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Sample records for bambui group neoproterozoic

  1. Influence of geological and hydrogeological factors on the high natural fluoride concentrations in groundwaters in Bambui Group (Neoproterozoic), northern of Minas Gerais state, Brazil

    International Nuclear Information System (INIS)

    In the northern semi-arid and semi-humid region of Minas Gerais State, in the southeast Brazil, substantial part of the water supplying is produced by means of deep wells. In several localities the fluoride concentrations are higher than 1.5 mg/L, maximum acceptable limit for drinking water, endangering the public supply and the public health. Endemies of dental fluorosis have been detected since the decade of 1990. The cause of this problem has been associated to the consumption of local drinking water. Current studies indicate the occurrences of fluorite in the limestones of the Bambui Group as the main mineral-source for the fluoride content in the groundwater, however without identifying the specific contribution of each hydrostratigraphic unit. This work shows the results of stratigraphic studies and hydro-chemical analysis of 144 deep wells and the influence of the carbonatic facies in the fluoride concentrations of the water. Fluoride concentrations are related to fluorite occurrences/mineralizations (lithostratigraphic control) and to circulation depth of groundwater (geochemical control), newly distinguishing three hydrostratigraphic units. The correlation analysis of hydrogeochemic parameters (F-, Mg2+, SO42- and electric conductivity) corroborates these grouping into three units. The probability of the contamination by fluoride, as a function of the hidroestratigraphic units, in decreasing order, seems to be: top level of the Sete Lagoas Formation; Lagoa do Jacare Formation; and botton and middle levels of the Sete Lagoas Formation. (Author)

  2. The origin of the Bambui group in the context of the geotectonic evolution and radiometric ages

    International Nuclear Information System (INIS)

    The fragmentation of the Rodinia Supercontinent, around 1000 Ma, produced rifted fragments of continental masses, some of which suffered important sedimentation processes under the influence of large scale continental glaciations. Among these deposits, over the Sao Francisco Craton, the Macaubas Group, the Ibia Group, as well as the Bebedouro and Jequitai Formations, may be mentioned. The sedimentation of the Bambui Group is related to the successive large geotectonic process of agglutination of Gondwana, during the Neoproterozoic to Early paleozoic Brasiliano Orogenic Cycle. The principal evidence are as follows: - sedimentary, structural and metamorphic unconformities between the Bambui group and the Macaubas and Bebedouro sequences: - sedimentation of the Bambui group directly over the basement exposures of the Sao Francisco Craton; - drastic shift from glacial (Macaubas Group and Bebedouro Formation) to the platform carbonatic sedimentary environment of the Bambui Group; and - polimictic megaconglomeratic layers, including deformed basement detrital fragments, inter bedded with thick pelites and limestones of the Bambui Group, indicating a source are with rugged topography. The above evidences converge to the interpretation of the Bambui Group as formed in a foreland basin over the Sao Francisco Craton, and associated to the successive activities of thrust fronts originated in the adjacent mobile belt. This resulted in a cyclic sedimentation, followed by the final molassic-type sedimentation of the Tres Marias Formation. SInce the compressive pulses of the Brasiliano Orogenic Cycle, as determined in the adjacent Aracuai mobile belt, are comprised in the 650-500 Ma interval, the present authors indicate that the maximum sedimentation age of the Bambui group shall be close to 650 Ma. (author)

  3. Considerations on the age of the Bambui Group (MG, Brazil) based on isotopic analyses of Sr and Pb

    International Nuclear Information System (INIS)

    Based on radiometric ages, the Bambui Group deposition time is related to the end of the Precambrian. However, the ages determined and released through scientific magazines are mot in agreement (600-1350 m.y.) and many doubts about the geochrological picture of this important lithostratigraphic unit remained for a long time. As a result of the work developed by Metamig, CPGeo (IG-USP) and IPEN (SP), Rb/Sr and Pb/Pb isotopic determinations were done on 31 rocks samples and 17 galenas collected from the Bambui Basin distributed in Minas Gerais State. The Rb/Sr ages of 590 m.y. for Pirapora Formation, 620 m.y. for Tres Marias Formation, and 640 m.y. for the Paraopeba Formation situated in the stable area are linked to sedimentation processes. In the Paracatu region the age of 680 m.y. found for the Paraopeba Formation is related to metamorphic events. The lead isotopic ratios from the galenas suggest an isotopic evolution in two stages. The first ended with the lead separation from the mantle and its incorporation to the crust during events of the Transamazonic Cycle. The second ended when the lead were incorporated to the galenas and seems to be related to one or more events of the Brazilian Cycle. (Author)

  4. Isotopic measurements of carbon and oxygen in carbonates from Bambui Group in the center-north region of Bahia State

    International Nuclear Information System (INIS)

    Analyses of 85 carbonate samples of the Bambui Group from the Chapada de Irece, Bahia, exhibit four distinct 13C and 18O isotopic ratio groupings. Based on these results the following sedimentation model for the Bambui Group is proposed: 1. A continental environment originating the basal dolomitic limestones and argillacceous dolomites. Isotopic ratios from these rocks fall within ranges considered typical of continental sedimentation: delta18C between -2.9 and -6.4%o, and delta18O from -5.3 to -10.7%o (PDB). 2. An alternating continental and restricted marine environment resulting in the deposition of laminated dolomitic limestones with thin interbeds of muddy sediments. Delta13C ratios of +0.1 to -4.9%o and a mean value of -8.2+-0.3%o delta18O are compatible with such an environment. 3. A restricted marine environment dominated by sedimentation of the black, fetid limestones of the upper portion of the sequence. Isotopic ratios for 13C are all over -1.8%o, up to about +7.5%o, and 18O ratios vary from-4.9 to -10.0%o. A number of light-grey sileceous dolomites is interbered with the lowermost black limestones of this sequence. Isotopic data for these rocks show a narrow range for delta18C values (-0.5 to 1.0%o) and a broader variation for delta18O ratios (0.0 to -8.3%o). This latter may be interpreted as indicative of intense evaporation during deposition of the dolomitic facies

  5. The Neoproterozoic Tillite Group from Ella Ø, East Greenland

    DEFF Research Database (Denmark)

    Buchardt, Bjørn; Kristiansen, Kasper K.; Houmark-Nielsen, Michael

    The Neoproterozoic sediments in East Greenland are found in an N-S trending belt in the Fjord Region. Overlying the Eleonora Bay Supergroup is the Tillite Group, which for long has been interpreted as a series of glacially derived deposits including two diamictitic units. The Tillite Group itself...... ~250 m thick Area Fm consisting of organic-rich black shales and fine-grained sandstones. The age of the Tillite Group has not been established with certainty, but an Ediacaran age has been suggested. Based on correlations to similar deposits on Svalbard the lower Ulvesø Fm has been assigned a Sturtian...... between the two diamictitic units. The Canyon Fm overlying the Storeelv diamictite shows a gradual shift in d13C(carbonate) to values close to 0‰ as also found in the Cambrian rocks above. Comparison to published carbon isotope curves from other Neoproterozoic glacial events makes it tempting to correlate...

  6. Pb/Pb isochron ages and Pb isotope geochemistry of Bambui Group carbonate rocks from the southern portion of the Sao Francisco Basin

    International Nuclear Information System (INIS)

    This study involves the establishment of chemical and analytical procedure for Pb/Pb dating of Neo proterozoic carbonate rocks and their application to obtaining isochron ages of Bambui Group rocks from the southern portion of the Sao Francisco Basin, Minas Gerais State. The Pb isotopic compositions and U and Pb concentrations determined on more than 90 samples (≅ 600 analyses) from Sete Lagoas do Jacare formations, Bambui Group, from different parts of the basin, showed four distinct types of Pb, here called types I, II, III and IV. Type I Pb was found in samples with low Pb concentrations and relatively high U concentrations. Type II Pb is present in samples with relatively high Pb concentrations and low U concentrations it is non-radiogenic crustal Pb. Type III Pb is also found in samples with high Pb concentrations and low U concentrations but it is radiogenic crustal Pb. Type IV Pb occurs in samples with U/Pb ratios lower than 1 and is intermediate in composition between Type III and Type I Pb. According to the data presented in this paper it is suggested that carbonate rocks from Sete Lagoas Formations were deposited before 686±69 Ma. Rocks from the Lagoa do Jacare Formation, contained only Type II Pb, which does not permit determination of a Pb/Pb age. During the interval from 690 to 500 Ma, the Pb isotope system of the carbonate rocks from the Sao Francisco Basin was disturbed, and in some areas it was totally reset. The imprecise U/Pb ages of 550-600 Ma obtained from some of the carbonate rocks reflect this disturbance. The ages determined in this study are in agreement with most of the published ages of the tectonism from the Brasiliano fold belts marginal to Sao Francisco Craton, showing that the isotopic systems of Sao Francisco Basin rocks were largely affected by brasiliano tectonism. (author)

  7. Profile characterization of soil developed on pelitic rocks from the Bambui Group through chemical analysis, X-ray diffraction and Moessbaur spectroscopy

    International Nuclear Information System (INIS)

    Five sample from a Red-yellow latosol developed on pelitic rocks from the Bambui Group, located close to Paraopeba, state of Minas Gerais, Brazil, were collected and studied. The sample with color patterns varying from yellowish (sample SL11; 0.3m depth), in superficial horizons, to reddish (SL12; 1.0m) in intermediate profile positions, and various shades (SL14A and SL14V; 3.0m), in deeper horizons, were studied through Moessbauer spectroscopy in order to characterize, in detail, the ferruginous species present. The total iron content within the soil is practically constant in relation to the depth. Yet, the hematite/goethite content ratio varies within the expected sequence according to the color. A linear relationship was observed between the reddish intensity and the hematite content of the argillaceous fraction. The hematite contents are proportionally less in the SL14A sample, apparently due to deficient drainage in the past, and in the SL11 sample, due to organic matter effects. This latter sample is also characterized by at least two goethite populations: one with 20% mol replacing aluminum and another with certainly more than 30% mol. In to explan this difference, three hypothesis were elaborated. The most suitable one suggests that the goethite is destroyed and formed again through the soil column, in response to pedo environmental changes closer to the surface. (D.J.M.)

