Zircon U-Pb shrimp dating of the Serra dos Órgãos and Rio de Janeiro gneissic granitic suites: implications for the (560 Ma) Brasiliano/Pan-African collage

Abstract

Recent systematic geological mapping at a scale of 1:400,00 scale revealed that the State of Rio de Janeiro State is an important field-laboratory to test the connections of the Costeiro Domain of the Ribeira Belt (former Rio Doce Orogen) and the Araçuaí Orogen. The regional geological mapping was supported by zircon U-Pb SHRIMP geochronological data of three syn- orogenic, thrust-related key plutons, namely the pre- to syn-collisional Serra dos Órgãos Batholith and the syn-collisional Corcovado and Pão de Açúcar gneissic granites (Rio de Janeiro Suite). These plutons have a chemical and tectonic signatures akin to the Australian I-and S-type continental arc granitoids. The Serra dos Órgãos Batholith yielded a crystallization age of 569± 6 Ma, whereas the syn- collisional Pão de Açúcar and Corcovado gneissic granites ages of 559 ± 4 Ma and 560± 7 Ma, respectively. The new data, supported by the integration of the geochronological data on the Araçuaí Orogen magmatism in Espírito Santo and Minas Gerais states, cast new lights on the regional Neoproterozoic (Brasiliano) evolution. Similar late Precambrian ages, spanning from ca. 580-560 Ma, recently obtained on similar syn-collisional plutons from the northern segment of the Araçuaí Orogen, highlights the synchronous development of the collisional event in Costeiro Domain of Rio de Janeiro State and in the northern domain of the Araçuaí Orogen and, accordingly, the synchronicity of the Neoproterozoic orogenic collage in both domains. As far as the Pan-African connections are related, the age of the collisional peak in the western African orogens (West Congo, Kaoko, Damara, Gariep and Saldania) are also synchronous with the ca. 560 Ma Brasiliano collisional event. However, the data do not confirm previous correlation of this segment with the adjacent southwestern Paranapiacaba Orogen (Ribeira Belt), owing to the much older collisional climax (ca. 630 Ma) dated on the latter