Orogenic magmatic events and their relations with the Nova Venécia complex in the southeastern sector of the Araçuaí orogen, Brazil

• Autor(a) principal: Cristina Santos Araujo
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/60874
• topic: U-Pb geochronology; Hf-Nd isotopes; Slab retreat; Active margin; Brasiliano orogeny; Orogenic magmatism; Araçuaí orogen; Tempo geológico; Isótopos; Magmatismo – Brasil

The Araçuaí – West Congo Orogenic System constitutes a confined orogen to a large sheath of the São Francisco – Congo Craton, amalgamated into the Gondwana Paleocontinent at the end of the Neoproterozoic. A long-lasting succession of granite production events (ca. 630 – 480 Ma) associated to the orogenic stages is a remarkable feature of the Araçuaí orogen. Located in the easternmost sector, the study area includes rocks of pre-, sin-, and post-collisional orogenic stage intruded in the Nova Venécia migmatitic paragneisses, interpreted as an arc-related basin. The new petrological investigation, bulk-rock chemistry, and isotopic analyses (zircon U-Th-Pb and Lu-Hf by LA-ICPMS, and whole-rock Sm-Nd) were carried out in representative rocks from the orogenic magmatism and the Nova Venécia complex. In this context, Santa Tereza and Jequitibá suites represent the more eastern expression of pre-collisional magmatism associated with the Rio Doce magmatic arc, while Ataléia suite represent the syn-collisional rocks, and the Aracê – Pedra Azul, Vitória, and Mestre Álvaro plutons record the post-collisional event. The Santa Tereza and Jequitibá suites yield a concordant age of 612 ± 3 Ma and 594 ± 3 Ma, respectively. Their isotopic data represent the least evolved magmatism record in this orogen (Santa Tereza suite: εHf(612) of +2.3 to -4.8 with TDM of 1.33 to 1.65 Ga and εNd(612Ma) of -0.06 to -7.05 with TDM of 1.4 a 2.04; Jequitibá suite: εHf(594) of -1.7 to -36.4 with TDM of 1.33 to 3.21 Ga and εNd(594) of -6.67 to -8.8 with TDM of 1.64 to 1.87). These suites consist of I-type intermediate to acid intrusions, metaluminous to slightly peraluminous, mainly magnesian and calcic to alkali-calcic compositions, with portions of Opx-bearing and subordinate gabbroic rocks. Data from the S-type Ataléia granite (583 ± 3 Ma; εHf(t) -3.2 to -8.1, TDM ages from 1.42 to 1.64 Ga) and Nova Venécia migmatitic paragneisses (582 ± 7 to 2363 ± 26 Ma - with age peaks at 617 ± 4 Ma (68%), 719 ± 22 Ma (14%), 839 ± 46 Ma (8%), and 922 ± 31 Ma (10%); εHf(t) +4.1 to -39.2, TDM ages from 1.20 to 3.47 Ga) suggest the proximity of the Nova Venécia basin to the continental margin and that this basin received significant sediment from the Rio Doce magmatic arc. Furthermore, the dataset for the post-collisional intrusions (Aracê – Pedra Azul pluton: 523 ± 2 Ma, εHf(t) -18.6 to -23.8, TDM ages from 2.25 to 2.47 Ga; Vitória pluton: 505 ± 1 Ma, εHf(t) -7.4 to -10.3, TDM ages from 1.58 to 1.71 Ga; Mestre Álvaro pluton: 527 ± 2 Ma, εHf(t) -0.7 to -8.8, TDM ages from 1.27 to 1.66 Ga) indicates magma hybridization at high temperature, involving country rocks in the petrogenesis of post-collisional intrusions. The rocks studied reflect a crustal section composed of I-type intermediate to acid intrusions, S-type metagranites, and paragneiss framework rocks metamorphosed under amphibolite to granulite facies, commonly migmatized. Compared to a wide compiled dataset, our data suggest that a magmatic arc is likely to have developed in the region with an initial extensional phase followed by a compressional phase and an arc migration westward.