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‣ The link between partial melting, granitization and granulite development in central Ribeira Fold Belt, SE Brazil: New evidence from elemental and Sr-Nd isotopic geochemistry

SANTOS, Telmo M. Bento dos; MUNHA, Jose M.; Tassinari, Colombo Celso Gaeta; FONSECA, Paulo E.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
Português
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Elemental and Sr-Nd isotopic data on metatexites, diatexites, orthogneisses and charnockites from the central Ribeira Fold Belt indicate that they are LILE-enriched weakly peraluminous granodiorites. Harker and Th-Hf-La correlation trends suggest that these rocks represent a co-genetic sequence, whereas variations on CaO, MnO, Y and HREE for charnockites can be explained by garnet consumption during granulitic metamorphism. Similar REE patterns and isotopic results of epsilon(565)(Nd) = -5.4 to -7.3 and (87)Sr/(86)Sr(565) = 0.706-0.711 for metatexites, diatexites, orthogneisses and charnockites, as well as similar T(DM) ages between 2.0 and 1.5 Ga are consistent with evolution from a relatively homogeneous and enriched common crustal (metasedimentary) protolith. Results suggest a genetic link between metatexites, diatexites, orthogneisses and charnockites and a two-step process for charnockite development: (a) generation of the hydrated igneous protoliths by anatexis of metasedimentary rocks; (b) continuous high-grade metamorphism that transformed the ""S-type granitoids"" (leucosomes and diatexites) into orthogneisses and, as metamorphism and dehydration progressed, into charnockites. (C) 2011 Elsevier Ltd. All rights reserved.; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); POCA-PETROLOG; POCA-PETROLOG; GEODYN; GEODYN[POCTI - ISFL - 5-32]; FCT[SFRH/BD/17014/2004]; Fundação para a Ciência e a Tecnologia de Portugal (FCT); FEDER; FEDER; POCTI/FEDER; POCTI/FEDER[263]

‣ Sr and Nd isotopic geochemistry of the early ultramafic-mafic rocks of the Mako bimodal volcanic belt of the Kedougou-Kenieba inlier (Senegal)

NGOM, Papa Malick; Cordani, Umberto Giuseppe; Teixeira, Wilson; Janasi, Valdecir de Assis
Fonte: SPRINGER HEIDELBERG Publicador: SPRINGER HEIDELBERG
Tipo: Artigo de Revista Científica
Português
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The Mako bimodal volcanic belt of the Kedougou-Kenieba inlier is composed of volcanic basalts and peridotites interbedded by quartzites and limestones intruded by different generations of granitoids. The early volcanic episode of the belt is constituted of submarine basalts with peridotite similar to those of the oceanic abyssal plains. It is intruded by the Badon Kakadian TTG-granitic batholite dated around 2200 Ma. The second volcanic phase is constituted of basaltic, andesitic, and felsitic flows exhibit structures of aerial volcanic rocks. It is intruded by granites dated between 2160 and 2070 Ma. The general pattern of trace element variation of submarine volcanic rocks is consistent with those of basalts from oceanic plateaus which are the modern equivalent of the Archean greenstones belts. The Nd and Sr isotopic systematics typical of juvenile material indicates that the source of these igneous rocks is derived from a depleted mantle source. These results are consistent with the idea of a major accretion within the West African Craton occurring at about 2.1 Ga and corresponding to an important process of mantle-oceanic lithosphere differentiation.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP

‣ Whole-rock geochemistry and Sr-Nd isotopic composition of the pre-rift sequence of the Camamu Basin, northeastern Brazil

Silva, D. R. A.; Mizusaki, A. M. P.; Milani, E. J.; Pimentel, M.; Kawashita, Koji
Fonte: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD Publicador: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD
Tipo: Artigo de Revista Científica
Português
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Whole-rock geochemistry, combined with Sr-Nd isotopic composition of pelitic sedimentary rocks, have been considered to be useful parameters to estimate not only their provenance but also to make inferences about their depositional environment as well as the weathering processes they have been through. The basal sedimentary units of the basins of the northeastern Brazilian continental margin, particularly those of the pre-rift sequence, have been subject of interest of studies based on chemical and isotopic data, since they lack fossil content to establish their age and, therefore, stratigraphic correlations are difficult. The major and trace element contents as well as Sr-Nd isotopic compositions of whole-rock shale samples from five outcrops attributed to the pre-rift supersequence of the Camamu Basin were analyzed with the purpose of characterizing and obtaining further information that would allow a better correlation between the sites studied. The geochemical data suggest that the rocks exposed in the studied outcrops are part of the same sedimentary unit and that they might be correlated to the Capianga Member of the Alianca Formation of the Reconcavo Basin, exposed to the north of the Camamu Basin. The chemical index of alteration (CIA) suggests conditions associated with a humid tropical/subtropical climate at the time of deposition. Nd isotopic compositions indicate provenance from the Paleoproterozoic rocks of the Sao Francisco craton. The results presented here...

