Navegando por Assunto "Granitoides arqueanos"

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Geologia, geoquímica e petrologia magnética dos granitoides Arqueanos da Porção Nordeste de Água Azul do Norte - Província Carajás
(Universidade Federal do Pará, 2012-09-10) GABRIEL, Eleilson Oliveira; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
Petrographic and geochemical studies of Archean granitoids under taken during the geological mapping of the NE portion of the Água Azul do Norte area - Carajás Province, allowed the identification of new units that were previously inserted into the Xingu Complex. The granitoids individualized are: (i) the Água Azul and Água Limpa granodiorites, which are high-Mg granitoids, similar geochemical to the Archaean sanukitoid occurring in other areas of the Carajás Province as well as in the Karelian and Superior provinces; (ii) a pluton of Trondhjemite with affinity to the classical TTG, not identified in previous studies in this area; (iii) three bodies of Leucogranodiorites and one of Leucogranite all of them with calc-alkaline signature and geochemically similar to the leucogranodiorites-granites of the Guarantã Suite of the Rio Maria Domain. These Archaean granitoid are intrusive in the supracrustal sequences of the Sapucaia Group and occur as deformed bodies, generally elongated along EW. The Água Azul and Água Limpa granodiorites are composed essentially of (epidote)- amphibole-biotite granodiorite and tonalite with (muscovite)-(epidote)-biotite granodiorite and monzogranites. Biotite trondhjemites and subordinate biotite tonalites are the rock varieties identified in the Trondhjemite pluton. The occurrences of Leucogranodiorites consist of biotite granodiorites, and the Leucogranite body is composed of biotite monzogranites. The Água Azul and Água Limpa granodiorites are predominantly metaluminous and exhibit higher values of Mg#, Cr and Ni when compared to the calc-alkaline series from continental margins and Archean TTG suites and leucogranodiorites of the Rio Maria Domain. The magnetic susceptibility (MS) values obtained in the rocks of these two bodies are relatively low (average 17.54 x10-4 SIv for the Água Limpa and average 4.19 x10-4 SIv for the Água Azul granodiorites). Magnetite and hematite are the more common opaque minerals and ilmenite is absent in these rocks. The magnetite crystals are more abundant and larger in the Água Limpa Granodiorite compared to the Água Azul Granodiorite, justifying the highest values of MS found in this pluton. In general there is a tendency of increasing of MS values in the sense of the less evolved facies (amphibole tonalite + amphibole granodiorite) to more evolved facies (biotite granodiorite + biotite monzogranite). The more magnetic samples are related to magnetite formed during deformational processes in shear zones. Because of the geochemical and mineralogical similarities between these rocks and sanukitoids of Rio Maria, it is assumed conditions of the fO2 between HM and FMQ buffers for granitoids of the Água Azul do Norte.
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Geologia, petrografia e geoquímica dos granitóides arqueanos de Sapucaia - Província Carajás-PA
(Universidade Federal do Pará, 2013) TEIXEIRA, Mayara Fraeda Barbosa; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Geological mapping performed in the eastern portion of the Transition Subdomain, Carajás Province, southern of Canaã dos Carajás and the northern of Sapucaia cities, allowed the identification, individualization and characterization of a variety of Archean rocks, previously encompassed in the Xingu Complex. The oldest unit identified in this area is a hornblende tonalite, correlated to São Carlos Tonalite (~2.93 Ga), which is exposed as blocks or outcrop and commonly present foliation (NW-SE to E-W) or homogeneous aspect. Its geochemical signatures differ from the typical Archean tonalite-trondhjemite-granodiorite (TTG) associations due to show enrichment in TiO2, MgO and CaO, low contents of Sr, and Rb contents similar to samples with lower concentrations of silica, which are reflected in higher Rb/Sr ratios and lower Sr/Ba ratios. The REE patterns reveal low to moderate fractionation of HREE compared to LREE, and discrete or moderate negative Eu anomalies. It is stratigraphycally followed by TTG association correlated to Colorado Trondhjemite (~2.87 Ga) which displays gray color, medium-grained, and commonly a NW-SE to E-W foliation. In the southern of area, outcrops a body of 40 km 2, which comprises a small mountain of porphyritic leucogranodioritic rocks named Pantanal Leucogranodiorite . It is emplaced at TTG association and crosscutted, on its western portion, by deformed leucogranites. The Pantanal Leucogranodiorite shows peraluminous character and calc-alkaline affinity, with high contents of Ba and Sr. The REE patterns show nosignificant Eu anomalies and HREE are strongly fractionated, which is geochemically similar to Guarantã Suite (~2.87 Ga) from the Rio Maria Domain. Its origin may be related to low degrees of melting of TTG, probably accompanied by interaction with fluids enriched in K, Ba and Sr, derived from a metasomatized mantle. The leucogranites exhibit A-type geochemical signature and reduced character, and may have originated from the melt of dehydrated peraluminous calcic-alkaline rocks, during the Neoarchean. In the eastern portion of the Pantanal Leucogranodiorite was also identified ahornblende-biotite monzogranite which is geochemically similar to oxidized A-type granites, correlated to Neoarchean Vila Jussara Suite. Also, it correlated to Neoarchean subalkaline magmatism in the northern area, occur two granitic stocks. They comprise (i) tonalite to granodiorite with geochemical signature similar to oxidized A-type granites and show affinity with Vila Jussara Suite; and (ii) monzogranites which show reduced A-type granites signature and could be compared to Planalto Suite. At northern of the study area was identified an association of mafic-enderbitic rocks which comprises intensely deformed and recrystallized hornblende norite, pyroxene-hornblende gabbros, pyroxeneix hornblende monzonite, hornblende gabbros, amphibolites and enderbites, which are represented in the geological map as a WNW-ESE small elongated body , and a semicircular body controlled by shear zones. The textures observed in these rocks indicate that recrystallization occurs under relatively high temperatures, 6000C or above, and those rocks show metamorphic features. The geochemical behavior of these rocks suggests that the hornblende-norite, hornblende-gabbros and amphibolites are tholeiitic subalkalines, whereas enderbites, pyroxene-hornblende gabbro and pyroxene-hornblende monzonite exhibit calcalkaline signature. The low La/Yb ratios for mafic rocks indicate low degree of fractionation, whereas the high La/Yb ratios for enderbites reveal significant fractionation of HREE during formation and differentiation of its magmas, and the concavity of HREE pattern indicates probably influence of amphibole fractionation during its evolution. In the central and northcentral of area was recognized biotite-monzogranites with peraluminous and calc-alkaline signature and distinct REE patterns, which allowed us to distinguish two groups. The first shows higher REE enrichment, weak enrichment in LREE relative to HREE, and exhibit moderate negative Eu anomalies, indicating no significant fractionation of phases enriched in HREE and show possibly affinity with Bom Jesus Granite from Canaã dos Carajás area. The second group shows a sharp fractionation of HREE relative to LREE, with discrete or absent Eu anomalies, and concave HREE patterns indicating that amphibole was important phase during the fractionation of these rocks, like Serra Dourada and Cruzadão granites, also located in the Canaã dos Carajás area. This comparison should be enhanced as soon as further geochemical and geochronological data are available in order to a correlation can be evaluated.