  8. Possible organisms similar to Ediacaran forms from the Bhander Group, Vindhyan Supergroup, Late Neoproterozoic of India

    Science.gov (United States)

    De, Chirananda

    2003-01-01

    Fossil Medusoid genera resembling Ediacaria ( Sprigg 1947) and Hiemalora ( Fedonkin 1982) and having distinctive Ediacaran affinity have been discovered in a shale horizon occurring at the base of the Bhander Group, the uppermost unit of the Vindhyan Supergroup of central India. This is the first record of unequivocal occurrence of Ediacara-like fossils in a Proterozoic basin of the Peninsular India. This finding substantially extends the previously known biogeographic range of the Ediacaran elements to Peninsular India and further enhances their biostratigraphpic potential for correlation of the upper Vindhyans with some Ediacaran horizons of Canada, Australia, South Africa and Russian Platforms. With this extension, the representatives of the genus Ediacaria can be regarded as having a global distribution in places now occupying both lower and higher latitudes. The genus Hiemalora, which appeared to be endemic to the Russian block, also has wide biogeographic coverage. These fossils assign an Ediacaran (550-543 Ma) age for the host Lakheri Limestone and suggest that the Lakheri unit was deposited within 6 million years of the Precambrian-Cambrian boundary. They also support and refine the traditional view of the Late Neoproterozoic age for the lower Bhander Group. These fossils provide positive stratigraphic clues for locating the Precambiran-Cambrian boundary strata in the overlying Lakheri-Sirbu segment of the Vindhyan sequence. They also indicate a depositional environment typical of a muddy shallow shelf setting above storm wave-base.

  9. Stratigraphic, Microfossil, and Geochemical Analysis of the Neoproterozoic Uinta Mountain Group, Utah: Evidence fo a Eutrophication Event?

    OpenAIRE

    Hayes, Dawn Schmidli

    2011-01-01

    Several previous Neoproterozoic microfossil diversity studies yield evidence for arelatively sudden biotic change prior to the first well‐constrained Sturtian glaciations. In an event interpreted as a mass extinction of eukaryotic phytoplankton followed by bacterial dominance, diverse assemblages of complex acritarchs are replaced by more uniform assemblages consisting of simple leiosphaerid acritarchs and bacteria. Recent data from the Chuar Group of the Grand Canyon (770‐742 Ma) suggest thi...

  10. Organotemplate structures in sedimentary manganese carbonates of the Neoproterozoic Penganga Group, Adilabad, India

    Indian Academy of Sciences (India)

    Joydip Mukhopadhyay; Jens Gutzmer; Nicolas J Beukes

    2005-06-01

    Manganese carbonates interstratified with bedded chert in the Chanda Limestone of the Neoproterozoic Penganga Group at Adilabad, south India, have been studied for possible evidence that microbiota played a role in the mediation of early diagenetic Mn-carbonate formation in Precam- brian marine sedimentary successions. The manganese carbonate and chert beds occur within a below wave base, deep-water distally steepened ramp succession. High resolution SEM petrogra- phy of the manganese carbonates revealed two basic morphologies — spherical to oval-cylindrical shaped microconcretions, and tubular to irregular, elongated, film-like microstructures. Infolded filmy to hollow tubular strand-like internal morphologies of the spherical to oval-cylindrical shaped microconcretions suggest their microbial affinity. The tubular and film morphologies with mesh- like interconnections closely resemble architectures of microbial extracellular polymeric substance (EPS). Mineralization took place on these organotemplates by the process of permineralization as well as replacement in an early diagenetic pore-water environment with reduction of higher manganese oxy-hydroxides by organic matter and consequent increase in dissolved carbonate.

  11. Southern Brasilia Belt (SE Brazil): tectonic discontinuities, K-Ar data and evolution during the Neoproterozoic Brasiliano orogeny

    International Nuclear Information System (INIS)

    This paper focuses the tectonic evolution of the southern brasilia belt, with emphasis on the Furnas segment, along the 21 deg C S parallel. The uppermost structural unit (Passos Nappe - PN) comprises a highly deformed metasedimentary succession interpreted as a fragment of the Neoproterozoic passive margin of western Sao francisco craton. An inverted metamorphic gradient ranging from greensvhits to lower granulite facies of medium to high-pressure regime characterizes the PN as relict of a subduction zone. The External Domain display a complex imbrication of basement rocks (Archean Piumhi greenstones, a turbiditic gaywacke succession and a calc-alkaline granitoid suite) with undated siliciclast low-grade metasedimentary rocks. The Sao Francisco Craton (SFC) comprises pre-1.8 Ga basement rocks covered by anchimetamorphic Neoproterozoic carbonatic shallow marine platform deposits of the Bambui group. The Brasiliano thrust stacking generated a coarse clastic influx of molassic character on the foreland zone of Sao Francisco Craton, coeval with the exhumation of the External Domain thrust sheets. New K-Ar determinations on mineral separates are presented an interpreted among previous data. The SFC basement rocks display Paleo-to Meesoproterozoic cooling ages. The allochthonous units, in contrast, display K-Ar ages within the 560-675 Ma range. Brasiliano thrust stacking is therefore interpreted to have taken place onto a cold Sao Francisco craton foreland, in a thin-skinned style, as basement rocks were not heated enough to have their-K-ar systems reset during the allochthony. (author)

  12. Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K.: MORB and OIB in the Iapetus Ocean

    Science.gov (United States)

    Saito, Takuya; Uno, Masaoki; Sato, Tomohiko; Fujisaki, Wataru; Haraguchi, Satoru; Li, Yi-bing; Sawaki, Yusuke; Yamamoto, Shinji; Maruyama, Shigenori

    2015-11-01

    The Gwna Group in Anglesey-Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent mélanges that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group. Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey-Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.

  13. Chemostratigraphy of Neoproterozoic Banded Iron Formation (BIF)

    DEFF Research Database (Denmark)

    Gaucher, Claudio; Sial, Alcides N.; Frei, Robert

    2015-01-01

    Neoproterozoic banded iron formations (BIFs) are not restricted to the middle Cryogenian, c. 715 Ma glaciation, occurring in Tonian, Cryogenian, and Ediacaran successions. Many Neoproterozoic BIFs were deposited in glacially influenced settings, such as the Rapitan Group (Canada), Jacadigo Group (W...... study of BIFs include rare earth element distribution, especially Eu and Ce normalized concentrations, iron speciation, and Nd and Cr isotopes (δ53Cr). Whereas Rapitan type BIFs exhibit no Eu or Ce anomalies, the Algoma-type Neoproterozoic BIFs show both. Positive δ53Cr values characterize glacially...

  14. High frequency peritidal cycles of the upper Araras Group: Implications for disappearance of the neoproterozoic carbonate platform in southern Amazon Craton

    Science.gov (United States)

    Rudnitzki, Isaac Daniel; Romero, Guilherme Raffaeli; Hidalgo, Renata; Nogueira, Afonso Cesar Rodrigues

    2016-01-01

    The Araras Group is an extensive carbonate platform developed at the southeastern margin of the Amazon Craton during the Neoproterozoic. The Nobres Formation corresponds to the upper unit of the Neoproterozoic Araras Group. It is exposed in road cuts and quarries in the Northern Paraguay Belt, and is characterized by meter-scale shallowing upward cycles. Forty-four fourth-to fifth-order parasequence cycles are enclosed into three third order sequences/megacycles, unconformably overlain by siliciclastic deposits of the Alto Paraguay Group. The cycles are generally of peritidal type, limited by exposure surfaces composed of asymmetrical tidal flat/sabkha lithofacies in the basal Nobres Formation. They consist of fine dolostone, intraclastic dolostones with megaripples, stromatolites biostrome, sandy dolostone with enterolithic structures and silicified evaporite molds. Upsection, the cycles progressively become symmetrical, comprising arid tidal flat deposits with abundant stromatolite biostrome, fine-grained sandstone and rare evaporitic molds. The stacking patterns for hundreds of meters indicate continuous and recurrent generation of accommodation space, probably triggered by subsidence concomitant with relative sea-level changes. Palynomorphs found in the upper part of Nobres Formation comprehend spheroidal forms, such as Leiospharidia, rare filamentous and acanthomorphous acritarchs, mostly Tanarium correlated to the Ediacaran Complex Acantomorph Palynoflora of ˜580-570 Ma. Previous data of carbon isotopes and paleogeographic reconstructions, and also the presence of evaporites and storm-influenced deposits in the Araras Group, suggest a wet to tropical setting for Amazonia during the Mid-Ediacaran, which is incompatible with previous claims for Gaskiers-related glacial sedimentation in the region. During the final stages of evolution of the Araras carbonate platform, a progressive input of terrigenous has occurred in the peritidal setting likely due tectonic

  15. Neoproterozoic Chuar Group (˜800-742 Ma), Grand Canyon: a record of cyclic marine deposition during global cooling and supercontinent rifting

    Science.gov (United States)

    Dehler, Carol M.; Elrick, Maya; Karlstrom, Karl E.; Smith, Gary A.; Crossey, Laura J.; Timmons, J. Michael

    2001-06-01

    Chuar Group sediments were deposited in a marine cratonic basin synchronously with marine deposition in other basins of western North America and Australia. The top of the Chuar Group is 742 Ma; thus, this succession offers a potentially important record of global climatic and tectonic changes during the mid-Neoproterozoic — a critical time leading to possible global glaciation during supercontinent rifting. Chuar Group cycles and sequences may record glacioeustatic fluctuations during the climatic transition into the Sturtian Ice Age (˜750-700 Ma), as well as extension related to the dispersal of Rodinia. The mid-Neoproterozoic Chuar Group (1600 m thick) is predominantly composed of mudrock with subordinate meter-scale beds of dolomite and sandstone. Facies analysis leads to the interpretation of a wave- and tidal-influenced marine depositional system. Diagnostic marine features include: (1) marine fossils and high local pyrite content in the mudrock facies; (2) mudcracked mud-draped symmetric ripples and reverse flow indicators in the sandstone facies; (3) facies associations between all facies; and (4) no unequivocal terrestrial deposits. Chuar facies stack into ˜320 dolomite- and sandstone-capped meter-scale cycles (1-20 m thick) and non-cyclic intervals of uniform mudrock facies (20-150 m thick). Nearly all cycles have mudrock bases indicating subtidal water depths. Dolomite-capped cycles shallow to peritidal environments (peritidal cycles), some indicating subaerial exposure of varying degrees (exposure cycles). Sandstone-capped cycles shallow to peritidal environments with no evidence of prolonged exposure (peritidal cycles). Non-cyclic intervals represent the deepest water depths (˜10s of meters). Peritidal cycles and non-cyclic intervals dominate the lower and middle Chuar Group. In the upper Chuar Group, the percentage of exposure cycles increases, as does the thickness of individual cycles and non-cyclic intervals, and the degree of subaerial