‣ Petrology and Sr-Nd characteristics of the Nova Lacerda dike swarm, SW Amazonian Craton: new insights regarding its subcontinental mantle source and Mesoproterozoic geodynamics

Girardi, Vicente Antonio Vitorio; Correa da Costa, P. C.; Teixeira, Wilson
Fonte: TAYLOR & FRANCIS INC; PHILADELPHIA Publicador: TAYLOR & FRANCIS INC; PHILADELPHIA
Tipo: Artigo de Revista Científica
Português
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The NNW-trending Nova Lacerda tholeiitic dike swarm in Mato Grosso State, Central Brazil, intrudes the Nova Lacerda granite (1.46 Ga) and the Jauru granite-greenstone terrain (ca. 1.79-1.77 Ga). The swarm comprises diabases I and II and amphibolites emplaced at ca. 1.38 Ga. Geochemical data indicate that these are evolved tholeiites characterized by high LILE/HSFE and LREE/HSFE ratios. Isotopic modelling yields positive epsilon(Nd)(T) values (+0.86 to +2.65), whereas values for epsilon(Sr)(T) range from positive to negative (+1.96 to -5.56). Crustal contamination did not play a significant petrogenetic role, as indicated by a comparison of isotopic data (Sr-Nd) from both dikes and country rocks, and by the relationship between isotopic and geochemical parameters (SiO2, K2O, Rb/Sr, and La/Yb) of the dikes. We attribute the origin of these tholeiites to fractional crystallization of evolved melts derived from a heterogeneous mantle source. Comparison of the geochemical and isotopic data of the studied swarm and other tholeiitic Mesoproterozoic mafic intrusions of the SWAmazonian Craton the Serra da Providencia, Colorado, and Nova Brasilandia bimodal suites - indicates that parental melts of the Nova Lacerda swarm were derived from the most enriched mantle source. This enrichment was probably caused by the stronger influence of the EMI component on the DMM end-member. These data...

‣ Geocronologia, geoquímica isotópica e litoquímica do plutonismo diorítico-granítico entre Lavras e Conselheiro Lafaiete: implicações para a evolução paleoproterozóica da parte central do Cinturão Mineiro; Geocronology, isotopic geochemistry and geochemical of the dioritic-granitic plutonism between Lavras and Conselheiro Lafaiete: implicatins to paleoproterozoic evolution of Mineiro Belt central part

Nunes, Luciana Cabral
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/10/2007 Português
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A área de estudo localiza-se na borda sul do Cráton São Francisco, no Cinturão Mineiro, este é porção integrante da Província Sul Mineira. Neste contexto ocorre um mosaico de terrenos arqueanos e paleoproterozóicos de alto a médio grau metamórfico e associações granitogreenstone. Os corpos plutônicos, estudados neste trabalho, fazem parte do abundante plutonismo paleoproterozóico intrusivo nos greenstone belts Nazareno (Arqueano) e Rio das Mortes (Proterozóico). Dentro deste contexto ocorre a zona de Cisalhamento do Lenheiro (ZCL), que delimita estes greenstones belts: Nazareno (ao sul da falha) e Rio das Mortes (ao norte da falha); assim como plutons paleoproterozóicos. Os plutons escolhidos para este trabalho foram: Gnaisse Granítico Fé, Granito Mama Rosa, Tonalito/Trondhjemito Cassiterita, Granito Ritápolis, Diorito Brumado e Quartzo Monzodiorito Glória, localizados ao norte da ZCL; e: Granitóide do Lajedo, Granitóide Gentio, Quartzo Diorito Dores do Campo, Quartzo Diorito do Brito, Granodiorito Brumado de Baixo e Granodiorito Brumado de Cima, localizados ao sul da ZCL. Os estudos petrográficos indicam as seguintes características para os corpos: Gnaisse Granítico Fé (monzogranito a sienogranito), Granito Mama Rosa (monzogranito)...

