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Sample records for argentina edades u-pb

  1. Proterozoico medio y Paleozoico inferior de la sierra de Umango, antepaís andino (29°S), Argentina: edades U-Pb y caracterizaciones isotópicas

    OpenAIRE

    Ricardo Varela; Ana M. Sato; Miguel A.S. Basei; Oswaldo Siga Jr.

    2003-01-01

    En el basamento cristalino de la sierra de Umango se han distinguido varias unidades ígneo-metamórficas, formadas principalmente entre el Proterozoico medio y el Paleozoico inferior. Incluye ortogneises graníticos, una sucesión de esquistos y mármoles, anfibolitas, y tres plutones graníticos de reducido tamaño. Se han realizado análisis químicos de granitoides y anfibolitas, y determinaciones de edad por los métodos U-Pb y K-Ar. La edad U-Pb en circón del Ortogneis Juchi (1108 ± 13 Ma) ratifi...

  2. Los esquistos neoproterozoicos de Santa Helena, Provincia de La Pampa, Argentina: edades u-pb shrimp, composición isotópica de hafnio e implicancias geodinámicas The Neoproterozoic Santa Elena Schists, La Pampa Province, Argentina: SHRIMP U-Pb ages, Hf isotope composition and geodynamic implications

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    Eduardo O Zappetini

    2010-03-01

    Full Text Available Los Esquistos Santa Helena comprenden esquistos biotítico-granatíferos predominantes y lentes gneisoides subordinadas sillimanítico- granatíferos, subaflorantes en la Estancia Santa Helena, que alcanzaron el grado metamórfico de facies anfibolita alta a granulita baja. Los circones detríticos de los esquistos datados por el método U-Pb SHRIMP son en su mayoría mesoproterozoicos y neoproterozoicos, habiendo también escasos granos paleoproterozoicos. La casi totalidad de los circones mesoproterozoicos y neoproterozoicos son de origen magmático y cristalizaron en una fuente magmática juvenil (εHf positivo, presentando edades modelo TDM de Hf entre 1127 y 1625 Ma, y entre 948 y 1274 Ma, respectivamente. Los circones paleoproterozoicos son de origen magmático y tienen una edad modelo TDM de Hf de 2310 Ma. La edad del circón detrítico más joven de los esquistos es 556 Ma, lo cual corresponde a la edad máxima de depositación, indicando que la sedimentación se habría iniciado hacia el Neoproterozoico. La completa ausencia de circones metamórficos de edad pampeana sugiere que durante la época de depositación de los Esquistos Santa Helena el núcleo metamórfico del orógeno pampeano aún no estaba constituido y expuesto. Esto contrasta con los patrones de proveniencia de los Esquistos Green, donde los circones metamórficos cámbricos son predominantes, indicando que durante su época de sedimentación (ca. 500 Ma a ca. 465 Ma el orógeno pampeano ya estaba exhumado y sujeto a denudación. Se interpreta que los Esquistos Santa Helena pertenecerían a una secuencia supracortical depositada entre los 556 y ca. 530-520 Ma en el margen sudoccidental de Gondwana en una cuenca de antepaís equivalente a la etapa tardía de la cuenca Puncoviscana. Se interpreta también que el principal aporte de los sedimentos habría provenido de la denudación de un arco magmático mesoproterozoico localizado hacia el este de los esquistos. Este arco

  3. Primera edad U-Pb en circón usando LA-ICP-MS de un dique traquiandesítico emplazado en el granito tipo-A Los Árboles, Sierras Pampeanas Orientales

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    Juan A Dahlquist

    2012-06-01

    Full Text Available La edad de cristalización de diques subvolcánicos emplazados en plutones graníticos carboníferos, Sierras Pampeanas Orientales, permanece incierta. La primera edad U-Pb en circón usando LA-ICP-MS obtenida en un dique que intruye al plutón Los Árboles (sierra de Fiambalá, revela una edad de cristalización de 311 ± 3 Ma.

  4. U-Pb zircon constraints on the age of the Cretaceous Mata Amarilla Formation, Southern Patagonia, Argentina: Its relationship with the evolution of the Austral Basin

    International Nuclear Information System (INIS)

    Despite the abundant fossil content of the Mata Amarilla Formation (Southern Patagonia, Santa Cruz Province, Argentina), its age has always generated a considerable number of questions and debates. The chronological data provided by invertebrates, dinosaurs, fish, turtles, plesiosaurs and fossil flora are contradictory. In this work, twenty U-Pb spot analyses by laser ablation were carried out on the outer parts of the zoned zircon crystals from a tuff layer of the middle section of the Mata Amarilla Formation, yielding a U-Pb concordia age of 96.23±0.71 Ma, which corresponds to the middle Cenomanian. The deposition of the lower section of the Mata Amarilla Formation marks the onset of the foreland stage of the Austral Basin (also known as Magallanes Basin); this transition is characterized by the west-east shift of the depositional systems, which is consistent with the progradation of the Cretaceous fold-and-thrust belt. Thus, the onset of the foreland stage could have occurred between the upper Albian and lower Cenomanian, as the underlying Piedra Clavada Formation is lower Albian in age. On comparing the data obtained with information from the Ultima Esperanza Province in Chile, it can be suggested that the initiation of the closure of the Rocas Verdes Marginal Basin occurred simultaneously

  5. Rb/Sr and U/Pb isotopic ages in basement rocks of Mina Gonzalito and Arroyo Salado, Atlantic North-Patagonian Massif, Rio Negro, Argentina

    International Nuclear Information System (INIS)

    Isotopic ages from metamorphic and plutonic rocks of the Atlantic area of North Patagonian basement indicate that the main crustal tectonic events occurred during the late Proterozoic to early Paleozoic times. Rb/Sr and U/Pb data in the 550-470 Ma interval suggest an old tecto-thermal activity during the upper Brazilian Cycle (Rio Doce Orogeny). At regional scale, the comparable Neo proterozoic basement of Ventania and sedimentary for eland cover of Tandilia continues to the Northeast, in the Dom Feliciano Belt. A possible correlation of the North Patagonian basement with igneous-metamorphic relics of Central Argentina (Pampean Ranges of San Luis-Cordoba and at La Pampa province) is also indicated. (author)

  6. U-Pb zircon constraints on the age and provenance of the Rocas Verdes basin fill, Tierra del Fuego, Argentina

    Science.gov (United States)

    Barbeau, David L.; Gombosi, David J.; Zahid, Khandaker M.; Bizimis, Michael; Swanson-Hysell, Nicholas; Valencia, Victor; Gehrels, George E.

    2009-12-01

    The Late Jurassic to Early Cretaceous Rocas Verdes basin constitutes one of the most poorly understood components of the southernmost Andes. As a result, accurate reconstructions and interpretations of deformation associated with the Andean orogeny and the kinematics of Scotia arc development also remain poorly constrained. In this data brief, we report U-Pb zircon ages from sandstones of the Rocas Verdes basin fill and from a crosscutting pluton in the southernmost Andes of Argentine Tierra del Fuego. Detrital samples contain predominant Early to early Middle Cretaceous (circa 130-105 Ma) U-Pb zircon age populations, with very small or single-grain middle Mesozoic and Proterozoic subpopulations. A very small subpopulation of Late Cretaceous ages in one sample raises the unlikely possibility that parts of the Rocas Verdes basin are younger than perceived. A sample from a crosscutting syenitic pegmatite yields a crystallization age of 74.7 +2.2/-2.0 Ma. The data presented herein encourage further geochronologic evaluation of the Rocas Verdes basin in order to better constrain the depositional ages and provenance of its contents.

  7. High Precision U/Pb Geochronology of Eocene-Miocene South American Land Mammal Ages at Gran Barranca, Argentina

    Science.gov (United States)

    Dunn, R. E.; Kohn, M. J.; Madden, R. H.; Strömberg, C. E.; Carlini, A. A.

    2009-12-01

    Constraining the ages and duration of Cenozoic South American Land Mammal Ages (SALMAs) has been based on 40Ar/39Ar dating and magnetic polarity stratigraphy. At Gran Barranca (68.7°W, 45.7°S) - South America’s most important site and sequence for constraining SALMAs -uncertainties of ~ 1 Myr persist. To better constrain the ages of mammalian and plant assemblages and stable isotope stratigraphies, we employed high-precision (±50 kyr) single-crystal zircon U/Pb dating. These results generally confirm previous chronologies, but change the timing or duration of some SALMAs at Gran Barranca by 0.5-1 Myr. We collected 23 tuffs from six members of the Sarmiento Formation that contain 7 successive formally recognized SALMAs spanning the middle Eocene through the early Miocene. These strata include the type faunas for the Barrancan, Mustersan and Colhuehuapian SALMAs. Zircons were separated and chemically treated using standard techniques, spiked with EARTHTIME ET535, and analyzed for U-Pb ratios at Boise State University. Simpson’s Y, a prominent marker tuff within the Barrancan SALMA, yielded a date of ˜40.0 Ma. The Rosado Tuff, in the Rosado Member, contains Mustersan SALMA age mammals and yields a date of ˜38.3 Ma. Two tuffs in the Lower Puesto Almendra Member (Bed 10 and the Kay Tuff, stratigraphically above a Mustersan SALMA mammal assemblage) yielded ages of ˜37.0 and ˜36.9 Ma respectively. The Big Mammal Tuff at the base of the Colhuehuapian SALMA is ˜20.9 Ma, and the MMZ24.5 Tuff between the Colhuehuapian and Pinturan SALMAs is ˜19.1 Ma. Together with published magnetostratigraphy, these U/Pb dates have the following implications: (a) The known duration of the Barrancan SALMA is shortened by ~ 1 Myr and spans 40.5-39.0 Ma, (b) The Mustersan SALMA at Gran Barranca is between ˜38.3 and ˜37.0 Ma, (c) The Colhuehuapian SALMA must fall between ˜20.9 and ˜19.8 Ma, and (d) the fossil levels referred to the Pinturan SALMA are bracketed between ˜19.1 and

  8. Geochemistry, U-Pb SHRIMP zircon dating and Hf isotopes of the Gondwanan magmatism in NW Argentina: petrogenesis and geodynamic implications

    International Nuclear Information System (INIS)

    We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations as well as geochemical analyses on three plutonic units of Gondwanan magmatism that crop out in NW Argentina. Two episodes of different age and genesis have been identified. The older one includes gabbros and diorites (Rio Grande Unit) of 267±3 Ma and granitoids (belonging to the Llullaillaco Unit) of 263±1 Ma (late Permian, Guadalupian); the parent magmas were generated in an intraplate environment and derived from an enriched mantle but were subsequently contaminated by crustal components. The younger rocks are granodiorites with arc signature (Chuculaqui Unit) and an age of 247±2 Ma (middle Triassic-Anisian). Hf isotope signature of the units indicates mantle sources as well as crustal components. Hf model ages obtained are consistent with the presence of crustal Mesoproterozoic (mainly Ectasian to Calymnian (TDM(c)=1.24 to 1.44 Ga-negative εHf m) and juvenile Cryogenian sources (TDM=0.65 to 0.79 Ga-positiveεHf(T), supporting the idea of a continuous, mostly Mesoproterozoic, basement under the Central Andes, as an extension of the Arequipa-Antofalla massif. The tectonic setting and age of the Gondwanan magmatism in NW Argentina allow to differentiate: a. Permian intra-plate magmatism developed under similar conditions to the upper section of the Choiyoi magmatism exposed in the Frontal Cordillera and San Rafael Block, Argentina; b. Triassic magmatism belonging to a poorly known subduction-related magmatic arc segment of mostly NS trend with evidence of porphyry type mineralization in Chile, allowing to extend this metallotect into Argentina

  9. Las rocas monzoníticas del sector oriental del plutón de Cachauta, Precordillera mendocina: características geoquímicas y edad U/Pb (LA-ICP-MS

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    Carlos A Cingolani

    2012-06-01

    Full Text Available En el sur de la Precordillera mendocina, afora el plutón de Cacheuta formado por un borde de tipo monzonítico a granodiorítico (Boca del Río gris-verdoso y otro posterior de mayor superficie aforante de composición granítica y tonos rosados-rojizos. Se ofrecen en este trabajo nuevos datos geoquímicos sobre las rocas monzoníticas y el análisis geocronológico por el método U/Pb (LA-ICP-MS sobre 25 cristales de circones extraídos de tres muestras. Las rocas monzoníticas analizadas son de características subalcalinas, metaaluminosas y presentan enriquecimiento en LREE, diseño plano o ligeramente inclinado de HREE y leve anomalía negativa de Eu. La signatura geoquímica es de rocas calco-alcalinas de arco magmático. El análisis geocronológico por U/Pb permitió definir un histograma con una moda principal de edades entre 253 - 258 Ma correspondiente al Pérmico Tardío. Luego los datos isotópicos se extienden entre el Carbonífero Tardío con 302 Ma para un circón de una de las muestras como registro más antiguo y otra que presenta la edad de 249 Ma correspondiendo ya al Triásico más bajo. Con estos datos se confirma que el magmatismo del plutón de Cacheuta pertenece al ciclo gondwánico, resultando coetáneo con parte de la actividad volcánica del Grupo Choiyoi.

  10. Las rocas monzoníticas del sector oriental del plutón de Cachauta, Precordillera mendocina: características geoquímicas y edad U/Pb (LA-ICP-MS The monzonitic rocks of the eastern sector of the Cacheuta Pluton, Precordillera of Mendoza: geochemical signature and U/Pb age (LA-ICP-MS

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    Carlos A Cingolani

    2012-06-01

    Full Text Available En el sur de la Precordillera mendocina, afora el plutón de Cacheuta formado por un borde de tipo monzonítico a granodiorítico (Boca del Río gris-verdoso y otro posterior de mayor superficie aforante de composición granítica y tonos rosados-rojizos. Se ofrecen en este trabajo nuevos datos geoquímicos sobre las rocas monzoníticas y el análisis geocronológico por el método U/Pb (LA-ICP-MS sobre 25 cristales de circones extraídos de tres muestras. Las rocas monzoníticas analizadas son de características subalcalinas, metaaluminosas y presentan enriquecimiento en LREE, diseño plano o ligeramente inclinado de HREE y leve anomalía negativa de Eu. La signatura geoquímica es de rocas calco-alcalinas de arco magmático. El análisis geocronológico por U/Pb permitió definir un histograma con una moda principal de edades entre 253 - 258 Ma correspondiente al Pérmico Tardío. Luego los datos isotópicos se extienden entre el Carbonífero Tardío con 302 Ma para un circón de una de las muestras como registro más antiguo y otra que presenta la edad de 249 Ma correspondiendo ya al Triásico más bajo. Con estos datos se confirma que el magmatismo del plutón de Cacheuta pertenece al ciclo gondwánico, resultando coetáneo con parte de la actividad volcánica del Grupo Choiyoi.In the south of the Precordillera of Mendoza crops out the Cacheuta Pluton formed with an eastern belt of gray-green monzonite to granodiorite type rocks (Boca del Rio and a subsequent larger surface outcrop of pink granitic rocks. In this work are offered new whole rock geochemical and geochronological U/Pb (LA-ICP-MS data on 25 zircon crystals extracted from three monzonitic rock samples. These rocks have subalkaline and metaaluminous signature, with enrichment in light REE with less negative Eu anomaly. The analyses of zircon crystals by U/Pb geochronology show that a main mode of ages is 253 -258 Ma that represent the Late Permian. Then the isotopic data span

  11. Geología, petrografía y edad u-pb de un enjambre longitudinal NO-SE de diques del macizo nordpatagónico oriental, Río negro

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    Santiago N González

    2014-06-01

    Full Text Available En esta contribución se revisan las relaciones estratigráficas y la petrografía de un enjambre de diques longitudinales de rumbo NO-SE, en un amplio sector del Macizo Nordpatagónico oriental (Río Negro. Se presenta además una edad U-Pb en circón correspondiente a la cristalización magmática de los diques. El enjambre se extiende por alrededor de 100 km de largo en dirección NO, entre Punta Pórfido y Rincón de Pailemán, y en una faja de aproximadamente 35 km de ancho. Su composición es esencialmente andesítica y traquiandesítica e internamente los diques exhiben variaciones en la distribución de sus texturas subvolcánicas, producidas por sus diferentes historias térmicas de enfriamiento. Las relaciones estratigráficas del enjambre con sus rocas de caja y un dato U-Pb circones de 243 Ma, indican que es postorogénico respecto de la deformación pérmica del ciclo Gondwánico, y anterior a la efusión de las rocas volcánicas y piroclásticas del Complejo Volcánico Marifil. Los diques se alojan a lo largo de las mismas estructuras de rumbo NO que los cuerpos intrusivos y extrusivos de dicho complejo. El enjambre tiene distribución regional en el Macizo Nordpatagónico oriental y es un episodio ígneo transicional entre el magmatismo Gondwánico y el Complejo Marifil.

  12. New SHRIMP U-Pb data from the Famatina Complex : constraining Early-Mid Ordovician Famatinian magmatism in the Sierras Pampeanas, Argentina

    OpenAIRE

    J.A. Dahlquist; Pankhurst, Robert; C.W. Rapela; C. Galindo; Alasino, P.; Fanning, C. M.; J. Saavedra; Baldo, E.

    2008-01-01

    New SHRIMP U-Pb zircon ages are reported for igneous and sedimentary rocks of the Famatina Complex, constraining the age of the magmatism and the ensialic basins. Together with whole-rock and isotope geochemistry for the igneous rocks from the complex, these ages indicate that the voluminous parental magmas of metaluminous composition were derived by partial melting of an older lithosphere without significant asthenospheric contribution. This magmatism was initiated in the Early Ordovician (4...

  13. SHRIMP U-Pb zircon dates from igneous rocks from the Fontana Lake region, Patagonia: Implications for the age of magmatism, Mesozoic geological evolution and age of basement Datación de circón por U-Pb SHRIMP en rocas ígneas de la región del lago Fontana, Patagonia: Implicancia para la edad del magmatismo, la evolución geológica mesozoica y edad del basamento

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    A.P. Rolando

    2004-12-01

    ánicas y sedimentarias del Jurásico medio a Cretácico temprano fueron intruidas por cuerpos graníticos durante el Cretácico. La reconstrucción de la evolución magmática jurásico-cretácica en la región del lago Fontana y en el batolito patagónico adyacente fue posible considerando las siguientes características: distribución en el tiempo y el espacio de varios cuerpos intrusivos, la formación de una cuenca de retro-arco y la intensidad volcánica. Datación de cristales de circón (U-Pb SHRIMP de una ignimbrita, un pórfido dacítico y dos rocas graníticas dieron edades de 148,7 ± 2,3, 144,5 ± 1,6, 117 ± 1,7 y 99,6 ± 2,8 Ma, respectivamente. La Ignimbrita Cerro Bayo (148,7 ± 2,3 Ma, Jurásico tardío fue incluida en la Formación Lago La Plata; esta unidad hospeda un depósito del tipo epitermal. El pórfido dacítico de laguna Escondida (144,5 ± 1,6 Ma, límite jurásico-cretácico intruyó rocas metasedimentarias de la Formación Lago La Plata; este cuerpo sub-volcánico puede vincularse cronológicamente al batolito patagónico. Después de los eventos volcánicos jurásicos, una cuenca de retroarco se formó en el sector oriental de la cordillera Patagónica aproximadamente a los 140-115 Ma (Berriasiano-Barremiano tardío y el magmatismo cesó durante este evento. La datación de granitoides (117 ± 1,7 y 99,6 ± 2,8 Ma en la región del lago Fontana confirma una continuidad magmática temporal con el batolito patagónico. Estas edades coinciden con la presencia en la región de rocas volcánicas del Grupo Divisadero y depósitos epitermales (yacimiento La Ferrocarrilera. Uno de los granitoides analizado (Dedo Chico, 99,6 ± 2,8 Ma ha heredado cristales de circón de aproximadamente 2.100 y 3.410 Ma, confirmado otras evidencias isotópicas previas sobre la presencia de un basamento precámbrico subyacente en la región.

  14. Intraplate Late Jurassic deformation and exhumation in western central Argentina: Constraints from surface data and U-Pb detrital zircon ages

    Science.gov (United States)

    Naipauer, Maximiliano; García Morabito, Ezequiel; Marques, Juliana C.; Tunik, Maisa; Rojas Vera, Emilio A.; Vujovich, Graciela I.; Pimentel, Marcio P.; Ramos, Victor A.

    2012-02-01

    Intraplate deformation has been described in several tectonic settings and recently in western central Argentina it has been proposed to explain the complex structural patterns developed between Early Jurassic and Cretaceous times along the Huincul deformation zone. We integrate new field data and detrital zircon ages of the exposed portion of the Huincul High that permit us to quantify the significance of this intraplate deformation in the relief generation. A stratigraphic and structural record of a Jurassic pulsed contractional deformation is derived from field surveys. It is documented through multiple unconformities and growth geometries linked to NE and E-W oriented growth structures extensively developed across the studied region. The pattern of zircon ages from the analyzed Late Jurassic successions indicates that they have a clear provenance from sources located along the Huincul deformation zone. The Tordillo Formation outcrops north of the Huincul High have a dominant provenance from the Andean Jurassic arc; while the Quebrada del Sapo Formation, south of the Huincul High, has a significant input from Late Triassic (220-200 Ma) and Late Permian (280-260 Ma) sources of the axial exposures of the Huincul High. Surface data, combined with detrital zircon ages proved to be a powerful method to confirm the presence of an ancient positive element developed within the southern Neuquén basin. Its genesis falls within the early history of the Huincul deformation zone, where several structural features indicate pulses of growth since Early Jurassic times prior to the main Andean contractional cycle that started in the Late Cretaceous. Therefore, these data document for the first time the importance of the early contractional phases in the relief construction in the southern Central Andes, reinforcing previous hypotheses about pre-Andean intraplate deformation concentrated along this extensive east-west oriented basement weakness zone.

  15. Edad dental vs. edad ósea

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    Baffi, Elvira Inés

    2007-01-01

    Full Text Available En el presente trabajo se analizan, en restos de subadultos, los valores obtenidos para la edad al morir, evaluados a través de indicadores de edad dental y edad ósea, recuperada mediante la longitud de los huesos largos. La muestra considerada corresponde a subadultos recuperados por E. Boman en los cementerios prehispánicos de San Blas de los Sauces, provincia de La Rioja, Argentina. Se evalúan diferencias y coincidencias en las edades obtenidas por ambos métodos en esta muestra, y en otras procedentes del Noroeste Argentino y norte de Chile. Se proponen posibles explicaciones par las divergencias encontradas.

  16. Detrital and volcanic zircon U-Pb ages from southern Mendoza (Argentina): An insight on the source regions in the northern part of the Neuquén Basin

    Science.gov (United States)

    Naipauer, Maximiliano; Tapia, Felipe; Mescua, José; Farías, Marcelo; Pimentel, Marcio M.; Ramos, Victor A.

    2015-12-01

    The infill of the Neuquén Basin recorded the Meso-Cenozoic geological and tectonic evolution of the southern Central Andes being an excellent site to investigate how the pattern of detrital zircon ages varies trough time. In this work we analyze the U-Pb (LA-MC-ICP-MS) zircon ages from sedimentary and volcanic rocks related to synrift and retroarc stages of the northern part of the Neuquén Basin. These data define the crystallization age of the synrift volcanism at 223 ± 2 Ma (Cerro Negro Andesite) and the maximum depositional age of the original synrift sediments at ca. 204 Ma (El Freno Formation). Two different pulses of rifting could be recognized according to the absolute ages, the oldest developed during the Norian and the younger during the Rhaetian-Sinemurian. The source regions of the El Freno Formation show that the Choiyoi magmatic province was the main source rock of sediment supply. An important amount of detrital zircons with Triassic ages was identified and interpreted as a source area related to the synrift magmatism. The maximum depositional age calculated for the Tordillo Formation in the Atuel-La Valenciana depocenter is at ca. 149 Ma; as well as in other places of the Neuquén Basin, the U-Pb ages calculated in the Late Jurassic Tordillo Formation do not agree with the absolute age of the Kimmeridgian-Tithonian boundary (ca. 152 Ma). The main source region of sediment in the Tordillo Formation was the Andean magmatic arc. Basement regions were also present with age peaks at the Carboniferous, Neoproterozoic, and Mesoproterozoic; these regions were probably located to the east in the San Rafael Block. The pattern of zircon ages summarized for the Late Jurassic Tordillo and Lagunillas formations were interpreted as a record of the magmatic activity during the Triassic and Jurassic in the southern Central Andes. A waning of the magmatism is inferred to have happened during the Triassic. The evident lack of ages observed around ca. 200 Ma suggests

  17. Estructura de Edades de la Fuerza Laboral y Distribución del Ingreso: Un Análisis Empírico para la Argentina

    OpenAIRE

    Winkler, Hernán Jorge

    2004-01-01

    El objetivo de este análisis es investigar en qué dirección puede moverse la desigualdad de la distribución del ingreso laboral horario ante cambios en la estructura de edades de la fuerza de trabajo de la República Argentina. Los resultados indican que los efectos distributivos de una mayor participación de trabajadores jóvenes en el total son contrapuestos. Por un lado, la desigualdad total puede caer dado que este grupo se caracteriza por una menor dispersión de ingresos. Por otro, la desi...

  18. U-Pb Ages of Lunar Apatites

    Science.gov (United States)

    Vaughan, J.; Nemchin, A. A.; Pidgeon, R. T.; Meyer, Charles

    2006-01-01

    Apatite is one of the minerals that is rarely utilized in U-Pb geochronology, compared to some other U-rich accessory phases. Relatively low U concentration, commonly high proportion of common Pb and low closure temperature of U-Pb system of apatite inhibit its application as geochronological tool when other minerals such as zircon are widely available. However, zircon appear to be restricted to certain type of lunar rocks, carrying so called KREEP signature, whereas apatite (and whitlockite) is a common accessory mineral in the lunar samples. Therefore, utilizing apatite for lunar chronology may increase the pool of rocks that are available for U-Pb dating. The low stability of U-Pb systematics of apatite may also result in the resetting of the system during meteoritic bombardment, in which case apatite may provide an additional tool for the study of the impact history of the Moon. In order to investigate these possibilities, we have analysed apatites and zircons from two breccia samples collected during the Apollo 14 mission. Both samples were collected within the Fra Mauro formation, which is interpreted as a material ejected during the impact that formed the Imbrium Basin.

  19. Engineering cyber infrastructure for U-Pb geochronology: Tripoli and U-Pb_Redux

    Science.gov (United States)

    Bowring, J. F.; McLean, N. M.; Bowring, S. A.

    2011-06-01

    In the past decade, major advancements in precision and accuracy of U-Pb geochronology, which stem from improved sample pretreatment and refined measurement techniques, have revealed previously unresolvable discrepancies among analyses from different laboratories. One solution to evaluating and resolving many of these discrepancies is the adoption of a common software platform that standardizes data-processing protocols, enabling robust interlaboratory comparisons. We present the results of a collaboration to develop cyber infrastructure for high-precision U-Pb geochronology based on analyzing accessory minerals by isotope dilution-thermal ionization mass spectrometry. This cyber infrastructure implements an architecture specifying the workflows of data acquisition, statistical filtering, analysis and interpretation, publication, community-based archiving, and the compilation and comparison of data from different laboratories. The backbone of the cyber infrastructure consists of two open-source software programs: Tripoli and U-Pb_Redux. Tripoli interfaces with commercially available mass spectrometers using standardized protocols, statistical filtering, and interactive visualizations to aid the analyst in preparing raw data for analysis in U-Pb_Redux. U-Pb_Redux implements the architecture by orchestrating the analyst's workflow with interactive visualizations and provides data reduction and uncertainty propagation that support data interpretations. Finally, U-Pb_Redux enables production of publication-ready graphics and data tables, the archiving of results, and the comparative compilation of archived results to support cooperative science.

  20. Composicion corporal y prevalencia estandarizada de desnutricion en niños de 6 a 12 años de edad, La Costa, Argentina

    Directory of Open Access Journals (Sweden)

    Bolzán Andrés

    2003-01-01

    Full Text Available OBJETIVOS: evaluar la composición corporal y la prevalencia estandarizada de desnutrición en niños de seis a 12 años de edad de La Costa, Argentina. MÉTODOS: se midieron la estatura, perímetro braquial y el pliegue cutáneo tricipital, calculando los siguientes indicadores: circunferencia muscular braquial, área muscular braquial, área grasa braquial (AGB, índice área muscular braquial/estatura (AMBE, índice energía/proteína (EP e índice grasa/músculo braquiales. Se calculó la prevalencia estandarizada de desnutrición (PE. Se consideraron además tres indicadores sociales. El análisis estadístico incluyó ANOVA multifactorial, correlación de Pearson y de Spearman. RESULTADOS: existió dimorfismo sexual sólo para el AGB. A mayor tamaño de la familia los indicadores antropométricos fueron menores. La PE mostró diferencias con el estándar. El tejido muscular resultó más desviado que el adiposo, aunque el índice AMBT se mantuvo dentro de la normalidad. CONCLUSIONS: El tamaño de la familia modificó el crecimiento global de la población viéndose más afectados los indicadores que incluyen tejido adiposo. Las PE reflejaron mayor sesgo de los indicadores de reserva proteica: AM, PMB que los de reserva energética: PCT, AG.

  1. Argentina

    International Nuclear Information System (INIS)

    The history of Argentina nuclear development can be summarized into two periods: 'splendour' and 'stand-by'. The former starting in the decade of the 1950s until the late 1970s while the latter period goes from the late 1970s to 2006. The first period (1950-1980) was characterized by a national policy of scientific and technological development; State intervention in the area of industrial production. The military aspects, if any, were marginal in the context of the overall development. During this period, important public scientific technological projects were carried out: the production and sale of experimental reactors, nuclear plants (Atucha I and Embalse), and some projects aimed to developing national industry. The stimulus experienced in the country in this period accompanied the role of nuclear technology worldwide due to the Cold War and the persuasion factor among the main powers. However, during the 1970s and 1980s the whole world started questioning these technologies which ran parallel to the liberalization of the countries economies. The second period (1980s onwards) was characterized by many economic problems and the consequent transitory stop of national nuclear projects; e.g. Argentina transitory stopped its third nuclear plant (at present under construction). At that moment, neoliberal politics were aimed at reducing the role of the State and promoting privatization, separating nuclear projects from governmental control, trying to privatize the nuclear plants, and cutting scientific budgets. Argentina has two nuclear power plants in operation providing 8.6% of the total country's electricity. A third one, 692 MW(e) power reactor PHWR Atucha-2 construction was stopped in the 1990s and re-started in 2007 it is expected to be in commercial operation by 2011). Argentina nuclear power plants utility, NA S.A. is preparing the refurbishment of its CANDU-6 reactor. Argentina Atomic Energy Commission (CNEA) has a prototype of its CAREM nuclear power plant

  2. Oxygen isotopic composition and U-Pb discordance in zircon

    Science.gov (United States)

    Booth, A.L.; Kolodny, Y.; Chamberlain, C.P.; McWilliams, M.; Schmitt, A.K.; Wooden, J.

    2005-01-01

    We have investigated U-Pb discordance and oxygen isotopic composition of zircon using high-spatial resolution ??18O measurement by ion microprobe. ??18O in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance. Our results suggest that three characteristics of zircon are interrelated: (1) U-Pb systematics and concomitant age discordance, (2) ??18O and the water-rock interactions implied therein, and (3) zircon texture, as revealed by cathodoluminescence and BSE imaging. A key observation is that U-Pb-disturbed zircons are often also variably depleted in 18O, but the relationship between discordance and ??18O is not systematic. ??18O values of discordant zircons are generally lighter but irregular in their distribution. Textural differences between zircon grains can be correlated with both U-Pb discordance and ??18O. Discordant grains exhibit either a recrystallized, fractured, or strongly zoned CL texture, and are characteristic of 18O depletion. We interpret this to be a result of metamictization, leading to destruction of the zircon lattice and an increased susceptibility to lead loss. Conversely, grains that are concordant have less-expressed zoning and a smoother CL texture and are enriched in 18O. From this it is apparent that various stages of water-rock interaction, as evidenced by systematic variations in ??18O, leave their imprint on both the texture and U-Pb systematics of zircon. Copyright ?? 2005 Elsevier Ltd.

  3. Argentina

    Energy Technology Data Exchange (ETDEWEB)

    1999-09-01

    This report presents a brief overview of the socio-economic, energy and environmental context in which climate change mitigation actions in Argentina shall be inserted. To that end, the dynamic of the Argentine economic development, its influence on the energy system and environmental impacts is summarised. From the environmental standpoint, emphasis shall only be made on the impact of economic development patterns and energy policies on GHG emission. (au) 73 refs.

  4. Argentina

    International Nuclear Information System (INIS)

    Argentina has embarked on an ambitious domestic nuclear research and energy program. The venture promises to provide the nation with the infrastructure to play an important role in the nuclear export market in the years ahead. Buenos Aires built its program on a foundation of international support and assistance that overlay an emerging sophisticated industrial and scientific establishment. The foreign contribution sensitized Argentina to opportunities in the global market. This paper reports that Argentina operates two heavy-water/natural uranium reactors, Atucha I and Embalse. Producing, respectively, 320 MW(e) and 600 MW(e), they supply roughly 10 percent of the country's electricity. With a capacity factor of 84 percent, Atucha I is among the best operated plants in the world. Plans call for a third, 745 MW(e) power plant, Atucha II, to go on line in the early 1990s. During this period, construction also may begin on three 300 MW(e) plants, although the country's foreign indebtedness plus cost overruns in earlier construction will place a heavy burden on these plans

  5. Argentina

    International Nuclear Information System (INIS)

    One article from Argentina where is developed the proceedings before the Federal criminal court of First instance concerning environmental radiological contamination near the Eizeiza centre. A second article from Canada treats the federal court of appeal decision respecting the Mac Clean lake project; two articles from France, judgement of the court of appeal on Caen on the licence to reprocess Australian spent fuel, and judgement of the magistrates court of Limoges concerning dumping of radioactive waste by COGEMA; the last one article from Japan, concerns the judgement of the japanese supreme court confirming the validity of the licence to establish the Monju reactor. (N.C.)

  6. Argentina.

    Science.gov (United States)

    1993-02-01

    Background notes on Argentina provide a profile of the geography, selected demographic features, government and economic conditions. Descriptive text includes a discussion of the people, their history and political conditions, the government and officials, the state of the economy, their defense, foreign relations, and relations with the US. The 1992 estimated population was about 33 million of whom 97% are European (mostly Spanish and Italian). Religions represented are Roman Catholic (92%), Protestant (2%), Jewish (2%), and other (4%). Adult literacy is 95%. 36% are engaged in industry and commerce, 20% in services, 19% in agriculture, 6% in transport and communications, and 19% other. Per capita gross domestic product was $4,500. There are only 50,000 native Indians remaining in peripheral provinces. The population enjoys a high standard of living and a low growth rate. The country was shaped by dominant forces: modern agricultural techniques and the integration of the country into the world economy. Foreign investment aided the economic revolution. Conservative and radical rule has swung the country back and forth politically since 1916. Colonel Juan Domingo Peron led a successful military coup in 1943 and was elected in 1946. Policies were instituted to give a greater voice to the working class, and with the influences of his wife, women's groups. In 1955, he was ousted by the military, which failed to revive the economy and quiet increasing terrorism. After a number of difficult elections, Peron was reinstated as president in 1973. Extremists on the left and right threatened public order; the military as a consequence imprisoned persons indefinitely. Peron's wife succeeded him after his death, but was removed from office in the military coup of 1976. Basic human rights were violated during this period. By 1983, a fair election was held and support increased for a democratic system. In 1989, Carlos Saul Menem, a Peronist candidate, won and established

  7. Argentina

    Directory of Open Access Journals (Sweden)

    G. Benedetti

    2007-01-01

    Full Text Available El presente trabajo tiene como objetivo realizar un diagnóstico ambiental de un sector de la ciudad de Bahía Blanca, Argentina basado en el arbolado urbano de alineación. El arbolado constituye un componente fundamental de los paisajes artifi ciales ya que contribuye al aumento del confort y al mejoramiento de la calidad del medio. En este sentido, actúa como un factor moderador de las condiciones climáticas, la contaminación y la salud de la población. El municipio de la ciudad de Bahía Blanca tiene como proyecto la realización de inventarios del arbolado en los distintos barrios, para lograr optimizar la relación entre la cantidad de ejemplares arbóreos y la densidad poblacional. Es importante considerar la variedad de ejemplares en función del uso del suelo y de las características ambientales de cada sector. Por lo tanto, este trabajo presenta un diseño metodológico para la elaboración del plano verde de la ciudad.

  8. Argentina

    Directory of Open Access Journals (Sweden)

    Hernan Galperin

    2004-01-01

    Full Text Available En este trabajo se analizan las bases sobre las que se está desarrollando el proceso de transición hacia la TV digital en Brasil y Argentina, y se discuten las posibilidades que la transición presenta para replantear la estructura de mercado y el modelo de regulación de la TV abierta en los países del Mercosur. La principal hipótesis es que la TV digital abre una oportunidad única para reformar el actual modelo de radiodifusión basado en la concesión de un número reducido de licencias a operadores de tipo generalista. Al multiplicar la capacidad de transmisión y facilitar el desarrollo de servicios interactivos tanto de entretenimiento como educativos y de información, la transición a la TV digital se ofrece como instrumento de política pública para alcanzar objetivos clave en materia de comunicación, como el pluralismo, la apertura del mercado y el achicamiento de la llamada brecha digital.

  9. Calculation of uncertainties of U-Pb isotope data

    Science.gov (United States)

    Ludwig, K. R.

    1980-01-01

    Equations are derived for the estimation of errors and error correlations for various types of U-Pb isotope data, taking into account ion-beam instabilities, run-to-run variability in mass-discrimination, uncertainties in Pb and U concentrations, and uncertainties in initial-Pb and blank-Pb amount and isotopic composition. Equations are also given for the calculation of concordia intercept errors. ?? 1980.

  10. Air abrasion experiments in U-Pb dating of zircon

    Science.gov (United States)

    Goldich, S.S.; Fischer, L.B.

    1986-01-01

    Air abrasion of zircon grains can remove metamict material that has lost radiogenic Pb and zircon overgrowths that were added during younger events and thereby improve the precision of the age measurements and permit closer estimates of the original age. Age discordance that resulted from a single disturbance of the U-Pb isotopic decay systems, as had been demonstrated by T.E. Krogh, can be considerably reduced, and, under favorable conditions, the ages brought into concordancy. Two or more events complicate the U-Pb systematics, but a series of abrasion experiments can be helpful in deciphering the geologic history and in arriving at a useful interpretation of the probable times of origin and disturbances. In east-central Minnesota, U.S.A., Penokean tonalite gneiss is dated at 1869 ?? 5 Ma, and sheared granite gneiss is shown to have been a high-level granite intrusion at 1982 ?? 5 Ma in the McGrath Gneiss precursor. Tonalite gneiss and a mafic granodiorite in the Rainy Lake area, Ontario, Canada, are dated at 2736 ?? 16 and 2682 ?? 4 Ma, respectively. The tonalitic phase of the Morton Gneiss, southwestern Minnesota, is dated at 3662 ?? 42 Ma. ?? 1986.

  11. Datación U-PB del pranito Paimán, Sierra de Paimán, Chilecito, La Rioja

    Directory of Open Access Journals (Sweden)

    Ricardo Varela

    2008-03-01

    Full Text Available Se da a conocer los resultados de la datación U-Pb convencional en circones del Granito Paimán, uno de los componentes del flanco oriental del Sistema de Famatina. Fueron analizadas cinco fracciones de cristales de circón de un granito porfiroide, característico de la unidad. Los resultados son coherentes entre sí y proveen una edad de 477,6 ± 4,1 Ma, que ubican la edad de cristalización y emplazamiento en el Ordovícico Temprano. La datación corrobora su asignación a la fase magmática oclóyica y específicamente al cinturón famatiniano. El análisis del presente y otros datos U-Pb previos de otras rocas graníticas del cinturón famatiniano entre los 28º y 33º S, permiten delimitar un estrecho lapso (alrededor de 20 Ma de actividad ígnea, sin poderse determinar ninguna polaridad en la producción del magmatismo.

  12. Provenance from zircon U-Pb age distributions in crustally contaminated granitoids

    Science.gov (United States)

    Bahlburg, Heinrich; Berndt, Jasper

    2016-05-01

    The basement of sedimentary basins is often entirely covered by a potentially multi-stage basin fill and therefore removed from direct observation and sampling. Melts intruding through the basin stratigraphy at a subsequent stage in the geological evolution of a region may assimilate significant volumes of country rocks. This component may be preserved in the intrusive body either as xenoliths or it may be reflected only by the age spectrum of incorporated zircons. Here we present the case of an Ordovician calc-alkaline intrusive belt in NW Argentina named the "Faja Eruptiva de la Puna Oriental" (Faja Eruptiva), which in the course of intrusion sampled the unexposed and unknown basement of the Ordovician basin in this region, and parts of the basin stratigraphy. We present new LA-ICP-MS U-Pb ages on zircons from 9 granodiorites and granites of the Faja Eruptiva. The main part of the Faja Eruptiva intruded c. 445 Ma in the Late Ordovician. The zircon ages obtained from the intrusive rocks have a large spread between 2683.5 ± 21.6 and 440.0 ± 4.9 Ma and reflect the underlying crust and may be interpreted in several ways. The inherited zircons may have been derived from the oldest known unit in the region, the thick siliciclastic turbidite successions of the upper Neoproterozoic-lower Cambrian Puncoviscana Formation, which is inferred to represent the basement of the NW Argentina. The basement to the Puncoviscana Formation is not known. Alternatively, the inherited zircons may reflect the geochronological structure of the entire unexposed Early Paleozoic crust underlying this region of which the Puncoviscana Formation was only one component. This crust likely contained rocks pertaining to and detritus derived from earlier orogenic cycles of the southwestern Amazonia craton, including sources of Early Meso- and Paleoproterozoic age. Detritus derived, in turn, from the Faja Eruptiva intrusive belt reflects the origin of the granitoids as well as the inherited

  13. U-Pb isotope systematics in josephinites and associated rocks

    International Nuclear Information System (INIS)

    Josephinite nodules are composed of metallic nickel iron alloy intergrown with andradite garnet. They are found in the peridotitic section of an obducted ophiolite in SW Oregon. The origin of josephinite is widely debated: for example, previous investigation have proposed it as a byproduct of low temperature synserpentinization processes linked to the intrusion of dikes or and its derivation from primitive mantle, conceivably from as deep as the core mantle boundary. We report U-Pb data from josephinites, wyrdite (a rock associated with josephinite) consisting of rutile and ilmente intergrown with silicates, and their surrounding rocks (hornblende diorites and harzburgites). The measured Pb isotopic composition of all decontaminated, leached josephinite metal samples plots in the Pb-Pb diagram just above/in the MORB field, while the first leachates are characterized by higher 207Pb/204Pb ratios. The isotopic Pb composition measured in the leachates of the wyrdite defines a line whose slope corresponds to an age of 159±8 Myr. The harzburgites show a wide spread in Pb isotopic compositions; all samples lie above the MORB field and three samples plot to the left side of the 4.55 AE geochron. The hornblende diorite dikes, characterized by the highest U and Pb concentrations of all studied rocks, plot in the MORB field. None of these different rocks is characterized by a single or homogeneous Pb composition. All samples are affected by secondary alteration processes: the circulation of hydrothermal fluids disturbed the dikes and ultramafic rocks and serpentinization processes have affected harzburgites, josephinites, and wyrdites. Thus the Pb isotopic composition measured today represents a mixture of initial Pb, radiogenic Pb and inherited Pb in variable proportions. Concerning the origin of josephinite these results show a close relationship between josephinite, wyrdite, and the dikes. (orig./WB)

  14. New natural zircon standard for laser ablation ICP-MS U-Pb geochronology

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Košler, J.; Schaltegger, U.; Tubrett, M.; Gutjahr, M.

    Amherst : I C P Information Newsletter, Inc, 2006 - (Barnes, R.). --- [2006 Winter Conference on Plasma Spectrochemistry. 09.01.2006-14.01.2006, Tucson] Keywords : zircon * ICP-MS * U-Pb dating * reference material Subject RIV: DD - Geochemistry

  15. U/Pb Geochronology of the Maya Block, Guatemala

    Science.gov (United States)

    Martens, U.; Ratschbacher, L.; McWilliams, M.

    2005-12-01

    The Maya Block can be defined as Guatemala north of the Motagua transform fault, Belize, and part of southern Mexico. The absence of radiometric ages has hindered an understanding of the geologic evolution of the Maya Block and its connections with adjacent blocks in North America, South America and the Caribbean. We present an exploratory study of SHRIMP U/Pb ages from zircons collected in central and western Guatemala that shows ubiquitous Grenvillian inheritance, magmatism at ~ 1020 Ma, ~ 975 Ma and ~ 175 Ma, Devonian-Silurian and Triassic tectonomagmatic events, and Cretaceous metamorphism. Grenvillian orthogneisses were identified in the northern flank of the Sierra de Chuac'{u}s whose magmatic ages are 1020 ± 35 Ma and 975 ± 15 Ma with possible Pb-loss at ~ 420 Ma. Zircons of the Rabinal Granite show an important ~ 975 Ma inheritance and concordant ages in the 400-500 Ma range. We interpret the Devonian-Silurian ages as magmatic and correlate the peraluminous Rabinal Granite with similar intrusions in the Maya Mountains of Belize. Coeval events recorded in Chuac'{u}s orthogneisses and the Rabinal Granite suggest connections since Early Paleozoic time between the Chuac'{u}s complex and the Maya Block north of the Baja Verapaz shear zone that separates rocks of contrasting metamorphic grade. The magmatic age for deformed granites south of Sacapulas in central-western Guatemala is 174 ± 3 Ma. Migmatitic paragneisses collected south of Huehuetenango yield Triassic metamorphic ages at 223 ± 4 Ma, coeval with anatexis in the basement of Chiapas, Mexico. Medium to high-grade metasedimentary rocks on the southern flank of the Sierra de Chuac'{u}s do not record a Silurian-Devonian provenance. Instead, they yield clear Grenvillian and Triassic (240-210 Ma) components. Dating of zircon rims at 74 ± 1 Ma yields a precise age for the peak Cretaceous epidote-amphibolite metamorphic event in the Chuac'{u}s complex. Ductile structures exhibiting at least 4 tectonic

  16. U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

    Science.gov (United States)

    Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.; Lin, Y. T.; Liu, Y.; Tang, G. Q.

    2012-01-01

    Zircon U-Pb geochronology has made a great contribution to the timing of magmatism in the early Solar System [1-3]. Ca phosphates are another group of common accessory minerals in meteorites with great potential for U-Pb geochronology. Compared to zircons, the lower closure temperatures of the U-Pb system for apatite and merrillite (the most common phosphates in achondrites) makes them susceptible to resetting during thermal metamorphism. The different closure temperatures of the U-Pb system for zircon and apatite provide us an opportunity to discover the evolutionary history of meteoritic parent bodies, such as the crystallization ages of magmatism, as well as later impact events and thermal metamorphism. We have developed techniques using the Cameca IMS-1280 ion microprobe to date both zircon and phosphate grains in meteorites. Here we report U-Pb dating results for zircons and phosphates from lunar meteorites Dhofar 1442 and SaU 169. To test and verify the reliability of the newly developed phosphate dating technique, two additional meteorites, Acapulco, obtained from Acapulco consortium, and angrite NWA 4590 were also selected for this study as both have precisely known phosphate U-Pb ages by TIMS [4,5]. Both meteorites are from very fast cooled parent bodies with no sign of resetting [4,5], satisfying a necessity for precise dating.

  17. Timing of the magmatism of the paleo-Pacific border of Gondwana: U-Pb geochronology of Late Paleozoic to Early Mesozoic igneous rocks of the north Chilean Andes between 20o and 31oS

    International Nuclear Information System (INIS)

    U-Pb zircon geochronological data provide record of about 130 Ma of igneous activity in the Andes of northern Chile, which extended episodically from the latest Early Carboniferous to Early Jurassic (328-194 Ma). The overall U-Pb data show that volcanism and plutonism were essentially synchronous and major episodes of igneous activity developed during the Late Carboniferous to Mid-Permian (310 to 260 Ma) and from Late Permian to Late Triassic (255-205 Ma), with less prominent episodes in the mid-Carboniferous (330 to 320 Ma), and Early Jurassic (200-190 Ma). Thus, from the Carboniferous to the Early Triassic dominantly silicic magmatism developed along the Chilean segment of the southwestern border of Gondwana supercontinent. Further magmatism developed during the Mid-Late Triassic (250-194 Ma) was bimodal and synchronous with rift-related, continental and/or marine sedimentary strata related to the early stages of break-up of Gondwana. Most of the silicic volcanic rocks of the Precordillera and Domeyko Cordillera of northern Chile (21o 30o to 25o30oS) are older than the silicic rocks assigned to the Choiyoi succession in Argentina, being instead equivalent in age to Carboniferous to Early Permian marine sedimentary sequences present in the eastern Argentinean foreland. On the other hand, silicic volcanic successions exposed in the easternmost part of northern Chile are equivalent in age to the Choiyoi succession of the San Rafael Block of Argentina. An eastward expansion or migration of the volcanism during the Mid-Permian to Early Triassic is inferred, interpretation that is consistent with expansion of the volcanism at that time in Argentina. The timing of the Late Paleozoic to Early Jurassic magmatism is coincident with that of the Andes of Peru and of western Argentina according to the available U-Pb data, revealing a rather consistent evolution in time of the magmatism along the southwestern, paleo-Pacific border of Gondwana

  18. Datación U-PB del pranito Paimán, Sierra de Paimán, Chilecito, La Rioja U-Pb dating of the Paimán Granite, Sierra de Paimán, Chilecito, La Rioja

    Directory of Open Access Journals (Sweden)

    Ricardo Varela

    2008-03-01

    Full Text Available Se da a conocer los resultados de la datación U-Pb convencional en circones del Granito Paimán, uno de los componentes del flanco oriental del Sistema de Famatina. Fueron analizadas cinco fracciones de cristales de circón de un granito porfiroide, característico de la unidad. Los resultados son coherentes entre sí y proveen una edad de 477,6 ± 4,1 Ma, que ubican la edad de cristalización y emplazamiento en el Ordovícico Temprano. La datación corrobora su asignación a la fase magmática oclóyica y específicamente al cinturón famatiniano. El análisis del presente y otros datos U-Pb previos de otras rocas graníticas del cinturón famatiniano entre los 28º y 33º S, permiten delimitar un estrecho lapso (alrededor de 20 Ma de actividad ígnea, sin poderse determinar ninguna polaridad en la producción del magmatismo.Conventional U-Pb zircon ages for the Paimán Granite are presented. The magmatic unit crops out in the eastern border of the Famatina range. Five zircon fractions were analysed from a coarse porphyritic granitoid, the major component in the Paimán-Chilecito area. Results are concordant for the five fractions and the mean 206 Pb/ 238 U age of 477.6 ± 4.1 Ma is Early Ordovician. This age confirms that the Paimán Granite is part of the Ocloyic magmatic phase and Famatinian belt. The present age together with the previous U-Pb ages from granitoids of the Famatinian belt between 28º and 33º S suggest that the magmatic activity occurred over a short time span of about 20 Ma, following no noticeable internal polarity within the belt.

  19. New interpretive procedure for whole rock U-Pb systems applied to the Vredefort crustal profile

    International Nuclear Information System (INIS)

    Granulite grade Precambrian gneisses have usually undergone at least one period of strong U depletion. While rock U-Pb isotope studies can determine the time(s) of the severe depletion, and this work attempts to place such studies on a more rigorous footing. Two-stage U-Pb systems can be described in terms of one major, episodic differentiation into rocks with varying U/Pb ratios, while three-stage systems can be described by two such distinct episodes. Most of the Precambrian granulites that have been isotopically analyzed have histories too complex to be described as two-stage systems. However, it is demonstrated here that U-Pb data on whole rock suites can yield the complete U-Pb chemical history of a three-stage system (in terms of U/Pb ratios). For a suite of granulites, present-day 207Pb/204Pb and 206Pb/204Pb ratios and element concentration data allow these ratios to be calculated at a number of specific past times and plotted as an array. The degree of scatter in each of these 'past arrays' is graphed as a function of time. The point of least scatter denotes the age of the end of stage 2 in the history of the system. The array slope and the dating of the end of stage 2 also permit the beginning of stage 2 to be calculated. All other parameters in the system (U and Pb concentrations, Pb isotopic ratios) can now be determined for each individual rock throughout its history. The new interpretive method also distinguishes sensitively among various kindds of uranium fractionation which may have operated during the differentiation episodes. It is applied here to uranium-depleted granulites in the deeper part of the Vredefort crustal profile. The times of the two fractionating episodes are calculated at approx.3860 and approx.2760 m.y., respectively

  20. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    Science.gov (United States)

    Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

    2002-01-01

    The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

  1. Recrystallization of zircon and its effect on U-Pb dating

    International Nuclear Information System (INIS)

    Zircon is the most preferred mineral for U-Pb geochronology to obtain high precision mineral growth ages of crystalline rocks. In this work, a suite of discordant zircons from a leucosome of a garnet biotite gneiss from the Kerala Khondalite Belt, India were investigated by a combination of back-scattered electron imaging and SHRIMP analyses to ponder over the pattern of Pb-loss in recrystallized zircon. Previous attempts for U-Pb zircon dating of this rock type in the area have all resulted highly discordant ages

  2. Evaluation of uranium-lead (U-Pb) and thermoluminescence (TL) methods in dating fossil bones

    International Nuclear Information System (INIS)

    Uranium-lead (U-Pb) and thermoluminescence (TL) methods of dating have been used on samples of fossil bones of the Holocene, Pleistocene, Pliocene and Miocene Periods. In applying the U-Pb method it was deduced that a significant part of the lead found in fossil bones does not have a radiogenic origin and, as far as the TL method is concerned, saturation effects occur in the thermoluminescence of such materials if the accumulated radiation dose is > 0.1 kGy (10 krads). (Author)

  3. Improved laser ablation U-Pb zircon geochronology through robust downhole fractionation correction

    DEFF Research Database (Denmark)

    Paton, Chad

    2010-01-01

    Elemental fractionation effects during analysis are the most significant impediment to obtaining precise and accurate U-Pb ages by laser ablation ICPMS. Several methods have been proposed to minimize the degree of downhole fractionation, typically by rastering or limiting acquisition to relativel...

  4. Crete and the Minoan Terranes: Age constraints from U-Pb dating of detrital zircons

    Czech Academy of Sciences Publication Activity Database

    Zulauf, G.; Romano, S. S.; Dörr, W.; Fiala, Jiří

    Colorado : Boulder, 2007 - (Linnemann, U.), s. 401-411 ISBN 978-0-8137-2423-2. - (Special papers- Geological Society of America . 423) Institutional research plan: CEZ:AV0Z30130516 Keywords : Crete * Minoan terranes * peri-Gondwanan terranes * U-Pb-TIMS * Gondwana * detrital zircons Subject RIV: DB - Geology ; Mineralogy

  5. U-Pb geochronology of Carajas metallogenic province, Para, Brazil: preliminary results

    International Nuclear Information System (INIS)

    The region of Carajas is located in the eastern Guapore craton, south of the Amazon river, in the south of the state of Para. A program of U-Pb geochronology was recently started and the first progress report, bearing on the ages of seven of the main units, is presented here. (author)

  6. Precise U-Pb Zircon Dating of the Syenite Phase from the Ditrau Alkaline Igneous Complex

    Directory of Open Access Journals (Sweden)

    Pană Dinu

    2000-04-01

    Full Text Available The Ditrău igneous complex represents the largest alkaline intrusion in the Carpathian-Pannonian region consisting of a plethora of rock types formed by complicated magmatic and metasomatic processes. A detailed U-Pb zircon age study is currently underway and the results for the syenite intrusion phase is reported herein. The U-Pb zircon emplacement age of the syenite of 229.6 +1.7/-1.2 Ma documents the quasi-contemporaneous production and emplacement of the gabbro and syenite magmas. We suggest that the syenite and associated granite formed by crustal melting during the emplacement of the mantle derived gabbroic magma around 230 Ma. The thermal contact aureole produced by the Ditrău alkaline igneous complex constrains the main tectonism recorded by surrounding metamorphic lithotectonic assemblages to be pre-Ladinian.

  7. SHRIMP U-Pb dating of zircon from the Xugou UHP eclogite, Sulu terrane, eastern China

    Science.gov (United States)

    Zhao, R.; Liou, J.G.; Zhang, R.Y.; Wooden, J.L.

    2005-01-01

    Eclogites, together with garnet clinopyroxenites, occur as lenses within the Xugou garnet peridotite body in the southern Sulu ultrahigh-pressure (UHP) terrane. Combined cathodoluminescence (CL) imaging and SHRIMP U-Pb dating of zircon from two Xugou mafic eclogites provide added constraints on the timing of UHP metamorphism in this area. Zircons from both samples show subrounded to rounded shapes and patchy CL patterns without inherited igneous cores, indicating that they are metamorphic zircons. SHRIMP U-Pb analyses of these zircons yielded apparent U-Pb ages of 214-280 Ma, with a weighted mean age of 237 ?? 8 Ma, which is consistent with previous reported UHP metamorphic ages from eclogite pods and country-rock gneisses. The Xugou mafic lenses may have formed by partial melting of the enclosing peridotites in the mantle before subduction (Zhang et al., 2003); then these eclogites, together with the host peridotites, were tectonically emplaced into the subduction zone and subjected to UHP metamorphism at 237 ?? 8 Ma. Copyright ?? 2005 by V. H. Winston & Son, Inc. All rights reserved.

  8. U-Pb dating by zircon dissolution method using chemical abrasion

    Energy Technology Data Exchange (ETDEWEB)

    Takehara, Lucy, E-mail: lucytakehara@gmail.com.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil); Chemale Junior, Farid [Universidade de Brasilia (UnB), Brasilia, DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia; Hartmann, Leo A. [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Inst. de Geociencias; Dussin, Ivo A.; Kawashita, Koji [Universidade de Sao Paulo (USP), SP, (Brazil). Centro de Pesquisa Geocronologicas

    2012-06-15

    Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-Multi Collector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3 +- 4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using {sup 235}U-{sup 205}Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7 +- 1.8 Ma (error 0.43 %) based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I - 416.75 +- 1.3 Ma; Temora II - 416.78 +- 0.33 Ma) and established as 416 +- 0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error < 1 %), mainly for high resolution stratigraphic studies of Phanerozoic sequences. (author)

  9. U-Pb dating by zircon dissolution method using chemical abrasion

    International Nuclear Information System (INIS)

    Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-Multi Collector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3 +- 4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using 235U-205Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7 +- 1.8 Ma (error 0.43 %) based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I - 416.75 +- 1.3 Ma; Temora II - 416.78 +- 0.33 Ma) and established as 416 +- 0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error < 1 %), mainly for high resolution stratigraphic studies of Phanerozoic sequences. (author)

  10. U-Pb Thermochronology of lower crustal xenoliths: creating a temporal record of lithosphere thermal evolution

    Science.gov (United States)

    Blackburn, T.; Bowring, S. A.; Schoene, B.; Dudas, F. O.; Mahan, K. H.

    2009-12-01

    Lower crustal xenoliths often contain U-bearing accessory minerals (titanite, apatite, rutile) with a range of closure temperatures for Pb-diffusion (~400-700 °C). These minerals record a time-temperature path which can be then be related to the thermal history of the underlying lithosphere mantle from igneous crystallization through multiple periods of metamorphism and thermal relaxation. In this study, we constrain the age and evolution of lithospheric thermal structure of Medicine Hat Block beneath Montana using geochronology, thermochronology, and thermal/diffusion modeling of lower crustal xenoliths. The cooling history of individual xenoliths is recorded by the Pb diffusion profiles within xenolithic rutile and titanite grains. Pb diffusion profiles can be inferred by making multiple measurements of grains with varying diffusion domain sizes (grain size). These analyses yield a dispersion in measured U-Pb dates that when plotted on a U-Pb Concordia diagram define a linear array. Xenoliths derived from depths between 20 and 30km have Proterozoic upper intercept dates and lower intercepts 700-900 Ma younger. This extreme discordance indicates a loss of equilibrium within the U-Pb system that could potentially be interpreted as the result of two different t-T paths: 1) reheating and 2) slow-cooling. To test the validity of each model, finite-difference approximations to the diffusion equation allow us to determine Pb diffusion profiles, and thus modeled U-Pb dates for any pre-assumed t-T path. Forward modeling of slow-cooling and reheating t-T paths reveals that each t-T path has a very unique data topology that allows us to distinguish between extreme examples of each case. This technique has been applied to accessory minerals from xenoliths from the Sweet Grass Hills, Montana where an Eocene minette that has exhumed lower crustal xenoliths from the Archean Medicine Hat Block. Rutile U-Pb thermochronologic analyses from three xenoliths that record metamorphic

  11. New Australopithecus robustus fossils and associated U-Pb dates from Cooper's Cave (Gauteng, South Africa).

    Science.gov (United States)

    de Ruiter, Darryl J; Pickering, Robyn; Steininger, Christine M; Kramers, Jan D; Hancox, Phillip J; Churchill, Steven E; Berger, Lee R; Backwell, Lucinda

    2009-05-01

    Australopithecus robustus is one of the best represented hominin taxa in Africa, with hundreds of specimens recovered from six fossil localities in the Bloubank Valley area of Gauteng Province, South Africa. However, precise geochronological ages are presently lacking for these fossil cave infills. In this paper, we provide a detailed geological background to a series of hominin fossils retrieved from the newly investigated deposit of Cooper's D (located partway between Sterkfontein and Kromdraai in the Bloubank Valley), including uranium-lead (U-Pb) ages for speleothem material associated with A. robustus. U-Pb dating of a basal speleothem underlying the entire deposit results in a maximum age of 1.526 (+/-0.088) Ma for Cooper's D. A second U-Pb date of ca. 1.4 Ma is produced from a flowstone layer above this basal speleothem; since this upper flowstone is not a capping flowstone, and fossiliferous sediments are preserved above this layer, some of the hominins might be slightly younger than the calculated age. As a result, we can broadly constrain the age of the hominins from Cooper's D to between 1.5 and approximately 1.4 Ma. Extinct fauna recorded in this comparatively young deposit raise the possibility that the Bloubank Valley region of South Africa represented a more stable environmental refugium for taxa relative to tectonically more active East Africa. The sediments of the deposit likely infilled rapidly during periods when arid conditions prevailed in the paleoenvironment, although it is unclear whether sediment deposition and bone deposition were necessarily contemporaneous occurrences. We reconstruct the paleoenvironment of Cooper's D as predominantly grassland, with nearby woodlands and a permanent water source. The hominin teeth recovered from Cooper's D are all from juveniles and can be confidently assigned to A. robustus. In addition, two juvenile mandibular fragments and an adult thoracic vertebra are tentatively attributed to A. robustus. PMID

  12. Discursos polémicos sobre el derecho a la identidad de género en menores de edad: análisis de los debates parlamentarios de la Ley de Identidad de Género (Argentina, 2011

    Directory of Open Access Journals (Sweden)

    Anahí Farji Neer

    2016-01-01

    Full Text Available [es] En el presente trabajo se analizan los discursos polémicos que circularon durante el debate parlamentario de la Ley de Identidad de Género (Ley 26.743. El corpus de estudio está constituido por las transcripciones taquigráficas que las discusiones parlamentarias desarrolladas en la Cámara de Diputados del Congreso Nacional argentino del día 30 de Noviembre del año 2011. Se abordan una selección de alocuciones que versaron sobre aquellos aspectos de la Ley que afectan a los menores de edad (artículos N° 5 y N° 11. Para el análisis utilizamos las herramientas teóricas ofrecidas por la corriente francesa de análisis del discurso sobre el “discurso polémico” o “argumentación dialogada”. El artículo se propone al estudio de los debates públicos contemporáneos en torno a la identidad de género, la autonomía de decisión sobre el propio cuerpo y el acceso a las tecnologías médicas de transformación corporal. El análisis realizado permitió dar cuenta que el debate en torno del derecho a la identidad de género en menores de edad estuvo atravesado por una disputa simbólica sobre el modo de entender las intervenciones quirúrgicas que la Ley legaliza. [en] The aim of this paper is to analyze the polemical discourses developed during the parliamentary debate that ended with the enactment of the Gender Identity Law (Law 26,743. The study consists of an analysis of verbatim transcripts of parliamentary discussions held in the Chamber of Deputies of the Argentine National Congress on November 2011. A selection of speeches focused on those articles of the Law involving minors is analyzed. Particularly, discussions referred to articles No. 5 and No. 11. We employ theoretical and methodological tools offered by the French discourse theory centered on the problem of “controversial speech” or “dialogic argumentation”. This paper aims to collaborate to the study of contemporary public debates concerning the issues of

  13. A Zircon U-Pb Study of the Evolution of Lunar KREEP

    Science.gov (United States)

    Meyer, Charles; Nemchin, A.; Pidgeon, R.; Whitehouse, M.; Vaughan, J.

    2007-01-01

    SIMS U-Pb analyses show that zircons from breccias from Apollo 14 and Apollo 17 have essentially identical age distributions in the range 4350 to 4200 Ma but, whereas Apollo 14 zircons additionally show ages from 4200 to 3900 Ma, the Apollo 17 samples have no zircons with ages <4200 Ma. The zircon results also show an uneven distribution with distinct peaks of magmatic activity. In explaining these observations we propose that periodic episodes of KREEP magmatism were generated from a primary reservoir of KREEP magma, which contracted over time towards the centre of Procellarum KREEP terrane.

  14. The U-Pb age of the Posselandia Diorite, Hidrolina, Goias State, Brazil

    International Nuclear Information System (INIS)

    The Posselandia Diorite intrudes Archean granite-greenstone terrains of the region of Hidrolina, Central Goias, Brazil. U-Pb radiometric determinations in two fractions of zircon crystals from the diorite yield an age of 2,146 ± 1,6 Ma, interpreted as the crystallization age of the intrusion. The lack of deformation in the intrusion demonstrates that consolidation of the granite-greenstone terrains in the Hidrolina-Pilar de Goias-Crixas area took place before 2,146 Ma. (author). 3 figs., 2 tabs

  15. Prostate cancer mortality trends in Argentina 1986-2006: an age-period-cohort and joinpoint analysis Tendencias en la mortalidad por cáncer de próstata en Argentina 1986-2006: análisis joinpoint y de edad-período-cohorte

    OpenAIRE

    Camila Niclis; Sonia A. Pou; Rubén H. Bengió; Alberto R. Osella; María del Pilar Díaz

    2011-01-01

    The aim of this study was to give an overview of the magnitude, variation by age and time trends in the rates of prostate cancer mortality in Córdoba province and in Argentina as a whole from 1986 to 2006. Mortality data were provided by the Córdoba Ministry of Health and the World Health Organization cancer mortality database. Prostate cancer mortality time trends were analyzed using joinpoint analysis and age-period-cohort models. In Argentina prostate cancer age-standardized mortality rate...

  16. The age and origin of some Norwegian eclogites: a U-Pb ziron and REE study

    International Nuclear Information System (INIS)

    U-Pb zircon data from five different eclogites and one amphibolite, all occurring as boudinaged lenses within the 1.7-Ga old Basal Gneisses of western Norway, are reported along with eleven REE patterns on eclogites, amphibolite and country rocks. Based on the size, morphology and zoning patterns of zircon as well as the degree of U-Pb discordance, protoliths of both basaltic or gabbroic origin can be distinguished. Whereas zircons from eclogites formed from tholeiitic and calc-alkaline basaltic protoliths allow dating of the Caledonian eclogite-facies event at approx. 400 Ma, no precise information on their primary magnetic age is possible. On the other hand, eclogites formed from gabbroic precursors allowed the dating of both the primary magnetic age at approx. 1.5 Ga, and in one case at more than 1.76 Ga, as well as a Caledonian eclogitization. One amphibolite sample, probably of prograde metamorphic origin, yielded a Sveconorwegian primary age (approx. 950 Ma) and a Caledonian age of metamorphism. (Auth.)

  17. Late cenozoic magmatism in the South Patagonian batholith: SHRIMP U-Pb zircon age evidence

    International Nuclear Information System (INIS)

    The North Patagonian Batholith (NPB) has a zonal age pattern which includes a well defined belt of Miocene and Mio-Pliocene plutons in its central portion (Pankhurst et al., 1999) which are spatially, and probably genetically related to the Liquine-Ofqui Fault Zone. Previous geochronological studies in the Southern Patagonian Batholith (SPB), as summarized by Bruce et al. (1991), have yielded 9 late Cenozoic K-Ar or Ar-Ar ages out of a total of 116 age determinations. None of these young ages correspond to U-Pb determinations on zircons, and some of the young ages correspond to satellite plutons east of the SPB proper, such as the Torres del Paine intrusion. In this paper we present the first late Cenozoic SHRIMP U-Pb zircon ages in the area of the SPB. The morphology of the analysed zircon crystals is described and leads to some inferences on the methodology and on the geological interpretation of the obtained ages (au)

  18. U-Pb (Zircon Ages of Metavolcanic Rocks From the Itaiacoca Group: Tectonic Implications

    Directory of Open Access Journals (Sweden)

    Oswaldo Siga Jr.

    2003-08-01

    Full Text Available The main aim of this work is to present and discuss the U-Pb ages obtained for zircon grains from metavolcanic rocks of theItaiacoca Group. The Itaiacoca Group is a metavolcano-sedimentary sequence, which occurs as a narrow belt between theCunhaporanga granitic batholith to the northwest and the Itapirapuã shear zone to the south and southwest, which separates thesequence from the Três Córregos granite batholith and metasedimentary rocks of the Açungui Group. Geological studies of thesouthern part of the Itaiacoca belt led to the recognition of three units, represented (from base to top by metawackes with animportant volcanic component, metacarbonate, and metapelitic and metapsammitic rocks. The U-Pb geochronological analyses ofzircon grains from two outcrops of metavolcanic rocks yield ages of 628 ± 18 Ma (SHRIMP and 636 ± 30 Ma (conventional multigrainanalyses. These ages are quite close to the metamorphic event recorded in the Itaiacoca Group (628 – 610 Ma, suggesting ashort interval between the formation of these rocks and closure of the basin. Furthermore, this volcanism is very close to the age offormation of the Três Córregos (630 Ma and Cunhaporanga (590 Ma granitic batholiths, admitted as associated with a probablemagmatic arc. Such an isotopic pattern characterizes a Neoproterozoic tectonic scenario involving volcanism, metamorphism andgranitic plutonism, interpreted here as the final stages in the evolution of the Itaiacoca Basin.

  19. U-Pb ages of meta volcanic rocks from the Itaiacoca group: tectonic implications

    Energy Technology Data Exchange (ETDEWEB)

    Siga Junior, Oswaldo; Basei, Miguel Angelo Stipp [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica]. E-mail: osigajr@usp.br; Sato, Kei; Passarelli, Claudia Regina [Sao Paulo Univ., SP (Brazil). Centro de Pesquisas Geocronologicas; Prazeres Filho, Helcio Jose dos; Cury, Leonardo Fadel; Weber, Werner; Harara, Ossama Mohamed [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Programa de Pos-graduacao em Geoquimica e Geotectonica; Reis Neto, Jose Manoel dos [Parana Univ., (UFPR), Curitiba (Brazil). Dept. de Geologia

    2003-08-15

    The main aim of this work is to present and discuss the U-Pb ages obtained for zircon grains metavolcanic rocks of the Itaiacoca Group. The Itaiacoca Group is a metavolcano-sedimentary sequence, which occurs as a narrow belt between the Cunhaporanga granitic batholith to the northwest and the Itapirapua shear zone to the south and southwest, which separates the sequence from the Tres Corregos granite batholith and meta sedimentary rocks of the Acungui Group. Geological studies of the southern part of the Itaiacoca belt led to the recognition of three units, represented (from base to top) by metawackes with an important volcanic component, metacarbonate, and metapelitic and metapsammitic rocks. The U-Pb geochronological analyses of zircon grains from two outcrops of metavolcanic rocks yield ages of 628 +- 18 Ma (SHRIMP) and 636 +- 30 Ma (conventional multigrain analyses). These ages are quite close to the metamorphic event recorded in the Itaiacoca Group (628-610 Ma), suggesting a short interval between the formation of these rocks and closure of the basin. Furthermore, this volcanism is very close to the age of formation of the Tres Corregos (630 Ma) and Cunhaporanga (590 Ma) granitic batholiths, admitted as associated with a probable magmatic arc. Such an isotopic pattern characterizes a Neoproterozoic tectonic scenario involving volcanism, metamorphism and granitic plutonism, interpreted here as the final stages in the evolution of the Itaiacoca Basin. (author)

  20. Isotope dating of alkaline rocks from the Urals using U-Pb zircon data

    International Nuclear Information System (INIS)

    Uranium-lead isotope-geochronologic studying of zircons from miaskites and carbonatites of the ilmenorock-wischnevorock complex is carried out by methods and low-background analysis technique. A tendency to inverse relationship between the degree of U-Pb-dating discordanticity and uranium concentration in a sample. The point positions in discordanticity correlate with morphological zircon peculiarities. The two-stage history of zircon (crystallization-metamorphism) and the model of its U-Pb system, in which is assumed to be U, Th and radiogenic Pb concentrations in microinclusions of Th-U-mineral in zircon are based. Synchronism of events in miaskite and carbonatite history is shown. Rock metamorphization accompanied by Pbrad loss is dated by concordia in 261 ± 14 and 261 ± 6 for miaskite and carbonatites. The age of zircon crystallization is determined 422 ± 10 and 432 ± 12 mln years correspondingly. Pre-folded (Ordovician) age of alkaline rocks of the Urals and manifestation of their metamorphism in the Variscian epoch of regional folding is based

  1. Geology and U-Pb geochronology of the Banabuiu granite, Northeastern Ceara, Brazil; Geologia y geocronologia U-Pb del granito de Banabuiu, Noreste de Ceara, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Lima, M. N.; Nogueira Neto, J. A.; Azevedo, M. R.; Valle Aguado,

    2010-07-01

    The Banabuiu massif crops out in the Central Ceara Domain (DCC) of the Borborema Province (NE Brasil), as an N-S elongate granite intrusion, concordant with the regional structures. It was emplaced into basement rocks of Paleoproterozoic age, extensively transformed into gneisses and migmatites during the Brasilian orogeny ({approx}600 Ma). Using U-Pb zircon dating, the crystallization age of the Banabuiu syn-kinematic two-mica granite was estimated at 578.6 {+-} 6.5 Ma. The granite is strongly peraluminous (A/CNK 1,098 - 1,134) and shows a typical S-type geochemical signature. The {epsilon}Nd{sub 5}80 values are strongly negative ({epsilon}Nd{sub 5}80 = -19 a - 23) and partially overlap with those of the Paleoproterozoic gneissmigmatite complex ({epsilon}Nd{sub 5}80 = -12 to -26), suggesting that the parental magmas of the Banabuiu granite could have been produced by partial melting of similar crustal materials. (Author) 21 refs.

  2. Emeishan volcanism and the end-Guadalupian extinction: New U-Pb TIMS ages

    Science.gov (United States)

    Mundil, Roland; Denyszyn, Steve; He, Bin; Metcalfe, Ian; Yigang, Xu

    2010-05-01

    High-resolution geochronology with an age resolution at the permil level is instrumental in testing proposed causal links between continental-scale, short-term volcanic events and environmental crises that affect life globally. Synchroneity with large-scale volcanic events has been shown for three of the five most severe extinctions, namely the end-Permian extinction coinciding with Siberian Trapp volcanism, the end-Triassic extinction with Central Atlantic Magmatic Province) volcanism and the end-Cretaceous with Deccan Trapp volcanism. Recent studies also show that the magnitude of the extinction is not solely a function of the size (volume) of the volcanic event but more importantly of the eruption rate and also the nature of the host rock that is intruded, and the resulting reactions and release of gases that can affect climate. The end-Guadalupian (end Middle Permian, ca 260 Ma) biotic crisis has traditionally not been included in the 'big five' mass extinctions, possibly because of its close proximity in time to the end-Permian event, although its magnitude (in terms of total extinction rate) is comparable to the three most severe extinctions (end-Ordovician, end-Permian, end-Cretaceous). As a result, research of the end-Guadalupian event has so far been neglected and its timing as well as the temporal relation to the Emeishan volcanic province in western China is as yet not fully studied. Geochronological data are so far mostly based on ambiguous 40Ar/39Ar analyses of commonly altered basaltic products and U-Pb zircon analyses on felsic products using micro-beam techniques that typically result in radio-isotopic ages with percent-level uncertainty, and thus insufficient for high-resolution correlations of events. In addition, no precise and accurate radio-isotopic data exist from this time period so that evolutionary events (extinction and recovery) on land and in the ocean are notoriously difficult to correlate though biostratigraphic records are available

  3. Ion microprobe U-Pb dating and strontium isotope analysis of biogenic apatite

    Science.gov (United States)

    Sano, Y.; Toyoshima, K.; Takahata, N.; Shirai, K.

    2012-12-01

    Conodonts are micro-fossils chemically composed of apatite which occurred in the body of one animal. They are guide fossils to show formation ages of sedimentary sequences with the highest resolution [1] and good samples to verify the dating method. We developed the ion microprobe U-Pb dating of apatite [2] and applied the method to a Carboniferous conodont [3] by using a SHRIMP II installed at Department of Earth and Planetary Sciences, Hiroshima University. Recently we have developed the NanoSIMS U-Pb dating method and successfully measured the formation ages of monazite [4] and zircon [5] at Atmosphere and Ocean Research Institute, University of Tokyo. In this work we carried out the NanoSIMS U-Pb dating of biogenic apatite such as conodont. Since the spot size of NanoSIMS is smaller than SHRIMP II, it is easier to have multi-spots on the single fragment of biogenic apatite. Based on the isochron method of U-Pb system, we have calculated the formation ages. They are consistent with those in literature. In order to study the chemical evolution of ocean during the past 600 Million years, strontium isotopes (87Sr/86Sr) of fossil marine carbonate such as coral skeletons and foraminifera tests were measured and compiled [6]. However they are not robust when the age is older than 500Ma, partly due to post-depositional histories. Apatite is more stable and more resistant to the alteration than carbonate [7]. Recently we have developed the method of NanoSIMS strontium isotopic analysis of a fish otolith, which composed of aragonite [8]. In this work we carried out the strontium isotopic analysis of biogenic apatite. The advantage of the ion microprobe technique over the TIMS (thermal ionization mass spectrometer) and MC-ICP-MS (multi-collector inductively coupled argon plasma mass spectrometer) method is preservation of the important textural context and to provide an opportunity for other simultaneous analytical work with high spatial resolution. This is the case for

  4. A feasibility study of U-Pb and Pb-Pb dating of kimberlites using groundmass mineral fractions and whole-rock samples

    International Nuclear Information System (INIS)

    This paper describes partly successful attempts to determine emplacement ages of kimberlites by U-Pb and Pb-Pb methods involving groundmass minerals with high U content (notably perovskite) and whole-rock kimberlite samples. U/Pb ratios in perovskite in the matrix of kimberlites can be two orders of magnitude larger than in the rest of the kimberlite material, and with simple mineral separation techniques moderate success was achieved in U-Pb dating of fresh samples of younger kimberlites (around 100 Ma). The differences in U/Pb ratios between kimberlite samples from different parts of the same pipe have also been found to be large enough, in some cases, to allow reasonably accurate U-Pb age determination. In older kimberlites the U-Pb ages obtained were mostly imcompatible with geological constraints and results obtained by other methods. However, for such pipes use of Pb-Pb systematics yields realistic age limits in some cases

  5. El basamento cristalino de los Andes norpatagónicos en Argentina: geocronología e interpretación tectónica The Crystalline Basement in the Argentinian North-Patagonian Andes: geochronology and tectonic interpretation

    Directory of Open Access Journals (Sweden)

    Ricardo Varela

    2005-07-01

    Full Text Available Se presentan los resultados obtenidos en el estudio isotópico de rocas del basamento ígneo-metamórfico de los Andes expuesto en Argentina, aproximadamente a los 40°S, en las provincias de Neuquén y Río Negro. Fueron utilizadas metodologías isotópicas, para obtener información sobre la edad de emplazamiento de cuerpos ígneos deformados dúctilmente (U-Pb en circones, tiempo de enfriamiento luego de los procesos ígneos y metamórficos que modelaron a este basamento (K-Ar en micas; U-Pb en titanita y la historia cortical involucrada (Sm-Nd en roca total. No se obtuvieron edades proterozoicas, como lo sugerían anteriores determinaciones Rb-Sr y K-Ar. Los datos definen en la región dos eventos ígneo metamórficos. El más antiguo, conservado en tonalitas y granitos deformados de los alrededores de San Martín de los Andes, tiene edades U-Pb en circones de 420 a 380 Ma (Devónico y edades K-Ar en micas de 375 a 310 Ma. El más joven está bien representado en los afloramientos al sur del Río Limay, desde Paso Flores a Río Chico-Cushamen y tiene edades U-Pb en circones de rocas metaígneas en torno a 280 Ma (Pérmico inferior y edades de enfriamiento en micas próximas a 260-250 Ma. Ambos conjuntos se generaron en ambiente de arco magmático y denotan la acción de dos episodios principales separados por ca. 100 Ma, posibles de relacionar con los Movimientos Chánicos y Gondwánicos, respectivamente. Las edades modelo Sm-Nd T DM, con valores entre 1907 y 1165 Ma, eNd para el momento de cristalización de las rocas de preferencia entre -3,0 y -8,4 y e Nd(0 preferentemente entre -6,9 a -11,9 sugieren reciclado de corteza proterozoica con escasa adición de corteza juvenil durante el PaleozoicoIsotopic data are presented for rocks of the Andean crystalline basement at 40°S, in Neuquén and Río Negro provinces. The methods used were U-Pb in zircon (crystallization ages of plutonic rocks, K-Ar in micas and U-Pb in titanite (metamorphism

  6. Augen gneisses versus Augen gneisses from the Jaguaribeana Belt, northeastern region from Brazil: stratigraphy, geochemistry and U-Pb ages; Augen gnaisses versus Augen gnaisses da faixa Jaguaribeana, NE do Brasil: estratigrafia, geoquimica e idades U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Sa, Jaziel Martins; Silva, Elvis Roberto da [Rio Grande do Norte Univ., Natal, RN (Brazil). Dept. de Geologia; Bertrand, Jean Michel [Savoie Univ., 73 - Chambery (France). Lab. de Geodynamique; Leterrier, Jacques [Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques

    1997-12-31

    The Jaguaribeana Belt is located at Borborema Province, Ceara State, Brazil and this study aims to present Uranium-Lead (U-Pb) data and the augen gneisses petrographic and geochemical study of the Jaguaribe Belt, and to realize comparisons between these and the augen gneisses from the Oros Belt. It describes the geological characteristics of this region, the augen gneisses petrography and geochemical data and the U-Pb method results for a discussion about the augen gneisses from the Oros and Jaguaribe Belt 10 refs., 6 figs.