  16. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt

    International Nuclear Information System (INIS)

    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and εNd(T) =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and εNd(T) = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  17. U-Pb SHRIMP and Sm-Nd geochronology of the Anapolis-Itaucu complex, Araxa group and associated granites: Neoproterozoic high grade metamorphism and magmatism in the Central part of the Brasilia Belt, Goias

    International Nuclear Information System (INIS)

    The Tocantins Province (Almeida et al. 1981) in central Brazil is a Neoproterozoic orogenic zone developed between the Amazon and Sao Francisco cratons and possibly a third continental block, known as Parapanema Block, hidden below the sedimentary rocks of the Parana Basin. The Tocantins Province comprises the eastward vergent Brasilia Belt, adjacent to the Sao Francisco Craton (Marini et al. 1984), and the westward vergent Paraguay and Araguaia belts, developed on the eastern margin of the Amazon Craton. According to Trompette (1997), the Brasilia and Araguaia belts had sedimentation starting at around 1.1-1.0 Ga and final closure at 0.6 Ga. In the northern part of the Brasilia Belt occur the Barro Alto, Canabrava and Niquelandia maficultramafic layered complexes. Inconclusive U-Pb isotopic data indicate ages between ca. 1600 and 2000 Ma for these intrusions that were affected by highgrade metamorphism ca. 740-790 Ma ago, during the Neoproterozoic (Ferreira Filho et al. 1994; Suita et al. 1994; Correia et al. 1997). In the southern part of the Brasilia Belt, in central Goias , is the Anapolis-Itaucu granulite complex. It consists of a large complex of high-grade rocks, volcano-sedimentary sequences and granites, exposed in between metasediments of the Araxa Group, the main constituent of the internal zone of the Neoproterozoic Brasilia Belt (Fuck et al. 1994). These granulites have traditionally been interpreted as the exposure of Archean sialic basement to the sediments of the Brasilia Belt (Danni et al. 1982, Marini et al. 1984; Lacerda Filho and Oliveira 1995). This work reports the results of a regional Sm- Nd isotopic investigation and U-Pb SHRIMP data in order to assess (i) the nature of the protoliths of the Araxa Group in this area; (ii) the nature and the high grade metamorphism of rocks from Anapolis-Itaucu Complex; (iii) the crystallization and metamorphism of aluminous granites (au)

  18. Modal analysis and geochemistry of two sandstones of the Bhander Group (Late Neoproterozoic) in parts of the Central Indian Vindhyan basin and their bearing on the provenance and tectonics

    Indian Academy of Sciences (India)

    Apurba Banerjee; D M Banerjee

    2010-12-01

    The Neoproterozoic Bhander Group in the Son Valley, central India conformably overlying the Rewa Group, is the uppermost subdivision of the Vindhyan Supergroup dominantly composed of arenites, carbonates and shales. In Maihar –Nagod area, a thick pile of unmetamorphosed clastic sedimentary rocks of Bhander Group is exposed, which provides a unique opportunity to study Neoproterozoic basin development through provenance and tectonic interpretations. The provenance discrimination and tectonic setting interpretations are based on modal analysis and whole rock geochemistry. The average framework composition of the detrital sediments composed of quartz and sedimentary lithic fragments are classified as quartz arenite to sublitharenite. The sandstone geochemically re flects high SiO2 moderate Al2O3 and low CaO and Na2O type arenite. The high concentration of HFSE such as Zr, Hf , and Th/Sc, Th/U ratios in these sandstones indicate a mixed provenance. The chondrite normalized REE pattern shows moderate to strong negative Eu anomaly which suggests that major part of the sediments were derived from the granitic source area. The sandstone tectonic discrimination diagrams and various geochemical plots suggest that the provenance of the lower and upper Bhander sandstone formations was continental interior to recycled orogen.

  19. Aplication of uranium isotopes as tracers in ground water studies (Bambui - Bahia, Brazil)

    International Nuclear Information System (INIS)

    Analyses of 234U/238U activity ratios and the uranium concentration in 42 underground water samples have provided better in formation about the recharge area and the flow direction in the Bambui limestone, Bahia (Brazil). In the main recharge area, the activity ratios were found to range from 3 to 6 and the uranium concentration averaged 1 μg/l. The activity ratio increases northward with the highest values close to 10. The 234U excess from a basic of ratio of activity (fundamental leaching ratio) also increases northward in agreement with the age of the water, an observation confirmed by C-14. This 234U excess is attributed to the alpha-recoil process. The system was calibrated and the age of the waters in the calcareous region was determined. (Author)

  20. Stratigraphy of neoproterozoic sedimentary and volcano sedimentary successions of Uruguay

    International Nuclear Information System (INIS)

    Based on the new data the different characteristics of the Neoproterozoic (volcano) sedimentary succesions of Uruguay are described and discussed. Their stratigraphic tectonics and palaeoclimatic implications are analyzed.The results of the present investigations also allow to define the Maldonado Group which would beintegrated by the Playa Hermosa and Las Ventanas formations.

  1. The use of chemical and isotopic data as indicators of the origin of waters and dissolved salts in the Bambui calcareous aquifer (Bahia-Brazil)

    International Nuclear Information System (INIS)

    Samples of 25 wells located in the Bambui limestone aquifer in the region of Irece - Bahia, have been analised for the isotopic ratio 18O/16O and the major chemical species Ca, Mg, Na, K, Cl, SO4 and bicarbonate. The oxygen-18 data have been found to range between -2,62/00(in a thousand) to -6,66/00(in a thousand) relative to the universal Standard Mean Ocean Water (SMOW) and are compared with the values of the precipitation in the localities of Jacobina and Lencois (meteorological stations nearby) and with the values of the groundwater in sedimentary basins in northeastern Brazil. The comparison suggests that aquifer system is recharged by precipitation originated in northeastern Brazil, instead of originating on coast of Bahia, east of the area. Furthermore, the waters in aquifer are not found homogenized, having widely varying 18O and chemical composition and being of different ages. The strong correlation between the observations Ca, Mg, Na, Cl and TDS (total dissolved solids) suggests an aerosol origin of salts, not excluding the hypothesis of dissolution of rock, which concentrations. The comparison of characteristic ratios Mg/Ca, SO4/Cl and (Cl-Na)/Cl, a Piper diagrama and a dendrogram established by cluster analysis, indicates that the wells may be separated in to two groups according to the isotopic or geochemical environment to which they belong. These groups may represent the differents sources of salt proposed, one being from the limestone, the other having come from aerosols. (Author)

  2. Reservoir quality in the A2C-Stringer interval of the late Neoproterozoic Ara-Group of the South Oman Salt Basin. Diagenetic relationships in space and time

    Energy Technology Data Exchange (ETDEWEB)

    Becker, S. [RWTH Aachen (Germany). LuFG Reservoir Petrology; Reuning, L.; Kukla, P.A. [RWTH Aachen (Germany). Geological Inst.; Abe, S.; Li, Shiyan; Urai, J.L. [RWTH Aachen (Germany). Structural Geology, Tectonics and Geomechanics; Farqani, S.; Lopes Cardozo, G.; Rawahi, Z. [Petroleum Development Oman (Oman)

    2013-08-01

    The Ediacaran-Early Cambrian Ara Group of the South Oman Salt Basin consists of six carbonate to evaporite (rock salt, gypsum) sequences. These Ara Group carbonates are termed A0C to A6C from the bottom towards the top of the basin. Differential loading of locally 5 km thick Cambrian to Ordovician clastics onto the mobile rock salt of the Ara Group caused growth of isolated salt diapirs, which resulted in strong fragmentation and faulting of the carbonate intervals into several isolated so-called 'stringers'. These carbonate stringers represent a unique intra-salt petroleum system, which has been successfully explored in recent years. However, some of the stringers failed to produce at significant rates due to the complex diagenetic history from the shallow to the deep burial realm. The goal of this study is twofold. Firstly, to unravel the complex diagenesis and its relative timing and link them to the burial history of the salt basin. Secondly, to detect spatial distribution patterns of diagenetic phases and their effect on reservoir properties. Mineralogy, rock fabrics, paragenetic relationships and geochemistry of {proportional_to} 400 samples from several petroleum wells from the late Neoproterozoic A2C interval were analyzed and combined with pre-existing data. The spatial distribution of diagenetic phases and petrophysical characteristics will be displayed in field-scale distribution maps. These maps comprise crucial information for better prediction of reservoir quality in the analyzed fields, planning of new exploration wells and better volumetric calculations. An integration of the paragenetic sequence derived from thin-section analysis with results from finite element and discrete element models further helps to constrain the effect of salt tectonics on fracture formation and fluid evolution within the stringers.