‣ Geoquímica elemental e isotópica (Sr e Nd) como traçadores de poluentes antrópicos, caso de estudo: fosfogesso de Cubatão (SP); Isotopic (Sr and Nd) and elementary geochemistry as anthropic poluent tracers, study case: the phosphogypsum of Cubatão (SP)

Calado, Bruno de Oliveira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/04/2008 Português
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O objetivo deste estudo foi aplicar técnicas de geoquímica de elementos maiores, menores e isótopos de Sr e Nd para identificar contaminação por fosfogesso em sedimentos fluviais da bacia hidrográfica Mogi/Piaçaguera. Para isto, foram analisados perfis de sedimento das margens dos rios Cubatão, Pereque, Mogi (montante, meio e jusante), Piaçaguera e Jurubatuba, inseridos no alto estuário santista, assim como solos, rochas e águas superficiais. Os métodos utilizados foram fluorescencia e difratometria de raios-x, microscopia ótica e analises isotópicas de Sr e Nd. Os resultados demonstraram fator de enriquecimento de Sr, Nd, Nb, La, F e Ce nos sedimentos superficiais do Rio Mogi jusante, comparado aos demais sedimentos fluviais analisados. As composições isotópicas dos sedimentos fluviais regionais foram dentro do padrão das rochas e solos da bacia hidrográfica. A exceção se deve aos sedimentos fluviais superficiais do Rio Mogi jusante que apresentaram assinaturas química e isotópica semelhantes do fosfogesso. O cálculo de proporção de mistura de composições isotópicas de Sr e Nd proveniente do fosfogesso indicou significativa discrêpancia para os dois métodos, de até 6% para Sr e 35% para Nd. Pelo contrário...

‣ Origin of geochemical heterogeneity in the mantle : constraints from volcanism associated with Hawaiian and Kerguelen mantle plumes

Xu, Guangping
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 338 p.
Português
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Lavas derived from long-lived mantle plumes provide important information of mantle compositions and the processes that created the geochemical heterogeneity within the mantle. Kerguelen and Hawaii are two long-lived mantle plumes and lavas associated with them have very different geochemical characteristics. In this thesis I studied the geochemical compositions of the lavas associated with Kerguelen plume (Mt. Capitole in Kerguelen Archipelago) and Hawaiian plume (Mauna Kea, East Molokai and West Molokai volcanoes) to understand what processes contributed to the geochemical variations observed in Kerguelen and Hawaiian lavas and the geochemical structure of the mantle beneath them. Mt. Capitole is in the central part of the Kerguelen Archipelago and is attributed to Cenozoic volcanism arising from the Kerguelen hotspot. Based on the study of Mt. Capitole and previous isotopic data for the Kerguelen Plateau, Kerguelen Archipelago and Heard Island, I propose that two stages of mixing can explain the significant Sr, Nd, Hf and Pb isotopic heterogeneity. The first mixing process, best shown by the submarine lavas from Northern Kerguelen Plateau, is between a depleted component (i.e., relatively low 87Sr/86Sr with high 143Nd/144Nd and 176Hf/177Hf)...

‣ Source and significance of the felsic magmatism in the paleoproterozoic to Mesoproterozoic Broken Hill Block, New South Wales

Raveggi, M.; Giles, D.; Foden, J.; Raetz, M.; Ehlers, K.
Fonte: Taylor & Francis Ltd. Publicador: Taylor & Francis Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2008 Português
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Major, trace, rare-earth elements and isotopic (Sm - Nd and Rb - Sr) data from the ca 1704 - 1685 Ma Alma, Farmcote, Rasp Ridge and Hores-Potosi felsic magmatic gneisses and the ca 1600 Ma syn-orogenic felsic intrusions of the Willyama Supergroup in the Broken Hill Block of western New South Wales are documented. The ca 1704 - 1685 Ma felsic melts were generated by anatexis of the Willyama Supergroup metasediments with variable degrees of mixing of a juvenile, mantle-derived component represented by coeval high Fe - Ti metatholeiitic rocks. This is consistent with previous interpretations for bimodal magmatism occurring in an extensional environment with an elevated geothermal gradient driven by lithospheric thinning and mafic magmatism. Interpretations involving the presence of a mafic underplate as a source for the ca 1704 - 1685 Ma felsic melts are not supported by these data. The ca 1600 Ma syn-orogenic felsic intrusions are a direct product of partial melting of the sedimentary sequences of the Willyama Supergroup as a response to the high-temperature, low-pressure amphibolite- to granulite-facies metamorphic event accompanying the Olarian Orogeny. The presence of an Archean basement for the Willyama Supergroup remains unclear...