  7. U-Pb ages of Kude and Sajia leucogranites in Sajia dome from North Himalaya and their geological implications

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hongfei; Nigel Harris; Randy Parrish; ZHANG Li; ZHAO Zidan

    2004-01-01

    U-Pb ages of zircon, monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Himalayan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leucogranite are 27.5 ±0.5 and 14.4± 0.2 Ma, respectively. Combined with published U-Pb data from the North Himalayan leucogranites, the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma, instead of previous 15 to 10 Ma. According to the U-Pb ages, the petrogenesis for the North Himalayan leucogranites can be constrained. It is suggested that the North Himalayan leucogranites have variety in their petrogenesis.

  8. U-Pb ages of detrital zircon from Pegasus Group, Stewart Island

    International Nuclear Information System (INIS)

    Stewart Island (New Zealand) is relatively unaffected by Cenozoic deformation related to the present-day plate boundary and has thus been a locale of investigations that focus on the relationship between Mesozoic continental margin magmatic rocks and the Western Province (WP) of NZ. Pegasus Group metasedimentary rocks represent the only candidate for WP equivalents on Stewart Island. We measured U-Pb and 207Pb / 206Pb ages of detrital zircons from the Pegasus Group in an effort to validate the correlation with the WP. On SI, Pegasus Group is exposed over a small area in the southern Tin Range where it forms amphibolite facies roof pendants and screens among plutons of mid Paleozoic to mid Cretaceous age. Mica schists predominate, with lesser amounts of psammite and metaquartzite and rare calcareous schist and amphibolite. Zircons were extracted from metaquarzite and 24 grains were chosen on the basis of morphology for geochronologic investigation. Sixteen single crystals were dated by U-Pb TIMS; 8 additional grains were studied by the total evaporation method described by Kober. Despite vigorous air abrasion prior to processing, the 16 grains measured by conventional U-Pb TIMS yielded slightly normally discordant ages that we interpret to reflect minor Pb-loss. The 8 grains studied by the total evaporation method yielded more than four analytically identical /sup 207Pb / 206Pb ages within each grain at progressively higher temperatures (1515-1580 degrees C) of evaporation. The results permit the following general conclusions: 1) the age range of 420-2700 Ma is grossly similar to that reported from the Greenland Group/Victoria Paragneiss (Ireland 1992) of the Buller Terrane, WP; 2) the zircon population is dominantly 530-680 Ma but a subsidiary population is 900-1100 Ma; 3) no zircons with ages that match the timing of the Ross Orogen (530-480 Ma) were identified; 4) two grains of 420 Ma and a 453 Ma are probably too young for the paleontogically-known Ordovician

  9. Petrogenesis and Zircon U-Pb radiometric dating in Herris granite (NW Shabestar) East Azarbaijan Province

    International Nuclear Information System (INIS)

    Heris intrusive body has cut Kahar Formation and has been covered by Permian basal sediments, non-conformably. The composition of this body is granite- alkali granite with meta luminous to weak peraluminous nature. The strong negative anomaly of Eu in REE diagram indicates the presence of plagioclase in the source area or differentiation of it during evolution of the magma. Negative anomaly of Ba and enrichment of Rb and Th relative to Ta and Nb is an indicator of crustal origin. These granites are within-plate and A-type granites, which have been formed by partial melting of tonalitic- granodioritic source in extensional setting. Zircon U-Pb dating yields 306±34 Ma for crystallization of these rocks. This age is consistent with primary extensions of rifting in Arabian- Iranian platform.

  10. Petrology and U-Pb geochronology of buried Avalonian plutonic rocks on southeastern Cape Cod

    Science.gov (United States)

    Leo, G.W.; Mortensen, J.K.; Barreiro, B.; Phillips, J.D.

    1993-01-01

    Plutonic rocks have been intersected by two separate drill holes on souteastern Cape Cod. Hole CC2 is located about 7 km south of the Nauset anomaly, an east-northeast-trending magnetic lineament that was considered to separate the distinct plutonic zones of Avalon terrane. This drill hole intersected weakly foliated, fairly homogeneous biotite granite. Zircons from this granite give a U-Pb age of 584+9/-8 Ma. Hole CC1 is located about 12 km north of the Nauset anomaly. The drill core intersected foliated, sheared, biotite granodiorite and biotite-hornblende-clinopyroxene-quartz gabbro, metamorphosed to greenschist facies. The deformed and altered state of these rocks, as well as their geochemistry, suggest that their origin and possibly their ages are distinct from the granite in hole CC2. No datable zircons were obtained from rocks in CC1. -from Authors

  11. Ion microprobe U-Pb dating and REE abundance of biogenic apatite

    Science.gov (United States)

    Sano, Y.; Terada, K.; Ueki, S.

    2001-12-01

    If the direct U-Pb dating of a fossil itself is possible, the method could have great impact on stratigraphic studies in establishing the absolute chronology of sedimentary sequences. Micro fossil ?conodont? are candidates for this purpose since they consist of apatite (Ca2(PO5)3 (F,Cl,OH)), which would uptake U, Th and Pb after sedimentation no longer than a few million years and is supposed to remain closed to U and Pb under relatively low effective closure temperature. We report here results of direct ion microprobe U-Th-Pb dating of two conodonts; Trichognathus from Kinderhookian stage of Mississippian sedimentary sequence from Illinois Basin region in North America and Panderodus from a Llandoverian sedimentary sequence on Langkawi Island, northern Malaysia. Secondary purpose of the study is to indicate in situ analysis of all REE on the same spots of U-Pb measurements. Samples were cast into epoxy resin discs with a few grains of standard apatite, PRAP, derived from an alkaline rock of Prairie Lake circular complex in the Canadian Shield and polished until they were exposed through their mid-sections. U, Th and REE abundances, and Pb isotopic compositions were measured by using SHRIMP installed at Hiroshima University. Thirteen spots on Trichognathus yield a 238U/206Pb isochron age of 323+/-36 Ma, which is consistent with the depositional and early diagenetic ages. Fifteen spots on Panderodus give 232Th/208Pb isochron age of 429+/-50 Ma, which is again comparable to an early Silurian. Shale-normalized REE of Trichognathus shows a broadly flat pattern from light to middle REE and a decrease from middle to heavy REE with negative anomalies of Ce and Eu. In contrast Panderodus indicates a concave-shape pattern with middle REE enrichment. These characteristics are probably due to a different formation environment as suggested by other workers.

  12. U-Pb geochronology of Gangdese (Transhimalaya) plutonism in the Lhasa-Xigaze region, Tibet

    International Nuclear Information System (INIS)

    A series of different plutons from the Lhasa-Xigaze segment of the Gangdese (Transhimalaya) belt has been studied by high-resolution U-Pb analyses of zircon (using zircon fractions of 5-100 grains each, selected upon specific grain characteristics). For two diorites, located east of Xigaze (Dazhuka), the zircons yield concordant ages of 93.4 +- 1.0 and 94.2 +- 1.0 m.y., respectively. Also concordant ages of 41.1 +- 0.4 and 41.7 +- 0.4 m.y. have been obtained for two granodiorites, collected southwest of Lhasa (Qushui). The precision on the ages of two granites from the Xigaze and Lhasa area, is limited by two factors: the presence of inherited radiogenic lead and the occurrence of subsequent lead loss. However, some concordant zircons, detected in both granites, define approximate ages of about 67 and 53 m.y., respectively. The inherited lead components show the melting of Precambrian material was involved in magma genesis. The U-Pb ages substantiate a magmatic activity lasting from mid-Cretaceous (Cenomanian) to Eocene (Lutetian) time. Such a period of plutonism at the southern margin of Eurasia, as well as the occurrence of magma generation from continental crust, suggest that the Gangdese range results from the subduction of Tethys oceanic lithosphere (Indian plate) underneath Eurasia (Eurasian plate). If this model is true, the collision of India with Eurasia (Along the Lhasa-Xigaze sector) postdates the emplacement of the 41 m.y. old Gangdese granodiorites, i.e. the collision occurred after Lutetian time. (orig.)

  13. Zircon U-Pb ages and geochemical characteristics of granitoids in Nagqu area, Tibet

    Science.gov (United States)

    Sun, Sai-Jun; Sun, Wei-Dong; Zhang, Li-Peng; Zhang, Rong-Qing; Li, Cong-Ying; Zhang, Hong; Hu, Yong-Bin; Zhang, Zhao-Rong

    2015-08-01

    This paper reports zircon LA-ICP-MS U-Pb ages and Hf-O isotopic ratios, and whole-rock major and trace element data of Early Cretaceous felsic intrusive rocks from Nagqu area, the northern Lhasa subterrane, southern Tibet. LA-ICP-MS zircon U-Pb dating of biotite granites and biotite monzogranites in the area yields magmatic crystallization ages of ca. 112 Ma, which suggests that they were emplaced in the late Early Cretaceous. Both rocks show high-K calc-alkaline to shoshonitic composition and slightly-moderately peraluminous signature. They are enriched in the alkalis, Rb, Th, K, U and light rare earth elements, depleted in Nb, Ta, Ti and P, and characterized by high Al2O3 contents (12-16 wt.%), high Rb/Sr ratios (1.3-33) and low Mg# values (15-39). Their magmatic zircons have negative εHf(t) values (from - 25.9 to 0.5) and high positive δ18O values (from 7.9‰ to 11.5‰). All the above characteristics indicate that Nagqu biotite monzogranites and biotite granites were likely derived from hybrid melts of sediments from the continent crust with minor mantle-derived input, then experienced varied degrees of fractional crystallization. The Nagqu intrusion is a component of the late Early Cretaceous magmatic flare-up event that occurred during ~ 120-100 Ma in the northern and partly central Lhasa subterranes. This magmatic flare-up is marked with a great compositional diversity (basalt, rhyolite, adakitic rocks, dioritic enclave, biotite monzogranite and granite) that might be caused by the slab breakoff of the southward subducting Bangong-Nujiang oceanic lithosphere, or more likely by slab window opening, which may have significantly contributed to juvenile crustal growth of the northern Lhasa subterrane.

  14. New U-Pb zircon ages and the duration and division of Devonian time

    Science.gov (United States)

    Tucker, R.D.; Bradley, D.C.; Ver Straeten, C.A.; Harris, A.G.; Ebert, J.R.; McCutcheon, S.R.

    1998-01-01

    Newly determined U-Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: 1) 417.6 ?? 1.0 Ma for an ash within the conodont zone of Icriodus woschmidti/I. w. hesperius Lochkovian); 2) 408.3 ?? 1.9 Ma for an ash of early Emsian age correlated with the conodont zones of Po. dehiscens--Lower Po. inversus; 3) 391.4 ?? 1.8 Ma for an ash within the Po. c. costatus Zone and probably within the upper half of the zone (Eifelian); and 4) 381.1 ?? 1.3 Ma for an ash within the range of the Frasnian conodont Palmatolepis punctata (Pa. punctata Zone to Upper Pa. hassi Zone). U-Pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites-lepidophyta spore zone, are dated at 363.8 ?? 2.2 Ma and 363 ?? 2.2 Ma and 363.4 ?? 1.8 Ma, respectively, suggesting an age of ~363 Ma for a level within the late Famennian Pa. g. expansa Zone. These data, together with other published zircon ages, suggest that the base and top of the Devonian lie close to 418 Ma and 362 Ma, respectively, thus lengthening the period of ~20% over current estimates. We suggest that the duration of the Middle Devonian (Eifelian and Givitian) is rather brief, perhaps no longer than 11.5 Myr (394 Ma-382.5 Ma), and that the Emsian and Famennian are the longest stages in the period with estimated durations of ~15.5 Myr and 14.5 Myr, respectively.

  15. SHRIMP U-Pb zircon dating of Pedras Grandes Suite, southern Santa Catarina State, Brazil

    Directory of Open Access Journals (Sweden)

    Andréa R. Jelinek

    2005-03-01

    Full Text Available Two major magmatic pulses of the granitic Florianópolis Batholith in Santa Catarina State, southern Brazil, occurred between 613±5Ma and 595±5 Ma, during the Neoproterozoic Brasiliano Cycle. These ages were obtained by U-Pb isotopic determinations with the sensitive high mass-resolution ion microprobe on igneous zircons from Pedras Grandes Suite in Santa Catarina State. Euhedral zircons remained unaltered close to a fluorite vein deposited at 180?C or more. These ages suggest a northern limit for the Pedras Grandes Suite, explaining the spatial relationship between the fluorite veins and the source rock.Dois dos principais pulsos da atividade granítica no Batólito Florianópolis em Santa Catarina ocorreram entre 613 ±5 Ma e 595 ±5 Ma, durante o Neoproterozóico do Ciclo Brasiliano. Estas idades foram obtidas a partir dedeterminações isotópicas U-Pb em cristais de zircão da Suite Pedras Grandes por "Sensitive high-resolution íon microprobe" - SHRIMP II. Os cristais de zircão permaneceram inalterados mesmo mediante condições hidrotermais com temperaturas iguais e, até mesmo, superiores a 180ºC. Estas idades sugerem a delimitação norte do Maciço Pedras Grandes, explicando a relação espacial existente entre os filões de fluorita e a rocha fonte destas mineralizações.

  16. U-Pb dating by zircon dissolution method using chemical abrasion

    Directory of Open Access Journals (Sweden)

    Lucy Takehara

    2012-06-01

    Full Text Available Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-MultiCollector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3±4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using 235U-205Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7±1.8 Ma (error 0.43 % based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I – 416.75±1.3 Ma; Temora II – 416.78±0.33 Ma and established as 416±0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error Este trabalho apresenta a técnica de abrasão química em zircões do padrão Temora II aplicada em datação de U-Pb por Dissolução Isotópica e Espectrometria de Massa por Ionização Térmica, método DI-ESIT. O emprego deste método tem como princípio diminuir os efeitos da perda secundária de Pb radiogênico antes da dissolução. Em primeira instância, os zircões foram analisados pelo método in situ com uso de Microssonda Laser acoplada a um Espectrômetro de Massa Multicoletor com Plasma Acoplado Indutivamente (MC-ICP-MS, cujo objetivo foi identificar os grãos de zircão de fase de cristalização simples sem sobrecrescimento. Nove cristais de zircão analisados com microssonda a

  17. Garnet Sm-Nd and U-Pb systems: A case study of a granulite from the European Variscan belt

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    This study presents zircon and garnet ages of a mafic granulite from the high-grade Variscan basement of the Black Forest, Germany and discuss isotope closure temperature of garnet Sm-Nd and U-Pb systems. Zircon grains yield 207Pb/206Pb ages between ~340 and ~414 Ma by the U-Pb and evaporation methods. In contract, garnet dating gives Sm-Nd and Pb-Pb isochron ages of (398±3) Ma and (411±14) Ma, respectively, which are older than most of zircon ages. These data imply that most of zircons lost radiogenic Pb, probably due to metamictization or recrystallisation during the granulite-facies metamorphism (~800℃) at ~340 Ma. Garnet Sm-Nd and U-Pb systems preserve chronological information of pro-grade metamorphism, probably profiting from a fluid-absence metamorphic environment. These results demonstrate that garnet mineral can be a better candidate than zircon mineral to date high-grade metamorphism by the U-Pb and Sm-Nd methods in some cases.

  18. A new U/Pb date for the basal Meishucun section and implications for the age of the Cambrian explosion

    Science.gov (United States)

    Brooks, B. J.; Crowley, J. L.; Bowring, S. A.; Cervato, C.; Jin, Y.

    2006-12-01

    The Early Cambrian of southern China has long been recognized to record the spectacular transition from microscopic small shelly fossils to a fauna characterized by large, diverse higher bilaterians during part of the Early Cambrian evolutionary explosion. Understanding the timing and rate of this evolutionary transition has been aided through the integration of U/Pb geochronology into Cambrian fossil biozones, which has established strong tie-points between platforms. The Meishucun section (Yunnan, China) is one of the units that best preserves what could be considered the prelude to the Cambrian explosion. Several attempts at dating volcanic horizons within this section have resulted in U/Pb zircon dates that range from 538 to 525 Ma, making correlations to sections further afield problematic. This new high-precision U/Pb date of 533 Ma for Meishucun's Bed 5 is in broad agreement but considerably more precise than previous U/Pb ages. This indicates that the low diversity fauna of the Anabarites trisulcatus--Protohertzina anabarica zone persisted for no less than the first 9 m.y. of the Cambrian in China, and sets an additional lower bracket age for the emergence of higher bilaterians (e.g. trilobites, soft-bodied fauna).

  19. U-Pb dating of speleogenetic dolomite: A new sulfuric acid speleogenesis chronometer

    Directory of Open Access Journals (Sweden)

    Victor Polyak

    2016-05-01

    Full Text Available The 1100-meter Big Room elevation level of Carlsbad Cavern, New Mexico USA, formed 4 Ma by hypogenic sulfuric acid speleogenesis (SAS. The age of the Big Room level of 4.0 ± 0.2 Ma was previously determined by dating alunite, a byproduct of speleogenesis, using the 40Ar/39Ar method. Duplication of these results is possible by radiometric dating of other byproducts interpreted to be speleogenetic (a byproduct of speleogenesis such as calcite and dolomite in certain settings. XRD and TEM analyses of sample 94044, a piece of crust collected within the Big Room level of SAS just below Left Hand Tunnel indicate that this dolomite sample we interpret to be speleogenetic is as well-ordered crystallographically as the Permian bedrock dolomite, possibly reflecting its SAS origin. Three U-Pb analyses were performed on subsamples A1, A2, and A3 of sample 94044, and two, A1 & A2, produced out-of-secular equilibrium results due to the presence of authigenic quartz and/or later re-distribution of uranium in the dolomite crust, which prevented the calculation of an isochron age. Because subsample 94044-A3 exhibited δ234U and 230Th/238U values consistent with secular equilibrium, we were able to generate a 238U/204Pb-206Pb/204Pb model age of 4.1 ± 1.3 Ma on the dolomite crust (94044 that we interpret to be reliable. The 4.1 Ma age of the speleogenetic dolomite crust agrees with the 4 Ma 40Ar/39Ar age for the timing of speleogenesis of the Big Room level. While 40Ar/39Ar-dating of speleogenetic alunite- and jarosite-group minerals remains the primary way to determine absolute timing of hypogenic SAS, here we demonstrate that U-Pb dating of speleogenetic dolomite can be used to compliment or independently measure the timing of SAS. This method of dating SAS could be applicable in caves where the more soluble SAS-indicator minerals such as gypsum, alunite, and jarosite have been removed.

  20. Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuejun; SUN Chunlin; SUN Yuewu; SUN Wei

    2008-01-01

    Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area. Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China. Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning, a number of researchers have focused on Mesozoic volcanic events. The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb. The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age, the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma, the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma, respectively. Combined with the data of recent publication on volcanic rocks ages; the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods: 119 Ma, 113 Ma and 103 Ma. The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province, establishing Mesozoic volcanic event sequence, discussing geological tectonic background, and surveying the relation between noble metals to the Cretaceous volcanic rocks, but also otters important information of Mesozoic volcanism in northeastern China.

  1. Constraining the Flux of Impactors Postdating Heavy Bombardment Using U-Pb Ages of Impact Glasses

    Science.gov (United States)

    Nemchin, A. A.; Norman, M. L.; Ziegler, R. A.; Grange, M. L.

    2013-01-01

    Spherules of glass varying in size from a few micrometres to a few millimetres are common in the lunar regolith. While some of these glass beads are products of pyroclastic fire fountains others originate as impact melt ejected from the target that breaks into small droplets and solidifies as spherical particles while raining back to the lunar surface. These glasses preserve information about the chemical composition of the target and often contain sufficient amount of radioactive nuclides such as 40K to enable Ar-40-Ar-39 dating of individual beads. Studies measuring the age of glass beads have been used in attempts to establish variations in the flux of impactors hitting the Moon, particularly during the period that postdates the formation of major impact basins [1,2]. These studies proposed a possibility of spike in the impact flux about 800 Ma [2] and over the last 400 Ma [1]. More recently U-Th-Pb isotopic systems have been also utilized to determine the age of impact glasses from the Apollo 17 regolith [3]. Our aim is to extend the application of the U-Pb system in impact glasses to spherules isolated from Apollo 14 soil 14163 in an attempt to further investigate the applicability of this isotopic system to the chronology of impact glass beads and gain additional information on the impact flux in the inner Solar system.

  2. First SHRIMP U Pb zircon dating of granulites from the Kontum massif (Vietnam) and tectonothermal implications

    Science.gov (United States)

    Nam, Tran Ngoc; Sano, Yuji; Terada, Kentaro; Toriumi, Mitsuhiro; Van Quynh, Phan; Dung, Le Tien

    2001-02-01

    The Kontum massif in Central Vietnam represents the largest continuous exposure of crystalline basement of the Indochina craton. The central Kontum massif is chiefly made of orthopyroxene granulites (enderbite, charnockite) and associated rocks of the Kannack complex. Mineral assemblages and geothermobarometric studies have shown that the Kannack complex has severely metamorphosed under granulite facies corresponding to P-T conditions of 800-850°C and 8±1 kbars. Twenty-three SHRIMP II U-Pb analyses of eighteen zircon grains separated from a granulite sample of the Kannack complex yield ca 254 Ma, and one analysis gives ca 1400 Ma concordant age for a zoned zircon core. This result shows that granulites of the Kannack complex in the Kontum massif have formed from a high-grade granulite facies tectonothermal event of Indosinian age (Triassic). The cooling history and subsequent exhumation of the Kannack complex during Indosinian times ranged from ˜850°C at ca 254 Ma to ˜300°C at 242 Ma, with an average cooling rate of ˜45°C/Ma.

  3. Metamorphic zircon from Xindian eclogite, Dabie Terrain: U-Pb age and oxygen isotope composition

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Detailed CL image, U-Pb age and oxygen isotope composition in situ analyses for two metamorphic zircons from ultra-high pressure Xindian eclogite, Southern Dabie Terrain were carried out. There are two kinds of zircon in eclogite. The major subpopulation is podgy and isometric, and interpreted as protolith magmatic zircon with partial recrystallization. Its formation age is 811±22 Ma.The less abundant one is euhedral prismatic with core-rim structure and the rim being metamorphic overgrowth and formed at 221 -217 Ma. Zircon CL image strength is mainly controlled by U and Th contents. The magmatic zircon has its Th/U ratio around 1.3 and decreasing with recrystallization,whereas metamorphic zircon has Th/U ratio of lower than 0.1. Magmatic and metamorphic zircon domains all show very low oxygen isotopic compositions with average δ8O values of 1.8‰ and 2.8‰,respectively. The low δ18O values in protolith zircon indicated meteoric water involvement in their magma source region. It may correlate with snowball earth event during Neoproterozoic. It also indicates that protolith zircon could survive its oxygen isotope signature during Dabie eclogite facies UHP metamorphism.

  4. Discordance of the U Pb system in detrital zircons: Implication for provenance studies of sedimentary rocks

    Science.gov (United States)

    Nemchin, Alexander A.; Cawood, Peter A.

    2005-12-01

    Provenance studies involving U / Pb analysis of detrital zircons have become increasingly popular through the application of microanalytical techniques. Adopted one-dimensional methods for the presentation of detrital zircon data, such as probability density distribution plots, generally require various degrees of filtering of discordant analyses. However, a uniform approach for filtering does not exist, making comparison of data from different samples and sedimentary units, as well as different studies of detrital populations, extremely difficult. The problem is further complicated by the need to switch from 207Pb / 206Pb based ages to 206Pb / 238U ages when zircon populations within a sample show a range of ages from Archean to Proterozoic or even Phanerozoic. Ion probe analysis of multiple spots within a single zircon crystal and calculation of an internal isochron can potentially eliminate problems associated with discordance, but this is a time consuming approach. Comparison of internal isochron ages for zircons generated by multiple ion probe intra-grain zircon analyses from a sample of psammite within the Dalradian Supergroup of Scotland with a data set from the same sample based on single grain ion probe analysis using various filtering methods suggests good agreement between the two approaches particularly when filtering is based on the probability of concordance. However, when precise information is required, such as the age of the youngest zircon grains so as to accurately constrain the maximum depositional age of the strata, then multiple analyses of individual zircon grains may be required.

  5. Proterozoic tectonostratigraphy and paleogeography of central Madagascar derived from detrital zircon U-Pb age populations

    Science.gov (United States)

    Cox, R.; Coleman, D.S.; Chokel, C.B.; DeOreo, S.B.; Wooden, J.L.; Collins, A.S.; De Waele, B.; Kroner, A.

    2004-01-01

    Detrital zircon U-Pb ages determined by SHRIMP distinguish two clastic sequences among Proterozoic metasedimentary rocks from central Madagascar. The Itremo Group is older: zircon data, stromatolite characteristics, and carbon isotope data all point to a depositional age around 1500-1700 Ma. The Molo Group is younger, deposited between ???620 Ma (the age of the youngest zircon) and ???560 Ma (the age of metamorphic overgrowths on detrital cores). Geochronologic provenance analysis of the Itremo Group points to sources in East Africa as well as local sources in central and southern Madagascar but provides no evidence for a detrital contribution from northern and eastern Madagascar nor from southern India. Detrital zircon and sedimentologic similarities between rocks of the Itremo Group and the Zambian Muva Supergroup suggest a lithostratigraphic correlation between the two. The Molo Group has a strong 1000-1100 Ma detrital signature that also indicates an east African provenance and suggests a Neoproterozoic geographic connection with Sri Lanka but shows no indication of input from the Dharwar craton and eastern Madagascar. Central Madagascar was probably juxtaposed with the Tanzanian craton in the Paleo- and Mesoproterozoic, whereas northern and eastern Madagascar were connected to India. Internal assembly of Madagascar postdates Neoproterozoic Molo Group sedimentation and is likely to have occurred at about 560 Ma. ?? 2004 by The University of Chicago. All rights reserved.

  6. U-Pb zircon geochronology and evolution of some Adirondack meta-igneous rocks

    Science.gov (United States)

    Mclelland, J. M.

    1988-01-01

    An update was presented of the recent U-Pb isotope geochronology and models for evolution of some of the meta-igneous rocks of the Adirondacks, New York. Uranium-lead zircon data from charnockites and mangerites and on baddeleyite from anorthosite suggest that the emplacement of these rocks into a stable crust took place in the range 1160 to 1130 Ma. Granulite facies metamorphism was approximately 1050 Ma as indicated by metamorphic zircon and sphene ages of the anorthosite and by development of magmatitic alaskitic gneiss. The concentric isotherms that are observed in this area are due to later doming. However, an older contact metamorphic aureole associated with anorthosite intrusion is observed where wollastonite develops in metacarbonates. Zenoliths found in the anorthosite indicate a metamorphic event prior to anorthosite emplacement. The most probable mechanism for anorthosite genesis is thought to be ponding of gabbroic magmas at the Moho. The emplacement of the anorogenic anorthosite-mangerite-charnockite suite was apparently bracketed by compressional orogenies.

  7. Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India

    International Nuclear Information System (INIS)

    South Kerala in southwestern India offers interesting khondalite-charnockite assemblages suitable for detailed multidisciplinary case studies on granulite petrogenesis. Arrested charnockite formation is also characteristic of the terrain. Absolute ages of the khondalites are poorly constrained; limited U-Pb zircon data for various rock types of south Kerala khondalite belt have been obtained. Zircons from khondalite sensu-stricto and garnet-biotite gneiss of possible sedimentary origin give a concordia upper-intercept apparent age of ca. 2200 Ma, suggesting that the khondalites contain detrital material that is at least early Proterozoic in age; the data yield a lower intercept apparent age of ca. 400-600 Ma, but it is not clear if this represents new zircon growth and episodic Pb loss at that time (preferred) or is an artifact of normal diffusive loss of radiogenenic Pb. Zircons from retrograded granulitic gneisses have zircon upper-intercept apparent ages of ca. 1550 Ma, indicating either a younger protolith age or, more probably, greater radiogenic Pb loss during subsequent migmatite-grade metamorphism that caused retrogression of the granulite. Since all the zircon populations are complex, more detailed analyses will need to be pursued to resolve age relationships of these rocks with greater certainty. Monazite from a retrograded granulitic gneiss, yields a concordant age of ca. 520 Ma; this age is probably related to late Proterozoic-early Cambrian regional thermal event is south Kerala and is correlative with a similar event in Sri Lanka. (author). 25 refs., 4 figs., 1 tab

  8. U-Pb ages of uranium ores in the Church Rock uranium district, New Mexico

    International Nuclear Information System (INIS)

    Examines samples from the largest US uranium-producing region in order to determine ages of mineralization of different orebodies. Uranium from this area has come mainly from arkosic and subarkosic sandstones of the Upper Jurassic Morrison Formation. Several lines of evidence suggest that ages range from Late Jurassic or Early Cretaceous to at least as young as Tertiary. Geologic observations indicate that the oldest (primary) orebodies are tabular in shape and rich in amorphous organic material, whereas the youngest orebodies tend to be poor in amorphous organic material, display roll-front geometry, and are commonly spatially associated with Laramide or younger faults. Both types of ore were formed by relatively lowtemperature, dilute fluids that were essentially ground water in nature. Concludes that the 0- to 1-m.y. U-Pb apparent ages of the United Nuclear Corporation Church Rock Mine relate to redistribution, by roll-front processes, of earlier-formed ores by oxidizing Pleistocene ground waters, perhaps those that resulted in the present-day limonitic zone of the Westwater Canyon Member. Suggests that the 10-m.y. apparent age of sample KM-17-1 may represent an earlier phase of redistributed ore formation, perhaps related to the Tertiary oxidation front that resulted in the present-day hematitic zone of the Westwater Canyon Member

  9. Apatite U-Pb thermochronolgy applied to complex geological settings - insights from geo/thermochronology and geochemistry

    Science.gov (United States)

    Paul, Andre; Spikings, Richard; Ulyanov, Alexey; Chew, David

    2016-04-01

    Application of high temperature (>350oC) thermochronology is limited to the U-Pb system of accessory minerals, such as apatite, under the assumption that radiogenic lead is lost to thermally activated volume diffusion into an infinite reservoir. Cochrane et al. (2015) have demonstrated a working example from the northern Andes of South America. Predictions from volume diffusion theory were compared with measured single grain U-Pb date correlated to shortest diffusion radius and in-situ profiles measured by LA-ICP-MS. Results from both techniques were found to be in agreement with predictions from thermally activated, volume diffusion. However, outliers from the ID-TIMS data suggested some complexity, as grains were found to be too young relative to their diffusion radius. Interaction of multiple processes can be responsible for the alteration of apatite U-Pb dates such as: (1) metamorphic (over)growth, (2) fluid aided alteration/recrystallization and (3) metamictization and fracturing of the grain. Further, predictions from volume diffusion rely on the input parameters: (a) diffusivity, (b) activation energy and (c) shortest diffusion radius. Diffusivity and activation energy are potentially influenced by the chemical composition and subsequent changes in crystal structure. Currently there is one value for diffusion parameter and activation energy established for (Durango) apatite (Cherniak et al., 1991). Correlation between diffusivity/activation energy and composition has not been established. We investigate if correlations exist between diffusivity/activation energy and composition by obtaining single grain apatite U-Pb date and chemical compostion and correlating these to their diffusion radius. We test the consistency of apatite closure temperature, by comparing the apatite U-Pb dates with lower temperature thermochronometers such as white mica and K-feldspar Ar/Ar and by petrographic observations. We test if chemical information can be a proxy to identify

  10. Craneofaringioma en la tercera edad

    Directory of Open Access Journals (Sweden)

    Verónica García Yllán

    2014-11-01

    Full Text Available Los craneofaringiomas representan del 6 al 10 % de las neoplasias intracraneales en la infancia y el 30 % en adultos; infrecuentes en la tercera edad. Las manifestaciones clínicas diversas (síntomas visuales, endocrinos y neurológicos de la esfera psíquica superior dificultan su diagnóstico en la tercera edad, de ahí la importancia de la presentación de este caso. Paciente masculino de la séptima década de la vida, con cefalea y déficit visual progresivos. Los estudios neuroimageológicos avalaron la cirugía. La evolución fue satisfactoria. El examen histopatológico confirmó el diagnóstico de craneofaringioma. Se trata de un tumor benigno intracraneal infrecuente en la tercera edad, que debe tenerse en cuenta en pacientes con estos síntomas

  11. Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT

    Science.gov (United States)

    Koenig, Alan E.; Lucas, Spencer G.; Neymark, Leonid A.; Heckert, Andrew B.; Sullivan, Robert M.; Jasinski, Steven E.; Fowler, Denver W.

    2012-01-01

    Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), Fassett et al. (2011) claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that directly questions their stratigraphic interpretations (Lucas et al., 2009), and fail to provide sufficient descriptions of instrumental, geochronological, and statistical treatments of the data to allow evaluation of the potentially complex diagenetic and recrystallization history of bone. These shortcomings lead us to question the validity of the U-Pb dates published by Fassett et al. and their conclusions regarding the existence of Paleocene dinosaurs.

  12. Single zircon LAM-ICPMS U-Pb dating of Guidong complex (SE China) and its petrogenetic significance

    Institute of Scientific and Technical Information of China (English)

    XU Xisheng; DENG Ping; S. Y. O'Reilly; W. L. Griffin; ZHOU Xinmin; TAN Zhengzhong

    2003-01-01

    Single zircon LAM-ICPMS U-Pb dating indicates that the Guidong granitic complex is a multistage batholith formed during Indosinian-Yanshanian time. The Luxi body (239 ± 5 Ma) and the Xiazhuang body (235.8 ± 7.6 Ma) intruded during Indosinian time, whereas the Aizi body (160.1 ± 6.1 Ma) and the Siqian body (151 ± 11 Ma) formed during Yanshanian time. Inherited zircons (1275-2137 Ma) in the Xiazhuang body imply that at least part of the source rocks of the Guidong complex are from the Proterozoic basement of southeast China. Detailed single zircon LAM-ICPMS U-Pb dating results provide important evidence for understanding the evolution, tectonic setting and mineralisation of the complex.

  13. Emission of intermediate mass fragments in the heavy ion interaction of (14.0 MeV/u) Pb + Au

    International Nuclear Information System (INIS)

    We have studied the heavy ion interactions of (14.0 MeV/u) Pb+Au using two threshold detectors, mica and CN-85. A thin layer of Au was deposited on each of the three mica and two CN-85 detector pieces. These target-detector assemblies were exposed to a beam of 14.0 MeV/u Pb ions having the fluence of 1.5x106/cm2 at GSI, Darmstadt, Germany. After removing the target material and etching the samples in appropriate etchants, we scanned 32.20 cm2 and 24.97 cm2 area of mica and CN-85, respectively. Based on the observed number of events of various multiplicities, we have determined the total as well as partial experimental reaction cross sections. It is shown that a significant number of intermediate mass fragments are emitted along with the heavy fragments in the present reaction. (author)

  14. Craneofaringioma en la tercera edad

    OpenAIRE

    Verónica García Yllán; Lourdes María García Yllán; Miriam Sifontes Estrada

    2014-01-01

    Los craneofaringiomas representan del 6 al 10 % de las neoplasias intracraneales en la infancia y el 30 % en adultos; infrecuentes en la tercera edad. Las manifestaciones clínicas diversas (síntomas visuales, endocrinos y neurológicos de la esfera psíquica superior) dificultan su diagnóstico en la tercera edad, de ahí la importancia de la presentación de este caso. Paciente masculino de la séptima década de la vida, con cefalea y déficit visual progresivos. Los estudios neuroimageológicos ava...

  15. Late Precambrian U-Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

    OpenAIRE

    Tanner, P.W.G.; Evans, J. A.

    2003-01-01

    There has been controversy over the number and timing of orogenies in the Precambrian Moine block in the Scottish Caledonides since the earliest radiometric dating in the 1960s. This work challenges a recent hypothesis, that this sector of the Laurentian margin was subjected to continuous crustal extension between greater than 900 and 470 Ma. U-Pb dating (thermal ionization mass spectrometry) of titanite from a calcsilicate pod in the Moine (Morar Group) of the western Highlands gives an age ...

  16. U-Pb age of magnetic rocks of the Ulkan graben (south-eastern part of Aldan Shield)

    International Nuclear Information System (INIS)

    By the U-Pb method for zircon and monazite is carried out isotopic age determination of the Ulkan volcanic-plutonic complex. Magmatic rock formation is in the age interval from 1727±11 to 1703±18 mln years and agrees with the modern stratigraphic scale. Description of the investigated dimensional mineral fractions and analytical results are presented. 14 refs., 3 figs., 1 tab

  17. Geochronological constaints on the evolution of the Witwatersrand basin, as deduced from single zircon U/Pb ion microprobe studies

    International Nuclear Information System (INIS)

    The economic importance of the Witwatersrand Supergroup has resulted in this basin being one of the most extensively studied of its kind. The Witwatersrand basin has traditionally been grouped together with the underlying Dominion Group and the overlying Ventersdorp Supergroup into the so-called Witwatersrand triad. The present study has sought, by means of single zircon U-Pb age determinations using ion microprobe SHRIMP, to establish a precise and accurate chronostratigraphy for the Witwatersrand triad. 4 refs., 2 figs

  18. Late archean initial potassic magmatism of the Aldan shield (the Ukduska massif): evidence from U-Pb single zircon dating

    International Nuclear Information System (INIS)

    The U-Pb isotope studies of zircon from alkaline-feldspars syenites of the Ukduska massif were carried out for analyzing the manifestations and age of potassium magmatism in area of the Aldan shield. It is shown that the obtained age estimate (2719 ± 14 mln. years) corresponds to crystallization period of the massif laminated rock series, which are the most ancient potassium-ultrapotassium rocks of the Aldan shield and Siberian craton

  19. Plešovice zircon -- a new natural reference material for U-Pb and Hf isotopic microanalysis

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Košler, J.; Condon, D. J.; Crowley, J. L.; Gerdes, A.; Hanchar, J. M.; Horstwood, M. S. A.; Morris, G. A.; Nasdala, L.; Norberg, N.; Schaltegger, U.; Schoene, B.; Tubrett, M. N.; Whitehouse, M. J.

    2008-01-01

    Roč. 249, 1-2 (2008), s. 1-35. ISSN 0009-2541 Grant ostatní: GA ČR(CZ) GA205/05/0381 Institutional research plan: CEZ:AV0Z30130516 Keywords : zircon reference material * lase ablation ICP-MS * U-Pb dating * Hf isotopes * Plešovice, Bohemian Massif Subject RIV: DD - Geochemistry Impact factor: 3.531, year: 2008

  20. U-Pb thermochronology, geochronology and geochemistry of NW South America: rift to drift transition, active margin dynamics and implications for the volume balance of continents

    OpenAIRE

    Cochrane, Ryan

    2013-01-01

    We investigate the Permian – Early Cretaceous (~280 – 113 Ma) tectonic evolution of north-western South America. A new quantitative isotopic and geochemical dataset is presented, which includes, i) 53 U-Pb zircon dates of magmatic rocks and 8 detrital zircon U-Pb age spectra of metasedimentary rocks, ii) 49 weighted mean zircon Hf isotopic analyses of magmatic rocks, iii) 82 whole rock geochemical analyses, including Sr-Pb-Nd isotopic analyses, and iv) apatite U-Pb and 40Ar/39Ar thermochronol...

  1. Tracking the growth of plutons: the contribution of high-precision U-Pb zircon dating

    International Nuclear Information System (INIS)

    Full text: A growing body of high-precision U-Pb data from magmatic zircon indicates that plutons grow over timescales of 105-106 years. A complex interplay of processes - including accumulation of melt batches from lower and middle crustal levels, crystallization, remelting of solidified crystal mushes, mixing and mingling, transfer of pheno- and xenocrysts between melt portions, and many more - results in equally complicated pluton structures and rock textures. The use of (202Pb-) 205Pb-233U-235U tracer solutions in U-Pb dating of magmatic zircon can lead to a precision of 0.1 % in the 206Pb/238U age of an individual zircon analysis, and to as low as 0.02 % for a weighted mean of 6-10 coeval analyses. Such uncertainty is well within the time interval of zircon crystallization and residence in intermediate and acid magmatic liquids and allows resolution of incremental accumulation of melt batches in plutons. We demonstrate that we can achieve sub-permil precisions with MSWD values of around 1 on weighted mean dates by analyzing simultaneously precipitated zircon from H2O-enriched residual liquids within zircon-undersaturated basalt. Any age variation in granitoid rocks beyond this analytical spread is therefore considered real age dispersion, leading to an array of non-equivalent, analytically concordant points (within decay constant uncertainty). The reasons for such age dispersion may be the following: incorporation of antecrystic zircon from earlier magma batches of the same magmatic system, which have crystallized 104 to 105 years earlier; protracted zircon crystallization within a single batch of magma during its ascent and emplacement; presence of smallest xenocrystic cores in the analyzed zircons which contain a small proportion of older lead; minor degrees of unresolved lead loss that lead to slightly young ages. Though Pb-loss can largely be avoided by applying chemical abrasion prior to analysis, its effects are difficult to rule out completely

  2. Determination of the Rubidium Decay Constant by Age Comparison Against the U-Pb System

    Science.gov (United States)

    Nebel, O.; Mezger, K.; Scherer, E. E.; Davies, G. R.

    2006-12-01

    The currently accepted Rb decay constant (λ 87Rb) was suggested by the Subcommission on Geochronology [1] is 1.42 x 10-11yr-1, and has a potential precision at the percent level at best [2]. This value has been used in most Rb-Sr studies in the last three decades. Several attempts to refine λ87Rb by different techniques yielded results that, despite excellent reported precisions, differed from the proposed value and also from each other. In a recent evaluation of published calibrations of the decay constant, Begemann et al. [2] suggested a lower value [~ 1.40 x 10-11yr-1] but also called for a re-determination of λ87Rb to check its accuracy and significantly improve the precision. Subsequent re-determinations [3,4] yielded values that differ significantly from each other and from that proposed by the Subcommission on Geochronology [1], one of which being higher [3], the other one lower [4] than the recommended value. Therefore, at present, there is no consensus on the λ87Rb to be used in Rb-Sr chronology. Here we report three individual determinations of λ87Rb by the method of age comparison. This entails solving for λ87Rb using 1) the measured slopes of high precision Rb-Sr isochrons from igneous rocks and minerals and 2) the emplacement ages of these samples as determined by the precise and presumably accurate U-Pb method. The precision of the measured 87Rb/86Sr has been improved to ~0.2% by measuring Rb concentrations by isotope dilution MC-ICPMS [5] (cf. ~1% for TIMS data). A challenging aspect of Rb-Sr studies is that of spike calibration, which is generally performed using standards prepared from salts of Rb and Sr rather than pure metals. The Rb/Sr values of individual spikes calibrated against two standard solutions made from different salts (iodide and carbonate) agree to within 0.15%, strongly suggesting that the stoichiometry of the salts, after careful dehydration, is sufficiently ideal for accurate spike calibrations. The calibration was checked

  3. {U}/{Pb} geochronology and significance of Late Permian ignimbrites in Northern Chile

    Science.gov (United States)

    Breitkreuz, Christoph; Van Schmus, W. R.

    1996-11-01

    {U}/{Pb} zircon ages of four ignimbrite samples from a Late Paleozoic volcaniclastic succession in northern Chile are presented. The 2 km thick succession consists of the Peine Fm. and the overlying Cas Fm., which crop out at the eastern margin of the Salar de Atacama near the village of Peine. One sample was collected from the oldest ignimbrite of the succession (Lower Member of the Peine Fm.); the other three samples were collected from the Middle Member of the Cas Fm. and its assumed equivalents. The {206Pb }/{238U } ages of all samples overlap within their analytical uncertainties, which results in a best estimate of 248 ± 3 Ma (Late Permian: Harland, 1990) for deposition of the entire succession. The age for the stratigraphically older sample is statistically indistinguishable from the other three samples, so that the depositional interval could have been less than 1 million years; maximum errors in the data allow that the Peine and Cas Fms. could have formed during a time span of 6 Ma. The data provide tight constraints on the age of these units, part of which formed in the Lanquir Caldera Complex. They also have implications for the stratigraphy and paleoclimatic models of the Southern Central Andes during the Late Permian. Although the zircon fractions analyzed here document Late Permian ages, they show varying amounts of inheritance of early Paleoproterozoic (to Late Archean?) zircons and also indicate the incorporation of ca. 2.5 Ga initial common lead to varying degrees. This and results from other studies in the area lead us to infer the existence, at least during the Paleozoic, of Precam-brian basement located below the Salar de Atacama area.

  4. Detrital zircon U-Pb reconnaissance of the Franciscan subduction complex in northwestern California

    Science.gov (United States)

    Dimitru, Trevor; Ernst, W. Gary; Hourigan, Jeremy K.; McLaughlin, Robert J.

    2015-01-01

    In northwestern California, the Franciscan subduction complex has been subdivided into seven major tectonostratigraphic units. We report U-Pb ages of ≈2400 detrital zircon grains from 26 sandstone samples from 5 of these units. Here, we tabulate each unit's interpreted predominant sediment source areas and depositional age range, ordered from the oldest to the youngest unit. (1) Yolla Bolly terrane: nearby Sierra Nevada batholith (SNB); ca. 118 to 98 Ma. Rare fossils had indicated that this unit was mostly 151-137 Ma, but it is mostly much younger. (2) Central Belt: SND; ca. 103 too 53 Ma (but poorly constrained), again mostly younger than previously thought. (3) Yager terrane: distant Idaho batholith (IB); ca. 52 to 50 Ma. Much of the Yager's detritus was shed during major core complex extension and erosion in Idaho that started 53 Ma. An eocene Princeton River-Princeton submarine canyon system transported this detritus to the Great Valley forearc basin and thence to the Franciscan trench. (4) Coastal terrane: mostly IB, ±SNB, ±nearby Cascade arc, ±Nevada Cenozoic ignimbrite belt; 52 to <32 Ma. (5) King Range terrane: dominated by IB and SNB zircons; parts 16-14 Ma based on microfossils. Overall, some Franciscan units are younger than previously thought, making them more compatible with models for the growth of subduction complexes by positive accretion. From ca. 118 to 70 Ma, Franciscan sediments were sourced mainly from the nearby Sierra Nevada region and were isolated from southwestern US and Mexican sources. From 53 to 49 Ma, the Franciscan was sourced from both Idaho and the Sierra Nevada. By 37-32 Ma, input from Idaho had ceased. The influx from Idaho probably reflects major tectonism in Idaho, Oregon, and Washington, plus development of a through-going Princeton River to California, rather than radical changes in the subduction system at the Franciscan trench itself.

  5. U-Pb age of the Diana Complex and Adirondack granulite petrogenesis

    Indian Academy of Sciences (India)

    Asish R Basu; Wayne R Premo

    2001-12-01

    U-Pb isotopic analyses of eight single and multi-grain zircon fractions separated from a syenite of the Diana Complex of the Adirondack Mountains do not define a single linear array, but a scatter along a chord that intersects the Concordia curve at 1145 ± 29 and 285 ± 204 Ma. For the most concordant analyses, the 207Pb/206Pb ages range between 1115 and 1150 Ma. Detailed petrographic studies revealed that most grains contained at least two phases of zircon growth, either primary magmatic cores enclosed by variable thickness of metamorphic overgrowths or magmatic portions enclosing presumably older xenocrystic zircon cores. The magmatic portions are characterized by typical dipyramidal prismatic zoning and numerous black inclusions that make them quite distinct from adjacent overgrowths or cores when observed in polarizing light microscopy and in back- scattered electron micrographs. Careful handpicking and analysis of the "best" magmatic grains, devoid of visible overgrowth of core material, produced two nearly concordant points that along with two of the multi-grain analyses yielded an upper-intercept age of 1118 ± 2.8 Ma and a lower- intercept age of 251 ± 13 Ma. The older age is interpreted as the crystallization age of the syenite and the younger one is consistent with late stage uplift of the Appalachian region. The 1118 Ma age for the Diana Complex, some 35 Ma younger than previously believed, is now approximately synchronous with the main Adirondack anorthosite intrusion, implying a cogenetic relationship among the various meta-igneous rocks of the Adirondacks. The retention of a high-temperature contact metamorphic aureole around Diana convincingly places the timing of Adirondack regional metamorphism as early as 1118 Ma. This result also implies that the sources of anomalous high- temperature during granulite metamorphism are the syn-metamorphic intrusions, such as the Diana Complex.

  6. Eocene Kashmar granitoids (NE Iran): Petrogenetic constraints from U-Pb zircon geochronology and isotope geochemistry

    Science.gov (United States)

    Shafaii Moghadam, Hadi; Li, Xian-Hua; Ling, Xiao-Xiao; Santos, Jose F.; Stern, Robert J.; Li, Qiu-Li; Ghorbani, Ghasem

    2015-02-01

    Kashmar granitoids outcrop for ~ 100 km along the south flank of the Sabzevar ophiolite (NE Iran) and consist of granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and western granitoids. Five samples of granite have identical zircon U-Pb ages of ca. 40-41 Ma. The granitoids have quite high K2O (~ 1.3-5.3 wt.%) and Na2O (~ 1.1-4.6 wt.%) with SiO2 ranging between ~ 62 and 77 wt.%. They are metaluminous to peraluminous, calc-alkaline and I-type in composition. Their chondrite-normalized REE patterns are characterized by LREE enrichment and show slight negative Eu anomalies. Kashmar granitoids have low whole rock εNd (- 0.43 to - 2.3), zircon εHf values (- 1.9 to + 7.2), and somewhat elevated δ18O (+ 6.1 to + 8.7‰) in the range of I-type granites. The Kashmar granitoids show Early Neoproterozoic zircon second-stage Hf and bulk rock Nd model ages at ca. 500-1000 Ma (associated with ca. 640 Ma old inherited zircons). Bulk rock Nd-Sr isotopic modeling suggests that 10-20% assimilation of Cadomian lower crust by juvenile mantle melts and then fractional crystallization (AFC process) can explain the Sr-Nd isotopic compositions of Kashmar granitoids. Kashmar granitoids are products of crustal assimilation by mantle melts associated with extension above the subducting Neotethyan Ocean slab beneath SW Eurasia. Similar subduction-related extension was responsible for the flare-up of Eocene-Oligocene magmatism across Iran, associated with core complex formation in central Iran.

  7. Geochemistry and U-Pb zircon geochronology of Late-Mesozoic lavas from Xishan, Beijing

    Institute of Scientific and Technical Information of China (English)

    YUAN; Honglin; LIU; Xiaoming; LIU; Yongsheng; GAO; Shan; LING; Wenli

    2006-01-01

    Zircon U-Pb dating by both SHRIMP and LA-ICP-MS and geochemical study of the Tiaojishan Formation and the Donglintai Formation from Xishan, Beijing, reveal that ages of upper lavas of Tiaojishan Formation and Middle of Donglintai Formation are 137.1±4.5 Ma(2σ) and 130-134 Ma, respectively. The fomer is slightly older than the latter and the age difference between these two formations is less than 5 Ma. These lines of evidence prove that the two volcanoes erupted within a short time. The age of the Tiaojishan Formation from Xishan, Beijing is distinctively different from that of the Chende Basin. This indicated that the ages of Tiaojishan lavas varied in different regions. The Tiaojishan Formation consists of typical adakite (SiO2=56%, Na2O = 3.99-6.17, Na2O/K2O = 2.2-3.1, Sr = 680-1074×10-6, Y = 13.2-16.3×10-6, Yb = 1.13-1.52×10-6, Sr/Y = 43-66), high-Mg adakite and high-Mg andesite (Mg# = 54-55). Features of continental crust of adakite from the Tiaojishan Formation and its syngeneric middle silicic vocanic rocks, such as typical Nd-Ta negative abnormality and Pb possive abnormality, indicate that these lavas are originated from partial melts of continental crust. These results suggest that the adakite from the Tiaojishan Formation of Xishan, Beijing derived from thickened eclogitic lower crust and lithosphere beneath the North China craton at mesozoic that was foundered into the aesthenosphere, and subsequenctly partially melted and interacted with mantle olivine during melts upward migration. The age of lavas from the Tiaojishan Formation restrained the foundation which should last at least until 137 Ma. Lavas of the Donglintai Formation are rhyolith and andesite with normal Mg# and thus they did not interact with the mantle. These lavas represent remobilized melts of lower crust material caused by mantle aesthenosphere upwelling migration induced by foundation.

  8. U-Pb systematics of the unique achondrite Ibitira: Precise age determination and petrogenetic implications

    Science.gov (United States)

    Iizuka, Tsuyoshi; Amelin, Yuri; Kaltenbach, Angela; Koefoed, Piers; Stirling, Claudine H.

    2014-05-01

    discuss the implications of the U-Pb systematics for the origin and differentiation of the parent body.

  9. Improved Methods for U/Pb Geochronology of Baddeleyite by LA-ICPMS

    Science.gov (United States)

    Sylvester, P. J.; Souders, A. K.; Tubrett, M. N.

    2009-05-01

    Hz and 2 to 5 J/cm2, Pb/U fractionation in baddeleyite is reduced significantly. Over 150 pulses (30 sec) of ablation, 206Pb/238U ratios increase by less than 15% with less than 5% RSD variation from line scan to line scan. Using Forest Center baddeleyite as the calibration standard, we find U-Pb concordia ages of 377+/-8 Ma for Kovdor, and 2053+/-12 Ma for Phalaborwa.

  10. Dating prograde fluid pulses during subduction by in situ U-Pb and oxygen isotope analysis

    Science.gov (United States)

    Gauthiez-Putallaz, Laure; Rubatto, Daniela; Hermann, Jörg

    2016-02-01

    The Dora-Maira whiteschists derive from metasomatically altered granites that experienced ultrahigh-pressure metamorphism at ~750 °C and 40 kbar during the Alpine orogeny. In order to investigate the P-T-time-fluid evolution of the whiteschists, we obtained U-Pb ages from zircon and monazite and combined those with trace element composition and oxygen isotopes of the accessory minerals and coexisting garnet. Zircon cores are the only remnants of the granitic protolith and still preserve a Permian age, magmatic trace element compositions and δ18O of ~10 ‰. Thermodynamic modelling of Si-rich and Si-poor whiteschist compositions shows that there are two main fluid pulses during prograde subduction between 20 and 40 kbar. In Si-poor samples, the breakdown of chlorite to garnet + fluid occurs at ~22 kbar. A first zircon rim directly overgrowing the cores has inclusions of prograde phlogopite and HREE-enriched patterns indicating zircon growth at the onset of garnet formation. A second main fluid pulse is documented close to peak metamorphic conditions in both Si-rich and Si-poor whiteschist when talc + kyanite react to garnet + coesite + fluid. A second metamorphic overgrowth on zircon with HREE depletion was observed in the Si-poor whiteschists, whereas a single metamorphic overgrowth capturing phengite and talc inclusions was observed in the Si-rich whiteschists. Garnet rims, zircon rims and monazite are in chemical and isotopic equilibrium for oxygen, demonstrating that they all formed at peak metamorphism at 35 Ma as constrained by the age of monazite (34.7 ± 0.4 Ma) and zircon rims (35.1 ± 0.8 Ma). The prograde zircon rim in Si-poor whiteschists has an age that is within error indistinguishable from the age of peak metamorphic conditions, consistent with a minimum rate of subduction of 2 cm/year for the Dora-Maira unit. Oxygen isotope values for zircon rims, monazite and garnet are equal within error at 6.4 ± 0.4 ‰, which is in line with closed

  11. U-Pb and Al-Mg systematics of the ungrouped achondrite Northwest Africa 7325

    Science.gov (United States)

    Koefoed, Piers; Amelin, Yuri; Yin, Qing-Zhu; Wimpenny, Josh; Sanborn, Matthew E.; Iizuka, Tsuyoshi; Irving, Anthony J.

    2016-06-01

    Northwest Africa (NWA) 7325 is a unique ungrouped gabbroic achondrite which has characteristics consistent with a possible link to the planet Mercury. In order to understand the origin of this meteorite and the nature of its parent body, we have determined its crystallisation age using the long-lived U-Pb and short-lived Al-Mg chronometers. An internal Pb-Pb isochron defined by six acid leached pyroxene fractions yields an age of 4563.4 ± 2.6 Ma, assuming that the 238U/235U ratio for NWA 7325 is identical to the bulk Earth and Solar System value of 137.794. The Al-Mg isotope analyses of seven fractions (four plagioclase, one pyroxene, one olivine and one whole rock) define a regression line corresponding to 26Al/27Al0 = (3.03 ± 0.14) × 10-7 and an initial δ26Mg∗ of 0.093 ± 0.004‰. When anchored to the D'Orbigny angrite, this initial 26Al/27Al yields an age of 4563.09 ± 0.26 Ma. The Pb-Pb age of 4563.4 ± 2.6 Ma and Al-Mg age of 4563.09 ± 0.26 Ma are in complete agreement, but the low U concentrations of NWA 7325 resulted in a relatively low precision Pb-Pb age. The observed excess in initial δ26Mg∗ can be explained by 27Al/24Mg fractionation and subsequent Mg isotopic evolution after planetary differentiation. Furthermore, the parental magma of NWA 7325 most likely formed within 1.72 Ma after calcium-aluminium rich inclusion (CAI) formation. NWA 7325 formed near simultaneously with quenched angrites and a number of ungrouped achondrites at ∼4563 Ma, suggesting that a multitude of planetary bodies had formed and differentiated by ∼4-5 Myr after CAI formation. This ancient age may be interpreted as an argument against NWA 7325 originating from Mercury, however it does not completely rule it out.

  12. Evaluation of fission-track and U-Pb double dating method for identical zircon grains. Using homogeneous zircon grains in Kawamoto Granodiorite in Shimane prefecture, Japan

    International Nuclear Information System (INIS)

    Using the double-dating approach, we have conducted fission-track (FT) and U-Pb age dating on the same zircon grain to evaluate the reliability of the resulting age data. The zircon grains (OD-3) used for the investigation were collected from the Mihara Body of the Kawamoto Granodiorite, Shimane Prefecture, Japan. The zircon crystals yielded a FT age of 33 Ma, with a spontaneous FT density of 106-107 cm2. The U-Pb age data were obtained using inductively coupled plasma-mass spectrometry (ICP-MS) combined with a frequency quintupled Nd-YAG (λ=213 nm) laser ablation (LA) sample introduction system. The U-Pb age determinations on the zircon samples were performed after chemical leaching using 47% HF for 20 hrs at room temperature, or after FT etching using a KOH-NaOH eutectic solution for 20 hrs at 225degC. The resulting U-Pb age of 33 Ma was concordant with the FT age data, suggesting that there was no significant loss of Pb during etching or chemical preparation, thus indicating the feasibility of FT and U-Pb double dating of single zircon grains. The results indicate that the zircon grains (OD-3) from the Kawamoto Granodiorite (Mihara Body) can become a new working standard for precise U-Pb age determinations of young zircons. (author)

  13. EDADES DE COSECHA EN CAPRINOS

    Directory of Open Access Journals (Sweden)

    Pablo Andr\\u00E9s Chac\\u00F3n-Hern\\u00E1ndez

    2010-01-01

    Full Text Available El objetivo de este trabajo fue determinar la edad del pasto Pennisetum purpureum cv. king grass, a la cual los caprinos presentan un mayor consumo y aprovechamiento de nutrientes. El experimento se llevó a cabo durante el segundo semestre del 2007 en la Estación Experimental Alfredo Volio Mata de la Universidad de Costa Rica, ubicada a 1542 msnm. Se obtuvo la cantidad de pasto Pennisetum purpureum cv. king grass producida a los 60, 75 y 90 días de rebrote, consumida por caprinos (peso promedio 45 kg de las razas Saanen Lamancha y Toggenburg, distribuidas en un cuadrado latino con tres repeticiones. El mayor consumo de materia verde se obtuvo cuando el forraje fue cosechado a 60 días (p0,05. Se observó una disminución gradual en el consumo de materia seca y proteína cruda conforme aumentó la edad de cosecha y la proporción de tallos en el forraje; mientras que la fibra neutro detergente y la fibra ácido detergente se comportaron de manera contraria. A menor edad del material y mayor relación hoja:tallo, las cabras aumentaron el consumo de forraje y el aprovechamiento de los nutrientes del mismo.

  14. Chemical abrasion-SIMS (CA-SIMS) U-Pb dating of zircon from the late Eocene Caetano caldera, Nevada

    Science.gov (United States)

    Watts, Kathryn E.; Coble, Matthew A.; Vazquez, Jorge A.; Henry, Christopher D.; Colgan, Joseph P.; John, David A.

    2016-01-01

    Zircon geochronology is a critical tool for establishing geologic ages and time scales of processes in the Earth's crust. However, for zircons compromised by open system behavior, achieving robust dates can be difficult. Chemical abrasion (CA) is a routine step prior to thermal ionization mass spectrometry (TIMS) dating of zircon to remove radiation-damaged parts of grains that may have experienced open system behavior and loss of radiogenic Pb. While this technique has been shown to improve the accuracy and precision of TIMS dating, its application to high-spatial resolution dating methods, such as secondary ion mass spectrometry (SIMS), is relatively uncommon. In our efforts to U-Pb date zircons from the late Eocene Caetano caldera by SIMS (SHRIMP-RG: sensitive high resolution ion microprobe, reverse geometry), some grains yielded anomalously young U-Pb ages that implicated Pb-loss and motivated us to investigate with a comparative CA and non-CA dating study. We present CA and non-CA 206Pb/238U ages and trace elements determined by SHRIMP-RG for zircons from three Caetano samples (Caetano Tuff, Redrock Canyon porphyry, and a silicic ring-fracture intrusion) and for R33 and TEMORA-2 reference zircons. We find that non-CA Caetano zircons have weighted mean or bimodal U-Pb ages that are 2–4% younger than CA zircons for the same samples. CA Caetano zircons have mean U-Pb ages that are 0.4–0.6 Myr older than the 40Ar/39Ar sanidine eruption age (34.00 ± 0.03 Ma; error-weighted mean, 2σ), whereas non-CA zircons have ages that are 0.7–1.3 Myr younger. U-Pb ages do not correlate with U (~ 100–800 ppm), Th (~ 50–300 ppm) or any other measured zircon trace elements (Y, Hf, REE), and CA and non-CA Caetano zircons define identical trace element ranges. No statistically significant difference in U-Pb age is observed for CA versus non-CA R33 or TEMORA-2 zircons. Optical profiler measurements of ion microprobe pits demonstrate consistent depths of ~ 1.6

  15. Shock Recovery and Heating Experiments on Baddeleyite: Implications for U-Pb Isotopic Systematics of Martian Meteorites

    Science.gov (United States)

    Misawa, K.; Niihara, T.; Kaiden, H.; Sekine, T.; Mikouchi, T.

    2009-12-01

    Introduction: Radiometric ages of Martian meteorites, shergottites are generally young (i.e., ~165-475 Ma), and are in the late Amazonian chronostratigraphic unit [1]. Bouvier et al. [2-4] reported ~4.1-4.3 Ga old Pb-Pb ages for shergottites, and suggested that young Rb-Sr, Sm-Nd, and Lu-Hf ages so far obtained were affected by alteration of phosphates, interaction with Martian subsurface fluids, or intense shock metamorphism. Baddeleyite (ZrO2) with apparently primary igneous morphology is an important phase in shergottites for U-Pb age determination. In order to investigate shock effects on U-Pb isotopic systematics of baddeleyite, we undertook shock recovery and heating experiments on baddeleyite. Experimental: We used coarse-grained baddeleyite from Phalaborwa for a starting material. The baddeleyite was mixed with a coarse-grained terrestrial basalt with a weight ratio of 1:2. Shock-recovery experiments were performed using a propellant gun at NIMS [5]. The run products were placed in a vertical gas-mixing furnace and heated for 1-3 h at 1000-1300oC under log fO2 of IW+2.5 at 105 Pa. Textures were observed by a scanning electron microprobe and Raman spectra of shocked baddeleyite were obtained. In situ U-Th-Pb isotopic analysis was carried out with the SHRIMP II at NIPR [6]. Results and Discussion: We observed Raman peak shifts of 2-4 cm-1 in the 34-57 GPa samples. Lead loss from baddeleyite was not observed for the experimentally shocked samples. In addition, the U-Pb and Pb-Pb ages of shocked and heated baddeleyites are indistinguishable from those of unshocked baddeleyite within errors except minor lead loss from the baddeleyite shocked at 57 GPa and heated for 1 h at 1300oC. Although duration of peak shock-pressure and grain size of baddeleyite are different from the nature of basaltic shergottites, our experimental results suggest that it is hard to completely reset U-Pb isotopic systematics of baddeleyite in Martian meteorite by shock events below ~60

  16. Outline of Upper Precambrian and Lower Paleozoic evolution of the Iberian Peninsula according to U-Pb dating of zircons

    International Nuclear Information System (INIS)

    In the northwestern part of the Iberian Peninsula, recent geological studies have defined the following stratigraphic sequence from bottom to top: basal orthogneiss of Miranda do Douro is overlain by a complex of schist and greywacke which have been assigned to the Cambrian or late Precambrian; these are followed by the Ollo de Sapo gneisses of volcanic-sedimentary origin which in turn are overlain by the fossiliferous layers of the lower Ordovician. The schist and greywacke complex and the lower part of the Ollo de Sapo Formation are transected by granitic dikes (Viana del Bollo orthogneiss). All these rocks were folded, faulted, metamorphosed, and intruded by granite plutons during Variscan times. The emplacement of the Miranda do Douro and Viana del Bollo orthogneisses have been respectively dated at 618+-9 Ma and 465+-10 Ma by the U-Pb method on zircons. These data yield lower and upper limits for the deposition of the Ollo de Sapo Formation and demonstrate the occurrence of a Precambrian basement (''Pan-African'' or ''Cadomian'' orogeny) in the Variscan belt in the northwestern part of the Iberian Peninsula. The emplacement of Viana del Bollo orthogneiss could be genetically related to the main phase of crustal thinning (470-520 Ma) characteristic of the Prevariscan evolution of western Europe. Typology and U-Pb data of the Ollo de Sapo zircons indicate the occurrence of inherited old Precambrian zircons and yield an age of 325+-3 Ma for the Variscan main thermal event in the area considered. Four possible evolutionary models for the U-Pb system of the Ollo de Sapo zircons are discussed. (orig.)

  17. Outline of Upper Precambrian and Lower Paleozoic evolution of the Iberian Peninsula according to U-Pb dating of zircons

    Science.gov (United States)

    Lancelot, Joël R.; Allegret, André; Ponce de Leon, Moises Iglesias

    In the northwestern part of the Iberian Peninsula, recent geological studies have defined the following stratigraphic sequence from bottom to top: basal orthogneiss of Miranda do Douro is overlain by a complex of schist and greywacke which have been assigned to the Cambrian or late Precambrian; these are followed by the Ollo de Sapo gneisses of volcanic-sedimentary origin which in turn are overlain by the fossiliferous layers of the lower Ordovician. The schist and greywacke complex and the lower part of the Ollo de Sapo Formation are transected by granitic dikes (Viana del Bollo orthogneiss). All these rocks were folded, faulted, metamorphosed, and intruded by granite plutons during Variscan times. The emplacement of the Miranda do Douro and Viana del Bollo orthogneisses have been respectively dated at 618±9 Ma and 465±10 Ma by the U-Pb method on zircons. These data yield lower and upper limits for the deposition of the Ollo de Sapo Formation and demonstrate the occurrence of a Precambrian basement ("Pan-African" or "Cadomian" orogeny) in the Variscan belt in the northwestern part of the Iberian Peninsula. The emplacement of Viana del Bollo orthogneiss could be genetically related to the main phase of crustal thinning (470-520 Ma) characteristic of the Prevariscan evolution of western Europe. Typology and U-Pb data of the Ollo de Sapo zircons indicate the occurrence of inherited old Precambrian zircons and yield an age of 325±3 Ma for the Variscan main thermal event in the area considered. Four possible evolutionary models for the U-Pb system of the Ollo de Sapo zircons are discussed.

  18. Paleomagnetism, U-Pb geochronology, and geochemistry of Marathon dykes, Superior Province, and comparison with the Fort Frances swarm

    International Nuclear Information System (INIS)

    We report the first detailed study of the paleomagnetism, U - Pb geochronology and major element geochemistry of Paleoproterozoic north-trending Marathon dykes north of Lake Superior. The paleomagnetic and geochemical results demonstrate that Marathon dykes can be divided into two subsets, one of normal magnetic polarity, the other of reverse polarity. Normal and reverse Marathon paleomagnetic poles, at 43oN, 196oE (dm = 9o, dp = 7o, number of dykes N = 16) and 51oN, 175oE (dm = 9o, dp = 6o, N 12), respectively, are statistically distinct and may indicate different ages of normal and reverse dyke emplacement. A U-Pb baddeleyite age of 2121-7+14 Ma has been obtained at a normally magnetized Marathon paleomagnetic site. The reversely magnetized Marathon dykes are undated, but have a paleopole rather close to that of the reversely magnetized 2076-4+5 Ma Fort Frances dykes and major element geochemical signatures as portrayed on Jensen plots that are identical to those of the Fort Frances swarm. Therefore, reverse Marathon and Fort Frances dykes could define a giant radiating dyke swarm focused south of Lake Superior, supporting models that associate these dykes with Paleoproterozoic rifting along the southern margin of the Superior Province. The Marathon and Fort Frances paleopoles continue a northwesterly trend in southern Superior Province paleopoles, which has recently been defined by results for 2216-4+8 Ma Senneterre dykes and 2167 ± 2 Ma Biscotasing dykes. This trend contrasts with previous widely used polar wander paths for the same period that young in the opposite direction and illustrates the importance of collaborative studies of paleomagnetism and U - Pb geochronology. (author). 36 refs., 4 tabs., 10 figs

  19. U-Pb isotopic evidence pertaining to the age and genesis of uranium mineralisation in Karoo sediments

    International Nuclear Information System (INIS)

    Preliminary investigations have been carried out, using the uranium-lead isotopic method, on the uranium mineralisation that occurs within the Karoo sediments. Two occurences were studied, namely the lower Beaufort sediments (Adelaide Subgroup) in the Beaufort West area and the Molteno Formation sediments in the Ficksburg area. The objective were to determine the age of the mineralisation and to study the mode of formation of the ores. The pattern of U-Pb apparent ages for all the Karoo samples is 207Pb/206Pb age >> 207Pb*235U age > 206Pb*238U age

  20. U-Pb zircon ages for the Luzhenguan Complex in northern part of the eastern Dabie orogen

    Institute of Scientific and Technical Information of China (English)

    JIANG; Laili; Wolfgang; Siebe; CHEN; Fukun; LIU; Yican

    2005-01-01

    The study presents U-Pb zircon ages for granitic gneiss and amphibolite from the Luzhenguan Complex (LZC) in northern part of the eastern Dabie Orogen and their geological significance. Two granitic gneisses and one amphibolite give protolith zircon U-Pb ages of 740 Ma and 725 Ma, respectively. The ages show that the LZC is composed mainly of Neoproterzoic acid and basic igneous rocks, suggesting that there is no Paleozoic active continental marginal rock association in the southern margin of the North China Block in northern part of the eastern Dabie Mountain. Based on the ages and combining the geological and geophysical analyses, the middle-low grade metamorphic rocks in the North Huiyang Belt (NHB) can be divided into three parts, which are the LZC composed mainly of the Neoproterzoic acid and basic igneous rocks, the Neoproterzoic Xianrechong Formation and Xiangyunzhai Formation and the Devonian Zhufoan Formation and Pangjialing Formation of the Foziling Group, and the suture zone between the Yongtze Block and the North China Block is inferred to be thrust under the NHB.

  1. Geochemical and zircon U-Pb dating analysis of metamagmatic rocks from the Yuli belt in Taiwan

    Science.gov (United States)

    Hung, Chia-Chia

    2016-04-01

    The Tananao Schist Complex of the oldest rocks in Taiwan is exposed at the eastern limb of Backbone Range. Based on the lithologic and metamorphic characteristics, the complex can be divided into the Tailuko and Yuli belts. The Tailuko belt consists of marble, gneiss, and subordinate scattered metabasite; the Yuli belt is composed of greenschist, serpentinite, meta-tuff, meta-gabbro, metabasite, and glaucophane-schist blocks which enclosed by spotted schist of the host rocks. The metamorphic belts were inferred as a Mesozoic mélange. It's still controversial due to the difficulty of analyzing metamorphic rocks. In this study, we focus on the zircon U-Pb dating, geochemistry, and petrographic analysis of spotted schist, metabasite, meta-gabbro, and meta-tuff in order to constrain the formation and crystallization ages and interpret its tectonic setting. Based on zircon U-Pb dating, the host rocks of spotted schist and the exotic blocks of meta-tuff, meta-gabbro (the peak age of 14.4, 15.8, and 16.7 Ma), and metabasite occurred at Miocene. Geochemical characteristics for metabasite and meta-gabbro blocks show Ta-Nd-Ti depletion and LREE depletion in spidergram occurring volcanic arc and N-MORB type affinities, respectively. Results as above mentioned, we suggest that the metamagmatic rocks in the Yuli belt occur within a mélange during the Eurasia continental margin subduction at the Middle-Late Miocene.

  2. U-Pb Ages of Secondary Silica at Yucca Mountain, Nevada: Implications for the Paleohydrology of the Unsaturated Zone

    International Nuclear Information System (INIS)

    U, Th, and Pb isotopes were analyzed in layers of opal and chalcedony from individual millimeter- to centimeter-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of 206Pb/204Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotopes in opal samples at Yucca Mountain are complicated by the incorporation of excess 234U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the 207Pb/235U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, 207Pb/235U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. 234U and 230Th in most silica layers deeper in the coatings are in secular equilibrium with 238U, which is consistent with their old age and closed system behavior during the past 0.5 m.y. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average depositional rates of 1 to 5 mm/m.y. These data imply that the deeper parts of the UZ at Yucca Mountain maintained long

  3. U-Pb Ages of Secondary Silica at Yucca Mountain, Nevada: Implications for the Paleohydrology of the Unsaturated Zone

    Energy Technology Data Exchange (ETDEWEB)

    L.A. Neymark; Y. Amelin; J.B. Paces; Z.E. Peterman

    2001-08-20

    U, Th, and Pb isotopes were analyzed in layers of opal and chalcedony from individual millimeter- to centimeter-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of {sup 206}Pb/{sup 204}Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotopes in opal samples at Yucca Mountain are complicated by the incorporation of excess {sup 234}U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the {sup 207}Pb/{sup 235}U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, {sup 207}Pb/{sup 235}U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. {sup 234}U and {sup 230}Th in most silica layers deeper in the coatings are in secular equilibrium with {sup 238}U, which is consistent with their old age and closed system behavior during the past 0.5 m.y. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average depositional rates of 1 to 5 mm/m.y. These data imply that the deeper

  4. A new single-crystal U-Pb geochronological laboratory in the geological survey of India : principles, procedure and some initial results

    International Nuclear Information System (INIS)

    U-Pb geochronology of single-crystal zircon using conventional Isotope Dilution Thermal Ionisation Mass Spectrometry (IDTIMS) is regarded as the most powerful and precise geochronological technique for determining crystallisation ages of acidic and intermediate rocks. Setting up and maintenance of such a laboratory, however, demands painstaking efforts-reason why there are only a handful of such laboratories the world over. A new U-Pb IDTIMS laboratory, the first U-Pb laboratory in India, has recently been set up in the Geological Survey of India. This laboratory has been able to achieve very-high-quality geochronological data. The procedure for U-Pb zircon analysis along with some aspects of setting up of such a laboratory is discussed in this paper. Some of the significant preliminary new U-Pb zircon geochronological data from this laboratory are: (i) the 3.56-Ga crystallisation age of a tonalite from the Kapsi area in the central part of the Bastar craton, (ii) -2530- Ma and -2505-Ma emplacement ages respectively of the oldest and the youngest rhyolite layers of the Kotri Supergroup in the Kotri Linear Belt, Chhattisgarh. The -3.56-Ga tonalite forms the basement of the Kotri Supergroup and is the oldest dated rock from the Indian Peninsula so far. (author)

  5. Archean and proterozoic in the West-European Hercynian chain: isotopic geochemistry (Sr-Nd-Pb) and U-Pb geochronology on zircons

    International Nuclear Information System (INIS)

    The first part of this research thesis reports the study of isotopic (Sr-Nd-Pb) geochemistry and U-Pb geochronology on zircons in the immersed granulites of the Bay of Biscay: U-Pb geochronology on zircons, Nd isotopic geochemistry, Sr isotopic geochemistry, common Pb, Rb-Sr, Sm-Nd and rare earth data on minerals, comparison with other European granulites, comparison with West-Africa, study of Archean and proterozoic in the Hercynian chain. The second part reports the study of the U-Pb geochronology on zircon in the Cadomian, and the third part addresses the Sr-Nd isotopic geochemistry of some Cadomian granitoid, and the crust contamination in different regions

  6. Geochemistry and geochronology U-Pb and Sm/Nd data of the orthogneiss from Pontalina region (GO), Brazil; Geoquimica e geocronologia U-Pb e Sm-Nd dos ortognaisses da regiao de Pontalina (GO), Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Navarro, Guillermo Rafael Beltran, E-mail: grbnavarro@yahoo.com.br [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Inst. de Geociencias e Ciencias Exatas. Programa de Pos-Graduacao em Geologia Regional; Zanardo, Antenor, E-mail: azanardo@rc.unesp.br [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Dept. de Petrologia e Metalogenia; Conceicao, Fabiano Tomazini da, E-mail: ftomazini@rc.unesp.br [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Dept. de Planejamento Territorial e Geoprocessamento; Montibeller, Cibele Carolina, E-mail: cibelegeologia@uol.com.br [Universidade Estadual Paulista Julio de Mesquisa Filho (UNESP), Rio Claro, SP (Brazil). Curso de Geologia

    2013-04-15

    Orthogneisses of tonalitic to granodioritic composition with calc-alkaline, metaluminous to peraluminous characteristics crop out at the region of Pontalina. The orthogneisses exhibit negative anomalies of Nb, Ta, P and Ti relative to rare earth elements (REE) and litophile elements, besides low contents of Nb, Ta, Y and Yb, similar to the rocks formed in subduction environments. U-Pb geochronological data show a neoproterozoic (681.5 {+-} 7.7 Ma) crystallization for the orthogneisses. The Nd isotope data yielded weakly negative to positive {epsilon}{sub Nd}(T) (+3.2 up to -0.1), with T{sub DM} model ages of {approx} 1.2 Ga. The combined geochemical and isotopic data suggest that the protolith of these orthogneisses are representative of neoproterozoic juvenile magmas, probably developed in an island arc system, generated during a ca.700 and 600 Ma event of crustal accretion in the western edge of the Sao Francisco Craton. (author)

  7. Community-based Approaches to Improving Accuracy, Precision, and Reproducibility in U-Pb and U-Th Geochronology

    Science.gov (United States)

    McLean, N. M.; Condon, D. J.; Bowring, S. A.; Schoene, B.; Dutton, A.; Rubin, K. H.

    2015-12-01

    The last two decades have seen a grassroots effort by the international geochronology community to "calibrate Earth history through teamwork and cooperation," both as part of the EARTHTIME initiative and though several daughter projects with similar goals. Its mission originally challenged laboratories "to produce temporal constraints with uncertainties approaching 0.1% of the radioisotopic ages," but EARTHTIME has since exceeded its charge in many ways. Both the U-Pb and Ar-Ar chronometers first considered for high-precision timescale calibration now regularly produce dates at the sub-per mil level thanks to instrumentation, laboratory, and software advances. At the same time new isotope systems, including U-Th dating of carbonates, have developed comparable precision. But the larger, inter-related scientific challenges envisioned at EARTHTIME's inception remain - for instance, precisely calibrating the global geologic timescale, estimating rates of change around major climatic perturbations, and understanding evolutionary rates through time - and increasingly require that data from multiple geochronometers be combined. To solve these problems, the next two decades of uranium-daughter geochronology will require further advances in accuracy, precision, and reproducibility. The U-Th system has much in common with U-Pb, in that both parent and daughter isotopes are solids that can easily be weighed and dissolved in acid, and have well-characterized reference materials certified for isotopic composition and/or purity. For U-Pb, improving lab-to-lab reproducibility has entailed dissolving precisely weighed U and Pb metals of known purity and isotopic composition together to make gravimetric solutions, then using these to calibrate widely distributed tracers composed of artificial U and Pb isotopes. To mimic laboratory measurements, naturally occurring U and Pb isotopes were also mixed in proportions to mimic samples of three different ages, to be run as internal

  8. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies

    International Nuclear Information System (INIS)

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul

  9. Datafile: Argentina

    International Nuclear Information System (INIS)

    Consideration is given to modern state and prospects of development of nuclear power in Argentina, the role and tasks of regulating bodies, specific features of fuel cycle, international relations and nuclear safequards. The first NPP was put in operation in 70-s. Technical and economical indices of Atucha-1 NPP were among the best in the world till 1983, the total load factor was equal to 75%. Later on the load factor decreased down to 67% for different reasons. In 1988 the power plant was shutdown. Argentina cooperates with many countries including Brazil, Cuba, Turkey, Nigeria and Algeria. Negotiations about drawing up conditions of including Argentina NPPs into the system of nuclear safeguides are carried on with IAEA

  10. U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications

    Institute of Scientific and Technical Information of China (English)

    王岳军; 范蔚茗; 郭锋; 李惠民; 梁新权

    2002-01-01

    The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some of the zircon grains give an upper intercept age of about 1753 Ma and 207Pb/206Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components during the melting process.

