2019-02-272019-02-272017-09-22PINA NETO, Acacio Nunes de. Caracterização geológica, petrográfica e geoquímica das rochas máficas da região de Tangará da Serra - MT. Orientador: Paulo Sergio de Sousa Gorayeb. 2017. 62 f. Trabalho de Curso (Bacharelado em Geologia) - Faculdade de Geologia, Instituto de Geociências, Universidade Federal do Pará, Belém, 2017. Disponível em: http://bdm.ufpa.br/jspui/handle/prefix/1098. Acesso em:.http://bdm.ufpa.br/jspui/handle/prefix/1098The mafic rocks from the Tangará da Serra region, southwest of Mato Grosso State, distant about 250 km from Cuiabá, include basaltics flows of fissural character, sills and dikes of olivine diabase and diabase which are associate with sandstones and limestone from Araras, Parecis and Alto Paraguai Groups. The thicknesses of these mafic rocks range 15-310 m and are known in the literature as basaltic volcanic rocks from Tapirapuã Formation, located at the Jurassic-Triassic boundary. The fieldwork data and the petrographic analysis allowed the description and characterization of mafic and their wall rocks (sandstones and limestones), and were characterized as basalts and diabases in flows and sills, respectively, besides rare diabase dykes.The basalts are fine grained and exhibit gray-lead color with aphanitic and isotropic texture. Microscopically, they exhibit porphyritic texture with intersertal, intergranular and amygdaloidal textures in matrix. They consist essentially of plagioclase, clinopyroxene (augite) and orthopyroxene (enstatite). Some subhedral to euhedral plagioclase phenocrysts appear to be concentrically zoned while others, in matrix, exhibit quenching textures as acicular crystals and "swallowtail" texture in plagioclase terminations associated with volcanic glass. In matrix, occurs a greenish-colored cryptocrystalline material, opaque minerals and glass occur interstitially of the plagioclase slats and pyroxenes. The olivine diabases are medium grained and exhibit predominantly intergranular texture and consist essentially of plagioclase, olivine and pyroxene. The plagioclase is labradorite (An60), are lath shaped andand show albite and albita-calrsbad twin laws. Among the pyroxenes, it is recognized the augita, in greater modal proportion, and enstatite. While the diabases, without olivine, are textually similar to the previous one and they are quite altered. The characterization of some minerals difficult to identify through optical technics such as opaque minerals, alteration minerals as well as the amygdala’s material in the basalts was performed through scanning electron microscope analysis which imaged and chemically characterized the minerals such as plagioclase, augite and titanomagnetite in basalts. In the olivine diabases were identified augite, plagioclase, olivine, biotite, ilmenite, pyrite and badelleyite. Geochemically, it was possible to identify three distinct compositional groups and compatible with the petrographic analysis: olivine diabases (characterized by low concentrations of SiO2, high MgO, Al2O3 and intermediate subalcaline trend), basalts (characterized by high SiO2, lower MgO,Al2O3 and tholeiitic trend) and diabases which are characterized by, relatively, higher amounts of TiO2, low concentration of MgO and tholeiitic trend. These rocks reveal subalcaline and tholeiitic nature. The CIPW normative composition allows to classify the x olivine diabases in olivine tholeites and the basalts and diabases in tholeites. Regarding trace elements, it is possible to observe that the olivine diabases and the basalts are enriched in large ion litophile elements in relation to the light rare-earth elements and high ionic potential elements, whereas the diabases show an anomalous pattern. The rare-earth elements showed similar and subhorizontal behavior among the studied samples, with moderate fractionation and enrichment in light rare-earth elements in relation to heavy rare-earth elements. Olivine diabases have (Ce/Yb)N ratios between 4.9 to 4.5, (Ce/Sm)N from 1.8 to 1.7 and ratios (Gd/Yb)N between 2.1 to 2.2, in addition to a discrete positive anomaly of Eu(Eu/Eu*=1.28–1.34). Whereas the basalts have ratios (Ce/Yb)N between 2.2 to 2.4, (Ce/Sm)N of 1.5 and ratios (Gd/Yb)N between 1.4 and 1.5, and a discrete negative anomaly of Eu (Eu/Eu*=0.8-0.9). The diabase, in turn, is more enriched in rare-earth elements, lower ratio (Ce/Yb)N, (Ce/Sm)N and a discrete negative anomaly of Eu (Eu/Eu*=0.8). In tectonic setting discrimination diagrams the samples exhibit within-plate basalts affinities. The integration of the fieldwork, petrographic, geochemical and comparative data allows the interpretation that the mafic rocks from the Tangará da Serra region represent a continental toleitic magmatism that can be related to basaltic magmatism of the same age as the basalts of the Mosquito Formation in the Parnaíba Basin; The Anari Formation in the Parecis Basin; to Penatecaua Magmatism of the Amazon Basin; and to the basalts of Guianas and West Africa as well as to the Cassiporé dykes swarms in Amapá. Its occurrence is linked to the distensive regime prevailing during the Jurassic and that would result in the separation of Pangea and the formation of the central Atlantic Ocean.Acesso AbertoPetrologiaFormações - GeologiaDiabásioBasaltoTangará da Serra - MTCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::PETROLOGIATrabalho de Curso - Graduação - Monografia