Serra do Barro Branco orthogneiss: untimely record of the West Gondwana amalgamation in the São Roque Domain

• Autor(a) principal: Balis, Mikaella
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/44/44143/tde-28062021-143557/
• topic: Isotope geochemistry; não disponível; Orthogneiss; São Roque Domain; Tectonic evolution; U-Pb geochronology

Large volumes of high-K calc-alkaline metaluminous to peraluminous granitoids are intrusive in south-eastern Brazil. In particular, the high-K geochemical affinity extends from the batholiths of the Socorro-Guaxupé Nappe to smaller intrusions in the São Roque Domain. The fault-bounded São Roque Domain is a relatively small crustal block that comprises two metavolcano-sedimentary sequences of Statherian maximum depositional age. Detrital zircon provenance points to a Rhyacian (2.17 Ga) proximal source area with patterns matching the southern portion of the Socorro-Guaxupé Nappe. The domain records magmatic activity initiated at ca. 685 Ma with the crystallisation of the Barro Branco biotite orthogneiss of intermediate SiO2 composition. Unprecedented zircon ages around 740 and 800-900 Ma found in a metavolcaniclastic rock suggest older magmatism also might have taken place. The Barro Branco orthogneiss has an inequigranular facies dated at ca. 625 Ma of more \"evolved\" peraluminous affinity. The Moinho is a (hornblende)-biotite granodiorite emplaced at ca. 620 Ma with more \"primitive\" SiO2 range, typically metaluminous. The most voluminous Ediacaran magmatism occurred within 610-590 Ma represented by several circumscribed biotite granites. All granitoids have high Sr/Y and LREE, low Nb and Ti and lack negative Eu anomaly that suggest a deep lower crustal source with residual garnet (±amphibole ±rutile). Whereas the Socorro-Guaxupé arc rocks have intermediate Sr/Y and moderate to absent, negative Eu anomalies but share the trace-elemental imprints of subduction zones. Nd and Hf isotopes indicate that the Barro Branco orthogneiss carries a significant juvenile component while the inequigranular orthogneiss and Moinho granodiorite have typically crustal signatures that seem to partially originate from the country metasedimentary rocks. During the temporal gap between the Barro Branco emplacement and the magmatism that followed from ca. 635 Ma on, the mantle beneath the São Roque Domain might have been fertilized by crustal additions. Enriched mantle and low-degree partial melting probably produced high-K enriched melts. Thus, we propose the São Roque Domain developed on the Paranapanema active margin and records the initiation of subduction in the retro-arc domain. The magmatic \"shut-down\" of ca. 35 m.y. could result from a slab retreat that caused magmatism to migrate northwards in the Socorro-Guaxupé arc domain. Magmatism followed at ca. 635 Ma with crustal signatures that support mantle enrichment from the last-longing subduction beneath the Paranapanema. A metasedimentary rock with monazite age of ca. 600 Ma and two cores of ca. 630 Ma may be evidence of an ongoing thermal episode in the São Roque Domain, overlapping the metamorphism in the neighbour Socorro-Guaxupé Nappe.