  11. The contorted New England Orogen (eastern Australia): New evidence from U-Pb geochronology of early Permian granitoids

    Science.gov (United States)

    Rosenbaum, Gideon; Li, Pengfei; Rubatto, Daniela

    2012-02-01

    A series of sharp bends (oroclines) are recognized in the Paleozoic to early Mesozoic New England Orogen of eastern Australia. The exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated. Here we present zircon U-Pb ages that confirm the lateral continuation of early Permian (296-288 Ma) granitoids and shed new light on the oroclinal structure. Orogenic curvature is defined by the alignment of early Permian granitoids parallel to the structural grain of the orogen, as well as the curved geometry of sub-vertical deformation fabrics, forearc basin terranes, and serpentinite outcrops. Alternative geometrical interpretations may involve two bends (Texas and Coffs Harbour Oroclines), three bends (+Manning Orocline), or even four bends (+Nambucca Orocline). We argue that the model involving four bends is most consistent with available data, although further kinematic constraints are required to confirm the existence of the Manning and Nambucca Oroclines. A subsequent phase of younger magmatism (Bowen orogeny.

  12. Permian depositional age of metaturbidites of the Duque de York Complex, southern Chile: U-Pb SHRIMP data and palynology

    International Nuclear Information System (INIS)

    The Duque de York Complex (DYC) is part of the low grade metamorphic accretionary complexes of the pre-Andean Patagonian 'basement'. It is a sedimentary succession exposed along the western margin of southernmost South America. New U-Pb zircon ages and palynological data restrict the maximum depositional age of the DYC to the limit between the early Permian (Kungurian) and the middle Permian (Roadian). The palynological association recorded in the DYC, characterized mainly by Gymnospermopsida pollen, indicates a humid environment of forest with an under-growth of ferns. Regional paleogeographic correlations point out that an interpretation of DYC as an autochthonous terrane cannot be discarded, contrasting with previous hypotheses which suggest an allochthonous character for this complex

  13. Combined U-Pb and Lu-Hf isotope analyses by laser ablation MC-ICP-MS: methodology and applications

    Directory of Open Access Journals (Sweden)

    Massimo Matteini

    2010-06-01

    Full Text Available The Lutetium-Hafnium isotopic system represents one of the most innovative and powerful tools for geochronology and isotopic studies. Combined U-Pb and Lu-Hf in situ analyses on zircon by LA-MC-ICP-MS permit to characterize isotopically the host magma from which it crystallized furnishing significant information for sediment provenance and crustal evolution studies. In this paper e describe the Lu-Hf systematic by LA-MC-ICP-MS developed in the laboratory of Geochronology of the University of Brasilia and report the results obtained by repeated analyses of 176Hf/177Hf isotopic ratio of three zircon standards: GJ-1 = 0.282022 ± 11 (n=56, Temora 2 = 0.282693 ± 14 (n=25 and UQZ = 0.282127 ± 33 (n=11. The 176Hf/177Hf ratio (0.282352 ± 22, n=14 of gem quality zircon used as in-house standard have been also characterized. As a geological application, we analyzed two complex zircons selected from a migmatitic rocks from the Borborema Province, NE Brazil. On the basis of U-Pb and Lu-Hf data, two main crystallization events have been identified in both studied zircons. An older event at ca. 2.05 Ga recognized in the inherited cores represents a well-characterized paleoproterozoic magmatic event that affected the whole Borborema Province. A second crystallization event at ~ 575 Ma, recognized at the rims, represents a Neoproterozoic (Brazilian high grade metamorphic-magmatic event.O sistema isotópico Lutécio-Hafnio representa uma das ferramentas mais recentes e poderosas para estudos isotópicos e geocronológicos. Análises combinadas in situ de U-Pb e Lu-Hf sobre zircão pelo LA-MC-ICP-MS permitem caracterizar iso-topicamente o magma onde ele cristalizou, fornecendo valiosas informações para estudos de proveniência de sedimento e de evolução crustal. Nesse trabalho descrevemos a sistemática de Lu-Hf pelo LA-MC-ICP-MS implantada no laboratório de Geocronologia da Universidade de Brasília e reportamos os resultados obtidos de repetidas an

  14. The age of mid Proterozoic phosphatic metasediments in Finland as indicated by radiometric U-Pb dates

    International Nuclear Information System (INIS)

    Two uranium-bearing phosphatic metasedimentary occurrences at Lampinsaari, Vihanti and Temo, Nilsiae, in Finland have been dated by isotopic U-Pb analyses of whole rock samples to be 1876+-2 Ma old. The dates reflect the time of the Svecokarelian regional metamorphism in high amphibolite facies. An analysis of a uranium thucolite from the deposit at Nuottijaervi, Paltamo, that was metamorphosed in intermediate greenschist facies gives a date of 1897+-7 Ma, suggesting that the phosphatic sedimentation had occurred before that time. An upper time limit for the sedimentation is set by a previous date of 2080+-45 Ma, which was obtained from a banded iron ore formation. The absence of thorium in the deposits suggests a marine environment of deposition. (Auth.)

  15. U-Pb isotopic evidence for accretion of a continental microplate in the Zalm region of the Saudi Arabian Shield

    Science.gov (United States)

    Stacey, J.S.; Agar, R.A.

    1986-01-01

    The region covered by this work includes three of the main tectonic units of the Arabian Shield: the Afif continental terrane, the Nabitah suture with its associated mobile belt, and the Asir ensimatic arc terrane. The geology of the area is well understood, and this geochronologic and isotopic study confirms that the Afif terrane was a continental microplate in the late Proterozoic. The study also provides a time frame for the crustal evolution of this part of the Shield. U-Pb zircon age data from a pelitic garnet-sillimanite gneiss of the Kabid formation shows that this part of the continental basement in the Afif terrane may be as old as 1830 Ma. Isotope data indicate that lead from the Kabid gneiss resided in the upper continental crust for a long period before 1830 Ma, and require that Archean rocks exist at depth beneath the Afif terrane.

  16. Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province.

    Science.gov (United States)

    Blackburn, Terrence J; Olsen, Paul E; Bowring, Samuel A; McLean, Noah M; Kent, Dennis V; Puffer, John; McHone, Greg; Rasbury, E Troy; Et-Touhami, Mohammed

    2013-05-24

    The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon uranium-lead (U-Pb) geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over about 600,000 years, indicating expansive volcanism even as the biologic recovery was under way. PMID:23519213

  17. Mesoproterozoic Continental Arc Type Granite in the Central Tianshan Mountains: Zircon SHRIMP U-Pb Dating and Geochemical Analyses

    Institute of Scientific and Technical Information of China (English)

    YANG Tiannan; LI Jinyi; SUN Guihua; WANG Yanbin

    2008-01-01

    The Central Tianshan belt in northwestern China is a small Precambrian block located in the southern part of the Central Asia Orogenic Belt (CAOB), which is considered as "the most voluminous block of young continental crust in the world" that comprises numerous small continental blocks separated by Paleozoic magmatic arcs. The Precambrian basement of the central Tianshan Mountains is composed of volcanic rocks and associated volcano-sedimentary rocks that were intruded by granitic plutons. Geochemical analyses demonstrate that the granitic plutons and volcanic rocks were generated in the Andean-type active continental arc environment like today's Chile, and the zircon U-Pb SHRIMP dating indicates that they were developed at about 956 Ma, possibly corresponding to the subduction of the inferred Mozambique Ocean under the Baltic-African super-continent.

  18. Nd isotopes, U-Pb single grain and SHRIMP zircon ages from basement rocks of the Tocantin Province

    International Nuclear Information System (INIS)

    Large areas of the northern part of the Brasilia Belt, Tocantins Province, central Brazil, are underlain by basement granite-gneiss terrain and associated volcano-sedimentary sequences, as well as felsic and mafic-ultramafic intrusions. The basement rocks are covered by the late Paleoproterozoic-Mesoproterozoic rift-related Arai and Natividade groups and intruded by 1.77 to 1.58 Ga an orogenic granites of the Goias Tin Province (Pimentel and Botelho, 2001). To the southwest they are un conformably overlain by the low-grade late Proterozoic Paranoa Group, whereas to the east they are in faulted contact with the Neoproterozoic Bambui Group at the western edge of the Sao Francisco Craton. To the north they are covered by Phanerozoic sediments of the Parnaiba and Sanfranciscana basins. Despite their large extension, granite-gneiss and associated supracrustals of SE Tocantins and NE Goias are still poorly known. Previous regional Rb-Sr and K-Ar isotopic studies indicated dominant early Proterozoic ages and late Proterozoic cooling ages (Hasui, et al. 1980, Fernandes et al. 1982). More detailed studies in the Almas-Dianopolis area (Costa, 1984) came up with similar results, although the region was interpreted as underlain by Archean granite-greenstone terrain, following previous suggestions by Costa et al. (1976). Recent work recognized the presence of two suites of deformed granitoids (Cruz and Kuyumjian, 1996, 1998). The oldest suite intruded the supracrustals and comprises hornblende-bearing tonalite gneiss, with minor trondhjemite, granodiorite, and quartz diorite. The younger suite comprises oval shaped biotite-bearing tonalite, trondhjemite, and granodiorite intrusions. Both suites display low-K calc-alkaline affinity, the younger being more Al-rich. Both are interpreted as TTG suites and were dated at 2,2 Ga using U-Pb SHRIMP (Cruz et al 2000). In the Porto Nacional area, Gorayeb et al. (2000) determined single zircon Pb-evaporation ages of 2.15 Ga in granulites

  19. U-Pb geochronology of porphyry bodies of the gold district Vetas California (Depto of Santander, Colombia)

    International Nuclear Information System (INIS)

    Two riodacite porphyry bodies, located in the central sector of the Santander Massif (Cordillera Oriental), were dated by U-Pb method, using the LA-MC-ICPMS technique: Multi collector-Laser Ablation- Inductively Coupled Plasma-Mass Spectrometer. The obtained ages (8.4 ± 0.2 and 9.0 ± 0.2 Ma), evidences a magmatic phase during the Late Miocene (Tortoniano), which took place during the Andean Orogeny. The identification of this magmatic pulse, in addition to provide new information on the geological history of the Santander Massif, deserves special attention, from the point of view of mineral deposit exploration, considering that rocks with the same age and features are related to the formation of important magmatic-hydrothermal deposits, as has been recognized in other regions of the Andean orogenic system.

  20. Polymetamorphic history of the Crixas-Acu gneiss, central Brazil: SHRIMP U-Pb evidence from titanite and zircon

    International Nuclear Information System (INIS)

    A sample of the Crixas-Acu gneiss in Central Brazil contains protolith and metamorphic zircons, and two generations of metamorphic titanite. SHRIMP U-Pb data of these different mineral generations indicate the following temporal sequence: tonalitic magmatism at 2817 ± 9 M.y derived from an older source region (3050 to 2930 M.y zircon cores); Archaen metamorphic at 2772±6 M.y (from zircon)with cooling to the blocking temperature of titanite (at 2711 ±34 Ma); followed by Paleoproterozoic metamorphism and weak fabric development at 2011 ±+ 15 Ma, and a possible Neoproterozoic metamorphism. The field relations and these age data indicate the polymetamorphic history of the area and demonstrate the value of in situ age determinations on well-characterized rocks. (author)

  1. Zircon SHRIMP U-Pb Dating, Geochemical Characteristics and Tectonic Significance of Granitic Gneisses in Amdo, Tibet

    Institute of Scientific and Technical Information of China (English)

    Lu Lu; Zhenhan Wu; Zhen Zhao; Daogong Hu; Peisheng Ye

    2014-01-01

    The Amdo microcontinent is located within the middle of Bangong-Nujiang suture (BNS) zone in the shape of lens. The basic geological research restricts geologists from understand-ing the histories of tectonic evolution of BNS and regional geology more deeply. This paper system-atically studies the geochronology and geochemistry of granitic gneisses from Amdo basement. These data provide constraints on formation age, source characteristics and tectonic setting of their protolith. The SHRIMP zircon U-Pb dating is operated for granitic gneisses. Samples AGS-2 and AGS-3 (granitic gneiss) yield average zircon U-Pb ages of 485±14 and 487±6 Ma, respectively. These ages should represent the formation age of protolith and indicate that they are formed in the Early Ordovician. Granitic gneisses are characterized by high SiO2, Na2O, K2O and Al2O3, low Fe and Mg, enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), deple-tion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), with negative Eu anomaly. The Rittmann index (σ) is 1.77 to 2.60, less than 3.3. The aluminum saturation index (A/CNK) values range from 0.88 to 1.26. These features suggest that protolith of granitic gneisses from Amdo basement show characteristics of calc-alkaline and S-type granite, and they could be de-rived from partial melting of metamorphic greywackes in the upper crust of low maturity. The tec-tonic setting is syn-collision. These all suggest that the formation of protolith of granitic gneisses from Amdo are caused by the Early Paleozoic orogeny, which could be related to proto-Tethyan oceanic subduction along Gondwana continental margins, and does not result from the production of Pan-African orogenesis.

  2. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    International Nuclear Information System (INIS)

    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  3. First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

    Directory of Open Access Journals (Sweden)

    Vozárová Anna

    2015-10-01

    Full Text Available Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU. The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44–0.27 and for the Nb/U ratio at (9.55–4.18, which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U–238Pb zircon ages (concordia age at 269 ± 7 Ma confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

  4. First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

    Science.gov (United States)

    Vozárová, Anna; Presnyakov, Sergey; Šarinová, Katarína; Šmelko, Miloš

    2015-10-01

    Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44-0.27) and for the Nb/U ratio at (9.55-4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U-238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

  5. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros Junior, Edgar Batista; Marques, Rodson Abreu, E-mail: edgarjr@ymail.com, E-mail: rodson.marques@ufes.br [Universidade Federal do Espirito Santo (UFES), Alegre, ES (Brazil). Departamento de Geologia; Jordt-Evangelista, Hanna; Queiroga, Glaucia Nascimento, E-mail: hanna@degeo.ufop.br, E-mail: glauciaqueiroga@yahoo.com.br [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Schulz, Bernhard, E-mail: bernhard.schulz@mineral.tu-freiberg.de [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)

    2016-01-15

    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  6. High precision time calibration of the Permo-Triassic boundary mass extinction by U-Pb geochronology

    Science.gov (United States)

    Baresel, Björn; Bucher, Hugo; Brosse, Morgane; Schaltegger, Urs

    2014-05-01

    U-Pb dating using Chemical Abrasion, Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) is the analytical method of choice for geochronologists, who are seeking highest temporal resolution and a high degree of accuracy for single grains of zircon. The use of double-isotope tracer solutions, cross-calibrated and assessed in different EARTHTIME labs, coinciding with the reassessment of the uranium decay constants and further improvements in ion counting technology led to unprecedented precision better than 0.1% for single grain, and 0.05% for population ages, respectively. These analytical innovations now allow calibrating magmatic and biological timescales at resolution adequate for both groups of processes. To construct a revised and high resolution calibrated time scale for the Permian-Triassic boundary (PTB) we use (i) high-precision U-Pb zircon age determinations of a unique succession of volcanic ash beds interbedded with shallow to deep water fossiliferous sediments in the Nanpanjiang Basin (South China) combined with (ii) accurate quantitative biochronology based on ammonoids and conodonts and (iii) carbon isotope excursions across the PTB. Using these alignments allows (i) positioning the PTB in different depositional environments and (ii) solving age/stratigraphic contradictions generated by the index, water depth-controlled conodont Hindeodus parvus, whose diachronous first occurrences are arbitrarily used for placing the base of the Triassic. This new age framework provides the basis for a combined calibration of chemostratigraphic records with high-resolution biochronozones of the Late Permian and Early Triassic. Besides the general improvement of the radio-isotopic calibration of the PTB at the ±100 ka level, this will also lead to a better understanding of cause and effect relations involved in this mass extinction.

  7. Pb-Pb and U-Pb zircon ages of archean syntetocnic granites of the Carajas metallogenic province, northern Brazil

    International Nuclear Information System (INIS)

    The Carajas Metallogenic Province is located in the southeastern Amazonian Craton. It has been divided in two domains, the southernmost comprises the Rio Maria region and the northernmost corresponds to Caraj region (Souza et al. 1996). The former domain is made up of Archean greenstone sequences (2,97 Ga), TTG (2,9 Ga) and calc-alkaline granitoids (2,87 Ga) (Macambira and Lafon 1995, Leite et al. 1999, Althoff et al. 2000). The Carajas block is constituted of minor mafic granulites (3,00 Ga) and quartzofeldspathic gneisses (2,81 Ga), metavolcanosedimentary sequences (2,76 Ga) and granites (2,76 to 2,56 Ga) (Machado et al. 1991; Huhn et al. 1999, Pidgeon et al. 2000). Widespread anorogenic A-type granites are found in both areas (Docegeo 1988; Dall'Agnol et al. 1994). In the last two decades several authors (Lindenamyer et al. 1994, Barros and Barbey 1998, Huhn et al. 1999 and others) have emphasized the role of the Archean granite magmatism in the tectonicthermal evolution in the Carajas Province. In this paper we discuss the tectonic significance of the Pb- Pb and U-Pb ages obtained in some granitoids from the Carajas region. The Estrela Granite Complex and the granitoids located to the north of Parauapebas were dated by Pb- Pb evaporation zircon method (cf. Kober 1987). Data are presented considering 2σ∼. The Pb corrections have been done in the basis of the evolution model of Pb in double stage (cf. Stacey and Kramers 1975). U-Pb zircon method (cf. Krogh 1973, Stacey and Kramers 1975, Parrish 1987, Ludwuig 1999), recently put on routine in the Para-Iso laboratories, was employed to date the granite from the Serra do Rabo area. Analyses were carried on the Finnigan Mat 262 spectrometer (au)

  8. Provenance and sediment dynamics within river basins in Western Peru through detrital zircons U-Pb ages

    Science.gov (United States)

    Camille, Litty; Pierre, Lanari; Marco, Burn; Fritz, Schlunegger

    2016-04-01

    U-Pb dating of detrital zircons from clastic sediments by LA-ICPMS has become a popular method in sedimentary correlation and provenance studies. Because of remarkable durability, detrital zircons may be reworked through multiple sedimentary cycles and provide an ideal material to study the sedimentary provenance in rivers and the erosional characteristics. The Western side of the Peruvian Andes has experienced multiple pluvial periods induced phases of erosion and the formation of subsequent cut-and-fill terrace sequences since the Pleistocene. The aim of the study is to estimate the source areas of the terrace and modern deposits to infer changes in sediment dynamics through time and correlate them with the climatic change and especially precipitation patterns. To this extent, we determined the provenance of 4 dated terrace deposits along with modern sediments from the same streams by matching detrital-zircon ages with crystallization ages of source rocks. Age populations of detrital zircons are derived using U-Pb LA-ICP-MS analysis of about 50 zircons. Results show changes in the sediment provenance through time. Nowadays, sediment source areas are mainly located on the uppermost reach of the rivers whereas during the Pleistocene, sediment source areas were both located in the headwaters and along the middle reach of the rivers. These differences in terms of provenance could correlate with a change in precipitation locations and rates. Indeed a scenario where the locus of precipitation occurrence shifted from the middle reaches including the Altiplano during the past, to the Altiplano only as observed today, along with higher precipitation rates during the periods of terraces formation, offers an explanation to explain the erosional patterns recorded by detrital zircons.

  9. U-Pb circon ages from the Milford Orthogneiss, Milford Sound, northern Fiordland : Paleozoic igneous emplacement and Early Cretaceous metamorphism

    International Nuclear Information System (INIS)

    Milford Orthogneiss is an extensive hornblende-metadiorite/gabbro unit centred on Milford Sound, northern Fiordland. U-Pb TIMS data from zircon indicate both Paleozoic and Early Cretaceous age components, but cannot distinguish between a Palozoic or Early Cretaceous age for the igneous protolith. U-Pb zircon ion probe analyses, guided by cathodoluminescence images of the internal structure of the zircons, indicate that individual grains are either essentially Paleozoic (355 +/-10 Ma oscillaroty zoned igneous grains) or Early Cretaceous (134 +/-2 Ma patchy/sector zoned grains) in age. Rare grains show patchy/'sector' zones apparently overprinting and replacing oscillatory zonation. In most cases both types of grain are also rimmed by low-U zircon (120 +/-2 Ma) that may date the breakdown of a Zr-containing mafic phase during a second phase of prograde metamorphism. Other than the low U-rims, a (igneous) Cretaceous overgrowth over a Paleozoic core is not observed. We interpret these data to indicate that the protolith of the Milford Orthogneiss was emplaced at ∼360 Ma and subsequently metamorphosed in two distinct events in the Early Cretaceous (∼134 and ∼120 Ma. Thus 1) the Milford Orthogneiss cannot represent the metamorphic equivalent of the high-level Darran Complex (138 Ma) to the east, despite lithological and chemical similarities, and a major shear zone is confirmed between these two units; 2) Paleozoic 'cover' rocks in Fiordland may have suffered high-pressure metamorphism in the Cretaceous; 3) annealing or recrystallisation of zircon at ∼134 Ma is believed to record a high-pressure metamorphic event possibly related to subduction of the continental margin; and 4) Milford Orthogneiss may represent McCulloch et al.'s (1987) hypothesised source from which the Western Fiordland Orthogneiss was derived. (author). 36 refs., 9 figs., 2 tabs

  10. Acerca de la edad de inimputabilidad en Argentina/About the age of insanity in Argentina

    Directory of Open Access Journals (Sweden)

    Osvaldo N. Tieghi (Argentina

    2010-01-01

    Full Text Available Se dice que desde hace muchos años (aproximadamente 30 o más, se venía alertando sobre la corrupción en todas las etapas de la vida, la causa principal es por la disminución educativa moral. No solamente el delito y la generación de tendencias juveniles cromógenas son las consecuencias del aprendizaje subcultural del delito. Así mismo encontramos el despreciable abandono de la educación virtuosa, que también conocida como la crisis institucional del aprendizaje social de índole moral. Se puede considerar que los factores de riesgo son los periodos transicionales críticos, porque al tiempo que las sociedades, los estados y las repúblicas evolucionan de forma moderara e imperceptible o brusca, las personas van asimilando y/o adquiriendo mayor incompatibilidad y mayor agresividad, incluyendo los niños de la segunda infancia (desde los 7 a los 12 años.

  11. Rafaela, Argentina

    OpenAIRE

    Omar Perotti

    2004-01-01

    Brinda información acerca de la provincia de Rafaela, Argentina. Da a conocer el planeamiento estratégico de Rafaela, los temas a resolver con el sector privado, así como las acciones para abordar la relación público-privada.

  12. Argentina; Argentine

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-04-01

    This economical study summarizes the energy situation of Argentina: energy institutions and policy, energy companies (oil, electricity, gas, coal), energy supplies (resources, power production, petroleum, natural gas), prices and tariffs, consumption, economical stakes and perspectives (investments, agreements, projects). Energy data for the 1971-1999 period are summarized in graphs and tables. (J.S.)

  13. Carboniferous-Permian volcanic evolution in Central Europe-U/Pb ages of volcanic rocks in Saxony (Germany) and northern Bohemia (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Hoffmann, U.; Breitkreuz, Ch.; Breiter, Karel; Sergeev, S.; Stanek, K.; Tichomirowa, M.

    2013-01-01

    Roč. 102, č. 1 (2013), s. 73-99. ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : pyroclastic rocks * dykes * stratigraphy * SHRIMP U/Pb ages * Pb/Pb single zircon age * Variscides Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.084, year: 2013

  14. U-Pb zircon ages and structural development of metagranitoids of the Teplá crystalline complex: evidence for pervasive Cambrian plutonism within the Bohemian massif (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Dörr, W.; Fiala, Jiří; Vejnar, Zdeněk; Zulauf, G.

    1998-01-01

    Roč. 87, č. 1 (1998), s. 135-149. ISSN 0016-7835 R&D Projects: GA AV ČR KSK1012601 Grant ostatní: DFG(DE) Zu73/1-3 Keywords : Cambrian plutonism * U-Pb analyses * Bohemian massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.841, year: 1998

  15. Variable microstructural response of baddeleyite to shock metamorphism in young basaltic shergottite NWA 5298 and improved U-Pb dating of Solar System events

    Science.gov (United States)

    Darling, James R.; Moser, Desmond E.; Barker, Ivan R.; Tait, Kim T.; Chamberlain, Kevin R.; Schmitt, Axel K.; Hyde, Brendt C.

    2016-06-01

    The accurate dating of igneous and impact events is vital for the understanding of Solar System evolution, but has been hampered by limited knowledge of how shock metamorphism affects mineral and whole-rock isotopic systems used for geochronology. Baddeleyite (monoclinic ZrO2) is a refractory mineral chronometer of great potential to date these processes due to its widespread occurrence in achondrites and robust U-Pb isotopic systematics, but there is little understanding of shock-effects on this phase. Here we present new nano-structural measurements of baddeleyite grains in a thin-section of the highly-shocked basaltic shergottite Northwest Africa (NWA) 5298, using high-resolution electron backscattered diffraction (EBSD) and scanning transmission electron microscopy (STEM) techniques, to investigate shock-effects and their linkage with U-Pb isotopic disturbance that has previously been documented by in-situ U-Pb isotopic analyses. The shock-altered state of originally igneous baddeleyite grains is highly variable across the thin-section and often within single grains. Analyzed grains range from those that preserve primary (magmatic) twinning and trace-element zonation (baddeleyite shock Group 1), to quasi-amorphous ZrO2 (Group 2) and to recrystallized micro-granular domains of baddeleyite (Group 3). These groups correlate closely with measured U-Pb isotope compositions. Primary igneous features in Group 1 baddeleyites (n = 5) are retained in high shock impedance grain environments, and an average of these grains yields a revised late-Amazonian magmatic crystallization age of 175 ± 30 Ma for this shergottite. The youngest U-Pb dates occur from Group 3 recrystallized nano- to micro-granular baddeleyite grains, indicating that it is post-shock heating and new mineral growth that drives much of the isotopic disturbance, rather than just shock deformation and phase transitions. Our data demonstrate that a systematic multi-stage microstructural evolution in

  16. Characterization and zircon SHRIMP U-Pb geochronology of the subvolcanic rocks from Yarumalito Porphyry System, Marmato District, Colombia; Caracterizacao e geocronologia SHRIMP U-Pb em zircao das rochas subvulcanicas do sistema porfiro Yarumalito, Distrito de Marmato, Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Henrichs, Isadora A.; Frantz, Jose Carlos; Marques, Juliana C.; Castoldi, Marco S., E-mail: isahenrichs@gmail.com, E-mail: jose.frantz@ufrgs.br, E-mail: juliana.marques@ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Instituto de Geociencias; Ordonez-Carmona, Oswaldo, E-mail: oswaldo.geologo@gmail.com [Universidad Nacional de Colombia, Medellin (Colombia). Facultad de Minas; Sato, Kei, E-mail: keisato@usp.br [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Centro de Pesquisas Geocronologicas

    2014-09-15

    The mining District of Marmato, located in the Central Cordillera, is considered one of the oldest gold districts in Colombia and its exploration dates back to the Inca’s times, being exploited regularly for more than a thousand years. Inserted in this context lies the Yarumalito porphyry system (YPS), characterized to concentrate ore in structure related veins and stockworks. The YPS is related to the Miocene magmatism of the Combia Formation. In this paper, the subvolcanic rocks directly associated with the mineralized zones were described in order to obtain U-Pb ages in zircon to the intrusions. Selected samples from two fertile intrusions, one andesitic (more abundant in the area) and other dioritic (more restricted), were carefully described and dated by SHRIMP. The results points to a very restricted interval for the ages, with weighted average {sup 206}Pb/{sup 238}U varying from 7,00 ± 0,15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results constrain the Yarumalito system to the final stages of the Combia magmatism and suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and in the Marmato District. (author)

  17. Edades del basamento pre-varisco en Iberia: Herencia Icartiense, Grenville y Cadomiense en rocas del Complejo Olio de Sapo (NW de España). Estudio geocronológico mediante ablación láser

    OpenAIRE

    Fernández Suárez, Javier; Gutiérrez Alonso, Gabriel; Jenner, G. A.; Tubrett, M.

    1998-01-01

    [ES] Se han datado circones extraídos de rocas pertenecientes al complejo ígneo-vulcanosedimentario Olio de Sapo mediante la técnica de Ablación Laser ICPMS. Los resultados U-Pb en cristales individuales de circón indican la existencia de, al menos, tres eventos pre-Paleozoicos de formación de corteza en el NW de Iberia. Las edades más antiguas (ca 1,9-2 Ga) corresponden al evento Icartiense, que se ha identificado en otras áreas de la cadena Varisca de Europa occidental. El segundo evento (c...

  18. SHRIMP zircon U-Pb geochronology of early Mesozoic felsic igneous rocks from the southern Lancangjiang and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    PENG Touping; WANG Yuejun; FAN Weiming; LIU Dunyi; SHI Yuruo; MIAO Laicheng

    2006-01-01

    The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzonitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean 206pb/238U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean 206Pb/238U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (~230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic 206Pb/238U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of development of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.

  19. SHRIMP U-Pb geochronology of the detrital zircons from the Longshoushan Group and its tectonic significance

    Institute of Scientific and Technical Information of China (English)

    KuoAn TUNG; HoungYi YANG; LIU DunYi; ZHANG JianXin; ChienYuan TSENG; WAN YuSheng

    2007-01-01

    Sixty-two geologically meaningful U-Pb dates were obtained by using SHRIMP technique for the detrital zircons in three mettasedimentary rocks from stratigraphically uppermost parts of the Longshoushan Group in the present study.Eighty percents of these dates range from 1.7 Ga to 2.2 Ga with a peak at 1.8-2.0 Ga and twenty percents from 2.3 Ga to 2.7 Ga.The youngest detrital zircon is dated at 1724±19Ma which is interpreted as the maximum depositional age of the metasedimentary rocks.Therefore,the age for the diagenesis and lithification of the original sedimentary rocks of the Longshoushan Group before the metamorphism must be younger than 1724±19 Ma.Comparison of the age histograms of these detrital zircons with the ages of the igneous rocks on the surrounding older massifs suggests that the sediments of the Longshoushan Group were most likely derived from the Alaxa Block and Tarim Craton.This implies that the affinity between Alaxa Block and Tarim Craton was strong and that they might have been a unified craton during middle-early Proterozoic time

  20. SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Complex in Western Shandong and Its Geological Implications

    Institute of Scientific and Technical Information of China (English)

    HU Huabin; MAO Jingwen; LIU Dunyi; NIU Shuyin; WANG Yanbin; LI Yongfeng; SHI Ruruo

    2005-01-01

    The SHRIMP U-Pb zircon dating result of the Tongshi magmatic complex in western Shandong is presented in this paper.The Tongshi magmatic complex comprises fine-grained porphyritic diorite and syenitic porphyry.Eighteen analyses for fine-grained porphyritic diorite gave two concordia ages,in which ten analyses constitute the young age group,giving 206Pb/238U ages ranging from 167.9 Ma to 183 Ma with a weighted mean age of 175.7±3.8 Ma,and the other eight yielded 207Pb/206Pb ages of 2502 Ma to 2554 Ma with a weighted mean 2518±11 Ma.Two analyses for syenitic porphyry gave ages of 2485 Ma and 2512 Ma,respectively.The age of 175.7±3.8 Ma indicates that the crystallization of the Tongshi magmatic complex occurred in the Middle Jurassic,whereas that of 2518±11 Ma is interpreted as the age of inherited magmatic zircons in the Neoarchean Wutai period.

  1. Detrital U-Pb zircon dating of lower Ordovician syn-arc-continent collision conglomerates in the Irish Caledonides

    Science.gov (United States)

    Clift, P.D.; Carter, A.; Draut, A.E.; Long, H.V.; Chew, D.M.; Schouten, H.A.

    2009-01-01

    The Early Ordovician Grampian Orogeny in the British Isles represents a classic example of collision between an oceanic island arc and a passive continental margin, starting around 480??Ma. The South Mayo Trough in western Ireland preserves a complete and well-dated sedimentary record of arc collision. We sampled sandstones and conglomerates from the Rosroe, Maumtrasna and Derryveeny Formations in order to assess erosion rates and patterns during and after arc collision. U-Pb dating of zircons reveals a provenance dominated by erosion from the upper levels of the Dalradian Supergroup (Southern Highland and Argyll Groups), with up to 20% influx from the colliding arc into the Rosroe Formation, but only 6% in the Maumtrasna Formation (~ 465??Ma). The dominant source regions lay to the northeast (e.g. in the vicinity of the Ox Mountains, 50??km distant, along strike). The older portions of the North Mayo Dalradian and its depositional basement (the Annagh Gneiss Complex) do not appear to have been important sources, while the Connemara Dalradian only plays a part after 460??Ma, when it supplies the Derryveeny Formation. By this time all erosion from the arc had effectively ceased and exhumation rates had slowed greatly. The Irish Grampian Orogeny parallels the modern Taiwan collision in showing little role for the colliding arc in the production of sediment. Negligible volumes of arc crust are lost because of erosion during accretion to the continental margin. ?? 2008 Elsevier B.V.

  2. Detrital zircon U-Pb geochronology of the Siwalik Group of the Nepal Himalaya: implications for provenance analysis

    Science.gov (United States)

    Baral, Upendra; Lin, Ding; Chamlagain, Deepak

    2016-04-01

    This paper deals with the provenance analysis of the Neogene foreland basin sediments of the Siwalik Group in the Nepal Himalaya. This study adopts the techniques of the optical petrography and detrital zircon U-Pb ages from two river sections: the Koshi Nadi in eastern Nepal and the Surai Khola in western Nepal Himalaya. The optical petrography data and resulting QFL plot show a "recycled orogeny" field for the studied sandstone samples, indicating northern lithotectonic units; Tethys Himalaya, Higher Himalaya and Lesser Himalaya as the source of the foreland basin sediments. The detrital zircon geochronological data set has clearly revealed that the cluster ages are younger than ~1000 Ma; however, the older grains (>1000 Ma) are significantly fewer. The obtained age spectrum is similar to the Tethys Himalaya and the upper Lesser Himalaya, but the lower Lesser Himalayan rocks were not distinct, which indicates that sediments in the Neogene foreland basin of the Nepal Himalaya were primarily sourced from the Tethys Himalaya and upper Lesser Himalaya. The minor subordinate scattered peaks that roughly correspond to the age of the Higher Himalaya and lower Lesser Himalaya may indicate that a lower proportion of the sediments might have a link with the Higher Himalaya and lower Lesser Himalaya. Therefore, the provenance of the Siwalik Group in the Nepal Himalaya might have witnessed a mixed type of provenance similar to the northwestern Himalaya.

  3. Formation and evolution of the Cigar Lake uranium deposit based on U-Pb and K-Ar isotope systematics

    International Nuclear Information System (INIS)

    A systematic geochronological study was conducted on the Cigar Lake uranium deposit. U-Pb and Pb-Pb systematics were applied to different types of uranium ore, and various associated sheet silicates were dated by the K-Ar method. These two approaches define a widespread retrograde metamorphic event in the basement, which occurred at about 1780 Ma during the Hudsonian orogeny, and a four-stage evolutionary model for the ore deposit. This model is compatible with the history of other unconformity-type uranium deposits in the Athabasca Basin. The first stage in the evolution of the Cigar Lake uranium deposit is marked by uraninite crystallization at 1341 ± 17 Ma, which, in association with arsenides and sulfarsenides, constitutes the mineralization of economic interest (main orebody). The second stage, characterized by a Fe-kaolinite and Fe-illite paragenesis, occurred locally at about 900 Ma. The third stage involved uranium mobilization at about 325 Ma and is characterized by (i) preferential loss of radiogenic lead from primary uraninite and crystallization of pitchblende at the rims of uraninite grains and (ii) formation of pitchblende associated with Fe sulfides or hematite in the main and perched orebodies. The last stage is characterized by recent alteration and coffinitization which have affected all ore types. 40 refs., 8 figs., 3 tabs

  4. Multi-stage evolution of gneiss from North Dabie:evidence from zircon U-Pb chronology

    Institute of Scientific and Technical Information of China (English)

    XIE Zhi; GAO Tianshan; CHEN Jiangfeng

    2004-01-01

    TTG gneiss is a common rock to outcrop in the northern part of the Dabie orogen, a few of which are closely associated with eclogites that experienced the Triassic ultrahigh pressure metamorphism. Although they were thermally metamorphosed by a large-scale magma activity in this region at the Early Cretaceous, it is unclear whether or not they are also affected by the Triassic metamorphism during continental subduction and exhumation. In order to resolve this issue, SHRIMP zircon U-Pb dating was carried out for the host gneiss of eclogites in North Dabie. The results show that cores from the gneiss have an age of 746±31 Ma, consistent with the protolith ages of granitic gneisses in the Dabie orogen. Zircon overgrowing with different U and Th concentrations give concordant ages of 212±21 and 120±11 Ma, respectively. Th/U ratios of overgrown zircons are both lower than 0.1, suggesting a metamorphic genesis. The present results suggest that the gneiss in North Dabie has the similar protolith ages of Neoproterozoic to those granitic gneisses elsewhere in the Dabie orogen, and experienced not only the Triassic metamorphism but also the thermal metamorphism due to the Early Cretaceous magmatism. This provides an important insight into the geodynamic evolution of gneissic rocks in the Dabie orogen.

  5. Petrogenesis of keratophyes in the Pingshui Group,Zhejiang: Constraints from zircon U-Pb ages and Hf isotopes

    Institute of Scientific and Technical Information of China (English)

    CHEN ZhiHong; XING GuangFu; GUO KungaYi; DONG YongGuan; CHEN Rong; ZENG Yong; LI LongMing; HE ZhengYu; ZHAO Ling

    2009-01-01

    Zircon LA-ICP-MS U-Pb ages and Hf isotopic as well as whole-rock geochemical data are reported for keratophyes in the Pingshui Group, Zhejiang. The results are used to discuss their petrogenesis and geological significance. The keratophyes were dated at 904±8 to 906±10 Ma. These intermediate-felsic rocks are characterized by high LREE contents end depletion of HREE and HFSE (e.g., Nb, Ta, Ti, P), resembling arc-derived rocks. The keratophyes exhibit positive εHf(t) values of 8.6 to 15.4, consistent with their εNd(t) values of 6.4 to 7.9 but far away from those of crust-derived rocks. Such features indicate that they were likely originated from prompt reworking of juvenile crust by arc-continent collision during the early-Neoproterozoic assembly between the Cathaysia and Yangtze Blocks. Combining with their Hf model ages, we suggest that there may exist not only remarkable growth of juvenile crust at ca.1.3-1.1 Ga but also production of juvenile arc-derived crust along the southeastern margin of the Yangtze Block (e.g., the Pingshui area) at ca.1.0-0.9 Ga.

  6. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizario ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    International Nuclear Information System (INIS)

    The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizario ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702+- 21 Ma during a greenschist facies event M2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257 ± 12 Ma) and Camboriu Orogeny (∼1989 Ma) of the Trans-Amazonian Cycle, followed by an orogenic event (702 ± 21 Ma) of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma) corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton. (author)

  7. Sm-Nd isotope geochemistry and U/Pb geochronological data of the Campina Grande complex, Paraiba State, NE Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, C.N. [Pernambuco Univ., Recife, PE (Brazil). Pos-Graduacao em Geociencias; Guimaraes, I.P.; Silva Filho, A.F. da [Pernambuco Univ., Recife, PE (Brazil). Dept. de Geologia; Beurlen, H. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Engenharia de Minas

    1997-12-31

    The Campina Grande Complex (CCG) constitutes a 250 Km{sup 2} intrusion within the high grade gneiss-migmatitic terrain, in the contact zone between the Mesoproterozoic Pajeu-Paraiba Fold Belt and the Archean Caldas Brandao Massif of the Borborema Province, NE Brazil. The contact of the complex is made by the Guarabira Shear Zone (west) and the Campina Grande Shear Zone in the south. The CCG is composed of coarse grained porphyritic quartz-monzonites, quartz-monzodiorites and medium grained porphyritic granodiorites. Mafic enclaves are common and show composition ranging from diorites to quartz diorites. Field and petrographic features point out to magma mixing and mingling processes involved in the CCG evolution. Basalts of probably Cretaceous age occur as dykes cutting in the CCG. This work presents and discusses the Sm-Nd isotope geochemistry of the CCG and a gabro which occur very close to the south contact of the CCG. This also presents the U/Pb in zircon geochronological data for the CCG. (author) 4 refs., 2 figs.

  8. Late Neoproterozoic magmatism in South Qinling, Central China: Geochemistry, zircon U-Pb-Lu-Hf isotopes and tectonic implications

    Science.gov (United States)

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Yao, Yuan; Gao, Li'e.; Liu, Chunhua

    2016-06-01

    The Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block in South China remains debated. In this study, we present results from LA-ICP-MS zircon U-Pb geochronology on a suite of intermediate-felsic rocks in South Qinling, Central China which show a mean age of ca. 630 Ma. The zircon εHf(t) values of these rocks mostly range from + 0.44 to + 14.78. Geochemically, the granites and syenite show high total alkali contents, with enrichment in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), and depletion in Sr, P, and Ti, similar to the features of A-type granites. The meta-diorite shows high Na2O, with depletion in Eu, Ti, and LILE (Sr, Rb, Ba, and K), and enrichment in HFSE (Th, U, Nb, Ta, Zr, and Hf). The geochemical features are consistent with formation of the intermediate-felsic suite through fractionation from underplated basaltic magma that originated from sub-continental lithospheric mantle metasomatized by asthenosphere-derived oceanic-island-basalt-like (OIB-like) melts, coupled with minor crustal contamination. We correlate the ca. 630 Ma magmatism with a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.

  9. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

    Energy Technology Data Exchange (ETDEWEB)

    Chemale Junior, Farid, E-mail: fchemale@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Kawashita, Koji; Dussin, Ivo A. [Universidade de Sao Paulo (USP), SP (Brazil). Centro de Pesquisas Geocronologicas; Avila, Janaina N. [Australian National University, Canberra, (Australia). Research School of Earth Sciences; Justino, Dayvisson; Bertotti, Anelise [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Curso de Pos-Graduacao em Geociencias

    2012-06-15

    The LA-MC-ICP-MS method applied to U-Pb in situ dating is still rapidly evolving due to improvements in both lasers and ICP-MS. To test the validity and reproducibility of the method, 5 different zircon samples, including the standard Temora-2, ranging in age between 2.2 Ga and 246 Ma, were dated using both LA-MC-ICP-MS and SHRIMP. The selected zircons were dated by SHRIMP and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. The data were collected with a routine spot size of 25 {mu}m and, in some cases, of 15 and 40 {mu}m. A careful cross-calibration using a diluted U-Th-Pb solution to calculate the Faraday reading to counting rate conversion factors and the highly suitable GJ-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. All age results were concordant within the experimental errors. The assigned age errors using the LA-MC-ICP-MS technique were, in most cases, higher than those obtained by SHRIMP, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages. (author)

  10. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

    International Nuclear Information System (INIS)

    The LA-MC-ICP-MS method applied to U-Pb in situ dating is still rapidly evolving due to improvements in both lasers and ICP-MS. To test the validity and reproducibility of the method, 5 different zircon samples, including the standard Temora-2, ranging in age between 2.2 Ga and 246 Ma, were dated using both LA-MC-ICP-MS and SHRIMP. The selected zircons were dated by SHRIMP and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. The data were collected with a routine spot size of 25 μm and, in some cases, of 15 and 40 μm. A careful cross-calibration using a diluted U-Th-Pb solution to calculate the Faraday reading to counting rate conversion factors and the highly suitable GJ-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. All age results were concordant within the experimental errors. The assigned age errors using the LA-MC-ICP-MS technique were, in most cases, higher than those obtained by SHRIMP, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages. (author)

  11. U-Pb isotopic systematics of zircons from prograde and retrograde transition zones in high-grade orthogneisses, Sri Lanka

    Energy Technology Data Exchange (ETDEWEB)

    Baur, N.; Liew, T.C.; Todt, W.; Hofmann, A.W. (Max-Planck-Institut fuer Chemie, Mainz (West Germany)); Kroener, A. (Univ. Mainz (West Germany)); Williams, I.S. (Australian National Univ., Canberra (Australia))

    1991-07-01

    The authors present U-Pb zircon isotopic data from locally restricted prograde (arrested in situ charnockitization) and retrograde metamorphic transition zones, which are well exposed in Proterozoic orthogneisses tectonically interbanded with granulite facies supracrustal rocks of the Highland Group in Sri Lanka. These granitoid rocks yield apparent ages of 1942 {plus minus} 22 Ma, {approximately} 770 Ma, {approximately} 660 Ma, and {approximately} 560 Ma. All samples show severe Pb-loss some 550-560 Ma ago. The main phase of granulite-formation could not be dated unambiguously but is bracketed between {approximately} 660 Ma and {approximately} 550 Ma. The pervasive Pb-loss event around 550-560 Ma reflects the end of this period of high-grade metamorphism and was associated with widespread igneous activity and retrogression. This is constrained by the 550 {plus minus} 3 Ma intrusion age for a post-tectonic granite. They relate this late phase of thermal activity to crustal uplift of the Sri Lankan granulites. This data unambiguously prove the high-grade history of the Sri Lanka gneisses to be a late Precambrian event that may be related to the Pan-African evolution along the eastern part of Africa.

  12. Characterization and zircon SHRIMP U-Pb geochronology of the subvolcanic rocks from Yarumalito Porphyry System, Marmato District, Colombia

    International Nuclear Information System (INIS)

    The mining District of Marmato, located in the Central Cordillera, is considered one of the oldest gold districts in Colombia and its exploration dates back to the Inca’s times, being exploited regularly for more than a thousand years. Inserted in this context lies the Yarumalito porphyry system (YPS), characterized to concentrate ore in structure related veins and stockworks. The YPS is related to the Miocene magmatism of the Combia Formation. In this paper, the subvolcanic rocks directly associated with the mineralized zones were described in order to obtain U-Pb ages in zircon to the intrusions. Selected samples from two fertile intrusions, one andesitic (more abundant in the area) and other dioritic (more restricted), were carefully described and dated by SHRIMP. The results points to a very restricted interval for the ages, with weighted average 206Pb/238U varying from 7,00 ± 0,15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results constrain the Yarumalito system to the final stages of the Combia magmatism and suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and in the Marmato District. (author)

  13. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies; Evolucao geologica do complexo Paraiba do Sul, no segmento central da faixa Ribeira, com base em estudos de geoquimica e geocronologia U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Claudia Sayao

    1996-12-31

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul 157 refs., 54 figs., 17 tabs.

  14. Accurate and Precise in Situ Zircon U-Pb age Dating With High Sample Throughput by Automated LA-SF-ICP-MS

    Science.gov (United States)

    Frei, D.; Gerdes, A.; Schersten, A.; Hollis, J. A.; Martina, F.; Knudsen, C.

    2006-12-01

    Zircon is an ubiquitous mineral in most crystalline rocks as well as clastic sediments. The high resistance to thermal resetting and physical erosion makes zircon an exceptionally useful mineral for precise and accurate dating of thermal geological events. For example, the analysis of the U-Pb ages of detrital zircon grains in clastic sediments is a powerful tool in sedimentary provenance studies. Accurate and precise U-Pb ages of > 100 zircon grains in a sample usually allow to detect all major sedimentary source age components with statistical confidence. U-Pb age dating of detrital zircons is generally the domain of high resolution ion microprobe techniques (high resolution SIMS), where relatively rapid in situ analysis can be achieved. The major limitations of these techniques are sample throughput (about 75 zircon age dates per 24 hours), the very high purchasing and operating costs of the equipment and the need for highly specialised personnel, resulting in high cost. These high costs usually impose uncomfortable restrictions on the number of samples that can be analysed in a provenance study. Here, we present a high sample throughput technique for highly accurate and precise U-Pb dating of zircons by laser ablation magnetic sectorfield inductively coupled plasma mass spectrometry (LA-SF-ICP-MS). This technique takes advantage of recent progress in laser technology and the introduction of magnetic sectorfield ICP-MS instruments. Based on a ThermoFinnigan Element2 magnetic sctorfield ICP-MS and a New Wave UP 213 laser ablation system, this techniques allows U-Pb dating of zircon grains with precision, accuray and spatial resolution comparable to high resolution SIMS. Because an individual analysis is carried out in less than two minutes and all data is acquired automated in pre-set mode with only minimal operator presence, the sample throughput is an order of magnitude higher compared to high resolution SIMS. Furthermore, the purchasing and operating costs of

  15. Advances in ID-TIMS and LA-MC-ICP-MS U-Pb mass spectrometry with applications to geochronology and environmental U analysis

    Science.gov (United States)

    Parrish, R. R.; Noble, S. R.; Condon, D. J.; Horstwood, M. S.; Bowring, S.; Schoene, B.; Crowley, Q.

    2006-12-01

    Recent advances highlighted are the analysis of tiny quantities of U and Pb isotopes, ID-TIMS U-Pb dating using EARTHTIME double spike tracers and improved detectors, and the performance of integrated LA-MC- ICP-MS systems for U-Pb dating. Detector improvements: The use of 1012 ohm resistors with faraday detectors has shown that their noise levels conform closely to prediction and overlap ion intensities previously in the realm of ion counting detectors, enabling multiple faraday ion detection for improvements in chemical separation and purification to measure uranium isotopes in urine with detection limits of a few fg. In a large study >95% of samples intentionally blind-doped with very small amounts (~3 fg to 40 pg) of either depleted uranium or pure ^{236}U were accurately quantified from a sample cohort of more than 300 urine samples. ID-TIMS: Recent developments spearheaded by the EARTHTIME project (www.earth-time.org) has driven a community effort to improve inter-laboratory U-Pb comparability (and accuracy) via the development of mixed U-Pb tracer solutions for community use. In addition a ^{202}Pb-^{205}Pb-^{233}U-^{235}U double spike has been mixed as part of this project aimed at achieving increased precision via real time Pb mass bias determination. LA-MC-ICP-MS: The Pb/U and 207Pb/206Pb precision by LA-(MC)-ICP-MS can be comparable to SIMS U-Pb dating of zircon. A weakness of LA-ICP-MS U-Pb analysis has been the large consumption of sample, compromising both spatial resolution and the potential for subsequent Hf-O isotopes and/or trace element analysis. New protocols involving the New Wave 193nm solid state laser with the Nu Plasma HR configured with multiple SEMs and faraday cups (including Hg and 204Pb correction) demonstrate that for most zircons this problem has been overcome. 95% confidence Pb/U uncertainties of continue to challenge detectors on TIMS and MC-ICP-MS instruments for years to come.

  16. Geochemistry and Geochronology U-Pb SHRIMP of granites from Peixoto de Azevedo: Alta Floresta Gold Province; Geoquimica e geocronologia U-Pb (SHRIMP) de granitos da regiao de Peixoto de Azevedo: Provincia Aurifera Alta Floresta, MT

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fernanda Rodrigues da; Barros, Marcia Aparecida Sant' Ana; Pierosan, Ronaldo; Pinho, Francisco Edigio Cavalcante; Tavares, Carla; Rocha, Jhonattan, E-mail: geologia.fernanda@gmail.com, E-mail: mapabarros@yahoo.com, E-mail: ronaldo.pierosan@gmail.com.br, E-mail: aguapei@yahoo.com, E-mail: carlageologia@hotmail.com, E-mail: geologojrocha@live.com [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra; Rocha, Mara Luiza Barros Pita; Vasconcelos, Bruno Rodrigo; Dezula, Samantha Evelyn Max, E-mail: marapita1@yahoo.com.br, E-mail: brunovasc@gmail.com, E-mail: samanthadezula@gmail.com [Universidade de Brasilia (UNB), Brasilia, DF (Brazil). Programa de Pos-Graduacao em Geologia

    2014-09-15

    The analysis of petrographic, geochemical and geochronological data of granites in the Peixoto de Azevedo region, Mato Grosso, Brazil, in the eastern portion of the Alta Floresta Gold Province, led to the recognition of two granitic bodies bounded by regional major faults and shear zones. In the northwestern portion a body with featured as biotite granodiorite, coarse-grained, with porphyritic to inequigranular texture, metaluminous to peraluminous, high-K calc-alkaline and magnesium character. In the southeastern portion of the area, a biotite monzogranite coarse-grained, with equigranular to porphyritic texture, slightly peraluminous, high-K calc-alkaline and dominantly of ferrous character. U- Pb dating (SHRIMP) showed that the biotite monzogranite has an age of 1869 ± 10 Ma, similar to the Matupa Intrusive Suite, while the biotite granodiorite has an age of 1781 ± 10 Ma, that is the age expected to Peixoto Granite. Both units show patterns of rare earth elements with enrichment of light over heavy and negative Eu anomaly (La{sub N}/Yb{sub N} » 7.6 to 17.31 and ratios Eu/EU{sup ⁎} between 0.46 – 0.72 for biotite monzogranite and La{sub N}/Yb{sub N} » 7.13 to 29.09 with ratios Eu/Eu{sup ⁎} between 0.25 - 0.40 for the biotite granodiorite). Trace elements pattern for both present negative anomalies of Ba, P, Ti and Nb indicating an evolution from mineral fractionation and subduction related sources. In this paper, it is suggested that the monzogranite Matupa was developed in mature arc tectonic environment. For the Peixoto Granite, two hypotheses are suggested: (a) it was developed in younger magmatic arc environment associated with the Colider Magmatism or (b) it was generated in extensional tectonic environment during the Columbia Super continent break up. (author)

  17. Edad motora versus edad corregida en infantes prematuros y con bajo peso al nacer

    Directory of Open Access Journals (Sweden)

    Adriana Lucía Castellanos-Garrido

    2014-04-01

    Full Text Available Antecedentes. El desarrollo motor en niños prematuros es reconocido como un desarrollo lento y con diferente calidad de movimiento (1; por tal motivo, se hace necesario que en la valoración de las habilidades motoras de esta población se utilicen herramientas sensibles a la detección de sus características motrices. Objetivo. Identificar la diferencia entre la edad corregida versus edad motora en los infantes pertenecientes al Programa Madre Canguro del Hospital de Suba, de la ciudad de Bogotá, durante el segundo periodo del 2013. Materiales y métodos. Estudio descriptivo correlacional con una muestra n=15 infantes prematuros o con bajo peso al nacer, valorados a través de la Escala Motora del Infante de Alberta (EMIA. Se realizaron correlaciones entre variables, como edad cronológica en meses, edad corregida, semanas de gestación y peso. Resultados. Se encontró relación entre la edad cronológica del infante, la edad corregida y el peso (p<0,05; a medida que cualquiera de estas variables incrementa, la edad motora también lo hace. Se encontró 1,5 meses de diferencia entre la edad corregida y la edad motora (p<0,05. Conclusiones. La edad motora y la edad corregida de los infantes pertenecientes al Programa Madre Canguro del Hospital de Suba presenta diferencias significativas, ratificándose que las intervenciones desde fisioterapia necesitan ser constantes y tempranas.

  18. Timing of the granulite facies metamorphism in the Sanggan area, North China craton: zircon U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    GUO; Jinghui

    2001-01-01

    on the Early Precambrian grey gneiss and Khondalitein Nei Mongol-Shanxi-Hebei junction region, north China, Acta Petrologica Sinica (in Chinese with English abstract), 1996, 12(2): 329-342.[19]Guo, J. H., Shi, X., Bian, A. G. et al., Pb isotopic composition of feldspar and U-Pb age of zircon from early Proterozoic granite in Sanggan area, North China craton: Metamorphism, crustal melting and tectono-thermal event, Acta Petrologica Sinica (in Chinese with English abstract), 1999, 15(2): 199-207.[20]Krogh, T. E., A low contamination method for the hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations, Geochim. Cosmochim. Acta, 1973, 37: 485-494,[21]Xu, R. H., The single zircon U-Pb dating method, Acta Petrologica Sinica (in Chinese with English abstract), 1989, 5(2):88-93.[22]Stacey, J. S., Kramers, J. D., Approximation of terrestrial lead isotopes evolution by a two-stage model, Earth Planet. Sci.Lett., 1975, 26: 207-221.[23]Wiedenbeck, M., An example of reverse discordance during ion microprobe zircon dating: an artifact of enhanced ion yields from a radiogenic labile Pb, Chem. Geol., 1995, 125: 197-218.[24]Williams, I. S., Compston, W., Black, L. P. et al., Unsupported radiogenic Pb in zircon: a cause of anomalously high Pb-Pb, U-Pb and Th-Pb ages, Contrib. Mineral. Petrol., 1984, 88: 322-327.[25]Chen, F., Siebel, W., Satir, M., Zircon and zircons; unveiled by the stepwise leach experiment (abstr.), EUG-I 1 (European Union of Geosciences), Strasbourg, France, 2001, 37.[26]Pidgeon, R. T., Aftalion, M., Cogenetic and inherited zircon U-Pb systems in granites: Paleozoic granites of Scotland and England, in Crustal Evolution of Northwestern Britain and Adjacent Regions (eds. Bowes, R. D., Leake, B. E.), Geological Journal (special issue), 1978, 10: 183-220.[27]Schenk, V., U-Pb and Rb-Sr radiometric dates and their correlation with metamorphic events in the granulite facies basement of the

  19. Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS

    Institute of Scientific and Technical Information of China (English)

    YUAN Honglin; WU Fuyuan; GAO Shan; LIU Xiaoming; XU Ping; SUN Deyou

    2003-01-01

    Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.

  20. U-Pb zircon age from the base of the Ediacaran Doushantuo Formation in the Yangtze Gorges,South China: constraint on the age of Marinoan glaciation

    Institute of Scientific and Technical Information of China (English)

    ChongyuYin; FengTang; YongqingLiu; LinzhiGao; PengjuLiu; YushengXing; ZhiqingYang; YushengWan; ZiqiangWang

    2005-01-01

    The reported new U-Pb age by sensitive high-resolution ion microprobe (SHRIMP Ⅱ) on zircon was obtained from a tuff sample at the basal Doushantuo Formation in the Jiuqunao section, which situated at the western limb of the Huangling anticline in the Yangtze Gorges in Zigui, Hubei, South China. Eighteen spots of zircons were analyzed and they form two clusters: one includes three spots, with an inherited age of 784+ 15 Ma (MSWD=0.05); the other consists of 15 spots and gives a weighted mean 206pb/238U age of 628.3±5.8 Ma (MSWD=0.86). It is the first SHRIMP U-Pb zircon age obtained nearly the base of the Doushantuo Formation of Ediacaran and represents a maximum age of the Doushantuo Formation It also forms an age constraint on the upper limit age of the Nantuo (Marinoantype) glaciation.

  1. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    OpenAIRE

    LÉO A. HARTMANN; João O. S Santos; Jayme A.D. Leite; Carla C. Porcher; McNaughton, Neal J.

    2003-01-01

    The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at ...

  2. U-Pb geochronology of Permian plutonic rocks, Longwood Range, New Zealand : implications for Median Batholith-Brook Street Terrane relations

    International Nuclear Information System (INIS)

    We present U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon ages from gabbros and associated intrusive rocks of the Longwood Range, Southland. U-Pb zircon ages of 257.6 ± 2.5 Ma, 256.5 ± 1.8 Ma and 251.6 ± 2.0 Ma (2σm) have been obtained from the layered, platiniferous Hekeia Gabbro. These are 5-10 Ma older than cooling ages previously obtained by Ar-Ar dating of hornblendes. A revised U-Pb zircon age of 252.8 ± 2.7 Ma is reported for a sample of western Pourakino Trondhjemite [previously dated at 292 ± 8 Ma by multicrystal 207Pb/206Pb thermal ionization mass spectrometry (TIMS) methods] and a dike of the trondhjemite that cuts the Hekeia Gabbro is dated at 254.8 ± 2.6 Ma. Our new zircon ages show that the Hekeia Gabbro and Pourakino Trondhjemite were intruded within the same, relatively narrow interval from 261 to 252 Ma. This age range is substantially younger than Early Permian (c. 276-288 Ma) ages inferred from fossil evidence of major Takitimu Group volcanism in the adjacent Brook Street Terrane. We make the novel suggestion that the Hekeia and Pourakino bodies, along with plutons at Bluff and Oraka Point, constitute a new Longwood Suite of the Median Batholith that is spatially and temporally distinct from allochthonous Brook Street Terrane volcanic magmatism. A U-Pb zircon age of 232.3 ± 1.5 Ma from a western Longwood Range granodiorite is the oldest Darran Suite pluton so far recognized and represents the start of a major, isotopically more evolved, pulse of the Median Batholith. (author)

  3. U-Pb aging of the sodalite-syenite (Blue-Bahia) mineralization in the Lichfield stock of Itaju do Colonia, southern Bahia, Brazil

    International Nuclear Information System (INIS)

    The Litchfieldite Stock of Itaju do Colonia is one of the intrusions from the Alkaline Province of the South Bahia State, which host the blue coloured sodalite-syenite ore. The U-Pb isotopic results for titanite from the sodalite-syenites of this complex yield an age of 732 ± 8 Ma, which is interpreted as the crystallization age for the blue-sodalite-ore. (author)

  4. U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based Assessment of Plutons with Comments on Their Regional Tectonic Significance

    OpenAIRE

    Wilson, John Robert

    2001-01-01

    The rocks of the Appalachian orogen are world-class examples of collisional and extensional tectonics, where multiple episodes of mountain building and rifting from the pre-Cambrian to the present are preserved in the geologic record. These orogenic events produced plutonic rocks, which can be used as probes of the thermal state of the source region. SIMS (secondary ion mass spectrometry) U/Pb ages of zircons were obtained for ten plutons (Leatherwood, Rich Acres, Melrose, Buckingham, Diana ...

  5. Evidence for multi-cycle sedimentation and provenance constraints from detrital zircon U-Pb ages: Triassic strata of the Lusitanian basin (western Iberia)

    Science.gov (United States)

    Pereira, M. F.; Gama, C.; Chichorro, M.; Silva, J. B.; Gutiérrez-Alonso, G.; Hofmann, M.; Linnemann, U.; Gärtner, A.

    2016-06-01

    Laser ablation ICP-MS U-Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U-Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U-Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa-Morena and Central Iberian zones that outcrop in and close to the Porto-Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian-Carboniferous ages (age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U-Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia.

  6. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events

    Science.gov (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  7. SHRIMP zircon U-Pb dating of the intrusives in the Tongling metallogenic cluster and its dynamic setting

    Institute of Scientific and Technical Information of China (English)

    WU GanGuo; ZHANG Da; DI YongJun; ZANG WenShuan; ZHANG XiangXin; SONG Biao; ZHANG ZhongYi

    2008-01-01

    This paper selected five typical Mesozoic intrusives from the Tongling metallogenic cluster (Xiaotongguanshan,Fenghuangshan,Xinqiao,Dongguashan,and Shatanjiao plutons),and made a systemic SHRIMP zircon U-Pb dating for the five plutons,which produced an age range of 151.8±2.6-1 42.8±1.8 Ma.This work put an accurate constraint on the formation age of the intrusives in the Tongling metallogenic cluster.These age data indicate that magmatic activity reached a peak during Late Jurassic.The intrusive sequence of magma is generally from quartz monzonite(porphyry)through monzonite to granodiorite to quartz monzodiorite to pyroxene monzodiorite to gabbro-diabase.The intrusives of different lithology differed in crystallization age,probably implying the intrusives in the Tongling area underwent an evolutional process of magma,which was closely related to geodynamical setting in the depths of the area.A dynamic model was presented for the origin of the igneous rocks in the study area as follows.The assembly between the Yangtze craton and the North China craton finished at the end of T3,and then the stage of another compressional orogeny began in the Tongling area,i.e.,Pacific dynamic system.Along with the subduction of the Izanagi plate underneath the Eurasian plate at J2-J3,NW-trending compression toward the East China continent was produced,and compressional deformation also took place,forming NE-trending fold and resulting in thickening of the crust in the Tongling area.High-density eclogite-facies rocks were produced in the low part of the crust,resulting in the delamination of mantle lithosphere and lower crust,and upwelling of materials in asthenosphere.Decompression melting produced basaltic magma,and the materials in lower crust were heated by the underplating of the basaltic magma.Thus,melting of lower crust yielded granitic magma,which intruded along deep and large faults through various geological processes(J3-K1).The SHRIMP U-Pb zircon age of 151.8±2

  8. 1,100,000 year history of Siberian permafrost based on U-Pb chronology of speleothems

    Science.gov (United States)

    Vaks, Anton; Mason, Andrew J.; Breitenbach, Sebastian F. M.; Kononov, Alexander M.; Osintcev, Alexander V.; Henderson, Gideon M.

    2014-05-01

    We have used U-Pb dating of the speleothems from Siberian Ledyanaya Lenskaya Cave for tracing of permafrost thawing events during the last 1.1 million years. Rain and snowmelt waters can penetrate into caves only when the soil and subsoil temperatures are above 0° C and permafrost above the cave is discontinuous or absent. Therefore, speleothems in regions currently affected by permafrost provide a tracer of past permafrost thawing events. Ledyanaya Lenskaya Cave is located at 60° 22'N-116° 57'E, on the southern boundary of continuous permafrost zone, with no present-day water seepage in the cave. Temperatures in the region range from -32° C (January) to +18° C (July), with mean annual temperature of ~-6° C. U-Th dating of speleothems from this cave in a previous study [1] showed that the youngest speleothem growth period occurred at 427±23 thousand years ago (ka), during the early Marine Isotope Stage (MIS) 11. During this episode global temperature was 1.5° C higher than pre-industrial levels, and ~0.7° C above the present. In the current study two horizons at the base of a stalagmite were dated using U-Pb chronology [2]. Isochron ages of 1074.1 +7.9/-6.9 ka and 951.4 +3.6/-4.4 ka were obtained. Timing of these permafrost thawing events correlates with events of exceptionally high Pacific Warm Pool sea surface temperature (~+30° C)[3]. During these warm episodes the average global temperature was 1.2-1.3° C higher than pre-industrial temperatures. These findings put the threshold of thawing of the continuous permafrost near its southern boundary slightly lower than it was found previously. The dating work is still in process and is now focusing on growth periods older than MIS-11 but younger than 950 ka. The oldest horizon of the stalagmite grew on the bedrock. This layer was probably amongst the first vadose speleothems that formed after the cave was uplifted above the groundwater table (associated with the nearby Lena River). Today the cave is ~50

  9. SHRIMP zircon U-Pb dating of the intrusives in the Tongling metallogenic cluster and its dynamic setting

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    This paper selected five typical Mesozoic intrusives from the Tongling metallogenic cluster (Xiaotongguanshan, Fenghuangshan, Xinqiao, Dongguashan, and Shatanjiao plutons), and made a systemic SHRIMP zircon U-Pb dating for the five plutons, which produced an age range of 151.8±2.6- 142.8±1.8 Ma. This work put an accurate constraint on the formation age of the intrusives in the Tongling metallogenic cluster. These age data indicate that magmatic activity reached a peak during Late Jurassic. The intrusive sequence of magma is generally from quartz monzonite (porphyry) through monzonite to granodiorite to quartz monzodiorite to pyroxene monzodiorite to gabbro-diabase. The intrusives of different lithology differed in crystallization age, probably implying the intrusives in the Tongling area underwent an evolutional process of magma, which was closely related to geodynamical setting in the depths of the area. A dynamic model was presented for the origin of the igneous rocks in the study area as follows. The assembly between the Yangtze craton and the North China craton fini- shed at the end of T3, and then the stage of another compressional orogeny began in the Tongling area, i.e., Pacific dynamic system. Along with the subduction of the Izanagi plate underneath the Eurasian plate at J2-J3, NW-trending compression toward the East China continent was produced, and compres- sional deformation also took place, forming NE-trending fold and resulting in thickening of the crust in the Tongling area. High-density eclogite-facies rocks were produced in the low part of the crust, re- sulting in the delamination of mantle lithosphere and lower crust, and upwelling of materials in as- thenosphere. Decompression melting produced basaltic magma, and the materials in lower crust were heated by the underplating of the basaltic magma. Thus, melting of lower crust yielded granitic magma, which intruded along deep and large faults through various geological processes (J3-K1). The

  10. Morphology versus U-Pb systematics in zircon: A high-resolution isotopic study of a zircon population from a Variscan dike in the Central Alps

    International Nuclear Information System (INIS)

    U/Pb isotopic measurements on individual zircon crystals combined with morphological analyses permit the identification of three distinct components within the zircon population of the Saedelhorn diorite, a Variscan dike from the western Gotthard (Central Alps, Switzerland): (i) 94% of the grains in the zircon population are elongate crystals with pronounced skeletal morphology indicative of rapid growth from a supercooled melt. (ii) 5% of the population consist of turbid, mostly subhedral zircons frequently showing D-type morphology and elevated uranium contents compared to the skeletal variety. Single-crystal and multi-grain U-Pb isotopic data of group (i) and (ii) zircons define an intrusion age of 293 + 5/ -4 m.y. for the dike. (iii) Rare, transparent zircon crystals (< 1% of the zircons population) yield apparent U-Pb ages in the range of 370-490 m.y. and display morphological and isotopic characteristics closely resembling those of a Caledonian orthogneiss intruded by the dike. This implies presence of assimilated wall-rock components in the macroscopically homogeneous dike sample. (orig./WB)

  11. Constraints on a Late Cretaceous uplift, denudation, and incision of the Grand Canyon region, southwestern Colorado Plateau, USA, from U-Pb dating of lacustrine limestone

    Science.gov (United States)

    Hill, Carol A.; Polyak, Victor J.; Asmerom, Yemane; P. Provencio, Paula

    2016-04-01

    The uplift and denudation of the Colorado Plateau is important in reconstructing the geomorphic and tectonic evolution of western North America. A Late Cretaceous (64 ± 2 Ma) U-Pb age for the Long Point limestone on the Coconino Plateau, which overlies a regional erosional surface developed on Permo-Triassic formations, supports unroofing of the Coconino Plateau part of Grand Canyon by that time. U-Pb analyses of three separate outcrops of this limestone gave ages of 64.0 ± 0.7, 60.5 ± 4.6, and 66.3 ± 3.9 Ma, which dates are older than a fossil-based, early Eocene age. Samples of the Long Point limestone were dated using the isotope dilution isochron method on well-preserved carbonates having high-uranium and low-lead concentrations. Our U-Pb ages on the Long Point limestone place important constraints on the (1) time of tectonic uplift of the southwestern Colorado Plateau and Kaibab arch, (2) time of denudation of the Coconino Plateau, and (3) Late Cretaceous models of paleocanyon incision west of, or across, the Kaibab arch. We propose that the age of the Long Point limestone, interbedded within the Music Mountain Formation in the Long Point area, represents a period of regional aggradation and a time of drainage blockage northward and eastward across the Kaibab arch, with possible diversion of northward drainage on the Coconino Plateau westward around the arch via a Laramide paleo-Grand Canyon.

  12. History of the Pasamonte achondrite: relative susceptibility of the Sm-Nd, Rb-Sr, and U-Pb systems to metamorphic events

    International Nuclear Information System (INIS)

    The Rb-Sr, Sm-Nd, and U-Pb systematics of the eucrite Pasamonte have been studied in order to investigate the relative susceptibility of the different systems to post-crystallization events and to determine the age and history of the meteorite. The Rb-Sr and 238U-206Pb data of mineral separates do not define an isochron but the Sm-Nd data define an internal isochron which corresponds to the formation age of 4.58+-0.12 b.y. (109 years). The 207Pb- 206Pb data of mineral separates define an apparent age of 4.53+-0.03 b.y., however it is concluded that this age, while in agreement with the Sm-Nd age, is not strictly valid since the U-Pb data indicate at least three stages of evolution. The U-Pb data indicate that the parent body of the meteorite experienced brecciation shortly after the formation of the parent body surface (approximately 4.2-4.45 b.y. ago) and a recent disturbance (collision) 6+-30 m.y. ago. The latter age is within the range of cosmic ray exposure ages for achondrites. (Auth.)

  13. Provenance records of the North Jiangsu Basin,East China:Zircon U-Pb geochronology and geochemistry from the Paleogene Dainan Formation in the Gaoyou Sag

    Institute of Scientific and Technical Information of China (English)

    Chun-Ming; Lin; Xia; Zhang; Ni; Zhang; Shun-Yong; Chen; Jian; Zhou; Yu-Rui; Liu

    2014-01-01

    Detailed zircon U-Pb dating and whole-rock geochemical analyses were carried out on the sedimentary rocks of the Paleogene Dainan Formation from Gaoyou Sag in the North Jiangsu Basin,East China.Whole-rock rare earth element characteristics suggest that the provenance was mainly from the Late Proterozoic low-grade metamorphic felsic rocks in the Dabie-Sulu orogenic belt,with the parent rocks probably being the I-type high-potassium granite gneiss.Cathodoluminescence images indicate that most of the detrital zircons are originally magmatic.A few zircons show overgrowths,indicating multiple-episode tectonic events.The U-Pb age distribution patterns of the detrital zircons suggest four main magmatic episodes in the provenance:Late Archean-Early Proterozoic(2450-2600 Ma),Early Proterozoic(1700-1900 Ma),Late Proterozoic(700-850 Ma),and Late Paleozoic-Mesozoic(100-300 Ma).These zircon U-Pb age and whole-rock geochemical results suggest that the sediments of the Dainan Formation were mainly sourced from the recycled orogenic belts within and/or around the North Jiangsu Basin,including the basement of the Yangtze Block,the Neoproterozoic rocks in the Dabie-Sulu orogenic belt,and the Mesozoic igneous rocks in the south part of Zhangbaling Uplift.

  14. Paleozoic accretionary orogenesis in the eastern Beishan orogen: constraints from zircon U-Pb and 40Ar/39Ar geochronology

    Science.gov (United States)

    Ao, Songjian; Xiao, Wenjiao; Windley, Brian; Mao, Qigui

    2016-04-01

    The continental growth mechanism of the Altaids in Central Asia is still in controversy between models of continuous subduction-accretion versus punctuated accretion by closure of multiple oceanic basins. The Beishan orogenic belt, located in the southern Altaids, is a natural laboratory to address this controversy. Key questions that are heavily debated are: the closure time and subduction polarity of former oceans, the emplacement time of ophiolites, and the styles of accretion and collision. This paper reports new structural data, zircon ages and Ar-Ar dates from the eastern Beishan Orogen that provide information on the accretion process and tectonic affiliation of various terranes. Our geochronological and structural results show that the younging direction of accretion was northwards and the subduction zone dipped southwards under the northern margin of the Shuangyingshan micro-continent. This long-lived and continuous accretion process formed the Hanshan accretionary prism. Our field investigations show that the emplacement of the Xiaohuangshan ophiolite was controlled by oceanic crust subduction beneath the forearc accretionary prism of the Shuangyingshan-Mazongshan composite arc to the south. Moreover, we address the age and terrane affiliation of lithologies in the eastern Beishan orogen through detrital zircon geochronology of meta-sedimentary rocks. We provide new information on the ages, subduction polarities, and affiliation of constituent structural units, as well as a new model of tectonic evolution of the eastern Beishan orogen. The accretionary processes and crustal growth of Central Asia were the result of multiple sequences of accretion and collision of manifold terranes. Reference: Ao, S.J., Xiao, W., Windley, B.F., Mao, Q., Han, C., Zhang, J.e., Yang, L., Geng, J., Paleozoic accretionary orogenesis in the eastern Beishan orogen: Constraints from zircon U-Pb and 40Ar/39Ar geochronology. Gondwana Research, doi: http://dx.doi.org/10.1016/j

  15. First U-Pb detrital zircon ages from Numidian sandstones in Southern Apennines (Italy): Evidences of African provenance

    Science.gov (United States)

    Fornelli, Annamaria; Micheletti, Francesca; Langone, Antonio; Perrone, Vincenzo

    2015-05-01

    Two samples of quartz-rich sandstones collected in the Numidian Flysch of Southern Apennines (Italy) have been studied to highlight the provenance of detritus using radiometric dating by LA-ICP-MS of detrital zircons and to compare the obtained ages with those of the Betic and Maghrebian Chains. The provenance of quartzose detritus from European or African Plates is still debated in these Chains, accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply. The U-Pb zircon ages (n = 47) vary from 3047 ± 13 Ma (Mesoarchean) to 516 ± 19 Ma (Cambrian). The predominance of Paleo-Proteozoic ages (2500-1600 Ma) and the lack of Hercynian and Alpine ones suggest a provenance of the Numidian supply from North-African cratonic areas during the early-middle Langhian, when the Numidian successions of Southern Apennines were deposited. In addition, a cluster of ages at 773 ± 24 Ma and 668 ± 12 Ma in one sample and at 664 ± 17 Ma in the other sample, calculated on zircon domains with magmatic zoning, testify to an important contribution from Neo-proterozoic "granitic" rocks widely outcropping in the North-African Craton. The age data on detrital zircons from Numidian sandstones in Southern Apennines overlap those found in the Numidian sandstones widespread in the Betic Cordillera and in the Maghrebian Chain from south Spain to Sicily. This suggests that the entire depositional zone in which Numidian Flysch deposited, was fed from a southerly source represented by the African Craton where Archean, Proterozoic and Cambrian rocks widely crop out from the Atlantic coast to the Hoggar and Tibesti Massifs. Finally, it must be outlined that a Meso-Archean zircon age (3047 Ma) has been found in the Numidian Flysch of the Southern Apennines whereas in the Numidian Flysch of the Maghrebian Chain, zircons older than Paleo-proterozoic (1840 Ma) have not yet been found.

  16. Coronitic metagabbro and eclogite from the Grenville Province of western Quebec: interpretation of U-Pb geochronology and metamorphism

    Energy Technology Data Exchange (ETDEWEB)

    Indares, A.; Dunning, G. [Memorial Univ. of Newfoundland, Dept. of Earth Sciences, St. John' s, Newfoundland (Canada)]. E-mail: afin@sparky2.esd.mun.ca

    1997-07-15

    We present new U-Pb and metamorphic data on high-pressure coronitic metagabbros from three distinct structural settings in the Parautochthonous belt of the Grenville Province in western Quebec. Intrusive ages are (i) 1217{sub -10}{sup +15} Ma, for metagabbro close to the Grenville Front, correlative with the Sudbury dykes, defined in Ontario; (ii) 1403{sub -11}{sup +14} Ma for an eclogitized lens at the base of the highest structural level (SL4), a new age for mafic magmatism in the western Grenville; and (iii) 1218{sub -34}{sup +53} Ma for metagabbro from SL4, interpreted as correlative with metagabbros from the Algonquin and Shawanaga domains in Ontario. Metamorphism in all cases is Grenvillian, with the best constrained age of 1069 {+-} 3 Ma for the metagabbro of SL4. Metamorphic grade increases from the Grenville Front to the south. The mafic rocks preserve relict igneous textures overprinted by garnet + clinopyroxene that developed as coronas and (or) pseudomorphs after igneous phases. The highest grade metagabbros contain omphacite and some lack primary plagioclase, therefore being eclogites. However, interpretation of textures and mineral chemistry indicates that they were equilibrated during decompression (at 1350 MPa and 720{sup o}C, sample 51: and at 1200 MPa and 740{sup o}C, sample 29), so maximum depths of burial remain unconstrained. Their evolution is interpreted as follows: (i) high-pressure metamorphism by burial of the Laurentian margin under accreted terranes thrust toward the northwest between 1080 and 1060 Ma; (ii) residence at intermediate crustal levels, for a few tens of millions of years; and (iii) rapid exhumation by renewed thrusting that led to the emplacement of the high-pressure units over the northerly adjacent structural units of the Parautochthonous Belt. (author)

  17. Coronitic metagabbro and eclogite from the Grenville Province of western Quebec: interpretation of U-Pb geochronology and metamorphism

    International Nuclear Information System (INIS)

    We present new U-Pb and metamorphic data on high-pressure coronitic metagabbros from three distinct structural settings in the Parautochthonous belt of the Grenville Province in western Quebec. Intrusive ages are (i) 1217-10+15 Ma, for metagabbro close to the Grenville Front, correlative with the Sudbury dykes, defined in Ontario; (ii) 1403-11+14 Ma for an eclogitized lens at the base of the highest structural level (SL4), a new age for mafic magmatism in the western Grenville; and (iii) 1218-34+53 Ma for metagabbro from SL4, interpreted as correlative with metagabbros from the Algonquin and Shawanaga domains in Ontario. Metamorphism in all cases is Grenvillian, with the best constrained age of 1069 ± 3 Ma for the metagabbro of SL4. Metamorphic grade increases from the Grenville Front to the south. The mafic rocks preserve relict igneous textures overprinted by garnet + clinopyroxene that developed as coronas and (or) pseudomorphs after igneous phases. The highest grade metagabbros contain omphacite and some lack primary plagioclase, therefore being eclogites. However, interpretation of textures and mineral chemistry indicates that they were equilibrated during decompression (at 1350 MPa and 720oC, sample 51: and at 1200 MPa and 740oC, sample 29), so maximum depths of burial remain unconstrained. Their evolution is interpreted as follows: (i) high-pressure metamorphism by burial of the Laurentian margin under accreted terranes thrust toward the northwest between 1080 and 1060 Ma; (ii) residence at intermediate crustal levels, for a few tens of millions of years; and (iii) rapid exhumation by renewed thrusting that led to the emplacement of the high-pressure units over the northerly adjacent structural units of the Parautochthonous Belt. (author)

  18. U-Pb zircon geochronology, Sr-Nd isotope geochemistry, and petrogenesis of oxidant granitoids at Keybarkuh, southwest of Khaf

    Directory of Open Access Journals (Sweden)

    Ehsan Salati

    2012-10-01

    Full Text Available Keybarkuh area is located 70 km southwest of Khaf, Khorasan Razavi province. The study area is situated in northeastern Lut block. The rock units in the area are Paleozoic metamorphic rocks and Cretaceous to Tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. Based on magnetic susceptibility, the intrusive rocks are divided into oxidant and reduced series. In this study, the oxidant intrusions are discussed. These intrusions are mostly high-K to shoshonitic and also meta-aluminous type. Their magma formed in subduction magmatic arc and they belong to I-type granitoid series. Enrichment of Large Ion Lithophile Elements (LILE such as Rb, Cs, K, Ba, and Th relative to High Field Stength Elements (HFSE such as Nb, Zr, and Ti supported the idea. Enrichment of Light Rare Earth Elements (LREE and depletion of Heavy Rare Earth Elements (HREE are also typical of subduction magmatism. Negative anomalies of Eu/Eu* can be attributed to the presence of residual plagioclase in a mantle source and contamination of magma by reduced continental crust. The amount of Nb > 11 ppm, lower ratio of Zr/Nb 0.706, initial 143Nd/144Nd (> 0.512 and εNd (< -3.5 indicate that magma contaminated by reduced continental crust. Hornblende biotite granodiorite porphyry dated using U-Pb zircon geochronology at 43.44 Ma (Middle Eocene. Based on calculated TDM, magma derived from ancient slab with 820 Ma age in the Keybarkuh area, was affected by the highest continental crust contamination during its ascent.

