/j.gsf.2022.101366

2588-9192

Igor de Camargo Moreira, Elson P. Oliveira, Daniel Francisco Martins de Sousa,

Geochemistry and Geologic Mapping

• The Mairi Gneiss Complex contains the oldest rocks of São Francisco Craton and South America. • Multiple magmatic episodes from the Eo- to the Palaeoarchaean and in the Neoarchaean. • No Mesoarchaean rocks occur in the Mairi Complex. • Lu-Hf isotope data show a progressive evolution of depleted-mantle, and crustal growth and recycling. • Interaction of pre-existing crust and juvenile contribution. The composition and formation of the Earth’s primitive continental crust and mantle differentiation are key issues to understand and reconstruct the geodynamic terrestrial evolution, especially during the Archean. However, the scarcity of exposure to these rocks, the complexity of lithological relationships, and the high degree of superimposed deformation, especially with long-lived magmatism, make it difficult to study ancient rocks. Despite this complexity, exposures of the Archean Mairi Gneiss Complex basement unit in the São Francisco Craton offer important information about the evolution of South America’s primitive crust. Therefore, here we present field relationships, LA-ICP-SFMS zircon U-Pb ages, and LA-ICP-MCMS Lu-Hf isotope data for the recently identified Eoarchean to Neoarchean gneisses of the Mairi Complex. The Complex is composed of massive and banded gneisses with mafic members ranging from dioritic to tonalitic, and felsic members ranging from TTG (Tonalite-Trondhjemite-Granodiorite) to granitic composition. Our new data point to several magmatic episodes in the formation of the Mairi Gneiss Complex: Eoarchean (ca. 3.65–3.60 Ga), early Paleoarchean (ca. 3.55–3.52 Ga), middle-late Paleoarchean (ca. 3.49–3.33 Ga) and Neoarchean (ca. 2.74–2.58 Ga), with no records of Mesoarchean rocks. Lu-Hf data unveiled a progressive evolution of mantle differentiation and crustal recycling over time. In the Eoarchean, rocks are probably formed by the interaction between the pre-existing crust and juvenile contribution from chondritic to weakly depleted mantle sources, whereas mantle depletion played a role in the Paleoarchean, followed by greater differentiation of the crust with thickening and recycling in the middle–late Paleoarchean. A different stage of crustal growth and recycling dominated the Neoarchean, probably owing to the thickening of the continental crust by collision, continental arc growth, and mantle differentiation.