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‣ Geochemistry of the Rio Espinharas hybrid complex, northeastern Brazil

Campos, T. F. C.; Neiva, A. M. R.; Nardi, L. V. S.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
Português
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The Rio Espinharas pluton, northeastern Brazil, belongs to the shoshonitic series and consists mainly of syenogranite, quartz-monzonite and porphyritic quartz-monzonite, but diorite, quartz-monzodiorite, quartz-syenite and microsyenogranite also occur containing microgranular enclaves, except for the diorite. Most variation diagrams of rocks, amphiboles, biotites and allanites show linear trends, but K, Zr, Sr and Ba of rocks display curved scattered trends. The rocks ranging from diorite to syenogranite define a pseudo-errorchron and have similar REE patterns. Syenogranite and microsyenogranite are derived from two distinct pulses of granite magma with initial 87Sr/86Sr ratio of 0.7083±0.0003 and 0.7104±0.0007, respectively. Modelling of major and trace elements shows that the syenogranite evolved by fractional crystallization of plagioclase, microcline, edenite, biotite and titanite, whereas quartz-monzonite, porphyritic quartz-monzonite, quartz-monzodiorite and quartz-syenite resulted from simple mixing between an upper mantle-derived dioritic magma and the upper crust-derived syenogranite magma. Dioritic enclaves are globules of a mafic magma from the upper mantle.; http://www.sciencedirect.com/science/article/B6V6J-46X86NR-5/1/0e5ce1dcc0c8fe91ebd680e6f2ac523b

‣ Age and geochemistry of mantle peridotites and diorite dykes from the Baldissero body: Insights into the Paleozoic-Mesozoic evolution of the Southern Alps

MAZZUCCHELLI, Maurizio; ZANETTI, Alberto; RIVALENTI, Giorgio; VANNUCCI, Riccardo; Correia, Ciro Teixeira; Tassinari, Colombo Celso Gaeta
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
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Trace element and isotopic data obtained for mantle spinel Iherzolites and diorite dykes from the Baldissero massif (Ivrea-Verbano Zone, Western Italy) provide new, valuable constraints on the petrologic and geodynamic evolution of the Southern Alps in Paleozoic to Mesozoic times. Whole rock and mineral chemistry indicates that Baldissero Iherzolites can be regarded as refractory mantle residues following limited melt extraction. In particular, the Light Rare Earth Elements (LREE)-depleted and fractionated compositions of whole rock and clinopyroxene closely match modelling results for refractory residues after low degrees (similar to 4-5%) of near-fractional melting of depleted mantle, possibly under garnet-facies conditions. Following this, the peridotite sequence experienced subsolidus re-equilibration at lithospheric spinel-facies conditions and intrusion of several generations of dykes. However, Iherzolites far from dykes show very modest metasomatic changes, as evidenced by the crystallisation of accessory titanian pargasite and the occurrence of very slight enrichments in highly incompatible trace elements (e.g. Nb). The Re-Os data for Iherzolites far from the dykes yield a 376 Ma (Upper Devonian) model age that is considered to record a partial melting event related to the Variscan orogenic cycle s.l. Dioritic dykes cutting the mantle sequence have whole rock...

‣ 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)...

‣ Enclaves microgranulares máficos e rochas híbridas associadas com os granitóides da Suíte Encruzilhada do Sul, RS./ Maciel Gilmar Jacobs.

Jacobs, Maciel Gilmar
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
Português
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A Suíte Encruzilhada do Sul ocorre na porção norte-noroeste do Batólito Pelotas como um corpo contínuo e alongado na direção N30oE. A suíte é composta dominantemente por rochas graníticas, com ocorrência subordinada de corpos dioríticos e de enclaves microgranulares. As relações de contato entre as rochas graníticas e máficas observadas em campo são caracterizadas por estruturas que identificam a mistura física e química entre estes dois termos composicionais. Para investigar a evolução petrológica deste magmatismo bimodal foram realizados estudos petrográficos e litoquímicos. Os granitos possuem composição monzogranítica com textura heterogranular grossa nas porções centrais do corpo, gradando para termos porfiríticos de matriz média nas porções de bordo do corpo. A mineralogia é caracterizada por elevado percentual de megacristais de K-feldspato com tamanhos entre 2 a 5 cm imersos em matriz equigranular média a grossa rica em quartzo, teores variáveis de plagioclásio e biotita, apatita, zircão e minerais opacos como acessórios. As rochas máficas ocorrem de modo mais abundante associadas à fácies porfirítica, localizada nas porções de bordo da suíte. Composicionalmente são caracterizadas por dioritos...