  19. U-Pb age and Hf-O isotopes of detrital zircons from Hainan Island: Implications for Mesozoic subduction models

    Science.gov (United States)

    Jiang, Xiao-Yan; Li, Xian-Hua; Collins, W. J.; Huang, Hui-Qing

    2015-12-01

    A compilation of magmatic ages from the Mesozoic South China Block suggests a number of "magmatic quiescence" periods at ca. 205-195 Ma, ca. 150-140 Ma and ca. 125-115 Ma, casting doubt on tectonic models that suggest ongoing Andean-type subduction along the South China continental margin. However, SIMS U-Pb analyses on two detrital zircon samples from the Cretaceous Lumuwan Formation on Hainan Island, southeast China, reveal three major age peaks at ca. 120 Ma, ca. 155 Ma and ca. 235 Ma. Zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning, suggesting short-distance transport from nearby magmatic sources. The extremely rare occurrence of ca. 120 Ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to Hainan Island but presently missing. Therefore, our data provide new evidence for ongoing magmatic activity in late Mesozoic South China. In situ Hf and O isotope analyses of the Mesozoic detrital zircons reveal large variations in both εHf(t) (- 21.2 to 10.5) and δ18O (4.4‰ to 13.6‰) values. A general negative correlation between them suggests the reworking of old supracrustal materials (average crustal residence age of ca. 2.0 Ga) by juvenile mantle-derived magmas. The progression of increasing εHf(t) and decreasing δ18O values of zircons from the Triassic to the Cretaceous suggests progressive crustal growth during the Mesozoic. The results are consistent with hybridization at an active continental margin. We briefly review tectonic models for the Indosinian orogeny and suggest that the petrologic evidence indicates that Mesozoic magmatism was part of the circum-Pacific accretionary orogens that formed along the continental margin of East Asia no later than ca. 250 Ma and continued at least to the late Cretaceous.

  20. U-Pb detrital zircon age patterns of Cenozoic clastic sedimentary rocks in Trinidad and its implications

    Science.gov (United States)

    Xie, Xiangyang; Mann, Paul

    2014-06-01

    The Cenozoic evolution of northern South America can be simplified as a diachronous, west-to-east change from north-facing passive margin, to active convergence and transcurrent plate margin. As the current eastern end of the Caribbean-South America plate boundary, the Trinidad area records the most recent tectonic regime transition. Documenting the provenance of Cenozoic clastic rocks in Trinidad provides insights into the spatial and temporal relationships between mountain range uplifting, sediment dispersal, and drainage system development along the eastern end of the Caribbean-South American plate boundary. Four Eocene to Pliocene age outcropping sandstone samples were collected from Trinidad and 545 detrital zircon grains were analyzed using the U-Pb LA-ICP-MS method. A total of 404 analyses with less than 10% discordance were used for the final interpretation. Results show that the age distribution of the Eocene to the Early Oligocene samples is very restricted and dominated by Precambrian age grains with age peaks at ~ 1400 Ma, ~ 1800 Ma, and ~ 2000 Ma, typically derived from the Guyana Shield. In contrast, the Late Oligocene and younger samples show much broader and mixed age distribution that includes Mesozoic, Paleozoic, and Precambrian peaks. This age shift was interpreted as arriving of the Great Caribbean Arc and oblique collision between the South America and Caribbean plates. Continuing collision uplifted the Andes belts to the west. The Eastern Cordillera of Colombia, the Merida Andes, and the northern Venezuela coastal ranges then became the second primary sources. Offshore sedimentation switched from the passive margin with multiple small drainage systems to the active convergent and transcurrent plate margin with a single large river-dominated delivery system.

  1. Precise zircon U-Pb ages from the Marra Mamba iron formation and Wittenoom formation, Hamersley Group, Western Australia

    International Nuclear Information System (INIS)

    The Mt Bruce Supergroup of the Pilbara Craton of Western Australia was laid down in the Hamersley Basin, unconformably over a basement of granite-greenstone terrane, and consists of the Fortescue. Hamersley and Turee Creek Groups. The base of the -230 m-thick Marra Mamba Iron Formation, the lowest formation of the Hamersley Group. marks the onset of the major banded iron-formation deposition that characterizes the group. Ion microprobe U-Pb isotope analyses of zircons from a tuff band (NS3) within a high-grade iron orebody in the uppermost (Mt Newman) member show two distinct, and non-overlapping, age populations. Fifteen grains from the younger group of 16 have a pooled age of 2597±5 Ma (95% confidence), interpreted as the age of syndepositional volcanism: individual grains of the older group of 8, with ages between ca 2950 Ma and ca 2820 Ma, are interpreted as xenocrysts derived from basement rocks transected by the rising magma. The conformably overlying Wittenoom Formation, ∼300-600 m thick, consists largely of dolomitic rocks. Zircons from a submarine fallout tuff within the uppermost (Bee Gorge) member also have two non-overlapping zircon age populations. Most of the 23 zircons analysed belong to an older population with near-concordant ages between ca 2750 and ca 2650 Ma., but 12 analysed spots from 7 grains have a pooled age of 2561 ±8 Ma. This is interpreted to be the age of volcanism coeval with deposition. The older zircons were probably derived from tuffs of Fortescue Group age, entrained with the Crystal-rich Tuff ejectamenta during its explosive, probably phreatoplinian, eruption. Copyright (1998) Blackwell Science Asia

  2. U-Pb data on zircons for the thermal peak of metamorphism in the Variscan Odenwald, Germany

    International Nuclear Information System (INIS)

    U-Pb data are presented for zircons from metamorphic rocks of the crystalline Odenwald that comprises part of the Mid-German Crystalline Rise. The Odenwald can be divided into four principal domains wiht different magmatic and metamorphic histories on the basis of published structural and petrological data and the presented ages. In the eastern (Boellstein) Odenwald the metasedimentary rocks contain zircons derived from basement rocks that exceed 2.2 Ga in age. The intrusion of granitic magmas into these metasedimentary rocks took place before or close to the end of the thermal peak of metamorphism at 375±5 Ma ago. Rapid uplift of the Boellstein Odenwald occurred at about 320 Ma bp, later than in the Bergstraesser Odenwald. The western (Bergstraesser) Odenwald can be subdivided, by geochronological, petrological and especially structural data, into a northern, a central and a southern part. In the northern part basic magmatism has an age of 362±7 Ma. Th peak of thermal metamorphism in the southernmost Odenwald was accompanied by partial melting of metasedimentary rocks and the formation of new zircons with ages between 332 and 342 Ma. Probable peak metamorphic conditions, revealed by two samples from the heterogeneous central part, occurred at about 336 Ma, i.e. in the same time span as in the southernmost part, but later than in the Boellstein area and the northern Odenwald. Rapid uplift started earlier in the central and southern part and 10-20 Ma earlier than in the Boellstein Odenwald. Cooling from 500 to 300 C occurred in the northern part in the time interval between the elevation of the other parts of the Bergstraesser Odenwald and the Boellstein Odenwald. There is no indication for any thermal equilibium between 2.25 Ga and 375 Ma recorded in the zircons of both areas. (orig.)

  3. Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

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    Wen-Yu Shao

    2014-01-01

    Full Text Available This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1 seven andesites from four volcanic units and three river/beach sands from Lutao and (2 five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from ~1.54 to ~1.24 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 1.31 ±± 0.03 Ma (n = 190, MSWD = 2.6. This is slightly older than, or broadly coincident with, a mean 206Pb/238U age of 1.23 ±± 0.03 Ma (n = 103, MSWD = 1.9 given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from ~2.72 to ~2.35 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 2.61 ±± 0.13 Ma (n = 11, MSWD = 1.8. This accords with a mean 206Pb/238U age of 2.69 ±± 0.11 Ma (n = 34, MSWD = 4.7 obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at ~1.3 and ~2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, ~11% in Lutao and up to ~82% in Lanyu, which together with detrital zircons from the sands show main age peaks at ~150 Ma and ~1.9 and ~2.5 Ga, consistent with the notion for a _ continental crust involved in the genesis of the northern Luzon magmatic arc.

  4. Age of uranium mineralization at the Highland mine, Powder River Basin, Wyoming, as indicated by U-Pb isotope analyses

    International Nuclear Information System (INIS)

    Most of the uranium deposits in the Powder River basin occur at various stratigraphic levels in the Wasatch Formation of Eocene age, but pollen and spores found in the Highland mine host rocks indicate that the deposits here may be in the upper part of the Fort Union Formation of Paleocene age. Analyses of U-Pb isotopes in several samples of ore from the Highland mine were made in order to compare the apparent age of mineralization of this deposit with that of host rocks of equivalent age at Gas Hills, Crooks Gap, and Shirley basin, Wyoming. The samples used for age determinations were collected in the southernmost of a series of open pit mines and in the uppermost of the three host units. All samples contain only reduced uranium minerals which are mainly coprecipitated mixtures of pitchblende and coffinite. Sample EP17-7 consists of ore at the boundary with oxidized yellow sandstone and sample EP17-8 of ore 6 m (20 ft) from the interface with oxidized sandstone. Sample J represents calcite-cemented ore from a thin zone at the base of the upper host sandstone unit (lower limb ore). The others are randomly selected grab samples of mineralized material in the ore deposit at the same level as EP-17-7. With the exception of sample J, all samples were collected from exposures of ore on the pit floor 60 m (200 ft) below the original land surface and at an elevation of 5,060 feet. Sample J came from the pit floor at an elevation of about 5,040 ft

  5. The SHRIMP zircon U-Pb dating of felsic volcanic rocks and its geological significance from yutian group in southern jiangxi

    International Nuclear Information System (INIS)

    Past researches have showed that the Rb-Sr isochron ages of felsic end member for rhyolite-basaltbimodal volcanic rocks of Yutian Group in the Changpu and Longnan Basin in Southern Jiangxi Province are 175 ∼ 148 Ma, not only does its amplitude change more significantly, but it does not match with the Rb-Sr isochron ages (179 ∼ 173 Ma) of basic end member. As a result, I choose a method of zircon U-Pb dating with a higher accuracy, to obtain the rhyolite in the bottom of bimodal volcanic rocks in the Changpu Basin and the dacite in the top of of bimodal volcanic rocks in the Longnan Basin, whose zircon SHIRMP U-Pb age are respectively (195.2 ± 2.8) Ma and (191 ± 1.7) Ma. What's more, they are both almost the same in the error limit. It shows that the bimodal volcanic rocks in these both two basins are the product of the same session of magma movement. Simultaneously, it explains they form in a flash during the eruption intervals. According to the the newest International Stratigraphic Chart (Gradsrein et al. , 2004), in terms of geological age, the bimodal volcanic rocks in Changpu Basin and Longnan Basin, belonging to the early Early Jurassic. The zircon SHIRMP U-Pb age are distinctly older than the whole-rock Rb-Sr isochron age, it is probably because of the deviation of the dating method for the wholerock Rb-Sr isochron age. The zircon SHIRMP U-Pb age of bimodal volcanic rocks are 191 ∼ 195 Ma in Southern Jiangxi Province, which indicates that there had been an extensional environment. And after the bimodal volcanic activity, The zircon SHIRMP U-Pb age of felsic volcanic rocks are 145 ∼ 130 Ma. Both of the ages shows a as long as 45 Ma quiet period between 190 Ma and 145 Ma. It is unreasonable possible to interpreted by the single pattern of pacific plate subducting to eurasian plate. (authors)

  6. Edad sexual en escolares de Cali, Colombia.

    Directory of Open Access Journals (Sweden)

    Luis H. Conde

    2009-11-01

    Full Text Available Se ha observado en países de ingresos altos y medios que la edad de maduración sexual es cada vez más temprana; esto se puede explicar por el desarrollo socioeconómico, los estilos de vida de las poblaciones urbanas y la disminución de la desnutrición. En Colombia se encontró sólo un estudio donde se determinan algunos estadíos de maduración por aparición de vello pubiano mamas y genitales externos. Varias publicaciones aseguran que las edades de maduración sexual son tardías y similares en los países del tercer mundo aunque este hecho es debatible como lo indican otros estudios. Es necesario determinar la edad de la pubertad para evitar riesgos para enfermedades de trasmisión sexual, embarazo y enfermedades crónicas. El propósito general del estudio fue evaluar los de factores de riesgo para enfermedades crónicas no trasmisibles en población escolarizada y entre ellos la determinación de maduración sexual. Se realizó este estudio en Cali, Colombia, ciudad de unos dos millones de habitantes, promedio anual de temperatura de 28º C, dividida en seis estratos socioeconómicos. Se evaluaron 2821 escolares de diferentes instituciones educativas del área urbana, con representación de edad, género y estratos socioeconómicos. Los resultados indican que la edad de maduración sexual en esta población es igual a la informada en varios países de ingresos altos y medios en varios continentes. La edad promedio para las etapas de maduración de Tanner suceden a edades inferiores a las que se asignan a países del tercer mundo. Los estratos bajos tienen aún un retardo del promedio de edad alrededor de seis meses en comparación con estratos medio y alto. Además de la importancia que implica por sí mismo el desarrollo o la maduración sexual, es importante relacionarlo con otras manifestaciones tales como la velocidad de crecimiento, los cambios en masa corporal, lípidos sanguíneos y la determinación temprana de riesgos para

  7. New Robust Reference Materials for In Situ Single Grain Rutile U-Pb Geochronology and Method Refinements for Detrital Rutile Analysis by LA-MC-ICP-MS

    Science.gov (United States)

    Parrish, R. R.; Bracciali, L.; Condon, D. J.; Horstwood, M. S.; Najman, Y.

    2012-12-01

    While rutile (TiO2) occurs in the heavy mineral suite of detrital sediments and originates mainly in medium- to high-grade metamorphic and some igneous rocks, there are very few applications of U-Pb dating of rutile to provenance studies; this is due to an overreliance on zircon, low U content of rutile limiting measurement quality by in situ methods, a higher proportion of common Pb relative to zircon, and a lack of widely available good quality reference materials. We have addressed these issues and characterized two ~ 1.8 Ga rutile reference materials by SEM, trace elements, U-Pb ID-TIMS, and intra-grain and inter-grain U-Pb LA-MC-ICP-MS analysis using mixed faraday and multiple ion counting detectors with high sensitivity. We have assessed U-Pb discordance and in situ variations in relative common Pb and age and their bearing on the quality of the reference materials for in situ U-Pb dating. The rutiles (Sugluk-4 and PCA-S207) come from granulite facies belts of the Canadian Shield, namely the northern Cape Smith Belt of Quebec and the Snowbird Tectonic Zone (Sasatchewan). The ID-TIMS data are slightly discordant due to variable common Pb and limited Pb loss; the variation in 6 single grains of Sugluk-4, that we use as the primary reference material, is standards, this being due to the real variation in measured values arising from limited Pb loss, age variation, and common Pb variability [1]. We have applied our refined method to the provenance of rutile from drainages from British Columbia, Bhutan, and the Brahmaputra River of NE India (predominant rutile ages ~ 50, 15, and 2 Ma, respectively; Bracciali et al., this meeting). Our method successfully dates >75% of all rutile grains in a sediment; unsuccessful analyses are due to poor quality rutiles with massive common Pb and/or U contents < ~1ppm. While some analyses are therefore unusable, unlike zircon age zoning is rare to absent in rutile and there is little need to image grains to identify 'inheritance

  8. Mortalidad infantil, edad cronológica y morfometría del esqueleto apendicular en una colección osteológica contemporánea

    OpenAIRE

    García Mancuso, Rocío; Salceda, Susana Alicia; Desántolo, Bárbara; Plischuk, Marcos

    2009-01-01

    En este trabajo se analiza la relación entre la edad cronológica documentada y la descripción métrica del esqueleto apendicular de una muestra osteológica contemporánea de 88 individuos con edades comprendidas entre no-natos y 11 meses posteriores al nacimiento con el propósito de establecer la congruencia de las categorías de edad documentadas. El material procede del cementerio Municipal de la ciudad de La Plata (Buenos Aires, Argentina) y actualmente integra la Colección Osteológica "Prof....

  9. Patagonia Argentina

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    A.J. Acuña

    2008-01-01

    Full Text Available La zona central de la Patagonia, Argentina, se encuentra sometida a explotación petrolera y sus suelos se caracterizan por ser deficientes en nitrógeno. Esto causaría un efecto negativo en los procesos de atenuación natural que se desarrollan en los suelos contaminados con hidrocarburos. El objeto de este estudio fue determinar cual es el efecto de la deficiencia de nitrógeno sobre la biodegradación de los hidrocarburos en un suelo de la Patagonia, Argentina. Se trabajó con tres microcosmos a los que se les realizó tratamientos diferentes. En uno se monitoreo la atenuación natural del sistema, en otro la fertilización con nitrógeno (N, fósforo (P y potasio (K, y en el último la fertilización con P y K. Durante el seguimiento se determinaron mineralización y medición de hidrocarburos, y se realizaron recuentos bacterianos y determinación de nitrato, nitrito y amonio. Los resultados indican que es posible la biodegradación de hidrocarburos en el suelo deficiente de nitrógeno de la Patagonia estudiado en tiempos mas prolongados que en aquellos que se realiza una fertilización con nitrógeno. El nitrógeno necesario para el proceso sería obtenido por los microorganismos del suelo por fijación biológica.

  10. Three cycles of sedimentation in ancient sedimentary basins of southern Ireland: insights from detrital zircon U-Pb ages

    Science.gov (United States)

    Fairey, Brenton; Kerrison, Aidan; Meere, Patrick; Mulchrone, Kieran; Linnemann, Ulf; Hofmann, Mandy; Gaertner, Andreas; Sonntag, Benita-Lisette; Byrne, Keith

    2016-04-01

    Previous work has shown that sedimentary rocks from the Lower Devonian Dingle Basin were uplifted and recycled by Acadian orogenic activity into the Upper Devonian Munster Basin. This is particularly applicable for sediments deposited in the western part of the Munster Basin. In the present study, a new dataset of U-Pb ages for detrital zircons has been established that spans a large geographic area which includes the Dingle and Munster basins as well as the offshore Mesozoic North Celtic Sea, South Celtic Sea, 'Goban Spur' and Fastnet basins. The study is the first of its kind in any of these sedimentary basins. The aim is to investigate whether sediments deposited in the offshore basins during the Mesozoic reflect three erosion-deposition cycles. Detritus that has undergone three sedimentary cycles would yield super-mature sediments suitable for hydrocarbon storage. Detrital zircon age spectra for Lower Devonian Dingle Basin samples indicate strong sediment input from Avalonian (~600 Ma) and Laurentian (~1.7 Ga and ~1.1 Ga) sources with some input from Caledonian orogenic sources (400-480 Ma). Detrital zircon age spectra in the western Munster Basin largely reflect input from Caledonian-aged igneous crustal input (400-480 Ma) and Laurentian sources. An Avalonian component is not detected in any of the samples from the western Munster Basin. In the central and eastern parts of the Munster Basin, detrital zircon age spectra indicate that the dominant sources of detritus are derived from Laurentia and from Caledonian igneous rocks. In contrast to the western part of the basin, age components around 600 Ma are present in some samples and represent an Avalonian source. These signals are echoed, at varying degrees, in detrital age spectra from Jurassic and Cretaceous samples of the central North Celtic Sea Basin. These age spectra also indicate a significant contribution of detritus from Avalonian terrane. The Avalonian signature is completely absent from Jurassic

  11. Petrology and SHRIMP U-Pb dating of Xitieshan eclogite, North Qaidam UHP metamorphic belt, NW China

    Science.gov (United States)

    Zhang, Cong; Zhang, Lifei; Roermund, Herman Van; Song, Shuguang; Zhang, Guibin

    2011-09-01

    Normal bimineralic and phengite-bearing eclogites have been recognized within mafic boudins (or lenses) enclosed in granitic and pelitic gneisses in the Xitieshan terrane, NW China. Bimineralic eclogite contains the primary M1 mineral assemblage Grt + Omp + Rt + Qtz+/-Zrn. Inclusions in M1 omphacite may be coesite pseudomorphs. Phengite eclogite consists of the M1 mineral assemblage Grt + Omp + Phn + Qtz + Rt+/-Zrn. Most eclogites are retrogressed to various degrees and contain hornblende, diopside and plagioclase, which commonly form symplectitic and/or kelyphitic intergrowths. The peak M1 P-T conditions of the Xitieshan eclogite are calculated to be P = 2.71-3.17 GPa and T = 751-791 °C, consistent with the presence of coesite pseudomorphs in omphacite. In addition, we have identified two stages of retrograde metamorphism; an early isothermal decompression stage (M2) followed by a later stage (M3) that developed under decreasing temperatures and pressures. During M2 internally-derived fluids played an important role, whereas during M3 and below externally-derived fluids dominated. The composition of garnet in M1changed little during M2 isothermal decompression (ITD), although pyrope contents in garnet locally decrease from core to rim where the grains have amphibole and pargasite + plagioclase coronas. Also the jadeite content (56%) of M1 omphacite decreased in the presence of active fluids during retrograde metamorphism. M1 phengite is replaced by the M2 assemblage Ms + Bt accompanied by K-feldspar + quartz. Amphibole compositions changed from magnesio-katophorite in M2 to pargasite in M3. Zircon U-Pb SHRIMP dating shows that the bimineralic eclogite has a magmatic protolith age of 877 ± 8 Ma and a metamorphic age of 439 ± 8 to 461 ± 4 Ma. We conclude that the Xitieshan metabasic rocks formed in the late Proterozoic and were subsequently subducted to depths of about 100 km, where they were metamorphosed to UHP eclogite during the late Ordovician (440-460 Ma

  12. Zircon U-Pb geochronological framework of Qitianling granite batholith, middle part of Nanling Range, South China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The Qitianling granite batholith (QGB) is located in the southern Hunan Province, middle part of the Nanling Range, South China. Its total exposure area is about 520 km2. Based on our 25 single grain zircon U-Pb age data and 7 published data as well as the geological, petrological, and space distribution characteristics, we conclude that QGB is an Early Yanshanian (Jurassic) multi-staged composite pluton. Its formation process can be subdivided into three major stages. The first stage, emplaced at 163―160 Ma with a peak at about 161 Ma, is mainly composed of hornblende-biotite monzonitic granites and locally biotite granites, and distributed in the eastern, northern, and western peripheral parts of the pluton. The second stage, emplaced at 157―153 Ma with a peak at 157―156 Ma, is mainly composed of biotite granites and locally containing hornblende, and distributed in the middle and southeastern parts of the pluton. The third stage, emplaced at 150―146 Ma with a peak at about 149 Ma, is mainly composed of fine-grained (locally porphyritic) biotite granites, and distributed in the middle-southern part of the pluton. Each stage can be further disintegrated into several granite bodies. The first two intrusive stages comprise the major phase of QGB, and the third intrusive stage comprises the additional phase. Many second stage fine-grained granite bosses and dykes intruded into the first stage host granites with clear chilling margin-baking phenomena at their intrusive contacts. They were emplaced in the open fracture space of the earlier stage consolidated rocks. Their isotopic ages are mostly 2―6 Ma younger than their hosts. Conceivably, the time interval from magma emplacement, through cooling, crystallization, solidification, up to fracturing of the earlier stage granites cannot exceed 2―6 Ma. During the Middle-Late Jurassic in the Qitianling area and neighboring Nanling Range, the coeval granitic and basic-intermediate magmatic activities were widely

  13. Zircon and baddeleyite U-Pb geochronology and Hf isotopes from the Central Atlantic Magmatic Province (CAMP)

    Science.gov (United States)

    Davies, Joshua; Marzoli, Andrea; Bertrand, Herve; Youbi, Nasrrddine; Schaltegger, Urs

    2016-04-01

    Large Igneous Provinces (LIPs) are anomalously large volumes of dominantly mafic magma that erupted and intruded into the upper crust over short time scales. The origin of these volcanic provinces is very likely specific for each case, partly explained by plate tectonic processes or mantle plumes. Despite an ambivalent plate tectonic connection, there is a striking temporal correlation between the timing of LIPs and periods of mass extinction on Earth. However, establishing the relationship between these two is quite complicated since mass extinctions are typically recognised in the marine record, and LIPs are usually terrestrially emplaced. High precision geochronology of LIPs is essential to (i) establish the synchrony and infer the causal relationship with mass extinctions, and (ii) to understand how LIPs form. In this study, we apply high-precision zircon and baddeleyite U-Pb geochronology to rocks from the ~200 Ma Central Atlantic Magmatic Province (CAMP), in an attempt to reconstruct the overall timing of the event, its spatial distribution in time, and determine its relationship with the end-Triassic mass extinction. We also present Hf isotope data from the separated zircon and baddeleyite to both elucidate the origin of the LIP and also to determine if the magmas all originate from the same source. Our data suggest that the majority of the CAMP magmas were emplaced over a 0.5 Ma period from ~201.5 Ma to ~201.0 Ma with a possible small secondary event occurring much later at ~199 Ma. Spatially, it appears that CAMP magmatism occurred roughly simultaneously over the entire province (i.e. ~8000 Km North to South). However, the Hf isotopic composition varies over this length with the highest values (~5.5 ɛHf) occurring in a small area to the south of the province in Brazil and Sierra Leone. Towards the north, the ɛHf values become negative, indicating the presence of an older or more enriched component in the magmas. Our geochronology also indicates that CAMP

  14. LA-ICP-MS U-Pb apatite dating of Lower Cretaceous rocks from teschenite-picrite association in the Silesian Unit (southern Poland

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    Szopa Krzysztof

    2014-08-01

    Full Text Available The main products of volcanic activity in the teschenite-picrite association (TPA are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre and subalkaline (dolerite. Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7. The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128-120 Ma.

  15. REE, Sm-Nd and U-Pb zircon study of eclogites from the Alpine External Massifs (Western Alps): Evidence for crustal contamination

    International Nuclear Information System (INIS)

    A geochemical and geochronological study of the Alpine External Crystalline Massifs (AECM) of Aiguilles Rouges, Belledonne and Argentera was undertaken in order to constrain the geodynamic evolution of this segment of the Variscan foldbelt. Another aim of the study is to characterize the behaviour of isotopic markers, in particular the U-Pb zircon system, under high-grade metamorphic conditions. The whole-rock geochemistry of eclogites and amphibolites was investigated using major and trace element (including the REE) analytical techniques; isotopic studies were performed by application of the Sm-Nd whole-rock and U-Pb zircon methods. In terms of regional geological history, the early development of metamorphic and magmatic activity in the AECM is typical of the extensional tectonic regime observed throughout the Variscan foldbelt during the Cambro-Ordovician (i.e. basic magmatism dated at 475-450 Ma). The composition of the metabasic rocks is closely similar to tholeiites emplaced into thinned continental crust which are generally associated with the initial stages of oceanic rifting. The source regions for these metabasics are characterized by initial εNd values between +6 and +8, suggesting depleted mantle sources influenced by a weak crustal component and/or the existence of a metasomatised lithosphere. The multi-stage eclogite-facies metamorphism is dated at 425-395 Ma (i.e. Silurian). An application of the U-Pb method, associated with the artificial abrasion of zircon grains, has led to the recognition of a weak crustal contamination in the metabasic protoliths. This is implied by the Archaean and Lower Proterozoic upper intercepts on Concordia - devoid of geological significance - which reflect the presence of a pre-existing basement to the AECM. (orig./WL)

  16. Integrated Paleomagnetism and U-Pb Geochronology of Mafic Dikes of the Eastern Anabar Shield Region, Siberia: Implications for Mesoproterozoic Paleolatitude of Siberia and Comparison with Laurentia.

    Science.gov (United States)

    Ernst; Buchan; Hamilton; Okrugin; Tomshin

    2000-07-01

    This article reports the first joint paleomagnetic and U-Pb geochronologic study of Precambrian diabase dikes in the Anabar Shield and adjacent Riphean cover of Siberia. It was undertaken to allow comparison with similar published studies in Laurentia and to test Proterozoic reconstructions of Siberia and Laurentia. An east-trending Kuonamka dike yielded a provisional U-Pb baddeleyite emplacement age of 1503+/-5 Ma and a virtual geomagnetic pole at 16 degrees S, 221 degrees E (dm=17&j0;, dp=10&j0;). A paleomagnetic pole at 6 degrees N, 234 degrees E (dm=28&j0;, dp=14&j0;) was obtained from five Kuonamka dikes. An east-southeast-trending Chieress dike yielded a U-Pb baddeleyite emplacement age of 1384+/-2 Ma and a virtual geomagnetic pole at 4 degrees N, 258 degrees E (dm=9&j0;, dp=5&j0;). Kuonamka and Chieress poles are interpreted to be primary but do not average out secular variation. Assuming that the Siberian Plate has remained intact since the Mesoproterozoic, except for mid-Paleozoic opening of the Viljuy Rift, then the above results indicate that the Siberian Plate was in low latitudes at ca. 1503 and 1384 Ma, broadly similar to low latitudes determined for Laurentia from well-dated paleopoles at 1460-1420, 1320-1290, and 1267 Ma. This would allow Laurentia and Siberia to have been attached in the Mesoproterozoic, as suggested in several recent studies based on geological criteria. However, because paleomagnetic results from the Anabar Shield region do not average out secular variation and the ages of poles from Siberia and Laurentia are not well matched, it is not yet possible to distinguish between these reconstructions or to rule out other configurations that also maintain the two cratons at low paleolatitudes. PMID:10856011

  17. Double dating of detrital zircon by fission-track and LA-ICPMS U/Pb analysis: new perspectives in decomposing mixed provenance signatures

    Science.gov (United States)

    Mikes, Tamás.; Jeffries, Teresa E.; Dunkl, István.; Tolosana-Delgado, Raimon; von Eynatten, Hilmar

    2010-05-01

    A novel approach combining fission track (FT) and in-situ LA-ICPMS U/Pb isotopic analyses in single detrital zircon grains is used to trace the exhumed sources of Tertiary synorogenic sediments in the Dinarides. Grains were dated by the FT method, and their interiors were imaged by SEM-CL to avoid ablation of inherited or other unsuitable domains. U/Pb isotopic compositions were determined by an instrument setup of a 213 nm Nd:YAG laser source coupled to a quadrupole-based ICP-MS, and an analytical protocol providing a cost-effective sample throughput (70-100 grains per day) while maintaining high analytical precision and accuracy. CL-control and a good spatial resolution helped suppressing age bias, as justified by a notably high proportion (>90%) of concordant (±5%) grain ages. Finally, the FT and U/Pb ages were integrated for each grain using a bivariate statistical algorithm that takes the different precisions permitted by the two dating techniques into account. The zircon double dating approach yields valuable insights into the thermal history of source terrains of synorogenic sediments both in the Outer Dinaride foreland basin and in the Dinarides-Tisza collisional zone. We can isolate several clusters of characteristic pairs of crystallization/cooling ages, which pin-point Alpine tectonostratigraphic units with a confidence that could not be achieved by using the two dating techniques separately. The Adriatic basement of the Dinarides affected by the major Jurassic-Early Cretaceous cooling event was not the exclusive source for the siliciclastic fill of these Tertiary basins. The distributary systems involved much detritus from Ordovician and Late Permian magmatic units affected by a Late Cretaceous thermal event; such units are not typical in the Dinarides. A major sediment input from the Austroalpine, Tisza and Pelagonian Units in the Tertiary is the most likely scenario for the evolution of the Dinaride basins.

  18. Insights from heavy minerals and zircon U-Pb ages into the middle Miocene-Pliocene provenance evolution of the Yinggehai Basin, northwestern South China Sea

    Science.gov (United States)

    Jiang, Tao; Cao, Licheng; Xie, Xinong; Wang, Zhenfeng; Li, Xushen; Zhang, Yingzhao; Zhang, Daojun; Sun, Hui

    2015-08-01

    The well-preserved Cenozoic sedimentary record in the Yinggehai Basin, South China Sea, is suitable to explore the tectonic and climatic evolution of SE Asia. Red River, a large-scale fluvial system in this region, was previously regarded as the major sediment source for the basin. Here we combine heavy mineral analysis and detrital zircon U-Pb dating to shed new light on the middle Miocene-Pliocene provenance evolution at a basin scale. The results clearly reveal potential source areas additional to the Red River. Sediments have been delivered to the proximal areas from Hainan Island, as indicated by the high zircon content and the Yanshanian U-Pb ages in the southern segment of the Yingdong Slope. A provenance from Central Vietnam is explicitly discerned in the upper Miocene of the Central Depression, where sediments are characterized by few metamorphic heavy minerals and the U-Pb age pattern peaking at around 250 Ma and 440 Ma. Coeval large-scale relative sea-level fall and rapid exhumation along the Vietnamese margin together may have facilitated this long-distance sediment transport. Provenance of sediments from the Red River seems to change over time. Song Lo River, on the north side of the main stream, probably flowed from the NE and carried Neoproterozoic-early Paleozoic zircons to the Yinggehai Basin during the middle Miocene. Since the late Miocene, rocks along the Red River Fault Zone have become the dominant source. Subsequently, widespread metamorphic minerals in the Central Depression of the Yinggehai Basin, combined with the strong river incision and high offshore sedimentation rates, indicate an increased sediment supply from the Red River in the Pliocene.

  19. Response of detrital zircon and monazite, and their U-Pb isotopic systems, to regional metamorphism and host-rock partial melting, Cooma complex, southeastern Australia

    International Nuclear Information System (INIS)

    Progressive Early Silurian low-pressure greenschist to granulite facies regional metamorphism of Ordovician flysch at Cooma, southeastern Australia, had different effects on detrital zircon and monazite and their U-Pb isotopic systems. Monazite began to dissolve at lower amphibolite facies, virtually disappearing by upper amphibolite facies, above which it began to regrow, becoming most coarsely grained in migmatite leucosome and the anatectic Cooma Granodiorite. Detrital monazite U-Pb ages survived through mid-amphibolite facies, but not to higher grade. Monazite in the migmatite and granodiorite records only metamorphism and granite genesis at 432.8 ± 3.5 Ma. Detrital zircon was unaffected by metamorphism until the inception of partial melting, when platelets of new zircon precipitated in preferred orientations on the surface of the grains. These amalgamated to wholly enclose the grains in new growth, characterised by the development of (211) crystal faces, in the migmatite and granodiorite. New growth, although maximum in the leucosome, was best dated in the granodiorite at 435.2 ± 6.3 Ma. The combined best estimate for the age of metamorphism and granite genesis is 433.4 ± 3.1 Ma. Detrital zircon U-Pb ages were preserved unmodified throughout metamorphism and magma genesis and indicate derivation of the Cooma Granodiorite from Lower Palaeozoic source rocks with the same protolith as the Ordovician sediments, not Precambrian basement. Cooling of the metamorphic complex was relatively slow (average ∼12 deg C/106 y from ∼ 730 to ∼170 deg C), more consistent with the unroofing of a regional thermal high than cooling of an igneous intrusion. The ages of detrital zircon and monazite from the Ordovician flysch (dominantly composite populations 600-500 Ma and 1 2-0.9 Ga old) indicate its derivation from a source remote from the Australian craton. Copyright (2001) Geological Society of Australia

  20. Morphology and U-Pb ages of zircons from the high-grade metamorphic Precambrian in the Sirdal-Oersdal area, SW Norway

    International Nuclear Information System (INIS)

    The U-Pb systematics of seven suites of zircons and two apatites were investigated in an attempt to obtain data about the pre-Sveconorwegian geochronology. Very little was known about this earlier history, as previous studies have shown that the high-grade metamorphism has obliterated most of the older Rb-Sr record. Three samples were investigated from the augengneisses, two from the pyroxene syenites, one garnetiferous migmatite and one magnetite-ilmenite-zircon veinlet cross-cutting the charnockitic migmatites. (Auth.)

  1. Assessment of the 187Re decay constant by cross calibration of Re Os molybdenite and U Pb zircon chronometers in magmatic ore systems

    Science.gov (United States)

    Selby, David; Creaser, Robert A.; Stein, Holly J.; Markey, Richard J.; Hannah, Judith L.

    2007-04-01

    The past decade has seen renewed interest in 187Re- 187Os geochronology using a variety of matrices including sulfide minerals, shales and meteorites. The most widely used value of the 187Re decay constant ( λ187Re) is 1.666 ± 0.005 × 10 -11 a -1 (±0.31%), which is based on cross calibration of Re-Os and Pb-Pb chronometers for certain meteorites [Smoliar M. I., Walker R. J., and Morgan J. W. (1996) Re-Os isotope constraints on the age of Group IIA, IIIA, IVA, and IVB iron meteorites. Science271, 1099-1102]. However, other recent studies have yielded alternate values of λ187Re, based upon either direct counting experiments or analysis of meteorites. Here, we provide an independent assessment of λ187Re, using methodology, sample materials, and preparation of Os standard solutions different from those of Smoliar et al. (1996). Combining Re-Os age data for molybdenite formed in magmatic ore deposits, with the U-Pb zircon age of the magmatic rocks, a refined λ187Re value is determined by averaging 11 individual cross-calibration experiments spanning ca. 2700 Ma of Earth history. Using the U decay constants of Jaffey [Jaffey A. H., Flynn K. F., Glendenin L. E., Bentley W. C., and Essling A. M. (1971) Precision measurement of half-lives and specific activities of 235U and 238U. Phys. Rev.4, 1889-1906], a value for λ187Re of 1.6668 ± 0.0034 × 10 -11 a -1 is determined. Using the λ238U value of Jaffey et al. (1971) and λ235U value of Schoene [Schoene B., Crowley J. L., Condon D. J., Schmitz M. D., and Bowring S. A. (2006) Reassessing the uranium decay constants for geochronology using ID-TIMS U-Pb data. Geochim. Cosmochim. Acta70, 426-445], a value for λ187Re of 1.6689 ± 0.0031 × 10 -11 a -1 is determined. These values are nominally higher (ca. 0.1 and ca. 0.2%) than the value determined by Smoliar et al. [Smoliar M. I., Walker R. J., and Morgan J. W. (1996) Re-Os isotope constraints on the age of Group IIA, IIIA, IVA, and IVB iron meteorites. Science271

  2. Early vendian age of polyphase gabbro-granites complexes of Karalon-Mamakan Zone of Baikal-Muisky Belt: U-Pb-zircon dating

    International Nuclear Information System (INIS)

    For confirming the assumption on the formation of magmatic rocks in the Karalon segment of the Baikal-Muisky Belt in a narrow time range of early vendian age the U-Pb zircon dating of the Tallainsky complex gabbroids and Padorinsky complex granites in Karalon-Mamakan Zone was conducted. Estimated isotopic age of the gabbroids and granites mentioned amounts to 604±7 m.a. and 598±4 m.a. respectively. The early vendian age is shown to be a period of large-scale magmatism in the history of the Baikal-Muisky Belt formation, which gave rise to folded deformations, their boundary 590 m.a

  3. A precise zircon U-Pb age for the base of the BIF of the Mulaingiri formation, (Bababudan group, Dharwar supergroup) of the Karnataka craton

    International Nuclear Information System (INIS)

    SHRIMP U-Pb analyses of zircon grains from two thin dark shales believed to be syndepositional ashfall tuffs close to the base of the banded iron-formation (BIF) within the Mulaingiri formation of the Bababudan group (Dharwar supergroup) of the western Karnataka craton provide a precise age for the onset of BIF deposition in the basin. Sample 120019C, from the exact base of the BIF, gave an age of 2720 ± 7 Ma, while sample 120018C, 14.5m above the base, gave an age of 2718 ± 6 Ma. The second sample contained younger grains which may have been affected by a late thermal event. (author)

  4. Ion microprobe U-Pb dating and REE analysis of apatite from kerogen-rich silica dike from North pole area, Pilbara Craton, Western Australia

    International Nuclear Information System (INIS)

    In order to provide a time constraint on the 13C-depleted kerogen formation in silica dikes that intruded 3.5 Ga greenstone from Pilbara Craton in Western Australia, we have carried out an ion microprobe U-Pb dating and rare earth element (REE) analysis of apatite from one of the dikes. Two types of apatite were identified in the dike, based on their occurrences. One is stick-shape apatites (Type 1 apatite) in secondary silica micro-veins that cut the silica dike. The other is granular apatites (Type 2 apatite) that occur in matrix of the silica dike. Occurrence in the secondary miro-veins (Type 1), non-igneous REE patterns (Type 1 and 2), chemical zoning (some of Type 1 and 2), iron sulfide within apatite (some of Type 2), and intergrowth of apatite and sulfide (some of Type 2) suggest that both types of apatite were crystallized in the silica dike. Ion microprobe U-Pb dating of Type 1 apatite did not give a well-constrained age, while Type 2 apatite yields a Tera-Wasserburg concordia intercept age of 3214 ± 140 Ma (95% confidence level, MSWD = 0.6) in a three-dimensional 238U/206Pb-207Pb/206Pb-204Pb/206Pb diagram, and a 204Pb/206Pb-207Pb/206Pb isochron age of 3191 ± 150 Ma (95% confidence level, MSWD = 0.5). It is difficult to judge whether the U-Pb and Pb-Pb age of Type 2 apatite is crystallization age or metamorphic age, since the estimated range of closure temperature of U-Pb system in the apatite and that of metamorphic temperature is partly overlapped. In either case, it can be safely concluded that the minimum age of the dike and kerogen is 3.2 Ga. These ages might allow the interpretation that the kerogen was produced by biological carbon fixation and/or abiological reaction at least before 3.2 Ga. (author)

  5. A combined Sm-Nd, Rb-Sr, and U-Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

    Energy Technology Data Exchange (ETDEWEB)

    Edmunson, J; E.Borg, L; Nyquist, L E; Asmerom, Y

    2008-11-17

    Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 {+-} 37 Ma and an initial {var_epsilon}{sub Nd}{sup 143} value of -0.27 {+-} 0.74. The age-initial {var_epsilon}{sub Nd}{sup 143} (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiation was completed by 4492 {+-} 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 {+-} 53 Ma. The other is 4003 {+-} 95 Ma and is concordant with an Ar-Ar age for 78236. The {sup 207}Pb-{sup 206}Pb age of 4333 {+-} 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged {mu} ({sup 238}U/{sup 204}Pb) value of the source can be estimated at 27 {+-} 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low {mu} value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high {mu} value.

  6. Veränderungen des Rb-Sr- und U-Pb-Systems im Granit von Soultz-sous-Forêts unter dem Einfluss hydrothermaler Fluide

    OpenAIRE

    Traxel, Sven

    2007-01-01

    In der vorliegenden Arbeit wurden Untersuchungen mit der Rb-Sr- und U-Pb-Methode an Bohrkernproben des Granits von Soultz-sous-Forêts/Frankreich durchgeführt. Die Proben stammen aus 1500 – 2200 m Tiefe und waren dort multiepisodischen Hydrothermalereignis-sen bei erhöhten Temperaturbedingungen (100 – 150°C) ausgesetzt. Das untersuchte Hartge-stein eignet sich als natürliches Archiv der komplexen Geschichte der Fluid-Gesteins-Wech-selwirkungen, die sich im Untergrund des heutigen Rheingrabens ...

  7. Geology, geochemistry, and geochronology (U-Pb) of the Rio Fortuna Gneiss - Serra do Bau intrusive Suite - Paragua Terrane SW Amazonian Craton

    Energy Technology Data Exchange (ETDEWEB)

    Faria, Debora Almeida; Ruiz, Amarildo Salina; Matos, Joao Batista; Sousa, Maria Zelia Aguiar de; Lima, Gabrielle Aparecida de [Research Group on Crustal and Tectonic Evolution, Guapore, RS (Brazil); Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Instituto de Ciencias Exatas e da Terra; Inst. Nacional de Ciencia e Tecnologia de Geociencias da Amazonia (GEOCIAM), Belem, PA (Brazil); Moacir Jose Buenano Macambira, E-mail: defaal.debora@gmail.com, E-mail: gabilimagel@gmail.com, E-mail: asruiz@gmail.com, E-mail: jmatos@ufmt.br, E-mail: prof.mzaguiar@gmail.com, E-mail: moamac@ufpa.br [Research Group on Crustal and Tectonic Evolution, Guapore, RS (Brazil); Universidade Federal do Para (UFPA), Belem, PA (Brazil)

    2014-07-01

    The Rio Fortuna Gneiss crops out in the Serra Santa Barbara, near the Fortuna military headquarters, on the Brazil-Bolivia border. These orthogneisses are located in a portion of the Paragua terrain affected by the Sunsas Orogeny (1.0-0.9 Ga.). They are classified as monzo to granodiorite orthogneisses and underwent at least three episodes of deformation. The U-Pb zircon age of 1,711 ± 13 Ma obtained by laser ablation MC-ICP-MS is interpreted as the crystallization age of this orthogneiss. Geochemically, these rocks form a sequence comprising acidic subalkaline magmatism, calc-alkalic-type high-K, and metaluminous to peraluminous. (author)

  8. U-Pb zircon and biostratigraphic data of high-pressure/low-temperature metamorphic rocks of the Talea Ori: tracking the Paleotethys suture in central Crete, Greece

    Science.gov (United States)

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

    2016-03-01

    Inherited deformation microfabrics of detrital quartz grains and U-Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite-Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds includes Cambrian and Neoproterozoic rounded zircons with main U-Pb age peaks at 628 and 988 Ma. These and minor Paleoproterozoic and Archean peaks, together with the lack of Variscan-aged and Mesoproterozoic zircons, are similar to the age spectra obtained from the Phyllite-Quartzite Unit s.str. of the Peloponnesus and eastern Crete and from the Taurides. All of these zircons should be derived from the northeastern passive margin of Gondwana (Cimmeria). Metatuffites of the uppermost Rogdia Beds and metasandstone of Bali beach, on the other hand, include euhedral detrital zircons displaying a Variscan U-Pb age spectra at ca. 300 Ma with concordia ages at 291 ± 3, 300 ± 1 Ma (Rogdia) and 286 ± 3, 300 ± 3, 313 ± 2 Ma (Bali). Both types of metasediments and their zircons are similar to those of the pre-Alpine basement and overlying Tyros Beds of eastern Crete, revealing a provenance at the southern active margin of Laurasia. Thus, in central Crete the Paleotethys suture should be situated inside the Rogdia Beds. Magmatic zircons separated from a rhyolite boulder of the lower Achlada Beds yielded a concordant U-Pb zircon age at 242 ± 2 Ma placing a maximum age for the deposition of the (meta)conglomerate from which the boulder was collected. This age is compatible with an Olenekian-early Anisian age of the underlying Vasilikon marble suggested by new findings of the foraminifera Meandrospira aff. pusilla. Both the Achlada Beds and the Vasilikon marble can be attributed to the lower Tyros Beds of eastern Crete. The Alpine deformation led to a pervasive mylonitic foliation, which is affecting most of the studied rocks. This foliation results from D2 top

  9. Geology, geochemistry, and geochronology (U-Pb) of the Rio Fortuna Gneiss - Serra do Bau intrusive Suite - Paragua Terrane SW Amazonian Craton

    International Nuclear Information System (INIS)

    The Rio Fortuna Gneiss crops out in the Serra Santa Barbara, near the Fortuna military headquarters, on the Brazil-Bolivia border. These orthogneisses are located in a portion of the Paragua terrain affected by the Sunsas Orogeny (1.0-0.9 Ga.). They are classified as monzo to granodiorite orthogneisses and underwent at least three episodes of deformation. The U-Pb zircon age of 1,711 ± 13 Ma obtained by laser ablation MC-ICP-MS is interpreted as the crystallization age of this orthogneiss. Geochemically, these rocks form a sequence comprising acidic subalkaline magmatism, calc-alkalic-type high-K, and metaluminous to peraluminous. (author)

  10. U/Pb, Sm/Nd and Rb/Sr geochronological and isotopic study of northern Sierra Nevada ophiolitic assemblages, California

    Science.gov (United States)

    Saleeby, J. B.; Shaw, H. F.; Niemeyer, Sidney; Moores, E. M.; Edelman, S. H.

    1989-06-01

    Distinct ophiolitic assemblages occur as oceanic basement within three of the four regional tectonic belts of the northern Sierra Nevada. New U/Pb zircon, Sm/Nd and Rb/Sr data are presented for each assemblage, providing critical geochronological and isotopic constraints on the petrogenesis and tectonic evolution of the ophiolitic and associated ensimatic assemblages. Ophiolitic assemblages include from west to east the Smartville complex, Central belt and Feather River belt. The Smartville complex represents an island arc volcanic-plutonic sequence with a major late-stage sheeted dike swarm. The Sm/Nd systems from a wide compositional spectrum of rocks record a 178±21 Ma petrogenetic age and an ɛ Nd(T)=+9.2±0.6. Zircon U/Pb systems on an uppermost dacite yield a 164±2 Ma age, and on a number of plagiogranite screens and dikes from the sheeted complex 162±1 Ma ages. The Central and Feather River belts are structurally complex polygenetic assemblages. The U/Pb zircon and Sm/Nd systems record major ˜205 Ma and ˜315 Ma petrogenetic events respectively both involving depleted mantle derived magmas. Such magmatism probably occurred in marginal basin/transform systems developed within an older oceanic depleted mantle basement regime. Both Sm/Nd and U/Pb zircon systems show local components of Proterozoic sialic material. The sialic contaminants were probably introduced into the system as craton derived detritus. It is doubtful that any of the ophiolitic assemblages studied represent genetically related crust-upper mantle sequences generated during the development of new oceanic lithosphere. Integration of the geochronological data with geological relations reveals a pattern of petrogenesis and tectonics whereby progressively younger ensimatic terranes were added to the continental margin through time by plate convergence, and were ultimately welded into North American sial by a crosscutting batholithic belt. This accretionary pattern is reflected in both the

  11. Metasedimentary melting in the formation of charnockite: Petrological and zircon U-Pb-Hf-O isotope evidence from the Darongshan S-type granitic complex in southern China

    Science.gov (United States)

    Jiao, Shu-Juan; Li, Xian-Hua; Huang, Hui-Qing; Deng, Xi-Guang

    2015-12-01

    Charnockites are Opx-bearing igneous rocks commonly found in high-grade metamorphic terranes. Despite being volumetrically minor, they show a wide range in both bulk geochemistry and intensive parameters. They form a characteristic component of the AMCG (anorthosite-mangerite-charnockite-granite) suite, but their association with typical S-type granites is less well-known. The Darongshan S-type granitic complex (DSGC) in Guangxi Province, southern China, contains granites varying in mafic silicate mineral assemblages from Bt + Crd (Darongshan suite) to Opx + Grt + Bt + Crd (Jiuzhou suite) and Opx + Crd ± Bt (Taima suite), corresponding to a geochemical transition from magnesian calc-alkalic to ferroan calc-alkalic. However, its genesis, even the accurate age of intrusion, remains highly contentious despite intensive research. In order to understand the genesis of charnockite and its genetic relationship with S-type granite; here, we first determined zircon U-Pb ages of each suite using a SIMS on the basis of a detailed petrological study. Zircon U-Pb ages show that all suites of the complex were emplaced contemporaneously at ca. 249 Ma. Monazite apparent U-Pb ages are indistinguishable from zircon U-Pb ages within analytical error. Further in situ zircon Hf-O isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks (δ18Ozircon = ca. 11‰; εHf(t)zircon = ca. - 10; Δlog FMQ ≤ 0; Mn in apatite oxybarometer) with rare material input from the mantle. The variation in δ18O (7.8‰-12.9‰) is more likely a result of hybridization, whereas that in εHf(t) (- 31.9 to - 1.8) is a result of both hybridization and disequilibrium melting. The variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite-dehydration melting. Nevertheless, heat input from mantle through basaltic intrusion/underplating is considered to play a major role in high

  12. SHRIMP U-Pb zircon geochronological constraints on Cryogenian-Ediacaran tectonomagmatic events in the northwestern Arabian Shield

    Science.gov (United States)

    Kozdrój, Wiesław; Kennedy, Allen; Johnson, Peter R.; Ziółkowska-Kozdrój, Małgorzata; Kadi, Khalid

    2014-05-01

    The northwestern Arabian Shield is dominated by juvenile Neoproterozoic crust of the Midyan terrane (MT), composed of volcanosedimentary and multiple phases of intrusive rocks. Terrane protoliths are ~780-550 Ma, and reflect geotectonic changes within a regional framework of the East African Orogeny reflecting progression from a juvenile oceanic island arc and suprasubduction ophiolite to arc-arc collision to continental magmatic arc to crustal thickening with thrusting and strike-slip shearing (Najd fault system) to extensional collapse, within-plate magmatism and final cratonization. The oldest intrusive rocks (the Muwaylih suite) yield middle Cryogenian SHRIMP U-Pb zircon ages: 748±9 Ma for Imdan complex gabbro, and 736.6±9.6 Ma and 738.8±4.2 Ma for Nabt complex diorite and tonalite. They represent pretectonic intrusions in a ~750-720 Ma oceanic island arc made up of Zaam group volcanosedimentary rocks, diamictite, and banded iron formation. Bayda group subaerial felsic metavolcanic rocks (Hijr formation: ~710±12 Ma) are believed to stratigraphically overlie the Zaam group and are interpreted as volcanic equivalents of a younger phase of Muwaylih suite magmatism (~720-710 Ma). Arc-arc collision at ~710-700 Ma between the MT and the Jiddah terrane (JT) to the south resulted in the Yanbu suture and formation of an Andean-type, continental magmatic arc. This phase of continental magmatism is represented by syntectonic, calc-alkaline intrusions such as granodiorite of the Buwaydah complex (686.5±3.7 Ma), a rhyolite dike that intrudes the granodiorite (687.4±2.2 Ma), and late gabbro/diorite of the Imdan complex (676±6 Ma), all of which are assigned to the Hamadat suite (700-680 Ma). Exhumation and erosion of the magmatic arc resulted in formation of post-amalgamation (as related to the already sutured MT and JT), syntectonic basins. One of the oldest basins in the MT, filled with the few-km thick Thalbah group, appears to be intruded by granitic bodies

  13. The onset of flood basalt volcanism, Northern Paraná Basin, Brazil: A precise U-Pb baddeleyite/zircon age for a Chapecó-type dacite

    Science.gov (United States)

    Janasi, Valdecir de Assis; de Freitas, Vivian Azor; Heaman, Larry H.

    2011-02-01

    We report the first U-Pb baddeleyite/zircon date for a felsic volcanic rock from the Paraná Large Igneous Province in south Brazil. The new date of 134.3 ± 0.8 Ma for a hypocrystalline Chapecó-type dacite from Ourinhos (northern Paraná basin) is an important regional time marker for the onset of flood basalt volcanism in the northern and western portion of the province. The dated dacite was erupted onto basement rocks and is overlain by a high-Ti basalt sequence, interpreted to be correlative with Pitanga basalts elsewhere. This new U-Pb date for the Ourinhos dacite is consistent with the local stratigraphy being slightly older than the few reliable step-heating 40Ar/39Ar dates currently available for overlying high-Ti basalts (133.6-131.5 Ma). This indicates an ~ 3 Ma time span for the building of the voluminous high-Ti lava sequence of the Paraná basin. On the other hand, it overlaps the 40Ar/39Ar dates (134.8-134.1 Ma) available for the stratigraphically older low-Ti basalt (Gramado + Esmeralda types) and dacite-rhyolite (Palmas type) sequences from South Brazil, which is consistent with the short-lived character of this volcanism and its rapid succession by the high-Ti sequence.

  14. Petrography and zircon U-Pb isotopic study of the Bayanwulashan Complex: Constrains on the Paleoproterozoic evolution of the Alxa Block, westernmost North China Craton

    Science.gov (United States)

    Wu, Sujuan; Hu, Jianmin; Ren, Minghua; Gong, Wangbin; Liu, Yang; Yan, Jiyuan

    2014-11-01

    The Bayanwulashan Metamorphic Complex (BMC) exposes along the eastern margin of the Alxa Block, the westernmost part of the North China Craton (NCC). BMC is principally composed of metamorphic rocks with amphibole plagiogneiss, biotite plagioclase gneiss and granitic gneiss. Our research has been focused on the petrography and zircon U-Pb geochronology of the BMC to better understand the evolution of the Alxa Block and its relationship with the NCC. Evidences from field geology, petrography, and mineral chemistry indicate that two distinct metamorphic assemblages, the amphibolite and greenschist facies, had overprinted the preexisting granitic gneiss and suggest that the BMC experienced retrograde metamorphic episodes. The LA-ICP-MS zircon U-Pb ages reveal that the primary magmatic activities of BMC were at ca. 2.30-2.24 Ga and the two metamorphic events were at ca. 1.95-1.91 Ga and ca. 1.88-1.85 Ga respectively. These ages indicate that BMC initially intruded during Paleoproterozoic, not as previously suggested at Archean period. The Early Paleoproterozoic metamorphic records and the magmatic thermochronological data in BMC exhibit different evolution paths between the Alxa Block and the NCC. The Alxa Block was most likely an independent Early Paleoproterozoic terrain. Following different amalgamation processes, The Alxa Block combined with Western Block at ca. 1.95 Ga and then united with NCC at ca. 1.85 Ga.

  15. 1.57 Ga protolith age of the Neoproterozoic Forquilha eclogites, Borborema Province, NE-Brazil, constrained by U-Pb, Hf and Nd isotopes

    Science.gov (United States)

    Amaral, Wagner; Santos, Ticiano José; Ancelmi, Matheus Fernando; Fuck, Reinhardt Adolfo; Dantas, Elton Luiz; Matteini, Massimo; Moreto, Carolina Penteado

    2015-03-01

    The 30 km-long, N-S-trending Forquilha eclogite zone, occurs within a Paleoproterozoic block mainly composed of gneisses and migmatites, in the Ceará Central domain, Borborema Province, NE Brazil. The Forquilha eclogite zone contains lenses of high to ultra-high pressure metamafic rocks, found as granulites and amphibolites associated with kyanite-sillimanite gneisses. Three samples of clinopyroxene-garnet amphibolite yielded the U-Pb zircon ages of 1566 ± 9 Ma, 1547 ± 37 Ma and 1532 ± 24 Ma, interpreted as the timing of igneous crystallization of the mafic protolith. Additionally, zircon grains of a leucocratic layer of a metamafic rock and a retrograded eclogite provided the less precise U-Pb ages of 1613 ± 40 Ma and 1454 ± 120 Ma, respectively. Lu-Hf and Sm-Nd model ages provided TDM (Hf) between 1.55 and 1.81 Ga with positive ɛHf values of +7.50 to +10.48, and TDM (Nd) ranging between 1.57 and 1.92 Ga with positive ɛNd values of +1.84 to +4.36. It is believed that part of the rocks of the Forquilha eclogite zone were emplaced as mafic dikes in an extensional setting at ca. 1.57 Ga.

  16. U-Pb zircon and Rb-Sr mineral dating of eclogites and their country rocks. Example- Muenchberg Gneiss Massif, northeast Bavaria

    International Nuclear Information System (INIS)

    In order to evaluate the usefulness of the U-Pb zircon suite method to date eclogitic rocks, zircon populations have been analyzed from two eclogites and one cogenetic metagabbro. Samples were taken from the Muenchberg Gneiss Massif (northeast Bavaria) containing the largest B-type eclogite body of the non-Alpine part of Central Europe. All nine analyzed grain size and magnetic fractions plot linearly on a U/Pb evolution diagram and yield intercept ages at 525sub(-31)sup(+40) m.y. and 380sub(-22)sup(+14) m.y., respectively, indicating a Lower to Middle Devonian eclogitization of a Cambrian tholeiitic protolith. Rb-Sr analyses have been carried out on the post-eclogitic mineral paragenesis, hornblende and phengite, in order to find out whether or not it belongs to the same Acadian cycle (ca. 380 m.y.) as the high-pressure assemblage. An initial Sr isotopic ratio of 0.7031 can be calculated for the tholeiitic protolith of the eclogites which is in agreement with a primary magmatic mantle origin. (Auth.)

  17. U-Pb geochronology and Sr-Nd isotopes of Galileia and Urucum neo proterozoic granitoids suites in south-eastern Brazil

    International Nuclear Information System (INIS)

    U-Pb zircon and monazite dating and whole-rock Sr-Nd isotopes have been applied on Neo-Proterozoic granitoids from the Atlantic shear belt, south-eastern Brazil. U-Pb zircon results on the Galileia met-aluminous and Urucum per-aluminous suites indicate crystallisation ages of 594 ± 6 Ma and 582 ± 2 Ma respectively. Whole-rock Rb-Sr and Sm-Nd analyses on representative samples from both suites demonstrate that they mainly derive from melting of older crustal rocks. The occurrence of an old isotopic memory in the zircons from the Urucum granitoids around 2.2 Ga, in agreement with Nd model ages, suggests a Palaeo-Proterozoic age for the crustal proto-lith of these two suites, probably associated with the Transamazonico event. Owing to these new dating results and previous regional geochronological data, it can be proposed that the met-aluminous magmatism ended around 590 Ma and that the collisional peraluminous magmatism associated with the Brasiliano orogeny occurred between 584 and 570 Ma. (authors)

  18. SIMS zircon U-Pb dating of the Late Cretaceous dinosaur egg-bearing red deposits in the Tiantai Basin, southeastern China

    Science.gov (United States)

    He, Huaiyu; Wang, Xiaolin; Wang, Qiang; Jiang, Shunxing; Cheng, Xin; Zhang, Jialiang; Zhou, Zhonghe; Zhao, Zikui; Jiang, Yangen; Yu, Fangming; Deng, Chenglong; Yang, Jinhui; Zhu, Rixiang

    2013-01-01

    Dinosaur eggs or fragments are abundant and extensively distributed in China. They can be very informative in biostratigraphic division and correlation of continental strata where other fossils are relatively lacking. Despite remarkable discoveries of vertebrate fossils, particularly dinosaur eggs and skeletons from the middle and Late Cretaceous of both northern and southern China, there is hardly any direct evidence for the ages of the vertebrate-bearing terrestrial deposits. To constrain their depositional ages, here we have obtained SIMS U-Pb zircon ages from the tuffs interbedded with dinosaur egg-bearing sediments from the Laijia and Chichengshan formations of the terrestrial red deposits of the Late Cretaceous in the Tiantai Basin, Zhejiang Province, southeastern China. The SIMS zircon U-Pb ages from the Laijia and Chichengshan formations are about 96-99 Ma (Cenomanian) and 91-94 Ma (Turonian), respectively, providing direct time constraints on the vertebrate and dinosaur egg evolution in the Late Cretaceous as well as a basis for correlation with terrestrial Cretaceous deposits in other regions of southern and northern China.

  19. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goias, Central Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio M.; Dantas, Elton L.; Fuck, Reinhardt A. [Brasilia Univ., DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia]. E-mail: marcio@unb.br; mmp1103@terra.com.br; Armstrong, Richard A. [Australian National Univ., Canberra (Australia). Research School of Earth Sciences

    2003-03-15

    The Itapuranga alkali granite and Uruana quartz syenite are large K-rich E W-elongated intrusions, in the central part of the Neoproterozoic Brasilia Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 {+-} 10 Ma and 618 {+-} Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd T{sub DM} ages for both intrusions are 1.44 Ga and epsilon{sub Nd}(T) values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic) sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasilia Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults. (author)

  20. U-Pb SHRIMP ages of detrital zircons from Hiriyur formation in Chitradurga Greenstone belt and its implication to the Neoarchean evolution of Dharwar craton, South India

    International Nuclear Information System (INIS)

    We report newly obtained U-Pb SHRIMP ages of detrital zircons from metagreywackes in the Hiriyur Formation (Chitradurga Group, Dharwar Supergroup) from the central eastern part of the Chitradurga greenstone belt. U-Pb analyses yield three major Neoarchean age populations ranging from 2.70 - 2.54 Ga with some minor age population of Mesoarchean. The maximum age of deposition is constrained by the youngest detrital zircon population at 2546 Ma. This is the first report of the occurrence of supracrustal rocks less than 2.58 Ga in the central part of Chitradurga greenstone belt. Close evaluation of detrital ages with the published ages of surrounding igneous rocks suggest that the youngest detrital zircons might be derived from rocks of the Eastern Dharwar craton and the inferred docking of the western and eastern Dharwar cratons happened prior to the deposition of the Hiriyur Formation. The Chitradurga shear zone, dividing the Dharwar craton into western and eastern blocks, probably developed after the deposition. Furthermore, the lower intercept is interpreted as evidence for the Pan-African overprints in the study area. (author)

  1. Detrital zircon U-Pb geochronology, Lu-Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

    Science.gov (United States)

    Wang, Ce; Liang, Xinquan; Foster, David A.; Fu, Jiangang; Jiang, Ying; Dong, Chaoge; Zhou, Yun; Wen, Shunv; Van Quynh, Phan

    2016-05-01

    In situ U-Pb geochronology, Lu-Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian-Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618-532 Ma, 1160-1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician-Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U-Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

  2. Provenance and depositional age of metavolcano-sedimentary sequences of the Santa Terezinha de Goias, based on Sm-Nd and U-Pb zircon single grain

    International Nuclear Information System (INIS)

    Supracrustal rocks of the Santa Terezinha de Goias region, Central Brazil, presumably represent a southern extension of the Mara Rosa magmatic arc tectonically juxtaposed to Archean terrains and consist of a meta volcanic unit and a meta sedimentary unit. The aim of the paper is to present and discuss the first U-Pb and Sm-Nd data of rocks belonging to both units of that region. U-Pb data of zircons from a felsic meta volcanic rock inter layered with chlorite-rich schists (metandesites?) yield a concordant age of of 660 My, while the Sm-Nd model age of a variety of chlorite-schists indicate a juvenile age between 1.1 and 1.3 Ga. These data indicate that the meta volcanic rocks are Neo proterozoic in age and may be correlated with rocks of the Mara Rosa magmatic arc. On the other hand, the prevailing provenance of rocks belonging to the meta sedimentary unit indicate a Paleoproterozoic, or older, source. Thus, the deposition of both units are explained by means of the erosion of source-areas of variable age. (author)

  3. U-Pb isotopic evidence for the accretion of a continental microplate in the Zalm region of the Saudi Arabian Shield.

    Science.gov (United States)

    Stacey, J.S.; Agar, R.A.

    1985-01-01

    This area includes three of the main tectonic units of the Arabian Shield: the Afif continental terrain, the Nabitah suture with its associated mobile belt, and the Asir ensimatic arc terrain. U/Pb zircon data from a pelitic garnet-sillimanite gneiss show that the Kabib formation in the S of the Afif terrain may be as old as 1770 m.y. Pb and Rb/Sr isotopic data in the Zalm region reveal a change in the nature of the underlying crust, from continental basement in the NE to less radiogenic marginal arc rocks in the SW. Miogeosynclinal continental shelf facies of the Siham group lie unconformably over the Kabid formation. U/Pb zircon age determinations show that this 'Andean' continental margin developed before approx 720 m.y. and the emplacement of calc-alkaline plutonic rocks continued until approx 690 m.y. During the period 685-640 m.y. the continental Afif microplate collided with the Asir terrain as part of the Nabitah orogeny. At approx 640 m.y. age the Najd strike-slip faulting commenced, with a dextral phase that controlled emplacement of granite plutons as well as the development of large pull-apart grabens. Some of the latter were floored by new oceanic crust and filled with volcanosedimentary rocks of the Bani Ghayy group.-R.A.H.

  4. SHRIMP U-Pb zircon age,geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan:Petrogenesis and tectonic significance

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super- continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780―760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplace- ment, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.

  5. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goias, Central Brazil

    International Nuclear Information System (INIS)

    The Itapuranga alkali granite and Uruana quartz syenite are large K-rich E W-elongated intrusions, in the central part of the Neoproterozoic Brasilia Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 ± 10 Ma and 618 ± Ma, respectively. Three zircon cores from the Itapuranga granite yielded U-Pb ages between 1.79 and 1.49 Ga. Sm-Nd TDM ages for both intrusions are 1.44 Ga and epsilonNd(T) values are -5.1 and -5.7, suggesting the input of material derived from older (Paleo- to Mesoproterozoic) sialic crust in the origin of the parental magmas. Magma mixing structures indicate co-existence of mafic and felsic end-members. The felsic end-member of the intrusions is dominantly represented by crust-derived melts, formed in response to the invasion of Paleo/Mesoproterozoic sialic crust by alkali-rich mafic magmas at ca. 620 Ma. These intrusions are roughly contemporaneous with, or perhaps slightly younger than, the peak of regional metamorphism in the southern Brasilia Belt. Their emplacement along the Pireneus lineament suggest a syn-tectonic origin for them, most probably in transtensional settings along these faults. (author)

  6. Funciones ejecutivas en niños escolarizados: efectos de la edad y del estrato socioeconómico

    Directory of Open Access Journals (Sweden)

    Vanessa Arán Filippetti

    2011-01-01

    Full Text Available En los últimos años, se ha incrementado notoriamenteel estudio sobre las funciones ejecutivasprefrontales en niños de edad escolar. El objetivodel presente estudio es analizar la influencia dela edad y del estrato socioeconómico (ESE en eldesempeño de tareas ejecutivas y conocer cuálesson las variables socioeconómicas que predicenuna mejor ejecución. Participaron 254 niños de 7a 12 años de edad de diferentes estratos socioeconómicosde la ciudad de Santa Fe, Argentina. Seutilizó una batería de pruebas ejecutivas sensiblesa la función prefrontal. Los resultados obtenidosseñalan un efecto significativo de la edad y delESE sobre las funciones ejecutivas estudiadas.Los diferentes dominios del constructo siguen unatrayectoria diferente según el desarrollo y el efectodel ESE. Además, en todas las funciones ejecutivasse evidencia un patrón de funcionamiento cognitivoinferior en los niños de estrato socioeconómico bajo(ESB. Finalmente, se encontró que, de las variablesincluidas en el análisis, solo el nivel educativode la madre y las condiciones de alojamiento de lafamilia se asocian al funcionamiento ejecutivo delos niños. Se discuten los resultados en funciónde la influencia que ejerce la maduración cerebraly las variables ambientales en el funcionamientoejecutivo.

  7. U-Pb ages for two tonalitic gneisses, pegmatitic granites, and K-feldspar porphyries, Olkiluoto study site, Eurajoki, SW Finland

    International Nuclear Information System (INIS)

    Secondary ion microprobe zircon U-Pb ages have been determined for two tonalitic gneisses, two pegmatitic granites, and two potassium feldspar porphyry samples from the Olkiluoto study site, Eurajoki, S-W Finland. Moreover, monazites from the Kfeldspar porphyries were dated using TIMS U-Pb method. The tonalitic gneiss A1879 TTG 1 reveals bimodal zircon population and for A1880 TTG it is homogeneous. The samples yield similar overlapping concordia ages of 1851 ± 5 Ma and 1856 ± 5 Ma, respectively. The pegmatitic granite samples A1881 PGR 1 and A1883 PGR 2 have mostly zircons resembling those of the TTG's. The supposed pegmatitic zircons with high U and low Th are strongly altered. The zircon U-Pb data of A1881 PGR 1 plot roughly in two separate lines on a concordia diagram. The apparently younger ∼1.79 Ga data are all from the high U and low Th/U zircons and therefore certainly set the minimum age for the A1881 PGR 1. It is suggested, that the ∼1.85 Ga data comprise analyses from inherited zircons as it include both lower and higher Th/U zircons and 1.85 Ga coevals with age of the tonalitic gneisses. Thus, the apparent age for the A1881 PGR 1 is ∼1.79 Ga. The U-Pb data of sample A1883 PGR 2 also divide into two groups. The higher Th/U, inherited zircons determine an age of 1852 ± 9 Ma which is the same as that of the TTG's. The low Th/U zircon data scatter and the age of 1.83 Ga for A1883 PGR 2 is only poorly determined. The both potassium feldspar porphyry samples A1882 KFP 1 and A1884 KFP 2 reveal heterogeneous zircon populations. The A1882 KFP 1 zircons showing magmatic zoning in BSE images conceivably determine a concordia age of 1842± 6 Ma for the rock. In addition to that a few ∼1.9 Ga inherited zircon and metamorphic low Th/U rims with ages between 1.88 Ga and 1.83 Ga were detected. The age for the youngest metamorphic zircon rims overlaps with that of the magmatic zircons. The zircons in the other KFP sample A1884 show a wide range of ages

  8. Impact of hydrothermal alteration on the U-Pb isotopic system of zircons from the Fangcheng syenites in the Qinling orogen, Henan Province, China

    Institute of Scientific and Technical Information of China (English)

    BAO Zhiwei; WANG Qiang; BAI Guodian; ZHAO Zhenhua

    2009-01-01

    Disturbance of the zircon U-Pb isotopic system has been investigated extensively, but mostly in lab, in the last decades. Here, we reported a field-based study on intensive sericitization, K-feldsparthization and the impacts of mylonitization on zircons from the Fangcheng syenites.The Fangcheng syenites occur in the eastern part of the Qinling orogen and consist mainly of aegirine-augite syenite, aegirine nepheline syenite, biotite syenite and hornblende nepheline syenite. Zircons from the slightly sericitized aegirine augite syenite are colorless, transparent crystals and exhibit well-developed oscillatory and sector zoning on the cathodoluminescence (CL) images which are typical of magmatic zircons from alkaline rocks. Zircon U-Pb determinations by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) showed that the syenite was formed in Neoproterozoic time, the weighted average of 206Pb/238U ages is 844.3±1.6 Ma (MSWD=0.86). In contrast, the hydrothermally altered zircons (hydrothermal zircon) from the intensively sericitized, K-feldsparthized, and weakly mylonitized aegirine augite syenite are conglomerates, yellowish to brown in color, generally translucent and internally textureless. The CL and backscatter electron (BSE) images of hydrothermal zircons exhibit fractured, textureless or mosaic textures, and occasionally show "sponge texture" with the veinlets and inclusions of K-feldspar; however, relicts of magmatic oscillatory zoning can still be discerned locally in individual grains. LA-ICPMS analyses of the hydrothermal zircons demonstrated that the zircons are chemically inhomogeneous, with enhanced and widely varied Pb, U, and Th contents. The U and Th contents of the hydrothermal zircons are estimated to be 32×10-6-1550×10-6 and 188×10-6-4059×10-6, respectively, with Th/U ratios within the range of 0.7-44.9. 206Pb/238U apparent ages of the hydrothermal zircons are negatively correlated with the contents of U, and radiogenic and

  9. Geology, mineralization, U-Pb dating and Sr-Nd isotope geochemistry of intrusive bodies in northeast of Kashmar

    Directory of Open Access Journals (Sweden)

    Alireza Almasi

    2015-04-01

    Full Text Available Alireza Almasi1, Mohammad Hassan Karimpour1*, Khosrow Ebrahimi Nasrabadi1, Behnam Rahimi1, Urs KlÖtzli2 and Jose Francisco Santos3 Introduction The study area is located in central part of the Khaf- Kashmar-Bardeskan belt which is volcano-plutonic belt at the north of the Dorouneh fault in the north of Lut block. The north of the Lut block is affected by tectonic rotation and subduction processes which occur in the east of Iran (Tirrul et al., 1983. The magmatism of Lut block begins in Jurassic and continues in Tertiary (Aghanabati, 1995. Karimpour (Karimpour, 2006 pointed out the Khaf-Kashmar-Bardeskan belt has significant potential for IOCG type mineralization such as Kuh-e-Zar, Tannurjeh, and Sangan (Karimpour, 2006; Mazloumi, 2009. The data gathered on the I-type intrusive rocks include their field geology, petrography, U–Pb zircon dating and Sr–Nd isotope and also alteration and mineralization in the study area. Materials and methods - Preparation of 150 thin sections of rock samples for study of petrography and alteration of the intrusive rocks. - Magnetic susceptibility measuring of intrusive rocks. - U-Pb dating in zircon of I-type intrusive rocks by Laser-Ablation Multi Collector ICP-MS method. - Sr-Nd analysis on 5 samples of I-type intrusive rocks by Multi-Collector Thermal Ionization Mass Spectrometer (TIMS VG Sector 54 instrument. - Mineralography and paragenetic studies of ore-bearing quartz veins and geochemical analysis for 28 samples. - Production of the geology, alteration and mineralization maps by scale: 1:20000 in GIS. Results Oblique subduction in southern America initiated an arc-parallel fault and shear zones in the back of continental magmatic arc (Sillitoe, 2003. Because of this event, pull-apart basins were formed and high-K to shoshonitic calc-alkalineI- and A-type magmatism occur (Sillitoe, 2003. Most important deposits accompany with this magmatism are Au-Cu deposits types and Fe-Skarns (Sillitoe, 2003. We have

  10. Toxocariosis Ocular en Menores de Edad

    Directory of Open Access Journals (Sweden)

    Norma Ocampo

    2001-04-01

    Full Text Available La toxocariosis es una geohelmintiosis producida por la ingestión de
    huevos de Toxocara canis y T. catis, cuyos hospederos definitivos son el perro y el gato. En el humano las larvas producen el Síndrome de Migración Larvaria Visceral y Ocular; en este último produce una enfermedad grave que puede semejar un retinoblastoma (1,2. Los niños son más susceptibles a adquirir esta infección (3. Nuestro objetivo es determinar la frecuencia de toxocariosis ocular en menores de edad con sintomatología ocular.

  11. La dislexia, en todas las edades

    OpenAIRE

    Portellano, José Antonio

    2004-01-01

    La dislexia constituye un frecuente motivo de fracaso escolar, siendo una alteración neuropsícológica que se caracteriza por la dificultad para el aprendizaje del lenguaje escrito,como consecuencia de trastornos en el funcionamiento del sistema nervioso que seproducen durante las fases precoces del desarrollo o que tienen una causa genética. Esfrecuente que, si no se trata adecuadamente durante la infancia, sus secuelas persistandurante la edad adulta, produciendo no sólo dific...

  12. Guerra y diplomacia en la edad moderna

    OpenAIRE

    Fernández Carrasco, Eulogio

    2012-01-01

    La guerra es juzgada como la única solución cuando los caminos de la diplomacia no sirven para resolver los conflictos. La diplomacia es el primer paso para la resolución de los conflictos y la guerra como única solución final de ello. Los términos guerra y diplomacia fueron las dos actividades interestatales principales de los reinos europeos durante la Edad Moderna. La guerra fue una actividad feudal que la nobleza se vio obligada a innovar relativamente pronto debido a...

  13. El entrenamiento integrado en edades tempranas

    OpenAIRE

    Ortega Caballero, Manuel

    2003-01-01

    La caracter??stica principal de los alumnos en edades tempranas es su car??cter notablemente activo, lo que nos lleva a los adultos formadores en la educaci??n f??sica y/o deportiva del ni??o que el trabajo que se presente, de entrenamiento o de formaci??n f??sica, sea llevadera, variada y atractiva pues la demanda de atenci??n para que sea efectivo el trabajo f??sico es de gran magnitud. Este entrenamiento nos aportar?? la ventaja de acercarnos con la mayor similitud posibl...

