The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulites as well as lower grade gneisses and mylonites. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometric calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulites based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 ºC and pressures between of 5.0 and 9.9 kbar and a retrometamorphic path characterized by near-isobaric cooling. Part of the granulites was affected by anatexis. The melting of felsic granulites resulted in the generation of pegmatites and two aluminous lithotypes. These are: i) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and ii) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronologically related to the lower grade Mantiqueira Complex.

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.

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