  3. Sediment-hosted stratabound copper assessment of the Neoproterozoic Roan Group, central African copperbelt, Katanga Basin, Democratic Republic of the Congo and Zambia: Chapter T in Global mineral resource assessment

    Science.gov (United States)

    Zientek, Michael L.; Bliss, James D.; Broughton, David W.; Christie, Michael; Denning, Paul D.; Hayes, Timothy S.; Hitzman, Murray W.; Horton, John D.; Frost-Killian, Susan; Jack, Douglas J.; Master, Sharad; Parks, Heather L.; Taylor, Cliff D.; Wilson, Anna B.; Wintzer, Niki E.; Woodhead, Jon

    2014-01-01

    This study estimates the location, quality, and quantity of undiscovered copper in stratabound deposits within the Neoproterozoic Roan Group of the Katanga Basin in the Democratic Republic of the Congo and Zambia. The study area encompasses the Central African Copperbelt, the greatest sediment-hosted copper-cobalt province in the world, containing 152 million metric tons of copper in greater than 80 deposits. This study (1) delineates permissive areas (tracts) where undiscovered sediment-hosted stratabound copper deposits may occur within 2 kilometers of the surface, (2) provides a database of known sediment-hosted stratabound copper deposits and prospects, (3) estimates numbers of undiscovered deposits within these permissive tracts at several levels of confidence, and (4) provides probabilistic estimates of amounts of copper and mineralized rock that could be contained in undiscovered deposits within each tract. The assessment, conducted in January 2010 using a three-part form of mineral resource assessment, indicates that a substantial amount of undiscovered copper resources might occur in sediment-hosted stratabound copper deposits within the Roan Group in the Katanga Basin. Monte Carlo simulation results that combine grade and tonnage models with estimates of undiscovered deposits indicate that the mean estimate of undiscovered copper in the study area is 168 million metric tons, which is slightly greater than the known resources at 152 million metric tons. Furthermore, significant value can be expected from associated metals, particularly cobalt. Tracts in the Democratic Republic of the Congo (DRC) have potential to contain near-surface, undiscovered deposits. Monte Carlo simulation results indicate a mean value of 37 million metric tons of undiscovered copper may be present in significant prospects.

  4. Sedimentary talc in Neoproterozoic carbonate successions

    Science.gov (United States)

    Tosca, Nicholas J.; Macdonald, Francis A.; Strauss, Justin V.; Johnston, David T.; Knoll, Andrew H.

    2011-06-01

    Mineralogical, petrographic and sedimentological observations document early diagenetic talc in carbonate-dominated successions deposited on two early Neoproterozoic (~ 800-700 million years old) platform margins. In the Akademikerbreen Group, Svalbard, talc occurs as nodules that pre-date microspar cements that fill molar tooth structures and primary porosity in stromatolitic carbonates. In the upper Fifteenmile Group of the Ogilvie Mountains, NW Canada, the talc is present as nodules, coated grains, rip-up clasts and massive beds that are several meters thick. To gain insight into the chemistry required to form early diagenetic talc, we conducted precipitation experiments at 25 °C with low-SO 4 synthetic seawater solutions at varying pH, Mg 2+ and SiO 2(aq). Our experiments reveal a sharp and reproducible pH boundary (at ~ 8.7) only above which does poorly crystalline Mg-silicate precipitate; increasing Mg 2+ and/or SiO 2(aq) alone is insufficient to produce the material. The strong pH control can be explained by Mg-silica complexing activated by the deprotonation of silicic acid above ~ 8.6-8.7. FT-IR, TEM and XRD of the synthetic precipitates reveal a talc-like 2:1 trioctahedral structure with short-range stacking order. Hydrothermal experiments simulating burial diagenesis show that dehydration of the precipitate drives a transition to kerolite (hydrated talc) and eventually to talc. This formation pathway imparts extensive layer stacking disorder to the synthetic talc end-product that is identical to Neoproterozoic occurrences. Early diagenetic talc in Neoproterozoic carbonate platform successions appears to reflect a unique combination of low Al concentrations (and, by inference, low siliciclastic input), near modern marine salinity and Mg 2+, elevated SiO 2(aq), and pH > ~ 8.7. Because the talc occurs in close association with microbially influenced sediments, we suggest that soluble species requirements were most easily met through microbial influences on

  5. Evidence of Neoproterozoic back arc basin development in the Central Ribeira Belt, southeastern Brazil: new geochronological and geochemical constraints from the Sao Roque - Acungui Groups

    International Nuclear Information System (INIS)

    The Ribeira Belt (RB) of southeastern Brazil represents an important manifestation of the Brasiliano Orogeny formed during the assembly of West Gondwana. Contemporaneous sedimentation and volcanism within the RB provide a basis for helping understand its tectonic evolution and paleogeography. U-Pb monazite data from the basal metavolcanic rocks of the Sao Roque Group indicate a crystallization age of 628 Ma and the upper sequence is cut by a 605 Ma (U-Pb zircon) rhyolite intrusion. Zircon and monazite analyses of metavolcanic (mafic) rocks and from metagabbros of the lower Acungui supergroup yield crystallization ages of 614 and 617 ma, respectively. This supergroup is intruded by a 607 ma granite. Geochemical signatures of basal mafic units in both sequences are characteristic of E-MORB subalkaline tholeitic basaltic rocks. Nd isotopic signatures of the metamafic rocks indicate that they were derived in part from the asthenospheric mantle (consistent with emplacement in an extensional setting), whereas the felsic bodies appear to have come from the melting of paleoproterozoic lithosphere. The paleogeographic reconstruction of part of the RB suggests that the Sao Roque/Acungui groups represent extensional sequences, with features of backarc basins, which evolved during the syn-collisional phase of the Brasiliano Orogeny. These data support the hypothesis that we have a rapid evolution (10-20 ma) between extensional and compressional tectonics during the geological history of the Sao Roque/Acungui Backarc. (author)

  6. The use of carbon isotopes in the study of groundwater of the Bambui calcareous-central region of Bahia (Brazil)

    International Nuclear Information System (INIS)

    Groundwater of 34 wells and of a spring of the Bambui limestone aquifer, in central Bahia, Brazil, were analized for the 14C and 13C content. One sample of soil CO2 and four of soil organic matter were analized for 13C. From these data were calculated the 14C ages of these waters. A major difficulty in the use of radiocarbon in groundwater hydrology is the estimation of the initial 14C concentration. In many cases, this can be simply determined by the fraction of carbon derived from soil gas, relative to the total carbon dissolved, by the use of Δ13C of the soil organic matter, limestone and dissolved carbon in water. This approach does not seem to be completely valid in arid ou semi-arid regions, specially where the pH of the soil is relatively high. In this case, the isotopic composition of the soil water can be determined if the pCO2 and pH of the soil can be estimated and if the isotopic composition of the soil CO2 can be known. The final isotopic composition of the groundwater is a combination of the isotopic composition of the soil water and any limestone thereafter dissolved. The 14C ages of the water samples analized ranged from modern to about 13000 years. The recharge areas of the aquifer are clearly indicated, as the probable underground flow directions. The interpretation of the radiocarbon data is in accord with the hydrologic data. (Author)

  7. Neoproterozoic Glaciations and the Early Evolution of Animals

    Science.gov (United States)

    Narbonne, G. M.

    2004-05-01

    The intense climatic changes that characterized the Neoproterozoic world were marked by equally profound evolutionary changes that ultimately led to the Cambrian Explosion. Early and Middle Neoproterozoic oceans contained prokaryotes and diverse eukaryotic lineages, including crown-group red, green, and heterokont algae. The survival of diverse eukaryotic lineages through the Sturtian, Marinoan, and Gaskiers glaciations implies that, although these were among the most extreme glaciations Earth has ever experienced, sea ice was not as thick or pervasive as required by earlier "hard Snowball" models. Most molecular clocks predict the existence of animals well before 600 Ma and a few tantalizing hints have been found, but the oldest definite evidence of animal life are phosphatized eggs and embryos overlying Marinoan glacial deposits in China. The subsequent Late Neoproterozoic is characterized by the global occurrence of the Ediacara biota, an assemblage of cm- to m-scale fossils of soft-bodied organisms that probably represent a mixture of stem groups of modern phyla and "failed experiments" in evolution. The oldest Ediacaran fossils occur in eastern Newfoundland, and postdate the glacial diamictites and cap carbonate of the Gaskiers Formation (580 Ma) by only 5 million years, implying a causal relationship between the end of the Neoproterozoic glaciations and the proliferation of animal life. These fossils include architecturally complex fronds up to two metres long, implying either extremely rapid rates of evolution or a pre-glacial origin of the Ediacara biota. Fossils of the Mistaken Point biota (575-560 Ma) were completely sessile and show a similar fractal architecture that is difficult to relate to any existing life forms. Some of these taxa persisted into the White Sea biota (560-550 Ma), which also contains trace fossils and metameric fossils that confirm the evolution of mobile bilaterians. The youngest Ediacaran fossils (550-543 Ma) exhibit the first

  8. Birth cohort differences in physical functioning levels among elderly Brazilians: findings from the Bambui Cohort Study of Aging (1997-2008)

    OpenAIRE

    Oliveira, C. M.; M.F. Lima-Costa

    2011-01-01

    The aim of this study was to investigate the cohort differences in physical functioning levels among the older (cohort members born in 1916-1926 and in 1927-1937) participants of the Bambui Cohort Study of Aging. The data came from participants aged 71-81 who took part at baseline in 1997 (n = 491) and in the 11th wave in 2008 (n = 620). The physical functioning variables included the following self-reported measures: activities of daily living, the instrumental activities of daily living and...

  9. Genomic African and Native American Ancestry and Chagas Disease: The Bambui (Brazil) Epigen Cohort Study of Aging

    Science.gov (United States)

    2016-01-01

    Background The influence of genetic ancestry on Trypanosoma cruzi infection and Chagas disease outcomes is unknown. Methodology/Principal Findings We used 370,539 Single Nucleotide Polymorphisms (SNPs) to examine the association between individual proportions of African, European and Native American genomic ancestry with T. cruzi infection and related outcomes in 1,341 participants (aged ≥ 60 years) of the Bambui (Brazil) population-based cohort study of aging. Potential confounding variables included sociodemographic characteristics and an array of health measures. The prevalence of T. cruzi infection was 37.5% and 56.3% of those infected had a major ECG abnormality. Baseline T. cruzi infection was correlated with higher levels of African and Native American ancestry, which in turn were strongly associated with poor socioeconomic circumstances. Cardiomyopathy in infected persons was not significantly associated with African or Native American ancestry levels. Infected persons with a major ECG abnormality were at increased risk of 15-year mortality relative to their counterparts with no such abnormalities (adjusted hazard ratio = 1.80; 95% 1.41, 2.32). African and Native American ancestry levels had no significant effect modifying this association. Conclusions/Significance Our findings indicate that African and Native American ancestry have no influence on the presence of major ECG abnormalities and had no influence on the ability of an ECG abnormality to predict mortality in older people infected with T. cruzi. In contrast, our results revealed a strong and independent association between prevalent T. cruzi infection and higher levels of African and Native American ancestry. Whether this association is a consequence of genetic background or differential exposure to infection remains to be determined. PMID:27182885

  10. Neoproterozoic low latitude glaciations : an African perspective

    OpenAIRE

    Straathof, Gijsbert Bastiaan

    2011-01-01

    The Neoproterozoic is one of the most enigmatic periods in Earth history. In the juxtaposition of glacial and tropical deposits the sedimentary record provides evidence for extreme climate change. Various models have tried to explain these apparent contradictions. One of the most popular models is the Snowball Earth Hypothesis which envisages periods of global glaciations. All climatic models are dependent on palaeogeography which as yet remains poorly constrained for the Neopr...