‣ Geotectonics in the Gawler craton : constraints from geochemistry, U-Pb geochronology and Sm-Nd and Lu-Hf isotopes.

Howard, Katherine E.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2012 Português
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The southern Australian Mesoarchean to early Mesoproterozoic Gawler Craton holds a pivotal place in the architecture of Proterozoic Australia. Although in recent years a growing body of work has signifi cantly improved our understanding of the tectonic evoluti on of the Gawler Craton, the lack of outcrop across large areas is an impediment to determining the tectonic framework. This study uses geochemical, geochronological (U-Pb zircon and monazite) and isotopic (Whole rock Sm-Nd and zircon Lu-Hf) data on samples mostly obtained from drill holes in regions of limited to non- existent outcrop to better delineate the tectonic setting of Proterozoic metasedimentary and igneous units in the western, central and northern Gawler Craton and the orogenic events which have affected them. It is common practice in sedimentary provenance studies to use similarities in the detrital zircon age histograms from sedimentary systems to identify potential source regions, and therefore to make interpretations about paleogeographic settings. However, this method is limiting as the timing of zircon growth events is not a unique criterion of specific terrains. Nevertheless, these limitations can be overcome by employing additional isotopic data sets such as Sm - Nd and Lu - Hf that provide information on the crustal evolution of the source region. As an example...

‣ Petrologische und geochemische Untersuchungen an alkalinen, peralkalinen und agpaitischen Magmatiten der mittelproterozoischen Gardar-Provinz, Südgrönland; Petrological and gochemical investigations on alkaline, peralkaline and agpaitic magmatic rocks from the Mid-Proterozoic Gardar Province, south Greenland

Marks, Michael
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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Kapitel 1 stellt die Ergebnisse einer petrologischen und isotopengeochemischen Studie an relativ primitiven Ganggesteinen im Westen der Gardar-Provinz zusammen. Die detaillierte Untersuchung der Entwicklung der chemischen Zusammensetzung der wichtigsten Mineralphasen der Ganggesteine zeigen, dass fraktionierende Kristallisation dieser Mineralphasen eine bedeutende Rolle bei der Genese der verschiedenen Gesteinstypen spielt. Die O-, Sr-, Nd- und Os-isotopische Untersuchungen zeigen allerdings auch, dass die Mutterschmelzen der Isortoq-Gesteine zwar ursprünglich aus Mantelregionen stammen, diese jedoch durch Assimilation von krustalem Material chemisch und isotopisch verändert wurde. Eine Quantifizierung der Assimilationsvorgänge ergab maximal etwa 10 % Unterkrusteneinfluß bei den am stärksten kontaminierten Gesteinen. Kapitel 2 bis 4 beschäftigen sich mit der Petrologie und Geochemie der hochfraktionierten Alkalimagmatite der Gardar-Provinz. Die geochemische und isotopische Entwicklung der untersuchten Magmatite wird durch ein komplexes Zusammenspiel verschiedenster Prozesse gesteuert. Fraktionierende Kristallisation und krustale Kontamination sind die beiden wesentlichen Prozesse, die den Fraktionierungspfad der Mutterschmelze mitbestimmen. Das Auftreten von SiO2-untersättigten und SiO2-übersättigten Intrusionen innerhalb der Gardar-Provinz ist durch die unterschiedliche Bedeutung von krustaler Kontamination für die einzelnen Intrusivkörper zu erklären. SiO2-untersättigte Intrusionen entwickeln sich im wesentlichen durch fraktionierende Kristallisation von alkalibasaltischen Schmelzen im geschlossenen System. Im Gegensatz dazu stellen SiO2-übersättigte Intrusionen vermutlich stärker kontaminierte Äquivalente der selben Mutterschmelzen dar...