‣ Geologia, geocronologia, petrologia e metalogênese do prospecto Cu-Mo Yanac, ICA, PERU

Collado Medina, Carlos Javier
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
Português
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Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia. 2014.; O prospecto Yanac está localizado no nordeste de Chincha Alta, Ica, Peru, na superunidade Incahuasi, dentro do segmento Arequipa do batólito costeiro de Peru e na extremidade noroeste da faixa metalogenética de cobre do Cretáceo Superior dos Andes. Três principais rochas graníticas, contemporâneas com enclaves e diques interminerais diorito-gabróicos, dioríticos e monzodioríticos foram definidas no prospecto Yanac. Primeiramente, a rocha hospedeira do sistema porfirítico Yanac, com idade U/Pb em zircão de 70,6 ± 1,0 Ma, é um granodiorito equigranular com granulação média a grossa, pertencente à superunidade Incahuasi do batólito costeiro. Com uma diferença desprezível de edade e um erro dentro de 1 Ma., ambos, O granodiorito Incahuasi é intrudido por um granodiorito porfirítico, com granulação fina a média, com idade U/Pb em zircão de 71,0 ± 1,0 Ma, e por um granodiorito-diorito porfirítico, com granulação média a grossa, com idade U/Pb em zircão de 67,75 ± 0,80 Ma. Diques traquidacíticos e basálticos cortam as rochas graníticas. Eles são pós-mineralização e podem estar relacionados com os eventos de alojamento do batólito costeiro. O granodiorito Incahuasi...

‣ U–Pb zircon geochronology, petrochemical and Sr–Nd isotopic characteristic of Late Neoproterozoic granitoids of the Bornaward complex (Bardaskan-NE Iran)

Monazzami Bagherzadeh, R.; Karimpour, M. H.; Lang Farmer, G.; Stern, C. R.; Santos, J. F.; Rahimi, B.; Heidarian Shahri, M. R.
Fonte: Geological Survey of Iran Publicador: Geological Survey of Iran
Tipo: Conferência ou Objeto de Conferência
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The Bornaward granitoids in the Taknar zone are located in the northeast of the central Iranian block in northeast Iran (Khorasan Razavi province), about 280 km southwest of Mashhad city and 28 km northwest of Bardaskan city. Taknar zone is an exotic block, bordered by two major faults, the Great Kavir fault in the south and Rivash fault in the north. Intrusive rocks of the study area, called the Bornaward granitoid complex (BGC), include of granite, alkali granite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite, diorite and gabbro intruded into the center of Taknar zone. These intrusive rocks affected low grade metamorphism. The results of U-Pb zircon dating on two granite samples, one belonging to the Taknar mine west of the study area and the other the Bornaward granitoids in the eastern part of study area, and also one granodiorite the Taknar mine area and one diorite the Bornaward area, yield ages of the granites as 540.5±2.9 Ma (Taknar mine area) and 550.41 3.21,-4.54 Ma (Bornaward area), the granodiorite as 550±6.9 Ma and diorite as 551.96±4.32 Ma, all Late Neoproterozoic. The Bornaward intrusive bodies are classified as belonging to the ilmenite-series of reduced granitoids. Some small high magnetite-granite and tonalite outcrops in the study area are classified as belonging to the magnetite-series of oxidized granitoids. Chemically...

‣ The quartz-dioritic Hospitais intrusion (SW Iberian Massif) and its mafic microgranular enclaves: evidence for mineral clustering