  11. Biogeochemical and micropaleontological study of black chert, Sete Lagoas Formation, Bambui Group (Late Proterozoic), Sao Gabriel (GO), Brazil

    International Nuclear Information System (INIS)

    The biogeochemical study of amorphous and structured organic matter (OM) in two samples of thinly laminated black cherts (SG-1 and SG-2) from Sete Lagoas Formation, State of Goias, Brazil, is presented. The spectra analysis of infra-red, electron paramagnetic resonance and isotope ratio of C-12 and C-13 shown that: the amorphous OM consists of a soluble fraction (SF) and a insoluble fraction (Kerogen), which only the latter is syngenetic; the allochthonous SF comes from several sources, mainly from Phanerozoic sediments and soil contamination; the SG-1 and SG-2 Kerogens have δ 13C values (-27.2 per mille and - 29.2 per mille respectively), which suggest OM photosynthetized and submitted to a mild thermal hystory; although the preserved microbiota is dominated by allochthonous elements (colonial fragments) and planktonic forms, both Kerogens were derived for the most part from photo-autotrophic benthonic communities, probably responsible for the lamination in the original carbonate rock, both SG-1 and SG-2 Kerogens exhibits O/C and H/C ratios comparable to Proterozoic humic Kerogens (type IV); the preserved microflora represents a microbial community of the chert-algae facies typical of the Middle and upper Proterozoic; and the occurence of rare acritarchs (Kildinella spp.) in the microflora is biostratigraphically significant in that it suggests a Late Riphean or Vendian age (950-570 m.y.) for the Sete Lagoas Formation. (Author)

  12. Neoproterozoic Glacial Extremes: How Plausible is the

    Science.gov (United States)

    Peltier, W. R.

    2004-05-01

    The suggestion that the glaciation events of the Neoproterozoic could have been global in extent, so-called "snowball" glaciations, during which the oceans were entirely covered by sea ice and the continents by massive continental ice sheets, is an idea tha is recurrent in the geological and climate dynamics literature. It is an idea that haa both critics and defenders but concensus concerning it's plausiblity has yet to emerge. Previous work on this problem has led to the suggestion that a more likely scenario than the "hard snowball" is one in which open water continues to persist at the equator, thus enabling biological evolution into the Cambrian to proceed, perhaps stimulated by the transition from the cold conditions of the Neoproterozoic to the warm condition of the Cambrian, thus leading to the Cambrian "explosion of life". We will discuss recent extensions of our previous efforts to model the extreme climate of the Neoproterozoic, using both the University of Toronto Glacial Systems Model and the NCAR Community Climate System Model. With an appropriate choice for the albedo of sea ice, the former model conntinues to deliver hysteresis in the surface temperature vs. CO2 concentration space when solar luminosity is reduced by 6% below modern, and thus continues to suggest the existence of the previously hypothesized "CO2 attractor". We argue here that the system could be locked onto this attractor by the strong "out of equilibrium" effects of the carbon cycle recently discussed by Rothman et al. (PNAS, 2003). The open water solution is confirmed as the preferred mode of the system by the detailed CCSM integrations that we have performed.

  13. Geology, geochemistry and geochronology of Neoproterozoic rocks in western Shire, Northern Ethiopia

    OpenAIRE

    Gebreyohannes, Gebrehiwet Welay

    2014-01-01

    Based on the integration of U-Pb isotopic data, geochemical data, petrographic data and geological data of the Neoproterozoic granitic and metavolcanic rocks of southernmost ANS, Northern Ethiopia, western shire district, the following conclusions can be drawn: (1) The study area consists of low-grade metavolcano-sedimentary rock assemblages that belong to the Tsaliet and Tambien Groups of the Arabian-Nubian Shield. Six major lithological units have been identified in the area and include mai...

  14. Application of carbon isotope chemostratigraphy to the Renison dolomites, Tasmania: a Neoproterozoic age

    International Nuclear Information System (INIS)

    This study uses carbon isotope chemostratigraphy to propose an age for the Success Creek Group and Crimson Creek Formation in the absence of any direct radiometric dates, palaeomagnetic or reliable palaeontological data. The δ13C values were determined for the least-altered dolomite samples. Suitable samples were selected on the basis of grain size, cathodoluminescence petrography, most enriched δ18O values ( > -2%o) low Mn/Sr ratios and low Fe and Mn concentrations. The average least-altered, most 13C-enriched dolomicrite samples in the youngest (No. I) dolomite horizon are + 4.6%o. This is typical of Neoproterozoic (but not Cambrian) carbonates. The δ13C values of all dolomite samples in the succession are significantly positive (up to + 7.5%o) and the excursion characteristic of the Proterozoic/Cambrian boundary has not been observed. The lack of negative δ13C values in all dolomite samples studied also suggests an absence of correlatives of Sturtian and Varanger tillites in the dolomite successions. The δ13C values in all three dolomite horizons suggest a Neoproterozoic age between about 820 to 570 Ma (Cryogenian to Neoproterozoic III) on the current global compilation carbon isotope curves. This age for the Success Creek Group and Crimson Creek Formation, inferred from carbon isotope chemostratigraphy, can be substantiated by other evidence. The age of the Renison dolomites is constrained by K-Ar dates of 708 ± 6 Ma from detrital muscovite in the underlying Oonah Formation and 588 ± 8 and 600 ± 8 Ma from doleritic rock in a lithostratigraphic equivalent of the Crimson Creek Formation from the Smithton Basin. Furthermore, acritarchs and the stromatolite Baicalia cf. B. burra also suggest a Neoproterozoic rather than Cambrian age. (author)

  15. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt; Grupo Araxa em sua area tipo: um fragmento de crosta oceanica Neoproterozoica na faixa de dobramentos Brasilia

    Energy Technology Data Exchange (ETDEWEB)

    Seer, Hildor Jose [Centro Federal de Educacao Tecnologica de Araxa, (CEFET), MG (Brazil); Brod, Jose Affonso; Fuck, Reinhardt Adolfo; Pimentel, Marcio Martins; Boaventura, Geraldo Resende; Dardenne, Marcel Auguste [Brasilia Univ., DF (Brazil). Inst. de Geociencias

    2001-09-01

    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and {epsilon}{sub Nd(T)} =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and {epsilon}{sub Nd(T)} = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  16. Testing the "Mudball Earth" Hypothesis: Are Neoproterozoic Glacial Deposits Capped with Supraglacial Dust?

    Science.gov (United States)

    Goodman, J. C.; Alvim Lage, C.

    2014-12-01

    The Snowball Earth hypothesis has inspired several variants which may help to explain some of the great mysteries of the Neoproterozoic glaciations. One of these, the "Mudball Earth", proposes that as the Earth remained completely frozen for millions of years, a layer of dust accumulated on the ice surface. This dust layer would darken the planet, making it easier for the Earth to escape from the highly stable snowball climate state. This hypothesis is testable: after the ice melted at the end of a glacial era, this dust would sink to the bottom of the ocean, possibly forming a distinct clay, mud, or silt layer on the top of the glacial till deposits: this "clay drape" would then be covered by the cap carbonates that mark a return to warm climate. Sublimation and ice flow during the glacial episode should make this layer thicker at the equator and thinner or absent in the poles. Is this clay layer actually present in the rock record? Is it more prevalent at the paleoequator, as predicted? A clay drape has been noticed anecdotally, but no global survey has been done to date. We conducted a thorough literature review of all sites where Neoproterozoic glacial diamictites have been observed, identifying the type of rock that lies between the diamictite and the postglacial cap carbonate, when present, during both Sturtian and Marinoan glacial periods. Only a few publications identify a distinct clay/silt/mud layer that might represent weathered dust. These sites are not grouped by paleolatitude in any obvious way. With access only to published reports, we cannot determine whether such a layer is absent, went unreported, or was misinterpreted by us. With this work we hope to attract the attention of Neoproterozoic field geologists, inviting them to comment on the presence or absence of strata which could confirm or reject the "Mudball" hypothesis.

  17. Neoproterozoic diamictite-cap carbonate succession and δ13C chemostratigraphy from eastern Sonora, Mexico

    Science.gov (United States)

    Corsetti, Frank A.; Stewart, John H.; Hagadorn, James W.

    2007-01-01

    Despite the occurrence of Neoproterozoic strata throughout the southwestern U.S. and Sonora, Mexico, glacial units overlain by enigmatic cap carbonates have not been well-documented south of Death Valley, California. Here, we describe in detail the first glaciogenic diamictite and cap carbonate succession from Mexico, found in the Cerro Las Bolas Group. The diamictite is exposed near Sahuaripa, Sonora, and is overlain by a 5 m thick very finely-laminated dolostone with soft sediment folds. Carbon isotopic chemostratigraphy of the finely-laminated dolostone reveals a negative δ13C anomaly (down to − 3.2‰ PDB) characteristic of cap carbonates worldwide. Carbon isotopic values rise to + 10‰ across ∼ 400 m of section in overlying carbonates of the Mina el Mezquite and Monteso Formations. The pattern recorded here is mostly characteristic of post-Sturtian (ca. ≤ 700 Ma), but pre-Marinoan (ca. ≥ 635 Ma) time. However, the Cerro Las Bolas Group shares ambiguity common to most Neoproterozoic successions: it lacks useful radiometric age constraints and biostratigraphically useful fossils, and its δ13C signature is oscillatory and therefore somewhat equivocal.