  14. Kwangsian and Indosinian reworking of the eastern South China Block: Constraints on zircon U-Pb geochronology and metamorphism of amphibolites and granulites

    Science.gov (United States)

    Wang, Yuejun; Wu, Chunming; Zhang, Aimei; Fan, Weiming; Zhang, Yanhua; Zhang, Yuzhi; Peng, Touping; Yin, Changqin

    2012-10-01

    To constrain temporal-spatial patterns of the Kwangsian and Indosinian orogenic events and the Phanerozoic tectonic evolution of the eastern South China Block, this paper documents the zircon U-Pb geochronology of the high-grade metamorphic rocks for key outcrops in the eastern SCB and the P-T path for the Indosinian metamorphic amphibolites. Our data show that the representative amphibolites from the originally-defined Badou, Mayuan, Chencai, Zhoutan and Yunkai Groups and associated granulites yielded zircon U-Pb metamorphic ages of 428-468 Ma. The weighted mean ages of 221-246 Ma are also given by the metamorphic zircons from amphibolites and granulites in the Yunkai, Shiwandashan, northern Wuyi and southern Hunan regions. The two age groups are followed by the 40Ar/39Ar plateau ages of 406-438 Ma and 195-217 Ma for synkinematic minerals from major shear zones in the eastern South China Block, respectively. The age-spans of 406-468 Ma and 195-246 Ma roughly coincide with the formation time of the Kwangsian (396-462 Ma) and Indosinian (202-248 Ma) granites of the eastern South China Block, respectively. The strongly compressive deformation, metamorphism and granitic magmatism are roughly contemporaneous for the Kwangsian and Indosinian tectonothermal events in the eastern South China Block. They occurred over a similar spatial extent, only reaching westward to the Jiangnan-Xuefeng Domains across the Jiangshan-Shaoxing Fault. The amphibolites from Zhouyuan (SW Zhejiang Province) of the Cathaysia Block, which have the Indosinian zircon U-Pb metamorphic ages of 243-246 Ma, underwent three episodes of metamorphism (M1-M3) and yielded a near-isothermal decompression clockwise P-T path. In combination with other geological data, it is proposed that the ages of ca. 430 Ma and ca.230 Ma might be interpreted as the transformational time from the prograde- to retro-metamorphism for the Kwangsian and Indosinian events, respectively. The Kwangsian and Indosinian orogenic

  15. Southernmost Andes and South Georgia Island, North Scotia Ridge: Zircon U-Pb and muscovite {40Ar }/{39Ar } age constraints on tectonic evolution of Southwestern Gondwanaland

    Science.gov (United States)

    Mukasa, Samuel B.; Dalziel, Ian W. D.

    1996-11-01

    Zircon U-Pb and muscovite {40Ar }/{39Ar } isotopic ages have been determined on rocks from the southernmost Andes and South Georgia Island, North Scotia Ridge, to provide absolute time constraints on the kinematic evolution of southwestern Gondwanaland, until now known mainly from stratigraphic relations. The U-Pb systematics of four zircon fractions from one sample show that proto-marginal basin magmatism in the northern Scotia arc, creating the peraluminous Darwin granite suite and submarine rhyolite sequences of the Tobifera Formation, had begun by the Middle Jurassic (164.1 ± 1.7 Ma). Seven zircon fractions from two other Darwin granites are discordant with non-linear patterns, suggesting a complex history of inheritances and Pb loss. Reference lines drawn through these points on concordia diagrams give upper intercept ages of ca. 1500 Ma, interpreted as a minimum age for the inherited zircon component. This component is believed to have been derived from sedimentary rocks in the Gondwanaland margin accretionary wedge that forms the basement of the region, or else directly from the cratonic "back stop" of that wedge. Ophiolitic remnants of the Rocas Verdes marginal basin preserved in the Larsen Harbour complex on South Georgia yield the first clear evidence that Gondwanaland fragmentation had resulted in the formation of oceanic crust in the Weddell Sea region by the Late Jurassic (150 ± 1 Ma). The geographic pattern in the observed age range of 8 to 13 million years in these ophiolitic materials, while not definitive, is in keeping with propagation of the marginal basin floor northwestward from South Georgia Island to the Sarmiento Complex in southern Chile. Rocks of the Beagle granite suite, emplaced post-tectonically within the uplifted marginal basin floor, have complex zircon U-Pb systematics with gross discordances dominated by inheritances in some samples and Pb loss in others. Of eleven samples processed, only two had sufficient amounts of zircon for

  16. The Parana River Subprovince (Goias State, Central Region Brazil): an application example of the U-Pb and Pb-Pb cassiterite dating methods

    International Nuclear Information System (INIS)

    The Parana River Subprovince is part of the Goias Tin province. It includes a basement composed mainly by orthogneisses and migmatites, named Granite-Gneiss Complex, predominantly Paleoproterozoic in age, overlaid by a metasedimentary sequence of the Ticcunzal Formation, both of which were intruded by pegmatites. These units are overlain by metasedimentary and minor metavolcanic rocks of the Arai Group. Alkalic granites intrude these rocks, previously subdivided into the g1 (∼ 1,770 Ma) and g2 (∼1,580 Ma) families, the later being responsible for the tin mineralization. Rhyolites of the Arai Group are contemporaneous to the alkaline granites. Primary tin mineralization occurs associated with the pegmatites and with late to post-magmatic alterations (greisenization, albitization) in the alkaline granites. Coarse-grained muscovite from Xupe and Riacho dos Cavalos pegmatites yielded K-Ar ages of 2,129 ± 26 Ma and 2,006 ± 24 Ma, respectively. A cassiterite sample from Riacho dos Cavalos Pegmatite was analyzed by U-Pb, confirming the age between 2,023 Ma and 2,277 Ma as the time of tin mineralization. Isochronic Pb-Pb cassiterite dating of the pegmatites yield Archean ages, indicating that the lead incorporated by the cassiterite and its inclusions and aggregate minerals is old, probably derived from the basement. K-Ar dating of muscovite concentrates from the alkaline granites of the Mangabeira Massif yielded ages of 567 ± 14 Ma and 553± 11 Ma, indicating overprinting of the Brasiliano Cycle in the pluton. U-Pb cassiterite dating yield an age of 1,535± Ma, which is concordant with the time of crystallization of the granite and indicates that cassiterite has not behaved as an open system in relation to the Brasiliano deformation. Isochronic Pb-Pb age of the same cassiterite sample (1,425±79 Ma) agrees with the U-Pb age within the analytical error. From these data it is possible to identify two events of tin mineralization in the Subprovince, the oldest of

  17. El cine mexicano de la edad de oro y su impacto internacional

    Directory of Open Access Journals (Sweden)

    Maricruz Castro-Ricalde

    2014-06-01

    Full Text Available A partir de una investigación documental en publicaciones periódicas de Argentina, Colombia, Cuba, Chile, Estados Unidos, Honduras, México, Nicaragua y Venezuela, este artículo demuestra el interés que el cine mexicano producido entre 1936 y 1956 provocó en los espectadores de Hispanoamérica y Estados Unidos, al igual que la presencia de actores, cineastas, temas y personajes de otros países hispanohablantes en la industria cinematográfica mexicana durante la denominada edad de oro del cine mexicano. Se constató la influencia de este cine en la conformación de la identidad cultural de los mexicanos y su proyección internacional.

  18. SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Early Paleozoic volcanic rocks in Nuomuhong area occurred as basalt slice and meta-volcanic slice. SHRIMP zircon U-Pb dating of the basalt slice and the meta-volcanic slice show that the age of the basalt slice is 419±5 Ma, and that of the meta-volcanic slice is 401± 6 Ma. These ages directly testify that there existed Early Paleozoic ocean-continent transform in East Kunlun, the basalt slice was formed in an extensional mid-ocean ridge setting and the meta-volcanic rock slice was formed in an extrusion subduction and collision setting. The inherited zircon age of 1734 Ma in volcanic rocks reflects that the base of East Kunlun may be Middle Proterozoic.

  19. Geochronological data from the Faxinal coal succession, southern Parana Basin, Brazil: A preliminary approach combining radiometric U-Pb dating and palynostratigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Guerra-Sommer, M.; Cazzulo-Klepzig, M.; Menegat, R.; Formoso, M.L.L.; Basei, M.A.; Barboza, E.; Simas, M.W. [Universidade Federal do Rio Grande do Sul, Porto Alegre (Brazil)

    2008-03-15

    A radiometric zircon age of 285.4 {+-} 8.6 Ma (IDTIMS U-Pb) is reported from a tonstein layer interbedded with coal seams in the Faxinal coalfield, Rio Grande do Sul, Brazil. Calibration of palynostratigraphic data with the absolute age shows that the coal depositional interval in the southern Parana Basin is constrained to the Sakmarian. Consequently, the basal Gondwana sequence in the southern part of the basin should lie at the Carboniferous-Permian boundary, not within the Sakmarian as previously considered. The new results are significant for correlations between the Parana Basin and the Argentinian Paganzo Basin (302 {+-} 6 Ma and 288 {+-} 7 Ma) and with the Karoo Basin, specifically with the top of the Dwyka Tillite (302 {+-} 3 Ma and 299.2 {+-} 3.2 Ma) and the lowermost Ecca Group (288 {+-} 3 Ma and 289.6 {+-} 3.8 Ma). The evidence signifies widespread latest Carboniferous volcanic activity in western Gondwana.

  20. The history of a continent from U-Pb ages of zircons from Orinoco River sand and Sm-Nd isotopes in Orinoco basin river sediments

    Science.gov (United States)

    Goldstein, S.L.; Arndt, N.T.; Stallard, R.F.

    1997-01-01

    We report SHRIMP U-Pb ages of 49 zircons from a sand sample from the lower Orinoco River, Venezuela, and Nd model ages of the fine sediment load from the main river and tributaries. The U-Pb ages reflect individual magmatic or metamorphic events, the Sm-Nd model ages reflect average crustal-residence ages of the sediment sources. Together they allow delineation of the crust-formation history of the basement precursors of the sediments. The U-Pb ages range from 2.83 to 0.15 Ga, and most are concordant or nearly so. Discrete age groupings occur at ??? 2.8, ??? 2.1, and ??? 1.1 Ga. The oldest group contains only three samples but is isolated from its closest neighbors by a ??? 600 Ma age gap. Larger age groupings at ??? 2.1 and ??? 1.1 Ga make up about a third and a quarter of the total number of analyses, respectively. The remaining analyses scatter along concordia, and most are younger than 1.6 Ga. The ??? 2.8 and ??? 2.1 Ga ages correspond to periods of crust formation of the Imataca and Trans-Amazonian provinces of the Guyana Shield, respectively, and record intervals of short but intensive continental growth. These ages coincide with ??? 2.9 and ??? 2.1 Ga Nd model ages of sediments from tributaries draining the Archean and Proterozoic provinces of the Guyana Shield, respectively, indicating that the U-Pb ages record the geological history of the crystalline basement of the Orinoco basin. Zircons with ages corresponding to the major orogenies of the North Atlantic continents (the Superior at ??? 2.7 Ga and Hudsonian at 1.7-1.9 Ga) were not found in the Orinoco sample. The age distribution may indicate that South and North America were separated throughout their history. Nd model ages of sediments from the lower Orinoco River and Andean tributaries are ??? 1.9 Ga, broadly within the range displayed by major rivers and dusts. This age does not coincide with known thermal events in the region and reflects mixing of sources with different crust-formation ages. The

  1. U-Pb dating of zircon from the bed parallel anatectic granitic intrusion in the Baoban group in Hainan Island and the tectonic implication

    Institute of Scientific and Technical Information of China (English)

    DING Shijiang; HU Jianmin; SONG Biao; CHEN Mulun; XIE Shengzhou; FAN Yuan

    2005-01-01

    The petrological and geochemical features of the bed parallel granitic intrusion in the Pre-Cambrian Baoban group in Hainan Island attest to the anatexis origin of the granites. U-Pb dating analyses of zircons from the anatectic granite and the biotite two-feldspar gneiss in the Baoban group, using SHRIMP II in the Beijing Ion-probe Center, acquire 206Pb/238U ages of 368±3.5 Ma (of granite, 95% confidence level, MSDW=1.23) and 362.9±6.1 Ma (of gneiss, 95% confidence level, MSDW = 2.04) respectively. The two late Devonian ages indicate consistently a tectonic- thermal event experienced in Hainan Island, and are the first discovered record of the Devonian geological process in the district. This event possibly resulted from the deep thermal-dynamic process when the Gondwana continent began to break up in the Devonian period.

  2. Late Proterozoic-Paleozoic evolution of the Arctic Alaska-Chukotka terrane based on U-Pb igneous and detrital zircon ages: Implications for Neoproterozoic paleogeographic reconstructions

    Science.gov (United States)

    Amato, J.M.; Toro, J.; Miller, E.L.; Gehrels, G.E.; Farmer, G.L.; Gottlieb, E.S.; Till, A.B.

    2009-01-01

    The Seward Peninsula of northwestern Alaska is part of the Arctic Alaska-Chukotka terrane, a crustal fragment exotic to western Laurentia with an uncertain origin and pre-Mesozoic evolution. U-Pb zircon geochronology on deformed igneous rocks reveals a previously unknown intermediate-felsic volcanic event at 870 Ma, coeval with rift-related magmatism associated with early breakup of eastern Rodinia. Orthogneiss bodies on Seward Peninsula yielded numerous 680 Ma U-Pb ages. The Arctic Alaska-Chukotka terrane has pre-Neoproterozoic basement based on Mesoproterozoic Nd model ages from both 870 Ma and 680 Ma igneous rocks, and detrital zircon ages between 2.0 and 1.0 Ga in overlying cover rocks. Small-volume magmatism occurred in Devonian time, based on U-Pb dating of granitic rocks. U-Pb dating of detrital zircons in 12 samples of metamorphosed Paleozoic siliciclastic cover rocks to this basement indicates that the dominant zircon age populations in the 934 zircons analyzed are found in the range 700-540 Ma, with prominent peaks at 720-660 Ma, 620-590 Ma, 560-510 Ma, 485 Ma, and 440-400 Ma. Devonian- and Pennsylvanian-age peaks are present in the samples with the youngest detrital zircons. These data show that the Seward Peninsula is exotic to western Laurentia because of the abundance of Neoproterozoic detrital zircons, which are rare or absent in Lower Paleozoic Cordilleran continental shelf rocks. Maximum depositional ages inferred from the youngest detrital age peaks include latest Proterozoic-Early Cambrian, Cambrian, Ordovician, Silurian, Devonian, and Pennsylvanian. These maximum depositional ages overlap with conodont ages reported from fossiliferous carbonate rocks on Seward Peninsula. The distinctive features of the Arctic Alaska-Chukotka terrane include Neoproterozoic felsic magmatic rocks intruding 2.0-1.1 Ga crust overlain by Paleozoic carbonate rocks and Paleozoic siliciclastic rocks with Neoproterozoic detrital zircons. The Neoproterozoic ages are

  3. U-Pb dating on zircons for the la Borie eclogite (Haut-Allier, France) and consequences for the pre-Variscan evolution of the Western Europe

    International Nuclear Information System (INIS)

    A crystallization age of 432sub(-10)+20Ma has been determined for the 'La Borie' eclogite (Haut-Allier, France), by U-Pb dating on zircons. This age is yielded by the upper intercept with the Concordia curve. In agreement with recent dates obtained in the southern part of the Massif Central, in Brittany and in Vendee, these data indicate that the high-pressure/high-temperature-metamorphic phase representative of the pre-Variscan evolution of the western Europe, took place at the Silurian/Ordovician boundary. This high-pressure/high-temperature metamorphism could be significant of subduction processes more or less synchronous, preceeding the main continental collision responsible of the Variscan belt. (s.s.). (orig.)

  4. New Sm/Nd and U/Pb geochronological constraints of the Archean to neoproterozoic evolution of the Amparo basement complex of the Central Ribeira Belt, Southeastern Brazil

    International Nuclear Information System (INIS)

    The Amparo Basement Complex is a distinctive collage of migmatitic tronjhemitetonalite- granodiorite (TTG) orthogneisses that represents the older basement exposures within the Central Ribeira Belt, a Late Neoproterozoic (ca. 600 Ma) collisional belt in southeastern Brazil. These basement gneisses are overlain by Mesoproterozoic to Neoproterozoic supracrustal sequences, and intruded by Neoproterozoic collisional granitoids. Pioneering Rb/Sr, Pb/Pb and K/Ar geochronological studies of the Amparo Complex, e.g. (Wernick et al., 1981; Wernick and Oliveira, 1986; Arthur, 1988; Tassinari, 1988; Campos Neto, 1991) provided some initial insights into the antiquity and geologic evolution of the complex, but little about the crustal evolution of the constituent gneisses. Furthermore, the susceptibility of these systems to partial isotopic resetting, left some doubt about the timing and true number of geologic events recorded by these polydeformed rocks. Recent Sm/Nd whole rock (Dantas et al., 2000) and new U/Pb single crystal zircon and monazite data obtained from the Amparo Complex, however, now furnish information on the crustal growth history of the basement and provide precise age constraints on the timing of events related to the geologic evolution of the complex. Based on these new data, it appears that the oldest rocks within the complex are polymigmatized tronjhemitic gneisses located near the town of Amparo. The oldest phase of this migmatite yields a U/Pb zircon age of 3,024 +/- 9 Ma. Sm/Nd data from this locale yields a Nd T(DM) model age of 3.28 Ga suggesting that the genesis of this crustal unit involved some input from yet older crust. Data from banded tonalitic gneisses collected ca. 50 km south of Amparo indicate that subsequent Archean crustal growth around the older core occurred around 2.77 Ga (U/Pb zircon age of 2,772 +/- 26 Ma. A Nd T(DM) model age of 3.02 Ga obtained from these tonalites also indicate enrichment from older crustal sources during their

  5. Geochronology (U-Pb/Pb-Pb) and isotopic signatures (Rb-Sr/Sm-Nd) of the Paleoproterozoic Guanambi Batholith, southwest Bahia State (NE Brazil)

    International Nuclear Information System (INIS)

    The Guanambi batholith (GB) is located in south-western Bahia, Brazil, where it forms part of the Urandi-Paratinga mobile belt. The batholith extends over an area of almost 6,000 km2 and is mainly composed of syenites and monzonites, with subordinate granites, mafic syenites and lamprophyric dykes. Two main units can be recognized: the multiple intrusions, being divided into four regions (Paratinga, Laguna, Igapora and Guanambi) and the so-called late-intrusions forming the Cara Suja, Ceraima and Estreito massifs. U-Pb and Pb-Pb isotopic data demonstrate that the batholith was emplaced 2.05 Ga ago. GB has highly negative initial εNd (-7.4 to -10.6), pointing to an enriched source, and Sr initial ratios between 0.704 and 0.707. Both chemical and isotopic signatures suggest that GB formed by fractional crystallization of a lamprophiric magma derived from a Paleoproterozoic enriched mantle source. (author)

  6. New U-Pb SHRIMP zircon ages for pre-variscan orthogneisses from Portugal and their bearing on the evolution of the Ossa-Morena tectonic zone

    Directory of Open Access Journals (Sweden)

    Cordani Umberto G.

    2006-01-01

    Full Text Available New SHRIMP U-Pb zircon ages for the Portalegre and Alcáçovas orthogneisses document a complex pre- Variscan history for the Iberian basement in Portugal. The available geochemical and geochronological data for the Alcáçovas orthogneiss (ca. 540 Ma tend to favor its involvement in a Cadomian orogenic event. This is consistent with the development of an active continental margin setting at the end of the Proterozoic and supports a Gondwanan provenance for the Iberian crust. On the other hand, the Ordovician emplacement age obtained for the magmatic precursors of the Portalegre orthogneisses (497?10 Ma provides additional evidence for the occurrence of rift-related magmatic activity during the Lower Paleozoic.

  7. Precambrian ophiolites of Arabia; a summary of geologic settings, U-Pb geochronology, lead isotope characteristics, and implications for microplate accretion, Kingdom of Saudi Arabia

    Science.gov (United States)

    Pallister, John S.; Stacey, J.S.; Fischer, L.B.; Premo, W.R.

    1988-01-01

    Disrupted ophiolites occur in linear belts as much as 900 km long between micro plates that collided during the late Proterozoic to form the Arabian Shield. The U-Pb zircon ages and lead-isotope data from these ophiolitic rocks help constrain the history of accretion of the Arabian Shield and thereby contribute to the definition of its microplates and terranes. Microplates of the central and western Arabian Shield are generally thought to represent intra-oceanic island arcs that range in age from about 900 Ma to 640 Ma; however, a region of the eastern Arabian Shield contains rocks of early Proterozoic age and may represent an exotic continental fragment entrained between the arc complexes.

  8. U-Pb La-ICP-ms geochronology and regional correlation of middle Jurassic intrusive rocks from the Garzon Massif, Upper Magdalena Valley and central cordillera, southern Colombia

    International Nuclear Information System (INIS)

    New U-Pb zircon geochronology from four granitic units sampled along a southeast-northwest transect between the Garzon massif and the Serrania de las Minas (central cordillera), records a middle Jurassic magmatic activity with two different spatio-temporal domains at ca. 189 ma and 180-173 ma. Reconnaissance data suggest that the four granitoids are characterized by mineralogical and geochemical characteristics akin to a continental magmatic arc setting. The new results suggest that the southern Colombian continental margin includes remnants of tectonomagmatic elements formed by the subduction of the Farallon plate under the South American continental margin. This middle Jurassic arc magmatism is part of the broader Andean scale arc province, and is significant for understanding the tectonic and paleogeographic scenario that characterized the Mesozoic tectonic evolution of the northern Andes.

  9. Geochemistry and LA-ICP-MS zircon U-Pb dating of the Dongjiahe ophiolite complex from the western Bikou terrane

    Institute of Scientific and Technical Information of China (English)

    LAI; ShaoCong; LI; YongFei; QIN; JiangFeng

    2007-01-01

    The Dongjiahe ophiolite complex occurring in the western Bikou terrane that is composed chiefly of serpentinite, listwanitizational peridotite, gabbro, cumulus gabbro, and sub-alkaline meta-basalt, possesses a rock association of typical ophiolite sequence. The metaperidotite is depleted in light rare earth element (LREE), whereas the gabbro and meta-basalt from the studied ophiolite sequence, generated by the same parental magmas those have close affinity to the MORB (Mid-ocean ridge basalt), their REE and immobile elements patterns imply an ocean in the northern margin of the Yangtze plate during the Neoproterozoic period. The zircon LA-ICP-MS U-Pb dating for the gabbro yields a weighted mean age of 839.2±8.2Ma, suggesting that the basin occurred during the Neoproterozoic period.

  10. Zircon U-Pb geochronology of the volcanic rocks from Fanchang-Ningwu volcanic basins in the Lower Yangtze region and its geological implications

    Institute of Scientific and Technical Information of China (English)

    YAN Jun; LIU HaiQuan; SONG ChuanZhong; XU XiSheng; AN YaJun; LIU Jia; DAI LiQun

    2009-01-01

    The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation,respectively.The representative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating.The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks.The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation,and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation.These U-Pb ages are interpreted to represent the formation times of the volcanic rocks.In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region,it is proposed that the latest volcanic activations in the Jinniu,Luzong,Fanchang and Ningwu volcanic basins probably came to end prior to ca.128 Me.There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins,suggesting e short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region.Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension,followed by delaminating of the lower part of the thickened lithosphere,lithospheric thinning,asthenosphere upwelling,and crust-mantle interaction.

  11. Zircon U-Pb age, geochemical, and Sr-Nd-Pb isotopic constraints on the origin of alkaline intrusions in eastern Shandong Province, China

    Science.gov (United States)

    Liu, Shen; Feng, Caixia; Hu, Ruizhong; Gao, Shan; Wang, Tao; Feng, Guangying; Qi, Youqiang; Coulson, Ian M.; Lai, Shaocong

    2013-08-01

    Alkaline intrusions in the eastern Shandong Province consist of quartz monzonite and granite. U-Pb zircon ages, geochemical data, and Sr-Nd-Pb isotopic data for these rocks are reported in the present paper. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses yielded consistent ages ranging from 114.3 ± 0.3 to 122.3 ± 0.4 Ma for six samples of the felsic rocks. The felsic rocks are characterised by a wide range of chemical compositions (SiO2 = 55.14-77.63 wt. %, MgO = 0.09-4.64 wt. %, Fe2O3 = 0.56-7.6 wt. %, CaO = 0.40-5.2 wt. %), light rare earth elements (LREEs) and large ion lithophile elements (LILEs) (i.e., Rb, Pb, U) enrichment, as well as significant rare earth elements (HREEs) and heavy field strength (HFSEs) (Nb, Ta, P and Ti) depletion, various and high (87Sr/86Sr) i ranging from 0.7066 to 0.7087, low ɛ Nd (t) values from -14.1 to -17.1, high neodymium model ages (TDM1 = 1.56-2.38Ga, TDM2 = 2.02-2.25Ga), 206Pb/204Pb = 17.12-17.16, 207Pb/204Pb = 15.44-15.51, and 208Pb/204Pb = 37.55-37.72. The results suggested that these rocks were derived from an enriched crustal source. In addition, the alkaline rocks also evolved as the result of the fractionation of potassium feldspar, plagioclase, +/- ilmenite or rutile and apatite. However, the alkaline rocks were not affected by crustal contamination. Moreover, the generation of the alkaline rocks can be attributed to the structural collapse of the Sulu organic belt due to various processes.

  12. Simultaneous in-situ determination of U-Pb age and trace elements in zircon by LA-ICP-MS in 20 μm spot size

    Institute of Scientific and Technical Information of China (English)

    LIU XiaoMing; GAO Shan; DIWU ChunRong; YUAN HongLin; HU ZhaoChu

    2007-01-01

    Simultaneous in-situ determination of U-Pb agea and 20 trace elements of three international zircon standards (91500, GJ1 and TEMORA 1) and one laboratory zircon standard (SK10-2) separated from Cenozoic fine-grained gabbro was carried out on quadrupole ICP-MS equipped with 193 nm excimer laser in 20 μm spot size. The weighted mean 208Pb/238U ages of g1500, GJ1 and TEMORA 1 are 1064.4±4.8 Ma (2σ), 603.2±2.4 Ma (2σ) and 418.2±2.4 Ma (2σ), respectively. The relative standard deviations (RSDs) of 206Pb/238U ages (2σ) are less than 2.2% for single measurements and 0.6% for weighted means. The obtained weighted mean 206Pb/238U ages of three atandard zircons agree with the recommended values within 2σσerror. The weighted mean 206Pb/238U age of SK10-2 is 31.42±0.25 Ma (2σ)and the RSDs of 206Pb/238U ages (2σ) are between 2.4% and 5.7% for single measurements and less than 0.8% for weighted mean. The obtained weighted mean 206Pb/238U age is in good agreement with the age obtained by Yuan (2004). Trace element concentrations of NIST612 and NIST614 obtained under the same LA-ICP-MS operating conditions agree with the recommended values within analytical error. The results indicate that it is possible to measure U-Pb age and trace elements aimultaneously by LA-ICP-MS in a small spot size of 20 μm.

  13. Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry

    Institute of Scientific and Technical Information of China (English)

    HOU; Zhenhui; LI; Shuguang; CHEN; Nengsong; LI; Qiuli; LIU

    2005-01-01

    The mafic granulites from Huilanshan are outcropped on the center of the Luotian dome in the northern Dabie Mountains. The Sm-Nd isochron defined by granulite-facies metamorphic minerals (garnet + clinopyroxene + hypersthene) yields an age of 136(±)18 Ma indicating the early Cretaceous granulite-facies metamorphism. The cathodoluminescence (CL) images of zircons from the granulite show clearly core-mantle-rim structures. The zircon cores are characterized by typical oscillatory zoning and highly HREE enriched patterns, which suggests their magma origin. Some zircon cores among them with little Pb loss give SHRIMP U-Pb ages ranging from 753 to 780 Ma, which suggests that the protolith of Huilanshan granulite is Neoproterozoic mafic rocks. The zircon mantles usually cut across the oscillatory zone of the zircon cores have 3―10 times lower REE, Th, U, Y, Nb and Ta contents than the igneous zircon cores but have high common Pb contents. These characteristics suggest that they were formed by hydrothermal alteration of the igneous zircons. The part of zircon mantles with little Pb loss give a similar SHRIMP U-Pb age (716―780 Ma) to the igneous zircon cores, which implies that the hydrothermal events occurred closely to the magmatic emplacement. In view of the strong early Cretaceous magmatism in the Luotian dome, consequently, the Huilanshan mafic granulite was formed by heating of the Neoproterozoic mafic rocks in mid-low crust, which caused the granulite-facies metamorphism underneath the Dabie Mountains. The similarity between the granulite metamorphic age (136±18 Ma) defined by Sm-Nd isochron and K-Ar age of 123―127 Ma given by amphible from the gneiss in Luotian dome suggests a rapid uplifting of the Luotian dome, which may result in further exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains.

  14. Zircon U-Pb And Biotite 40Ar/39Ar Ages Of Kohistan Lower Crustal Tonalite And Their Implications For The History Of Continental Collision

    Science.gov (United States)

    Nakajima, T.; Williams, I. S.; Hyodo, H.; Miyazaki, K.; Sano, S.; Kausar, A. B.

    2002-12-01

    The Kohistan block in northern Pakistan exposes a crustal cross section through an ancient oceanic island arc, comprising garnet pyroxenite, garnet granulite, banded amphibolite, norite gabbro, metasediment and metavolcanics. The Dasu Tonalite intrudes the lower crustal Kamila Amphibolite. The tonalite is foliated and folded concordantly with the host amphibolite, indicating syn-tectonic intrusion, and contains abundant magmatic epidotes, indicating high-P crystallization. The Dasu Tonalite is extremely poor in K2O (0.6-0.9 wt.% for SiO2 64-70%) and has a low initial 87Sr/86Sr (0.7037-0.7038, similar to the associated lower crustal amphibolite and granulite), consistent with juvenile granitic magma free of contamination by recycled upper crust. The Dasu Tonalite gave SHRIMP zircon U-Pb ages of 97.6+/-1.0 Ma and 98.0+/-1.1 Ma on two samples, and biotite 40Ar/39Ar ages of 69.7+/-0.7 Ma and 69.7+/-0.9 Ma. The euhedral shape and lack of overgrowth or resorption features in CL images of the zircons suggest a simple magmatic history starting at ca. 98 Ma with no evidence for a later major thermal event. The large discrepancy between the U-Pb and Ar-Ar ages might record the deep crustal residence time of the Dasu Tonalite. The tonalite magma was probably generated and crystallized at ca. 98 Ma, then remained in the lower crust at a temperature of about 700C (which is given by geothermometry of the intercalating Kamila amphibolite), cooling down to ca.300C at 69.7Ma. 69.7Ma is a cooling age during the process of exhumation of the Kohistan arc caused by the Indian collision.

  15. High-precision U-Pb geochronologic constraints on the Late Cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the Songliao Basin, Northeast China

    Science.gov (United States)

    Wang, Tiantian; Ramezani, Jahandar; Wang, Chengshan; Wu, Huaichun; He, Huaiyu; Bowring, Samuel A.

    2016-07-01

    The Cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future. The Songliao Basin of Northeast China preserves a near-complete, predominantly lacustrine, Cretaceous succession, with sedimentary cyclicity that has been tied to Milankocitch forcing of the climate. Over 900 meters of drill-core recovered from the Upper Cretaceous (Turonian to Campanian) of the Songliao Basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high-resolution cyclostratigraphic, magnetostratigraphic and geochronologic investigations. Here we report high-precision U-Pb zircon dates (CA-ID-TIMS method) from four interbedded bentonites from the drill-core that offer substantial improvements in accuracy, and a ten-fold enhancement in precision, compared to the previous U-Pb SIMS geochronology, and allow a critical evaluation of the Songliao astrochronological time scale. The results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology, which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses, rather than suspected limitations of astronomical models applied to distant geologic time. Age interpolation based on our new high-resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the Cretaceous Normal Superchon (C34n-C33r chron boundary) in the Songliao Basin at 83.07 ± 0.15 Ma. This date also serves as a new and improved estimate for the global Santonian-Campanian stage boundary.

  16. The U-Pb chronometer in uraniferous environment: application to the hydrothermal uranium deposits spatially associated to the Mortagne batholith (Vendee, France)

    International Nuclear Information System (INIS)

    The use of U-Pb method for the metallogeny of uranium sets a mineralization at a given time in a geological area. The Pb/U ratio is easily obtained for pitchblendes on account of its richness in radiogenic lead (daughter) induced by high concentrations of uranium (parent). Nevertheless, in most cases, interpretation of the results raises difficulties linked with the study of pitchblende itself, a mineral very sensitive to alterations, in which diffusion of radiogenic lead is systematically observed. In this open system, an age may be proposed by shaking off lead losses inside the mineral; that is why a Concordia diagram is used: it shows alignments of variable slope, representative of samples whose age is given by the upper intersection with the concordia, corresponding to a cogenetic pitchblende population, the lower intersection passing through O, showing a lead loss by continuous diffusion. So, the last important geological event in relation to a mineralizing phase can be dated. The uranium deposits linked to the hercynian leucogranites in Western Europe are generally supposed to be of hydrothermal origin; the U-Pb geochronological study of the mineralisation linked to the Mortagne leucogranite confirms this hypothesis and shows that the different ages of uranium deposition correspond to the described paragenesis. Certain ores, like that of the Retail deposit, which is typically intrametamorphic can indicate as many as three mineralizing phases, separated by some considerable time. The proposal of a genetic regional model for uranium is based, on one hand, on the ante-hercynian metamorphic series and on leucogranite, on the other, on metallogenic periods closely related to local geological events

  17. Characterizing the U-Pb systematics of baddeleyite through chemical abrasion: application of multi-step digestion methods to baddeleyite geochronology

    Science.gov (United States)

    Rioux, Matthew; Bowring, Samuel; Dudás, Frank; Hanson, Richard

    2010-11-01

    U-Pb baddeleyite geochronology has become a major tool for dating mafic rocks, especially dikes associated with Large Igneous Provinces. However, in many cases, post-crystallization Pb-loss and intergrowth of baddeleyite and zircon limit the precision and/or accuracy of crystallization ages. We present results from multi-step digestion experiments designed to understand and reduce these effects. Experiments were carried out on Neoproterozoic baddeleyites with zircon inter- and over-growths from the Gannakouriep dike swarm, Namibia, and on fragments of a large Paleoproterozoic baddeleyite from the Phalaborwa carbonatite, South Africa. Multi-step digestion experiments on annealed Phalaborwa baddeleyite were designed to test whether the recently developed chemical abrasion technique for U-Pb zircon geochronology can be applied to baddeleyite. The experiments generated complex results—individual digestion steps were both normally and reversely discordant suggesting that U and Pb were decoupled in the multi-step digestions—and indicate that the current form of multi-step chemical abrasion is not an effective method for reducing the impact of Pb-loss in baddeleyite. A separate set of experiments on the Gannakouriep baddeleyite focused on isolating the zircon and baddeleyite components in composite grains. Conventional single-step digestion experiments for this sample resulted in a discordant suite of analyses with significant scatter attributed to inter- and over-grown zircon and highlight the difficulty of obtaining precise and accurate ages from composite grains. To isolate the baddeleyite and zircon in these grains, a two-step HCl-HF chemical abrasion procedure for annealed grains was developed. This technique was successful at selectively dissolving the baddeleyite and zircon components. Secondary zircon inter- and over-growths of baddeleyite can occur in samples affected by low-temperature alteration to granulite facies metamorphism, and the new HCl-HF chemical

  18. SHRIMP U-Pb zircon geochronology and thermal modeling of multilayer granitoid intrusions. Implications for the building and thermal evolution of the Central System batholith, Iberian Massif, Spain

    Science.gov (United States)

    Díaz Alvarado, Juan; Fernández, Carlos; Castro, Antonio; Moreno-Ventas, Ignacio

    2013-08-01

    This work shows the results of a U-Pb SHRIMP zircon geochronological study of the central part of the Gredos massif (Spanish Central System batholith). The studied batholith is composed of several granodiorite and monzogranite tabular bodies, around 1 km thick each, intruded into partially molten pelitic metasediments. Granodiorites and monzogranites, belonging to three distinct intrusive bodies, and samples of anatectic leucogranites have been selected for SHRIMP U-Pb zircon geochronology. Distinct age groups, separated by up to 20 Ma, have been distinguished in each sample. Important age differences have also been determined among the most representative age groups of the three analyzed granitoid bodies: 312.6 ± 2.8 Ma for the Circo de Gredos Bt-granodiorites (floor intrusive layer), 306.9 ± 1.5 Ma for the Barbellido-Plataforma granitoids (top intrusive layer) and 303.5 ± 2.8 Ma for Las Pozas Crd-monzogranites (middle intrusive layer). These age differences are interpreted in terms of sequential emplacement of the three intrusive bodies, contemporary with the Late Paleozoic D3 deformation phase. The anatectic leucogranites are coeval to slightly younger than the adjacent intrusive granodiorites and monzogranites (305.4 ± 1.6 Ma for Refugio del Rey leucogranites and 303 ± 2 Ma for migmatitic hornfelses). It is suggested that these anatectic magmas were generated in response to the thermal effects of granodiorite intrusions. Thermal modeling with COMSOL Multiphysics® reveals that sequential emplacement was able to keep the thermal conditions of the batholith around the temperature of zircon crystallization in granitic melts (around 750 °C) for several million of years, favoring the partial melting of host rocks and the existence of large magma chambers composed of crystal mush prone to be rejuvenated after new intrusions.

  19. U-Pb zircon geochronology and Sm-Nd-Pb isotopic constraint for precambrian plutonic rocks in the northeastern part of Ryeongnam massif, Korea

    International Nuclear Information System (INIS)

    The Ryeongnam massif is composed of Precambrian gneisses, Paleozoic and Mesozoic sedimentary rocks and extensive Triassic-Jurassic plutonic rocks of felsic to mafic composition. In the northeast Ryeongnam massif, the oldest rocks belong to the Sobaegsan gneiss complex, which is composed of orthogneisses, paragneisses and mafic plutonic rocks. U-Pb zircon ages for the felsic and mafic intrusive bodies within the Sobaegsan gneiss complex are: the Icheon granite gneiss, 2357±43 and 2342±47 Ma; the Buncheon granite gneiss, 1963±5 Ma; the Pyeonghae granite gneiss, 1936±21 Ma; the Ogbang amphibolite, 1918±10 Ma; the Imwon leucogranite gneiss, 1826±20 Ma. The Hyeondong biotite schist, which is intruded by the Buncheon granite gneiss and the Ogbang amphibolite, yielded an age of 2271±44 Ma. The Nd-Sm-Pb isotopic data indicate that the felsic plutonic rocks are derived from an older Archean crust. The Nd TDM ages are Archean, and the εNd values are negative for the felsic rocks and positive for the amphibolite. Common Pb isotope compositions also indicate a crustal source for the felsic intrusives. The U-Pb ages of Precambrian rocks of the Ryeongnam massifs are similar to those in the Gyeonggi massif, and may have a similar crustal evolutionary history. The Precambrian rocks of South Korea could be related either to the North China block or to the South China block, as the isotope ages and patterns are not unique to either block. Similarly, a geologic correlation with Japan, although possible, is tenuous at present. (author)

  20. From Gondwana to Europe: the journey of Elba Island (Italy) as recorded by U-Pb detrital zircon ages of Paleozoic metasedimentary rocks

    Science.gov (United States)

    Jacobs, Joachim; Sirevaag, Hallgeir; Ksienzyk, Anna K.; Rocchi, Sergio; Paoli, Gabriele

    2016-04-01

    The configuration of the northern Gondwana margin throughout the Paleozoic is difficult to reconstruct owing to the complex geodynamic setting of the Mediterranean region in Mesozoic to Cenozoic times. Detrital zircons in early Paleozoic to early Mesozoic metasedimentary rocks on Elba and mainland Tuscany record the Gondwana provenance of Adria and its rifting from the northern Gondwana margin. A large new LA-ICP-MS and SIMS U-Pb zircon data set allows us to trace this history. Three main stratigraphic units have been investigated on Elba Island. The oldest Porto Azzurro Unit was deposited in the early Cambrian and has zircon age distributions indicating a typical northern African provenance, most likely sourced from the Saharan Metacraton. The Ortano Unit has a simple, mostly unimodal Ordovician age distribution that is entirely dominated by metavolcanic rocks and their erosional products; a sample of the metavolcanic Ortano Porphyroids provided a SIMS U-Pb zircon age of 460 ± 3 Ma. This phase of intense volcanism is related to the subduction of the Rheic Ocean beneath Gondwana, terminating with initial rifting and subsequent opening of the Paleotethys. This also marks the onset of the separation of a range of European terranes, including Adria and future Elba Island, from Gondwana. The Permo-Triassic Monticiano-Roccastrada Unit is the first to show a European provenance with the appearance of large amounts of Variscan and late to post-Variscan detritus. The presence of Variscan detrital zircons in the Permo-Triassic sediments is unexpected, since a Variscan age signature is so far not well recorded in the Adria Plate. This dataset is the most comprehensive detrital zircon data set so far available for the Adria Plate and documents Adria's close affinity to Africa in the Lower Paleozoic, as well as its initial rifting within an active continental margin setting during the Ordovician and its final separation and independent evolution since late Palaeozoic times.

  1. Paleoproterozoic mojaveprovince in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

    Science.gov (United States)

    Lang, Farmer G.; Bowring, S.A.; Matzel, J.; Maldonado, G.E.; Fedo, C.; Wooden, J.

    2005-01-01

    Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ??? 1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleo- proterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States ?? 2005 Geological Society of America.

  2. Tectonic evolution of the Western Kunlun orogenic belt in northern Qinghai-Tibet Plateau: Evidence from zircon SHRIMP and LA-ICP-MS U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    ZHANG ChuanLin; LU SongNian; YU HaiFeng; YE HaiMin

    2007-01-01

    The Western Kunlun Range in northern Qinghai-Tibet Plateau is composed of the North Kunlun Terrane,the South Kunlun Terrane and the Karakorum-Tianshuihai Terrane. Here we report zircon SHRIMP and LA-ICP-MS U-Pb ages of some metamorphic and igneous rocks and field observations in order to provide a better understanding of their Precambrian and Palaeozoic-early Mesozoic tectonic evolution.Based on these data we draw the following conclusions: (1) The paragneisses in the North Kunlun Terrane are likely of late Mesoproterozoic age rather than Palaeoproterozoic age as previously thought,representing tectonothermal episodes at 1.0-0.9 Ga and ~0.8 Ga. (2) The North Kunlun Terrane was an orogenic belt accreted to the southern margin of Tarim during late Mesoproterozoic to early Neoproterozoic, the two episodes of metamorphisms correspond to the assemblage and breakup of Rodinia respectively. (3) The Bulunkuole Group in western South Kunlun Terrane, which was considered to be the Palaeoproterozoic basement of the South Kunlun Terrane by previous studies, is now subdivided into the late Neoproterzoic to early Palaeozoic paragneisses (khondalite) and the early Mesozoic metamorphic volcano-sedimentary series; the paragneisses were thrust onto the metamorphic volcano-sedimentary series from south to north, with two main teconothermal episodes (i.e., Caledonian,460-400 Ma, and Hercynian-Indosinian, 340-200 Ma), and have been documented by zircon U-Pb ages.(4) In the eastern part of the South Kunlun Terrane, a gneissic granodiorite pluton, which intruded the khondalite, was crystallized at ca. 505 Ma and metamorphosed at ca. 240 Ma. In combination with geochronology data of the paragneiss, we suggest that the South Kunlun Terrane was a Caledonian accretionary orogenic belt and overprinted by late Paleozoic to early Mesozoic arc magmatism.

  3. Tectonic evolution of the Western Kunlun orogenic belt in northern Qinghai-Tibet Plateau:Evidence from zircon SHRIMP and LA-ICP-MS U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Western Kunlun Range in northern Qinghai-Tibet Plateau is composed of the North Kunlun Terrane,the South Kunlun Terrane and the Karakorum-Tianshuihai Terrane. Here we report zircon SHRIMP and LA-ICP-MS U-Pb ages of some metamorphic and igneous rocks and field observations in order to pro-vide a better understanding of their Precambrian and Palaeozoic-early Mesozoic tectonic evolution. Based on these data we draw the following conclusions: (1) The paragneisses in the North Kunlun Terrane are likely of late Mesoproterozoic age rather than Palaeoproterozoic age as previously thought,representing tectonothermal episodes at 1.0―0.9 Ga and ~0.8 Ga. (2) The North Kunlun Terrane was an orogenic belt accreted to the southern margin of Tarim during late Mesoproterozoic to early Neopro-terozoic,the two episodes of metamorphisms correspond to the assemblage and breakup of Rodinia respectively. (3) The Bulunkuole Group in western South Kunlun Terrane,which was considered to be the Palaeoproterozoic basement of the South Kunlun Terrane by previous studies,is now subdivided into the late Neoproterzoic to early Palaeozoic paragneisses (khondalite) and the early Mesozoic metamorphic volcano-sedimentary series; the paragneisses were thrust onto the metamorphic vol-cano-sedimentary series from south to north,with two main teconothermal episodes (i.e.,Caledonian,460―400 Ma,and Hercynian-Indosinian,340―200 Ma),and have been documented by zircon U-Pb ages. (4) In the eastern part of the South Kunlun Terrane,a gneissic granodiorite pluton,which intruded the khondalite,was crystallized at ca. 505 Ma and metamorphosed at ca. 240 Ma. In combination with geochronology data of the paragneiss,we suggest that the South Kunlun Terrane was a Caledonian accretionary orogenic belt and overprinted by late Paleozoic to early Mesozoic arc magmatism.

  4. Age of meta-rhyolite of Marata sequence, Araxa Group, Goias: geochronology study by U-Pb in zircon, Rb-Sr and Sm-Nd methods

    International Nuclear Information System (INIS)

    U-Pb isotopic analyses in eight zircon fractions separated from a meta-rhyolite sample of the Marata sequence (Araxa Group, Goias) are presented. Two morphologically distinct zircon populations were identified: stubby prismatic crystals (width:length of 1:2 to 1:3) in which core-overgrowth relationships are observed; long prismatic crystals (needles) with width:length ratios of ca. 1:10. Analyses performed on group zircons indicated the presence of a ca. 2.0 Ga. old inherited component. Analyses of group zircons plot very close to the concordia and yield an upper intercepts age of 794 ± 10 Ma for the crystallization of the volcanic protolith. The study was complemented with whole-rock isotopic analyses by the Rb-Sr and Sm-Nd methods. Rb-Sr isochron obtained with samples from two different outcrops gave data of 829 ± 82 Ma (initial 87 Sr/86 Sr of 0.7057 ± 0.0157) and 691 ± 30 Ma (initial 87 Sr/86 Sr of 0.7337 ± 0.0034). The latter reflects a later Sr-isotopic re-homogenization episode, possibly associated with the intense deformation and metamorphism suffered by these rocks. Sm-Nd isotopic analyses on three samples reveal ENd (T) (T =794 Ma) values in the range of -6.1 to -9.5 which indicate the presence of older (early Proterozoic) crustal Nd. This is consistent with the inheritance pattern shown in the U-Pb isotopic results. (author)

  5. U-Pb zircon geochronology, petrochemical and Sr-Nd isotopic characteristic of Late Neoproterozoic granitoid of the Bornaward Complex (Bardaskan-NE Iran)

    Science.gov (United States)

    Bagherzadeh, R. Monazzami; Karimpour, M. H.; Farmer, G. Lang; Stern, C. R.; Santos, J. F.; Rahimi, B.; Heidarian Shahri, M. R.

    2015-11-01

    The Bornaward Granitoid Complex (BGC) in the Taknar Zone is located in the northeast of Central Iranian Block. The BGC consists of granite, alkaligranite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite and diorite that have intruded into the center of Taknar Zone. These intrusive rocks affected by low grade metamorphism. Because of there are no reliable isotope dating data, for the Bornaward Granitoid Complex rocks have been proposed discordant ages (Jurassic, Cretaceous or even younger ages) by many studies. In the present study, new isotopic information based on zircon U-Pb dating has revealed the origin and time of the formation of the BGC. These new results do not confirm previously proposed ages. The results obtained from zircon U-Pb dating of the BGC rocks suggest late-Neoproterozoic (Precambrian) age (540-550 Ma). The Bornaward Granitoid Complex is middle-high metaluminous to lower-middle peraluminous and belongs to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichment in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REE) plots indicate minor enrichment of LREE compared to HREE, and strong negative anomaly of Eu compared to other Rare Earth Elements. Furthermore, initial 87Sr/86Sr and 143Nd/144Nd range from 0.70351 to 0.71689 and 0.511585 to 0.512061, respectively, and initial εNd isotope values for granite, granodiorite and diorite range from -6.73 to 2.52. These all indicate that the BGC has derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr and undergoing extensive crustal contamination (S-type granite).

  6. Argentina Welcomes Chinese Enterprises

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    @@ On July 13,China-Argentina Entrepreneur Luncheon Meeting was held in Beijing.Cristina Fernandez de Kirchner,President of Argentina,Hui Liangyu,Vice Prime Minister of China and Wan Jifei,President of CCPIT attended the meeting.

  7. Edad de inicio como marcador de subtipos de enfermedad maniacodepresiva

    OpenAIRE

    Ricardo Sánchez Pedraza; Jorge Rodríguez Losada; Luis Eduardo Jaramillo

    2012-01-01

    Introducción: En los trastornos bipolares, la edad de inicio se ha sugerido como una variable que puede asociarse con diferentes subtipos clínicos. Objetivo: Identificar patrones en la distribución de la edad de inicio de la enfermedad bipolar y determinar si la edad de inicio se asocia con características clínicas específicas. Métodos: Se usó análisis de distribuciones normales mezcladas para identificar subtipos de trastorno bipolar de acuerdo con la edad de inicio. Se aplicó la escala EMUN...

  8. Volviendo a pensar la Edad del Hierro

    Directory of Open Access Journals (Sweden)

    Hill, J. D.

    1993-12-01

    Full Text Available This paper argues there is an urgent need to critically evaluate the basic assumptions used by Iron Age archaeologists across Europe. It suggests that the existing frameworks of explanation and interpretation are at best inadequate to understand the actual archaeological evidence for the period. At worst they are still unconsciously reproducing nineteenth century nationalist and racist ideologies (e. g. the preoccupations with the «Celts≫ or «Iberians≫, etc.. Drawing on examples from Britain, and the Czech and Slovak republics. We will argue that archaeological evidence Iron the Iron Age does not neatly fit our modernist and Eurocentric assumptions about what the period ought to have been like. It suggests Iron Age archaeology must recognise the difference of the past, that prehistoric societies in Europe may have had very different forms of social organisations, world views and economies than those in later European history. This means critically questioning archaeological evidence and being open to the possibility that existing interpretations are wrong (e. g. stressing the impact of the Mediterranean World Economy, that Oppidas were urban centres, or that settlement and subsistence data can be adequately understood in modern capitalist/functionalist terms, etc.. As such Iron Age studies can on/y be a «Contextual Archaeology≫.

    Este artículo defiende la urgente necesidad de evaluar críticamente las asunciones básicas manejadas por los arqueólogos de la Edad del Hierro en toda Europa. Sugiere que los marcos explicativos e interpretativos existentes son, en el mejor de los casos, inadecuados para comprender la evidencia arqueológica real sobre el período. En el peor, están reproduciendo todavía las ideologías nacionalistas y racistas decimonónicas (p. e. las preocupaciones por los “Celtas”, los “Iberos”, etc.. A partir de ejemplos de Gran Bretaña, y las Repúblicas Checa y Eslovaca, sostenemos que la evidencia

  9. Magma Mixing for the Origin of the Granites. Geochemistry, Sr-Nd Isotopic, Zircon U-Pb Dating and Hf Isotopic Evidences from the Triassic Mishuling Monzonitic Granite and Its Enclaves, Qinling Orogen (Central China)

    Institute of Scientific and Technical Information of China (English)

    QIN Jiang-feng; LAI Shao-cong; DIWU Chun-rong; JU Yin-juan; LI Yong-fei

    2008-01-01

    @@ Major and trace element, whole rock Sr-Nd isotope, mineral chemistry, zircon U-Pb and Hf isotope compositions are reported for a suite of I-type monzogranite and its marie microgranular enclaves from the Triassic (210±2 Ma) Mishuling pluton, Qinling orogen, central China, with the aim of investigating the sources and petrogenesis of I-type granites.

  10. Nové U-Pb datování zirkonů z bohutínského pně v příbramské rudní oblasti

    Czech Academy of Sciences Publication Activity Database

    Žák, Karel; Svojtka, Martin; Breiter, Karel; Ďurišová, Jana; Veselovský, F.; Pašava, J.

    2015-01-01

    Roč. 2014, č. 1 (2015), s. 43-49. ISSN 0514-8057 R&D Projects: GA ČR GA13-15390S Institutional support: RVO:67985831 Keywords : Bohemian Massif * Central Bohemian Pluton * Bohutím Stock * zircon U-Pb dating Subject RIV: DB - Geology ; Mineralogy

  11. New U-Pb and Sm-Nd isotope data of the age of formation and metamorphic alteration of the Kandalaksha-Kolvitsa gabbro-anorthosite complex (Baltic Shield)

    Science.gov (United States)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel; Chashchin, Viktor

    2016-04-01

    The aim of this research was to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) in Kandalaksha-Kolvitsa gabbro-anorthosite complex. Kandalaksha-Kolvitsa gabbro-anorthosite complex is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate metamorphism. New U-Pb and Sm-Nd isotopic and geochronological data for the rocks of the Kandalaksha-Kolvitsa Paleoproterozoic gabbro-anorthosite complex is presented. For the first time single zircon grains from metagabbros of Kolvitsa massif were dated 2448±5 Ma, using U-Pb method with an artificial 205Pb tracer. Sm-Nd isotopic age of the metamorphic minerals apatite, garnet and sulphide WR Kolvitsa array is 1985 ± 17 Ma, which is interpreted granulite metamorphism. Two fractions of single zircons from anorthosite of the Kandalaksha massif gave U-Pb age 2450± 3 Ma. Leucocratic gabbro-norite (Kandalaksha massif) were dated by U-Pb on single zircon, with age up to 2230±10 Ma. This age reflects the time of granulite metamorphism according to data of [1]. Two fractions of rutile from anorthosite of the Kandalaksha massif have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile 400-450 ° C [2], thus cooling of the massif to these temperatures was about 1.7 Ga. These data suggested two stages of metamorphic transformations of the massif. Sm-Nd research Kandalaksha massif reflected the age of the high-temperature metasomatic transformations -1887 ± 37 Ma. Time of regional fluid processing - 1692 ± 71 Ma. A model Sm-Nd age metagabbros Kolvitsa massif is 3.3 Ga with a negative value ɛNd = -4.6, which corresponds to the most likely primary enriched mantle reservoir of

  12. U-Pb geochronology and Sr-Nd isotopes of Galileia and Urucum neo proterozoic granitoids suites in south-eastern Brazil; Geochronologie U-Pb et geochimie isotopique Sr-Nd des granitoides neoproterozoiques des suites Galileia et Urucum, vallee du Rio Doce, Sud-Est du Bresil

    Energy Technology Data Exchange (ETDEWEB)

    Herminio Arias Nalini Jr [Universidade Federal de Ouro Preto, Dept. de Geologia, Minas Gerais (Brazil); Herminio Arias Nalini Jr; Essaid Bilal [Ecole Nationale Superieure des Mines, Dept. de Geochimie, Centre SPIN, 42 - Saint-Etienne (France); Paquette, J.L.; Pin, Ch. [Universite Blaise Pascal, Clermont-Ferrand II, (CNRS-UMR 6525), 63 - Aubiere (France); Romulo, M. [IGG Universite de Sao Paulo (Brazil)

    2000-10-01

    U-Pb zircon and monazite dating and whole-rock Sr-Nd isotopes have been applied on Neo-Proterozoic granitoids from the Atlantic shear belt, south-eastern Brazil. U-Pb zircon results on the Galileia met-aluminous and Urucum per-aluminous suites indicate crystallisation ages of 594 {+-} 6 Ma and 582 {+-} 2 Ma respectively. Whole-rock Rb-Sr and Sm-Nd analyses on representative samples from both suites demonstrate that they mainly derive from melting of older crustal rocks. The occurrence of an old isotopic memory in the zircons from the Urucum granitoids around 2.2 Ga, in agreement with Nd model ages, suggests a Palaeo-Proterozoic age for the crustal proto-lith of these two suites, probably associated with the Transamazonico event. Owing to these new dating results and previous regional geochronological data, it can be proposed that the met-aluminous magmatism ended around 590 Ma and that the collisional peraluminous magmatism associated with the Brasiliano orogeny occurred between 584 and 570 Ma. (authors)

  13. Provenance and depositional age of metavolcano-sedimentary sequences of the Santa Terezinha de Goias, based on Sm-Nd and U-Pb zircon single grain; Proveniencia e idade deposicional de sequencias metavulcano-sedimentares da regiao de Santa Terezinha de Goias, baseada em dados isotopicos Sm-Nd e U-Pb em monocristal de zircao

    Energy Technology Data Exchange (ETDEWEB)

    Dantas, Ellton Luiz; Jost, Hardy; Fuck, Reinhardt A.; Brod, Jose Afonso; Pimentel, Marcio Martins; Meneses, Paulo Roberto [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: elton@unb.br

    2001-09-01

    Supracrustal rocks of the Santa Terezinha de Goias region, Central Brazil, presumably represent a southern extension of the Mara Rosa magmatic arc tectonically juxtaposed to Archean terrains and consist of a meta volcanic unit and a meta sedimentary unit. The aim of the paper is to present and discuss the first U-Pb and Sm-Nd data of rocks belonging to both units of that region. U-Pb data of zircons from a felsic meta volcanic rock inter layered with chlorite-rich schists (metandesites?) yield a concordant age of of 660 My, while the Sm-Nd model age of a variety of chlorite-schists indicate a juvenile age between 1.1 and 1.3 Ga. These data indicate that the meta volcanic rocks are Neo proterozoic in age and may be correlated with rocks of the Mara Rosa magmatic arc. On the other hand, the prevailing provenance of rocks belonging to the meta sedimentary unit indicate a Paleoproterozoic, or older, source. Thus, the deposition of both units are explained by means of the erosion of source-areas of variable age. (author)

  14. Rapid and simultaneous determination of multi-element abundances and U-Pb age for zircon crystal using UV laser ablation ICP-MS technique: critical evaluation of the technique with 91500 zircon standard

    International Nuclear Information System (INIS)

    A new analytical technique for simultaneous determinations of REE, U, Th, Pb abundances and U-Pb age from a single analysis spot of zircon crystal is presented in this paper. It uses ultra-violet (U)-laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Coupling of multi-element abundance data and U-Pb age data can provide piercing information for petrogenetic studies of igneous rocks and for provenance studies of sedimentary and metamorphic rocks. The REE, U, Th and Pb abundances and 207Pb/206Pb and 206Pb/238U ratios for a 91500 zircon standard were simultaneously analyzed in order to test the accuracy of the measurement and to evaluated homogeneity within a grain of the standard sample. The resulted abundance data for almost of all rare earth elements (REE) show good agreement with those obtained by the secondary ion mass spectrometry (SIMS) and with LA-ICP-MS data. The data obtained in this study fell in the range of published data. Only exception is the abundance data for Er, Lu, Pb and U. These elements are differed largely from the published data beyond the precision of our measurements (∼10% in SD). The large discrepancy between present results and previous authors' data can be explained by heterogeneity among different grains of the zircon standard. In the case of U-Pb age, resulted 238U-206Pb and 207Pb-206Pb ages were 1131±152 Ma (2SD) and 1156±132 Ma (2SD), respectively, showing an excellent agreement with the TIMS data within analytical uncertainties achieved in this study (∼20%, 2SD). The abundance data for REE, U, Th and Pb, together with U-Pb isotopic ones demonstrate clearly that the present LA-ICPMS technique can provide a rapid and versatile tool for the multi-element abundances and U-Pb age determinations. (author)

  15. Permian U-Pb (CA-TIMS) zircon ages from Australia and China: Constraining the time scale of environmental and biotic change

    Science.gov (United States)

    Denyszyn, S. W.; Mundil, R.; Metcalfe, I.; He, B.

    2010-12-01

    In eastern Australia, the interconnected Bowen and Sydney Basins are filled with terrestrial sediments of late Paleozoic to early Mesozoic age. These sedimentary units record significant evolutionary events of eastern Gondwana during the time interval between two major mass extinctions (end Middle Permian and Permian-Triassic), and also provide lithological evidence for the Carboniferous-Permian Late Paleozoic Ice Age of southern Pangea, considered to be divisible into up to seven discrete glaciation events in Australia [e.g., 1]. These glaciations are currently assigned ages that indicate that the last of the glaciations predate the end Middle Permian mass extinction at ca. 260 Ma. However, the estimates for the time and durations are largely based on biostratigraphy and lithostratigraphy that, in the absence of robust and precise radioisotopic ages, are unacceptably fragile for providing an accurate high-resolution framework. Interbedded with the sediments are numerous tuff layers that contain zircon, many of which are associated with extensive coal measures in the Sydney and Bowen Basins. Published SHRIMP U-Pb zircon ages [2, 3] have been shown to be less precise and inaccurate when compared to ages applying the CA-TIMS method to the same horizons. Also within the late Middle Permian, the eruption of the Emeishan flood basalts in SW China has been proposed to have caused the end Middle Permian mass extinction [e.g., 4], though a causal link between these events demands a rigorous test that can only be provided by high-resolution geochronology. We present new U-Pb (CA-TIMS) zircon ages on tuff layers from the Sydney and Bowen Basins, with the purpose of generating a timescale for the Upper Permian of Australia to allow correlation with different parts of the world. Initial results, with permil precision, date a tuff layer within the uppermost Bandanna Fm. to ca. 252 Ma, a tuff within the Moranbah Coal Measures to ca. 256 Ma, and a tuff within the Ingelara Fm. to

  16. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    Science.gov (United States)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia

    2016-04-01

    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18‑24Ab79‑82Or0.3‑0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  17. Comparing Carbon and Strontium Isotope Chemostratigraphy against U-Pb Detrital Zircon Analysis in Dating Marbles of the Uppermost Allochthon in North Norway

    Science.gov (United States)

    Verellen, Devon; Yaw Agyei-Dwarko, Nana; Steltenpohl, Mark; Andresen, Arild

    2015-04-01

    The basal parts of the Uppermost Allochthon between latitudes N67oN (Fauske) and N68.45oN (Ofoten) comprise a thick sequence of platformal marbles that overlie a fragmented ophiolite complex. This basement-cover package can be traced discontinuously from Ofoten more than 150 kilometers northward to connect with the Lyngen ophiolite, the largest ophiolite complex in Scandinavia. U-Pb zircon geochronology documents an Early Ordovician age (469 ±5 Ma) for magmatic crystallization of the Lyngen ophiolite and for the Ofoten mafic complex (474 ±0.7 Ma). A regional unconformity separates the Lyngen ophiolite from overlying rocks of the Balsfjord Group. Halysitid corals from the Balsfjord Group constrain an Upper Llandoverian age for the unconformity. In Ofoten, metasedimentary rocks of the Evenes Group nonconformably overlie the mafic complex and are lithologically correlated to parts of the Balsfjord Group. The basal unit of the Evenes Group, the Elvenes Conglomerate, contains clasts of plutonic igneous rocks clearly derived from the underlying mafic complex (Lillevik dike complex). Suites of multiple phases of felsic intrusions occur within overlying (Bogen/Niingen nappes) and underlying (Narvik nappe) allochthons but are absent in the Evenes Group. Carbon and strontium isotopes reported on these amphibolite-facies marbles have been interpreted to place chemostratigraphic ages that range from Neoproterozoic to Silurian, requiring the placement of hypothetical thrusts and normal faults to explain their vertical stacking although no faults are yet recognized based on field and structural studies. We present LA-ICPMS U-Pb isotope data on detrital zircons from a siliciclastic layer within one of the carbonate units of the Evenes Group that had previously been assigned a Neoproterozoic chemostratigraphic apparent age. Twenty-seven percent of the ages are younger than 600 Ma and define a prominent 470 Ma age population with the 5 youngest ones giving a concordia age of 460

  18. U-Pb SHRIMP and Sm-Nd geochronology of the paleoproterozoic Silvania magmatic arc in the neoproproterozoic Brasilia Belt, Goias, Central Brazil

    International Nuclear Information System (INIS)

    The Brasilia Belt is a large Neoproterozoic orogen formed along the western margin of the Sao Francisco/Congo Craton in central Brazil. It comprises: (i) a thick Meso-Neoproterozoic metasedimentary/sedimentary pile with eastward tectonic vergence; (ii) a large Neoproterozoic juvenile arc in the west (Goias Magmatic Arc); and (iii) a micro-continent (or exotic sialic terrain) formed by Archean rock units (the Crixas -Goias granitegreenstones) and associated Proterozoic formations (Almeida et al. 1981, Fuck et al. 1993,1994, Pimentel et al. 2000a, b). The sialic basement on which the Brasilia Belt sediments were deposited is poorly understood, despite being well exposed in some areas of Goias and Tocantins. Gneiss and volcano-sedimentary units form most of this basement. Early studies have suggested that these rock units are dominantly Archean ( Danni et al. 1982, Marini et al. 1984). However, recent Sm- Nd isotopic studies have indicated that most of them are Paleoproterozoic (Sato 1998, Pimentel et al. 1999a, 2000b). Granite gneiss to the south and east of the Barro Alto mafic-ultramafic layered complex has been dated at 2128+/- 15 Ma (Correia et al. 1997). Calc-alkaline granite gneiss from Almas-Dianopolis is dated at ca. 2.2-2.45 Ga old (U-Pb SHRIMP on zircon and titanite, Cruz et al. 2000). The latter is probably the western extension of Paleoproterozoic rocks which underlie the San Francisco Craton to the east of the northern part of the Brasilia Belt. In central Goias, a large part of the Brasilia Belt is underlain by high-grade metamorphic rocks known as the Anapolis-Itaucu Complex, together with surrounding greenschist to amphibolite facies Mesoto Neoproterozoic cover metasediments of the Araxa group. These rocks represent the main constituent of the internal zone of the Brasilia Belt (Fuck et al. 1994, Pimentel et al. 2000b). Between the Araxa Group, and the easternmost part of the Anapolis-Itaucu Complex a volcano-sedimentary association known as Silvania

  19. Thermomagmatic evolution of Mesoproterozoic crust in the Blue Ridge of SW Virginia and NW North Carolina: Evidence from U-Pb geochronology and zircon geothermometry

    Science.gov (United States)

    Tollo, Richard P.; Aleinikoff, John N.; Wooden, Joseph L.; Mazdab, Frank K.; Southworth, Scott; Fanning, Mark C.

    2010-01-01

    New geologic mapping, petrology, and U-Pb geochronology indicate that Mesoproterozoic crust near Mount Rogers consists of felsic to mafic meta-igneous rocks emplaced over 260 m.y. The oldest rocks are compositionally diverse and migmatitic, whereas younger granitoids are porphyritic to porphyroclastic. Cathodoluminescence imaging indicates that zircon from four representative units preserves textural evidence of multiple episodes of growth, including domains of igneous, metamorphic, and inherited origin. Sensitive high-resolution ion microprobe (SHRIMP) trace-element analyses indicate that metamorphic zircon is characterized by lower Th/U, higher Yb/Gd, and lower overall rare earth element (REE) concentrations than igneous zircon. SHRIMP U-Pb isotopic analyses of zircon define three episodes of magmatism: 1327 ± 7 Ma, 1180–1155 Ma, and 1061 ± 5 Ma. Crustal recycling is recorded by inherited igneous cores of 1.33–1.29 Ga age in 1161 ± 7 Ma meta-monzogranite. Overlapping ages of igneous and metamorphic crystallization indicate that plutons of ca. 1170 and 1060 Ma age were emplaced during episodes of regional heating. Local development of hornblende + plagioclase + quartz ± clinopyroxene indicates that prograde metamorphism at 1170–1145 Ma and 1060–1020 Ma reached upper-amphibolite-facies conditions, with temperatures estimated using Ti-in-zircon geothermometry at ~740 ± 40 °C during both episodes. The chemical composition of 1327 ± 7 Ma orthogranofels from migmatite preserves the first evidence of arc-generated rocks in the Blue Ridge, indicating a subduction-related environment that may have been comparable to similar-age systems in inliers of the Northern Appalachians and the Composite Arc belt of Canada. Granitic magmatism at 1180–1155 Ma and ca. 1060 Ma near Mount Rogers was contemporaneous with anorthosite-mangerite-charnockite-granite (AMCG) plutonism in the Northern Appalachian inliers and Canadian Grenville Province. Metamorphism at ca. 1160

  20. U-Pb zircon and geochemical evidence for bimodal mid-Paleozoic magmatism and syngenetic base-metal mineralization in the Yukon-Tanana terrane, Alaska

    Science.gov (United States)

    Dusel-Bacon, C.; Wooden, J.L.; Hopkins, M.J.

    2004-01-01

    New SHRIMP (sensitive, high-resolution ion microprobe) U-Pb zircon ages and trace element geochemical data for mafic and felsic metaigneous rocks of the pericratonic Yukon-Tanana terrane in east-central Alaska help define the tectonic setting of mid-Paleozoic magmatism and syngenetic hydrothermal Zn-Pb-Ag mineralization along the ancient Pacific margin of North America. We compare data from similar greenschist-facies sequences of bimodal volcanic and subvolcanic rocks associated with carbonaceous and siliciclastic marine sedimentary rocks, in the Wood River area of the Alaska Range and the Salcha River area of the Yukon-Tanana Upland, and from amphibolite-facies augen gneiss and mafic gneiss (amphibolite) in the Goodpaster River area of the upland. Allowing for analytical uncertainties, igneous crystallization age ranges of 376-353 Ma, 378-346 Ma, and 374-358 Ma are indicated by 13 new SHRIMP U-Pb dates for the Wood River, Salcha River, and Goodpaster River areas, respectively. Bimodal magmatism is indicated by Late Devonian crystallization ages for both augen gneiss (371 ?? 3 and 362 ?? 4 Ma) and associated orthoamphibolite (369 ?? 3 Ma) in the upland and by stratigraphic interleaving of mafic and felsic rocks in the Alaska Range. Metabasites in all three study areas have elevated HFSE (high field strength element) and REE (rare earth element) contents indicative of generation in a within-plate (extensional) tectonic setting. Within-plate trace element signatures also are indicated for peralkaline metarhyolites that host the largest volcanogenic massive sulfide deposits of the Bonnifield district in the Wood River area and for metarhyolite tuff interlayered with the carbonaceous Nasina assemblage, which hosts sedimentary exhalative sulfide occurrences in the Salcha River area. Most of the other felsic metaigneous samples from the Alaska Range and the Yukon-Tanana Upland have geochemical signatures that are similar to those of both average upper continental crust

  1. Molybdenum mineralization at Alpeiner Scharte, Tyrol (Austria): results of in-situ U-Pb zircon and Re-Os molybdenite dating

    International Nuclear Information System (INIS)

    Vein-type Mo mineralization at Alpeiner Scharte occurs in the Penninic units of the western Tauern Window in the Eastern Alps. Three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks. The granitic protoliths represent fractionated late to post-orogenic, calc-alkaline, I-type magmas with minor S-type components. The Mo veins are restricted to a biotite and alkali feldspar-rich gneiss variety and occur in E-W trending normally sub-vertical quartz veins with adjacent thin discontinuous garnet- and biotite-rich zones; the latter are interpreted as metamorphosed vein selvages. Prior to this work the age of the intrusive host rocks as well as the age of Mo mineralization were unknown. The pre-Alpine Mo deposit and its host rocks were affected by four Alpine deformation events (D1-D4) and Young-Alpine regional metamorphism. The P-T conditions of this metamorphic event were ∼ 550 oC and ∼ 8 kbar and are in agreement with results of previous regional studies. Zircon grains from two orthogneiss samples were dated with the U-Pb method using ion probe techniques. Zircons from the metagranitic host rock of the Mo-veins yielded an emplacement age of 306.8 ± 3.8 Ma (2σ). A second sample from a more leucocratic gneiss lacking Mo-veins gave 305.0 ± 6.6 Ma (2 σ). Re-Os dating of molybdenite from the veins yielded an age of 306.8 ± 3.1 Ma in good agreement with the U-Pb zircon ages. This study confirms one of two alternative hypotheses discussed in the literature. lt supports the idea that vein-type Mo-mineralization in the western Tauern Window is genetically related to Late Carboniferous (Westphalian) granitoids that were emplaced during the late to post-orogenic stage of the Variscan orogeny. They do not constitute an Alpine metamorphic-hydrothermal deposit. This study further confirms the strength of the Re-Os molybdenite chronometer, in that it was unaffected

  2. Timing of post-collisional H-type to A-type granitic magmatism: U Pb titanite ages from the Alpine central Anatolian granitoids (Turkey)

    Science.gov (United States)

    Köksal, Serhat; Romer, Rolf L.; Göncüoglu, M. Cemal; Toksoy-Köksal, Fatma

    2004-12-01

    The last stages of the continental collision during the closure of the Neotethyan ocean in central Anatolia are characterized by post-collisional H- and A-type granitoids intruding both the metamorphic country rocks and allochthonous ophiolitic rocks of the central Anatolian crystalline complex. Available Rb Sr and K Ar whole-rock and mineral age data on the H- and A-type granitoids in central Anatolia are inconsistent. To better constrain the geological relevance and the timing of the change in the chemical character of magmatism in the wake of the Alpine orogeny in Anatolia, we re-evaluated the geochemical characteristics and dated titanite from representative H- (Baranadag quartz-monzonite: BR) and A-type (Çamsari quartz-syenite: CS) granitoids by the U Pb method. BR is a high-K calc-alkaline intrusion with mafic microgranular enclaves and shows enrichment of LILE relative to HFSE. The alkaline CS displays higher SiO2, Na2O+K2O, Fe/Mg, Rb, Th and HFSE with corresponding depletion in CaO, MgO, Fe2O3tot, P2O5, Ba, Sr, and Ti. Chondrite-normalized REE patterns of the BR and CS samples have LREE-enriched and flat HREE patterns, whereas CS differs from BR by higher LREE enrichment and lower MREE and HREE contents. Mineralogical and geochemical characteristics suggest that BR and CS were not products of the same magma source. BR was derived from a subduction-modified depleted hybrid-source and CS had an enriched mantle source with significant crustal contribution. The U Pb titanite ages of the H-type central Anatolian granitoids (BR) and the A-type granitoids (CS) are 74.0±2.8 and 74.1±0.7 Ma, respectively. The coeval evolution of post-collisional/calc-alkaline H- to A-type magmatism was possibly associated with source heterogeneity and variable involvement of continental materials during the evolution of these granitoids. These new age data constrain the timing of the onset of a post-collision extensional period following the Alpine thickening within the passive

  3. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    Léo A. Hartmann

    2003-09-01

    Full Text Available The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma and Camboriú Orogeny (~ 1989 Ma of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.O entendimento dos processos evolutivos do Complexo Encantadas no sul do Brasil foi aperfeiçoado através do estudo integrado do metamorfismo de um anfibolito ultramáfico e da geocronologia U-Pb SHRIMP de zircão. Os núcleos herdados de alguns cristais de zircão tem idades em torno de 2257 ±12 Ma e constituem a única evidência preservada do protólito ígneo, que pode ter sido um basalto magnesiano ou um piroxenito. O metamorfismo M de fácies anfibolito formou abundante hornblenda na amostra investigada, possivelmente há 1989 ±21 Ma. Esta rocha ultramáfica foi re-metamorfizada talvez há cerca de 702 ±21 Ma durante um evento M de fácies xistos verdes do metamorfismo regional. Durante o evento M, a hornblenda foi recristalizada e formou a assembléia actinolita + oligoclásio + microclínio + epidoto + titanita + monazita. Estes eventos foram a manifesta

  4. Geochemistry and U-Pb zircon geochronology of the pegmatites in Ede area, southwestern Nigeria: A newly discovered oldest Pan African rock in southwestern Nigeria

    Science.gov (United States)

    Adetunji, A.; Olarewaju, V. O.; Ocan, O. O.; Ganev, V. Y.; Macheva, L.

    2016-03-01

    Field and petrographic studies, whole rock geochemistry and in-situ LA-ICP-MS geochemical and isotopic U-Pb measurements on zircons have been performed on granitic pegmatites of Ede area, southwestern Nigeria with a view to characterize them, determining their mineralization potentials, petrogenetic attributes and emplacement age. The pegmatites are hosted by migmatite gneiss complex, biotite-muscovite schist and associated quartzite. The textural and mineralogical characteristics of these pegmatites indicate the occurrence of two main varieties, namely, muscovite pegmatite and garnet pegmatite. Of less importance are inclusions and pods of graphic granite, quartz-microcline aplitic and pegmatitic bodies. At the present level of erosion, the parent igneous rocks of the pegmatites are not exposed. The two dominant pegmatite varieties show slightly different chemical peculiarities but similar peraluminous character. The average K/Rb ratios of 165 and 163, respectively, for muscovite and garnet pegmatites combined with other trace element compositions are indicative of affinity to muscovite class of pegmatite which are generally not promising for rare elements mineralization. However, the unusually high concentration of bismuth in the zircons indicates Bi mineralization in the area which can either be in the pegmatites or host rocks. The Nb/Ta ratios for both muscovite and garnet pegmatites range from 0.7 to 15.2 and 1.0 to 14.8, respectively. These Nb/Ta ratios and Eu anomalies are statistically similar for both pegmatites. These probably indicate the pegmatites crystallized from a common source but separated into crystallization paths that produced different pegmatite varieties through liquid-liquid immiscibity mechanism. In-situ measurements of REE, P, Y, Nb, Hf, Ta, Bi, Th and U of individual zircon grains show the existence of two chemically and texturally different domains which are indicative of alteration that may be due to interface-coupled dissolution

  5. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia

    Science.gov (United States)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.

    2016-03-01

    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °C, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in the

  6. Evolution of the African continental crust as recorded by U-Pb, Lu-Hf and O isotopes in detrital zircons from modern rivers

    Science.gov (United States)

    Iizuka, Tsuyoshi; Campbell, Ian H.; Allen, Charlotte M.; Gill, James B.; Maruyama, Shigenori; Makoka, Frédéric

    2013-04-01

    To better understand the evolutionary history of the African continental crust, a combined U-Pb, Lu-Hf and O isotopic study has been carried out by in situ analyses of approximately 450 detrital zircon grains from the Niger, Nile, Congo, Zambezi and Orange Rivers. The U-Pb isotopic data show age peaks at ca. 2.7, 2.1-1.8, 1.2-1.0, ca. 0.8, 0.7-0.5 and ca. 0.3 Ga. These peaks, with the exception of the one at ca. 0.8 Ga, correspond with the assembly of supercontinents. Furthermore, the detrital zircons that crystallized during these periods of supercontinent assembly have dominantly non-mantle-like O and Hf isotopic signatures, in contrast to the ca. 0.8 Ga detrital zircons which have juvenile characteristics. These data can be interpreted as showing that continental collisions during supercontinent assembly resulted in supermountain building accompanied by remelting of older continental crust, which in turn led to significant erosion of young igneous rocks with non-mantle-like isotopic signatures. Alternatively, the data may indicate that the major mode of crustal development changed during the supercontinent cycle: the generation of juvenile crust in extensional settings was dominant during supercontinent fragmentation, whereas the stabilization of the generated crust via crustal accretion and reworking was important during supercontinent assembly. The Lu-Hf and O isotope systematics indicate that terreigneous sediments could attain elevated 18O/16O via prolonged sediment-sediment recycling over long crustal residence time, and also that reworking of carbonate and chert which generally have elevated 18O/16O and low Hf contents is minor in granitoid magmatism. The highest 18O/16O in detrital zircon abruptly increased at ca. 2.1 Ga and became nearly constant thereafter. This indicates that reworking of mature sediments increased abruptly at that time, probably as a result of a transition in the dynamics of either granitoid crust formation or sedimentary evolution

  7. U-Pb SHRIMP zircon dating of high-grade rocks from the Upper Allochthonous Terrane of Bragança and Morais Massifs (NE Portugal); geodynamic consequences

    Science.gov (United States)

    Mateus, A.; Munhá, J.; Ribeiro, A.; Tassinari, C. C. G.; Sato, K.; Pereira, E.; Santos, J. F.

