Orosirian I-type calc-alkaline granitoids from northern Brazil: Petrogenetic implications for evolution of the central Amazonian Craton

Abstract

New petrographic, lithochemical, in situ UPb geochronological and Nd isotopes data allowed to propose a petrotectonic model for 1.90–1.88 Ga I-type calc-alkaline granitoids (Terra Preta Massif - TPM, Água Branca Suite) from the southernmost Uatumã-Anauá Domain (UAD), Ventuari-Tapajós Province (VTP), central Amazonian Craton, Brazil. The main rock facies of the TPM (1898–1885 Ma) vary from quartz monzodiorite to syenogranite, which display dominantly metaluminous to weakly peraluminous composition. A quartz diorite displaying particular petrographic features can be associated with the TPM and it does not seem to have evolved by fractional crystallization. Field and petrographic evidences, supported by trace element modeling, suggest that the quartz diorite has an origin linked to mixing between the TPM granodioritic (60 wt%) and related quartz gabbro (40 wt%) magmas. Lithochemical data show that a great petrographic variation of the TPG's main facies was not caused by fractional crystallization and point to different degrees of melting of the enriched mantle. Main facies also indicate weak positive ƐNd(t) anomalies that suggests upwelling asthenospheric mantle that provided heat to remelt the lower continental crust. The dataset of Nd isotopes and inherited zircon crystals also suggests reworking of Rhyacian granulites (French Guyana Domain-FGD, Maroni-Itacaiúnas Province) and Orosirian granulites (Anauá Complex, UAD, VTP) and assimilation of metasedimentary rocks (Cauarane Group, Central Guyana Domain, VTP), collisional granitoids (Serra Dourada Suite, UAD, VTP) and Orosirian orthogneisses (Rio Urubu Complex, CGD, VTP). Sources modeling of lithospheric mantle indicated that it is possible to generate tholeiitic mafic and I-type calc-alkaline melts, by melting of 2.15 Ga komatiitic metabasalts from FGD. A melt fraction of 28 wt% of 2.03 Ga granulites was also able to generate a liquid compatible with the main facies of the TPM. Offset of the slab breakoff in the post-collisional setting caused the asthenospheric mantle input and mixture of depleted melts (highly positive ƐNdt) with enriched melts (negative ƐNdt), resulting in ƐNd(t) values close to zero, which renders the lithospheric mantle as the main isotopic reservoir for the TPM.