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

Abstract

The study area comprises the northwest region of Rio de Janeiro state where ortho- and paraderived rocks of Neoproterozoic-Cambrian age of the Oriental Terrane and the Central Superterrane of the Ribeira Belt occur. From field and petrography studies, this paper presents new data on mineral chemistry and conventional geothermobarometry, fundamental to the understanding the geology of the region. The metabasic rocks of the Cambuci Domain, associated with the retroarc basin of the Central Superterrane, recorded two metamorphic events: M0 (before the formation of the main foliation, under conditions of 788 °C) and M1 (contemporary to the main foliation, with peak at 718-752 ºC and 6.62 kbar). The rocks of the Costeiro Domain, interpreted as representatives of the Rio Doce arc (Angelim Suite) and retroarc basin (São Fidélis Goup) of the Oriental Terrane, recorded a metamorphic peak in granulite facies yielding the highest pressure and temperature among the studied domains (752-784oC and 8.2-9 kbar). For the Italva Domain, representative of the retroarc basin of the Oriental Terrane, the temperature and pressure values obtained for the metamorphic peak were 731 ºC and 6.78 kbar, in the transition zone between the conditions of upper amphibolite and granulite facies conditions. This work presents the newest record of metamorphic evolution in the Oriental Terrane of the Ribeira Belt, suggesting a anticlockwise P-T-t path and near-isobaric cooling (IBC) to the rocks of the Cambuci domain. Therefore, this result contributes to the understanding of the evolution of orogenic belts during the amalgamation of the Gondwana in the Neoproterozoic.