    2016-04-01

    Bragança and Morais Massifs are part of the mega-klippen ensemble of NW Iberia, comprising a tectonic pile of four allochthonous units stacked above the Central-Iberian Zone autochthon. On top of this pile, the Upper Allochthonous Terrane (UAT) includes different high-grade metamorphic series whose age and geodynamic meaning are controversial. Mafic granulites provided U-Pb zircon ages at 399 ± 7 Ma, dating the Variscan emplacement of UAT. In contrast, U-Pb zircon ages of ky- and hb-eclogites, felsic/intermediate HP/HT-granulites and orthogneisses (ca. 500-480 Ma) are identical to those of gabbros (488 ± 10 Ma) and Grt-pyroxenites (495 ± 8 Ma) belonging to a mafic/ultramafic igneous suite that records upper mantle melting and mafic magma crustal underplating at these times. Gabbros intrude the high-grade units of UAT and did not underwent the HP metamorphic event experienced by eclogites and granulites. These features and the zircon dates resemblance among different lithologies, suggest that extensive age resetting of older events may have been correlative with the igneous suite emplacement/crystallisation. Accordingly, reconciliation of structural, petrological and geochronological evidence implies that the development and early deformation of UAT high-grade rocks should be ascribed to an orogenic cycle prior to ≈ 500 Ma. Undisputable dating of this cycle is impossible, but the sporadic vestiges of Cadomian ages cannot be disregarded. The ca. 500-480 Ma time-window harmonises well with the Lower Palaeozoic continental rifting that trace the Variscan Wilson Cycle onset and the Rheic Ocean opening. Subsequent preservation of the high heat-flow regime, possibly related to the Palaeotethys back-arc basin development (ca. 450-420 Ma), would explain the 461 ± 10 Ma age yielded by some zircon domains in felsic granulites, conceivably reflecting zircon dissolution/recrystallisation till Ordovician times, long before the Variscan paroxysm (ca. 400-390 Ma). This

  8. Intracratonic Palaeoproterozoic granitoids in northern Finland: prolonged and episodic crustal melting events revealed by Nd isotopes and U-Pb ages on zircon

    Directory of Open Access Journals (Sweden)

    Niina Ahtonen

    2007-01-01

    Full Text Available Zircons from twelve Palaeoproterozoic granitoids from the Central Lapland Granitoid Complex (CLGC and from the Hetta Complex (HC in northern Finland were dated using the NORDSIM ion microprobe. In addition, U-Pb age determinations on zircons from two samples were made using TIMS. Results reveal a wide range of U-Pb ages from 2.13Ga to 1.76 Ga. The oldest samples include the porphyritic, weakly deformed Nilipää granite, which has an ion probe concordia age of 2126±5 Ma, compatible with the previously published TIMS age of 2136±5 Ma. The Tohmo granodiorite provided a slightly younger ion microprobe age of 2105±4 Ma. The age of these two granitoids overlaps the depositional age of Karelian cratonic metasediments, suggesting that they represent an unusual tectonic setting for granitoid magmatism in the Fennoscandian Shield. The Ruoppapalo granodiorite, which is also porphyritic and weakly deformed, yielded an ion probe zircon concordia age of 1905±5 Ma, in accord with the conventional TIMS result. The strongly deformed Molkoköngäs granite has an ion probe concordia age of 1855±13 Ma, which is within error limits the same as the TIMS age, 1843±23 Ma. The Pernu monzogranite has a concordia age of 1813±6 Ma. All other granitoids in the CLGC, including those of appinitic affinity, as well as a leucosome from the Kappera migmatite in the Hetta Complex, are dated at 1.79 – 1.76 Ga, although many granitoids have older inherited zircons. The abundance of deformed granitoids of this age show that intensive ductile deformation, metamorphism and melting occurred at around 1.79 – 1.76 Ga in the northern Fennoscandian Shield, coeval with post-collisional magmatism in the southern part of the Shield. Most granitoids in the Central Lapland Granitoid Complex have strongly negative εNd values (1.8 Ga, ranging from -8 to -5. It is evident that they have a major Archaean component in their source, indicating derivation from Archaean crust during

  9. Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

    Science.gov (United States)

    Zeng, Renyu; Lai, Jianqing; Mao, Xiancheng; Li, Bin; Ju, Peijiao; Tao, Shilong

    2016-05-01

    Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and LaN/YbN from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (TZr) from 947 to 1072 °C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, LaN/YbN ratios from 27 to 32. These I-type intrusions have no Eu anomalies and TZr ranges from 818 to 845 °C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 ± 3.7 Ma and 361.7 ± 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative εHf(t) values (-11 ± 0.5 to -9 ± 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have εHf(t) values that range from -8 ± 1.0 to +10 ± 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at ∼444 Ma. Geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence

  10. Structural observations and U-Pb mineral ages from igneous rocks at the Archaean-Palaeoproterozoic boundary in the Salahmi Schist Belt, central Finland: constraints on tectonic evolution

    Directory of Open Access Journals (Sweden)

    Pietikäinen, K.

    1999-06-01

    Full Text Available The study area in Vieremä, central Finland, contains part of Archaean-Palaeoproterozoic boundary. In the east, the area comprises Archaean gneiss and the Salahmi Schist Belt. The rocks of the schist belt are turbiditic metagreywackes, with well-preserved depositional structures, occurring as Proterozoic wedge-shaped blocks, and staurolite schists, the latter representing higher-strained and metamorphosed equivalents of the metagreywackes. In the west of the area there is an Archaean gneiss block, containing strongly elongated structures, and deformed Svecofennian supracrustal rocks, which are cut by deformed granitoids. These are juxtaposed with the schist belt. The boundaries of these tectonometamorphic blocks are narrow, highly strained mylonites and thrust zones. The metamorphic grade of the supracrustal rocks increases from east to west, the increase being stepwise across the mylonitic block boundaries. The rocks are more deformed from east to west with younger structures overprinting. In the staurolite schists of the Salahmi Schist Belt, the most prominent structure is a lineation (L2 that overprints the bedding and axial plane foliation. In Sorronmäki quarry, at the western boundary of the schist belt, this Palaeoproterozoic lineation dominates all the structures in tonalite gneiss, which gives a U-Pb age of 2731±6 Ma. Southeast of the quarry, at the same boundary, the Salahmi schists have been overturned towards the northeast, suggesting that the Archaean gneiss at Sorronmäki has been thrust towards the northeast over these rocks. In the western part of the study area, the Leppikangas granodiorite that intrudes the Svecofennian supracrustal rocks gives a U-Pb age of 1891+6 Ma. In the granodiorite, a strong lineation formed by the intersection of two foliations, which maybe L2 is associated with thrusting towards the northeast. The monazite age of the Archaean Sorronmäki gneiss is 1817+3 Ma, and the titanite age of the Svecofennian

  11. Latest Carboniferous closure of the Junggar Ocean constrained by geochemical and zircon U-Pb-Hf isotopic data of granitic gneisses from the Central Tianshan block, NW China

    Science.gov (United States)

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.; Sun, Min; Han, Yigui; Hou, Wenzhu; Liu, Dongxing; Wang, Bo; Liu, Qian; Xu, Bing

    2015-12-01

    Once situated between the Central Tianshan and Junggar terranes during Paleozoic time, the Junggar Ocean was a major southern branch of the Paleo-Asian Ocean. Thus, when and how it was closed are essential in understanding the final assembly of the Central Asian Orogenic Belt. However, the exact closure time of the Junggar Ocean remains unresolved due to the lack of reliable timing of collision-related regional metamorphism. This paper reports whole-rock geochemical and zircon U-Pb and Lu-Hf isotopic data for granitic gneisses from the northern margin of the Central Tianshan block, which can provide crucial constraints on the final closure of the Junggar Ocean. Mineral assemblages and geochemical suggest that the protoliths of the Central Tianshan gneisses are weakly peraluminous high-K calc-alkaline I-type granites, possessing typical subduction-related features such as strong enrichment in LREE and LILE and depletion in HFSE. Negative Eu anomalies (δEu = 0.46-0.81) and highly variable zircon Hf isotope compositions indicate various amounts of residual plagioclase in the source and crustal contamination during magma formation. LA-ICPMS U-Pb dating on magmatic-type zircons (72%), characterized by euhedral to subhedral shapes, concentric oscillatory zoning, high Th/U ratios (0.30-2.05) and large ranges of εHf(t) values (- 3.4 to + 8.7; up to 6 epsilon units in each sample), yields consistent weighted mean 206Pb/238U ages of ca. 325-320 Ma, interpreted as the crystallization ages of the granitic protoliths. Geochemical signatures and dominantly positive zircon εHf(t) values reveal that the protoliths were emplaced in a continental arc setting, pinpointing the development of a late Early to early Late Carboniferous continental arc system on the northern margin of the Central Tianshan block, probably related to the southward subduction of the Junggar oceanic plate. Meanwhile, younger ages at ca. 303-301 Ma were obtained on recrystallized zircon-rims and unzoned

  12. Astronomy in Argentina

    OpenAIRE

    Muriel, Hernán

    2012-01-01

    This article analyses the current state of Astronomy in Argentina and describes its origins. We briefly describe the institutions where astronomical research takes place, the observational facilities available, the training of staff and professionals, and the role of the institutions in scientific promotion. We also discuss the outreach of Astronomy towards the general public, as well as amateur activities. The article ends with an analysis of the future prospects of astronomy in Argentina.

  13. Astronomy in Argentina

    CERN Document Server

    Muriel, Hernán

    2013-01-01

    This article analyses the current state of Astronomy in Argentina and describes its origins. We briefly describe the institutions where astronomical research takes place, the observational facilities available, the training of staff and professionals, and the role of the institutions in scientific promotion. We also discuss the outreach of Astronomy towards the general public, as well as amateur activities. The article ends with an analysis of the future prospects of astronomy in Argentina.

  14. SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications

    Institute of Scientific and Technical Information of China (English)

    XIE Guiqing; MAO Jingwen; LI Ruiling; ZHOU Shaodong; YE Huishou; YAN Quanren; ZHANG Zusong

    2006-01-01

    The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important volcanic basins in East China. Volcanic rocks in the Jinniu Basin are distributed mainly in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation, consisting of rhyolite, basalt and basaltic andesite, (trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively, in which the Dasi volcanism is volumetrically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indicate that there exist a large amount of magmatic zircons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128±1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios, this age is considered to represent the crystallization time of the Dasi volcanism. The volcanic rocks in the Dasi, Majiashan and Lingxiang Formations share similar trace element and REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geology, it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Cretaceous, just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also suggested for tectonic regime in this region in the Cretaceous Period.

  15. New material of microfossils from the Ediacaran Doushantuo Formation in the Zhangcunping area,Yichang, Hubei Province and its zircon SHRIMP U-Pb age

    Institute of Scientific and Technical Information of China (English)

    LIU PengJu; YIN ChongYu; GAO LinZhi; TANG Feng; CHEN ShouMing

    2009-01-01

    The Zhangcunping area is located at the north limb of the Huangling anticline in Yichang, Hubei Province. Here, the sedimentary succession of the Ediacaran Doushantuo Formation is similar with that in the Weng'an area, Guizhou Province. A large number of new microfossils (mainly acanthoacritarchs) from the Doushantuo Formation in this area are reported in this paper. The fossil assemblage shows similarity as the phosphatized biota of the Doushantuo Formation at Wang'an, Guizhou Province and the silicified biota of the Doushantuo Formation at the Yangtze Gorges, which suggests that the Zhangcunping area is a key for correlation of the Doushantuo Formation between the Weng'an area,Guizhou Province and the Yangtze Gorges. Besides, a new zircon SHRIMP U-Pb age (614.0±7.6 Ma) is first obtained from a horizon underneath the exposed surface in the middle of the Doushantuo Formation in the Zhangcunping area. This age not only provides a new datum for subdivision of the Ediacaran Doushantuo Formation, but also indicates that the age of the exposed surface in the middle of the Doushantuo Formation in the Yangtze Platform should be posterior to 614.0±7.6 Ma. Due to the horizon of the Weng'an biota situated above the exposed surface, the age of the Wang'an biota should be posterior to 614.0±7.6 Ma as well.

  16. Zircon U-Pb ages of olivine pyroxenite xenolith from Hannuoba:Links between the 97-158 Ma basaltic under-plating and granulite-facies metamorphism

    Institute of Scientific and Technical Information of China (English)

    LIU Yongsheng; YUAN Honglin; GAO Shan; HU Zhaochu; WANG Xuance; LIU Xiaoming; LIN Wenli

    2004-01-01

    U-Pb zircon dating by LA-ICP-MS and SHRIMP for one olivine pyroxenite yields complex age populations including Mesozoic ages of 97-158 Ma and 228 ±8.7 Ma, Early Paleozoic ages of 418-427 Ma, Paleoproterozoic age of 1844±13 Ma, Neoarchean age of 2541 ± 54 Ma and middle Archean age of 3123 ± 4.4 Ma. The 97-158 Ma and 228 ± 8.7 Ma zircons show typical igneous oscillatory zonation in CL images, suggesting two episodes of magmatic events. Overlapping of the 97-158 Ma ages with that of granulite xenoliths indicates that the Mesozoic granulite-facies metamorphism was induced by heating from the basaltic underplating at the base of the lower crust. Both processes lasted at least from about 158 to 97 Ma. Ages of 418-427 Ma could be records of the subduction of Mongolia oceanic crust under the North China craton. Ages of 1.84 Ga,2.54 Ga and 3.12 Ga correspond to the three important crust-mantle evolutionary events in the North China craton,and imply preservation of Precambrian lower crust in the present-day lower crust.

  17. Archean crustal growth of the Imataca complex, Amazonian craton: Evidence from U-Pb-Sm-Nd and Rb-Sr geochronology

    International Nuclear Information System (INIS)

    The Archean Imataca Complex (IC), NW Amazonian Craton, forms a ENE-trending, fault-bounded block adjacent to the Paleoproterozoic Maroni-Itacai as magmatic arc (2.2 2.0 Ga) (Tassinari and Macambira, 1999). The IC rocks are complexely deformed, exhibiting elongated and symmetrical domes and thrusts combined with isoclinal folds. Transcurrent faults are also important, like the Guri Fault System - a zone of multiple faulting, shearing and mylonitization along the southeastern edge of the IC. In a pre-Pangean reconstruction using paleomagnetic data from rocks of the African counterpart, the Guri System is contiguous to the Sassandra (Ivory coast) and Zednes (Mauritaine) faults, in agreement also with the comparable geologic evolution between the NW Amazonian and the West Africa cratons, during the Archean and Late-Paleoproterozoic. The IC mainly composed of medium- to high grade quartz-feldspathic paragneiss, exhibits extensive mortar, augen, flaser and mylonitic textures. Calc-alkaline gneiss and granitoid rocks of igneous protolith are also present in the IC, as well as dolomitic marbles, orthopyroxene and magnetite quartzites, and BIFs that include huge ore deposits of Algoma type. Moreover, migmatite injections and anatexis (devoid of metasedimentary components) are widespread in the western part of Complex, the largest migmatite mass centered in Cerro La Ceiba. This paper reports zircon U-Pb SHRIMP, Sm-Nd and Rb-Sr isotopic data of different IC rocks in order to investigate their age and geological evolution within the tectonic framework of the Amazonian Craton (au)

  18. Zircon U-Pb and molybdenite Re-Os geochronology, and whole-rock geochemistry of the Hashitu molybdenum deposit and host granitoids, Inner Mongolia, NE China

    Science.gov (United States)

    Zhai, Degao; Liu, Jiajun; Wang, Jianping; Yang, Yongqiang; Zhang, Hongyu; Wang, Xilong; Zhang, Qibin; Wang, Gongwen; Liu, Zhenjiang

    2014-01-01

    The Hashitu deposit is a newly-discovered Mo deposit in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization occurs as quartz-sulfide veins within the Hashitu granite-porphyry composite pluton. The sulfide assemblage in the veins is dominated by molybdenite, with minor amounts of galena, sphalerite, chalcopyrite, pyrite and marcasite. The associated gangue minerals are quartz, fluorite, calcite, sericite, chlorite and epidote. Whole-rock chemical compositions show that the Hashitu granites belong to the A2-type. The U-Pb ages of zircons from the Hashitu granite and porphyry units are 147 ± 1 Ma and 143 ± 2 Ma, respectively. The Re-Os isochron age of molybdenites from the deposit is 150 ± 4 Ma. The molybdenite Re-Os model ages vary from 144 to 150 Ma, with a weighted mean of 147 ± 1 Ma. The results show that the ages of zircon crystallization and Mo mineralization are similar, mostly within analytical uncertainties, and that the host granite pluton is one of many late-Jurassic plutons in the Great Hinggan Range. The formation of the late-Jurassic granitic plutons in this region coincides with the subduction of the Pacific plate beneath the North China block which took place ˜2000 km to the east at the time. The occurrence of abundant late-Jurassic granitoids with compositions similar to the Hashitu pluton in the Great Hinggan Range is a positive sign for more discoveries of Mo deposits in this region.

  19. High-pressure granulite from Western Kunlun,northwestern China:Its metamorphic evolution,zircon SHRIMP U-Pb ages and tectonic implication

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were ob-tained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic con-dition of these high-pressure granulites is about 760―820℃,1.0―1.2 GPa and the retrograde meta-morphic condition is about 620―720℃,0.7―0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T path which suggests that the Western Kunlun underwent initial crustal thickening,subsequent exhumation and cooling. The SHRIMP zircon U-Pb dating gives two groups of ages for high-pressure granulites. One is 177±6 Ma which is obtained from the rim of the zircon. We consider this age should be the metamorphic age. And the other is 456±30 Ma which is obtained from the core of the zircon and should be the protolith age. The formation of these high-pressure granulites in western Kunlun is closely correlated with the evolution of the Paleo-Tethys and has important im-plications for the research on Tethys and Paleo-Asian tectonic zone.

  20. Amplifying Earth history: Zircon U-Pb geochronology by ID-TIMS at the 0.1 ‰ level using new 1013 ohm resistors

    Science.gov (United States)

    Wotzlaw, Jörn-Frederik; von Quadt, Albrecht

    2016-04-01

    Precise and accurate radiometric dating of volcanic ash beds in sedimentary successions is the backbone of the numerical calibration of Earth history. Uranium-lead geochronology by isotope dilution thermal ionization mass spectrometry (ID-TIMS) is the most precise and accurate dating technique and is applicable to most of Earth history from the Hadean to the Pleistocene. The accessory mineral zircon is the prime target material due to its commonly high U concentration, virtually no initial Pb and high daughter-product retentivity. However, complex crystallization histories as well as magmatic and sedimentary recycling of zircons require the analysis of single crystals resulting in small amounts of radiogenic Pb (Pb* usually dates with uncertainties <0.2 ‰ for high-Pb* zircons and weighted mean ages for populations of closed system zircons with uncertainties <0.1 ‰ . This level of temporal resolution will allow to better quantify the timing and durations of critical intervals in Earth history, evaluate causalities between different events such as flood basalt eruptions and mass extinctions, quantify rates of changes in biodiversity and assess the origin of cyclic patterns in the sedimentary records. [1] von Quadt, A., Wotzlaw, J.F., Buret, Y., Large, S., Peytcheva, I., Trinquier, A., 2016, High-precision zircon U/Pb geochronology by ID-TIMS using new 1013 ohm resistors. J. Anal. At. Spectrom., DOI: 10.1039/C5JA00457H

  1. The LA-ICP-MS zircons U-Pb ages and geochemistry of the Baihua basic igneous complexes in Tianshui area of West Qinling

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Baihua meta-igneous complex consists mainly of pyroxenite-gabbro(diorite)-diorite-quartz diorite. They form a complete comagmatic evolutionary series. The geochemical characteristics of basic-interme- diate basic igneous rocks indicate that they belong to a tholeiite suite. The REE distribution pattern is nearly flat type and LREE is slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider diagrams are generally similar; the LIL elements (LILE) Cs, Ba, Sr, Th and U are enriched, but Rb, K and the HFSEs Nb, P, Zr, Sm, Ti and Y are relatively depleted. All these show comagmatic evolution and origin characteristics. The tectonics environment discrimination of trace element reveals that these igneous complexes formed in an island-arc setting. The LA-ICP-MS single-zircons U-Pb age of Baihua basic igneous complex is 434.6±1.5 Ma (MSWD = 1.3), which proves that the formation time of the island-arc type magmatite in the northern zone of West Qinling is Late Ordovician or Early Silurian, also reveals that the timing of subduction of paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activities is probably Middle-Late Ordovician to Early Silurian.

  2. Geochemical characteristics and zircon U-Pb isotopic ages of island-arc basic igneous complexes from the Tianshui area in West Qinling

    Institute of Scientific and Technical Information of China (English)

    PEI Xianzhi; LI Zuochen; LIU Huibin; LI Gaoyang; DING Saping; LI Yong; HU Bo; GUO Junfeng

    2007-01-01

    The Liushuigou intermediate-basic meta-igneous complex at Guanzizhen, Tianshui area, is mainly composed of metagabbro, metagabbro diorite and metadiorite, while the Baihua basic meta-igneous complex consists mainly of pyroxenite, gabbro (gabbro diorite), diorite and quartz diorite.They form a relatively complete comagmatic evolutionary series. The geochemical characteristics of intermediate-basic igneous rocks indicate that they belong to a tholeiite suite.Their chondrite-normalized REE patterns are nearly flat and are LREE-slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider-grams are generally similar; the LILEs Cs, Ba, Sr, Th and U are enriched, while Rb and K and the HFSEs Nb, P, Zr,Sm, Ti and Y are depleted. All these show comagmatic evolu-tionary and genetic characteristics. The tectonic environment discrimination by trace element reveals that these igneous complexes formed in an island-arc setting. The Thermal Ionization Mass Spectrometry (TIMS) single-grain zircon U-Pb age for the Liushuigou intermediate-basic meta-igneous rocks in the Guanzizhen area is (507.5 ± 3.0) Ma, represent-ing the age of these igneous complexes, which indicates that island-arc-type magmatite rocks in the northern zone of West Qinling are Late Cambrian and also reveals that the timing of subduction of the paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magrnaticactivity are probably Late Cambrian to Early Ordovician.

  3. Zircon LA-ICP MS U-Pb Dating of the Longkang Andesitic Ignimbrites from Jiuzhaigou: Evidence of the Mianlue Suture Westward Extension

    Institute of Scientific and Technical Information of China (English)

    Qin Jiangfeng; Lai Shaocong; Zhang Guowei; Diwu Chunrong; Li Yongfei

    2008-01-01

    Genesis of metasedimentary-volcanics outcroped in Kangxian-Pipasi-Nanping (康县-琵琶寺-南坪) tectonic zone is closely related with tectonic evolution of the Mianlue (勉略) Ocean. In the west end of Kangxian-Pipasi-Nanping tectonic zone, there are hundred meters of andesitic ignimbrites and tuffites. Zircon U-Ph dating on these volcanies has great significance to the tectonic implication of zircons from Longkang andesitic ignimbrites are magmatic genesis with oscillatory zoning and high U ((35-750) ppm), Th ((311-717) ppm) contents with high Th/U (0.44-1.30) ratios. The measured 206pb/238U ratios are in good analytical precision, yielding a weighted mean age of (246±3) Ma (MSWD=2.6, n=12, 2σ). Some detrital zircons have also been observed, they have maximal concordia area. Combined with regional geology and the volcanic rocks in the studied area, the (246±3) Ma zircon U-Pb age suggests a Late Permian orogenic volcanism and provides important geochronology evidence for the Mianlue suture westward extension.

  4. The Early Jurassic magmatism in northern Guangdong Province, southeastern China: Constraints from SHRIMP zircon U-Pb dating of Xialan complex

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    This paper reports SHRIMP zircon U-Pb ages of 196±2 Ma for granite, and 195±1 Ma for gabbro from the Xialan complex in the Meizhou area, northern Guangdong Province. These results shed new light on the calm stage of magmatic activity in southeastern China during 200-180 Ma, and revealed that the back-arc extension induced by the subduction of the western Pacific plate may have begun at 195 Ma at least. Field observation on the fresh outcrops allows us to recognize some features formed by magma mixing. A part of the gabbro has a fine-grained rim of 20-30 cm at the margin, and thins gradually to-ward the granite; numerous dark fine-grained to microcrystalline dioritic enclaves developed in the granite. These enclaves vary in shape and size, dark minerals concentrated at the margin of enclaves, and the contact between enclaves and host rock is either obvious or obscure, or gradational. In addi-tion, needle-shaped apatites are included in the enclaves. The REE patterns of gabbros, as well as the trace element patterns, are generally consistent with those of granitic rocks. The above characters further suggest that in the Early Jurassic the injection of basic magma had melted deep continental crust and produced acidic magma, and the Xialan complex was produced by the mixing of them.

  5. The Early Jurassic magmatism in northern Guangdong Province, southeastern China: Constraints from SHRIMP zircon U-Pb dating of Xialan complex

    Institute of Scientific and Technical Information of China (English)

    YU XinQi; DI YongJun; WU GanGuo; ZHANG Da; ZHENG Yong; DAI YanPei

    2009-01-01

    This paper reports SHRIMP zircon U-Pb ages of 196+9 Ma for granite, and 195~1 Ma for gabbro from the Xialan complex in the Meizhou area, northern Guangdong Province. These results shed new light on the calm stage of magmatic activity in southeastern China during 200--180 Ma, and revealed that the back-arc extension induced by the subduction of the western Pacific plate 05 have begun at 195 Ma at least. Field observation on the fresh outcrops allows us to recognize some features formed by magma mixing. A part of the gabbro has a fine-grained rim of 20-30 cm at the margin, and thins gradually to-ward the granite; numerous dark fine-grained to microorystalline dioritic enclaves developed in the granite. These enclaves vary in shape and size, dark minerals concentrated at the margin of enclaves, and the contact between enclaves and host rock is either obvious or obscure, or gradational. In addi-tion, needle-shaped apatites are included in the enclaves. The REE patterns of gabbros, as well as the trace element patterns, are generally consistent with those of granitic rocks. The above characters further suggest that in the Early Jurassic the injection of basic magma had melted deep continental crust and produced acidic magma, and the Xialan complex was produced by the mixing of them.

  6. SHRIMP zircon U-Pb dating from K-bentonite in the top of Ordovician of Wangjiawan Section,Yichang,Hubei,China

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The Global boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the latest stage of the Ordovician System) is defined at a point 0.39m below the base of the Kuanyinchiao Bed in the Wangjiawan North Section, which is the upper most "golden spike" of the Ordovician. However, this "golden spike" is lack of reliable geochronology data. This article gives a sensitive high resolution ion microprobe (SHRIMPII) zircon U-Pb dating for a K-bentonite sample from the Kuany-inchiao Bed in the Wangjiawan North Section. The age of the K-bentonite sample is 443.2±1.6 Ma, that is to say, the isotopic age of the uppermost of Hirnantian Stage, the point of Ordovician-Silurian boundary, should be near to, but slightly younger than 443.2±1.6 Ma. This age is identical to the Ordovi-cian-Silurian boundary age 443.7±1.5 Ma as declared by International Commission on Stratigraphy (ICS). So, this research provides some good geochronlogical data for the Hirnantian Stage and the Ordovician-Silurian boundary as well as the global correlation.

  7. Monazite-(Ce in Hercynian granites and pegmatites of the Bratislava massif, Western Carpathians: compositional variations and Th-U-Pb electron-microprobe dating

    Directory of Open Access Journals (Sweden)

    Pavel Uher

    2014-12-01

    Full Text Available Monazite-(Ce represents a characteristic magmatic accessory mineral of the Hercynian peraluminous S-type granites to granodiorites and related granitic pegmatites of the Bratislava Granitic Massif (BGM, Malé Karpaty Mountains, Central Western Carpathians, SW Slovakia. Monazite forms euhedral to subhedral crystals, up to 200 μm in size, usually it is unzoned in BSE, rarely it reveals oscillatory or sector zoning. Thorium concentrations of 2 to 9 wt. % ThO2 (≤0.09 apfu and local elevated uranium contents (≤4.3 wt. % UO2, ≤0.04 apfu are characteristic for the pegmatite monazites. Both huttonite ThSiREE-1P-1 and cheralite Ca(Th,UREE-2 substitutions took place in the studied monazite. Electron-microprobe Th-U-Pb monazite dating of the granites and pegmatites gave an isochron age of 353±2 Ma (MSWD = 0.88, n = 290, which confirmed the meso-Hercynian, Carboniferous, Lower Mississipian magmatic crystallization. An analogous age (359±11 Ma was obtained from monazite from adjacent paragneiss, corresponding to the age of the Hercynian contact thermal metamorphism related to the granite intrusion of BGM. Monazite in some granite shows also older clastic or authigenic grains or zones (~505 to 400 Ma, with maximum of 420±7 Ma which probably represents inherited material from the Lower Paleozoic metapelitic to metapsammitic protolith of BGM.

  8. U-Pb geochronology and paleomagnetism of the Neoproterozoic St Simeon dolerite dykes, Quebec: an eastern Laurentian perspective of Ediacaran Rodinia breakup

    Science.gov (United States)

    Pisarevsky, Sergei; Murphy, Brendan; Hamilton, Mike; Söderlund, Ulf; Hodych, Joseph

    2013-04-01

    The St Simeon (SS) mafic dykes (150 km NE of Quebec City) are now dated at 548 ± 1 Ma (U-Pb; baddeleyite). This age is similar to a published LA-ICPMS zircon age of 550 ± 7 Ma for the Mt. St-Anselme (MS) basalts, which supports previous inferences of (i) a genetic relationship between them, (ii) the pene-contemporaneity of OIB-type mafic magmatism in East Laurentia and (iii) the existence of two late Ediacaran plumes that attended the final breakup of Rodinia and opening of the Iapetus Ocean and Tornquist Sea. Both the SS dykes and the MS basalts were sampled for paleomagnetic study. The paleomagnetic pole for SS is similar to the previously published pole for coeval basalts (Skinner Cove, SC) from Newfoundland. Unlike SC, the St Simeon pole represents rocks which are unambiguously coherent tectonically with the Laurentian Craton. This new pole is also coeval with high quality poles from the Winter Coast (Baltica) and provides paleomagnetic constraints on the history of the final breakup of Rodinia and opening of Eastern Iapetus and Tornquist Sea.

  9. In-situ U-Pb and Hf-isotopic characterization of the GJ-1 Zircon by Laser Ablation-ICPMS and MC-ICPMS

    International Nuclear Information System (INIS)

    Here we report new data from in-situ U-Pb and Hf-isotopic characterization of GJ-1 zircon standard distributed by GEMOC (ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents, Macquarie University, Australia). The study is undertaken to establish the analytical protocols for the in-situ chemical and isotopic analysis of zircons using New Wave Research UP 213nm Laser Ablation Microprobe (LAM), Thermo X SeriesII Inductively Coupled Plasma Mass Spectrometer (ICPMS) and Nu Plasma HR Multi-Collector ICPMS (MC-ICPMS) and also to constrain the GJ-1 zircon as a potential reference material. The GJ-1 reference zircon grains are several ∼1 cm sized crystals from African pegmatites with an apparent crystallization age of 608.5 ± 0.4 Ma2. GJ-1 is considered to be devoid of any banding and visible zoning and is homogeneous. Combined Back Scattered Electron (BSE) and Cathedoluminiscence (CL) images of the GJ-1 grains analysed by us also indicate their homogeneity

  10. U-Pb SHRIMP and 40Ar/39Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, Sao Luis cratonic fragment, Brazil

    International Nuclear Information System (INIS)

    Caxias is an orogenic gold deposit in the Sao Luis cratonic fragment, which is correlated with the Rhyacian terranes of the West-African Craton. The deposit postdates peak metamorphism (estimated at 2100 ± 15 Ma) and is hosted in a shear zone that cuts across schists of the Aurizona Group (2240 ± 5 Ma) and the Caxias Microtonalite. The emplacement age of the microtonalite, as determined in this work by SHRIMP U-Pb zircon dating, is 2009 ± 11 Ma and represents a latest age magmatic event in the Sao Luis cratonic fragment. Older zircon age of 2139 ± 10 Ma is interpreted as due to inheritance from the older granitoid or volcanic suites (magmatic sources?) or to contamination during emplacement. Lead isotope compositions indicate that the Pb incorporated in ore-related pyrite was probably sourced from regional, orogenic calc-alkaline granitoids of ca. 2160 Ma. Hydrothermal sericite from Caxias yielded a 40Ar/39Ar plateau age of 1990 ± 30 Ma, which combined with the emplacement age of the Caxias Microtonalite brackets the age of gold mineralization between 2009 ± 11 and 1990 ± 30 Ma. (author)

  11. The metamorphic sole of New Caledonia ophiolite: 40Ar/39Ar, U-Pb, and geochemical evidence for subduction inception at a spreading ridge

    Science.gov (United States)

    Cluzel, Dominique; Jourdan, Fred; Meffre, SéBastien; Maurizot, Pierre; Lesimple, StéPhane

    2012-06-01

    Amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of New Caledonia (termed Peridotite Nappe) recrystallized in the high-temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the Eocene metamorphic complex. Amphibolites mostly display the geochemical features of MORB with a slight Nb depletion and thus are similar to the youngest (Late Paleocene-Eocene) BABB components of the allochthonous Poya Terrane. Thermochronological data from hornblende (40Ar/39Ar), zircon, and sphene (U-Pb) suggest that these mafic rocks recrystallized at ˜56 Ma. Using various geothermobarometers provides a rough estimate of peak recrystallization conditions of ˜0.5 GPa at ˜800-950°C. The thermal gradient inferred from the metamorphic assemblage (˜60°C km-1), geometrical relationships, and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction/obduction system and recrystallized when they subducted below young and hot oceanic lithosphere. They were detached from the down-going plate and finally thrust onto unmetamorphosed Poya Terrane basalts. This and the occurrence of slab melts at ˜53 Ma suggest that subduction inception occurred at or near to the spreading ridge of the South Loyalty Basin at ˜56 Ma.

  12. First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation: insights on Late Cretaceous marine deposition in central Chile

    International Nuclear Information System (INIS)

    Upper Cretaceous marine rocks crop out along the Pacific coast of central and south-central Chile between 33o and 37oS. These strata constitute an important reference for the Upper Cretaceous of South America due to their diverse fossil fauna and flora. The type unit of these deposits is the Quiriquina Formation, near Concepcion. This unit is considered Maastrichtian in age based on ammonites. Upper Cretaceous marine strata from other localities of central and south-central Chile are largely unstudied and their biostratigraphic ages are not precisely known. We present the first radiometric dating (U-Pb on detrital zircons) for Upper Cretaceous marine strata of the Chilean forearc at Punta Topocalma that indicates a probable depositional age of 71.9+0.9 Ma (latest Campanian-earliest Maastrichtian). Provenance analysis indicates that the source of sediments of the Punta Topocalma Formation was plutonic and volcano-sedimentary rocks from the Coastal Cordillera and the Central Depression of central Chile. The Lo Valle Formation, a volcano-sedimentary unit in the Central Depression, recorded deposition of the Upper Cretaceous volcanic arc that was coeval with marine sedimentation in the Topocalma area

  13. Provenance and depositional age of the neoproterozoic volcanometasedimentary sequence in the Santa Terezinha region, Goias based on U-Pb single zircon and Sm-Nd isotope data

    International Nuclear Information System (INIS)

    Some of the volcano-sedimentary sequences of the Tocantins Province have been considered to be formed during the evolution of a Neoproterozoic intra oceanic island arc system (Pimentel et al., 2000). However, the interpretation of supra crustal rocks of some areas of the central portions of the Goias Massif, such as the region of Santa Terezinha de Goias, is still controversial. These rocks have been considered either as part of the Archean greenstone belts or as Paleoproterozoic sequences (Ribeiro Filho 1981, Souza and Le Neto 1981, Machado et al.1981, Ribeiro Filho and Lacerda Filho 1985, Biondi and Pidevin 1994, Arantes et al. 1991) rather than an extension of the Neoproterozoic Mara Rosa magmatic arc (Viana et al.1995, Pimentel et al. 1997). An area of about 800 km2 near the town of Santa Terezinha de Goias was recently mapped on a 1:25.000 scale (Jost et al. 2001). Its northern part consists of Proterozoic supra crustal rocks in tectonic contact with Archean rocks in the south. We present new Sm-Nd and U-Pb zircon data for the supra crustal rocks that crop out in the northern part of the area and discuss their provenance and depositional age (au)

  14. New Sakmarian ages for the Rio Bonito formation (Paraná Basin, southern Brazil) based on LA-ICP-MS U-Pb radiometric dating of zircons crystals

    Science.gov (United States)

    Cagliari, Joice; Lavina, Ernesto Luiz Correa; Philipp, Ruy Paulo; Tognoli, Francisco Manoel Wohnrath; Basei, Miguel Angelo Stipp; Faccini, Ubiratan Ferrucio

    2014-12-01

    Two ash fall beds (tonstein) sampled from the post-glacial Permian deposits of the Paraná Basin have provided new U-Pb radiometric age constraints for this stratigraphic interval. The zircon grains were recovered from tonstein layers interbedded with fine-grained and carbonaceous lithologies in the middle portion of the Rio Bonito Formation. In both samples, the dominant population is interpreted as generated by explosive volcanism, as having formed immediately before the eruption. Based on 238U/206Pb, the selected zircon grains from the dominant population have weighted mean ages of 290.6 ± 2.8 Ma and 281.7 ± 3.2 Ma, corresponding to the Sakmarian and Kungurian ages in the Cisuralian epoch, respectively. These ages constrain the time of the deposition of the tonstein horizons and have important stratigraphic implications for the Late Paleozoic evolution of both the Paraná Basin and the southwestern region of Gondwana. The results presented here and the radiometric data already published suggest that deposition of the post-glacial coal-bearing deposits of the Rio Bonito Formation was probably initiated before the Early Permian. Thus, we infer that the climate had already ameliorated by this period in order to allow for the formation and accumulation of peat in this region of Gondwana.

  15. U-Pb zircon ages of syenitic and granitic rocks in the Ashizuri igneous complex, southwestern Shikoku. Constraint for the origin of forearc alkaline magmatism

    International Nuclear Information System (INIS)

    We report two first U-Pb zircon ages of the felsic rocks in the Ashizuri igneous complex, southwestern Shikoku, using the LA-ICP-MS. Samples are a syenite (ASH54) and a biotite granite (ASH5). Weighted means of the 238U-206Pb ages of concordant data of ASH54 and ASH5 are 13.12±0.09 Ma (2σ) and 12.95±0.06 Ma (2σ), respectively. It is concluded that the felsic member of the Ashizuri complex was formed almost simultaneously at ca. 13 Ma after the major activity of the Outer Zone Granitic Rocks. Presence of alkali dolerite dike cutting the syenite indicates that the alkali basaltic magma intruded after the subduction of Shikoku Basin of the Philippine Sea plate beneath the southwest Japan arc. Alkali basaltic magma of Ashizuri complex may have been derived from a depth possibly deeper than that of subducted Shikoku Basin of the Philippine Sea Plate. (author)

  16. Extended history of a 3.5 Ga trondhjemitic gneiss, Wyoming Province, USA: Evidence from U-Pb systematics in zircon

    Science.gov (United States)

    Mueller, P.A.; Wooden, J.L.; Mogk, D.W.; Nutman, A.P.; Williams, I.S.

    1996-01-01

    The Beartooth-Bighorn magmatic zone (BBMZ) and the Montana metasedimentary province (MMP) are two major subprovinces of the Archean Wyoming province. In the northwestern Beartooth Mountains, these subprovinces are separated by a structurally, lithologically and metamorphically complex assemblage of lithotectonic units that include: (1) a strongly deformed complex of trondhjemitic gneiss and interlayered amphibolites; and (2) an amphibolite facies mafic unit that occurs in a nappe that structurally overlies the gneiss complex. Zircons from a trondhjemitic blastomylonite in the gneiss complex yield concordant U-Pb ages of 3.5 Ga, establishing it as the oldest rock yet documented in the Wyoming province. Two younger events are also recorded by zircons in this rock: (1) an apparently protracted period of high-grade metamorphism and/or intrusion of additional magmas at ??? 3.25 Ga; and (2) growth of hydrothermal zircon at ??? 2.55 Ga, apparently associated with ductile deformation that immediately preceded structural emplacement of the gneiss. Although this latter event appears confined to areas along the BBMZ-MMP boundary, evidence of ??? 3.25 Ga igneous activity is found in the overlying amphibolite (3.24 Ga) and throughout the MMP. These data suggest that this boundary first developed as a major intracratonic zone of displacement at or before 3.25 Ga. The limited occurrences of 2.8 Ga magmatic activity in the MMP suggest that it had a controlling influence on late Archean magmatism as well.

  17. Sociedad del aprendizaje y tercera edad

    Directory of Open Access Journals (Sweden)

    Agustín REQUEJO OSORIO

    2009-11-01

    Full Text Available RESUMEN: Desde hace tiempo se vienen analizando los fenómenos que acontecen en la denominada «sociedad cognitiva». Particularmente en Europa el tema cobra mayor interés a partir de la publicación: «Enseñary aprender: hacia la sociedad cognitiva».El presente artículo tiene como objetivo básico exponer los rasgos más importantes y las demandas de esta sociedad en relación con el grupo de personas cada vez más numeroso: las personas mayores o también denominadas de la «Tercera Edad».En este contexto se estudian las relaciones entre sociedad cognitiva y fenómeno demográfico que nos muestran un número cada vez más importante de personas mayores. Junto a este hecho sociológico se debate el problema de su formación a partir de los presupuestos de una educación permanente de carácter humanista y democrático frente a la visión neoliberal centrada en la propuesta unilateral del capital humano.Desde esta propuesta educativa se comentan los diversos programas que hoy existen para los mayores haciendo tanto un breve recorrido histórico de las distintas ofertas como un estudio de las más actuales que se realizan por parte de las universidades: universidades de la Tercera Edad, universidades de la Experiencia, «Cuartos Ciclos» universitarios para personas mayores.ABSTRACT: Analysis of the phenomena which occur in the so-called «cognitive society» has been going for a long time in education. Particulary in Europe, the issue of the «cognitive society» has gained interest since the publication of «Enseñar y aprender: hacia la sociedad cognitiva (Teaching and Learning: Aiming at the Cognitivy Society.The main purpose of this paper is to show the most relevant features and demands of this kind of society in relation to a group of people that is steadily growing in number: senior citizens (also named as the «Third Age».Within this context, we having studied the relations between the cognitive society and the demography, it can

  18. Plan de negocios Centro Cultural Edad de Oro

    OpenAIRE

    Cortés González, Zoraya; López Torres, Diana Cecilia

    2013-01-01

    Presenta el plan de negocios para crear la empresa “Centro Cultural Edad de Oro” y la viabilidad de la misma; todo esto mediante la prestación de un servicio que tiene como fin aportar a la calidad de vida de la población de personas que forman parte de la tercera edad; en pro de su bienestar, cuidado e integración; impulsando el protagonismo social

  19. Helosis (Balanophoraceae en Argentina Helosis (Balanophoraceae in Argentina

    Directory of Open Access Journals (Sweden)

    José Luis Fontana

    2006-07-01

    Full Text Available Se cita por primera vez para Argentina Helosis cayennensis (Swartz Sprengel var. cayennensis en base a colecciones hechas por los autores en la Isla argentina de Apipé Grande, Ituzaingó, provincia de Corrientes. Se describe e ilustra la especie, el desarrollo de la planta y su estado de conservación. Esta cita de Helosis corresponde a un género nuevo para la flora argentina.Helosis cayennensis var. cayennensis is reported for the first time for Argentina. The species is described and ilustrated. Developement and ecology are also given. Helosis is also a new generic record for Argentina.

  20. A combined study of SHRIMP U-Pb dating, trace element and mineral inclusions on high-pressure metamorphic overgrowth zircon in eclogite from Qinglongshan in the Sulu terrane

    Institute of Scientific and Technical Information of China (English)

    LI Qiuli; LI Shuguang; HOU Zhenhui1; HONG Jian; YANG Wei1

    2005-01-01

    Methods recently advanced for discrimination on the genesis of metamorphic zircon, such as analysis of mineral inclusions and trace elements, provide us powerful means to distinguish zircon overgrowth during high-pressure metamorphism. Zircons in ultrahigh-pressure eclogite from Qinglongshan in the Sulu terrane were studied by the SHRIMP U-Pb method in combining with trace element and mineral inclusion analyses. No inherited core was identified in the analyzed zircons by means of cathodoluminescence images. The occurrence of high-pressure metamorphic mineral inclusions in zircon, such as garnet, omphacite, rutile, and the flat HREE pattern in zircon indicate that the zircon formed at high-pressure metamorphic conditions. Therefore, a weighted average U-Pb age of 227.4 ± 3.5 Ma obtained from such a kind of zircon is interpreted to represent the timing of peak metamorphism for the Qinglongshan eclogite.

  1. Mortalidad por causa externas: un problema de salud pública. Argentina, Chile y Colombia. 2000-2008

    OpenAIRE

    Doris Cardona Arango; Gabriel Escanés; María Alejandra Fantín; Enrique Peláez

    2013-01-01

    Se realizó un estudio descriptivo de la mortalidad por causas externas en la población argentina, chilena y colombiana durante el período 2000-2008. Se analizaron las muertes por homicidios, suicidios y accidentes de tránsito, en función de la edad y sexo. Se observó una reducción del riesgo de morir por estas causas en el segundo trienio. Hubo diferencias en la mortalidad por sexo y edad dependiendo la causa externa de muerte. Los mayores niveles de mortalidad correspondieron a los homicidio...

  2. Evidence for prolonged mid-Paleozoic plutonism and ages of crustal sources in east-central Alaska from SHRIMP U-Pb dating of syn-magmatic, inherited, and detrital zircon

    Science.gov (United States)

    Dusel-Bacon, C.; Williams, I.S.

    2009-01-01

    Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of igneous zircons from the Lake George assemblage in the eastern Yukon-Tanana Upland (Tanacross quadrangle) indicate both Late Devonian (???370 Ma) and Early Mississippian (???350 Ma) magmatic pulses. The zircons occur in four textural variants of granitic orthogneiss from a large area of muscovite-biotite augen gneiss. Granitic orthogneiss from the nearby Fiftymile batholith, which straddles the Alaska-Yukon border, yielded a similar range in zircon U-Pb ages, suggesting that both the Fiftymile batholith and the Tanacross orthogneiss body consist of multiple intrusions. We interpret the overall tectonic setting for the Late Devonian and Early Mississippian magmatism as an extending continental margin (broad back-arc region) inboard of a northeast-dipping (present coordinates) subduction zone. New SHRIMP U-Pb ages of inherited zircon cores in the Tanacross orthogneisses and of detrital zircons from quartzite from the Jarvis belt in the Alaska Range (Mount Hayes quadrangle) include major 2.0-1.7 Ga clusters and lesser 2.7-2.3 Ga clusters, with subordinate 3.2, 1.4, and 1.1 Ga clusters in some orthogneiss samples. For the most part, these inherited and core U-Pb ages match those of basement provinces of the western Canadian Shield and indicate widespread potential sources within western Laurentia for most grain populations; these ages also match the detrital zircon reference for the northern North American miogeocline and support a correlation between the two areas.

  3. Response to comment on "Evaluating the temporal link between the Karoo LIP and climatic-biologic events of the Toarcian Stage with high-precision U-Pb geochronology"

    Science.gov (United States)

    Sell, Bryan; Ovtcharova, Maria; Guex, Jean; Bartolini, Annachiara; Jourdan, Fred; Spangenberg, Jorge E.; Vicente, Jean-Claude; Schaltegger, Urs

    2016-01-01

    Corfu et al. provide a thoughtful commentary on Sell et al.'s (2014) article entitled "Evaluating the temporal link between the Karoo LIP and climatic-biologic events of the Toarcian Stage with high-precision U-Pb geochronology." Their commentary offers alternative interpretations of Sell et al.'s data in terms of their own previously published research (Mazzini et al., 2010; Svensen et al., 2012, 2007) and offers new information regarding tracer or spike calibrations between different laboratories.

  4. The Ancestry and Affinity of Central Europe: New U-Pb (LA-PIMMS) Ages of Inherited Zircons From Early Palaeozoic Granitoids of the W Sudetes, NE Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Crowley, Q. G.; Patočka, František; Parrish, R. R.

    Ankara : Middle East Technical University, 2001. s. 11. [ESF EUROPROBE Meeting. Joint Meeting of Europrobe Tesz, Timpebar, Uralides and SW-Iberia projects. EUROPROBE Neoproterozoic-Early Palaeozoic Time-Slice Symposium: Orogeny and Cratonic Response on the Margins of Baltica.. 30.09.2001-02.10.2001, Ankara] R&D Projects: GA AV ČR IAA3111102 Keywords : granitoid gneisses * U-Pb zircon dating * N Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  5. Chemical and U-Pb dating investigation of zircons from alnöites on Malaita, Solomon Islands: evidence for prolonged kimberlite-type magmatic activity

    Science.gov (United States)

    Simonetti, A.; Neal, C. R.

    2009-12-01

    The Solomon Islands chain is located in an area dominated by the Ontong Java Plateau (OJP). The island of Malaita formed at the obducted leading edge of the OJP and is geologically distinct from the islands to the west. Occurrences of pipe-like bodies of alnöite outcrop within limestones and mudstones in northern Malaita and have been seismically imaged offshore within the OJP. The Malaita alnöite is silica-undersaturated and contains a rich and varied suite of peridotite xenoliths and megacrysts (clinopyroxene, garnet, ilmenite, phlogopite, and minor zircon). The alnöite and associated megacrysts have been the focus of detailed chemical and radiogenic isotope investigations but the exact age of alnöite emplacement remains debatable. Previously reported ages for minerals associated with the Malaita alnöites include an Ar-Ar date of 34 Ma for phlogopite from a mantle xenolith, and a single 206Pb/238U date of 33.9 Ma obtained from a single zircon megacryst. Here we report on a detailed chemical (major and trace element) and U-Pb age investigation of zircon crystals recovered from rivers in the Aluta, Kwainale, and Faufaumela regions of central Malaita. The major element (SiO2, ZrO2, and HfO2) composition and back scattered electron (BSE) imaging of mm- to cm-sized zircons from the three locations were conducted by electron microprobe analysis. The data reveal a variation in the Zr/Hf ratio (45 to 57) for zircons from the Aluta area, whereas this ratio is relatively uniform in most zircons from Kwainale (Zr/Hf 45 to 48). Of importance, the BSE imaging reveals the homogeneous nature of the grains and the lack of inherited components. Trace element compositions of the zircon crystals were obtained by laser ablation (LA)-ICP-MS and these reveal similar chondrite-normalized REE patterns at variable enrichment levels for all grains analyzed; these patterns along with the U, Th, and Pb contents are similar to those documented for mantle-derived zircons formed within

  6. New structural and U-Pb zircon data from Anafi crystalline basement (Cyclades, Greece): constraints on the evolution of a Late Cretaceous magmatic arc in the Internal Hellenides

    Science.gov (United States)

    Martha, Silviu O.; Dörr, Wolfgang; Gerdes, Axel; Petschick, Rainer; Schastok, Janina; Xypolias, Paraskevas; Zulauf, Gernold

    2016-06-01

    The Asterousia Crystalline Complex consists of Late Cretaceous amphibolite facies metamorphic rocks and associated granitoids, which can be found in exposures on Crete and the Cyclades (Greece). It is attributed to the Uppermost Unit and therefore to the Pelagonian domain of the Internal Hellenides. The tectonometamorphic evolution of this unit is still a matter of debate. We present new structural and petrological data of Asterousia-type rocks and greenschist facies metamorphic rocks from the island of Anafi in the southern Aegean Sea as well as U-Pb zircon ages of granitoids from Anafi. The crystalline sequence of Anafi rests on top of Eocene flysch and comprises from bottom to top: (a) Anafi Greenschist; (b) Anafi Amphibolite Group (orthoamphibolite with intercalations of metasedimentary rocks at the base); and (c) Chalepa Group (amphibolite facies metasediments with slices of serpentinite and granitoids). LA-ICP-MS and ID-TIMS 206Pb/238U zircon ages of granodiorite from the Chalepa Group reveal several similar zircon populations suggesting continuous emplacement of granitoids inside a magmatic arc from ca. 72.5 to 79 Ma. The minimum emplacement age of granodioritic magma, deduced from the 206Pb/238U median age of the youngest zircon population, is 72.6 +0.1/-0.2 Ma. Deformation (micro)fabrics of granodiorite result from low strain obtained at T > 600 °C. This along with the U-Pb ages and published K-Ar ages indicates intrusion of the plutonic rocks at deep structural levels followed by very slow cooling. Monzogranitic dykes cutting through granodiorite in north-eastern Anafi are undeformed and yielded a 206Pb/238U median age of 69.9 +0.7/-0.7 Ma. Based on the new and published data, the following implications for the tectonometamorphic evolution on Anafi can be made: (1) obduction and accretion of mantle slices (serpentinite) to the Asterousia-type rocks were prior to amphibolite facies metamorphism; (2) intrusion of granitoids during the middle to late

  7. 40Ar-39Ar and U-Pb ages of metadiorite from the East Kunlun Orogenic Belt: Evidence for Early-Paleozoic magmatic zone and excess argon in amphibole minerals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Single-grain zircon U-Pb and amphibole 40Ar-39Ar dating have beenconducted on a deformed and metamorphosed diorite in the East Kunlun Orogenic Belt, which intruded into the middle Proterozoic Kuhai Group exposed in the south of Xiangride region, Dulan County, NW Qinghai Province. The zircon gives a concordant U-Pb age of (446.5±9.1) Ma. The amphibole yields Ar plateau age of (488.0±1.2) Ma and an isochronal age of (488.9±5.6) Ma. Age results of both stepwise released Ar and conventional K-Ar analysis are remarkably higher than that of zircon U-Pb, suggesting that the amphibole contains excess argon and the amphibole plateau age cannot be taken as the timing of metamorphism or deformation. The zircon age is interpreted to be crystallization age of the diorite pluton, which suggests that an Early-Paleozoic magmatic zone indeed existed in the East Kunlun Orogenic Belt stretching along the region south to the Golmud, Normuhong and Xiangride.

  8. U-Pb (LA-ICPMS) zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quiteria Complex, Ceara Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Felipe Grandjean da; Araujo, Carlos Eduardo Ganade de; Vasconcelos, Antonio Maurilio, E-mail: felipe.costa@cprm.gov.br, E-mail: caegeo@gmail.com, E-mail: maurilio.vasconcelos@cprm.gov.br [Servico Geologico do Brasil (CPRM), Fortaleza, CE (Brazil); Amaral, Wagner da Silva, E-mail: wamaral@ufc.br [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Departamento de Geologia; Rodrigues, Joseneusa Brilhante, E-mail: joseneusa.rodrigues@cprm.gov.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)

    2013-06-15

    The Tamboril-Santa Quiteria Complex (TSQC) is one of the largest Neoproterozoic plutonic manifestations in the north Borborema Province (NE Brazil). It represents an anatectic/igneous association characterized by a number of magmatic pulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS) zircon ages and Nd isotopes for quartz monzonite and quartz diorites of the southern part of TSQC. The quartz monzonite belong to a hybrid granitoid association, including monzonite, syenites and quartz syenites, all with abundant mafic magmatic enclaves. A quartz monzonite sample yielded a U-Pb zircon age of 634 {+-} 10 Ma and a TDM age of 2.69 Ga. The quartz diorites are much more homogeneous in composition and yielded a U-Pb zircon age of 618 {+-} 23 Ma and a TDM age of 2.19 Ga. The presence of coeval mantle-derived magmatism and diatexites (crustal anatexis) post-dating high-pressure metamorphism (ca. 650 Ma), and together with high-temperature metamorphism (ca. 630-610 Ma), suggests that this large magmatic manifestation evolved in a collisional setting, probably related to slab break off during the Western Gondwana amalgamation. (author)

  9. U/Pb LA–ICP–MS age of metamorphic–metasomatic perovskite from serpentinized harzburgite in the Meliata Unit at Dobšiná, Slovakia: Time constraint of fluid-rock interaction in an accretionary wedge

    Directory of Open Access Journals (Sweden)

    Marián Putiš

    2015-06-01

    Full Text Available Perovskite-bearing harzburgites were discovered in a blueschist-bearing mélange complex in the Slovak Inner Western Carpathian Meliata tectonic unit at Dobšiná. Perovskite (1 exclusively occurs in serpentinized parts of harzburgite blocks, while perovskite (2 was found in rodingite veins crosscutting serpentinites. We separated metamorphic–metasomatic perovskite (1 from serpentinized orthopyroxene porphyroclasts of a harzburgite serpentinite in order to date fluid–rock interactions during serpentinization and/or rodingitization by in situ U/Pb LA–ICP–MS, and to compare its age with published ages (from 137±1 Ma to 135±1 Ma, with a mean age of 135.6±0.58 Ma by U/Pb SIMS from the same locality. Perovskite (1 age at ~135±2.0 Ma was determined in the serpentinized zone of the harzburgite by LA–ICP–MS. Perovskite (2 from a rodingite vein was unsuitable for dating by this method because of its very low U content and general high common lead content. The perovskite (1 age is interpreted to record the interaction of metamorphic fluids with harzburgite fragments in the Neotethyan Meliatic accretionary wedge. Since perovskite (1 is younger than the high-pressure metamorphism of this wedge dated at 160–150 Ma, it constrains the exhumation period of the harzburgite fragments at ca. 135 Ma that is compatible with ages of ~137–135 Ma by U/Pb SIMS.

  10. U-Pb (LA-ICPMS zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quitéria Complex, Ceará Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province

    Directory of Open Access Journals (Sweden)

    Felipe Grandjean da Costa

    2013-06-01

    Full Text Available The Tamboril-Santa Quitéria Complex (TSQC is one of the largest Neoproterozoic plutonic manifestations in the northBorborema Province (NE Brazil. It represents an anatectic/igneous association characterized by a number of magmaticpulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS zircon ages and Ndisotopes for quartz monzonites and quartz diorites of the southern part of TSQC. The quartz monzonites belong to a hybridgranitoid association, including monzonites, syenites and quartz syenites, all with abundant mafic magmatic enclaves.A quartz monzonite sample yielded a U-Pb zircon age of 634 ± 10 Ma and a TDM age of 2.69 Ga. The quartz diorites aremuch more homogeneous in composition and yielded a U-Pb zircon age of 618 ± 23 Ma and a TDM age of 2.19 Ga. Thepresence of coeval mantle-derived magmatism and diatexites (crustal anatexis post-dating high-pressure metamorphism(ca. 650 Ma, and together with high-temperature metamorphism (ca. 630-610 Ma, suggests that this large magmatic manifestationevolved in a collisional setting, probably related to slab breakoff during the Western Gondwana amalgamation.

  11. U-Pb (LA-ICPMS) zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quiteria Complex, Ceara Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province, Brazil

    International Nuclear Information System (INIS)

    The Tamboril-Santa Quiteria Complex (TSQC) is one of the largest Neoproterozoic plutonic manifestations in the north Borborema Province (NE Brazil). It represents an anatectic/igneous association characterized by a number of magmatic pulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS) zircon ages and Nd isotopes for quartz monzonite and quartz diorites of the southern part of TSQC. The quartz monzonite belong to a hybrid granitoid association, including monzonite, syenites and quartz syenites, all with abundant mafic magmatic enclaves. A quartz monzonite sample yielded a U-Pb zircon age of 634 ± 10 Ma and a TDM age of 2.69 Ga. The quartz diorites are much more homogeneous in composition and yielded a U-Pb zircon age of 618 ± 23 Ma and a TDM age of 2.19 Ga. The presence of coeval mantle-derived magmatism and diatexites (crustal anatexis) post-dating high-pressure metamorphism (ca. 650 Ma), and together with high-temperature metamorphism (ca. 630-610 Ma), suggests that this large magmatic manifestation evolved in a collisional setting, probably related to slab break off during the Western Gondwana amalgamation. (author)

  12. LA-ICP-MS zircon U-Pb dating from granitoids in southern basement of Songliao basin: Constraints on ages of the basin basement

    Institute of Scientific and Technical Information of China (English)

    GAO FuHong; XU WenLiang; YANG DeBin; PEI FuPing; LIU XiaoMing; HU ZhaoChu

    2007-01-01

    Seven LA-ICP-MS zircon U-Pb datings from granitoids in the southern basement of the Songliao basin were done in order to constrain the ages of the basin basement. The cathodoluminescence (CL) images of the zircons from seven granitoids indicate that they are euhedral-subhedral ones with striped absorption and obvious oscillatory zoning rims. The dating results show that a weighted mean 206Pb/238U age is 236±3 Ma for quartz diorite (sample No.T6-1) located in the western slope of the basin, that weighted mean 206Pb/238U ages are 319±1 Ma (2126 m) and 361±2 Ma (1994 m) for diorite (sample No.YC1-1) and granite (sample No.YC1-2) located in northern part of southeastern uplift of the basin, respectively, and that weighted mean 206Pb/238U ages are 161±5 Ma, 165±2 Ma, 165±1 Ma and 161±4 Ma for samples Q2-1, SN121, SN122, and SN72 granitoids located in southern part of southeastern uplift of the basin, respectively. The statistical results of ages suggest that the middle Jurassic granitoids constitute the main part of basement granitoids, and that the Hercynian and Indo-Sino magmatisms also occur in the basin basement. It is implied that the Songliao basin should be a rift one formed in the intracontinent or active continental margin settings in the late Mesozoic after the Middle Jurassic orogeny took place.

  13. Zircon U-Pb age and Hf isotope of Quanyishang A-type granite in Yichang: Signification for the Yangtze continental cratonization in Paleoproterozoic

    Institute of Scientific and Technical Information of China (English)

    XIONG Qing; ZHENG JianPing; YU ChunMei; SU YuPing; TANG HuaYun; ZHANG ZhiHai

    2009-01-01

    Zircon U-Pb age and Hf isotope, and major and trace element compositions were reported for granite at Quanyishang, which intruded into the Kongling complex in Yichang, Hubei Province. The results show that the Quanyishang granite is rich in silicon and alkalis but poor in calcium and magnesium, and displays enrichment in Ga, Y, Zr, Nb but depletion in Sr and Ba, exhibiting the post-orogenic A-type affinity. 90% zircons from the granite are concordant, and give a middle Paleoproterozoic magmatic crystallization age (mean 1854 Ma). Initial Hf isotope ratios (176Hf/177Hf)1 of the middle Paleoproterozoic zircons range from 0.280863 to 0.281134 and they have negative εHf(t) values with a minimum of -26.3. These zircons give the depleted mantle model ages (TDM) of 2.9-3.3 Ga (mean 3.0 Ga), and the average crustal model ages (Tcrust) of 3.6-4.2 Ga (mean 3.8 Ga)., A Mesoarchean grain with 207pb/206Pb age of 2859 Ma has a slightly high TDM (3.4 Ga) but similar Tcrust (3.8 Ga) to the Paleoproterozoic zircons. All these data suggest that the source materials of the Quanyishang A-type granite are unusually old, at least ≥2.9 Ga (even Eoarchean). The event of crustal remelting, which resulted in the formation of the Quanyishang granite in the middle Paleoproterozoic, recorded the cratonization of the Yangtze conti-nent. The process may have relation to the extension and collapse of the deep crust with Archean ages, in response to the transition stage of the assembly and breakup of the Columbia supercontinent.

  14. Cenozoic tectono-geomorphological growth of the SW Chinese Tian Shan: Insight from AFT and detrital zircon U-Pb data

    Science.gov (United States)

    Jia, Yingying; Fu, Bihong; Jolivet, Marc; Zheng, Shuo

    2015-11-01

    As a unique example of the intracontinental mountain building, the Cenozoic deformation of the Tian Shan has been widely studied. The onset of Cenozoic exhumation of the SW Chinese Tian Shan was constrained at the Oligocene-Miocene boundary. However, the Cenozoic tectono-geomorphological growth process of the SW Chinese Tian Shan and adjacent piedmont basins remains a challenge. In this study, we carried out the geological mapping of satellite images and field investigations together with the apatite fission track (AFT) and detrital zircon U-Pb analyses to get further understanding of the Cenozoic tectonic deformation and geomorphological growth of the SW Chinese Tian Shan. Our results indicate that the exhumation of the hanging wall of Maidan fault or topography growth of the Kokshaal Range commenced in the late Eocene-Oligocene (35-25 Ma). Then, the structural deformation migrated southward to the Muziduke fault and the Atushi Basin Thrust (ABT) at ∼15 Ma. The growth strata of 6-3 Ma on the south flank of Keketamu Anticline imply that tectonic deformation propagates further basinward. Furthermore, the uplift of the Kokshaal Range also strongly affected the evolution of piedmont basins. The results suggest that the Atushi Basin was still likely linked to the Aksai Basin during the early Miocene. They were separated into two independent basins since ca. 13.7-10.5 Ma, as a response to the rapid uplift of the Kokshaal Range. Finally, we infer that the southeastern part of dextral Talas-Fergana fault (TFF) is likely transferred to the NEE-trending thrust faults of the SW Chinese Tian Shan since ∼15 Ma.

  15. Coolwater culmination: Sensitive high-resolution ion microprobe (SHRIMP) U-Pb and isotopic evidence for continental delamination in the Syringa Embayment, Salmon River suture, Idaho

    Science.gov (United States)

    Lund, K.; Aleinikoff, J.N.; Yacob, E.Y.; Unruh, D.M.; Fanning, C.M.

    2008-01-01

    During dextral oblique translation along Laurentia in western Idaho, the Blue Mountains superterrane underwent clockwise rotation and impinged into the Syringa embayment at the northern end of the Salmon River suture. Along the suture, the superterrane is juxtaposed directly against western Laurentia, making this central Cordilleran accretionary-margin segment unusually attenuated. In the embayment, limited orthogonal contraction produced a crustal wedge of oceanic rocks that delaminated Laurentian crust. The wedge is exposed through Laurentian crust in the Coolwater culmination as documented by mapping and by sensitive high-resolution ion microprobe U-Pb, Sri, and ??Nd data for gneisses that lie inboard of the suture. The predominant country rock is Mesoproterozoic paragneiss overlying Laurentian basement. An overlying Neoproterozoic (or younger) paragneiss belt in the Syringa embayment establishes the form of the Cordilleran miogeocline and that the embayment is a relict of Rodinia rifting. An underlying Cretaceous paragneiss was derived from arc terranes and suture-zone orogenic welt but also from Laurentia. The Cretaceous paragneiss and an 86-Ma orthogneiss that intruded it formed the wedge of oceanic rocks that were inserted into the Laurentian margin between 98 and 73 Ma, splitting supracrustal Laurentian rocks from their basement. Crustal thickening, melting and intrusion within the wedge, and folding to form the Coolwater culmination continued until 61 Ma. The embayment formed a restraining bend at the end of the dextral transpressional suture. Clockwise rotation of the impinging superterrane and overthrusting of Laurentia that produced the crustal wedge in the Coolwater culmination are predicted by oblique collision into the Syringa embayment. Copyright 2008 by the American Geophysical Union.

  16. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    Science.gov (United States)

    Matthews, Naomi E.; Vazquez, Jorge A.; Calvert, Andrew T.

    2015-01-01

    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff. Tephra from the Lava Creek eruption is a key Quaternary chronostratigraphic marker, in particular for dating the deposition of mid Pleistocene glacial and pluvial deposits in western North America. To resolve the timing of eruption and crystallization history for the Lava Creek magma, we performed (1) 40Ar/39Ar dating of single sanidine crystals to delimit eruption age and (2) ion microprobe U-Pb and trace-element analyses of the crystal faces and interiors of single zircons to date the interval of zircon crystallization and characterize magmatic evolution. Sanidines from the two informal members composing Lava Creek Tuff yield a preferred 40Ar/39Ar isochron date of 631.3 ± 4.3 ka. Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 626.5 ± 5.8 ka, and have trace element concentrations that vary with the eruptive stratigraphy. Zircon interiors yield a mean 206Pb/238U date of 659.8 ± 5.5 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high U concentration cores that likely grew from highly evolved melt. The occurrence of distal Lava Creek tephra in stratigraphic sequences marking the Marine Isotope Stage 16–15 transition supports the apparent eruption age of ∼631 ka. The combined results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103−104 year interval before eruption.

  17. Paleocene and Early Eocene volcanic ash layers in the Schlieren Flysch, Switzerland: U-Pb dating and Hf-isotopes of zircons, pumice geochemistry and origin

    Science.gov (United States)

    Koch, Simone; Winkler, Wilfried; Von Quadt, Albrecht; Ulmer, Peter

    2015-11-01

    Thin mm to cm thick bentonite layers of Paleocene to Early Eocene age in the Tonsteinschichten of the Schlieren Flysch represent volcanic ash layers. Heavy mineral analysis of the layers indicates basic to acidic volcanic sources. U/Pb dating of single zircon crystals of a Paleocene layer (WW1948) by LA-ICP-MS points to an eruption at 59.87 ± 0.41 Ma, whereas ID-TIMS shows an eruption age of 60.96 ± 0.07 Ma. Taking into account the external precision of LA-ICP-MS analyses of 1-2% both ages are overlapping and indicate an apparent minimal durations of zircon crystallization of 350 ka. Hf-isotope analysis of the same zircon crystals reveals the hybrid character of the source magma. The geochemical composition of the pumice grains of all bentonite layers is strongly affected by alteration. Nevertheless, the original character of the volcanic source can be evaluated. The Paleocene ashes (Lower Tonsteinschichten, LT) show a more fractionated multi-element pattern than the ashes of Early Eocene (Upper Tonsteinschichten, UT). The LT ash series are of rhyodacite to dacite character whereas the UT ashes fall in the field of alkali basalts. Both ash series seem to originate from a within-plate volcanic setting according to their trace element concentrations. Geochemical and temporary counterparts can be found in ash layers from Anthering (Austria) and the Danish Basin. As proposed for those ashes, volcanism connected to the opening of the North Atlantic might be the source as well for the ashes in the Schlieren Flysch. By comparison of the composition of rocks from the British Paleogene Igneous Province BPIP and the Schlieren Flysch ashes many correlations can be drawn which supports the suggestion of a North Atlantic origin of the Alpine ashes.

  18. Geology, petrology, U-Pb (SHRIMP) geochronology of the Morrinhos granite - Paragua terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignacio orogeny

    Energy Technology Data Exchange (ETDEWEB)

    Franca, Ohana; Ruiz, Amarildo Salina; Sousa, Maria Zelia Aguiar de, E-mail: ohana.geo@gmail.com, E-mail: asruiz@gmail.com, E-mail: mzaguiar@terra.com.br [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Instituto de Ciencias Exatas e da Terra. Dept. de Geologia Geral; Batata, Maria Elisa Froes, E-mail: elisabatata@bol.com.br [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Grupo de Pesquisa em Evolucao Crustal e Tectonica; Lafon, Jean-Michel [Universidade Federal do Para (GEOCIAM/UFPA), Belem, PR (Brazil). Inst. Nacional de Cencia e Tecnologia de Geociencias da Amazonia

    2014-09-15

    Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km{sup 2} long; it is located in the municipality of Vila Bela da Santissima Trindade of the state of Mato Grosso, Brazil, in the Paragua Terrane, Rondonian-San Ignacio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the green schist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S{sub 1}) and open folds (D{sub 2}), and both phases were most likely related to the San Ignacio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350±12Ma, T{sub DM} of approximately 1.77 Ga and εNd{sub (1.35}) with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignacio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite. (author)

  19. LA-ICP-MS zircon U-Pb dating and phenocryst EPMA of dikes, Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the al- tered breccia gold deposits along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts and the presence of acicular apatites in these dikes. Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene phenocryst’s mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr2O3 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon U-Pb weighted mean 206Pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively. Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in these dikes. Magmatic zircons from GS1 and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude garnet presented in their source. Our results, combined with preciously pub- lished data, indicate that dike intrusion and gold mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout the Jiaodong Peninsula. These also imply that the intensive crust-mantle interaction and asthenospheric underplating had oc- curred in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the different stages of lithosphere thinning in the North China Craton (NNC).

  20. LA-ICP-MS zircon U-Pb dating and phenocryst of dikes, Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution

    Institute of Scientific and Technical Information of China (English)

    TAN Jun; WEI JunHao; GUO LingLi; ZHANG KeQing; YAO ChunLiang; LU JianPei; LI HongMei

    2008-01-01

    Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the altered breccia gold deposits along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts and the presence of acicular apatites in these dikes.Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene phenocryst's mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr203 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon U-Pb weighted mean 206pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively. Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in these dikes. Magmatic zircons from GSl and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude garnet presented in their source. Our results, combined with preciously published data, indicate that dike intrusion and gold mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout the Jiaodong Peninsula.These also imply that the intensive crust-mantle interaction and asthenospheric underplating had occurred in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the different stages of lithosphere thinning in the North China Craton (NNC).

  1. Geochemistry and detrital zircon U-Pb and Hf isotopes of the paragneiss suite from the Quanji massif, SE Tarim Craton: Implications for Paleoproterozoic tectonics in NW China

    Science.gov (United States)

    Zhang, Lu; Wang, Qinyan; Chen, Nengsong; Sun, Min; Santosh, M.; Ba, Jin

    2014-12-01

    The Delingha paragneiss suite in the Quanji massif, southeastern Tarim Craton, is composed of mica schist, paragneiss, leptynite and quartzite, similar to the 'khondalite suites' described from elsewhere in the world. The mica schist is rich in Al2O3 (up to ∼26 wt%) and contains graphite and diagnostic minerals including sillimanite and garnet, with metamorphism under amphibolite-facies to locally granulite-facies conditions as manifested by association with amphibolite and granulite. The detrital zircon U-Pb ages and geochemical data indicate that the protolith materials of the Delingha paragneiss suite were mainly sourced from 2.20 to 2.45 Ga granites, felsic volcanic rocks and TTG, and were deposited at 2.17-1.92 Ga. The detrital zircon Hf and whole-rock Nd isotopes document important crustal growth at ∼2.5-2.7 Ga. The detrital zircon age spectra, the whole rock Nd and zircon Hf model ages, the low-maturity of the protolith, and short-distance transportation suggest that the detritus were derived from the underlying Delingha Complex and the lower Dakendaban sub-Group. The timing of magmatic activities in the source region, the depositional age and metamorphic histories of the Delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the Ordos Block in the North China Craton. Our study shows that the 2.2-2.45 Ga magmatic rocks were generated in arc or active continental margin settings, suggesting a prolonged subduction and accretion history prior to final amalgamation (∼2.5-1.8 Ga) to form the unified North China Craton and the assembly of the Tarim Craton in NW China.

  2. Timing of Magma Mixing in the Gangdisê Magmatic Belt during the India-Asia Collision:Zircon SHRIMP U-Pb Dating

    Institute of Scientific and Technical Information of China (English)

    MO Xuanxue; DONG Guochen; ZHAO Zhidan; GUO Tieying; WANG Liangliang; CHEN Tao

    2005-01-01

    Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Quxu batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Quxu batholith, and subsequent zircon SHRIMP Ⅱ U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock,mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma,49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.

  3. Geology, petrology, U-Pb (SHRIMP) geochronology of the Morrinhos granite - Paragua terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignacio orogeny

    International Nuclear Information System (INIS)

    Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km2 long; it is located in the municipality of Vila Bela da Santissima Trindade of the state of Mato Grosso, Brazil, in the Paragua Terrane, Rondonian-San Ignacio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the green schist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S1) and open folds (D2), and both phases were most likely related to the San Ignacio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350±12Ma, TDM of approximately 1.77 Ga and εNd(1.35) with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignacio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite. (author)

  4. On the presence of upper paleocene rocks in the foreland succession at Cabo Nariz, Tierra del Fuego, Chile: Geology and new palynological and U-Pb data

    International Nuclear Information System (INIS)

    On the west coast of Tierra del Fuego, south of Cabo Nariz, in Chile, Upper Cretaceous to Paleocene sedimentary successions of the Magallanes foreland basin crop out. The presence of dinoflagellate cysts, as well as radiometric U-Pb SHPJMP dating of detrital zircons, indicate that this succession ranges from the Campanian to Thanetian (Late Paleocene) in age. The base of the exposed sedimentary succession comprises siltstones of external platform facies (Cerro Cuchilla Formation), which are thrust over the Cabo Nariz Beds. The latter fonnation is divided into two members: a lower siltstone-dominated turbidite facies member and an upper member of sandstone-dominated turbidites, with sandstone and conglomerate channel facies. The presence of dinocysts in the Cerro Cuchilla Formation suggests a late Campanian to early Danian age. The fossil content in the Cabo Nariz Beds indicate a Selandian (Middle Paleocene) depositional age in accordance with the detrital zircon ages which provide a maximum possible Campanian age (76.5±0.7 Ma), and very close to the Thanetian (Late Paleocene) (57.6±1 Ma) depositional ages for the lower and upper member, respectively. The sedimentary succession of Cabo Nariz Beds, is interpreted as a north-northwest prograding submarine fan of middle to Late Paleocene age. It is considered to represent the deposition of detritus derived from an uplifting orogen located to the south. The detrital zircon age spectra suggest that there was a period of low intensity of magmatic activity in the source area around the K-T boundary

  5. Calibration of the Late Cretaceous to Paleocene geomagnetic polarity and astrochronological time scales: new results from high-precision U-Pb geochronology

    Science.gov (United States)

    Ramezani, Jahandar; Clyde, William; Wang, Tiantian; Johnson, Kirk; Bowring, Samuel

    2016-04-01

    Reversals in the Earth's magnetic polarity are geologically abrupt events of global magnitude that makes them ideal timelines for stratigraphic correlation across a variety of depositional environments, especially where diagnostic marine fossils are absent. Accurate and precise calibration of the Geomagnetic Polarity Timescale (GPTS) is thus essential to the reconstruction of Earth history and to resolving the mode and tempo of biotic and environmental change in deep time. The Late Cretaceous - Paleocene GPTS is of particular interest as it encompasses a critical period of Earth history marked by the Cretaceous greenhouse climate, the peak of dinosaur diversity, the end-Cretaceous mass extinction and its paleoecological aftermaths. Absolute calibration of the GPTS has been traditionally based on sea-floor spreading magnetic anomaly profiles combined with local magnetostratigraphic sequences for which a numerical age model could be established by interpolation between an often limited number of 40Ar/39Ar dates from intercalated volcanic ash deposits. Although the Neogene part of the GPTS has been adequately calibrated using cyclostratigraphy-based, astrochronological schemes, the application of these approaches to pre-Neogene parts of the timescale has been complicated given the uncertainties of the orbital models and the chaotic behavior of the solar system this far back in time. Here we present refined chronostratigraphic frameworks based on high-precision U-Pb geochronology of ash beds from the Western Interior Basin of North America and the Songliao Basin of Northeast China that places tight temporal constraints on the Late Cretaceous to Paleocene GPTS, either directly or by testing their astrochronological underpinnings. Further application of high-precision radioisotope geochronology and calibrated astrochronology promises a complete and robust Cretaceous-Paleogene GPTS, entirely independent of sea-floor magnetic anomaly profiles.

  6. Late Paleozoic magmatic record of Middle Gobi area, South Mongolia and its implications for tectonic evolution: Evidences from zircon U-Pb dating and geochemistry

    Science.gov (United States)

    Zhu, Mingshuai; Miao, Laicheng; Baatar, Munkhtsengel; Zhang, Fochin; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo

    2016-01-01

    Late Paleozoic subduction-accretion complexes occur widely in Middle Gobi area and provide a good opportunity for unraveling the Paleozoic tectonic evolution of South Mongolia. The magmatic rocks in the Tsavchir hudug district mainly consist of rhyolites and volcaniclastic rocks. The rhyolites show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, indicating genesis in the subduction zone. A rhyolite sample from the Tsavchir hudug region yielded a SHRIMP 206Pb/238U zircon age of 315 ± 4 Ma (MSWD = 0.79, n = 15). The andesite overlying the Namdain hundy Early Paleozoic ophiolite shows adakite geochemical features, and the two andesite samples yielded SHRIMP 206Pb/238U zircon ages of 325 ± 3 Ma (MSWD = 1.6, n = 14) and 319 ± 4 Ma (MSWD = 0.56, n = 13), respectively, suggesting that the Carboniferous island arc formed on the basis of Early Paleozoic accretionary complex. The granodiorite sample that intrudes the Early Paleozoic accretion complex with adakite geochemical features yielded a SHRIMP 206Pb/238U zircon age of 333 ± 4 Ma (MSWD = 1.6, n = 16), representing the Late Paleozoic island arc intrusive. The SHRIMP U-Pb analyses for the tuff sandstones that occur associated with Early Paleozic oceanic inliers in Middle Gobi area suggest detrital zircons mainly stem from the Devonian-Carboniferous arc. The age data obtained from the ophiolite (528-509 Ma) and tuff sandstone indicate the accretion in Middle Gobi area lasted from Early Paleozoic to Late Paleozoic for at least ca. 200 Ma, suggesting the ocean of the accretionary complex was the major Paleo-Asain ocean basin. The subduction related magmatic belt in Middle Gobi area includes both Early Paleozoic and Late Paleozoic island arc activities, which is consistent with the accretion duration time obtained from accretionary complex and also attests the argument of major Paleo-Asain ocean basin.

  7. U-Pb geochronology and geochemistry of Bibi-Maryam pluton, eastern Iran: Implication for the late stage of the tectonic evolution of the Sistan Ocean

    Science.gov (United States)

    Delavari, Morteza; Amini, Sadraddin; Schmitt, Axel K.; McKeegan, Kevin D.; Mark Harrison, T.

    2014-07-01

    The Bibi-Maryam pluton crops out in the Sistan suture zone, eastern Iran. This pluton is a 1.5 × 2 km stock composed of leucocratic tonalite, granodiorite and granite. U-Pb zircon geochronology of a leucogranite indicates an emplacement age of 58.6 ± 2.1 Ma (95% confidence). The Bibi-Maryam rock suite is sodic with elevated Na2O/K2O (2.9 to 5.5), Sr/Y (15.6-62.2), La/Yb (13.3-22.2), and low MgO (0.86-1.81) abundances. It lacks significant Eu anomalies. Because of these geochemical characteristics, Bibi-Maryam rocks are similar to high-SiO2 adakites. Trace element modeling indicates that the Bibi-Maryam adakitic rocks could be produced by 5-8% non-modal batch partial melting from a source with composition of 95% N-MORB + 5% sediment in the presence of 35-40% amphibole + 5-10% garnet + 55-60% clinopyroxene + 1% apatite + 1% rutile. This source mineralogy is similar to hornblende eclogite or garnet amphibolites. Collectively, these data provide new constraints for the evolution of the Sistan suture zone and suggest that the Bibi-Maryam pluton formed via slab melting in an oceanic arc and pre-plate collision tectonic setting. This implies that the closure of the Sistan Ocean and Lut-Afghan continental blocks collision happened after the Bibi-Maryam emplacement at 58.6 ± 2.1 Ma.