Moita, P.; Santos, J. F.; Pereira, M. F.; Costa, M. M.; Corfu, F.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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The Hospitais pluton is an elliptical body, with its long axis oriented WNW–ESE, that belongs to the Évora Massif(Iberian Variscan belt). This intrusion has a quartz-dioritic composition, with plagioclase, quartz, amphibole(hornblende, but locally also cummingtonite) and biotite as the main mineral phases. Mafic microgranular enclaves in the quartz–diorite show the same minerals as the host, but with a greater abundance of amphibole and lower proportions of felsic minerals, especially quartz. U–Pb zircon ages obtained in one sample of the quartz–diorite and one sample of a mafic microgranular enclave gave identical ages, within error, of ca. 337 Ma. Geochemical data show that the quartz–diorite has a calc-alkaline signature with moderate enrichment in LILE/HFSE ratio (ThN/YN: 2.71–11.43) and clear negative Ti and Nb–Ta anomalies (ThN/NbN:1.33–6.22). The composition of the enclaves shows that they do not represent direct melt compositions. Instead, their geochemical features (namely the abundances of Fe andMn in variation diagrams and REE patterns in primitive mantle normalized diagrams) suggest that they correspond to mineral clustering formed during the previous crystallization stage of quartz-dioritic magma. Overlapping of mineral chemistry and Sr–Nd isotope compositions in the quartz–diorite and the enclaves provides further support to that conclusion. The values for [87Sr/86Sr]i and εNdi (calculated for 337 Ma) in the quartz–diorite vary from 0.706147 to 0.706491 and from −1.87 to −3.22...

‣ Ore forming systems in the western compartment of the Beja layered gabbroic sequence : (Ossa Morena zone Portugal)

Jesus, Ana Patrícia Marques de, 1975-
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Tese de Doutorado
Publicado em //2011 Português
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Tese de doutoramento, Geologia (Metalogenia), Universidade de Lisboa, Faculdade de Ciências, 2011; The western compartment of the Beja Layered Gabbroic Sequence (LGS) comprises seven Series hosting three mineralisation types and four suites of non-gabbroic rocks also included in the Beja Igneous Complex (BIC). The primary nature of the prevalent and penetrative fabrics in LGS (layering and compactioninduced magmatic foliation), indicate that the gabbroic suite emplacement occurred under P-T conditions above those of the amphibolite facies regional metamorphic peak. The LGS internal architecture grossly mimics the geometry of the Évora-Beja-Aracena Domain, defining a series of nested sigmoid-like shapes. The earliest record of ductile tectonic deformation (often with magmatic imprint) took place before the ≈ 340 Ma D2a- D2b regional rising of the ductile-brittle transition. Shearing progressed under gradually brittle conditions throughout the early stages of D3 causing E-W rotation of the layering southwards of each Series. Propagation/reactivation of late fault zones continued under fully brittle conditions until Late Variscan times. LGS rocks show subalkaline character compatible with low-pressure fractionation of tholeiitic suites revealing mild LREE+Ba enrichment...

‣ Field and petrographic data of 1.90 to 1.88 Ga I- and A-type granitoids from the central region of the Amazonian Craton, NE Amazonas State, Brazil

VALERIO, Crist?v?o da Silva; MACAMBIRA, Moacir Jos? Buenano; SOUZA, Valmir da Silva
Fonte: Universidade Federal do Pará Publicador: Universidade Federal do Pará
Tipo: Artigo de Revista Científica
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O SW do munic?pio de Presidente Figueiredo, localizado no Estado do Amazonas, Nordeste do Cr?ton Amaz?nico Central, Brasil, hospeda granitoides do tipo I de idade entre 1890 a 1898 Ma (Terra Preta Granito, Su?te ?gua Branca), hornblenda-sienogranitos do tipo A (Sienogranito Canoas da Su?te Mapuera), rochas vulc?nicas ?cidas ? intermedi?rias (Grupo Iricoum?) e granitos rapakivi de idades entre 1883 a 1889 Ma (Granito S?o Gabriel da Su?te Mapuera), e rochas afins (quartzo-gabro-anortosito e diorito), al?m de quartzo-monzonito Castanhal, milonitos e hornfels. A f?cies quartzo-diorito do granito Terra Preta foi formada por processos de mistura entre um dique quartzo-gabro sinplut?nico e um granodiorito hornblenda. Gl?bulos parcialmente assimilados de sienogranitos hornblenda Canoas e seus contatos com o granodiorito hornblenda Terra Preta sugerem que o sienogranito Canoas ? um pouco mais jovem do que o Granito Terra Preta. Xen?litos do sienogranito Canoas no interior do Granito S?o Gabriel mostram que o granito ? mais jovem do que o sienogranito Canoas. Novas evid?ncias geol?gicas e petrogr?ficas avan?am na compreens?o petrol?gica destas rochas e sugerem que, al?m de cristaliza??o fracionada, assimila??o e mistura de magma, desempenharam um papel importante...