‣ Petrogenesis and geochronology of the Deliktas, Sivrikaya and Devrekani granitoids and basement, Kastamonu belt-Central Pontides (NW Turkey): evidence for Late Palaeozoic-Mesozoic plutonism, and geodynamic interpretation; Petrogenese und Geochronologie der Deliktas-, Sivrikaya- und Devrekani-Granitoide sowie des Basements des Kastamonu-Gürtels, Zentralen Pontiden (NW Türkei): Nachweis für spätpaläozoisch-mesozoischen Plutonismus und dessen Geodynamische Interpretation

Nzegge, Odilia Mbonguh
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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The Pontides orogenic belt (Ketin, 1966), is the central portion of an extensive belt running from western Bulgaria (Rhodope Mountains) through northern Turkey to the Caucasus. Three tectono-stratigraphically different sectors can be distinguished: the Western Pontides (Istanbul zone), the Central Pontides and the Eastern Pontides (Sakarya zone). The Central Pontides, located between the Izmir-Ankara suture to the south and the Black Sea to the north is the geographical term for the arched central part of the Pontides orogenic belt (Fig. 1.1). The Central Pontides is one of the well preserved areas where the late Early Cretaceous juxtaposition of the Western Pontides (Istanbul Zone) and the Eastern Pontides (Sakarya Zone) (Okay and Tüysüz, 1999; Tüysüz, 1999) can be observed (Sengör and Yilmaz, 1981). Four main units are comprised in the Central Pontides: two major tectonic units, the Devrekani metamorphic unit (Eurasian-derived basement) and the Çangaldag arc complex separated by two oceanic basins, the Küre and the Domuzdag-Saraycikadag complexes. The study area is marked by the Çangaldag arc complex, and numerous granitoids and associated volcanics collectively called the Kastamonu granitoid belt (KGB) (Yilmaz and Boztug...

‣ Major and trace element compositions and strontium, neodymium, and lead isotopic ratios of late Cenozoic mafic lavas from the northern Basin and Range

Lum, Clinton Chew Lun
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 232 p.; application/pdf
Português
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During the late Cenozoic mafic lavas were emplaced contemporaneously with Basin and Range extension near Battle Mountain, Nevada. They display wide ranges in major and trace elements contents and Sr, Nd, and Pb ratios. The temporal and compositional characteristics of the basalts indicate that the effects of crustal contamination on the compositions of the younger lavas has decreased relative to the older lavas. Assimilation and fractional crystallization (AFC) modeling suggests that their compositional heterogeneity cannot be attributed solely to crustal contamination, and instead most likely reflects their derivation from a heterogeneous mantle source region. Regional variations in the trace element ratios (Rb/La and Ba/Zr) and Sr, Nd and Pb isotopic compositions of mafic lavas from the western U.S. indicate they were derived from a heterogeneous lithospheric mantle. Crustal contamination and subduction related processes appear to be unable to reproduce the range in $\sp{87}$Sr/$\sp{86}$Sr and low Rb/La of the lavas. Therefore, the variation in the basalts' isotopic ratios most likely reflects their derivation from a heterogeneous mantle source region. Plots of $\sp{87}$Sr/$\sp{86}$Sr versus $\sp{207}$Pb/$\sp{204}$Pb or $\sp{207}$Pb/$\sp{207}$Pb clearly illustrates the compositional characteristics of their source regions. The Snake River Plain and southern Sierran Province basalts display elevated $\sp{87}$Sr/$\sp{86}$Sr and varied Pb isotopic ratios indicating they were derived from a heterogeneous ancient lithospheric source with high time integrated Rb/Sr and U/Pb ratios. The low $\sp{87}$Sr/$\sp{86}$Sr and Pb isotopic ratios of the suggest the Colorado Plateau-Eastern Transition Zone basalts were derived from a heterogeneous ancient lithospheric source with low time integrated Rb/Sr and U/Pb ratios. Basalts from the Basin and Range...