  8. In situ determination of U-Pb ages and Sr-Nd-Hf isotopic constraints on the petrogenesis of the Phalaborwa carbonatite Complex, South Africa

    Science.gov (United States)

    Wu, Fu-Yuan; Yang, Yue-Heng; Li, Qiu-Li; Mitchell, Roger H.; Dawson, J. Barry; Brandl, Günther; Yuhara, Masaki

    2011-11-01

    The Phalaborwa carbonatite Complex, situated in the northeastern part of South Africa, is characterized by copper and zirconium mineralization, and is composed principally of pyroxenites, phoscorite and carbonatite (banded and transgressive). The complex is transected by mafic dykes, and is geographically associated with a satellite syenite and minor granite intrusions. Zircon and baddeleyite U-Pb isotopic age determinations using CAMECA 1280 secondary ion mass spectrometry have shown that the outer pegmatitic pyroxenite at the Loolekop pipe was emplaced at 2060 ± 4 Ma, and the main phoscorite at 2062 ± 2 Ma. Both ages are identical to those of 2060 ± 2 and 2060 ± 1 Ma for the banded and transgressive carbonatites, respectively. The satellite syenite, which forms plug-like bodies outside of the border of the main complex, and the later mafic dyke have “similar” emplacement ages of 2068 ± 17 and 2062 ± 53 Ma, indicating that these intrusions were apparently near-synchronously emplaced. In contrast to other carbonatites, the Phalaborwa Complex is characterized by high initial Sr and low initial Nd and Hf isotopic compositions. In situ isotopic analyses of apatite, calcite, zircon and baddeleyite indicate that the primary magma was derived from an enriched mantle. As the complex was emplaced slightly earlier at ~ 2060 Ma than the nearby mafic phase of the Bushveld Complex (~ 2055 Ma), it is proposed that the Phalaborwa carbonatite magmatism was triggered by the same mantle plume activity, which partially melted the overlying lithospheric mantle. This contribution also highlights that isotopic studies used to constrain the genesis of ancient igneous complexes should concentrate on minerals with low parent/daughter elemental ratios, such as apatite and calcite for Sr isotopes, and zircon and baddeleyite for Hf isotopes.

  9. Petrogenesis of subvolcanic rocks from the Khunik prospecting area, south of Birjand, Iran: Geochemical, Sr-Nd isotopic and U-Pb zircon constraints

    Science.gov (United States)

    Samiee, Somayeh; Karimpour, Mohammad Hassan; Ghaderi, Majid; Haidarian Shahri, Mohammad Reza; Klöetzli, Urs; Santos, José Francisco

    2016-01-01

    The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several outcrops of subvolcanic intrusions in the area which intruded into Paleocene-Eocene volcanic rocks (andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite. Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz. Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous, and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized REE plots show moderately LREE enriched patterns (7.45 diagrams also show affinities with modern convergent margin magmas, suggesting that magmas of Khunik area formed in volcanic arc setting related to subduction of the oceanic crust under the Lut Block plate. The initial 87Sr/86Sr ratios (0.704196-0.704772) and εNdi values (+1.3 to +3.3) are compatible with an origin of the parental melts in a supra-subduction mantle wedge. Zircon U-Pb dating by LA-ICP-MS indicates the age of 38 ± 1 Ma (late Eocene) for subvolcanic units that are related to mineralization. A biotite granodiorite porphyry is the testimony of the youngest magmatic activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted as magmatic crystallization ages of subvolcanic intrusions.

  10. Anorogenic nature of magmatism in the Northern Baikal volcanic belt: Evidence from geochemical, geochronological (U-Pb), and isotopic (Pb, Nd) data

    Science.gov (United States)

    Neymark, L.A.; Larin, A.M.; Nemchin, A.A.; Ovchinnikova, G.V.; Rytsk, E. Yu

    1998-01-01

    The Northern Baikal volcanic belt has an age of 1.82-1.87 Ga and extends along the boundary between the Siberian Platform and the Baikal foldbelt. The volcanic belt is composed of volcanics of the Akitkan Group and granitic rocks of the Irel and Primorsk complexes. The geochemistry of the rocks points to the intraplate anorogenic nature of the belt. U-Pb zircon dating of the Chuya granitoids revealed that they are older (2020-2060 Ma) than the Northern Baikal volcanic belt and, thus, cannot be regarded as its component. Data on the Pb isotopic system of feldspars from the granitoids confirm the contemporaneity of all volcanic rocks of the belt except the volcanics of the upper portion of the Akitkan Group (Chaya Formation). Our data suggest its possibly younger (???1.3 Ga) age. The isotopic Nd and Pb compositions of the acid volcanic rocks provide evidence of the heterogeneity of their crustal protoliths. The volcanics of the Malaya Kosa Formation have ??Nd(T) = -6.1, ??2 = 9.36, and were most probably produced with the participation of the U-depleted lower continental crust of Archean age. Other rocks of the complex show ??Nd(T) from -0.1 to -2.4, ??2 = 9.78, and could have been formed by the recycling of the juvenile crust. The depletion of the Malaya Kosa volcanics in most LILEs and HFSEs compared with other acid igneous rocks of the belt possibly reflects compositional differences between the Late Archean and Early Proterozoic crustal sources. The basaltic rocks of the Malaya Kosa Formation (??Nd varies from -4.6 to -5.4) were produced by either the melting of the enriched lithospheric mantle or the contamination of derivatives of the depleted mantle by Early Archean lower crustal rocks, which are not exposed within the area. Copyright ?? 1998 by MAEe Cyrillic signK Hay??a/Interperiodica Publishing.

  11. U-Pb and Sm-Nd data of the Rhyacian and Statherian Orthogneisses from Rio Piranhas-Seridó and Jaguaribeano Terranes, Borborema Province, Northeast of Brazil

    Directory of Open Access Journals (Sweden)

    Jaziel Martins Sá

    2014-09-01

    Full Text Available The Portalegre shear zone separates the Rio Piranhas-Seridó and the Jaguaribeano geological terranes in the Northern Domain of the Borborema Province. Banded gneisses of the Caicó and the Jaguaretama Complexes represent the basements of these terranes. U-Pb analyses yielded ages of 2,193 ± 16 Ma for the Jaguaretama Complex, which is similar to those obtained for the Caicó Complex. TDM Sm-Nd ages for these basement complexes showed Neoarchean values (ca. 2.5 Ga, with εNd(t values close to the CHUR composition. Elongated bodies were found intruding into the rocks of the Jaguaretama Complex. These foliated bodies with elongated phenocrysts are described as augen gneisses of the Serra do Deserto Suite. These gneisses yielded crystallization ages of 1,777 ± 8 Ma, confirming an extensional period during the Statherian, which is well represented in the Jaguaribeano Terrane by A-type plutonic rocks. Augen gneisses with similar textures, the so called Poço da Cruz Suite, are found intruding the Caicó Complex in the Rio Piranhas-Seridó terrane; however, the ages found throughout the domain are predominantly Rhyacian (ca. 2.2 Ga and present calc-alkaline affinities. These findings indicate that the augen gneisses, which are widely distributed in these two terranes, have different signatures and are temporally well separated. Furthermore, in agreement with previous geophysical data suggesting a division of terranes marked by the Portalegre Shear Zone, it also demonstrates that even though the Caicó and the Jaguaretama Complexes have similar ages, similar structural evolution and metamorphism under similar pressure and temperature conditions, they exhibit marked differences in composition.

  12. Petrology and U-Pb zircon dating of intrusive rocks from A, C-south, and Dardvay districts, Sangan iron stone mine, Khaf

    Directory of Open Access Journals (Sweden)

    Abbas Golmohammadi

    2013-10-01

    Full Text Available Sangan magnetite skarn mine is located 300 km southeast of Mashhad, along the eastern part of Khaf-Drouneh volcanic-plutonic belt. Granitoids from three areas within the Sangan mine A, C-North and Dardvay were studied. Within the study area, three intrusive rocks including biotite-hornblende monzonite porphyry, biotite syenite and syenogranite were recognized. Based on field cross cutting, absence of garnet-magnetite skarn around the contact, and alteration by younger hydrothermal fluids, these granitoids are older than the magnetite skarn. U-Pb zircon age of the granitoid is 42 Ma (Middle Eocene. Magnetic susceptibility of the granitoids are 310-900 × 10-5 (SI units and therefore, they are classified as belonging to the magnetite-series (oxidant type I-type. Chemically, these granitoids are metaluminous, alkali-calcic to alkali and shoshonite to ultrapotassic. Enrichment of LREE, relative to HREE and enrichment of LILE (Sr, Cs, Rb, K and Ba relative to HFSE (Nb, Ta, Ti, Hf and Zr indicate that the magma formed in island arc setting. This magma originated from low partial melting (<1% of garnet-spinel lherzolite (low garnet and was contaminated in the continental crust. Based on the ratio of (La/YbN 6.23-34.73, indicate that small amount of garnet was left in the source rock. High ration of Rb/Sr, LILE/HFSE and high content of K2O, Th and Nb indicative of continental crust contamination. Petrognesis and geochronology of Sangan granitoid will help to know more about tectonomagmatic of Khaf-Kashmar-Drouneh volcanic-plutonic belt and their mineralization.

  13. Large-scale displacement along the Altyn Tagh Fault (North Tibet) since its Eocene initiation: Insight from detrital zircon U-Pb geochronology and subsurface data

    Science.gov (United States)

    Cheng, Feng; Jolivet, Marc; Fu, Suotang; Zhang, Changhao; Zhang, Qiquan; Guo, Zhaojie

    2016-05-01

    Marking the northern boundary of the Tibetan plateau, the Altyn Tagh fault plays a crucial role in accommodating the Cenozoic crustal deformation affecting the plateau. However, its initiation time and amount of offset are still controversial despite being key information for the understanding of Tibet evolution. In this study, we present 1122 single LA-ICP-MS detrital zircon U-Pb ages obtained from 11 Mesozoic to Cenozoic sandstone samples, collected along two sections in the northwestern Qaidam basin (Eboliang and Huatugou). These data are combined with new 3D seismic reflection profiles to demonstrate that: (1) from the Paleocene to early Eocene, the Eboliang section was approximately located near the present position of Anxi, 360 ± 40 km southwest from its current location along the Altyn Tagh fault, and sediments were mainly derived from the Altyn Tagh Range. At the same period, the Huatugou section was approximately located near the present position of Tula, ca. 360 km southwest from its current location along the Altyn Tagh fault, and the Eastern Kunlun Range represented a significant sediment source. (2) Left-lateral strike-slip movement along the Altyn Tagh fault initiated during the early-middle Eocene, resulting in northeastward displacement of the two sections. (3) By early Miocene, the intensive deformation within the Altyn Tagh Range and northwestern Qaidam basin strongly modified the drainage system, preventing the materials derived from the Altyn Tagh Range to reach the Eboliang and the Huatugou sections. The post-Oligocene clastic material in the western Qaidam basin is generally derived from local sources and recycling of the deformed Paleocene to Oligocene strata. From these data, we suggest enhanced tectonic activity within the Altyn Tagh Range and northwestern Qaidam basin since Miocene time, and propose an early-middle Eocene initiation of left-lateral strike-slip faulting leading to a 360 ± 40 km offset along the Altyn Tagh fault.

  14. Contrasts between Sm-Nd whole-rock and U-Pb zircon systematics in the Tobacco Root batholith, Montana: Implications for the determination of crustal age provinces

    Science.gov (United States)

    Mueller, P.A.; Heatherington, A.L.; D'Arcy, K. A.; Wooden, J.L.; Nutman, A.P.

    1996-01-01

    Proper documentation of the extent and age of crust in the western US is critical for constraining a variety of geologic problems ranging from the growth rate of continents to Precambrian continental reconstructions. The secondary isotopic systematics of granitoids have been one of the principal means used to characterize continental crust in areas where the basement is covered. In southwestern Montana and eastern Idaho a group of Late Mesozoic to Cenozoic, dioritic to quartz monzonitic batholiths (e.g., Tobacco Root, Idaho, Pioneer, Boulder, etc.) share a limited range of Paleoproterozoic Sm-Nd depleted mantle model ages. The Tobacco Root batholith (TRB) has a Nd isotopic composition (??Nd = -17.9 to -19.1) and Sm-Nd model age (TDM = 1.63 to 1.90 Ga) typical of this group. The TRB, however, intruded Archean crust (???3.3 Ga, ??Nd = ??? -35), rather than the presumed Proterozoic crust intruded by the other plutons. The Archean heritage of the TRB is confirmed by the presence of premagmatic zircons which range from 2.2 to 3.0 Ga. The combination of U-Pb zircon and Nd model ages suggest that the batholith was derived from both Archean and Proterozoic crustal sources, as well as an ???80 Ma mantle component. This contrasts with a sample from the northern Idaho batholith which exhibits concordancy between its Sm-Nd and premagmatic zircon systems at ???1.74 Ga. These data point to the difficulties that can occur if crustal age provinces are defined solely on the basis of Nd model ages of younger plutons, particularly in areas such as the northwestern US where Archean and Proterozoic crust is poorly exposed and dispersed over a large area.

  15. Zircon U-Pb dating of Maherabad porphyry copper-gold prospect area: evidence for a late Eocene porphyry-related metallogenic epoch in east of Iran

    Directory of Open Access Journals (Sweden)

    Azadeh Malekzadeh Shafaroudi

    2011-04-01

    Full Text Available Eastern Iran has great potential for porphyry copper deposits, as a result of its past subduction zone tectonic setting that lead to extensive alkaline to calc-alkaline magmatic activity in Tertiary time. Maherabad is the first porphyry Cu-Au prospecting area which is discovered in eastern Iran. This is related to a succession o f monzonitic to dioritic porphyries stocks that were emplaced within volcanic rocks. Monzonitic porphyries have basic role in mineralization. Hydrothermal alteration zones are well developed including potassic, sericitic-potassic, quartz-sericite-carbonate-pyrite, quartz-carbonate-pyrite, silicified-propylitic, propylitic, carbonate and silicified zones. Mineralization occurs as Disseminated, stockwork and hydrothermal breccia. Based on early stage of exploration, Cu is between 179- 6830 ppm (ave. 3200 ppm and Au is up to 1000 ppb (ave. 570 ppb. This prospect is gold- rich porphyry copper deposit. Laser-ablation U-Pb dating of two samples from ore-related intrusive rocks indicate that these two monzonitic porphyries crystallized at 39.0 ± 0.8 Ma to 38.2 ± 0.8 Ma, within a short time span of less than ca. 1 Ma during the middle Eocene. This provides the first precise ages for metallogenic episode of porphyry-type mineralization. Also, the initial 87Sr/86Sr and (143Nd/144Ndi was recalculated to an age of 39 Ma. Initial 87Sr/86Sr ratios for monzonitic rocks are 0.7047-0.7048. The (143Nd/144Ndi isotope composition are 0.512694-0.512713. Initial ε Nd isotope values 1.45-1.81. Based on isotopic data the magma had originated beyond the continental crust. The study will be used for tectonic-magmatic setting and evolution of eastern Iran. Keywords: Lut block, Middle Eocene, Zircon, Geochronology, Laser ablation ICP-MS,

  16. Permian volcanisms in eastern and southeastern margins of the Jiamusi Massif, northeastern China: zircon U-Pb chronology, geochemistry and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    MENG En; XU WenLiang; YANG DeBin; PEI FuPing; Yu Yang; Zhang XingZhou

    2008-01-01

    LA-ICP-MS zircon U-Pb dating and geochemical data for the Late Paleozoic volcanic rocks from eastern and southeastern margins of the Jiamusi Massif are presented to understand the regional tectonic evolution. Zircons from eight representative volcanic rocks are euhedral-subhedral in shape and dis-play striped absorption and fine-scale oscillatory growth zoning as well as high Th/U ratios (0.33-2.37), implying a magmatic origin. The dating results show that the Late Paleozoic volcanic rocks in the study area can be divided into two stages, I.e., the Early Permian (a weighted mean 206pb/238U age of 288 Ma) and the Middle Permian volcanisms (a weighted mean 206Pb/238U age of 268 Ma). The former is com-posed mainly of basalt, basaltic-andesite, andesite and minor dacite. They are characterized by low SiO2 contents, high Mg# (0.40-0.59), enrichment in Na (Na2O/K2O = 1.26-4.25) and light rare earth elements (LREEs), relative depletion in heavy rare earth elements (HREEs) and high field strength ele-ments (HFSEs), indicating that an active continental margin setting could exist in the eastern margin of the Jiamusi Massif in the Early Permian. The latter consists mainly of rhyolite and minor dacite with high SiO2 (77.23%-77.52%), low MgO (0.11%-0.14%), enrichment in K2O (Na2O/K2O ratios <0.80) and Rb, Th, U and depletion in Eu, Sr, P and Ti, implying a crust-derived origin. Therefore, it is proposed that the Middle Permian volcanic rocks could have formed under the collision of the Jiamusi and the Khanka Massifs.

  17. Compilation of U-Pb zircon data from the Willyama Supergroup, Broken Hill region, Australia: evidence for three tectonostratigraphic successions and four magmatic events?

    International Nuclear Information System (INIS)

    The Willyama Supergroup of the Broken Hill region in southern Australia consists of supracrustal sedimentary and magmatic rocks, formed between 1810 and 1600 Ma. A statistical analysis of nearly 2000 SHRIMP U-Pb zircon spot ages, compiled from published and unpublished sources, provides evidence for three distinct tectonostratigraphic successions and four magmatic events during this interval. Succession 1 includes Redan Geophysical Zone gneisses and the lower part of the Thackaringa Group (Cues Formation). These rocks were deposited after 1810 Ma and host granite sills of the first magmatic event (1710-1700 Ma). Succession 2 includes the upper Thackaringa Group (Himalaya Formation), the Broken Hill Group and the Sundown Group and was deposited between 1710 and 1660 Ma. These rocks all contain detrital zircons from the first magmatic event (1710-1700 Ma) and in some cases from the second magmatic event (1690-1680 Ma). The second magmatic event (1690-1680 Ma) was bimodal, resulted from crustal extension, and was coeval with deposition of the Broken Hill Group and deepening of the basin. With this event a mafic sill swarm focused in the Broken Hill Domain. Mafic sills lack any trace of inheritance, unlike the granitoids that commonly contain inherited zircons typical of the supracrustal sediments. Succession 3, the Paragon Group and equivalents were deposited after 1660 Ma, but before a regional metamorphic event at 1600 Ma. Metamorphism was closely followed by inversion of the succession into a fold-and-thrust belt, accompanied by a fourth late to post-orogenic magmatic event (ca 1580 Ma) characterised by granite intrusion and regional acid volcanism (the local equivalents of the Gawler Range Volcanics in South Australia). Copyright (2002) Geological Society of Australia

  18. Granite-greenstone terranes in the Pilbara Block, Australia, as coeval volcano-plutonic complexes: Evidence from U-Pb zircon dating of the Mount Edgar Batholith

    International Nuclear Information System (INIS)

    The Mount Edgar Batholith in the Pilbara Block, Western Australia, consists, in part, of a gneiss complex that resembles other Archean high-grade gneiss terranes. The complex is extensively intruded by variably foliated granitoids which also intrude the surrounding greenstone succession, the Warrawoona Group. The contact between the greenstone belt and the gneiss complex is tectonic. Field evidence indicates that the banded gneisses are the oldest part of the batholith; zircon U-Pb ages for three samples are 3429±13 Ma, ≥ 3443±10 Ma and 3448±8 Ma, all very similar to the age of zircons in the felsic volcanic rocks near the base of the greenstone succession. Two granitoids, representing pre- and post-tectonic phases respectively, give zircon ages of 3304±10 Ma and 3314±13 Ma, thereby constraining the major structural events to be contemporary with granite magmatism, consistent with a diapiric model for the tectonic evolution of the batholith. These ages are similar to the zircon age for terminal volcanism in the Warrawoona Group, but are ≅ 100 Ma older than the precisely-defined Rb-Sr whole-rock ages obtained throughout the batholith. Batholith-wide resetting or late closure of Rb-Sr isotopic systems is implied, possibly associated with late fluid circulation. The temporal coincidence between plutonism and volcanism in the Mount Edgar region strongly suggests that the greenstone succession contains the extrusive equivalents of both the ≅ 3300 Ma granites and the ≅ 3440 Ma gneisses in the batholith. The isotopic evidence, combined with the structural data, indicates that the granites cannot be derived from the surrounding greenstone belt. Further, there is no compelling evidence for a sialic basement to the greenstone succession. (orig.)

  19. Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) of the Paleoproterozoic effusive rocks from Iricoume Group, Amazonian Craton, Brazil

    International Nuclear Information System (INIS)

    The southernmost region of the Guyana shield, Amazonian craton, hosts large record of Paleoproterozoic effusive rocks of the Iricoume Group. They present remarkably well-preserved igneous textures and structures. The SiO2 contents reveal a bimodal association marked by a compositional gap between acid (SiO2 > 67 wt%) and intermediate (SiO2 2, alkali, Rb, Zr, Nb + Ta, La + Ce and 104 Ga/Al content and low Fe2O3tot, TiO2, CaO, Sr and Co content. They exhibit subalkaline, metaluminous-to-peraluminous compositions, and geochemically compatible to A-type magmatism emplaced in post-collisional to within-plate tectonic settings. The intermediate rocks are andesitic/basalt to andesite relatively high contents of TiO2, Al2O3, Fe2O3total, MgO, CaO, Sr and Co; low SiO2, K2O, Rb, Zr, Nb + Ta, La + Ce. They have subalkaline and metaluminous geochemical composition and plot on within-plate basalt field. The acid rocks crystallized at 1882 ± 11 Ma in U-Pb analyses for LA-MC-ICPMS zircon data. The Sm-Nd isotopic data on all rocks reveal a Nd TDM model ages between 2.59 and 2.16 Ga and εNd(t) values between -5.78 and 0.03, indicate that the magmatic evolution was related to the reworking of older Paleoproterozoic at the Rhyacian-Siderian period, continental crust (Transamazonian crust-forming event) with some mixing with a limited amount mantle-derived magmas or with contamination by Archean crust. The petrographic, geochemical and geochronological data presented in this paper suggest a within-plate to post-collisional tectonic setting for the Iricoume volcanism, involving lower crust uplift and generation of basalt magma in an extensional regime. (author)

  20. U-Pb geochronology of the Upper Proterozoic - Lower Paleozoic geodynamic evolution in the Ossa-Morena Zone (SW Iberia): constraints on the timing of the Cadomian orogeny

    International Nuclear Information System (INIS)

    The Ossa-Morena Zone is situated at the southwestern margin of the European Hercynides and constitutes a prominent part of the pre-Mesozoic Iberian Massif. The occurrence of a tectonomagmatically diverse assemblage of Cadomian igneous suites and the predominant absence of penetrative tectometamorphic overprints makes the Ossa-Morena Zone a key area within the Avalonian-Cadomian belt for unravelling the Upper Proterozoic - Lower Paleozoic geodynamic evolution. The present state of knowledge, based upon a data synthesis of recent interdisciplinary investigations, confirms unambiguously the existence of Cadomian orogenic processes within the Ossa-Morena Zone. In the light of these data, an active continental margin setting (Andean-type) appears to be most likely geotectonic scenario for the formation of the orogenic complex. The limited availability of geochronologic results, however, whose geologic significance is additionally questionable due to shortcomings of the applied isotopic methods, prevent up to now a clear recognition of a well-defined sequence of Cadomian orogenic events. To remedy this defect, the study deals with the first systematic U-Pb study on magnetic rocks in the Ossa-Morena Zone, carried out on twelve Upper Proterozoic and Lower Paleozoic granitoids. Although orogenic processes are considered representing a continuum of events, the new geochronologic results enable a first recognition of six distinct magmatic episodes, each representative for a particular stage in the geodynamic evolution of the Cadomian orogenic belt. The six identified magmatic events cover the time interval of approximately 150 Ma from ca. 620 Ma up to 470 Ma and reflect a complete Cadomian Wilson cycle and the beginning of the Hercynian Wilson cycle. The main innovative contribution of this study concerns the attained high chronologic resolution of the Cadomian end-orogenic magmatic activity. (author) figs., tabs., refs

  1. SHRIMP U-Pb geochronological constraints on the timing of the intra-Alcudian (Cadomian) angular unconformity in the Central Iberian Zone (Iberian Massif, Spain)

    Science.gov (United States)

    Talavera, C.; Martínez Poyatos, D.; González Lodeiro, F.

    2015-10-01

    New SHRIMP U-Pb ages of detrital zircons from Neoproterozoic low-grade metasandstones of the Schist-Graywacke Complex (Central Iberian Zone, Iberian Massif) sampled just below and above the intra-Alcudian unconformity at two selected locations contribute to reconstruct the geodynamic evolution of Iberia during the Cadomian orogeny in the north Gondwana margin. The youngest zircons (i.e., maximum depositional age) in the Lower Alcudian are c. 580-576 Ma, while those in the Upper Alcudian are c. 555-552 Ma. The obtained remarkable time gap of about 21 Ma supports the existence of a tectonic event in between. This event resulted in moderate folding (without related foliation/metamorphism) that verticalized the Lower Alcudian previous to the deposition of the Upper Alcudian. Additional evidence of late Cadomian tectonothermal events elsewhere in Iberia also fit in the interval c. 560-550 Ma. Combined with other geological data, the most probable maximum depositional ages are c. 580-560 Ma for the Lower Alcudian (previous to the late Cadomian folding event) and c. 550-540 Ma for the Upper Alcudian (previous to the deposition of the overlying Pusian Group and Lower Cambrian sandstones and limestones). A comparison of the new zircon age spectra with possible source areas verifies recent studies that point to the Cadomian foreland in the north Gondwana continent affected by the Pan-African orogeny: the West African Craton and/or the Saharan Metacraton. Furthermore, ongoing Cadomian arc-related magmatism in Iberia (c. 605-545 Ma) could have contributed as a local zircon source. The end of the Cadomian activity is marked by a transient stage (ephemeral Lower Cambrian platform) which preceded widespread Cambro-Ordovician rifting of north Gondwana.

  2. U-Pb zircon geochronology of the Paleoproterozoic Tagragra de Tata inlier and its Neoproterozoic cover, western Anti-Atlas, Morocco

    Science.gov (United States)

    Walsh, G.J.; Aleinikoff, J.N.; Benziane, F.; Yazidi, A.; Armstrong, T.R.

    2002-01-01

    New U-Pb zircon data obtained by sensitive high resolution ion microprobe (SHRIMP) from the Tagragra de Tata inlier in the western Anti-Atlas, Morocco establish Paleoproterozoic ages for the basement schists, granites, and metadolerites, and a Neoproterozoic age for an ignimbrite of the Ouarzazate Series in the cover sequence. The age of interbedded felsic metatuff in the metasedimentary and metavolcanic sequence of the basement schists is 2072 ?? 8 Ma. This date represents: (1) the first reliable age from the metasedimentary and metavolcanic sequence; (2) the oldest reliable age for the basement of the Anti-Atlas; (3) the first date on the timing of deposition of the sediments on the northern edge of the Paleoproterozoic West African craton; (4) a lower age limit on deformation during the Eburnean orogeny; and (5) the first date obtained from the non-granitic Paleoproterozoic basement of Morocco. Ages of 2046 ?? 7 Ma (Targant granite) and 2041 ?? 6 Ma (Oudad granite) support earlier interpretations of a Paleoproterozoic Eburnean igneous event in the Anti-Atlas. The granites post-date the Eburnean D1 deformation event in the Paleoproterozoic schist sequence, and place a ???2046 Ma limit on short-lived Eburnean deformation in the area. Cross-cutting metadolerite is 2040 ?? 6 Ma; this is the first date from a metadolerite in the western Anti-Atlas. All of the dolerites in the area post-date emplacement of the two granites and the new age constrains the onset of late- or post-Eburnean extension. Ignimbrite of the Ouarzazate Series, immediately above the Paleoproterozoic basement is 565 ?? 7 Ma. This Neoproterozoic age agrees with ages of similar volcanic rocks elsewhere from the Ouarzazate Series. The date also agrees with the ages of associated hypabyssal intrusions, and marks the second and final stage of Pan-African orogenic activity in the western Anti-Atlas. ?? 2002 Elsevier Science B.V. All rights reserved.

  3. Tracing source terranes using U-Pb-Hf isotopic analysis of detrital zircons: provenance of the Orhanlar Unit of the Palaeotethyan Karakaya subduction-accretion complex, NW Turkey

    Science.gov (United States)

    Ustaömer, Timur; Ayda Ustaömer, Petek; Robertson, Alastair; Gerdes, Axel

    2016-04-01

    Sandstones of the Late Palaeozoic-Early Mesozoic Karakaya Complex are interpreted to have accumulated along an active continental margin related to northward subduction of Palaeotethys. The age of deposition and provenance of the sandstones are currently being determined using radiometric dating of detrital zircons, coupled with dating of potential source terranes. Our previous work shows that the U-Pb-Hf isotopic characteristics of the sandstones of all but one of the main tectonostratigraphic units of the Karakaya Complex are compatible with a provenance that was dominated by Triassic and Permo-Carboniferous magmatic arc-type rocks, together with a minor contribution from Lower to Mid-Devonian igneous rocks (Ustaömer et al. 2015). However, one of the tectono-stratigraphic units, the Orhanlar Unit, which occurs in a structurally high position, differs in sedimentary facies and composition from the other units of the Karakaya Complex. Here, we report new isotopic age data for the sandstones of the Orhanlar Unit and also from an extensive, associated tectonic slice of continental metamorphic rocks (part of the regional Sakarya Terrane). Our main aim is to assess the provenance of the Orhanlar Unit sandstones in relation to the tectonic development of the Karakaya Complex as a whole. The Orhanlar Unit is composed of shales, sandstone turbidites and debris-flow deposits, which include blocks of Devonian radiolarian chert and Carboniferous and Permian neritic limestones. The sandstones are dominated by rock fragments, principally volcanic and plutonic rocks of basic-to-intermediate composition, metamorphic rocks and chert, together with common quartz, feldspar and mica. This modal composition contrasts significantly with the dominantly arkosic composition of the other Karakaya Complex sandstones. The detrital zircons were dated by the U-Pb method, coupled with determination of Lu-Hf isotopic compositions using a laser ablation microprobe attached to a multicollector

  4. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

    Science.gov (United States)

    Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

    2014-07-01

    In order to understand the age and tectonic framework of Eastern to Peninsular Thailand from the viewpoint of basement (metamorphic and plutonic) geology, the LA-ICP-MS U-Pb zircon dating and the chemical Th-U-total Pb isochron method (CHIME) monazite dating were performed in the Khao Chao, Hub-Kapong to Pran Buri, and Khanom areas in Eastern to Peninsular Thailand. The LA-ICP-MS U-Pb zircon dating of the garnet-hornblende gneiss from the Khao Chao area gave 229 ± 3 Ma representing the crystallization age of the gabbro, and that of the garnet-biotite gneisses gave 193 ± 4 Ma representing the timing of an upper amphibolite facies metamorphism. The CHIME monazite dating of pelitic gneiss from the Khao Chao gneiss gave scattered result of 68 ± 22 Ma, due to low PbO content and rejuvenation of older monazite grains during another metamorphism in the Late Cretaceous to Tertiary time. The U-Pb ages of zircon from the Hua Hin gneissic granite in the Hub-Kapong to Pran Buri area scatter from 250 Ma to 170 Ma on the concordia. Granite crystallization was at 219 ± 2 Ma, followed by the sillimanite-grade regional metamorphism at 185 ± 2 Ma. Monazite in the pelitic gneiss from this area also preserves Early to Middle Jurassic metamorphism and rejuvenation by later contact metamorphism by non-foliated granite or by another fluid infiltration event in the Late Cretaceous to Tertiary time. The Khao Dat Fa granite from the Khanom area of Peninsular Thailand gave a U-Pb zircon age of 477 ± 7 Ma. This is the second oldest granite pluton ever reported from Thailand, and is a clear evidence for the Sibumasu block having a crystalline basement that was formed during the Pan-African Orogeny. The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses. Metamorphic rocks in the Doi Inthanon area

  5. Large-scale displacement along the Median Tectonic Line, Japan: evidence from SHRIMP zircon U-Pb dating of granites and gneisses from the South Kitakami and paleo-Ryoke belts

    Science.gov (United States)

    Sakashima, Toshihiko; Terada, Kentaro; Takeshita, Toru; Sano, Yuji

    2003-07-01

    In this paper we present new U-Pb zircon ages determined with Sensitive High-Resolution Ion MicroProbe (SHRIMP) for nine plutonic rocks or orthogneisses and one paragneiss from the Higo and Maana belts (here referred to as the paleo-Ryoke belt) in southwest Japan, and the South Kitakami belt in northeast Japan. Both belts are Paleozoic-Mesozoic continental terranes discontinuously distributed along the Median Tectonic Line (MTL), and structurally lying on the Sambagawa belt in the Japanese Islands. Three groups of U-Pb zircon ages showing the timing of different magmatic events were determined for the plutonic rock or orthogneiss samples: ca. 500 Ma (Early Ordovician, two samples), a mean age of 292.0±12.4 Ma (Late Carboniferous-Early Permian, one sample) and ca. 110 Ma (Early Cretaceous, six samples). Furthermore, zircons with core-rim microstructures from a garnet-biotite-cordierite paragneiss in the Higo belt were also dated with SHRIMP. The cores yielded 2155-184 Ma inherited U-Pb ages (mostly varying between 330 and 184 Ma), while the rims yielded a mean age of 116.5±18.7 Ma (Early Cretaceous) U-Pb recrystallization ages comparable with the igneous ages, limiting the sedimentary age of the protolith to between Early-Middle Jurassic (ca. 180 Ma) and Early Cretaceous time. These SHRIMP U-Pb ages of plutonism, metamorphism and sedimentation, together with previously reported radiometric ages, have revealed a strong similarity in the tectonic histories of the paleo-Ryoke and South Kitakami and Abukuma belts, suggesting that these belts can be correlated. At present the paleo-Ryoke belt and the South Kitakami and Abukuma belts are separated by more than 1000 km. However, these belts may have originally comprised a continuous continental terrane that was later displaced and juxtaposed, together with the underlying Sambagawa belt, against the Ryoke belt by large-scale sinistral faulting along the MTL and associated major strike-slip faults during the Latest

  6. fuego en Argentina, 1980-2012

    Directory of Open Access Journals (Sweden)

    Hugo Spinelli

    2015-01-01

    Full Text Available Este trabajo analiza el impacto de las armas de fuego en la mortalidad entre los años 1980-2012 en Argentina. Para ello se realiza un estudio epidemiológico descriptivo de la tendencia temporal, a través de las siguientes variables: sexo, grupos de edad, intencionalidad y jurisdicción. Los datos fueron obtenidos en la Dirección de Estadísticas e Información en Salud del Ministerio de Salud de la Nación. Se encontraron 87.671 muertes por armas de fuego. Los varones representaron el 85,7% y su tasa más alta fue para el año 2002 con 21,2 muertes por 100.000 habitantes. El grupo de edad que concentró la mayor cantidad de muertes por armas de fuego fue el de 20 a 29 años (25,6%. Las tasas ajustadas más altas corresponden a los años 2000-2002 con valores entre 10,0 y 11,6 muertes por cada 100.000 habitantes, período que coincide con la crisis económicoinstitucional que atravesó el país. La provincia de Buenos Aires fue el lugar de residencia del 49,1% de las muertes. En la discusión se abordan dimensiones político-económicas e ideológico-culturales en la relación entre armas, violencias, ciencia y sociedad.

  7. Geochemical, zircon U-Pb dating and Sr-Nd-Hf isotopic constraints on the age and petrogenesis of an Early Cretaceous volcanic-intrusive complex at Xiangshan, Southeast China

    Science.gov (United States)

    Yang, Shui-Yuan; Jiang, Shao-Yong; Jiang, Yao-Hui; Zhao, Kui-Dong; Fan, Hong-Hai

    2011-01-01

    The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U-Pb dating, and Sr-Nd-Hf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2 Myrs. The stratigraphically oldest rhyodacite yielded a zircon U-Pb age of 135 ± 1 Ma and the overlying rhyodacitic porphyry has an age of 135 ± 1 Ma. Three porphyritic lava samples yielded zircon U-Pb ages of 136 ± 1 Ma, 132 ± 1 Ma, and 135 ± 1 Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U-Pb ages of 137 ± 1 Ma and 137 ± 1 Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U-Pb age of 136 ± 1 Ma. All these newly obtained precise U-Pb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr-Nd-Hf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ɛNd(T) value higher than the other rocks

  8. A lab in Argentina

    Science.gov (United States)

    2016-06-01

    Mauricio Erben, a researcher at the National University of La Plata and the National Scientific and Technical Research Council, talks to Nature Chemistry about his experience of research in Argentina, and how it is inherently linked to the country's political climate.

  9. Radiation vulcanization in Argentina

    International Nuclear Information System (INIS)

    The possibilities of using in Argentina the radiation process to vulcanize natural latex are analyzed. Experimental studies to define the irradiation conditions have been carried out and the preliminary elaboration of an irradiation device that includes the chemical reactor has been started. (author)

  10. Mathematics Education in Argentina

    Science.gov (United States)

    Varsavsky, Cristina; Anaya, Marta

    2009-01-01

    This article gives an overview of the state of mathematics education in Argentina across all levels, in the regional and world contexts. Statistics are drawn from Mercosur and UNESCO data bases, World Education Indicators and various national time-series government reports. Mathematics results in national testing programmes, Programme for…

  11. Rickettsia parkeri in Argentina

    OpenAIRE

    Nava, Santiago; Elshenawy, Yasmin; Eremeeva, Marina E.; Sumner, John W.; Mastropaolo, Mariano; Paddock, Christopher D.

    2008-01-01

    Clinical reports of an eschar-associated rickettsiosis in the Paraná River Delta of Argentina prompted an evaluation of Amblyomma triste ticks in this region. When evaluated by PCR, 17 (7.6%) of 223 questing adult A. triste ticks, collected from 2 sites in the lower Paraná River Delta, contained DNA of Rickettsia parkeri.

  12. Albert Einstein visits Argentina

    CERN Document Server

    Gangui, A; Gangui, Alejandro; Ortiz, Eduardo L.

    2005-01-01

    This is a detailed, day by day, account of Albert Einstein's activities, both social and scientific, during his 30-day stay in Argentina in 1925, including his lectures on relativity at the various local universities and his visit to the National Academy of Sciences, as follows from his personal Diary of the trip to South-America and other contemporary documents.

  13. Petrogenesis and zircon U-Pb dating of skarnified pyroxene-bearing dioritic rocks in Bisheh area, south of Birjand, eastern Iran

    Directory of Open Access Journals (Sweden)

    Malihe Nakhaei

    2014-10-01

    Full Text Available Introduction The study area is located 196 km south of Birjand in eastern border of the Lut block Berberian and King, 1981 in eastern Iran between 59°05′35" and 59°09′12" E longitude and 31°42′29" and 31°44′13" N latitude. The magmatic activity in the Lut block began in the middle Jurassic such as Kalateh Ahani, Shah Kuh and Surkh Kuh granitoids that are among the oldest rocks exposed within the Lut block (Esmaeily et al., 2005; Tarkian et al., 1983; Moradi Noghondar et al., 2011-2012. Eastern Iran, and particularly the Lut block, has great potential for different types of mineralization as skarnification in Bisheh area which has been studied in this paper. The goal of this study is to highlight the geochronology, geochemistry of major and trace elements, Rb-Sr, Sm-Nd isotopes for skarnified pyroxene-bearing diorites. Materials and methods Major element compositions of thirteen samples were determined by wavelength-dispersive X-ray fluorescence (XRF spectrometry, using fused discs and the Phillips PW 1410 XRF spectrometer at Ferdowsi University, Mashhad, Iran. These samples were analysed for trace elements using inductively coupled plasma-mass spectrometry (ICP-MS in the Acme Analytical Laboratories, Vancouver, British Columbia, Canada. Zircon grains were separated from pyroxene diorite porphyrys using heavy liquid and magnetic techniques at the Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan. Zircon U-Pb dating was performed by laser ablation-inductively-coupled plasma-mass spectrometry (LA-ICP-MS, using an Agilent 7500 s machine and a New Wave UP213 laser ablation system, equipped at the Dr Shen-Su Sun memorial laboratory in the Department of Geosciences, National Taiwan University, Taiwan. Strontium and Nd isotopic analyses were performed on a six-collector Finnigan MAT 261 thermal-ionization mass spectrometer at the University of Colorado, Boulder, Colorado, United States. 87Sr/86Sr ratios were determined using four

  14. Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation

    Science.gov (United States)

    Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

    2009-01-01

    The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with {010} slip. The deformation bands are unlike curved

  15. Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) of the Paleoproterozoic effusive rocks from Iricoume Group, Amazonian Craton, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Marques, Suelen Nonata de Souza; Nascimento, Rielva Solimairy Campelo do, E-mail: suelen-marques@hotmail.com, E-mail: rielva@ufam.edu.br [Universidade Federal do Amazonas (UFAM), Manaus, AM (Brazil). Inst. de Geociencias; Souza, Valmir da Silva; Dantas, Elton Luiz, E-mail: vsouza@unb.br, E-mail: elton@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Valerio, Cristovao da Silva, E-mail: cristovao@igeo.ufrr.br [Universidade Federal de Roraima (UFRR), Boa Vista, RR (Brazil). Inst. de Geociencias

    2014-07-01

    The southernmost region of the Guyana shield, Amazonian craton, hosts large record of Paleoproterozoic effusive rocks of the Iricoume Group. They present remarkably well-preserved igneous textures and structures. The SiO{sub 2} contents reveal a bimodal association marked by a compositional gap between acid (SiO{sub 2} > 67 wt%) and intermediate (SiO{sub 2} < 57.7 wt%) rocks. The acid effusive rocks are rhyolites to rhyodacites with high SiO{sub 2}, alkali, Rb, Zr, Nb + Ta, La + Ce and 104 Ga/Al content and low Fe{sub 2}O{sub 3tot}, TiO{sub 2}, CaO, Sr and Co content. They exhibit subalkaline, metaluminous-to-peraluminous compositions, and geochemically compatible to A-type magmatism emplaced in post-collisional to within-plate tectonic settings. The intermediate rocks are andesitic/basalt to andesite relatively high contents of TiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3total}, MgO, CaO, Sr and Co; low SiO{sub 2}, K{sub 2}O, Rb, Zr, Nb + Ta, La + Ce. They have subalkaline and metaluminous geochemical composition and plot on within-plate basalt field. The acid rocks crystallized at 1882 ± 11 Ma in U-Pb analyses for LA-MC-ICPMS zircon data. The Sm-Nd isotopic data on all rocks reveal a Nd TDM model ages between 2.59 and 2.16 Ga and ε{sub Nd}(t) values between -5.78 and 0.03, indicate that the magmatic evolution was related to the reworking of older Paleoproterozoic at the Rhyacian-Siderian period, continental crust (Transamazonian crust-forming event) with some mixing with a limited amount mantle-derived magmas or with contamination by Archean crust. The petrographic, geochemical and geochronological data presented in this paper suggest a within-plate to post-collisional tectonic setting for the Iricoume volcanism, involving lower crust uplift and generation of basalt magma in an extensional regime. (author)

  16. U-Pb Zircon geochronology and Sr-Nd isotopic characteristic of Late Neo proterozoic Born award granitoids (Taknar zone exotic block), Iran

    International Nuclear Information System (INIS)

    The study area (Born award granite) is located in northeast of Iran (Khorasan Razavi province), about 280 km southwest of Mashhad city. Taknar zone is an exotic block, bordered by two major faults, Great Kavir fault (Drouneh) to the south and Rivash fault in the north. A complex of granite, granodiorite, monzonite and diorite crop out at the center of Taknar zone. They are named as Bornaward granite. Published data using Rb-Sr whole-rock and biotite isotopic methods on granitoid rocks (Born award granite) gave ages of 154 to 111 Ma. The results of U-Pb zircon dating of granodiorite is 552.69 ± 10.89 Ma and granite is 538.22 - 1.82, + 4.28 Ma (Late Neo proterozoic time). Both granite and granodiorite are classified as belonging to the ilmenite-series of reduced S-type granitoids. Chemically, they are per-aluminous, high-K calc-alkaline with relatively enriched in LILE, Rb, K and depleted in Sr, Ba, Nb, Ti, Ta, Y and Yb. Chondrite-normalized Rare Earth Element plots indicate minor enrichments of light Rare Earth Element in composition with heavy Rare Earth Element, with (La/Yb)N between 3.5-5.6 and high total Rare Earth Element (193-252) with strong negative anomaly of Eu. They have a initial 87Sr/86Sr and 143Nd/144Nd ranging from 0.713566 to 0.716888 and 0.511791 to 0.511842, respectively, when recalculated to an age of 553 and 538 Ma, consistent with the new radiometric results. Initial εNd isotope values for granite and granodiorite range from -2,62 to -2,01. Granite and granodiorite of Born award yields a TDM age of 1.4-1.41 Ga. This indicates that the granites and granodiorite being derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr.

  17. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    Science.gov (United States)

    Vazquez, J. A.; Matthews, N. E.; Calvert, A. T.

    2015-12-01

    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). Tephra from the eruption blanketed much of the western United States, and is a key Quaternary chronostratigraphic marker, in particular for dating deposition of mid-Pleistocene glacial and pluvial deposits in western North America. We performed 40Ar/39Ar dating of single sanidines to delimit eruption age, and ion microprobe U-Pb and trace-element analyses of crystal faces on single zircons to characterize magmatic evolution and date near-eruption crystallization, as well as analyses of crystal interiors to date the interval of zircon crystallization. Sanidines from the two LCT members A and B yield an 40Ar/39Ar isochron date of 631 ± 4 ka (2σ). Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 627 ± 6 ka (2σ) and have trace element concentrations that vary with eruptive stratigraphy. Zircon interiors yield a weighted mean 206Pb/238U date of 660 ± 6 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high-U concentrations and dark cathodoluminescence (CL) cores. These crystals with high-U cores are possibly sourced from 'defrosting' of melt-impregnated margins of the growing subvolcanic reservoir. LCT sanidines mirror the variation of zircon composition within the eruptive stratigraphy, with crystals from upper LCT-A and basal LCT-B having bright-CL rims with high Ba concentrations, suggesting late crystallization after addition of less evolved silicic magma. The occurrence of distal LCT in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ca. 631 ka. These results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval

  18. Petrogenesis of Tarom high-potassic granitoids in the Alborz-Azarbaijan belt, Iran: Geochemical, U-Pb zircon and Sr-Nd-Pb isotopic constraints

    Science.gov (United States)

    Nabatian, Ghasem; Ghaderi, Majid; Neubauer, Franz; Honarmand, Maryam; Liu, Xiaoming; Dong, Yunpeng; Jiang, Shao-Yong; von Quadt, Albrecht; Bernroider, Manfred

    2014-01-01

    Large-scale Upper Eocene plutons in the Western Alborz-Azarbaijan orogenic belt mostly show calc-alkaline and I-type geochemical features contrasted by the Tarom complex with its high-potassic to shoshonitic affinity. The pluton was emplaced in the Tarom subzone of the orogenic belt and its laser ICP-MS zircon U-Pb age of 41 Ma is interpreted as the age of magma crystallization. The Tarom complex is composed of quartz monzodiorite, quartz-monzonite and monzogranite, the SiO2 contents range from 57 to 70 wt.%, the K2O + Na2O content is high (5.0-8.9 wt.%) and K2O/Na2O ratio ranges from 0.4 to 1.9. All the investigated rocks are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), and bear a weak Eu anomaly (Eu/Eu* = 0.46 to 1.38) in chondrite-normalized trace element patterns. The samples display some variety in initial Sr and Nd isotopic compositions, marked with low ISr = 0.704-0.705 and ɛNd (40 Ma) = - 4.2 to + 3.4 (- 5.7 for an enclave) values. The Pb isotopic ratios are (206Pb/204Pb) = 18.52-18.86, (207Pb/204Pb) = 15.57-15.72 and (208Pb/204Pb) = 38.47-39.08. Comparison with experimental studies, together with mantle-like isotopic ratios and comparisons of REE patterns, points to an origin of chemically enriched lithospheric mantle source for the Tarom plutonic complex. Partial melting process involving different partial melting degrees affecting heterogeneously metasomatized mantle is a process that seems likely to have occurred in the studied complex as the major differentiation process. The Tarom monzonitic plutons are considered to be post-orogenic intrusions that were emplaced in an environment of lithospheric extension, causing asthenospheric upwelling. Asthenospheric upwelling induced a thermal anomaly which caused partial melting of metasomatized subcontinental lithospheric mantle in the Tarom area.

  19. Zircon U-Pb geochronology, geochemistry, and Sr-Nd-Hf isotopes of granitoids in the Yulekenhalasu copper ore district, northern Junggar, China: Petrogenesis and tectonic implications

    Science.gov (United States)

    Yang, Fuquan; Chai, Fengmei; Zhang, Zhixin; Geng, Xinxia; Li, Qiang

    2014-03-01

    The Yulekenhalasu porphyry copper deposit is located in the Kalaxiange'er metallogenic belt in northern Junggar, China. We present the results from zircon U-Pb geochronology, and geochemical and Sr-Nd-Hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting. The granitoids consist of quartz diorite, diorite porphyry, porphyritic monzonite, and quartz porphyry, emplaced at 382, 379, 375-374, and 348 Ma, respectively, which span Late Devonian to early Carboniferous ages. The ore-bearing intrusion is mainly diorite porphyry, with subordinate porphyritic monzonite. The Late Devonian intrusions are characterized by SiO2 contents of 54.5-64.79 wt.%, Na2O contents of 3.82-8.24 wt.%, enrichment in Na, light rare-earth elements (LREEs), and large ion lithophile elements. They also display relative depletion in Y, Ba, P, Nb, Ta, and Ti, and weak negative Eu anomalies (δEu = 0.6-0.87). The early Carboniferous quartz porphyry is characterized by high SiO2 content (72.26-73.35 wt.%), enrichment in LREEs, K, and Sr, and relative depletion in Y (10.82-12.52 ppm) and Yb (1.06-1.15 ppm). The Late Devonian and early Carboniferous granitoids are characterized by positive ɛNd(t) values (5.2-10.1, one sample at - 1.9), positive ɛHf(t) values (7.46-18.45), low (87Sr/86Sr)i values (0.70363-0.70476), and young crustal residence ages. These data indicate that the sources of the granitoids were mainly mantle-derived juvenile rocks. Geochemical and Nd-Sr-Hf isotopic data demonstrate that the Late Devonian granitoids formed in an oceanic island arc, and they were formed from different sources, among which the mineralized diorite porphyry might have originated from a mixed slab-derived and mantle wedge melt source. The early Carboniferous quartz porphyry was likely emplaced in a mature island arc environment, and was probably derived from juvenile crust.

  20. The link between volcanism and plutonism in epizonal magma systems; high-precision U-Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

    Science.gov (United States)

    Rioux, Matthew; Farmer, G. Lang; Bowring, Samuel A.; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.

    2016-02-01

    The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U-Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the final eruption. Calculated magmatic

  1. U-Pb zircon geochronology, Sr-Nd geochemistry, petrogenesis and tectonic setting of Mahoor granitoid rocks (Lut Block, Eastern Iran)

    Science.gov (United States)

    Beydokhti, Roohollah Miri; Karimpour, Mohammad Hassan; Mazaheri, Seyed Ahmad; Santos, José Francisco; Klötzli, Urs

    2015-11-01

    The Mahoor Cu-Zn-bearing porphyritic granitoid rocks belong to the Lut Block volcanic-plutonic belt (central Eastern Iran). These granitoid rocks occur mainly as dykes and stocks that intrude into Eocene volcanics and pyroclastic rocks. Petrographically, all the studied intrusives display porphyritic textures with mm-sized phenocrysts, most commonly of plagioclase and hornblende, embedded in a fine-grained groundmass with variable amounts of plagioclase, hornblende, clinopyroxene, quartz and opaque minerals. Hydrothermal alteration affected these granitoid rocks, as revealed by the common occurrence of sericite, chlorite, titanite, epidote and calcite. Chemical classification criteria show that the intrusives may be named as gabbrodiorites, diorites, monzodiorites and tonalites. Major elements geochemistry reveals that all the studied lithologies are typically metaluminous (A/CNK ⩽ 0.9). Magnetic susceptibility (1485 × 10-5 SI) together with mineralogical and geochemical features shows that they belong to magnetite granitoid series (I-type). Trace element patterns normalized to chondrite and primitive mantle are very similar to each other and show enrichments in LREE relative to HREE and in LILE relative to HFSE, as well as negative anomalies of Ta, Nb and Ti. Eu/Eu∗ ratios vary from 0.88 (in the most mafic composition) to 0.65, showing that plagioclase played a role in magma differentiation. LA-MC-ICP-MS U-Pb zircon data from a diorite, yielded similar concordia ages of ca. 31.88 ± 0.2 Ma (Error: 2σ), which corresponds to the Oligocene period. These granitoid rocks have (87Sr/86Sr)i values vary between 0.7055 and 0.7063. In terms of isotopic compositions, while εNdi is between -0.6 and -2.5, suggesting that magmas underwent contamination through being exposed to the continental crust. The whole set of geochemical data agree with the emplacement of the studied intrusions in a magmatic belt above a subduction zone. Primitive magmas should have formed by

  2. U-Pb geochronology and geochemistry of Zahedan and Shah kuh plutons, eastern Iran: Implication for the late stage of the tectonic evolution of the South Sistan Zone

    Science.gov (United States)

    Mohammadi, Ali; Burg, Jean-Pierre; Ruh, Jonas; Von Quadt, Albrecht; Peytcheva, Irena

    2015-04-01

    The N-S trending Sistan Suture Zone (SSZ) in eastern Iran is attributed to eastward subduction beneath the Afghan continental block of an inlet of the Mesozoic Tethys Ocean. We present U-Pb zircon crystallization ages combined with petrography, major and trace element analyses, Hf isotopes, Rb-Sr and Sm-Nd isotopes of intermediate to granitic intrusions stretched along the southern segment of the SSZ. We obtained two clearly separated clusters of concordant ages, which are taken as the crystallization age of the host plutonic rocks. The first cluster, between ca 42.5 and ca 44.5 Ma from euhedral zircons of the main granodiorite to diorite and related dykes. The second age cluster span from ca 28.3 to ca 31 Ma. These ages were obtained for granites and dykes, the latter being consistently slightly younger than the country rock. The high SiO2 content (62-75 wt %) of Eocene magmatic rocks points to melts with a high crustal contribution in consistency with their relatively high-K (3-4.4 wt %) calc-alkaline nature. The high SiO2 and K contents in the Oligocene calk-alkaline rocks series shows adakite-like fractionation. Oligocene adakite-like rocks have relatively low to medium 87Sr/86Sr and 143Nd/144Nd ratios, which are similar to typical lower thick crust-derived adakites. The mix positive and negative ɛHf(T) values of all zircons from the 42.5-44.5 Ma shows mix nature of magma (the contamination of subduction related magma with partial melting of crust). The positive ɛHf(T) values of all zircons from the 28-31 Ma adakite-like rocks indicate that the magma was not produced from pure depleted mantle. Instead, they are consistent with a host magma source within a largely juvenile and subduction-related mafic lower crust. Eocene granitoids represent anatectic melts emplaced at higher crustal levels; in addition slab melts modified the mantle wedge and subsequent, contaminated mantle magmas fed intrusions such as the Zahedan diorite.

  3. Structure and SHRIMP U/Pb zircon ages of granites adjacent to the Chitradurga Schist belt: implications for neoarchaean convergence in the Dharwar Craton, Southern India

    International Nuclear Information System (INIS)

    Neoarchaean granites adjacent to the Chitradurga schist belt were emplaced in thc inner margin of the foreland in the context of the Neoarchaean oblique convergent setting of the Dharwar craton. Two previously unreported granites, one 50 km and the other 80 km NW of Chitradurga town, and a mylonitised granite in the hanging wall of a duplex in the NW of the schist belt yielded SHRIMP U/Pb zircon emplacement ages of 2648±40 Ma, 2598± 19 Ma, and ca. 2600 Ma, respectively, the large errors being due to radiogenic Pb loss during an unidentified Neoproterozoic event. Some discrete zircon grains and xenocrystic cores yielded ≥3000 Ma ages that were derived from older rocks during anatexis or emplacement. The granites NW of Chitradurga town were emplaced as steep sheets trending NW-SE. The Chitradurga granite has a similar form, bifurcating N of Chitradurga town into two separate, steeply dipping, NW-SE sheets. Magmatic- and solid-state fabrics in these granites show that emplacement took place during, but was outlasted by, sinistral and dextral strike-parallel shear. Emplacement of the granite above the hanging wall of the duplex in the NW of the schist belt was outlasted by top-SW displacement. The shapes of the granites and their emplacement in relation to the structure of the Ranibennur and Chitradurga schist belts in the west of the craton are modelled as a mid-crustal part of a craton-wide imbricate fold-thrust belt. The relationships show that whereas some Neoarchaean granites in the craton were emplaced prior to, or during, SW -vergent thrust thickening, most granites and related plutonic suites in the foreland and accretionary complex were emplaced later as multipulse injections in steep NW-SE sheets or wedges during orogen-parallel, sinistral and dextral shear. Steep high- strain zones in the foreland and accretionary complex are interpreted as listric structures that root into an attachment at a depth of ca. 18-20 km in accord with the depth of the boundary

  4. U-Pb geochronological constraints on the timing of episodic regional metamorphism and rapid high-T exhumation of the Grand Forks complex, British Columbia

    Science.gov (United States)

    Cubley, J. F.; Pattison, D. R. M.; Tinkham, D. K.; Fanning, C. M.

    2013-01-01

    The Grand Forks complex (GFC) is a fault-bounded metamorphic core complex in the southern Omineca Belt of British Columbia, Canada. It experienced prograde metamorphism ranging from upper-amphibolite to granulite facies conditions during the Mesozoic to early Tertiary compressional stage of the Cordilleran orogeny. Peak metamorphism was followed by multi-stage exhumation in the Early Eocene. This study provides U-Pb monazite and zircon constraints on the timing of metamorphic episodes in the GFC and subsequent high-T, amphibolite facies decompression in the Early Eocene. Monazite LA-ICP-MS ages from metapelitic gneisses record episodic metamorphism from the Late Jurassic to Paleocene, with peak metamorphism occurring between ~ 59 and 50 Ma. Peak metamorphism was followed by rapid, near-isothermal decompression of the GFC between ~ 52 and 50 Ma, and leucosome crystallization at ~ 50 Ma. Thermodynamic modeling of metapelites in the system MnNCKFMASHPYCe predicts that monazite was not stable at peak metamorphic conditions, consistent with the dominant population of ~ 59 Ma ages representing growth along the prograde path, most likely at subsolidus conditions. Growth of widespread high-Y monazite rims (~ 50 Ma) is predicted along suprasolidus decompression and cooling paths. Zircon SHRIMP ages from igneous bodies in the GFC and hanging wall of the bounding Kettle River fault (KRF) suggest ductile deformation related to high-T decompression of the GFC was ongoing at 51 Ma but had ceased by 50 Ma, truncated by post-kinematic granitoids. This high-T deformation predates subsequent greenschist facies extension on the overlying KRF. A pre-KRF, hanging wall ductile shear zone is constrained to ~ 59-51 Ma. It deforms 59 Ma Ladybird suite leucogranites and may be related to high-T exhumation of the core complex. Rapid, > 100 °C/Ma cooling rates are required to accommodate high-T (amphibolite facies) exhumation of the GFC at 52-50 Ma followed by low-T (greenschist facies

  5. SHRIMP U-Pb zircon dates from igneous rocks from the Fontana Lake region, Patagonia: Implications for the age of magmatism, Mesozoic geological evolution and age of basement

    Directory of Open Access Journals (Sweden)

    A.P. Rolando

    2004-12-01

    Full Text Available In the eastern margin of the Patagonian Andes and between 44° 30´S and 45° 30´S (Fontana Lake region, Middle Jurassic to Early Cretaceous volcanic and sedimentary rocks were intruded by granitic bodies during the Cretaceous. The reconstruction of the Jurassic-Cretaceous magmatic evolution in the Fontana Lake region and in the adjacent Patagonian Batholith was made possible by the consideration of the following characteristics: distribution in time and space of several intrusive bodies, retro-arc basin formation and volcanic intensity. U-Pb SHRIMP dating of zircon crystals from an ignimbrite, a dacitic porphyry and two granitoid rocks yielded dates of 148.7 ± 2.3, 144.5 ± 1.6, 117 ± 1.7 and 99.6 ± 2.8 Ma, respectively. The Cerro Bayo Ignimbrite (148.7 ± 2.3 Ma, Late Jurassic was included in the Lago La Plata Formation; this unit hosts an epithermal ore deposit. The Laguna Escondida dacitic porphyry (144.5 ± 1.6 Ma, Jurassic-Cretaceous boundary intruded metasedimentary rocks of the Lago La Plata Formation; this sub-volcanic body can chronologically be linked to the Patagonian Batholith. After the Jurassic volcanic events, a retro-arc basin formed in the eastern sector of the Patagonian Range at about 140-115 Ma (Late Berriasian-Barremian and magmatism ceased during this event. The dating of granitoids (117 ± 1.7 and 99.6 ± 2.8 Ma in the Fontana Lake region confirms a temporal magmatic continuity with the Patagonian Batholith. These dates also are in agreement with the volcanic rocks of the Divisadero Group and epithermal deposits in the region (La Ferrocarrilera deposit. One of the analyzed granitoids (Dedo Chico, 99.6 ± 2.8 Ma has inherited zircon crystals of about 2,100 and 3,410 Ma, in agreement with other previous isotopic evidence for the occurrence of an underlying Precambrian basement in the region.

  6. Zircon U-Pb geochronology and geochemistry of low-grade metamorphosed volcanic rocks from the Dantazi Complex: Implications for the evolution of the North China Craton

    Science.gov (United States)

    Ge, Songsheng; Zhai, Mingguo; Li, Tiesheng; Peng, Peng; Santosh, M.; Shan, Houxiang; Zuo, Pengfei

    2015-11-01

    The late Neoarchean witnessed the cratonization of the North China Craton (NCC) through amalgamation of several micro-blocks to form a coherent basement. The Archean orthogneisses and supracrustal rocks in this craton have experienced various grades of metamorphism ranging up to upper amphibolite and granulite facies at ∼2500 Ma. Recently, a suite of low-grade metamorphosed (greenschist to lower amphibolite facies) volcanic rocks was discovered in the late Neoarchean Dantazi Complex in northern Hebei province. These meta-volcanic rocks consist of bimodal basalt-andesite and trachyte-dacite with a SiO2 gap between 54.4 wt.% and 60.7 wt.%. Here we report SHRIMP zircon U-Pb ages of 2490 ± 19 Ma (MSWD = 2.0) and 2502 ± 8 Ma (MSWD = 0.83) from the meta-mafic and meta-felsic volcanics, respectively, representing the timing of igneous activity. All the meta-mafic volcanic rocks display coherent trace element and REE patterns which are characterized by enriched LILE and LREE but depleted HFSE and HREE ((La/Yb)N = 6.29-15.10). Combining these trace element features with the positive zircon εHf(t) values (+1.3 to +6.6), we propose that the mafic rocks were likely derived from partial melting of a previously metasomatized lithospheric mantle. In the primitive mantle-normalized diagram, the felsic rocks display uniform patterns enriched in LILE but depleted in Nb and Ta, similar to those of lower crust. Furthermore, their strongly fractionated REE ((La/Yb)N = 15.24-61.20), lower HREE concentrations (Yb = 0.47-1.65 ppm) and positive zircon εHf(t) values (+1.6 to +5.3) suggest that they were derived from partial melting of the lower crust with garnet in the residue. This coeval occurrence of metasomatized mantle-derived mafic magmas and potassic felsic magmas from different source regions reflects an intracontinental extensional setting during the late Neoarchean to earliest Paleoproterozoic following the cratonization of the NCC. Our new data, combined with previous

  7. U-Pb SHRIMP-RG zircon ages and Nd signature of lower Paleozoic rifting-related magmatism in the Variscan basement of the Eastern Pyrenees

    Science.gov (United States)

    Martinez, F.J.; Iriondo, A.; Dietsch, C.; Aleinikoff, J.N.; Peucat, J.J.; Cires, J.; Reche, J.; Capdevila, R.

    2011-01-01

    The ages of orthogneisses exposed in massifs of the Variscan chain can determine whether they are part of a pre-Neoproterozoic basement, a Neoproterozoic, Panafrican arc, or are, in fact, lower Paleozoic, and their isotopic compositions can be used to probe the nature of their source rocks, adding to the understanding of the types, distribution, and tectonic evolution of peri-Gondwanan crystalline basement. Using SHRIMP U-Pb zircon geochronology and Nd isotopic analysis, pre-Variscan metaigneous rocks from the N??ria massif in the Eastern Pyrenean axial zone and the Guilleries massif, 70km to the south, have been dated and their Nd signatures characterized. All dated orthogneisses from the N??ria massif have the same age within error, ~457Ma, including the Ribes granophyre, interpreted as a subvolcanic unit within Caradocian sediments contemporaneous with granitic magmas intruded into Cambro-Ordovician sediments at deeper levels. Orthogneisses in the Guilleries massif record essentially continuous magmatic activity during the Ordovician, beginning at the Cambro-Ordovician boundary (488??3Ma) and reaching a peak in the volume of magma in the early Late Ordovician (~460Ma). Metavolcanic rocks in the Guilleries massif were extruded at 452??4Ma and appear to have their intrusive equivalent in thin, deformed veins of granitic gneiss (451??7Ma) within metasedimentary rocks. In orthogneisses from both massifs, the cores of some zircons yield Neoproterozoic ages between ~520 and 900Ma. The age of deposition of a pre-Late Ordovician metapelite in the Guilleries massif is bracketed by the weighted average age of the youngest detrital zircon population, 582??11Ma, and the age of cross-cutting granitic veins, 451??7Ma. Older detrital zircons populations in this metapelite include Neoproterozoic (749-610Ma; n=10), Neo- to Mesoproterozoic (1.04-0.86Ga; n=7), Paleoproterozoic (2.02-1.59Ga; n=5), and Neoarchean (2.74-2.58Ga; n=3). Nd isotopic analyses of the N??ria and Guilleries

  8. Petrology and U-PB geochronology of the Robertson River Igneous Suite, Blue Ridge province, Virginia - Evidence for multistage magmatism associated witn an early episode of Laurentian rifting

    Science.gov (United States)

    Tollo, R.P.; Aleinikoff, J.N.

    1996-01-01

    The Late Neoproterozoic (735-702 Ma) Robertson River Igneous Suite includes at least eight plutons ranging in composition from syenogranite to alkali feldspar granite to alkali feldspar syenite. These plutons intruded Mesoproterozoic (1.2-1.0 Ga) gneissic basement of the Blue Ridge anticlinorium in northern and central Virginia during an early episode of Laurentian rifting. Robertson River plutons range in composition from metaluminous to peralkaline and, relative to other granite types, exhibit compositional characteristics of A-type granitoids including (1) marked enrichment in Nb, Zr, Y, REE (except Eu), and Ga, (2) high Ga/Al and FeO(total)/MgO, and (3) depletion of Ba and Sr. High Ga/Al ratios are particularly diagnostic of the suite and serve as an effective discriminant between originally metaluminous and peralkaline bulk compositions, providing a useful proxy for widely used indicators based on major elements that are prone to remobilization. U-Pb isotopic analyses of zircons indicate that the suite was emplaced in two pulses, occurring at 735 to 722 and 706 to 702 Ma. Metaluminous magmas were emplaced during both pulses, formed most of the main batholith, and fractionated as independent, time-correlative groups. Peralkaline magmas were emplaced only during the final pulse, formed a volcanic center that erupted unknown quantities of rhyolite, and experienced a style of fractionation similar to the metaluminous types. Differences in Ce/Nb, Y/Nb, and Yb/Ta ratios suggest that the metaluminous and peralkaline magmas were derived from different sources. The Robertson River Igneous Suite is part of a regional group of Late Neoproterozoic (760-700 Ma) plutons including at least 20 other A-type granitoid bodies exposed throughout the Laurentian terrane of Virginia and northwestern North Carolina. Like the Robertson River, most of the other granitoids are metaluminous in composition, typically form multi-intrusive, elongate plutons, and are not geographically

  9. SHRIMP U-Pb dating of recurrent Cryogenian and Late Cambrian-Early Ordovician alkalic magmatism in central Idaho: Implications for Rodinian rift tectonics

    Science.gov (United States)

    Lund, K.; Aleinikoff, J.N.; Evans, K.V.; duBray, E.A.; deWitt, E.H.; Unruh, D.M.

    2010-01-01

    Composite alkalic plutonic suites and tuffaceous diamictite, although discontinuously exposed across central Idaho in roof pendants and inliers within the Idaho batholith and Challis volcanic-plutonic complex, define the >200-km-long northwest-aligned Big Creek-Beaverhead belt. Sensitive highresolution ion microprobe (SHRIMP) U-Pb zircon dates on these igneous rocks provide direct evidence for the orientation and location of the Neoproterozoic-Paleozoic western Laurentian rift margin in the northern U.S. Cordillera. Dating delimits two discrete magmatic pulses at ca. 665-650 Ma and 500-485 Ma at the western and eastern ends, respectively, of this belt. Together with the nearby 685 Ma volcanic rocks of the Edwardsburg Formation, there is a 200 Ma history of recurrent extensional magmatic pulses along the belt. A similar history of recurrent uplift is reflected in the stratigraphic record of the associated miogeoclinal and cratonal platform basins, suggesting that the Big Creek-Beaverhead belt originated as a border fault during continental rift events. The magmatic belt is paired with the recurrently emergent Lemhi Arch and narrow miogeoclinal facies belts and it lies inboard of a northwest-striking narrow zone of thinned continental crust. These features define a northeast-extending upper-plate extensional system between southeast Washington and southeast Idaho that formed a segment of the Neoproterozoic-Paleozoic miogeocline. This segment was flanked on the north by the St. Mary-Moyie transform zone (south of a narrow southern Canadian upper-plate margin) and on the south by the Snake River transfer zone (north of a broad Great Basin lower-plate margin). These are the central segments of a zigzagshaped Cordilleran rift system of alternating northwest-striking extensional zones offset by northeast-striking transfers and transforms. The data substantiate polyphase rift and continental separation events that included (1) pre-and syn-Windermere rifting, (2) Windermere

  10. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics

    International Nuclear Information System (INIS)

    Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were undertaken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32o and 34oS. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Meson Alto massif), 10.3±0.2 Ma (La Gloria pluton), 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock) and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith). Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32oS, slightly younger mineralized porphyries at Rio Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758- 0.512882), plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf-data variation for the younger age group (10-12 Ma; 7.04-9.54) and show a more scattered range for the older one (14-15 Ma; 8.50-15.34); both sets plot between the DM and CHUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Rio Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening across the NE

  11. U Pb, Hf and O isotope evidence for two episodes of fluid-assisted zircon growth in marble-hosted eclogites from the Dabie orogen

    Science.gov (United States)

    Wu, Yuan-Bao; Zheng, Yong-Fei; Zhao, Zi-Fu; Gong, Bing; Liu, Xiaoming; Wu, Fu-Yuan

    2006-07-01

    A combined study of internal structure, U-Pb age, and Hf and O isotopes was carried out for metamorphic zircons from ultrahigh-pressure eclogite boudins enclosed in marbles from the Dabie orogen in China. CL imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain, respectively. The metamorphic zircons have low Th and U contents with low Th/U ratios, yielding two groups of 206Pb/ 238U age at 245 ± 3 to 240 ± 2 Ma and 226 ± 4 to 223 ± 2 Ma, respectively. Anomalously high δ 18O values were obtained for refractory minerals, with 9.9 to 21.4‰ for garnet and 16.9‰ for zircon. This indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction-zone metamorphism. Most of the zircons are characterized by very low 176Lu/ 177Hf ratios of 0.000001-0.000028, indicating their growth in association with garnet recrystallization. A few of them falling within the older age group have comparatively high 176Lu/ 177Hf ratios of 0.000192-0.000383, suggesting their growth prior to the formation of garnet in the late stage of subduction. The variations in the Lu/Hf ratios for zircons can thus be used to correlate with garnet growth during eclogite-facies metamorphism. In either case, the zircons have variable ɛHf ( t) values for individual samples, suggesting that their protolith is heterogeneous in Hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle. Nevertheless, a positive correlation exists between 206Pb/ 238U ages and Lu-Hf isotope ratios for the metamorphically recrystallized zircons, suggesting that eclogite-facies metamorphism in the presence of fluid has the identical effect on zircon Lu-Hf and U-Th-Pb isotopic systems. We conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh-pressure metamorphism, whereas the younger zircons

  12. Gem-bearing basaltic volcanism, Barrington, New South Wales: Cenozoic evolution, based on basalt K-Ar ages and zircon fission track and U-Pb isotope dating

    International Nuclear Information System (INIS)

    Based on basalt K-Ar and zircon fission track dating, Barrington shield volcano was active for 55 million years. Activity in the northeast, at 59 Ma, preceded more substantial activity between 55 and 51 Ma and more limited activity on western and southern flanks after 45 Ma. Eruptions brought up megacrystic gemstones (ruby, sapphire and zircon) throughout the volcanism, particularly during quieter eruptive periods. Zircon fission track dating (thermal reset ages) indicates gem-bearing eruptions at 57, 43, 38, 28 and 4-5 Ma, while U-Pb isotope SHRIMP dating suggests two main periods of zircon crystallisation between 60 and 50 Ma and 46-45 Ma. Zircons show growth and sector twinning typical of magmatic crystallisation and include low-U, moderate-U and high-U types. The 46 Ma high-U zircons exhibit trace and rare-earth element patterns that approach those of zircon inclusions in sapphires and may mark a sapphire formation time at Barrington. Two Barrington basaltic episodes include primary lavas with trace-element signatures suggesting amphibole/apatite-enriched lithospheric mantle sources. Other basalts less-enriched in Th, Sr, P and light rare-earth elements have trace-element ratios that overlap those of HIMU-related South Tasman basalts. Zircon and sapphire formation is attributed to crystallisation from minor felsic melts derived by incipient melting of amphibole-enriched mantle during lesser thermal activity. Ruby from Barrington volcano is a metamorphic type, and a metamorphic/metasomatic origin associated with basement ultramafic bodies is favoured. Migratory plate/plume paths constructed through Barrington basaltic episodes intersect approximately 80% of dated Palaeogene basaltic activity (65-30 Ma) along the Tasman margin (27-37 deg S) supporting a migratory plume-linked origin. Neogene Barrington activity dwindled to sporadic gem-bearing eruptions, the last possibly marking a minor plume trace. The present subdued thermal profile in northeastern New South

  13. U-Pb zircon geochronology and geochemical constraints on the age and origin of late Neoarchean leucosomes in migmatites from the Maevatanana area, Madagascar

    Science.gov (United States)

    Yang, Xi-An; Liu, Shan-Bao; Hou, Ke-Jun

    2016-07-01

    Migmatites represent the dominant lithological facies in the Maevatanana area of Madagascar. The migmatites are composite rocks with hybrid metamorphic and magmatic features, comprising 60% melanosome bands that are interlayered and/or tectonically interleaved with 40% of centimeter-to decimeter-scale quartz-feldspar leucosome veins. The leucosome and granite veins are bordered by a series of gently dipping shear zones in the migmatites. U-Pb zircon dating shows that the leucosome veins formed at 2548.3 ± 5.3 Ma and are coeval with intrusion of the granite veins at 2552.2 ± 6.1 Ma. Furthermore, the leucosome and granite veins have uniform chondrite-normalized rare earth element (REE) patterns which are characterized by light REE enrichment relative to heavy REE, and negative or slightly positive Eu anomalies (δEu = 0.61-1.13). Primitive-mantle-normalized trace element patterns of the leucosome and granite veins are enriched in large-ion lithophile elements (Ba and K) and show pronounced depletions in high-field strength elements (Th, U, Ta, Nb, Zr, Hf, and Ti), suggesting that the leucosome and granite veins in the migmatites are syntectonic and synigneous intrusives. Primitive-mantle-normalized trace element patterns of the leucosome veins and melanosome bands in the migmatites are similar and suggest that the granite veins in the migmatites were generated by partial melting of medium-to high-K metabasalt, whereas the melanosome bands originated through metamorphism of calc-alkaline basalts. As such, the leucosome veins were likely generated by partial melting of melanosome bands in the migmatites. Calculated zircon saturation temperatures (TZr) of the leucosome veins are 599-685 °C, which represents the magma crystallization temperatures, and the pressures of magma formation range from 1.2 to 3.2 GPa. These P-T estimates for magma formation and crystallization are consistent with those of 605-658 °C and 1.22-1.43 GPa for metamorphism of the

  14. Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications

    Science.gov (United States)

    Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang

    2016-04-01

    Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

  15. Relación entre el tipo de educación, la edad y el rendimiento intelectual

    Directory of Open Access Journals (Sweden)

    Dorina Stefani

    1976-01-01

    Full Text Available En este estudio se analizó la influencia de la educación y la edad -en el rendimiento intelectual, medido a través de las siguientes pruebas del PMA de Thurstone: Significado de Palabras (SP, Espacio (E., R.azonamiento (R, Número (N y Fluencia Verbal (FV. Se aplicó el test a dos muestras de estudiantes de 16, 17 Y 18 .años que recibieron educación técnica y humanística, respectivamente. Por otra parte, se estudió la estabilidad factorial del instrumento -en muestras con distinto tipo de educación (técnica o humanística t en diferentes grupos socio-culturales (Argentina y Estados Unidos. Los resultados indican que el tipo de educación influye, en forma -díferente, en SP, E y FV. La variable edad afecta a los puntajes obtenidos en SP, N y FV. Por último, se verificó la similaridad de la estructura factorial del test en las muestras consideradas.

  16. Helosis (Balanophoraceae) en Argentina Helosis (Balanophoraceae) in Argentina

    OpenAIRE

    José Luis Fontana; Orlando Fabián Popoff

    2006-01-01

    Se cita por primera vez para Argentina Helosis cayennensis (Swartz) Sprengel var. cayennensis en base a colecciones hechas por los autores en la Isla argentina de Apipé Grande, Ituzaingó, provincia de Corrientes. Se describe e ilustra la especie, el desarrollo de la planta y su estado de conservación. Esta cita de Helosis corresponde a un género nuevo para la flora argentina.Helosis cayennensis var. cayennensis is reported for the first time for Argentina. The species is described and ilustra...

  17. Trastornos de personalidad y edad: Estudio con personas sin hogar

    OpenAIRE

    Salavera, Carlos; Puyuelo, Miguel; Orejudo Hernández, Santos

    2009-01-01

    En este estudio se lleva a cabo una investigación sobre trastor-nos de personalidad en personas sin hogar y su relación con la edad. El objetivo era analizar si existe relación entre edad y trastorno de personali-dad padecido por el sujeto. Para ello, se realizó un estudio ex post facto, de carácter prospectivo, con una muestra de personas sin hogar en un proce-so de inserción (N=77) a las que se aplicó una entrevista semiestructurada y el Inventario Clínico Multiaxial de Millon (Millon, 1997...

