Archean sodic metagranitoids from the Southern Sao Francisco Craton: Review, petrogenesis, and tectonic implications

Author(s)

Simon, Mauricio Bulhoes ^[1] ; Bongiolo, Everton Marques ^[2] ; Avila, Ciro Alexandre ^{[1, 3]} ; Teixeira, Wilson ^[4] ; Marimon, Rodrigo Schwantes ^[1] ; Oliveira, Elson Paiva ^[5]

Affiliation

^[1] Fed Univ Rio de Janeiro UFRJ, Inst Geosci, Programa Posgrad Geol, Rio De Janeiro, RJ - Brazil

^[2] Univ Fed Rio Grande do Sul UFRGS, IGEO, Programa Posgrad Geociencias, Porto Alegre, RS - Brazil

^[3] Fed Univ Rio de Janeiro UFRJ, Natl Museum, Rio De Janeiro, RJ - Brazil

^[4] Univ Sao Paulo, Inst Geosci, Sao Paulo, SP - Brazil

^[5] Univ Campinas UNICAMP, Inst Geosci, Campinas, SP - Brazil

• Document type: Review article
• Source: LITHOS; v. 398, OCT 2021.
• Web of Science Citations: 0

Abstract

Gray gneiss complexes comprise most of the Archean crust in the Southern Sao Francisco Craton and its surroundings, and their metagranitoid components can be distinguished using their petrological and geochemical attributes through time. This work discusses new and compiled geochemical and geochronological data of strikingly variable sodic metagranitoid types aiming to understand geodynamic-induced geochemical shifts. The sodic metagranitoids were divided into six geochemical types: low and high HREE (heavy rare earth elements) TTGs, medium-K metagranitoids 1 and 2, sodic sanukitoid-like metagranitoids, and HFSE-rich (high field strength elements) ferromagnesian metagranitoids. The low-HREE TTGs have higher Al2O3, Na2O, Sr, Sr/Y, LaN/YbN, and Eu anomaly (mostly neutral) values, lower Y and HFSE, and shorter silica range than the high-HREE TTGs. Such distinction reflects partial melting under diverse pressure conditions and/or different amounts of water and/or fractional crystallization processes. Four magmatic pulses of sodic metagranitoids, within 3.36-3.17, 3.07-3.00, 2.96-2.85, and 2.80-2.75 Ga, were identified in the Southern Sao Francisco Craton. The oldest TTG in this cratonic segment is disclosed here, a 3.26 Ga high-HREE TTG in the Sao Tiago Complex formed during the 3.36-3.17 Ga event identified in most of the metamorphic complexes. The 3.07-3.00 and 2.96-2.85 Ga events were dominated by TTGs and have built the extensive metamorphic complexes across the Southern Sao Francisco Craton and the basement of the adjoining Brasilia Orogen. Both low-and high-HREE TTGs have prevailed until being progressively outnumbered by enriched sodic metagranitoids between 2.8 and 2.7 Ga. These are represented by: (i) medium-K metagranitoids 1 and 2 (e.g. Florestal batholith in the Belo Horizonte Complex), faintly sodic rocks (0.5 < K2O/Na2O < 0.8) with moderate to low Sr and negative Eu anomalies, generated by water-fluxed melting of TTGs under high (type 1) or low pressure (type 2), fluid-absent melting of enriched mafic or intermediate sources, and/or interaction of TTG melts with potassic melts from metaigneous or metasedimentary sources; (ii) sodic sanukitoid-like metagranitoids in the Campo Belo Complex, formed through the melting and interaction of mafic crust and metasomatized mantle sources; (iii) HFSE-rich ferromagnesian metagranitoids, represented by the Samambaia metagranitoid in the Bonfim Complex and originated by melting of mafic mantelic and crustal metasedimentary sources. These types likely reflect increasing maturation and thickness of the felsic continental nuclei, achieved by the recycling, through modern-like subduction and collision, of felsic igneous and sedimentary rocks. Between 2.7 and 2.6 Ga, potassic plutonism replaced sodic magmatism and occurred during the 2.75-2.73, 2.72-2.68, and 2.66-2.61 Ga intervals. (C) 2021 Elsevier B.V. All rights reserved. (AU)

• 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