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In SW Amazon Craton, along the boundary between the Ventuari-Tapajós (1.9 to 1.8 Ga) and the Rio Negro-Juruena (1.8 to 1.55 Ga) provinces, an association of volcanic rocks and related epizonal granitic plutons crop out as a volcanic belt with more than 600 km long. This set of rocks, here called the Volcanic Domain (VD), has been the target of several studies due to its metallogenic importance as well as to the understanding of the geodynamic evolution of the Southwestern Amazon Craton, and various geodynamic models are considered for this plutono-volcanism at about 1.8 Ga, including taphrogenesis, accretionary margin volcanic belt, and late- to post-orogenic extensional magmatism.
In this work, based on whole rock geochemistry, and in U-Pb and Sm-Nd isotopic results we propose a geodynamic model that admit shifts in the tectonic regime through time and unifies the second and third interpretations above. We interpret the intermediate to acid, A-type, oxidized granitic and volcanic rocks from the Colíder Group and the Paranaíta Intrusive Suite as products of continental arc magmatism, whereas the acid, A-type reduced granitic and volcanic rocks resulted from late-stage extensional back-arc and forearc processes being respectively associated with the Teles-Pires Intrusive Suite and Roosevelt Group magmatism.
The continental arc interpretation for the VD is supported by the following lines of evidence: (1) spatial arrangement of the VD in the shape of a volcanic belt; (2) the large volume of volcaniclastic deposits and related epizonal granitic intrusions; (3) variable chemical signatures ranging from subalkaline mafic compositions to high-K calc-alkaline, A-type oxidized granites, showing REE and trace element patterns similar to those of subcontinental lithospheric mantle sources enriched by subduction-zone fluids, and subordinate involvement of continental crust; (4) crystallization and Sm-Nd TDM model ages, respectively, ranging between 1820 and 1780 Ma, and from 2.40 to 1.84 Ga, with eNd(t) values of -3.9 to +2.5, yielding an overlap in U-Pb and Sm-Nd ages of rocks from the Juruena Magmatic Arc; (5) the occurrence of epithermal-porphyry Au systems in the Alta Floresta Gold Province with ages compatible with those of the VD magmatic period.
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