‣ Constraints on Proterozoic crustal evolution from an isotopic and geochemical study of clastic sediments of the Gawler Craton, South Australia

Simpson, C. A.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //1994 Português
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The Gawler Craton comprises tocks varying in age from Archaean to more recent Phanerozoic sediments. The rocks of greatest interest in defining processes of early crustal formation and evolution in the Australian continent, are the basement material older than approximately 1400 Ma (pre-cratonisation), comprising deformed and metamorphosed rocks suites of Archaean and Proterozoic metasediments and gneisses. These suites span an immense period of intense geological history, and as such are a topic of much past and present study. Detailed mapping in the Tumby Bay region of eastern Eyre Peninsula outlines stratigraphic and structural evolution of a sequence of Proterozoic rock suites, these are proposed to be related to other recognised deformation episodes elsewhere within the Gawler Craton, thus regional correlation is inferred. A new theory for development of two lineations within the map region is postulated by two movement directions along the Kalinjala Mylonite Zone. Geochemically the Proterozoic sediments of the Gawler Craton are similar to upper crustal average values of Taylor & McClennan (1985). However, characteristic depletions in Nb and Sr are recognised. Consistency in trace element compositions for Archaean and Proterozoic samples would suggest recycling of older Archaean crust into Proterozoic sediments and granitoids. Analysis of representative trace element ratios and indices of alteration and weathering suggest some change in geochemistry throughout the Proterozoic period. Selected Proterozoic elastic sedimentary suites were geochemicaly and isotopically (Sm-Nd) analysed...

‣ Sources for magmatism in Central Sulawesi: Geochemical and Sr-Nd-Pb isotopic constrainsts.

Elburg, M.; Foden, J.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
Publicado em //1999 Português
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Middle Miocene to Quaternary magmatism in Central Sulawesi (Indonesia) is characterised by radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios. Although the geochemistry of the samples is heterogeneous, all samples show a distinct subduction signature (negative anomalies for Nb and Ti, positive for K and Pb) in their trace element patterns. Mafic magmatism is represented by lamprophyric magmas, and a suite of ‘gabbros' (ranging from gabbro to clinopyroxenite). The isotopic signature of the lamprophyres could be explained by simple mixing between a mantle source, similar to that for mid-ocean ridge basalts (MORB), and sediments, as is typical for subduction-related volcanics, but the Pb–Sr isotopic systematics of the gabbros preclude this interpretation. They are interpreted as containing an important contribution from an old sub-continental lithospheric source, located within a sliver of Australian continent that has been thrust underneath Central Sulawesi. Felsic magmatism is likely to reflect high degrees of crustal contamination or intracrustal melting. These interpretations suggests that contemporaneous subduction did not play a major role in determining the isotopic signature of Miocene–Pleistocene magmatism in the area...

‣ Nd and Sr Isotopic Study of the Bay of Islands Ophiolite Complex and the Evolution of the Source of Midocean Ridge Basalts

Jacobsen, Stein B.; Wasserburg, G. J.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 10/12/1979 Português
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Two Sm-Nd internal isochrons for pyroxene gabbros of the Bay of Islands Ophiolite Complex give well-defined ages of 508 ± 6 m.y. and 501 ± 13 m.y. with initial ^(143)Nd/^(144)Nd of ε_(Nd) = +7.7 ∓ 0.1 and ε_(Nd) = +7.5 ∓ 0.2, respectively. Total rock samples from pillow basalts, sheeted dikes, trondhjemites, hornblende gabbros, pyroxene gabbros, and an orthopyroxenite layer from the harzburgite give initial ε_(Nd) in the range from +6.5 to +8.1 with an average value of +7.6. The initial ^(87)Sr/^(86)Sr obtained on a pyroxenegabbro is ε_(Sr) = −19.3 ± 0.3, which is typical of oceanic samples. However, the initial ^(87)Sr/^(86)Sr within the different phases of the complex is found to be highly variable (∼52 ε units) and shows the effect of sea water alteration. The ε_(Nd) values demonstrate a clear oceanic affinity for the Bay of Islands complex and support earlier interpretations made on the basis of structure and geochemistry. The magnitudes of the initial ε_(Nd) values (+7.6) are somewhat smaller than for typical present-day midocean ridge basalts (MORB) (+10). This is most likely due to differential evolution over the past 0.5 aeon of the oceanic mantle relative to the bulk earth. The observed shift is quantitatively what should be expected for a simple single-stage evolution. For a model with a single differentiation event at time T_D to produce the depleted mantle...

