Navegando por Assunto "Apatita"

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Assinatura geoquímica de apatita de rochas sanukitoides do sudeste do cratón amazônico, Província Carajás.
(Universidade Federal do Pará, 2019-05-26) FONSECA, Camila Santos da; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The Rio Maria Sanukitoid Suite, included in the Rio Maria Domain, southern portion of the Carajás Province, is composed of granodiorites and associated mafic and intermediary rocks. It has large exposures in the north of Redenção city, south of Rio Maria, east of Bannach and northeast of Xinguara, SE portion of the Amazonian Craton, being intrusive in greenstones of the Andorinhas Supergroup, Arco Verde Tonalite and Complex Caracol Tonalitic. Other granodioritic rocks correlated to the Rio Maria sanukitoids were described in the regions of Água Azul do Norte, Ourilândia do Norte, Serra do Inajá and Xingu region, all of them included in the Carajás Province. The Rio Maria Sanukitoids are metaluminous rocks, calcic-alkaline affinity and enriched with Mg, Cr and Ni in relation to other granodiorite rocks. They present primary epidote, zircon, allanite, titanite, apatite and magnetite as main accessory phases. U-Pb and Pb-Pb zircon dates defined crystallization ages of 2,87 Ga for these rocks. Apatite is a generally early mineral in the order of crystallization of granitoid rocks. Because of its properties, it can incorporate variable contents of REE and other trace elements, such as Na, K, Mn, F, Cl, Sr, Y, Pb, Ba, Th, U, V, and has been used as a good petrological and metallogenetic indicator of its host rock. The objective of this dissertation was the morphological and compositional study, by electron microprobe, of apatite crystals of granodioritic rocks from Rio Maria Sanukitoid Suite in Rio Maria, Ourilândia do Norte and Bannach regions, Rio Maria Domain, Carajás Province. For comparative purposes apatites of Leucogranodiorite with high Ba-Sr from Água Azul do Norte and of the Trondhjemite Mogno from Bannach region, both archaeans, have been studied. It was also compared to the apatites of the Seringa and Antônio Vicente paleoproterozoic type A granites, the first weakly oxidized and sterile, and the second, reduced and mineralized to Sn. The apatites of the Ourilândia do Norte sanukitoids have compositional zonations concentric to oscillatory more evident and complex, with well defined light-dark zones. On the other hand, the apatites of the Rio Maria and Bannach sanukitoids form more homogeneous crystals, with not evident or non-existent zones. The apatites of high Ba-Sr Leucogranodiorite and Mogno Trondhjemite are equally developed (> 150 μm), but with rare zoning restricted to the edges of some crystals. Inclusions of zircon are common only in apatites of Mogno Trondhjemite. In the Seringa granite, the apatites are comparatively smaller (<100 μm), subhedral to euhedral and with well defined zonations, while those of the Antônio Vicente granite are poorly developed (<30 μm), subrounded and free of compositional zonations. The main compositional variations among the apatite of the Rio Maria Domain, in addition to CaO, P2O5 and F, are in the highest content of LREE (La, Ce, Pr, Sm, Eu) found in the apatite of Ourilândia do Norte and Rio Maria in relation to those of Bannach, which show lower concentrations and sub-horizontal trend in the diagram (La + Ce + Pr + Sm) vs. (Gd + Yb + Y). This enrichment in REE is more evident in the diagram ΣREE + Y vs (La + Ce + Pr + Sm + Eu), where the studied apatite form an enrichment trend towards the Bannach - Rio Maria - Ourilândia do Norte sanukitoid. Based on this geochemical signature, similar and more enriched magmatic sources in LREE are suggested for the apatites of Ourilândia do Norte and Rio Maria. On the other hand, the apatites of Bannach sanukitoids presented higher and more variable concentrations of CaO, P2O5 and F and lower LREE, suggesting origin from a compositionally different and more LREE depleted magma. The apatites of the Mogno Trondhjemite and the leucogranodiorite high Ba-Sr are also more impoverished in LREE and tend to follow the apatite of the Bannach sanukitoides in the diagrams, but the apatite of the leucogranodiorites show greater enrichment in Sr. The Seringa granite has apatites more enriched in F and REE + Y when compared to the apatite of the archaean rocks, and they stand out in all the geochemical diagrams. This fact demonstrated that apatite compositions can also be used to record petrogenetic processes and to differentiate magmatic compositions that marked changes during the crustal evolution of a region, for example, distinguishing between Archaean and Paleoproterozoic granitoids, and are, therefore, useful in studies of provenance. Apatites of Antônio Vicente paleoproterozoic granite, mineralized in Sn, show high concentrations of F, Mn, Fe, Y and REE (except Eu), in comparison to other granitoids and can be used as a good metallogenetic indicator.
