2023-01-242023-01-241996-09-09SILVA JÚNIOR, Renato Oliveira da. Geologia, petrografia e geoquímica dos diques da região de Rio Maria, SE-PA. Orientador: Roberto Dall' Agnol. 1996. 123 f. Dissertação (Mestrado em Geologia e Geoquímica) - Curso de Pós-Graduação em Geologia e Geoquímica, Centro de Geociências, Universidade Federal do Pará, Belém, 1996. ANO DE DEFESA. Disponível em: http://repositorio.ufpa.br:8080/jspui/handle/2011/15152. Acesso em:.https://repositorio.ufpa.br/handle/2011/15152In the region of Rio Maria, SE of Pará, several dykes were mapped, mainly intrusive in the Granodiorite Rio Maria (GdRM) and, subordinately, in the anorogenic granite Musa (GM). Forming small elongated ridges that stand out in the morphology with a positive relief, arranged mainly according to NW-SE and E-W trends and, subordinately, N-NE. The maximum width of these bodies is 30 m, and they have an outcropping length of 1,500 to 2,000 m, reaching 3,000 m. Five groups of dykes were identified petrographically: diabases, diorites, quartz-diorites, dacites and rhyolites. The transverse and longitudinal profiles in the direction of these bodies show a decrease in rock granulation, in the center-edge direction of the body, usually culminating in aphanitic rocks, which represent, as a rule, the cooling edge of the dyke. Close to these edges, enclaves and tonsils filled with quartz-feldspathic material are frequently observed. The contacts with its host country are abrupt, sometimes marked by the presence of cooling edges, whose thickness varies from a few centimeters to, exceptionally, 2 m. The K-Ar ages of these dykes are: (1) 700 ± 8 Ma in qz-diorite (whole rock); (2) 883 ± 10 Ma in diorite (plagioclase); (3) 1,099 ± 39 Ma in diabase (plagioclase); (4) 1,802 ± 22 Ma in diabase with olivine (mafic concentrate). The first three ages are interpreted as minimum ages for these bodies. The age of 1,802 ± 22 Ma is compatible with the age of 1,707 ± 17 Ma (Rb-Sr in RT) obtained for dacites and porphyry granites. The geochronological data available for the dikes in the Rio Maria region allow placing them in the Proterozoic, and the most reliable ages suggest that at least part of these dikes is contemporary with the anorogenic granitic magmatism. Diabases have been divided into four subtypes: (1) diabase with olivine - exhibits subophytic texture. It consists of labradorite (An55-65), augite + pigeonite, olivine, opaques and hornblende; (2) porphyritic microdiabase - cuts diabase with olivine, formed by plagioclase phenocrysts immersed in a pilotaxitic matrix formed by plagioclase, augite, opaque and amphibole slats; (3)) amphibole-diabase- exhibits a granular texture with a subphytic tendency, is made up of labradorite (An54-64), opaque minerals augite, late amphibole (tremolite-actinolite) and, rarely, hypersthene; (4) auginite-diabase (RJ-18B) with ophitic texture, it is formed by labradorite (An56), augite, opaques and, secondary amphibole. Diorites and quartz-diorites show, in general, a granular texture tending to subphytic or porphyritic with a matrix rich in granophyric intergrowths. Diorites are formed by very saussuritized plagioclase, augite, quartz, hornblende and opaques. Quartz-diorites have similar mineralogy to diorites, differing only in the modal content of quartz and granophyric intergrowths. Some diorites and diabases present plagioclase phenocrysts with sieve texture, suggesting the action of mixing and/or mingling processes. The dacites are formed by porphyry dacites and porphyry dacites rich in mafics. Both have a porphyritic texture, locally glomeroporphyritic, formed by aggregates of plagioclase phenocrysts, quite saussuritized, hornblende locally involving augite, in addition to isolated quartz phenocrysts. The two subtypes have a predominantly granophyritic matrix, sometimes spherulitic. The presence of microcrystalline quartz was noted forming almond-shaped aggregates (spots), attributed to mixing processes. The rhyolites exhibit a porphyritic texture, locally glomeroporphyritic, formed by plagioclase and quartz phenocrysts, immersed in a microcrystalline matrix with a micrographic tendency. Microcrystalline aggregates consisting of chlorite, biotite and opaques also occur. The TAS diagram shows good correlation between the modal classification and the geochemical data. In this diagram the diabases and diorites plot within the field of their volcanic counterparts. Quartz-diorites generally fall into the field of low-silica dacites. The dacites themselves are a little richer in silica than the preceding group, although both focus on the same field. In the AFM diagram the samples are located in the tholeitic subalkaline field. The presence of compositional gaps between groups, mainly between diabases and diorites, and from these to quartz-diorites, reinforces the hypothesis that these rock groups studied do not present a continuous magmatic evolution. The RJ-18B sample, although presenting characteristics of diabase, shows geochemically greater affinities with the diorites. The geochemical data also reinforce the hypothesis that the dikes of Rio Maria, although showing a tholeitic affiliation, were probably generated from different liquids, since the compositional gaps between the various groups are very accentuated. The dacites, although they present, in some diagrams, an overlap with the quartz-diorites, they differ from them petrographically and geochemically, too, and, in terms of occurrence in the field. There is petrographic evidence that the crystallization of diabases was driven mainly by the fractionation of olivine, while in diorites, augite and plagioclase played a dominant role. The petrographic and geochemical data show that the diabases, with the exception of sample RJ-18B, are entirely different from the other groups in terms of magmatic evolution. Diorites and quartz-diorites, in turn, although petrographically similar, present a compositional gap that weakens and immediate hypothesis since the latter represents a more evolved term, derived from the former. Sample RJ-18B is interpreted as a mafic concentrate of these diorites. This hypothesis can be justified by the modal and chemical composition of this sample. Dacites and rhyolites are probably genetically linked to anorogenic granitic magmatism, with probable associated mixing processes, mainly in the case of dacites.Acesso AbertoAttribution-NonCommercial-NoDerivs 3.0 Brazilhttp://creativecommons.org/licenses/by-nc-nd/3.0/br/GeologiaPetrografiaGeoquímicaDiquesDiques BásicosDiques IntermediáriosDiques ÁcidosRio Maria (PA)DissertaçãoCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIAPETROLOGIA E EVOLUÇÃO CRUSTALGEOQUÍMICA E PETROLOGIA