Geoquímica e geocronologia: minerais e rochas da região de Itataia, Estado do Ceará, Ne do Brasil

• Ano de defesa: 2019
• Autor(a) principal: Cavalcante, Ana Flávia da Conceição
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Domínio Ceará; Complexo Ceará; Termocronologia
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/52979

The area of the present work, in tectonoestratigraphic terms, is located in the Ceará Central Domain of the Northern Borborema Subprovince, placed to the SE of Santa Quitéria (CE), Northeast Brazil. Local lithostratigraphy is not yet in stratus to be followed by the most diverse strands of researchers, especially in comparing local and regional views. In this scenario, we seek to adopt a chrono-lithostratigraphy that meets historical principles and regional representativeness of lithological associations. Thus, the area surveyed corresponds to a segment of the neoproterozoic supracrustals of the Independence Unit, from Ceará Complex / Group, represented, predominantly, by an association of: - ± sillimanite-garnet-biotite paragnaisses and generally with low leukosome percentage; partly with metapsamitic beds and sparse chalcosilicate / scarnitic rock lenses; - metacarbonate rocks (marbles + chalcosilicate rocks), as the main depositors of the Itataia phosphorusuraniferous ore; - quartzites with or without muscovite and feldspar, in part subordinating narrow micaceous beds. In this context, the mineral chemistry of apatites extracted from various lithotypes showed literally compositions inherent to fluorapatites (XRD analysis also confirms this result); whereas that of amphiboles recorded crystals with nuclei of ca- amphiboles (magnesium hornblende and edinite hornblenda) and borders of sodium amphibole (arfvedsonite). The lithochemistry of mafic dike samples (classified, in microscopic scale, as diabase and related to Rio Ceará-Mirim magmatism) showed a composition of andesite to basaltic andesite of the high-Ti tholeitic series. Meanwhile, the episyenite-related apatite (U-Th) / He thermochronology (U-Th) / He, even though in small numbers for a relief region that oscillates between ca. 300 m (river valley Groairas) and ca.1100 m (Serra do Céu summit), which was subordinated to important tectonic vertical oscillations and denudation from the Mesozoic (Cretaceous) to the Cenozoic; suggest two cooling phases, one around 65.1 ± 0.7 Ma and one around 87.8 ± 0.1 Ma, this number approaching the AFT (Apatite Fission Tract) age of 91 ± 6 Ma exhibited by Netto et al. (1991) and related to the apatites of mineralized coal holes in the Itataia deposit. AFT thermochronological ages around 90 Ma have been considered to reflect the culmination of the most important drift phases between the South American and African continents in Cretaceous times. In its turn, U-Pb chronoradiometry (LAICPMS) of zircons of samples from said mafic dike revealed the existence of a domain of zircons inherited from an Archean-Paleoproterozoic basement (concord ages, upper intercept: between ca. 2.000 and ca. 2.295 Ma; ca. 2.695 Ma ) metamorphosed in the Neoproterozoic (concord ages, lower intercept: 635 ± 22, 594 ± 14 and 551 ± 11Ma; Brasilian/Pan-African cycle).