  18. The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints

    Science.gov (United States)

    López de Azarevich, Vanina L.; Escayola, Mónica; Azarevich, Miguel B.; Pimentel, Márcio M.; Tassinari, Colombo

    2009-12-01

    The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with ɛNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana.

  19. Towards a quantitative understanding of the late Neoproterozoic carbon cycle

    OpenAIRE

    Bjerrum, Christian J.; Donald E Canfield

    2011-01-01

    The cycles of carbon and oxygen at the Earth surface are intimately linked, where the burial of organic carbon into sediments represents a source of oxygen to the surface environment. This coupling is typically quantified through the isotope records of organic and inorganic carbon. Yet, the late Neoproterozoic Eon, the time when animals first evolved, experienced wild isotope fluctuations which do not conform to our normal understanding of the carbon cycle and carbon-oxygen coupling. We inter...

  20. Is the Neoproterozoic oxygen burst a supercontinent legacy?

    Science.gov (United States)

    Macouin, Melina; Roques, Damien; Rousse, Sonia; Ganne, Jerome; Denele, Yoann; Trindade, Ricardo

    2015-09-01

    The Neoproterozoic (1000-542 Myr ago) witnessed the dawn of Earth as we know it with modern-style plate tectonics, high levels of O2 in atmosphere and oceans and a thriving fauna. Yet, the processes leading to the fully oxygenation of the external envelopes, its exact timing and its link with the inner workings of the planet remain poorly understood. In some ways, it is a "chicken and egg" question: did the Neoproterozoic Oxygenation Event (NOE) cause life blooming, low-latitudes glaciations and perturbations in geochemical cycles or is it a consequence of these phenomena? Here, we suggest that the NOE may have been triggered by multi-million years oxic volcanic emissions along a protracted period at the end of the Neoproterozoic when continents were assembled in the Rodinia supercontinent. We report a very oxidized magma source at the upper mantle beneath a ring of subducting margins around Rodinia, and detail here the evidence at the margin of the Arabian shield. We investigate the 780 Ma Biotite and Pink granites and associated rocks of the Socotra Island with rock magnetic and petrographic methods. Magnetic susceptibility and isothermal remanent magnetization acquisitions show that, in these granites, both magnetite and hematite are present. Hematite subdivides magnetite grains into small grains. Magnetite and hematite are found to be primary, and formed at the early magmatic evolution of the granite at very high oxygen fugacity. Massive degassing of these oxidized magmas would reduce the sink for oxygen, and consequently contribute to its rise in the atmosphere with a net O2 flux of at least 2.25 x 107 Tmol. Our conceptual model provides a deep Earth link to the NOE and implies the oxygenation burst has occurred earlier than previously envisaged, paving the way for later changes in the outer envelopes of the planet epitomized on the extreme Neoproterozoic glaciations and the appearance of the first animals.

  1. Is the Neoproterozoic oxygen burst a supercontinent legacy?

    Directory of Open Access Journals (Sweden)

    Melina eMacouin

    2015-09-01

    Full Text Available The Neoproterozoic (1000–542 Myr ago witnessed the dawn of Earth as we know it with modern-style plate tectonics, high levels of O2 in atmosphere and oceans and a thriving fauna. Yet, the processes leading to the fully oxygenation of the external envelopes, its exact timing and its link with the inner workings of the planet remain poorly understood. In some ways, it is a chicken and egg question: did the Neoproterozoic Oxygenation Event (NOE cause life blooming, low-latitudes glaciations and perturbations in geochemical cycles or is it a consequence of these phenomena? Here, we suggest that the NOE may have been triggered by multi-million years oxic volcanic emissions along a protracted period at the end of the Neoproterozoic when continents were assembled in the Rodinia supercontinent. We report a very oxidized magma source at the upper mantle beneath a ring of subducting margins around Rodinia, and detail here the evidence at the margin of the Arabian shield. We investigate the 780 Ma Biotite and Pink granites and associated rocks of the Socotra Island with rock magnetic and petrographic methods. Magnetic susceptibility and isothermal remanent magnetization acquisitions show that, in these granites, both magnetite and hematite are present. Hematite subdivides magnetite grains into small grains. Magnetite and hematite are found to be primary, and formed at the early magmatic evolution of the granite at very high oxygen fugacity. Massive degassing of these oxidized magmas would reduce the sink for oxygen, and consequently contribute to its rise in the atmosphere with a net O2 flux of at least 2.25 x 107 Tmol. Our conceptual model provides a deep Earth link to the NOE and implies the oxygenation burst has occurred earlier than previously envisaged, paving the way for later changes in the outer envelopes of the planet epitomized on the extreme Neoproterozoic glaciations and the appearance of the first animals.

  2. Newly Discovered Exposures of Neoproterozoic Diamictite within the Samre Fold-Thrust Belt of Northern Ethiopia

    Science.gov (United States)

    Park, Y.; Anttila, E.; MacLennan, S. A.; Swanson-Hysell, N.; Maloof, A. C.; Schoene, B.; Haileab, B.

    2015-12-01

    Life and climate evolved dramatically during the early Neoproterozoic - sedimentary rocks from this period record both the diversification of eukaryotic life as well as large scale fluctuations of the carbon cycle and paleogeography during the lead up to Cryogenian glaciation. Understanding global change leading up to this glaciation is critical for interpreting the conditions that initiated dramatic climate and geochemical oscillations. The Tonian-Cryogenian Tambien Group (Tigray region, northern Ethiopia) is a mixed carbonate-siliciclastic sedimentary succession deposited in an arc proximal basin that culminates in the Negash diamictite interpreted to represent the ca. 717-662 Ma Sturtian Glaciation. The presence of intercalated tuffs suitable for high precision U-Pb geochronology makes these sedimentary rocks an ideal target to temporally constrain physical and isotopic stratigraphic data sets of the early Neoproterozoic. The lower Tambien Group has been temporally constrained and used to establish global synchroneity of large scale carbon isotopic change ca. 800 Ma (Swanson-Hysell et al., 2015). We report the discovery of extensive exposures of upper Tambien Group successions southeast of the town of Samre within a newly mapped fold-thrust belt. Stratigraphic study across these exposures opens an opportunity to document environmental change across the basin during the apparently conformable transition from a mixed carbonate-siliciclastic platform into the Negash diamictite of the Sturtian Glaciation. The presence of ashes within the sediments holds the promise of combining high-precision dates with chemostratigraphic data to constrain global change before and during the onset of Snowball Earth glaciation.

  3. Modelling the carbon cycle though Neoproterozoic Earth system changes

    Science.gov (United States)

    Bjerrum, C. J.; Canfield, D. E.

    2011-12-01

    The Neoproterozoic-Cambrian records major changes in geochemical proxies as a result of a profound reorganization of the Earth system. Extensive glaciations and the first oxygenation of the deep ocean with a shift from sulfidic/ferruginous conditions to more oxic conditions was accompanied by the radiation of the first animals. The reorganization was also recorded in enigmatic large-amplitude fluctuations in the isotopic composition of marine carbonate carbon (δ13CIC ), were only some are associated with major known glaciations. The carbon isotope events seem to grow in amplitude through the Neoproterozoic culminating in the Shuram anomaly - the largest in Earth history. The δ13CIC events are also accompanied by changes in the isotope composition of marine organic carbon (δ13COC), where the co-variation of δ13CIC and δ13COC seems to evolve from markedly positive relationship over a subdued δ13COC variation and an almost inverse pattern. There is limited understanding as to why or how the structure of these isotope events evolved over time and how these events may tie to the reorganization of the Earth system. We use our published quantitative model of the Shuram anomaly to explore carbon cycle dynamics during the Neoproterozoic. By changing in pre-event atmosphere-ocean chemistry we explore which factors contribute to the observed patterns of the large Neoproterozoic carbon isotope events. In particular, decreasing atmospheric CO2 and a slight increase of oxygen together with an increasing CO source from rising DOC concentrations results in progressively larger event amplitudes with changing co-variation between δ13CIC and δ13COC , culminating with the structure observed for the Shurum-Wonaka anomaly in the Ediacaran. In our model, the carbon isotope excursions were driven by methane from sediment-hosted clathrate hydrate deposits. Being a powerful greenhouse gas, methane increased temperature and melted icecaps. These combined to produce a negative 18O

  4. Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico

    Science.gov (United States)

    Gross, E.L.; Stewart, John H.; Gehreis, G.E.

    2000-01-01

    Eighty-five detrital zircon grains from Mesoproterozoic and/or Neoproterozoic to Middle Cambrian sedimentary strata in northwest Sonora, Mexico, have been analyzed to determine source terranes and provide limiting depositional ages of the units. The zircon suites from the Mesoproterozoic and/or Neoproterozoic El Alamo Formation and El Aguila unit yield ages between 1.06 Ga and 2.67 Ga, with predominant ages of 1.1 to 1.2 Ga. Zircons from the Lower? and Middle Cambrian Bolsa Quartzite show age groups from 525 Ma to 1.63 Ga, with a dominant population of 1.1 to 1.2 Ga grains. Grains older than 1.2 Ga in the samples were most likely derived from basement terranes and ???1.4 Ga granitic bodies of the southwest U.S. and northwest Mexico. It is also possible that the sediments were transported from the south, although source rocks of the appropriate age are not presently exposed south of the study area in northern Mexico. Three possibilities for the dominant 1.1 to 1.2 Ga grains include derivation from: (I) exposures of the Grenville belt in southern North America, (2) local 1.1-1.2 Ga granite bodies, or (3) a southern source, such as the Oaxaca terrane, that was subsequently rifted away. Sampling of additional units in the western U.S. and northern Mexico may help resolve the ambiguity surrounding the source of the 1.1 to 1.2 Ga grains.

