Contrasting P-T conditions of Oriental Terrane and Central Superterrane (Ribeira Belt), NW of Rio de Janeiro state, Brazil

Abstract

Neoproterozoic-Cambrian rocks from the Oriental Terrane and the Central Superterrane of the Ribeira Belt occur in northwest of Rio de Janeiro state. This paper presents new data on field research, petrology, mineral chemistry and conventional geothermobarometry, fundamental to understanding the geology of the region. The metabasic rocks from the Cambuci Domain are associated with the Central Superterrane retroarc basin and record two metamorphic events: M 0 (before the formation of the main foliation, under conditions of 788 °C) and M 1 (contemporary to the main foliation, with peak at 718-752 ºC and 6.62 kbar). The rocks from the Costeiro Domain, interpreted as the Rio Doce arc (Angelim Suite) and the retroarc basin (São Fidélis Goup) of the Oriental Terrane record a metamorphic peak at granulite facies yielding the highest pressure and temperature among the studied domains (752-784 °C and 8.2-9 kbar). The Italva Domain amphibolites represents the retroarc basin of the Oriental Terrane. Temperature and pressure values obtained for the Italva Domain metamorphic peak record 731 ºC and 6.78 kbar, respectively, in the transition zone between upper amphibolite and granulite facies conditions. This work presents the newest record of metamorphic evolution for the Oriental Terrane of the Ribeira Belt, suggesting an anticlockwise P-T-t path and near-isobaric cooling (IBC) for the rocks of the Cambuci Domain. Therefore, these results contribute to the understanding of the evolution of orogenic belts during the amalgamation of the Gondwana in the Neoproterozoic.

Rhyacian magmatic arc rocks with sanukitoid geochemical signature from the Juiz de Fora Complex, Minas-Bahia Orogenic System (SE-Brazil)

“…As evidenced by the morphology of the zircon grains and high Th/U ratios, the high metamorphic grade of the rocks is also evidenced by mineral peak metamorphic associations typical of the granulite facies (with orthopyroxene + clinopyroxene + plagioclase) in all study samples. The Neoproterozoic granulite metamorphism is common in the entire JFC (Duarte et al 1997, Heilbron et al 1998, Medeiros Júnior et al 2017) and is also observed in nearby units, such as the paragneisses from the Raposos and Bom Jesus do Itabapoana groups and in the orthogneisses from the Neoproterozoic Serra da Bolivia/Rio Doce magmatic arc (Karniol et al 2009, Santos et al 2011, Gouvêa et al 2020, Marques et al 2021). In addition, the observation of hornblende and biotite partially substituting orthopyroxene and clinopyroxene in some samples suggests retrometamorphism in conditions of upper amphibolite facies, also in agreement with regional works (Santos et al 2011, Ferreira et al 2020, Marques et al 2021.…”