Petrogênese da Suíte Intrusiva Santa Clara com base em litogeoquímica, geocronologia U-Pb e geoquímica isotópica Lu-Hf: registro de magmatismo rapakívitico no SW do Cráton Amazônico

Abstract

The Santa Clara Intrusive Suite is one of the seven intrusive suítes that comprise the Rondônia Tin province, in the SW Amazonian Craton. Recent studies have considered that this suíte is composed of seventeen bodies: Santa Clara, Oriente Novo, Oriente Velho, Jacundá, Massaranduba, Retiro, Moisés, Manteiga, Primavera, Montenegro, Jararaca, Jatuarana and other intrusive bodies with no geological data so far. In this thesis, eleven of these intrusive massifs were studied and new unpublished geological data are presented. The rocks of the Santa Clara Intrusive Suite are intrusive in orthogneisses, paragneisses and granitoids from the Jamari Complex. The studied lithotypes were grouped in amphibole-biotite quartz-monzonites and biotite granites. The amphibole-biotite quartz-monzonites are porphyritic medium to coarse grained rocks and show some features compatible with magma mixing, such as the presence of mafic clots (also known as mafic microgranular enclave, MME), needle-like apatite, evidence of mineral disequilibrium and rapakivi texture. The porphyritic to equigranular biotite granites are medium-grained rocks and show no evidence of magma mixing. The quartz-monzonites are enriched in Fe2O3, MnO, MgO, CaO, TiO2, P2O5, Ba, Sr, Zr, V and Sc when compared to the biotite granites. The rocks of the Santa Clara Intrusive Suite are subalkaline, metaluminous to slightly peraluminous in character and show geochemical characteristics compatible with A-type granites. These are ferroan A-type, alkali-calcic to calc-alkalic granites; the quartz-monzonites have an oxidized nature and the biotite granites are slightly reduced. The rocks of the Santa Clara Intrusive Suite are A2-type within-plate granites, which are associated with post-collisional/post-orogenic tectonic settings. U-Pb LA-ICP-MS data suggest magmatism ranging from 1061±11 Ma to 1099±17 Ma, with some very diferente ages for the Jatuarana (1126±7 Ma) and Jararaca (1138±16 Ma e 1123±13 Ma) massifs, which could actually represent older igneous intrusive bodies and therefore should be separated from the Santa Clara Intrusive Suite. Lu-Hf LA-ICP-MS analysis reveal that the quartz-monzonites show evidence of mixing from two different sources, since they have both positive and negative ƐHf values. The TDM ages are at least 180 Ma younger for the grains with positive ƐHf values when compared to the grains with negative ƐHf values. The data presented in this thesis suggest that the quartz-monzonites represent hybrid rocks generated through mixing process between a mafic end member which was injected in a magmatic chamber with a felsic component. The author considers that a mafic underplating took place during the final stages of the Nova Brasilândia Orogenesis and this underplating would be responsible for melting the lower crust, generating a felsic melt. The crystallization of this felsic melt would result in the homogeneous biotite granites