‣ Geology of the Sand Creek porphyry molybdenum prospect /

Dillon, David Lloyd.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
Português
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The Sand Creek Prospect is located within the eastern exposed margin of the Coast Plutonic Complex. The occurrence is a plug and dyke porphyry molybdenum deposit. The rock types, listed in decreasing age: 1) metamorphlc schists and gneisses; 2) diorite suite rocks - diorite, quartz diorite, tonalite; 3) rocks of andesitic composition; 4) granodiorites, coarse porphyritic granodiorite, quartzfeldspar porphyry, feldspar porphyry; and 5) lamprophyre. Hydrothermal alteration is known to have resulted from emplacement of the hornblende-feldspar porphyry through to the quartz-feldspar porphyry. Molybdenum mineralization is chiefly associated with the quartz-feldspar porphyry. Ore mineralogy is dominated by pyrite with subordinate molybdenite, chalcopyrite, covelline, sphalerite, galena, scheelite, cassiterite and wolframite. Molybdenite exhibits a textural gradation outward from the quartz-feldspar porphyry. That is, disseminated rosettes and rosettes in quartz veins to fine-grained molybdenite in quartz veins and potassic altered fractures to fine-grained molybdenite paint or 6mears in the peripheral zones. The quartz-feldspar porphyry dykes were emplaced in an inhomogeneous stress field. The trend of dykes, faults and shear zones is 0^1° to 063° and dips between 58° NW and 86* SE. Joint Pole distribution reflects this fault orientation. These late deformatior maxima are probably superimposed upon annuli representing diapiric emplacement of the plutons. A model of emplacement involving two magmatic pulses is given in the following sequence: Diorite pulse (i) dioritequartz diorite...

‣ The Tarcoola Goldfield of the Central Gawler Gold Province, and the Hiltaba Association Granites, Gawler Craton, South Australia

Budd, Anthony Ronald
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD)
Português
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The Tarcoola Goldfield, central South Australia, is one of a number within the Central Gawler Gold Province (CGGP) spatially related to Hiltaba Suite granites. This study investigates the origin of mineralisation at Tarcoola, and the petrogenesis of granites at and around Tarcoola. ‘Hiltaba Suite’ granites in the Tarcoola region are assigned to two supersuites, which is expanded to four once granites from the rest of the Gawler Craton are considered. The term Hiltaba Association Granites (HAG) is introduced as the parental unit of the Jenners, Malbooma, Venus and Roxby Supersuites. These criteria are applied to the felsic parts of the comagmatic Gawler Range Volcanics (GRV). The HAG and GRV are grouped as the bimodal Gawler Ranges–Hiltaba Volcano–Plutonic (GRHVP) Association. The felsic components generally have high K, HFSE, LIL, are fractionated and evolved, have moderate to high Fe/Mg, are slightly alkaline, metaluminous to slightly peraluminous, slightly oxidised and high-temperature. The supersuites of the Tarcoola region are the Malbooma Supersuite, which is more strongly evolved and fractionated than the Jenners Supersuite. Both Supersuites are I-type and evolved from a granodiorite composition by fractional crystallisation. The Pegler and Ambrosia Granites (Jenners Supersuite)...

‣ Portrait of a reference material: zircon production in the Middledale Gabbroic Diorite, Australia, and its implications for the TEMORA standard

Iles, Kieran A.; Hergt, Janet M.; Sircombe, Keith N.; Woodhead, Jon D.; Bodorkos, Simon; Williams, Ian S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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The Middledale Gabbroic Diorite (MGD) in New South Wales, Australia, is host to the internationally distributed TEMORA 2 zircon reference material and its prototype, TEMORA 1. The original characterisation of the source of the reference zircons revealed that the more altered TEMORA 2 host rock contains an order of magnitude more zircon than the TEMORA 1 host, despite similar bulk-rock Zr concentrations. Although TEMORA 1 and 2 preserve the same U-Pb age, they are variable in oxygen isotope composition.In this study, petrographic observations in concert with bulk-rock and mineral geochemistry and zircon U-Pb geochronology have been applied to new samples of the MGD to investigate the link between alteration and zircon abundance. Trace element maps reveal that the products of late-stage, deuteric alteration (particularly actinolite after hornblende) are depleted in Zr, and many other trace elements, relative to the unaltered mafic, magmatic phases. It is posited that the conversion of hornblende to secondary amphiboles in the latter stages of magma solidification liberated Zr, permitting the crystallisation of additional zircon.New high resolution SIMS U-Pb determinations on four samples confirm the age homogeneity of the zircon across the pluton and reaffirm the value of TEMORA 2 as a valuable geochronological reference material. Zircon oxygen isotope data have been acquired for these same samples and the mean δ18O values encompass the accepted values for TEMORA 1 and 2. Likewise...

