Evolution of the 3.65-2.58 Ga Mairi Gneiss Complex, Brazil: Implications for growth of the continental crust in the S?o Francisco Craton

Author(s)

Moreira, Igor de Camargo ; Oliveira, Elson Paiva ; de Sousa, Daniel Francisco Martins

• Document type: Journal article
• Source: GEOSCIENCE FRONTIERS; v. 13, n. 5, p. 19-pg., 2022-08-26.

Abstract

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 diffi-cult to study ancient rocks. Despite this complexity, exposures of the Archean Mairi Gneiss Complex basement unit in the Sao 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. (c) 2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). (AU)

• FAPESP's process: 18/25465-0 - The oldest rocks of the Sao Francisco Craton: Geological characteristics and tectonic significance
• Grantee: Elson Paiva de Oliveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/15824-6 - Evolution of archaean terranes of the São Francisco Craton and the Borborema Province, Brazil: global environmental and geodynamic implications
• Grantee: Elson Paiva de Oliveira
• Support Opportunities: Research Projects - Thematic Grants