Acesso aberto (Open Access)
Termocronologia por traços de fissão em apatita da Borba Sul da Bacia do Amazonas, na região de Itaituba (PA)
(Universidade Federal do Pará, 2010-11-09) PINA, Aline Carla Miranda de; LELARGE, Maria Lidia Vignol; http://lattes.cnpq.br/3165548495925769; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
The region of Itaituba (PA) located at the South portion of the sedimentary basin of the Amazon can be defined as a border zone between this basin and the Amazonian Craton. In this region outcrop sedimentary rocks, belonging to Pitinga, Maecuru, Ererê, Barreirinha, Curiri, Monte Alegre and Itaituba Formations, representatives of sineclise phase sedimentary basin of the Amazon; sedimentary rocks the stage rift gathered in Prosperança Formation; besides igneous rocks of Iriri Group, Parauari Intrusive Suite and Maloquinha Intrusive Suite, which compose the basement of the sedimentary basin. The fission track thermochronology of apatite was used in the investigation of thermotectonic evolution of the sedimentary basin of the Amazon region of Itaituba (PA), mainly from the dating of basement rocks of the basin. The method of fission tracks in apatite is a marker thermochronologic low temperature, recording temperatures of up to 120 º C. When subjected to conditions of temperatures above the traces of apatite fission are cleared, resetting the clock geochronological for this method, and registers, thus, a new event. Thus, this tool was used to investigate the age of the tectonic processes that affected the Amazon Basin, which were also recorded in the rocks of its basement. Given the scarcity of apatite in sedimentary rocks sampled units of the Amazon basin, only a sample of the Monte Alegre Formation sandstone has been dated by fission track method. However, in the basement could be dated 20 samples, representing various rocks including rhyolites, granites and olivine-diabase of Paleoproterozoic, belonging to the three units mentioned above. The sandstone of the Monte Alegre Formation, whose age of the lithostratigraphy and Mesocarbonífero, provided apparent ages in apatite fission track AFT) from 91 Ma. Statistically this sample revealed the existence of two populations of apatite grains: a population with a mean age of 105 Ma and another population with a mean age of 64 Ma, indicating that this sample was subjected to two events thermotectonic. This fact can be confirmed through the thermal modeling also showed that the presence of two events whose ages are 106 Ma and 58 Ma. Samples of the basement were divided into three groups according to ages TFA obtained and the results of mathematical models. In group 1 TFA ages ranged from 163.0 Ma and 258.7 Ma, for group 2 ages were established between 142.1 Ma and 147.4 Ma, while samples of group 3 were between 170.1 Ma and 180.9 Ma is noteworthy that the ages of crystallization of igneous bodies sampled are between 1.8 and 1.9 Ga. The mathematical modeling of samples of groups 1 and 2 record the same epsódios, a first cooling, followed by heating and finally an episode of cooling. This last cooling event occurred about 100 Ma for all samples of these groups, except the sample IT-16 passing through the final event of cooling for 62 Ma. The thermal histories of samples IT-22 and 23 show a period of accelerated cooling compared to previous samples, their thermal histories ending at 39 Ma and 35 Ma, respectively, suggesting the existence of neotectonic events in the region. The events of approximately 100 Ma recorded in the Monte Alegre Formation sandstone and models of the samples of the basement can be related to a compressional tectonics that occurred according to the opening of the eastern equatorial Atlantic and the convergent movement of Andean subduction zone, west of South American plate. In turn the events of Tertiary age (64-58 Ma) marked these rocks may show reflections of a process where dextral transform interacted plates South American, Caribean and Nazca, reactivating old fracture zones. The various ages obtained for samples of the basement (ranging from 142.1 Ma and 258.60 Ma) are markers of major tectonic events, but may be registering the different ages at which these samples passed by the isotherm of 120 ° C, indicating thus the occurrence of a tectonic with different behavior in different areas of this region.