‣ Petrography, mineralogy and trace element chemistry of Cu-Au-Mo mineralisation from Central Diorite, Boddington, W.A.

Guerin, R. J.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011 Português
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The world-class Boddington Cu-Au-Mo deposit has a complex genetic history. The relative importance of different ore-forming processes during the period 3.0 – 2.6 Ga is debated, particularly with respect to the role played by the 2611±3 Ma Wourahming granite. LA-ICP- MS analysis of trace element concentration in molybdenite represents a valuable new metallogenetic tool to track mineralising events in deposits with protracted geologic histories. The Re content and trace-element signatures in molybdenite from diorite and granite show three distinct populations, attributed to porphyry-style (hundreds of ppm) orogenic- and granite-related systems (<1 to a few ppm, respectively). Rhenium concentrations in molybdenite are highly variable on the deposit-scale. Economic concentrations of Re occur only at shallower levels in both Central Diorite and ABreccia. The Au content correlates with high-concentrations of chalcophile elements (CE). This is seen in the association of Au- minerals and Bi-(Pb)-tellurides present as inclusions in the molybdenite from diorite and is inferred from an LA-ICP-MS element map for molybdenite in granite. The FIB-SEM and TEM study show that visible telluride inclusions extend down to the nanoscale as coherent intergrowths with host molybdenite. Nanoporosity is accompanied by a whole range of structural defects and twinning. The telluride species identified include unnamed Bi4Pb7Te4S9. Analysis of stacking sequences show co-precipitation of Bi-tellurides and molybdenite under equilibrium conditions. In corroboration with EPMA data...

‣ Au-Sn-W-Cu-Mineralization in the Astaneh-Sarband Area, West Central Iran : including a comparison of the ores with ancient bronze artifacts from Western Asia; Mineralisationen von Au,Sn,W und Cu im Astaneh-Sarband-Gebiet, westlicher Zenraliran : und ein Vergleich der Erze mit antiken Bronzeartefakten aus Westasien

Nezafati, Nima
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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The present study deals with two primary aims; (1) geological, mineralogical, and geochemical investigations of the Deh Hosein, Astaneh, and Nezam Abad mineralizations in the Astaneh-Sarband area, west central Iran, with the aim to understand the characteristics of the occurrences and their conditions of formation, and (2) geochemical investigations on ancient bronze artifacts from Iran and Western Asia in order to compare their characteristics with the high-tin copper ore of Deh Hosein and examine their possible relationship. The Astaneh-Sarband area is located in the northern part of the NW-SE aligned Sanandaj-Sirjan metamorphic belt and consists mainly of Mesozoic schists, Middle Jurassic to Middle Tertiary intrusive rocks and related contact metamorphic aureoles, and pegmatites. Regional metamorphism in the area has reached a peak of greenschist facies, but further metamorphism has occurred locally, associated with granitoid emplacement. Magmatism has produced large felsic to intermediate intrusive bodies along a general northwest trend. The main trend of the faults, fractures and other structural features of the area is NW-SE. The Deh Hosein prospect is mainly hosted by Jurassic meta-sedimentary rocks, which have been intruded by the Astaneh complex. Mineralization continues into the southern part of the Astaneh intrusion. The meta-sedimentary rocks consist of alternating meta-sandstone...

‣ Diorite statue of King Khafre, builder of the Second Pyramid at Gizeh, Cairo, Egypt.(10)

Underwood & Underwood
Fonte: Electronic version published by Rice University, Houston, Texas. Publicador: Electronic version published by Rice University, Houston, Texas.
Tipo: stereographs; StillImage
Português
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front: "(10) Diorite statue of King Khafre, builder of the Second Pyramid at Gizeh, Cairo, Egypt"; Statue of seated figure

‣ Tectonic significance of Late Precambrian calc-alkaline and alkaline magmatism in Saint Katherina Area, Southern Sinai, Egypt

