Nd-Sr-Hf isotopes and U-Pb ages of mesoproterozoic Três Estradas Alkaline-Carbonatite Complex, Brazil: Implications for Sul-Riograndense Shield evolution and rodinia break-up

Abstract

The first occurrence of Mesoproterozoic carbonatite in the Rio de la Plata Craton – RDPC indicates extensional event prior to the opening of the Charrua Ocean. Nd-Sr-Hf Isotopic and U-Pb on zircon geochronological data are presented for the Três Estradas Alkaline-Carbonatite Complex – TEC, located in southernmost Brazil. The complex consists predominantly of ultramafic rocks, carbonatites and, subordinate, deformed fenitized syenites metamorphosed under greenschist to amphibolite facies conditions. U-Pb ages between 1110 ± 4.8 Ma and 1123 ± 15 Ma, respectively derived from a dolomite metacarbonatite and an associated metasyenite, constrain the TEC emplacement timing. The Nd-Sr-Hf isotopic signatures indicate that the TEC rocks were derived from a heterogeneous mantle, isotopically depleted in Sm-Nd and slightly depleted to enriched in Rb-Sr, with little influence of ancient crust and that these rocks are derived from the same source of parental magma probably submitted to intense metasomatism. The Nd-Sr isotopic signatures and crystallization ages of the TEC allow correlating it to the carbonatitic intrusions of the Alkaline provinces of Ontario and Grenville, Canada, in Laurentia, associated with the Keweenawan magmatic event (1.11–1.09 Ga), to which extension efforts would be related causing ruptures in RDPC edge and Laurentia, probably juxtaposed in that time interval. According to paleogeographic reconstructions of Rodinia, the Kalahari Craton would only have joined Laurentia and the RDPC at 1050 Ma. Around 920 Ma there is the generation of an oceanic crust in the Rio de la Plata Craton with the installation of the Charrua Ocean and the beginning of the formation of the Dom Feliciano Belt, concluded at 540 Ma, with peak deformation and metamorphism at 650–630 Ma.