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The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped.Both units,topped by chemical sediments and oceanic facies as rhyolite and andesite lavas,rhyodacite,and porphyritic dacite,with frequent intercalations of pyroclastic and epiclastic deposits.Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions.The analyzed rocks display calc-alka-line to shoshonitic affinity consistent with generation related to an active continental margin.The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial εNd values between-3 and-9,indicating the predomi-nantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca.2.5-2.0 Ga) depleted mantle model ages.