Navegando por Orientadores "ALBUQUERQUE, Carlos Alberto Ribeiro de"

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Evolução geológica da região de Araguacema-Pequizeiro-Goiás-Brasil
(Universidade Federal do Pará, 1981-12-21) GORAYEB, Paulo Sérgio de Sousa; ALBUQUERQUE, Carlos Alberto Ribeiro de
The region around Araguacema, Pequizeiro and Conceição do Araguaia, belongs to the Araguaia Fold Belt and exhibits a metasedimantary litological sequence which was subjected to deformation and metamorphism at least in the Upper Proterozoic. Geological mapping, structural-stratigraphic, petrographic and chemical analises permit the elucidation of the geological evolution of the ares. The sequences have been included in the Tocantins. Group constituted of Pequizeiro and Couto Magalhães Formations. Ultramafic and mafic-ultramafic bodies represent both pre and post-tectonic magmatic events. The Rio das Barreiras Formation overlays with an angular unconformity the Tocantins sequences. Pequizeiro Formation is the lower unit of the Tocantins Group and is litogically composed of micaschists, with some quartzites, calcschits, and magnetite-muscovite-phyllites. These rocks represente a metasedimentary sequence derived mostly of pelite and graywacks. The unit Couto Magalhães comprises essentially phyllites and slates with minor metapsammites, metapelites, cherts, lenses of limestones and metagraywackes. Most of these rocks represent an original pelitic sequence. Lenticular serpentinitic bodies of dunitic nature have been introduced in the Couto Magalhães Formation by tectonic processes. All of these bodies are associeted to fault zones and have N-S trends.. They are of alpine type but, they may represent ophiolitic bodies. These sequences underwent poliphasic deformational and metamorphic processes during the Middle Proterozoic and up to the Brasiliano Cycle. The structural evolution comprised three plastic deformation phases called F1, F2 and F3. The metamorphic history included two different events called M1 and M2 with synchronical relation between Ml-F1 and M2-F3, and has a large variation.from ankimetamorphism (west) to greenschist facies (east). Three isograds (sericite, chlorite and biotite) have been defined from W to E, as the temperature grows. In the Upper Proterozóic (Brasiliano Event) ruptural tectonic processes reactiveld ancient basement faults and formed new normal faults and fractures. Hornblends Peridotite plutons; diabase dikes and gabbro stocks were emplaced in the Couto Magalhães Formation, representing post-tectonic magMatfc events. Polymitic conglomerates and siltstonea of Rio das Barreiras Formatian acumuiated in grabens, reflecting the Brasiliano tectonic rellef. In the Phanerozoic, intensiva laterization and weathering have developed in an extensive area in the Araguaia valley with sandy and argillaceous sedimentation along the rivers.
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Petrologia da seqüência xistosa Seridó, Currais Novos - Parelhas (RN)
(Universidade Federal do Pará, 1981-03-13) GAMA JÚNIOR, Theodomiro; ALBUQUERQUE, Carlos Alberto Ribeiro de
This work deals with the metamorphism of the Seridó schists in the region Currais Novos - Parelhas, of the Seridó schist belt. The study involved the petrography of the rocks, the chemistry of rocks and selected minerals and the application of geothermometers and geobarometers as well as a correlation between deformation and metamorphic crystallization of the minerals. The three consecutive phases of deformation (F1, F2, F3) described have been recognized although F3 was seen only locally. Syntectonic crystallization (relative to F1) was noted for most minerals although post-tectonic crystallization is seen very often. The pressure and temperature of crystallization can be estimated at approximately 4 kb and 550°C, respectively. The occurrence of staurolite in metasedimentary aasemblages defines metamorphic conditions of the amphibolite facies. Garnet, with about 70% of the almandine molecule and 15% of the spessartite molecule, coexists with cordierite and andalusite for sillimanite). Therefore, the metamorphism is of the 1°w-to intermediate pressure type. The grade of metamorphism is almost constant in the region studied, without evidence of retrograde metamorphism except where intense deformation produced phyllonites. The conditions of metamorphism of this part of the Seridó schist belt can be compared to those of the Abukuma belt of Japan. The metasedimentary rocks were derived from sediments dominantly with a composition corresponding to a mixture of pelite and greywacke.