  5. Mesoproterozoic Neoproterozoic transition: Geochemistry, provenance and tectonic setting of clastic sedimentary rocks on the SE margin of the Yangtze Block, South China

    Science.gov (United States)

    Deru, Xu; Xuexiang, Gu; Pengchun, Li; Guanghao, Chen; Bin, Xia; Bachlinski, Robert; Zhuanli, He; Gonggu, Fu

    2007-03-01

    The SE margin of the Yangtze Block, South China is composed of the Mesoproterozoic Lengjiaxi Group and the Neoproterozoic Banxi Group, with Sinian- and post-Sinian-cover. A geochemical study was undertaken on the Mesoproterozoic-Neoproterozoic clastic sediments in order to delineate the characteristics of the sediment source and to constrain the tectonic development and crustal evolution of South China. Our results show that the Mesoproterozoic clastic sediments have a dominant component derived from a metavolcanic-plutonic terrane, with a large of mafic component. There is a minor contribution of mafic rocks and older upper crustal rocks to the provenance. Strong chemical weathering in the source area occurred before transport and deposition. The provenance for the Neoproterozoic clastic sediments was most likely old upper continental crust composed of tonalite-granodiorite-dominated, tonalite-granodiorite-granite source rocks, which had undergone strong weathering and/or recycling. A minor component of older K-rich granitic plutonic rocks and younger volcanogenic bimodal rocks is also indicated. Based on the regional geology, the geochemical data and the inferred provenance, the Mesoproterozoic Group is interpreted as a successive sedimentary sequence, deposited in an extensional/rifting back-arc basin, adjacent to a >1.80 Ga continental margin arc-terrane. The progressive extension/rifting of the back-arc basin was followed by increasing subsidence and regional uplift during continental marginal arc-continent (the Cathaysian Block) collision at ˜1.0 Ga caused the deposition of the Neoproterozoic Group into back-arc to retro-arc foreland basin. Therefore, the depositional setting of the Proterozoic clastic sediments and associated volcanic rocks within the back-arc basin reflected basin development from an active continental margin (back-arc basin), with extension or rifting of the back-arc basin, to a passive continental margin.

  6. The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling

    Science.gov (United States)

    Och, Lawrence M.; Shields-Zhou, Graham A.

    2012-01-01

    The oxygen content of the Earth's surface environment is thought to have increased in two broad steps: the Great Oxygenation Event (GOE) around the Archean-Proterozoic boundary and the Neoproterozoic Oxygenation Event (NOE), during which oxygen possibly accumulated to the levels required to support animal life and ventilate the deep oceans. Although the concept of the GOE is widely accepted, the NOE is less well constrained and its timing and extent remain the subjects of debate. We review available evidence for the NOE against the background of major climatic perturbations, tectonic upheaval related to the break-up of the supercontinent Rodinia and reassembly into Gondwana, and, most importantly, major biological innovations exemplified by the Ediacarian Biota and the Cambrian 'Explosion'. Geochemical lines of evidence for the NOE include perturbations to the biogeochemical cycling of carbon. Generally high δ 13C values are possibly indicative of increased organic carbon burial and the release of oxidative power to the Earth's surface environment after c. 800 Ma. A demonstrably global and primary record of extremely negative δ 13C values after about 580 Ma strongly suggests the oxidation of a large dissolved organic carbon pool (DOC), the culmination of which around c. 550 Ma coincided with an abrupt diversification of Ediacaran macrobiota. Increasing 87Sr/ 86Sr ratios toward the Neoproterozoic-Cambrian transition indicates enhanced continental weathering which may have fuelled higher organic production and burial during the later Neoproterozoic. Evidence for enhanced oxidative recycling is given by the increase in sulfur isotope fractionation between sulfide and sulfate, exceeding the range usually attained by sulfate reduction alone, reflecting an increasing importance of the oxidative part in the sulfur cycle. S/C ratios attained a maximum during the Precambrian-Cambrian transition, further indicating higher sulfate concentrations in the ocean and a

  7. Chemostratigraphy of early Neoproterozoic sedimentary rocks of Yenisei ridge (Siberia, Russia)

    Science.gov (United States)

    Vishnevskaya, Irina; Pisareva, Natalia; Kanygina, Nadejda; Proshenkin, Artem

    2014-05-01

    One of the biggest Proterozoic sedimentary basins in Russia is around the Siberian platform. This study about little part of them - Neoproterozoic sedimentary rocks of Yenisei ridge (Southwestern margin of Siberian Platform). Thise geological structure is ancient and very difficult for reaserch. It is a collage of different blocks: volcanic arcks, ophiolite complexes and sedimentary rocks of various ages and degrees of metamorphism. Sedimentary complexes of Siberian platform are outcropping along Angara River and its tributary. Neoproterozoic ones are presented by terrigenous-carbonate rocks of Tungusik and Oslyan groups. Despite the long study history of the area is still controversial question of time of formation of these rocks. As determination of the age of Precambrian sedimentary rocks is very difficult, Sr isotopic chemostratigraphy appears to be the only approach to establish the age of carbonate sequences. All Rb-Sr author's data was investigated by the method of selective dissolution with the preliminary removal of epigenetic carbonate phases. The isotope dilution method with mixed 87Rb + 84Sr spike was used to determine Rb and Sr concentrations in both fractions on the MI 1201AT mass spectrometer. Sr isotope ratios were measured on the Finnigan MAT-262 (BAC CU, Irkutsk, Russia) and Triton Plus (IGG UB RAS, Ekaterinburg, Russia). The C-O isotopic composition in carbon samples was measured on the Finnigan MAT-253 equipment. The main criteria for integrity were correlations of impurity-elements (Mn, Fe, Sr) and stable isotopes (C, O) with each other. The less altered rocks of the Tungusik Group are characterized by 87Sr/86Sr ratio of 0.7055-0.7058, and wide variations in the δ13CPDB values from 0 to +5o [1]. The primary 87Sr/86Sr of Dashka Formation (Oslyan Group) is 0.7057 - 0.7060 and δ13CPDB value varies in interval 3.7-4.3o like in upper part of Tungusik Group. High positive values of δ13CPDB indicate that carbonates had accumulated in warm sea

  8. Towards a quantitative understanding of the late Neoproterozoic carbon cycle

    DEFF Research Database (Denmark)

    Bjerrum, Christian J.; Canfield, Donald Eugene

    2011-01-01

    The cycles of carbon and oxygen at the Earth surface are intimately linked, where the burial of organic carbon into sediments represents a source of oxygen to the surface environment. This coupling is typically quantified through the isotope records of organic and inorganic carbon. Yet, the late...... Neoproterozoic Eon, the time when animals first evolved, experienced wild isotope fluctuations which do not conform to our normal understanding of the carbon cycle and carbon-oxygen coupling. We interpret these fluctuations with a new carbon cycle model and demonstrate that all of the main features of the...... carbonate and organic carbon isotope record can be explained by the release of methane hydrates from an anoxic dissolved organic carbon-rich ocean into an atmosphere containing oxygen levels considerably less than today....

  9. 华南西部新元古代中期沉积盆地性质及其动力学分析——来自桂北丹洲群的沉积学制约%An Analysis on Property and Dynamics of the Middle Neoproterozoic Sedimentary Basin in the Western of South China: Constraint from the Sedimentary Data of Danzhou Group in Northern Guangxi

    Institute of Scientific and Technical Information of China (English)

    杨菲; 汪正江; 王剑; 杜秋定; 邓奇; 伍浩; 周小琳

    2012-01-01

    在桂北,新元古代丹洲群出露在九万大山至越城岭一带,为一套角度不整合在中—新元古界四堡群变质岩系之上,整合于南华冰期沉积之下的浅变质/未变质沉积岩夹火山岩组合.本文通过对罗城黄金丹洲群剖面的沉积相及沉积序列研究表明:白竹组至合桐组为冲洪积相(移地滨岸相)、三角洲相、浅海陆棚相、碳酸盐缓坡(台地)、深水陆棚相(或欠补偿盆地相)等沉积组合,拱洞组为深水浊积岩、浅海陆棚相沉积组合,晚期为滨浅海相或三角洲相组合.综合剖面沉积相、沉积层序以及其中多幕式的火山—岩浆活动等沉积记录分析,作者认为与新元古代新生沉积盆地开启相伴的双模式的、同期的、一系列大火成岩省的形成,沉积盆地早期的海侵上超和饥饿沉积,晚期差异沉降和快速充填,以及与盆地演化阶段相伴的幕式火山岩浆活动等一系列事实与弧陆碰撞模式是相矛盾的,丹洲群及其相当层位地层应为裂谷盆地充填序列,其盆地演化的阶段性可能是地幔柱幕式活动的沉积响应.%The mid-Neoproterozoic Danzhou Group outcropped across the Jiuwandashan Mountains and the Yuecheng Mountains in Northern Guangxi. The Danzhou Group, which consisted of low metamorphic or normal sedimentation inter-bedded with igneous rocks, overlay the Metamorphite series of the Sibao Group with unconformity; and underlay the Nanhua glacial deposition with conformity. Writers characterized the sedimentary facies and depositional sequences of the Danzhou Group at the Huangjin section, Luocheng County, northern Guangxi, From the bottom to the top, the Baizhu Formation and Hetong Formation were composed of five kinds of facies, alluvial—fluvial facies (immigrating beach facies) , delta facies, shallow shelf facies, carbonate ramp (or platform) , deep shelf facies (or starved basin facies) ,respectively. The Gongdong Formation contained deep water

  10. Gammaspectrometry identification covering Neoproterozoic supracrustal sequences in the Serido Belt , northeastern Brazil

    International Nuclear Information System (INIS)

    Aerial gamma-ray survey data covering Neoproterozoic supracrustal sequences in the Serido Belt were processed and analyzed together with ground gamma-ray data, air photos and geological data for lithogeophysical characterization and mapping of granitic rocks, related pegmatites fields and lithological units of Serido Group. Interpretation was based on individual and ternary images of the three radio-elements and the eU/eTh and eTh/K ratios, and allowed the discovery of thorium anomalies associated with coarse-grained metarenites and metaconglomerates facies intercalated with quartzites of the Equador Formation. High contents of iron oxides, ilmenite, monazite, rutile, titanite and zircon were identified by ore microscopy of polished sections in the metaconglomerate's matrix. Semiquantitative scanning electron microscopy (SEM) analyses in minerals of two samples revealed up to 79.4% of Th02 and 87.7% of REE in monazites; up to 99.2% of Ti02 in ilmenite and rutile and up to 1.81 % of HfO2 in zircon. Gamma-ray anomalies due to thorium were also identified in association with sediments of Cenozoic age in the region. (author)

  11. Position of South China in configuration of Neoproterozoic supercontinent

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yongfei

    2004-01-01

    @@ Configuration and evolution of Neoproterozoic supercontinent and the position of South China within it have been very important targets in earth sciences concerningmany forefront topics of general interest. In the commonreconstruction of the supercontinent Rodinia, South Chinawas located between Australia and Laurentia, and thus liesin the center of the supercontinent and southeast of Aus-tralia[1]. According to the new paleomagnetic and geo-chronological data for the ~800 Ma Xiaofeng dyke in Yichang as well as existing data, Li et al.[2] suggest that Rodinia would probably spread from the equator to the polar region at about 800 Ma, followed by a rapid ca. 90( rotation around an axis near Greenland that brought the entire supercontinent to a low-latitude position by ca. 750 Ma. As a result, South China is reinterpreted to be placed adjacent to both Australia and India, with a rapid shift of rotation from a position northeast of Australia and southeast of India at about 800 Ma (Fig. 1(a)) to a position northwest of Australia and northeast of India at about 750 Ma (Fig. 1(b)).