Kamal Azer, Mokhles
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2007 Português
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Two magmatic rock suites are distinguished in the Late Precambrian basement of the Southern Sinai (NW Arabian-Nubian Shield, Egypt), namely (a) a calc-alkaline suite, and (b) an alkaline suite. The former includes Rutig Volcanics, quartz-diorite, quartz-monzonite and monzogranite, while the latter includes Katherina Volcanics and A-type granites. The minerals and textural features (kink, decussate and foliated textures) of the quartz-diorite reveal that it was subjected to deformation and thermal metamorphism. The Rutig Volcanics and quartz-diorite represent subduction related I-type magma, generated from anatexis of older crust with contribution of mantle-wedge magma. The quartz-monzonite and monzogranite are evolved from hybrid magma due to injection of the partly crystallized granitic magma by more basic melts. The mineralogical and geochemical characteristics of these granites indicate a mildly alkaline character and belonging to transitional magma type on the borderline between the calc-alkaline and alkaline magma. The mafic microgranular enclaves (MME) in the quartz-monzonite and monzogranite represent cooled globules from a dioritic magma mingled with the partly crystalline granitic magma. The association of rapakivi texture with the MME confirms the genetic link between the rapakivi texture and magma mixing. The overall characteristics of the Katherina Volcanics and Atype granite are consistent with within-plate tectonic setting. The Katherina Volcanics are derived from a crustal source with a mantle contribution...

‣ Palaeoproterozoic adakite- and TTG-like magmatism in the Svecofennian orogen, SW Finland

Väisänen, M.; Johansson, Å.; Andersson, U.B.; Eklund, O.; Hölttä, P.
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2012 Português
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The Palaeoproterozoic Svecofennian orogen in the Fennoscandian shield is an arc accretionary orogen that was formed at c. 1.92-1.86Ga. Arc accretion, magmatism and the subsequent continent-continent collision thickened the crust up to c. 70km, forming one of the thickest Palaeoproterozic orogens. At the end stage of accretionary tectonics, voluminous synorogenic magmatism occurred in southwestern Finland leading to the intrusion of intermediate to felsic plutonic rocks. Ion microprobe single zircon dating of one diorite sample yielded an age of 1872±3Ma (eNd=+2.2) and the trondhjemite sample an age of 1867±4Ma (eNd=+2.6). Inherited 2667-1965Ma cores and 1842±5Ma metamorphic rims were also found in zircons from the trondhjemite. The dioritic magmatism is mantle-derived and is slightly enriched by subduction-related processes. The felsic magmatism shows elevated Sr/Y and La/Yb ratios, which are typical for adakite- and TTG-like magmas. Their low Mg#, Ni and Cr contents argue against slab-melting and mantle-wedge contamination. We infer that the felsic magmatism was generated through crustal melting of the lower part of the previously generated volcanic-arc type crust. Based on published melting experiments and the Sr and Y contents of the felsic rocks we suggest that the melts were generated at a minimum pressure of 10kbar...

‣ Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran

Mirnejad, H.; Lalonde, A. E.; Obeid, M.; Hassanzadeh, J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; PeerReviewed Formato: application/vnd.ms-excel; application/vnd.ms-excel; application/vnd.ms-excel
Publicado em /06/2013 Português
Relevância na Pesquisa
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Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300 km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217–200 Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite–tonalite–granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite–tonalite–granodiorite stock from Dehnow–Vakilabad (217 ± 4–215 ± 4 Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212 ± 5.2 Ma and 199.8 ± 3.7 Ma, respectively. The high initial ^(87)Sr/^(86)Sr ratios (0.708042–0.708368), low initial ^(143)Nd/^(144)Nd ratios (0.512044–0.51078) and low ε_(Nd(t)) values (− 5.5 to − 6.1) of quartz diorite–tonalite–granodiorite stock along with its metaluminous to mildly peraluminous character (Al_2O_3/(CaO + Na_2O + K_2O) Mol. = 0.94–1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤ 18 ppm) and heavy REE (HREE) (Yb < 1.53 ppm) and high contents of Sr (> 594 ppm) and high ratio of Sr/Y (> 35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial ^(87)Sr/^(86)Sr ratios (0.705469–0.706356)...

‣ 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...

‣ Age and significance of the Marble Hall breccia, Bushveld Complex, South Africa

De Waal, S.A.; Graham, IT; Phillips, David
Fonte: Geological Society of South Africa Publicador: Geological Society of South Africa
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
279.91084%
Diorite and associated breccia form scattered outcrops on the Marble Hall Fragment, in the vicinity of the town of Marble Hall, Mpumalanga Province, South Africa. The diorite (2055.6 ± 3.1 Ma) intruded as sub-horizontal sills in highly deformed and metam