  18. Tu-U-Pb{sub T} ages of monazite and geothermobarometry of high level metapelitic rocks in the orogenic system Itabuna-Salvador-Curaca, state of Bahia, Brazil: a study in electron microprobe; Idades Th-U-Pb{sub T} de monazita e geotermobarometria de rochas metapeliticas de alto grau do sistema orogenico Itabuna-Salvador-Curaca, BA, Brasil: um estudo em microsonda eletronica

    Energy Technology Data Exchange (ETDEWEB)

    Vlach, Silvio Roberto Farias; Lama, Eliane Aparecida del [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica

    2002-12-15

    Electron microprobe Th-U-Pb T dating of monazite was performed on aluminous gneiss samples from the northern Jacurici and southern Ilheus areas of the Itabuna-Salvador-Curuca Orogenic System. Studied samples are spinel-sillimanite-cordierite-garnet gneiss and corundum-spinel-sillimanite-garnet gneiss that equilibrated during a high temperature metamorphism at T-P conditions of about 835 deg C/6,9 kbar and 890 deg C/7.4 kbar, respectively. Microprobe ages of monazite in equilibrium with these mineral associations are interpreted as true crystallization ages and date granulite facies metamorphism. Both samples gave ages of about 2.07 and 2.08 (+-0.02) Ga, in agreement with the known geochronological pattern in this system. The Ilheus sample contain a younger, contrasting monazite generation (e.g., with distinct REE patterns and Th/Gd ratios), dated at ca. 1.97 (+-0.04) Ga. Based on the occurrence of the corundum-sillimanite-quartz association in the sample and information from the literature, we suggest that this age may be related to a regional decompression event and/or a thermal overprint due to late intrusive magmatism (1.9 - 2.0 Ga) in the orogenic system. (author)

  19. The Salinas formation in the type-area, Northeastern Minas Gerais: a proposal to review the stratigraphy of the Aracuai belt on sedimentary, metamorphic and U-Pb SHRIMP evidences; A formacao Salinas na area-tipo, NE de Minas Gerais: uma proposta de revisao da estratigrafia da faixa Aracuai com base em evidencias sedimentares, metamorficas e idades U-Pb SHRIMP

    Energy Technology Data Exchange (ETDEWEB)

    Lima, Sirlene A. de Abreu [Universidade Federal de Ouro Preto, MG (Brazil). Escola de Minas. Dept. de Geologia; Martins Neto, Marcelo A. [Universidade Federal de Ouro Preto, MG (Brazil). Escola de Minas. Nucleo de Geologia do Petroleo (NUPETRO)]. E-mail: mamneto@uai.com.br; Pedrosa Soares, Antonio C. [Minas Gerais Univ., Belo Horizonte (Brazil). Inst. de Geociencias. Centro de Pesquisa Manuel Teixeira da Costa]. E-mail: pedrosa@igc.ufmg.br; Cordani, Umberto G. [Universidade de Sao Paulo, SP (Brazil). Inst. de Geociencias; Nutman, Allen [Australian National Univ., Canberra (Australia). Research School of Earth Sciences

    2002-12-15

    The Salinas Formation has been considered to be a stratigraphic unit of the Macaubas Group. This group comprises the rift to passive margin sequences of the precursor basin of the Neo proterozoic Aracuai Orogeny, eastern Brazil. However, new road cuts show extensive and spectacular outcrops with very well-preserved sedimentary structures, allowing detailed studies in the type-locality of this formation, located in the Salinas town and surroundings, northeast Minas Gerais State. In its type-locality, the Salinas Formation consists of graywacke, pelite and clast-supported conglomerate, metamorphosed in the green schist facies. The sedimentary lithofacies are grouped into three facies association (shelf, slope and deep-sea), indicating sedimentation from shelf deposits to deep-water turbidites. The shelf sedimentation was influenced by storm-wave during deposition. The slump and deep-sea deposits were generated by gravitational flows and high- to low-concentration turbidity currents. Shelf sandstone, clast-supported conglomerate and proximal to distal turbidites outline a submarine fan system. U-Pb SHRIMP data from detrital zircons of graywacke samples indicate a maximum sedimentation age of ca. 568 Ma. Thus, the Salinas Formation is much younger than the Macaubas Group, and represents late orogenic deposits (ca. 568- 500 Ma). The distal, passive margin unit of the Macaubas Group is now called Ribeirao da Folha Formation (ca. 800 Ma). (author)

  20. U-Pb ages in zircon of the Grao Mogol diamond-bearing conglomerate (Espinhaco supergroup): implications for the diamond origin in the Espinhaco range in Minas Gerais; Idades U-Pb em zircao do conglomerado diamantifero de Grao Mogol (supergrupo Espinhaco): implicacoes para a origem dos diamantes da Serra do Espinhaco em Minas Gerais

    Energy Technology Data Exchange (ETDEWEB)

    Chaves, Mario Luiz de Sa Carneiro; Silva, Marcio Celio Rodrigues da [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Inst. de Geociencias. Centro de Pesquisa Prof. Manoel Teixeira da Costa; Babinski, Marly [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias; Scholz, Rixcardo, E-mail: mchaves@ufmg.br, E-mail: babinski@usp.br, E-mail: celiogeo@gmail.com, E-mail: r_scholz_br@yahoo.com [Universidade Federal de Ouro Preto (UFOP), MG (Brazil). Escola de Minas. Dept. de Geologia

    2013-03-15

    The Espinhaco Range in the Grao Mogol region, center-north of Minas Gerais state, is composed by fine grained quartzites with large cross stratifications (Resplandescente Formation), which are covered with erosional unconformity by monomictic conglomerates, and medium to coarse grained quartzites (Grao Mogol Formation), both units belonging to the Espinhaco Supergroup, of Proterozoic age. At the locality known as 'Pedra Rica' (signify Rich Rock, an old diamond digging), rocks of these formations were sampled and separated detrital zircons to acquire U-Pb by Laser Ablation Inductively LA-ICPMS) ages. The analyzed grains are rounded to slightly rounded and show oscillatory zoning. The obtained results indicate a maximum depositional age of 1,595{+-}20 Ma for the Resplandescente Formation, and 1,052{+-}50 Ma for the Grao Mogol Formation. The comparison between the obtained data and the available ages for the Diamantina region and proximities, in the same diamond province, indicates a strong evidence for the existence of at least two primary mineralizing events in the basin, in the age range of 1.35 to 1.05 Ga. (author)

  1. Argentina set for privatization

    International Nuclear Information System (INIS)

    Buyers are lining up for Argentina's two big state-controlled petrochemical groups, Buenos Aires-based Petroquimica General Mosconi (PGM) and Petroquimica Bahia Blance (PBB). However, feedstock supply contracts with government-owned oil group Yacientos Petroliferos Fiscales (YPG) and gas group Gas del Estado hold the key to both sales. Shell Compania Argentina Petroleo SA (CAPSA), Perez Companc, and Global Petroleum have already bought PGM tender documentation. Shell says it will bid for PGM if the feedstock contract with YPF is acceptable. In addition to price and volume, Shell says the length is critical; it wants a 15-year deal, but would settle for 11. YPF initially sought a five-year contract. PGM, which produces 300,000 m.t./year of aromatics, plus oxo alcohols, methanol, and methyl tert-butyl ether, has sales of $150 million/year

  2. Diagenesis and metallogenetic mechanisms of the Tuanjiegou gold deposit from the Lesser Xing'an Range, NE China: Zircon U-Pb geochronology and Lu-Hf isotopic constraints

    Science.gov (United States)

    Sun, Jing-Gui; Han, Shi-Jiong; Zhang, Yong; Xing, Shu-Wen; Bai, Ling-An

    2013-01-01

    The Tuanjiegou gold deposit is a large-sized breccia-hosted epithermal gold deposit in Heilongjiang Province, eastern China, and was discovered in the late 1950s. The scale and unusual metallogenic setting of this gold deposit have made it the focus of many previous studies. We systematically analyzed ore samples, and volcanic and granitic rocks that are associated with the formation of the deposit by single zircon U-Pb dating, obtaining three distinct concordant groups of U-Pb ages from dacitic pyroclastic rocks and lavas: 119.3 ± 3.3 (n = 2), 113.2 ± 1.1 (n = 13), and 109.1 ± 1.4 Ma (n = 8); four groups of concordant U-Pb ages from an ore-bearing granite porphyry: 112.5 ± 2.2 (n = 2), 107.0 ± 1.2 (n = 4), 103.0 ± 0.70 (n = 10), and 99.9 ± 1.1 Ma (n = 4); two groups of concordant U-Pb ages from a pyrite-rich, quartz vein-cemented, brecciated and silicified granite porphyry: 104.23 ± 0.51 (n = 16) and 101.3 ± 1.3 Ma (n = 2); and five groups of concordant U-Pb ages from pyrite-rich, quartz vein-cemented, brecciated or chunky ore samples: 139 ± 4 to 144 ± 3 (n = 2), 127 ± 4 (n = 1), 113.8 ± 2.1 (n = 8), 101.3 ± 3.4 (n = 3), and 91 ± 3 Ma (n = 1). Combining the whole-rock and Lu-Hf isotope geochemistry with the geology of the mining area and these new U-Pb dates, we have redefined the ore deposit-related temporal history of the area, with formation age of the magma associated with the Ningyuancun Stage volcanics being 119 ± 1.4 Ma and eruption of the volcanics at 113 ± 1.1 Ma. The granodiorite-porphyry and granite porphyry were emplaced at 107.0 ± 1.2 Ma and 103-102 Ma, respectively, with ore deposit formation at 102-100 Ma. The magmato-hydrothermal interaction that formed the deposit was closely related to Late Mesozoic crust-mantle interaction, with the early stage calc-alkaline and high-K calc-alkaline magmatism in this area potentially being derived from interaction between asthenospheric mantle material and the underplated lower crust. However

  3. Ataxia enzoótica en ciervo rojo (Cervus elaphus) en Argentina Enzootic ataxia in red deer (Cervus elaphus) in Argentina

    OpenAIRE

    J P Soler; S B Cseh

    2007-01-01

    Se describe un caso de ataxia enzoótica (AE) en ciervos rojos en cautiverio ocurrido en Argentina. La AE es una patología de los ciervos que causa parálisis lenta y progresiva de las extremidades posteriores y ha sido asociada a la deficiencia de cobre. Su presentación suele ser a partir de los 9 meses de edad. El problema afectó a dos ciervas rojas con debilidad de los miembros posteriores. Se realizó necropsia a una hembra preñada. Se tomaron muestras de órganos en formol al 10%, de suero y...

  4. Fruit fly eradication: Argentina

    International Nuclear Information System (INIS)

    Fruit exports account for 9% of Argentina's total agricultural exports and generate annually close to $450 million. This could be increased but for fruit flies that cause damage equivalent to 15% to 20% of present production value of fruit and also deny export access to countries imposing quarantine barriers. The Department of Technical Co-operation is sponsoring a programme, with technical support from the Joint FAO/IAEA Division, to eradicate the Mediterranean fruit fly using the Sterile Insect Technique (SIT). (IAEA)

  5. The Huillin in Argentina

    OpenAIRE

    Chehebar C.

    1986-01-01

    We recommend re-introduction of huillines in Lanin, Puelo and Los Alerces National Parks, through translocations of animals, so as to minimize the risks involved in the present dependence on Nahuel Huapi and Staten Island (as far as we know) for the conservation of the species in Argentina. Also, we recommend careful monitoring and protection of the Nahuel Huapi population and protection of the Staten Island ecosystems.

  6. Psychology In Argentina

    OpenAIRE

    Modesto M. Alonso

    2016-01-01

    A summary on Psychology as science and profession in Argentina is presented. The report includes a historical review on places, criteria and results of psychologists'education, aspects of their professional practices; quantitative data on universities, graduates and students related to sociodemographic variables; characteristics of research activities, publications, legal frameworks and types of institutions where psychologists work. Some distinctive features of Argentine psychology are menti...

  7. Dollarization in Argentina

    OpenAIRE

    Francois R. Velde; Marcelo Veracierto

    1993-01-01

    Argentina became highly "dollarized" during its hyperinflations of 1989 and early 1990. Although inflation has returned to very low rates, a high degree of dollarization has persisted during the early 1990s, counter to what the currency substitution hypothesis predicts. This paper provides new evidence that explains the continued dollarization of the Argentine economy. ; First, we develop a new measure of dollar currency circulating in foreign countries. This measure improves our ability to a...

  8. Argentina [Country report

    International Nuclear Information System (INIS)

    The airborne geophysical surveys developed in Argentina are described. They have got more than 500.000 km2 acquiring data for U, Th, K and total background activity. Other types of published data are also mentioned (satellite imagery, seismic hazard, climate, soil distributions, etc.). The availability of maps with the abundances of elements analyzed at the country and also at laboratories from Canada is described, as well as data of analysis of several elements at two study areas proposed at the outset of the project. The availability of process rate data and epidemiological data is also explained. Argentina intended fully to participate in the CRP at the outset of the project. Due, however, to external resource constraints imposed on the participating organization (Comision Nacional de Energia Atomica, CNEA), the level of participation had to be significantly reduced. Nonetheless, in the first period of the CRP, Argentina undertook to collate existing geological and geochemical information within the country, and began to define potential areas for site specific natural systems safety indicator studies. (author)

  9. Shrimp U-Pb in zircon and lead-isotope constraints on the timing and source of an Archaean granulite-hosted lode-gold deposit at Griffin's Find, Yilgarn craton, Western Australia

    International Nuclear Information System (INIS)

    A SHRIMP U-Pb in zircon age of a syn- to late- gold mineralization pegmatite dyke from a granulite-hosted lode-gold deposit at Griffin's Find Western Australia, provides a minimum age constraint on gold mineralization of 2632±3 Ma. A nearby syenogranite has an indistinguishable SHRIMP U-Pb in zircon age of 2636±10 Ma. These age constraints are within error of a previously published age of 2636±3 Ma for gold mineralization and peak metamorphism at Griffin's Find, determined by a Pb-Pb isochron for ore and alteration minerals, and similar to a U-Pb in zircon age of 2640±1 Ma for peak metamorphism. This age is also compatible with that of other age determinations on gold mineralization from lower metamorphic-grade settings elsewhere in the Yilgarn Craton. A minimum age of 2669±36 (σ) Ma, determined by a concordant analysis on an inherited zircon core by SHRIMP II, is suggested for the source rock of the pegmatite dykes. Two other analyses, which yield 207Pb/206Pb ages of 2676±20 and 2660±20 Ma with 77-92% concordance, support the presence of an old inherited component in the source of the pegmatite magma A Pb-Pb isochron, comprising two whole-rock and two K-feldspar analyses for samples from the granite, gives a precise age of 2680±6 Ma, which is tentatively interpreted to reflect an old inherited component in a ca. 2636 Ma felsic intrusion. The geochronological results detailed in this study, together with previous data, suggest the emplacement of a regional granitic batholith in high-grade metamorphic settings at the time of fold mineralization. (authors)

  10. Mesozoic magmatism and timing of epigenetic Pb-Zn-Ag mineralization in the western Fortymile mining district, east-central Alaska: Zircon U-Pb geochronology, whole-rock geochemistry, and Pb isotopes

    Science.gov (United States)

    Dusel-Bacon, Cynthia; Aleinkoff, J.N.; Day, W.C.; Mortensen, J.K.

    2015-01-01

    The Mesozoic magmatic history of the North American margin records the evolution from a more segmented assemblage of parautochthonous and allochthonous terranes to the more cohesive northern Cordilleran orogenic belt. We characterize the setting of magmatism, tectonism, and epigenetic mineralization in the western Fortymile mining district, east-central Alaska, where parautochthonous and allochthonous Paleozoic tectonic assemblages are juxtaposed, using sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon geochronology, whole-rock geochemistry, and feldspar Pb isotopes of Mesozoic intrusions and spatially associated mineral prospects. New SHRIMP U-Pb zircon ages and published U-Pb and 40Ar/39Ar ages indicate four episodes of plutonism in the western Fortymile district: Late Triassic (216-208 Ma), Early Jurassic (199-181 Ma), mid-Cretaceous (112-94 Ma), and Late Cretaceous (70-66 Ma). All age groups have calc-alkalic arc compositions that became more evolved through time. Pb isotope compositions of feldspars from Late Triassic, Early Jurassic, and Late Cretaceous igneous rocks similarly became more radiogenic with time and are consistent with the magmas being mantle derived but extensively contaminated by upper crustal components with evolving Pb isotopic compositions. Feldspar Pb isotopes from mid-Cretaceous rocks have isotopic ratios that indicate magma derivation from upper crustal sources, probably thickened mid-Paleozoic basement. The origin of the mantle component in Late Cretaceous granitoids suggested by Pb isotopic ratios is uncertain, but we propose that it reflects asthenospheric upwelling following slab breakoff and sinking of an inactive inner subduction zone that delivered the previously accreted Wrangellia composite terrane to the North American continental margin, after the outer Farallon subduction zone was established.

  11. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating

    Institute of Scientific and Technical Information of China (English)

    WANG; Jianghai

    2002-01-01

    , China, Sci. in China, Ser. D, 2000, 43(2): 225-236.[11]Hacker, B. R., Wang, Q. C., Ar/Ar geochronology of ultrahigh-pressure metamorphism in Central China, Tectonics, 1995, 14: 994-1006.[12]Ge, N. J., Hou, Z. H., Li, H. M. et al., Zircon U-Pb ages of the Shacun gabbro body, Yuexi, Dabie orogen and its geological implications, Chinese Sci. Bull., 2000, 45(1): 74-79.[13]Xu, S. T., Liu, Y. C., Jiang, L. L. et al., Tectonic Regime and Evolution of the Dabie Mountains, Beijing: Science Press, 1994, 1-175.[14]Li, S. G., Ni, Y. H., Zheng, S. G. et al., Interaction between subducted continental crust and the mantle: I. Major and trace element geochemistry of syncollisional mafic-ultramafic intrusions in the Dabie Mountains, Sci. in China, Ser. D, 1998, 41(5): 545-553.[15]Blundy, J. D., Holland, T. J. B., Calcic amphibole equilibrium and a new amphibole plagioclase geothermometer, Contrib. Mineral. Petrol. 1990, 104: 208-224.[16]Hammartron, J. M., Zen, E. A., Aluminum in hornbole: an empirical igneous geobarometer, Amer. Mineral., 1986, 71: 1297-1313.[17]Hollister, L. S., Grisson, G. C., Peters, E. K. et al., Confirmation of the empirical correlation of Al in hornblende with pressure of solidification of calcalkaline plutons, Amer. Mineral., 1987, 72: 231-239.[18]Johnson, M. C., Rutherford, M. J., Experimental calibration of an aluminium-hornblende geobarometer applicable to calc-alkaline rocks, EOS, 1988, 69: 1511.[19]Whitney, J. A., Stormer, J. C., The distribution of NaAlSi3O8 between coexisting microcline and plagioclase and its effect on geothermometric calculations, Am. Mineral., 1977, 62: 687-691.[20]Zhang, R. Y., Cong, B. L., Mineral Thermometers and Barometers, Beijing: Geological Publishing House, 1983, 150-173.[21]Krogh, T. E., A low-contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations, Geochim. Cosmochim. Acta, 1973, 48: 505-511.[22]Krogh, T. E., Vapour

  12. 160 Ma of magmatic/hydrothermal and metamorphic activity in the Gällivare area: Re-Os dating of molybdenite and U-Pb dating of titanite from the Aitik Cu-Au-Ag deposit, northern Sweden

    Science.gov (United States)

    Wanhainen, Christina; Billström, Kjell; Martinsson, Olof; Stein, Holly; Nordin, Roger

    2005-12-01

    Host rocks to the Aitik Cu-Au-Ag deposit in northern Sweden are strongly altered and deformed Early Proterozoic mica(-amphibole) schists and gneisses. The deposit is characterised by numerous mineralisation styles, vein and alteration types. Four samples were selected for Re-Os molybdenite dating and 12 samples for U-Pb titanite dating in order to elucidate the magmatic/hydrothermal and metamorphic history following primary ore deposition in the Aitik Cu-Au-Ag deposit. Samples represent dyke, vein and alteration assemblages from the ore zone, hanging wall and footwall to the deposit. Re-Os dating of molybdenite from deformed barite and quartz veins yielded ages of 1,876±10 Ma and 1,848±8 Ma, respectively. A deformed pegmatite dyke yielded a Re-Os age of 1,848±6 Ma, and an undeformed pegmatite dyke an age of 1,728±7 Ma. U-Pb dating of titanite from a diversity of alteration mineral associations defines a range in ages between 1,750 and 1,805 Ma with a peak at ca. 1,780 Ma. The ages obtained, together with previous data, bracket a 160-Ma (1,890-1,730 Ma) time span encompassing several generations of magmatism, prograde to peak metamorphism, and post-peak cooling; events resulting in the redistribution and addition of metals to the deposit. This multi-stage evolution of the Aitik ore body suggests that the deposit was affected by several thermal events that ultimately produced a complex ore body. The Re-Os and U-Pb ages correlate well with published regional Re-Os and U-Pb age clusters, which have been tied to major magmatic, hydrothermal, and metamorphic events. Primary ore deposition at ca. 1,890 Ma in connection with intrusion of Haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism. Early metamorphism at 1,888-1,872 Ma overlapping with Haparanda (1,890-1,880 Ma) and Perthite-monzonite (1,880-1,870 Ma) magmatism clearly affected the Aitik area, as well as late metamorphism and Lina magmatism at 1,810-1,774 Ma and

  13. Precise zircon U-Pb chronological comparison of the volcano-sedimentary sequences of the Kaapvaal and Pilbara Cratons between about 3.1 and 2.4 Ga

    International Nuclear Information System (INIS)

    Within the last few years a number of studies have been carried out using the Sensitive High Resolution Ion MicroProbe (SHRIMP) in Canberra to provide precise U-Pb zircon control on parts of the supracrustal sequences of both Western Australian and South African cratons. The purpose of this paper is to review the significance of those results, and of other precise zircon ages already available, for temporal correlation (as distinct from lithostratigraphic correlation) of the relevant Kaapvaal and Pilbara sequences. 14 refs

  14. U-Pb SHRIMP and Sm-Nd geochronology of the Silvânia Volcanics and Jurubatuba Granite: juvenile Paleoproterozoic crust in the basement of the Neoproterozoic Brasília Belt, Goiás, central Brazil

    OpenAIRE

    FISCHEL DANIELLE P.; PIMENTEL MÁRCIO M.; FUCK REINHARDT A.; ARMSTRONG RICHARD

    2001-01-01

    U-Pb SHRIMP and Sm-Nd isotopic ages were determined for felsic metavolcanic rocks from the Silvânia Sequence and Jurubatuba Granite in the central part of the Brasília Belt. Zircon grains from a metavolcanic sample yielded 2115 ± 23 Ma and from the granite yielded 2089 ± 14 Ma, interpreted as crystallization ages of these rocks. Six metavolcanic samples of the Silvânia Sequence yielded a six-point whole-rock Sm-Nd isochron indicating a crystallization age of 2262 ± 110 Ma and positive epsilon...

  15. Shrimp and conventional U-Pb age, Sm-Nd isotopic characteristics and tectonic significance of the K-rich Itapuranga suite in Goiás, Central Brazil

    OpenAIRE

    PIMENTEL MÁRCIO M.; DANTAS ELTON L.; FUCK REINHARDT A.; ARMSTRONG RICHARD A.

    2003-01-01

    The Itapuranga alkali granite and Uruana quartz syenite are large K-rich EW-elongated intrusions, in the central part of the Neoproterozoic Brasília Belt, central Brazil. They are associated with Pireneus lineaments, which cut the regional NNW-SSE structures of the southern part of the belt. SHRIMP and conventional U-Pb data for the Itapuranga and Uruana intrusions indicate crystallization ages of 624 ± 10 Ma and 618 ± 4 Ma, respectively. Three zircon cores from the Itapuranga g...

  16. Neoproterozoic Anatexis of 2.9 Ga Old Granitoids in the Goiás-Crixás Archean Block, Central Brazil: Evidence From New SHRIMP U-Pb Data and Sm-Nd Isotopes

    OpenAIRE

    Márcio Martins Pimentel; Hardy Jost; Reinhardt Adolfo Fuck; Richard Austin Armstrong; Elton Luiz Dantas; Alain Potrel

    2003-01-01

    The first SHRIMP U-Pb ages for granitoid rocks from the southern part of the Goiás-Crixás Archean Block (Caiçara andUvá complexes) are presented and discussed in combination with Sm-Nd isotopic data in order to elucidate the main aspectsof the geological evolution of that part of the Brasília Belt in central Brazil. Zircon grains from a tonalitic gneiss (GOV-4) inthe Uvá Complex show that the original tonalite crystallized at 2934 ± 5 Ma. One metamorphic zircon crystal is concordantand indica...

  17. Detrital zircon U-Pb and (U-Th)/He double-dating of Upper Cretaceous-Cenozoic Zagros foreland basin strata in the Kurdistan Region of northern Iraq

    Science.gov (United States)

    Barber, D. E.; Stockli, D. F.; Koshnaw, R. I.; Horton, B. K.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The NW Zagros orogen is the result of the multistage collisional history associated with Late Cretaceous-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Siliciclastic strata preserved within a ~400 km segment of the NW Zagros fold-thrust belt and foreland basin in the Iraqi Kurdistan Region (IKR) provide a widespread record of exhumation and sedimentation. As a means of assessing NW Zagros foreland basin evolution and chronostratigraphy, we present coupled detrital zircon (DZ) U-Pb and (U-Th)/He geo-thermochronometric data of Upper Cretaceous to Pliocene siliciclastic strata from the Duhok, Erbil, and Suleimaniyah provinces of IKR. LA-ICP-MS U-Pb age analyses reveal that the foreland basin fill in IKR in general was dominantly derived from Pan-African/Arabian-Nubian, Peri-Gondwandan, Eurasian, and Cretaceous volcanic arc terrenes. However, the provenance of these strata varies systematically along strike and through time, with an overall increase in complexity upsection. DZ age distribution of Paleocene-Eocene strata is dominated by a ~95 Ma grain age population, likely sourced from the Late Cretaceous Hassanbag-Bitlis volcanic arc complex along the northern margin of Arabia. In contrast, DZ U-Pb age distributions of Neogene strata show a major contribution derived from various Eurasian (e.g., Iranian, Tauride, Pontide; ~45, 150, 300 Ma) and Pan-African (~550, 950 Ma) sources. The introduction of Eurasian DZ ages at the Paleogene-Neogene transition likely records the onset of Arabian-Eurasian collision. Along strike to the southeast, the DZ U-Pb spectra of Neogene strata show a decreased percentage of Pan-African, Peri-Gondwandan, Tauride, and Ordovician ages, coupled with a dramatic increase in 40-50 Ma DZ ages that correspond to Urumieh-Dokhtar magmatic rocks in Iran. Combined with paleocurrent data, this suggests that Neogene sediments were transported longitudinally southeastward through an unbroken foreland basin

  18. Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40/39Ar age determinations, Fuerteventura, Canary Islands

    Science.gov (United States)

    Allibon, James; Ovtcharova, Maria; Bussy, Francois; Cosca, Michael; Schaltegger, Urs; Bussien, Denise; Lewin, Eric

    2011-01-01

    High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699-988 °C) to amphibole (500-600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520,000 to 800,000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

  19. U-Pb zircon SHRIMP ages, geochemical and Sr-Nd isotopic compositions of the Early Cretaceous I-type Sarıosman pluton, Eastern Pontides, NE Turkey

    OpenAIRE

    KAYGUSUZ, ABDULLAH; Chen, Bin; Zafer ASLAN; ŞEN, WOLFGANG SIEBEL & CÜNEYT

    2009-01-01

    The petrogenesis and U-Pb SHRIMP zircon ages of the Late Cretaceous Sarıosman pluton in the Eastern Pontides is investigated by means of whole-rock Sr-Nd isotope data with field, petrographic and whole-rock geochemical studies. The bulk of the I-type Sarıosman pluton consists of biotite-hornblende monzogranite, with minor quantities of porphyritic hornblende-biotite monzogranite. The biotite-hornblende monzogranite contains a number of mafic microgranular enclaves (MMEs) of quartz monzodiorit...

  20. The late stages of the Pampean Orogeny, Córdoba (Argentina): Evidence of postcollisional Early Cambrian slab break-off magmatism

    Science.gov (United States)

    Ramos, Victor A.; Escayola, Mónica; Leal, Pablo; Pimentel, Marcio M.; Santos, João O. S.

    2015-12-01

    Widespread rhyolitic and mafic volcanism in the northern and southern sectors respectively of Eastern Sierras Pampeanas, central western Argentina, are associated with an important phase of extension and uplift linked to slab break-off on latest stages of the Pampean Orogeny. The main orogenic deformation took place between 540 and 535 Ma based on new ages available for this region. New U-Pb ages in zircons from the Oncán Rhyolite and new and old recalculated zircons from Los Burros Rhyodacite in the northern sector of Sierras de Córdoba, together with new U-Pb ages of the southern sector, indicate that volcanic and subvolcanic rocks of both sectors are partially coeval and unconformably overlying and/or intruding the basement rocks during a period of exhumation and subsequent cooling at 530-520 Ma. These data are in agreement with previous estimates for the final uplift of the Sierras de Córdoba based on the K-Ar cooling ages. The southern sector of Eastern Sierras Pampeanas may represent deeper structural levels within the crust and is characterized by the occurrence of small mafic bodies with OIB-like signature. New and reinterpreted U-Pb SHRIMP and TIMS ages on zircons and monazites in the metamorphic associated rocks date this episode, which is related to a rapid slab break-off event at 519-515 Ma. This episode is also associated with the emplacement of peraluminous granitoids, and with the extension, cooling and final uplift of the rocks affected by the Pampean Orogeny all along the Eastern Sierras Pampeanas.

  1. Zircon U-Pb age constraints on the Paleoproterozoic sedimentary basement of the Ediacaran Porongos Group, Sul-Riograndense Shield, southern Brazil

    Science.gov (United States)

    Pertille, Juliana; Hartmann, Léo Afraneo; Philipp, Ruy Paulo

    2015-11-01

    Thick quartzites record significant information on cratonic environments during long geological periods. The capacity to resist weathering and deformation turn the quartzite covers especially useful in the provenance studies of Precambrian basins. Provenance of 194 detrital zircon grains from two samples of thick quartzite cover on the Paleoproterozoic Encantadas Complex displays mostly Paleoproterozoic (95%) and minor Archean (5%) sources. The results indicate that sediments were derived from the La Plata Craton with the maximum depositional age at 2.03 Ga possibly up to 1.7 Ga. In comparison, the adjacent Porongos Group has provenance data of 61 detrital zircon grains indicating mostly Mesoproterozoic (69%), subordinately Paleoproterozoic (26%) and minor Archean ages (5%). Considering previous published data, the Porongos Group is Ediacaran in age and probably chronocorrelated with sedimentary basins from the Tandilia Belt (Argentina). Therefore, the quartzite cover and the Porongos Group require distinct evolution in time and in tectonic environment.

  2. Relaciones entre el aprendizaje implícito y la edad en niños de 7 a 12 años

    Directory of Open Access Journals (Sweden)

    María Fernanda López-Ramón

    2007-06-01

    Full Text Available El objetivo de este estudio es analizar las relaciones existentes entre el aprendizaje implícito (AI, el aprendizaje explícito (AE y la edad en niños de 7 a 12 años. Se trabajó con un diseño cuasi-experimental. Se administraron dos pruebas de aprendizaje: una prueba de AI de gramáticas artificiales con un diseño lúdico y figurativo diseñado para niños, y una prueba de AE figurativa. Se trabajó con una muestra de 49 niños de 7 a 12 años de la ciudad de Mar del Plata, Argentina. Los resultados obtenidos brindaron apoyo empírico a la afirmación de Reber sobre la independencia del AI con respecto a la edad de los sujetos. Se discute la importancia del AI como un mecanismo temprano de abstracción de regularidades que desempeña un destacado rol en la edad escolar y que permanece más estable que el aprendizaje explícito.

  3. Fractura de Cadera en los hospitales públicos de la Argentina Hip Fracture in Public Hospitals of Argentina

    Directory of Open Access Journals (Sweden)

    Mánica A Ercolano

    2012-03-01

    Full Text Available La fractura de cadera en población añosa constituye un problema creciente para los sistemas de salud a nivel mundial debido a su elevado impacto econámico y social. Objetivos: Evaluar los egresos por fractura de cadera en adultos mayores de 55 años informados al Ministerio de Salud de la Nación durante los años 2000, 2006, 2007 y 2008. Analizar el efecto de la edad y sexo sobre la incidencia de fracturas de cadera, los tipos de fractura y su variabilidad en el tiempo. Materiales y Métodos: Se obtuvieron los datos de egresos por fracturas de cadera en pacientes mayores de 55 años registrados en el Ministerio de Salud de la Nación. Se calculá la Tasa de Egresos (TE por fracturas de cadera, la TE estratificada por sexo (♀: mujer, ♂: varán y edad; Tasa de Crecimiento Interanual (TCI. Estadística: test de Chi cuadrado y test T de Student para datos no apareados. Resultados y Conclusiones: La fractura de cadera en los hospitales públicos de la Argentina durante los años evaluados, alcanzá un promedio de 5700 egresos/año, con una TE 280/100000. La relación ♀/♂ fue de 2,3. La edad de egreso promedio fue de 78,7 años siendo significativamente menor en los hombres en relación a las mujeres. La relación ♀/♂ aumentá tres veces con la edad. La edad fue un fuerte determinante de las fracturas, siendo la TE de 2800/100000 en los individuos mayores de 75 años. La TCI fue de 1,4 %. La fractura cervical de fémur fue la más frecuente, y fue aumentando progresivamente con la edad; la fractura de trocánter se mantuvo estable en los grupos de menor edad y solo aumentá en los mayores de 75 años. Ambos tipos de fractura predominaron en las mujeres. Este es el primer trabajo que establece datos sobre fractura de cadera en la Argentina. Con el envejecimiento de la población, la fractura de cadera se convertirá en una carga progresivamente mayor para los sistemas de salud.Hip fracture in the aged population constitutes a growing

  4. Zircon U-Pb and Lu-Hf isotopic and geochemical constraints on the origin of the paragneisses from the Jiaobei terrane, North China Craton

    Science.gov (United States)

    Shan, Houxiang; Zhai, Mingguo; Zhu, Xiyan; Santosh, M.; Hong, Tao; Ge, Songsheng

    2016-01-01

    Clastic sedimentary rocks are important tracers to understand the evolution of the continental crust. Whole-rock major and trace element data, zircon U-Pb dating and Hf isotopic data for the paragneisses from the Jiaobei terrane are presented in this study in order to constrain their protoliths, provenance and tectonic setting. The paragneisses are characterized by enrichment in Al2O3 and TiO2, negative DF (DF = 10.44 - 0.21SiO2 - 0.32Fe2O3T - 0.98MgO + 0.55CaO + 1.46Na2O + 0.54K2O) values and the presence of aluminum-rich metamorphic minerals (e.g., garnet and sillimanite). Together with the mineral assemblages and zircon features, it can be inferred that the protoliths of these rocks are of sedimentary origin. The K-A (A = Al2O3/(Al2O3 + CaO + Na2O + K2O), K = K2O/(Na2O + K2O)) and log(Fe2O3/K2O)-log(SiO2/Al2O3) diagrams indicate that they belong principally to clay-silty rocks with some contributions from graywacke. A series of geochemical indexes, such as the widely employed CIA (CIA = [Al2O3/(Al2O3 + CaO∗ + Na2O + K2O)] × 100; molar proportions) and ICV (ICV = (Fe2O3 + MnO + MgO + CaO + Na2O + K2O + TiO2)/Al2O3) values, and the A-CN-K diagram for the paragneisses indicate relatively weak weathering in the source rocks and negligible post-depositional K-metasomatism. In addition, their REE patterns, low Cr/Zr (0.61-1.99), high Zr/Y (4.81-23.59) and Th/U (3.21-40.67) ratios, the low to moderate contents of Cr (197-362 ppm) and Ni (6.68-233 ppm), and source rock discrimination diagrams collectively suggest that the sediments of the protoliths of the paragneisses in the Jiaobei terrane were derived from the source with intermediate-acidic composition, probably granitic-to-tonalitic rocks. In combination with geochronological and isotopic studies on the paragneisses and the basement rocks in the Jiaobei terrane, it is suggested that the Archean-early Paleoproterozoic granitic rocks in the Jiaobei terrane possibly provided the most important source materials. In

  5. Provenance of metasediments and Miocene exhumation history of the Lavrion Peninsula, South Attica, Greece: a combined structural, (U-Th)/He, and detrital zircon U-Pb study.

    Science.gov (United States)

    Seman, Spencer; Soukis, Konstantinos; Stockli, Daniel F.; Skourtsos, Emmanuel; Kranis, Haralambos; Lozios, Stylianos; Shin, Timothy

    2013-04-01

    Within the Hellenides of Greece, Attica and Evvia lie at the extreme northwestern limit of the highly attenuated Attic-Cycladic Crystalline Complex and the relatively unextended Pelagonian realm In this area, three different portions of the greater nappe stack of Greece are exposed: the Sub-Pelagonian nappe, the Cycladic Blueschist Unit (CBU) and the so-called Basal Unit, the para-autochthonous nappe to the CBU. The Basal Unit is defined by exposures of the Alymyropotamos Unit on Evvia Island. In Attica, the distinction between Basal Unit and CBU is not so clear due to similar histories of blueschist facies metamorphism and greenschist retrogression for both units. Based on the large amount of marbles exposed in Attica relative to CBU exposed in the Cyclades, much of Attica has previously been assigned to the Basal Unit. Detailed mapping in Lavrion peninsula (south Attica) has called into question the old association of many of these marbles with the Basal Unit. The dominant structure is a sub-horizontal detachment, the South Attican Detachment (SAD), which juxtaposes lower plate mylonitic to ultramylonitic rocks of the Kamariza Unit against the upper plate Lavrion Unit. The detachment marks a significant change in the structural inventory between upper and lower plate rocks. The Kamariza Unit exhibits an early stage mylonitic foliation with a NNE-SSW stretching lineation. On the other hand the main foliation in Lavrion Unit is a compressional crenulation cleavage with an ENE-WSW to NE-SW stretching and/or intersection lineation. Along the detachment both units and especially the hanging wall rocks are overprinted by late-stage cataclastic deformation. Numerous kinematic indicators reveal top-to the SSW sense of shear for the SAD, thus linking it kinematically with the Western Cycladic Detachment System (WCDS). Detrital zircon U-Pb geochronology was used in order to constrain provenance and depositional age for the clastic metasediments from both the footwall and

  6. Hyperextension in the pre-Caledonian margin of Baltica: new observations and U-Pb ages from the Samnanger Complex, Major Bergen Arc, western Norway.

    Science.gov (United States)

    Jakob, Johannes; Alsaif, Manar; Andersen, Torgeir; Corfu, Fernando

    2015-04-01

    The Samnanger Complex (SC) of the Major Bergen Arc in western Norway (Færseth et al., 1977) comprises a thick succession of original fine-grained marine sediments, now mica- and graphitic schists, some fine-grained impure marbles as well as local quartzite, meta-sandstones and meta-fanglomerates of continental affinity. There are also minor meta-igneous rocks including amphibolite, metagabbro as well as felsic and mafic gneisses. The most characteristic rocks in this heterogeneous unit, however, are numerous solitary mantle-peridotites now present as variably altered serpentinites and soapstones with commonly developed ophicarbonate alteration. Detrital serpentinite and soapstone deposits have also been identified in one locality, now mostly removed by quarrying for building and ornamental stones. The SC is continuous with a regional mélange unit, which can be traced across southern Norway towards Røros (Andersen et al., 2012). The mélange is structurally positioned below large crystalline nappes such as the Jotun Nappe and the SC is structurally positioned in-between the underlying Lower Bergsdalen and the overlying Lindås nappes (Færseth et al., 1977). The lithological association of the mélange with its common presence of solitary and detrital meta-peridotites suggests that it was formed by hyperextension in a magma poor margin. After early-Caledonian metamorphism and deformation associated with emplacement of gabbro and granitoids in the early Ordovician it was finally emplaced in the Caledonian nappe stack after the closure of the Iapetus Ocean. Late granitoid dikes cutting most of the deformation fabric are ~420 Ma. New ID-TIMS U-Pb ages of a pegmatitic meta-gabbro (~486 Ma) and a mylonitic granitoid (~476 Ma) indicate magma emplacement, probably related to subduction within distal parts of the hyperextended margin. We suggest that the exhumation and hydration of subcontinental lithospheric mantle in hyperextended basins may lead to a long

  7. Mineral inclusions and SHRIMP U-Pb dating of zircons from the Alamas nephrite and granodiorite: Implications for the genesis of a magnesian skarn deposit

    Science.gov (United States)

    Liu, Yan; Zhang, Rongqing; Zhang, Zhiyu; Shi, Guanghai; Zhang, Qichao; Abuduwayiti, Maituohuti; Liu, Jianhui

    2015-01-01

    Extending approximately 1300 km and located in the Western Kunlun Mountains, the Hetian nephrite belt is the largest nephrite belt in the world and contains approximately 11 major deposits and more than 20 orebodies including the Alamas deposit. Hetian nephrite deposits can be classified as Mg-skarn deposits with Precambrian dolomitic marble host rock and green, green-white and white nephrite zones are distributed gradually in the zone of a granodiorite pluton. The green nephrite is mainly predominately composed of tremolite with generally minor to trace constituents of diopside, grossularitic garnet, actinolite and other minerals. Also green nephrite has higher content of TFe2O3, than green-white and white nephrites have. We subdivided the zircons from the green nephrites into four types, depending on their internal textures, mineral inclusions, and SHRIMP U-Pb ages. Type I zircons are round instead of idiomorphic in shape and lack obvious zoning. Type II and IV zircons have broad, clear oscillatory zoning and are hypidiomorphic or idiomorphic in shape; they contain inclusions of diopside, tremolite, chlorite and calcite. Most Type III zircons are narrow rims (highly luminous brightness and no zoning. Both Type I and Type II zircons have individual ages of 411 to 445 Ma and Type IV zircons have younger ages (388 to 406 Ma). Among the concordant ages, 425.7 ± 5.8 Ma and 420.0 ± 9.9 Ma for the QYZr1 and QYZr2 are consistent within error, with the 418.5 ± 2.8 Ma of the Alamas granodiorite formation age and the maximum age of the Alamas nephrite deposit. The partially recrystallization of zircons during skarn formation possibly lead to some younger individual ages (406.5 to 308 Ma). In the Western Kunlun Mountain, both Buya granite and Alamas grandiorite are high Ba-Sr granites and crystallized in Western Kunlun Orogen. The Buya granite formed at about 430 Ma in a post-orogenic tectonic environment. Considering Alamas granodiorite formed at about 12 Ma younger than

  8. Accretionary wedge harzburgite serpentinization and rodingitization constrained by perovskite U/Pb SIMS age, trace elements and Sm/Nd isotopes: Case study from the Western Carpathians, Slovakia

    Science.gov (United States)

    Li, Xian-Hua; Putiš, Marián; Yang, Yue-Heng; Koppa, Matúš; Dyda, Marian

    2014-09-01

    . Overgrowths of spinel by andradite are occasionally observed in contact zones between the serpentinites and rodingites. LA-ICP-MS study revealed strong depletion in LREE from Prv (1) to Prv (2), and a more typically positive Eu anomaly for Prv (2). Our spider diagram depicts relative enrichment in U, Nb, La, Ce, Pr, Nd, and decreased Rb, Ba, Th, Ta, Pb, Sr, Zr in both Prv generations. The U/Pb SIMS concordia ages of Prv (1) from 3 samples range from 137 ± 1 Ma to 135 ± 1 Ma, with a mean of 135.6 ± 0.58 Ma, while Prv (2) was dated at 133.7 ± 5.4 Ma. Such negligible age differences imply a relatively short-lived rodingitization event responsible for crystallization of both Prv generations. The 143Nd/144Nd mean value of Prv (1) is 0.512153 ± 0.000017 by LA-MC-ICP-MS, thus corresponding to the initial ɛNd(t = 135) = - 8.2 ± 0.4 (math's mean). This suggests that the subducted and dehydrated continental crust was the main source of the interactive fluids which initiated serpentinization and rodingitization in the Neotethyan Meliatic accretionary wedge following closure of the Meliata-Hallstatt Triassic to Jurassic oceanic back-arc basin and the high-pressure metamorphism dated at ca. 160-150 Ma by 40Ar/39Ar.

  9. Argentina's radioactive waste disposal policy

    International Nuclear Information System (INIS)

    The Argentina policy for radioactive waste disposal from nuclear facilities is presented. The radioactive wastes are treated and disposed in confinement systems which ensure the isolation of the radionucles for an appropriate period. The safety criteria adopted by Argentina Authorities in case of the release of radioactive materials under normal conditions and in case of accidents are analysed. (M.C.K.)

  10. 鄂尔多斯盆地变质基底中碎屑锆石的 LA-ICP-MS U-Pb 年龄及其构造意义%LA-ICP-MS U-Pb Dating of Detrital Zircons of the Ordos Basin Metamorphic Basement and Its Tectonic Significance

    Institute of Scientific and Technical Information of China (English)

    吴素娟; 张永生; 邢恩袁

    2015-01-01

    根据鄂尔多斯盆地东北部钻孔的资料显示,鄂尔多斯盆地基底主要由一套变质沉积岩组成,对其中的二云母斜长片麻岩和矽线石片麻岩样品进行 LA-ICP-MS 锆石 U-Pb 年代学研究,两件样品单颗粒碎屑锆石共获得96个具有地质意义的年龄资料。二云母斜长片麻岩的部分锆石显示清晰的韵律环带,具有岩浆锆石的特征,其获得的207 Pb/206 Pb 年龄介于1898.2~2047.2Ma 之间,综合前人的研究数据,显示鄂尔多斯盆地基底东北部在古元古代2.0~2.1Ga 左右曾有岩浆活动。二云母斜长片麻岩的部分锆石和矽线石片麻岩的锆石具有变质锆石特征,获得的变质锆石年龄数据支持鄂尔多斯盆地东北部在古元古代发生过两期变质作用,早期的变质作用峰值年龄约为1.83Ga,代表着东部陆块和西部陆块碰撞拼合这期构造事件;晚期变质作用发生在约1.78Ga,可能记录了这一阶段的拉张抬升事件。%Basement rocks from drill cores at the northeastern margin of the Ordos Basin are mainly composed of meta-sedimentary rocks.LA-ICP-MS U-Pb zircon dating was conducted on two basement metamorphic rocks and yielded 96 valid data.A two-mica plagiogneiss yielded a restricted range of the magmatic zircon ages from 1898.2 Ma to 2047.2 Ma,which suggest the possible existences of a Paleoproterozoic intensive magmatic episode.A two-mica plagiogneiss and a sillimanite gneiss were overprited by two metamorphic events at ca.1.83Ga and ca.1.78Ga.The ages and characters of the zircons indicate that the basement of the northeastern Ordos Basin had undergone two metamorphic events at Late Paleoproterozoic.The ca. 1.83Ga metamorphic event indicates the northeastern Ordos Basin joined the final amalgamation of the NCC,while the ca.1.78Ga was probably a result of terrane uplift or regional extension.

  11. U-Pb zircon geochronology of intrusive and basement rocks in the Jacurici Valley region, Sao Francisco Craton, BA, Brazil; Geocronologia U-Pb em zircao de rochas intrusivas e de embasamento na regiao do Vale do Jacurici, Craton do Sao Francisco, BA

    Energy Technology Data Exchange (ETDEWEB)

    Silveira, Carlos Jose Sobrinho da; Frantz, Jose Carlos; Marques, Juliana Charao; Roos, Siegbert; Peixoto, Vinicius Medina, E-mail: silveira.carlosjose@hotmail.com, E-mail: jose.frantz@propesq.ufrgs.br, E-mail: juliana.marques@ufrgs.br, E-mail: sig_duda@yahoo.com.br, E-mail: vinimpeixoto@hotmail.com [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Laboratorio de Geologia Isotopica; Queiroz, Waldemir Jose Alves de, E-mail: waldemirqueiroz@hotmail.com [Companhia de Ferro Ligas da Bahia (FERBASA), Pojuca, BA (Brazil)

    2015-09-15

    The Jacurici Complex, located in the NE of the Sao Francisco Craton, is constituted by several Cr-mineralized mafic-ultramafic N-S bodies, possible fragments of a single sill disrupted during deformation. Some works suggest it is intruded on the Serrinha Block while others consider it in the Salvador-Curaca Belt. The basement on this region is informally divided into paragneisses and orthogneisses; the latter is supposed to be younger considering it is less deformed. Petrography revealed that some of the paragneisses are alkali-feldspar granite strongly milonitized. The orthogneisses occur at the north and consist, at least in part, of monzogranites with heterogeneous deformation, locally of low temperature. U-Pb zircon dating were performed for five representative samples. Just three provided good concordia ages. A mafic rock produced a 2102 ± 5 Ma age and it is petrographically similar to the metanorites described in the Jacurici Complex, being interpreted as the record of the first pulses of the mafic magmatism. A monzogranite yielded a 2995 ± 15 Ma age, older than expected, related to the Serrinha Block. The alkali-feldspar granite yielded a 2081 ± 3 Ma age. The Itiuba Syenite and the pegmatites that crosscut the Jacurici Complex have similar ages. Considering the lack of information about the supracrustal sequence that hosts the intrusive alkaline and mafic-ultramafic rocks at the Ipueira and the Medrado areas, it is possible that part of the terrain belongs to the Salvador-Curaca Belt. We suggest that the Jacurici Complex could be intruded after the tectonic amalgamation between the Serrinha Block and the older part of the Salvador-Curaca Belt and, therefore, could be hosted by both terrains. (author)

  12. Edad avanzada y factores de riesgo para infarto agudo de miocardio

    Directory of Open Access Journals (Sweden)

    M. A. Ciruzzi

    2002-12-01

    Full Text Available Este estudio caso-control analizó en los sujetos añosos el rol de los factores de riesgo coronario en el desarrollo del infarto agudo de miocardio (IAM, estableció la naturaleza de esta asociación y el grado de riesgo. Los datos fueron obtenidos en una investigación que incluyó 1060 casos y 1071 controles, realizada en 35 unidades coronarias de centros médicos de Argentina entre noviembre de 1991 y agosto de 1994. Nuestro análisis se basó en la información de los sujetos mayores de 65 años. Los casos fueron 427 pacientes con un primer IAM. Los controles fueron 396 sujetos sin evidencias clinicas de enfermedad cardiovascular, seleccionados en los mismos centros que los casos. Los Odds Ratios (OR y su intervalo de confianza del 95% (IC 95% se obtuvieron mediante un análisis de regresión logística, incluyendo variables como la edad, educación, clase social, tabaquismo, antecedente de diabetes o hipertensión arterial, índice de masa corporal e historia familiar de enfermedad coronaria. Los factores de riesgo relacionados independientemente con IAM fueron los siguientes: hipercolesterolemia (colesterol sérico > 240 mg/dl: OR=1.76 (IC 95%: 1.25-2.49, tabaquismo: OR=1.6 (IC 95%: 1.06-2.4, hipertensión arterial: OR=2.05 (IC 95%: 1.51-2.73, diabetes OR=1.71 (IC 95%: 1.12-2.70, historia de un familiar con enfermedad coronaria: OR=1.36 (IC 95%: 0.93-1.97 y de dos o más familiares: OR=2.63 (IC 95%: 1.21-5.71. Este estudio, confirma en los sujetos de edad avanzada la importancia de la hipercolesterolemia, del tabaquismo, la hipertesión arterial, la diabetes y la historia familiar de enfermedad coronaria como factores de riesgo de IAM

  13. Eolian deposits of the southwestern margin of the Botucatú paleoerg: Reconstruction of the Gondwana landscape in Central Northern Argentina

    Science.gov (United States)

    Peri, V. Gisel; Naipauer, Maximiliano; Pimentel, Marcio; Barcelona, Hernan

    2016-06-01

    The Mesozoic Botucatú paleoerg at the southwestern margin of Gondwana includes a succession of eolian dunes cross-strata which are presently exposed in Otumpa Hills (Central Northern Argentina). Here, the architectural facies, petrology, and provenance of those rocks were studied in order to investigate depositional environments and paleoclimates. The stratigraphic sequence included basal eolian two-dimensional crescentic dunes (Slp) overlain by three-dimensional crescentic dunes of smaller scale (Smt). These were correlated with the Upper Member Rivera of the Tacuarembó Formation (Uruguay), or its equivalent in Brazil, the Botucatú Formation. These outcrops partially mark the southwestern margin of the Botucatú paleoerg along the Chaco-Paraná Basin boundary. The paleocurrents from the W, NW, and SW and the U-Pb ages of detrital zircons indicate a main Pampean cratonic and secondary Andean magmatic arc (180 Ma) source. A detrital zircon of 180 Ma by U-Pb limits a maximum depositional age at 180 Ma (Toarcian) for facies Slp. Upwards, the phreatic silcrete and calcrete indicate semiarid conditions during the Paleocene, which are correlated with the Queguay Formation of Uruguay. A saprolite paleoweathering profile, recording wet tropical-hyper-tropical climate at the Early Eocene and representing the Gondwana landscape and climate conditions, crowns the sequence. This study represents the first provenance and surface texture analysis of minerals from the Botucatú paleoerg and was instrumental to unravel past environmental and sedimentary conditions.

  14. Geochemistry and U-Pb zircon ages of plutonic rocks from the Algodões granite-greenstone terrane, Troia Massif, northern Borborema Province, Brazil: Implications for Paleoproterozoic subduction-accretion processes

    Science.gov (United States)

    Costa, Felipe Grandjean da; Palheta, Edney Smith de Moraes; Rodrigues, Joseneusa Brilhante; Gomes, Iaponira Paiva; Vasconcelos, Antonio Maurilio

    2015-04-01

    The Algodões metavolcano-sedimentary sequence is located at the northern margin of the Archean/Paleoproterozoic Troia Massif, northern Borborema Province (NE Brazil). It represents a well-preserved Paleoproterozoic greenstone-like sequence affected by two major plutonic events. The early plutonism, represented by the Cipó orthogneisses, mainly comprises biotite-bearing metatonalites, which share similar geochemical signatures with Archean tonalite-trondjhemite-granodiorite (TTG). For these rocks, we report U-Pb (LA-ICPMS) zircon ages of 2189 ± 14 Ma and 2180 ± 15 Ma. A subsequent plutonic magmatism occurred at ˜2150-2130 Ma and is mainly represented by hornblende-bearing dioritic to tonalitic orthogneisses of the Madalena Suite and São José da Macaoca Complex. Geochemical data indicate that these dioritic/tonalitic orthogneisses have adakitic characteristics and strongly suggest mantle-related magmas. A (sensu stricto) granite plutonism (Serra da Palha orthogneisses) also intruded the Algodões sequence and yielded U-Pb (LA-ICPMS) zircon age of 2150 ± 16 Ma. These granitic orthogneisses show high-K content, A-type characteristics and probably derived from partial melting of a crustal (tonalitic) source. We suggest that the early ˜2190-2160 Ma TTG plutons probably developed in intra-oceanic arc setting, whereas the following ˜2150-2130 Ma adakitic plutons and A-type granitic magmatism developed in response to arc-continent collision.

  15. Geotectonic structural interpretation of the basement complex at the eastern border of the Espinhaco ridge, in Guanhaes and Gouveia region, based on an integration of their U/Pb and K/Ar geochronology united

    International Nuclear Information System (INIS)

    The basement complex at the eastern border of the Espinhaco ridge is composed of predominantly gneissic rocks which were subjected to migmatization and granitization. Overall the area shows complex tectonic evolution with recurrence of tectonomagmatic and metamorphic events as supported by geological, geochronological and structural studies. The Rb/Sr geochronology carried out on the basement rocks and metavolcanics from the Espinhaco interpreted together with the published U-Pb, Rb-Sr and K-Ar data defines the following scenario for the Precambrian crustal evolution. 1. Primary origin of a sialic crust at 2.97-2.84 Ga. ago as supported by U-Pb zircon ages. 2. Crustal reworking of the Archean crust and subordinate juvenile accretion from upper mantle during the 2.2-2.OGa. period, as suggested by the isochrons. 3. Recurrence of Middle Proterozoic events over the basement rocks (gneisses and charnockites) and metavolcanics of the Espinhaco as showed by isochrons. 4. Development of Late Proterozoic migmatization over the basement rocks (0.75 Ga., R.I.= 0.787) is association with Collisional tectonics and resetting of K-Ar mineral systems. (author)

  16. 40Ar/39Ar phlogopite and U - Pb perovskite dating of lamprophyre dykes from the eastern Lake Superior region: evidence for a 1.14 Ga magmatic precursor to Midcontinent rift volcanism

    International Nuclear Information System (INIS)

    Thin lamprophyre dykes are abundant in the vicinity of the ca. 1.1 Ga Midcontinent Rift System and the late Archean - Early Proterozoic Kapuskasing Uplift in the Canadian Shield northeast of Lake Superior. However, the relationship between these dykes and spatially associated alkalic-carbonatite complexes has been unclear. To ascertain the temporal relationship between the two, we have determined, by 40Ar/39Ar and U-Pb dating, precise emplacement ages for six lamprophyre dykes from the region. The 1144-4+6 Ma U - Pb date for perovskite from the western Marathon and Wawa areas is indistinguishable from the 1144 ± 7 Ma 40Ar/39Ar date for phlogopite from the eastern Kapuskasing Uplift, and it is concluded that these dykes are part of a regional 1.14 Ga swarm that extends over 300 km. These dykes were therefore emplaced some 35 Ma prior to the 1109 Ma commencement of Midcontinent Rift volcanism and coeval alkaline-complex activity, but essentially simultaneously with emplacement of the 1141 ± 2 Ma Abitibi diabase dyke swarm. It is suggested that these widespread 1144 Ma lamprophyre dykes and the Abitibi diabase dykes represent the first magmatic response of initiation of the Midcontinent rifting event, and were precursors to the main rift magmatism at 1109 Ma. (author). 32 refs., 2 tabs., 5 figs

  17. An in situ zircon Hf isotopic,U-Pb age and trace element study of banded granulite xenolith from Hannuoba basalt:Tracking the early evolution of the lower crust in the North China craton

    Institute of Scientific and Technical Information of China (English)

    ZHENG Jianping; LU Fengxiang; YU Chunmei; TANG Huayun

    2004-01-01

    Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied. The results show that the banded granulite is a sample derived from the early lower crust of the North China craton. It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes, however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting, metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40 Ma, except few ages of 3097-2824 Ma and 2489-2447 Ma. The zircons with ages older than 2447 Ma have high εHf (up to +18.3) and high Hf model age (2.5-2.6 Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHf of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHf up to +9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.

  18. U-Pb and origen of the Uruana quartz syenite and Itapuranga alkali granite in Goias, central Brazil: Late Braziliano alkali-rich magmatism in the Anapolis-Itaucu complex

    International Nuclear Information System (INIS)

    The Brasilia Belt is part of a Brasiliano/Pan African orogen developed between the Amazon and Sao Francisco cratons (for a review see Pimentel et al. 2000 and Dardenne 2000). The stabilization of the belt occurred after the last metamorphic event at ca. 620±20 Ma. Until recently, important late- to post-orogenic Neoproterozoic granitic magmatism was recognized mostly within the limits of the Goias Magmatic Arc, in the western part of the orogen. Recent studies by Pimentel et al. (1999) and Fischel et al (1999), as well as some unpublished U-Pb SHRIMP geochronological data, have also shown that Neoproterozoic granites represent an important component of the Anapolis- Itaucu Complex, a high grade terrain exposed in the central part of the Brasilia Belt, in between metasediments (Araxa Group) of the internal part of the belt. In the northern part of this granulitic complex, two alkali rich intrusions, the Uruana quartz syenite and the Itapuranga alkali suite (Lacerda Filho and Oliveira 1995) form large bodies elongated in the E-W direction. Their age and tectonic significance has been the matter of continuous debate. In this study we present new conventional and SHRIMP U-Pb results as well as whole-rock Sm-Nd data for samples of these intrusions (au)

  19. The rio Crespo intrusive suite: Geological U-Pb and Sm-Nd isotopic evidence for a major 1.43 Ga arc-related magmatism in the Rondonia state, SW Amazonian craton, Brazil

    International Nuclear Information System (INIS)

    On the basis of geological, petrological, U-Pb, and Sm-Nd geochronological data the basement rocks in the central-eastern part of Rondonia tin province (SW Amazonian Craton) are included into five lithological associations: (1) tonalitic gneiss (1.75 Ga), (2) enderbitic granulite (1.73 Ga), (3) paragneiss, (4) granitic and charnockitic augen-gneisses (1.57-1.53 Ga) and (5) fine-grained granitic gneiss and charnockitic granulite (1.43 Ga) (Payolla et al., subm.). The fine-grained granitic gneiss and charnockitic granulite association embraces the minor areal expression within the study area. However these rocks are widespread further south and west, and provide the first evidence of arc-related magmatism referred to the Rondonian-San Ignacio time, in Rondonia state (Payolla et al., subm.). In this paper, new data on the geology, geochemistry and an additional U-Pb zircon age, obtained from a sample of charnockite granulite, will be presented. Also a formal designation, 'Rio Crespo Intrusive Suite', for the fine-grained granitic gneiss and charnockite granulite association is herein proposed (au)

  20. RERTR activities in Argentina

    International Nuclear Information System (INIS)

    The Atomic Energy Commission of Argentina has been an active participant of the RERTR program since 1978. An important milestone of the Argentinean RERTR program was the development and manufacturing at industrial scale of U3O8 dispersed fuel and its subsequent application to the conversion of the RA-3 reactor core to LEU fuel. More recently, our activities were focused on the development of U3Si2 fuel with a density of 4.8 gU/cm3 and the improvement of the manufacturing process of this type of fuel. The program to qualify CNEA as a supplier U3Si2 dispersed fuels is scheduled to finalize by mid 2003. To hasten this program the main research reactor of Argentina, the RA3, raised its power from 5 MW to 8 Mw in October this year. This is an intermediate step in the program to increase RA-3 power to 10 MW Currently, one of the main objectives is to develop and qualify the technology for the production of high-density LEU fuel elements using U-Mo alloy. An original way to produce U-Mo powder (the HMD process) was developed and its being upgraded to plant scale production. Another significant progress was the development of LEU targets for the production of 99Mo, in the form of miniplates prepared with dispersed LEU U-Alx. The shipment to USA of 207 MTR spent fuels containing US origin highly enriched uranium, successfully carried out in the end of 2000, is another remarkable achievement of the Argentinean RERTR program. This activity was carried out in the framework of the United States Foreign Research Reactor Spent Nuclear Fuel Acceptance Program. The fuels were fabricated in Argentina and used in the RA-3 reactor from 1968 to 1987. The inventory of the shipped HEU spent fuel consisted in 166 standard assemblies and 41 control assemblies. (author)

  1. Case study - Argentina

    International Nuclear Information System (INIS)

    Antecedents and experience of nuclear activities in Argentina; the Atomic Energy Commission (CNEA). First development and research activities. Research reactors and radioisotopes plants. Health physics and safety regulations. - Feasibility studies for the first nuclear power plant. Awarding the first plant CNA I (Atucha I). Relevant data related to the different project stages. Plant performance. - Feasibility study for the second nuclear power plant. Awarding the second plant CNE (Central Nuclear Embalse). Relevant data related to established targets. Differences compared with the first station targets. Local participation. Plant performance. (orig./GL)

  2. Desobediencia civil en Argentina

    OpenAIRE

    Gustavo Fondevila

    2003-01-01

    Resumen: La crisis económica de Argentina en años recientes derivó en la pérdida de legitimidad de las instituciones políticas del país. La medida de suspensión de las libertades y garantías de derechos individuales provocó una desobediencia civil generalizada que llevó a miles de personas a manifestar pacíficamente su repudio al gobierno de Fernando de la Rúa. Este gesto ciudadano espontáneo, desorganizado y voluntario sirvió, entre otras cosas, para formar una autodeterminación primaria di...

  3. Salmonella enteritidis in Argentina.

    Science.gov (United States)

    Caffer, M I; Eiguer, T

    1994-01-01

    A significant increase in the number of isolations of Salmonella enteritidis has been observed in Argentina since 1986. Outbreaks of foodborne diseases in humans were associated with the consumption of raw or undercooked hens' eggs. Between 1986 and the first 6 months of 1993 there were 150 outbreaks reported, affecting more than 6000 persons. A total of 71.3% of these outbreaks were confirmed by stool cultures, and 47.3% by bacteriological study of the food implicated in the outbreak. A permanent surveillance of salmonellosis is imperative, taking into account the persistence of Salmonella enteritidis isolations in sporadic cases and in new outbreaks. PMID:8155472

  4. PyMEs en la Argentina: Geografía y Políticas

    OpenAIRE

    José Borello

    2012-01-01

    En este trabajo se presentan y analizan siete dimensiones que ayudan a entender las características y dinámica de las pymes en la Argentina, desde una perspectiva geográfica. Cuatro de esas dimensiones se refieren a la estructura de este tipo de empresas: edad, forma legal, característica de ocupación del local (alquila, propietario, etc.) y relaciones con instituciones públicas y privadas. Tres dimensiones describen aspectos más coyunturales de su situación actual: uso de la capacidad instal...

  5. Tendencia temporal de la mortalidad por armas de fuego en Argentina, 1980-2012

    OpenAIRE

    Hugo Spinelli; Adrián Santoro; Carlos Guevel; Marcio Alazraqui

    2015-01-01

    Este trabajo analiza el impacto de las armas de fuego en la mortalidad entre los años 1980-2012 en Argentina. Para ello se realiza un estudio epidemiológico descriptivo de la tendencia temporal, a través de las siguientes variables: sexo, grupos de edad, intencionalidad y jurisdicción. Los datos fueron obtenidos en la Dirección de Estadísticas e Información en Salud del Ministerio de Salud de la Nación. Se encontraron 87.671 muertes por armas de fuego. Los varones representaron el 85,7% y su ...

  6. Biomasa de Cornops aquaticum (Orthoptera: Acrididae) en humedales del nordeste de Argentina

    OpenAIRE

    Luciana Irene Gallardo; María Celeste Franceschini; Alicia Susana Guadalupe Poi; María Laura De Wysiecki

    2015-01-01

    La estimación de la biomasa en las poblaciones de insectos, es un factor clave para cuantificar los recursos disponibles y los flujos de energía en las redes tróficas de los ecosistemas. Cornops aquaticum es un herbívoro común en las plantas de Eichhornia en los humedales del nordeste de Argentina. Nuestro objetivo fue analizar la variación de su biomasa en relación a las distintas categorías de edades de la población de este acridio, en dos plantas huésped: Eichhornia azurea y Eichhornia cra...

  7. Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Dating of Amphibolites in the Songshugou Ophiolite in the Eastern Qinling

    Institute of Scientific and Technical Information of China (English)

    LIU Liang; CHEN Danling; ZHANG Anda; ZHANG Chengli; YUAN Honglin; LUO Jinhai

    2004-01-01

    in basalts from other regions of the world. The LA-ICP-MS trace element and U-Pb isotopic analyses show that the zircon grains from the amphibolites are similar to the typical magmatic zircon in terms of their very low U and Th contents (62.36-0.10 μg/g and 78.47-0.003 μtg/g, respectively). Seven pits from the core and core-mantle parts of the zircon grains yielded an average weighted 206Pb/238U age of 973+35 (2σ) Ma with the Th/U ratios range from 0.01 to 8.38 and mostly greater than 0.23. This age is consistent within the error range with the whole-rock Sm-Nd isochron age of 1030±46 Ma for the same kind of rocks reported by Dong et al. (1997a). In a combined analysis with the zircon positions on the CL images and the corresponding Th/U ratios, the age of 973±35 Ma is probably the formation age of tholeiite, the protolith of the Songshugou amphibolite. The geochronological determination gives further evidence that the Songshugou ophiolite was formed during the Neoproterozoic. In addition, there is one pit from the rim of a zircon grain giving a 206pb/238U age of 572+ 199 (1 σ) Ma with a Th/U ratio of 0.08. It may represent the age of the accretionary zircon in the amphibolite-facies metamorphism.

  8. Late Palaeozoic magmatism in the northern New England Orogen - evidence from U-Pb SHRIMP dating in the Yarrol and Connors provinces, central Queensland

    International Nuclear Information System (INIS)

    Full text: The northern part of the New England Orogen in central Queensland has been divided into three provinces, which are from east to west, the Wandilla, Yarrol and Connors Provinces. Previous workers suggested that the provinces are elements in an Early Carboniferous west-dipping subduction system with the Wandilla Province representing the accretionary wedge, the Yarrol Province a forearc basin and the Connors Province the volcanic arc. Farther west, a fourth province, the Drummond Basin, is interpreted as a back-arc basin. The Connors Province crops out in two areas, the Auburn Arch in the south and Connors Arch in the north. Prior to the present study, some workers recognised two superimposed volcanic arcs, one in the Late Devonian and a second in the Early Permian. Other workers have challenged this model suggesting that the rocks in the Connors Province were mainly Late Carboniferous to Early Permian and that they recorded a period of continental extension. U-Pb SHRIMP dating in the Connors Province has confirmed the existence of at least episodic Early Carboniferous magmatism from the Tournaisian to Namurian in both the Auburn and Connors Arches. We suggest that the Tournaisian rocks are vestiges of the Early Carboniferous volcanic arc suggested by earlier workers. Ages of ∼350Ma and ∼349Ma in the Connors Province are similar to ages for volcanics in Cycle 1 in the Drummond Basin and to volcanics in the lower part of the Rockhampton Group in the Yarrol Province. Magmatism in the Drummond Basin and Yarrol Province continued into the Visean although no early Visean rocks have yet been recognised in the Connors Province. The mid-Carboniferous (late Visean) may represent an important change in the evolution of the region. East of the Auburn Arch, in the Yarrol Province, this time corresponds to the boundary between the Rockhampton Group and Lorray Formation, and is marked by a sudden increase in regional radiometric response. It represents the start of

  9. Activities with Argentina

    International Nuclear Information System (INIS)

    In 1989, the US Department of Energy (DOE) responded to the need to redirect resources from weapons production to environmental restoration and waste management by establishing the Office of Environmental Management (EM) and delegated to this office the responsibility of cleaning up the US nuclear weapons complex. Now in its eight year, EM's mission has three central facets: (1) to assess, remediate, and monitor contaminated sites and facilities; (2) to store, treat, and dispose of waste from past and current operations; and (3) to develop and implement innovative technologies for environmental cleanup. To this end, EM has established domestic and international cooperative technology development programs, including one with the Republic of Argentina. Cooperating with Argentine scientific institutes and industries meets US cleanup objectives by: (1) identifying and accessing Argentine EM-related technologies, thereby leveraging investments and providing cost-savings; (2) improving access to technical information, scientific expertise, and technologies applicable to EM needs; and (3) fostering the development of innovative environmental technologies by increasing US private sector opportunities in Argentina in EM-related areas

  10. RERTR activities in Argentina

    International Nuclear Information System (INIS)

    The Atomic Energy Commission of Argentina has been involved in the Reduced Enrichment for Research and Test Reactors Program since 1978. The most relevant milestones of the program, regarding fuel R and D activities, were the development and manufacturing at industrial scale of U3O8 dispersed fuel assemblies and the conversion of the RA-3 reactor core to LEU fuel. More recently, the activities were focused in the development of high density U3Si2 fuel with a density of 4.8 gU/cm3 and the improvement of the manufacturing process of U3Si2 powder. Currently one of the main objectives is to develop and qualify the technology for the production of high-density LEU fuel elements using U-Mo alloy. Several alternative ways to obtain U-Mo powder are under development with the aim of evaluating plant scale production and costs. To boost this program the main research reactor of Argentina, the RA-3, will be upgraded to 10 MW early in 2001 and the hot cells at the Ezeiza Atomic Center are fully operational after important investments. Significant progresses were also carried out in the development of LEU targets for the production of Mo99. Experimental work has demonstrated the feasibility of the manufacturing and radiochemical processing of miniplate targets prepared with dispersed UAlx, maintaining the geometry and the alkaline processing of the HEU targets used so far. (author)

  11. Geology, petrology and U-Pb geochronology of Serra da Rajada Granitic Pluton: implications about ediacaran magmatic evolution in NE portion of the Rio Piranhas-Serido Domain (NE of Borborema Province); Geologia, petrologia e geocronologia U-Pb do Pluton Granitico Serra da Rajada: implicacoes sobre a evolucao magmatica ediacarana na porcao do Dominio Rio Piranhas-Serido (NE da Provincia Borborema)

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Alan Pereira da; Dantas, Alexandre Ranier, E-mail: alan.costa@cprm.gov.br, E-mail: alexandre.dantas@cprm.gov.br [Servico Geologico do Brasil (CPRM), Natal, RN (Brazil). Nucleo de Apoio de Natal/Superintendencia Regional de Recife; Nascimento, Marcos Antonio Leite do; Galindo, Antonio Carlos, E-mail: marcos@geologia.ufrn.br, E-mail: galindo@geologia.ufrn.br [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Departamento de Geologia

    2015-12-15

    The Ediacaran plutonic activity, related to the Brazilian/Pan-African orogeny, is one of the most important geological features in the Borborema Province, formed by batholiths, stocks and dikes. The Serra da Rajada Granitic Pluton (SRGP), located in the central portion of the Rio Piranhas-Serido Domain, is an example of these bodies. This site is the target of cartographic, petrographic, lithochemical and geochronological studies. Its rocks are described as monzogranites consisting of K-feldspar, plagioclase (oligoclase-An{sub 23-24%}), quartz and biotite (main mafic), having as accessory minerals opaque, titanite, allanite, apatite and zircon. Chlorite, white mica and carbonate are alteration minerals. Lithochemical data from 15 samples show quite evolved rocks (SiO{sub 2} , 69% to 75%), rich in alkalis (Na{sub 2}O + K{sub 2}O ≥ 8.0%), depleted in MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO{sub 2} (≤ 0.36%), and displaying moderate levels of Fe{sub 2}O{sub 3} t (2.16 to 3.53%). These rocks present a transitional nature between metaluminous and peraluminous (predominance of the latter) and have subalkaline/monzonitic affinity (high-K Calc-alkaline). Harker diagrams represent negative correlations in Fe{sub 2}O{sub 3}t, MgO and CaO, indicating fractionation of mafic and plagioclase. The REE spectrum show enrichment of light in relation to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in Eu (Eu/ Eu* = 0.70 to 10.13) suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows correlating the SRGP rocks with those described as Equigranular high-K Calc-alkaline Suite. The U-Pb geochronology and Sm-Nd isotope dating indicate that the biotite monzogranite have a crystallization age of 557 ± 13 Ma and TDM model age of 2.36 Ga, respectively, and ε{sub Nd} value of - 20.10 for the crystallization age, allowing to infer a crustal source for the magma generated in the Paleoproterozoic age. (author)

  12. U-Pb isotopic compositions of the ultrahigh pressure metamorphic (UHPM) rocks from Shuanghe and gneisses from Northern Dabie zone in the Dabie Mountains,central China: Constraint on the exhumation mechanism of UHPM rocks

    Institute of Scientific and Technical Information of China (English)

    李曙光; 黄方; 周红英; 李惠民

    2003-01-01

    The U-Pb isotopic study of the ultrahigh pressure metamorphic (UHPM) rocks and gneisses from the Dabie Mountains shows that the UHPM rocks exposed in the Southern Dabie zone have relatively low Pb contents (most 0.1), and a large variation of Pb isotopic ratios with relatively high radiogenic Pb (206Pb/204Pb = 17.026-20.781). Their low Pb contents could be the result of Pb loss caused by fluid expulsion during continental subduction, while their high radiogenic Pb values can be explained by the mixing of the upper crust Pb and the mantle Pb. In contrast, the gneisses exposed in the Northern Dabie zone have higher Pb contents (most > 4×10?6), lower U/Pb ratios (< 0.07), and lower Pb isotopic ratios (206Pb/204Pb = 15.799-17.204), which are similar to those of the Mesozoic granites developed in both Northern and Southern Dabie zones. It is suggested that the Northern Dabie zone may have experienced a smaller fluid expulsion and Pb loss during the continental subduction, and their Pb isotopic compositions could be explained by the mixing of the lower crust Pb and the mantle Pb. Their initial Pb isotope ratios at 230 Ma suggest that the U/Pb ratios of the UHPM rocks in the Southern Dabie zone are higher than those of the gneisses in the Northern Dabie zone in a long period of time before the continental subduction. The above observations suggest that the protoliths of the UHPM rocks in the Southern Dabie zone are upper crustal rocks in the subducted continental crust, while the gneisses in the Northern Dabie zone have the middle-lower crust features. Based on these observations, a model for the exhumation of UHPM rocks is proposed, i.e. the detachment between the upper crust and lower crust in the subducted continental crust could have occurred during subduction, thus the subducted upper crust was uplifted by buoyancy and moved southward along the thrust.

  13. Unraveling protolith ages of meta-gabbros from Samos and the Attic-Cycladic Crystalline Belt, Greece: Results of a U-Pb zircon and Sr-Nd whole rock study

    Science.gov (United States)

    Bröcker, Michael; Löwen, Kersten; Rodionov, Nikolay

    2014-06-01

    The focus of this study is on meta-ophiolitic rocks from Samos and the Attic-Cycladic Crystalline Belt, Greece. SHRIMP U-Pb zircon geochronology, Sr-Nd isotope and bulk-rock geochemistry have been applied to meta-gabbros that occur as blocks and lenses in blueschist-facies mélanges on Samos and Evia, and in the greenschist-facies Upper Unit on Tinos. The geodynamic significance of these meta-ophiolite fragments within the overall pattern of the Eastern Mediterranean region is unclear. Regional correlations within the Cyclades archipelago and with the Jurassic meta-ophiolites of the Balkan region or the Cretaceous occurrences in Turkey are uncertain. Although field, petrological and geochemical similarities among some mélange occurrences suggest a common genetic relationship, such interpretations remain speculative if not supported by robust geochronological data. SHRIMP U-Pb zircon dating of three meta-gabbro blocks from Samos yielded Cretaceous ages with weighted mean 206Pb/238U ages of 78.3 ± 1.3 Ma, 76.8 ± 1.4 Ma and 77.8 ± 1.4 Ma and almost identical intercept ages, interpreted to indicate the time of magmatic crystallization. These results further substantiate models suggesting a correlative relationship with mélanges on the islands of Syros and Tinos, central Aegean Sea, where similar rocks yielded almost identical U-Pb zircon ages. Published and new Sr-Nd isotope data of meta-gabbros from Andros, Samos, Tinos (Lower Unit) and from mainland Greece (Pindos, Othris) reveal distinctive differences among ion probe-dated samples with Jurassic and Cretaceous protolith ages. Three groups can clearly be distinguished in a 87Sr/86Sr vs. 143Nd/144Nd diagram. However, these geochemical parameters do not allow assigning tentative age estimates for yet undated meta-gabbros from southern Evia and the Upper Unit of Tinos. The situation is further complicated by the observation that the Jurassic and Cretaceous meta-gabbros do not show other discriminating geochemical

  14. Research reactors in Argentina

    International Nuclear Information System (INIS)

    Argentine Nuclear Development started in early fifties. In 1957, it was decided to built the first a research reactor. RA-1 reactor (120 kw, today licensed to work at 40 kW) started operation in January 1958. Originally RA-1 was an Argonaut (American design) reactor. In early sixties, the RA-1 core was changed. Fuel rods (20% enrichment) was introduced instead the old Argonaut core design. For that reason, a critical facility named RA-0 was built. After that, the RA-3 project started, to build a multipurpose 5 MW nuclear reactor MTR pool type, to produce radioisotopes and research. For that reason and to define the characteristics of the RA-3 core, another critical facility was built, RA-2. Initially RA-3 was a 90 % enriched fuel reactor, and started operation in 1967. When Atucha I NPP project started, a German design Power Reactor, a small homogeneous reactor was donated by the German Government to Argentina (1969). This was RA-4 reactor (20% enrichment, 1W). In 1982, RA-6 pool reactor achieved criticality. This is a 500 kW reactor with 90% enriched MTR fuel elements. In 1990, RA-3 started to operate fueled by 20% enriched fuel. In 1997, the RA-8 (multipurpose critical facility located at Pilcaniyeu) started to operate. RA-3 reactor is the most important CNEA reactor for Argentine Research Reactors development. It is the first in a succession of Argentine MTR reactors built by CNEA (and INVAP SE ) in Argentina and other countries: RA-6 (500 kW, Bariloche-Argentina), RP-10 (10MW, Peru), NUR (500 kW, Algeria), MPR (22 MW, Egypt). The experience of Argentinian industry permits to compete with foreign developed countries as supplier of research reactors. Today, CNEA has six research reactors whose activities have a range from education and promotion of nuclear activity, to radioisotope production. For more than forty years, Argentine Research Reactors are working. The experience of Argentine is important, and argentine firms are able to compete in the design and

  15. Operating practical experience at Argentina

    International Nuclear Information System (INIS)

    Operating experiences of Atucha-1 and Embalse Nuclear Power Plants were discussed in this work. The technical and economic aspects, such as reliability, availability, personnel training, operating costs, prices and market, which exercise influence upon Argentina nuclear energy policy, mainly on the power electric generation by nuclear power plants were considered. Finally the current status of the nucleoelectric sector in Argentina and forecasting were analysed

  16. Brasil y Argentina, 1990-2005

    Directory of Open Access Journals (Sweden)

    Marina Gabriela Zunino

    2008-01-01

    Full Text Available Con el objetivo de analizar la mortalidad por armas de fuego en Brasil y Argentina entre 1990 y 2005, se realizó un estudio epidemiológico descriptivo utilizando datos oficiales de mortalidad de ambos países. Se analizaron número, proporción y tasas crudas y ajustadas para cada tipo de muerte (catalogadas según la CIE-9a y CIE-10a, el total por año y el promedio anual del período, sexo y edad. Los perfiles globales de los dos países presentaron tendencia creciente, pero Brasil mostró valores superiores de muertes y homicidios por armas de fuego en todo el período. A partir de los resultados se discute la hipótesis: el perfil de Brasil, particularmente el de homicidios por armas de fuego, es consecuencia no solo de la violencia social que responde a la persistentemente alta desigualdad y exclusión en que vive gran parte de la población, sino también al surgimiento, expansión y fortalecimiento de diversos grupos armados en ese país. El perfil argentino resultaría en parte del aumento de la violencia social también como respuesta al deterioro socioeconómico imperante, y por otra parte, sería consecuencia de la histórica monopolización de la violencia por parte del Estado

  17. Zircon U-Pb geochronology and geochemical characteristics of neutral-acidic intrusions of Wuligou in South Qilian Mountains:their implications on forming gold deposit%党河南山乌里沟中酸性岩体锆石 U-Pb 年龄、地球化学特征及与金矿成矿关系

    Institute of Scientific and Technical Information of China (English)

    张翔; 张莉莉; 汪禄波; 刘博; 戴霜; 金治鹏; 蒙珍; 杨怀玉

    2015-01-01

    通过对南祁连山党河南山东段乌里沟金矿区中酸性侵入岩锆石 U-Pb 年龄测定及岩石地球化学分析,探讨了岩体形成的构造环境及其与金矿成矿的关系。矿区角闪石闪长岩体侵位年龄为457±6.3 Ma,岩石中各组分的质量分数:SiO2为48.98%~59.16%,Al2 O3为14.51%~16.77%,K2 O+Na2 O 为8.24%~9.47%,属准铝质、碱性-过碱性岩系列;DI 为58~79,属 I 型花岗岩类;岩石 Cr 和 Mg#值较低,Na2 O 和 K2 O 含量接近,表明源岩含有较多的壳源成分;稀土总量中等,轻稀土富集,具弱 Eu 负异常;相对富集大离子亲石元素 Rb、Ba、Th、K、U,亏损 Nb、Ta、P、Ti。矿区二长花岗岩属碱性岩系列,比角闪石闪长岩稀土总量低、更加亏损 Nb、Ta 等,与角闪石闪长岩属同一岩浆源,分异程度比角闪石闪长岩高。两种岩石均具岛弧岩浆岩特征,是中晚奥陶世南祁连俯冲到较浅部位熔融形成。岩体金含量高,目前探明的矿体产于岩体内部及接触带,围岩蚀变强烈,显示岩体为金矿成矿提供物质来源和成矿热液。%This paper reports the zircon U-Pb dating and the lithogeochemistry of the small-scale neutral-acidic intrusions in the Wuligou gold deposit in the east of Danghenanshan,South Qilian Mt., and interprets their tectonic settings and the linkage to gold mineralization.Our data show that the emplacement age of the amphibole diorite is 457 ±6.3 Ma.The mass fraction of SiO2 is 48.98% ~59.16%,that of A1 2 O3 is 14.51%~16.77%,that of (K