‣ Geoquímica e Assinaturas Nd-Sr do Complexo Granitoide Pensamiento, Província Rondoniana-San Ignacio, Pré-Cambriano de Bolívia Oriental: Caracterização Petrogenética de um Arco Magmático no Mesoproterozoico; Geochemistry and Nd-Sr Isotopic Signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, Eastern Precambrian Shield of Bolivia: Petrogenetic Constraints for a Mesoproterozoic Magmatic Arc Setting

Matos, Ramiro; Teixeira, Wilson; Geraldes, Mauro Cesar; Bettencourt, Jorge Silva
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/06/2009 Português
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O Complexo Granitoide Pensamiento (CGP) ocorre na porção norte do Pré-Cambriano Boliviano, estando tectonicamente associado à evolução da província Rondoniana-San Ignacio (1.55 - 1.30 Ga) do Craton Amazônico, constituído por uma província central de idade arqueana e províncias proterozoicas marginais. A evolução proterozoica resulta do desenvolvimento de cinturões acrescionários sucessivamente mais jovens para sudoeste, a exemplo das orogenias Rondoniana-San Ignacio (1.37 - 1.32 Ga) e Sunsás (1.20 - 1.00 Ga). O CGP ocorre na parte setentrional do Pré-Cambriano Boliviano, ao norte do cinturão Sunsás, sendo constituído por granitos e termos subvulcânicos. Subordinadamente ocorrem sienitos, granodioritos, tonalitos, trondjemitos e dioritos. Em termos tectônicos, essas rochas são classificadas em dois conjuntos: plutons sin a tardicinemáticos e tardi a pós-cinemáticos. Treze análises químicas em rocha total para elementos maiores, traços e ETR foram realizadas em rochas granitoides orogênicas do CGP. Diagramas de correlação geoquímica indicam tendência negativa entre os conteúdos de MgO, Al2O3 and CaO em função do aumento de SiO2, sugerindo processos de cristalização fracionada na petrogênese das rochas investigadas. Em adição os dados indicam uma composição principalmente peraluminosa...

‣ Características isotópicas (Nd e Sr) do plutonismo intrusivo no extremo NW do Cráton Amazônico, Venezuela, e implicações para a evolução paleoproterozóica

Teixeira, Wilson; Tassinari, Colombro Celso G.; Mondin, M.
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/12/2002 Português
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Rochas granitóides intrusivas em terrenos arqueanos e paleoproterozóicos contíguos, em território venezuelano, foram estudadas em termos da geoquímica isotópica de Nd e Sr, para fins de caracterização petrogenética. Tais plútons estão associados à evolução tectônica das províncias paleoproterozóicas Maroni-Itacaiúnas e Ventuari-Tapajós da parte setentrional do Cráton Amazônico. A suíte Encrucijada (2187 ± 94 Ma), intrusiva no Complexo Imataca, originou-se predominantemente da fusão parcial do substrato arqueano, conforme evidenciam parâmetros negativos de µNd(2, 1Ga) (-2,2 a -4,9) e idades T DM entre 2,82 e 2,49 Ga. Por outro lado, os plútons do Complexo Supamo (2230 - 2050 Ma) e do Grupo Cuchivero (1980 - 1830 Ma), que ocorrem nas províncias crustais adjacentes, são caracteristicamente juvenis (derivados de protólitos paleoproterozóicos). Suas idades T DM concentram-se entre 2,13 e 2,22 Ga, e os valores de µNd(2, 1Ga)são sistematicamente positivos, entre +0,74 e +3,05. Interpretação tectônica em diagramas de correlação isotópica (143Nd/144Nd vs. 147Sm/144Nd e 143Nd/144Nd vs. idade) comparando os dados das rochas plutônicas e do Complexo Imataca, tendo em consideração o acervo geocronológico e geológico da extremidade NW do Cráton Amazônico...