Acesso aberto (Open Access)
Petrologia do maciço alcalino de Peixe-Goiás
(Universidade Federal do Pará, 1983-12-21) LEMOS, Ronaldo Lima; ALBUQUERQUE, Carlos Alberto Ribeiro de
The Alkaline Fish Massif consists of a nepheline syenite gneiss body, leucocratic, foliated and banded. Foliation is accentuated at the edges and incipient or absent at the center, while banding is restricted to the edges. The Massif is surrounded by a narrow band of quartz syenite and granite gneisses, in contact with pre-Serra da Mesa Group metasediments, predominantly pelitic (graphite-sillimanite micaschist and sillimanite-quartz micaschist). The nepheline syenite gneiss consists essentially of nepheline, mesopertite, peristerite and microcline, with biotite being the mafic mineral and, more rarely, magnetite. Its agpaitic coefficient is typical of miaskitic rocks, and its mineralogy is also of this type. The different textural types of nepheline show variation in the Si/Al ratio, while the Na/K ratio is approximately constant. Peristerite has composition An4.0-5.1 -An0.5-2.8 and, in a narrow band of the edge, it is An7.0-10.7 -An0.4-4.0. The , microcline and potassium phase of mesopertite (microcline) have composition Or8 3.0-9 4.4, while the sodium phase of mesopertite is predominantly peristerite (An4.0-5.1 -An0.7-2.8) and sometimes it is albite (An0.4-2.6). Biotite is of the lepidomelane-siderophyllite type. The composition of nepheline syenite gneiss, similar to the minimum point in the Ne-Ks-Qz diagram, the variation in the ratio, Si/Al. of nepheline, typical of nepheline crystallized from a nepheline-like syenite magma under plutonic conditions, as well as the trends of the elements Si, Al, Na and K and the K/K + Na ratio in differentiation diagrams, which are coincident with the variation observed in series of alkaline igneous rocks, indicate that the nepheline syenite gneiss resulted from a nepheline syenitic magma, generated in the lower crust or upper mantle, in a tectonically stable environment. During the ascent of this magma, the increase in the geothermal gradient caused fusions in rocks of the crust, generating magmas of quartz syenitic and granitic composition. The nepheline syenite body, the quartz syenite and granite belt and the pre-Serra da Mesa Group metasediments were later affected, together with the sediments of the Uruaçú Development Belt (Serra da Mesa Group), by a regional medium pressure type metamorphism. in the amphibolite facies, with a temperature of 650 ± 30°C and a pressure of 6 ± 0.5 kb. The metamorphism took place in the presence of a fluid phase rich in H2O and CO2, in addition to S03, F and P originated by the decomposition of late-magmatic minerals from nepheline syenite, rich in volatile components, which had great importance during the metamorphism in the formation and recrystallization of minerals and, in local processes, of autometasomatism. This Massif presents striking analogies with the alkaline complexes of Blue Mountain, Bigwood and Darkainle.
Acesso aberto (Open Access)
Petrologia e geoquímica das rochas plutônicas da região de Conceição -Itaporanga (PB)
(Universidade Federal do Pará, 1983-12-22) BARRIGA, Vânia Maria Fernandes; ALBUQUERQUE, Carlos Alberto Ribeiro de
The igneous rocks of the Conceição-Itaporanga region (W of the State of Paraíba) are intrusive in metamorphic rocks of the basement and of the Piancó Alto Brígida fold belt, which is inserted in the Caririana folded region of northeastern Brazil. These rocks are represented by K-diorite, tonalite, granodiorite and granite, and are placed in metasedimentary rocks of the Cachoeirinha Group and gneisses of the Uauá Group and are considered to be post-tectonic in the Brasiliano cycle. Chemically these rocks have a special character where K-diorite, with a high K content, and tonalite, granodiorite and granite have a much more mafic chemistry than many other granitic rocks. The chemical compositions of these rocks when placed in the diagrams of variation of elements versus the modified Larsen Index and in the AFM diagram, show several trends that are not compatible with differentiation. Comparing the mineralogical associations of tonalitic, granodioritic and granitic rocks in the Conceição-Itaporanga region, with experimental work in granodiorite and granitic systems, it is observed that the most probable temperatures for crystallization of granodiorite magma are 680°-780° at a pressure of 8Kb. For the origin of K-diorites, it is assumed that they were formed from a primary K-rich magma, while the most likely genesis of tonalitic, granodiorite and granitic rocks is by partial melting in the crust from mafic gneisses or rocks. meta-basalt.