‣ Nd-Sr isotopic geochemistry and U-Pb geochronology of the Fé granitic gneiss and Lajedo granodiorite: implications for paleoproterozoic evolution of the mineiro belt, southern São Francisco Craton, Brazil

Teixeira, Wilson; Ávila, Ciro Alexandre; Nunes, Luciana Cabral
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/04/2008 Português
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O gnaisse granítico Fé e o granodiorito do Lajedo são plutons félsicos associados à evolução paleoproterozóica do Cinturão Mineiro na porção sul do Craton São Francisco. O pluton Fé está localizado ao norte da zona de cisalhamento do Lenheiro - importante feição estrutural associada a falhas compartimentando regionalmente o cinturão Mineiro. Esta intrusão possui xenólitos de gnaisse e anfibolito do greenstone belt Rio das Mortes e de rochas máficas de corpos piroxeníticos - gabróicos que afloram nas proximidades. O granodiorito do Lajedo está localizado ao sul da zona de cisalhamento do Lenheiro, possui xenólitos de anfibolito do greenstone belt Nazareno e é intrusivo nas rochas metamáficas do corpo peridotítico - piroxenítico Forro e em rochas anfibolíticas do greenstone belt Nazareno. A composição modal do gnaisse granítico Fé é variável, de monzogranito a sienogranito; o pluton é peraluminoso e apresenta conteúdos de K2O compatíveis com tendências cálcio-alcalina médio K e cálcio-alcalina alto K, enquanto o pluton do Lajedo varia de granodiorítico a tonalítico, é peraluminoso e tem natureza cálcio-alcalina. O gnaisse granítico Fé possui idade U/Pb em zircão de 2191 ± 9 Ma e o granodiorito do Lajedo 2208 ± 26 Ma. Os isótopos de Nd e Sr dos dois corpos revelam que componentes crustais participaram da gênese dos protólitos em ambiente de arco plutônico...

‣ Lithium isotopic compositions of the New England Batholith: correlations with inferred source rock compositions

Bryant, Colleen; Chappell, Bruce; Bennett, Victoria; McCulloch, Malcolm
Fonte: Royal Society of Edinburgh Publicador: Royal Society of Edinburgh
Tipo: Artigo de Revista Científica
Português
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A strong correlation exists between the Li isotopic compositions of Carboniferous-Triassic granites from the New England Batholith, and the previously inferred involvement of sedimentary and mantle/infracrustal source components. Isotopically (Nd and Sr)

‣ Geochemical and Sr-Nd isotopic characterization of the Miocene volcanic events in the Sierra Madre del Sur, central and southeastern Oaxaca, Mexico

Martínez-Serrano,Raymundo G.; Solís-Pichardo,Gabriela; Flores-Márquez,E. Leticia; Macías-Romo,Consuelo; Delgado-Durán,Jaime
Fonte: Instituto de Geología, UNAM Publicador: Instituto de Geología, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 Português
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The Etla, Mitla-Tlacolula and Nejapa volcanic regions in central and southeastern Oaxaca comprise the southeastern part of a wide Cenozoic magmatic arc in the Sierra Madre del Sur. Most volcanic events in these regions ocurred between 22 to 15 Ma, almost contemporaneously with the initial volcanic events of the Trans-Mexican Volcanic Belt. Petrographic, geochemical, and isotopic characteristics were determined for representative volcanic samples from the three regions, where ignimbrites, volcaniclastic and epiclastic deposits, lava flows and minor lacustrine deposits are found. In a SiO2 vs. alkalis diagram, chemical classification of volcanic products for the study area indicate variations from basaltic andesites to rhyolites, following a subalkaline trend, but with a bimodal pattern. Components with SiO2 concentrations between 58 to 67 wt. % are absent. The trace-element patterns for andesites and rhyolites are similar, with enrichment in the large-ion lithophile elements relative to the high-field-strength elements. Chondrite-normalized REE patterns display light rare earth element enrichment (La-Sm) with respect to the heavy rare earth elements (Eu-Lu), which show flat patterns. These chemical characteristics are typical of volcanic arc rocks. Initial Sr and Nd isotopic data show certain differences between samples from the Etla and Mitla-Tlacolula regions 87Sr/86Sr: 0.7047 to 0.7066 and εNd: -1.15 to 1.75) and the Nejapa region 87Sr/86Sr: 0.7035 to 0.7048 and εNd: +0.52 to +1.42). These data and those reported for the basement rocks suggest greater involvement of continental crust for the magmas of the two first regions in comparison to magmas of the Nejapa region. The isotopic compositions are similar to those observed in other volcanic regions of the SierraMadre del Sur. Early to middle Miocene volcanic events in central and southeastern Oaxaca...