  12. Neoproterozoic cap-dolostone deposition in stratified glacial meltwater plume

    Science.gov (United States)

    Liu, Chao; Wang, Zhengrong; Raub, Timothy D.; Macdonald, Francis A.; Evans, David A. D.

    2014-10-01

    Neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of Snowball Earth. Interpretation of these features has remained contentious, with hypotheses hinging upon timescale and synchronicity of deposition, and whether or not geochemical signatures of cap carbonates represent those of a well-mixed ocean. Here we present new high-resolution Sr and Mg isotope results from basal Ediacaran cap dolostones in South Australia and Mongolia. Least-altered Sr and Mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis. These data can be explained by the formation of these cap dolostones involving two chemically distinct solutions, a glacial meltwater plume enriched in radiogenic Sr, and a saline ocean residue with relatively lower 87Sr/86Sr ratios. Model simulations suggest that these water bodies remained dynamically stratified during part of cap-dolostone deposition, most likely lasting for ∼8 thousand years. Our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints. Geochemical data from cap carbonates used to interpret the nature of Snowball Earth and its aftermath should be recast in terms of a chemically distinct meltwater plume.

  13. Polyphase Neoproterozoic orogenesis within the east Africa- Antarctica orogenic belt in central and northern Madagascar

    Science.gov (United States)

    Key, R.M.; Pitfield, P.E.J.; Thomas, Ronald J.; Goodenough, K.M.; Waele, D.; Schofield, D.I.; Bauer, W.; Horstwood, M.S.A.; Styles, M.T.; Conrad, J.; Encarnacion, J.; Lidke, D.J.; O'connor, E. A.; Potter, C.; Smith, R.A.; Walsh, G.J.; Ralison, A.V.; Randriamananjara, T.; Rafahatelo, J.-M.; Rabarimanana, M.

    2011-01-01

    Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid- Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana. ?? The Geological Society of London 2011.

  14. Micropaleontology and chemostratigraphy of the Neoproterozoic Mbuji-Mayi Supergroup, Democratic Republic of Congo.

    Science.gov (United States)

    Baludikay, Blaise; Bekker, Andrey; Baudet, Daniel; Asael, Dan; Storme, Jean-Yves; Javaux, Emmanuelle

    2014-05-01

    The Mbuji-Mayi Supergroup, deposited between 1170 ± 22 Ma and ca. 800 Ma [1], outcrops in the eastern Oriental Kasai Province and western Katanga Province of the Democratic Republic of Congo. It is the youngest Precambrian unit of the Kasai block and was deposited in the SE-NW trending failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy basin filled with siliciclastic and carbonate sediments. In the northern part of this basin (Oriental Kasai Province), the Mbuji-Mayi Supergroup rests unconformably upon the Archean Dibaya Granite Complex, but in the southern part (northeastern Katanga Province), it overlies the Mesoproterozoic Kibaran Supergroup. The Supergroup is divided into two groups: the lower, ~ 500-m thick siliciclastics-rich BI Group and the upper, ~ 1000-m thick carbonate-rich BII Group. Our own and previous sedimentological observations [2] indicate facies ranging from subtidal, low-energy stromatolitic environments to overlying intertidal to supratidal evaporitic settings of lagoon and sabkha. In order to characterize the diversity of microfossil assemblages, their paleobiology and paleoecology as well as redox conditions in their depositional setting, we have sampled three drill cores (KAFUKU 15, B13 KANSHI, and S70 LUBI) from the collections of the Royal Museum for Central Africa (RMAC). Our biostratigraphic and chemostratigraphic data also provide further constraints on the age of the Mbuji-Mayi Supergroup. Here we present preliminary data on microfossil diversity from the Kanshi drill core and carbon isotope chemostratigraphy for all three drill cores. The well-preserved and diverse assemblage of acritarchs and filamentous forms includes prokaryotes and eukaryotes, and is similar to other coeval assemblages described worldwide outside of Africa. The presence of the acanthomorph acritarch Trachyhystrichosphaera aimika is significant as it is indicative of the late Meso- to early Neoproterozoic age elsewhere, and is reported for the first time in Central

  15. Geochronology of middle Neoproterozoic volcanic deposits in Yangtze Craton interior of South China and its implications to tectonic settings

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Here we report new SHRIMP dating results of the crystal tuff in Ejiaao Formation of middle Banxi Group in northern Guizhou. The results indicate that the volcanic deposition occurred at ~780 Ma. We also suggests that the igneous activities across Yangtze Craton with diabase dyke swarms and basal volcanic rocks during middle Banxi time are indicative of the episodic, extensive and vigorous great bimodal igneous events during middle Neoproterozoic (825-720 Ma) in South China. The characteristics of the igneous series are contrary to the model claiming they are of island-arc origin, but suggest that they are the records of rifting process and may be related to the episodic plume activities leading to the break-up of Rodinia.

  16. Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

    Science.gov (United States)

    Lenton, Timothy M.; Watson, Andrew J.

    2004-03-01

    It has been suggested that biological colonization of the land surface began in the Neoproterozoic 1000-544 million years ago (Ma). We hypothesize that this colonization involved selective weathering of P from rocks, as well as an amplification of overall weathering rates. We show that two recent models, despite differences in the feedback mechanisms represented, predict that an increase in the weathering flux of P to the ocean would have caused a rise in atmospheric O2 in the Neoproterozoic. This in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the 'Cambrian explosion'. Increased weathering of silicate rocks would also have caused a decline in atmospheric CO2, which could have been a causal factor in the Neoproterozoic glaciations.

  17. Relationship between the Neoproterozoic snowball Earth and Cambrian explosion

    Science.gov (United States)

    Maruyama, S.; Yoshihara, A.; Isozaki, Y.

    2007-12-01

    Origin of snowball Earth has been debated in terms of greenhouse gas (e.g., Hoffman and Schrag), obliqueness of Earth's rotation axis (Williams, 1975), true polar wander (Evans, 2003), Galactic cosmic ray radiation (Shaviv and Veizer, 2003; Svensmark, 2006), or weakened geomagnetism (Maruyama and Yoshihara, 2003). A major difficulty for the greenhouse gas hypothesis is the on-off switch causing decrease and increase of appropriate amounts of CO2 by plume- and plate tectonics, and also in available amount of CO2 in atmosphere to be consistent with the observations. In contrast, the cosmic ray radiation models due to the star burst peaked at 2.5- 2.1 Ga and 1.4-0.8 Ga can explain on-off switch more easily than the greenhouse gas model. Cosmic ray radiations, however, must be modified by the geomagnetic intensity, fluctuating 150"% to cause the snowball Earth. Time difference between the Neoproterozoic snowball Earth and Cambrian explosion is as large as 250 millions years, and this refuses their direct close-relationship. Role of frequent mass extinctions, i.e., 8 times during 100 m.y. from 585 Ma to 488 Ma, during the Ediacaran and Cambrian, has been proposed (Zhu et al., 2007). This frequency is one order of magnitude higher compared to that in the post-Ordovician time. Yet, the Cambrian explosion cannot be explained by mass extinction which replaced the vacant niches shortly after the mass extinction and never created a new animal with a new body plan. A new model proposed herein is derived from weakened geomagnetism and resultant extensive cosmic radiation to alter gene and genome for a long period over advancement of low magnetic intensity and cosmic radiations (Svensmark, 2006) from 1.2-0.8Ga. As to the new body plans of animals, it took an appreciably long time to prepare all 34 genometypes before the apparent Cambrian explosion. Geochemically extreme conditions and widened shallow marine environment on continental shelf by the return-flow of sweater into

  18. Geochronological constraints on terminal Neoproterozoic events and the rise of Metazoan

    Science.gov (United States)

    Bowring, S.; Myrow, P.; Landing, E.; Ramezani, J.; Grotzinger, J.

    2003-04-01

    A full understanding of Neoproterozoic history has been plagued by a lack of precise geochronological constraints. In particular the correlation and duration of global or "Snowball" glaciations has relied on physical stratigraphy and chemostratigraphy which has given rise to much debate about the number, magnitude, and duration of glacial deposits. New U-Pb constraints on the age of the Gaskiers Formation glacial deposits in Newfoundland, an age for the oldest Ediacaran fossils in the same area, and the age and significance of the Cambrian/Precambrian boundary in Oman have important implications for global correlation and the timing of the rise of Metazoans. In the central and eastern parts of the Avalon Peninsula, southeastern Newfoundland, the oldest rocks are arc-related tuffs, agglomerates, and flows of the Harbour Main Group (>1.5 km thick) that have published dates from 606-630 Ma. These are overlain by approximately 7.5 km of marine siliciclastic rocks of the Conception Group. Over 2,300 m of deep-water deposits of the Mall Bay and Drook formations are separated by the regionally extensive glacial diamictite of the Gaskiers Formation (up to 300 m-thick). This unit is often described as a Varanger-age glaciomarine deposit and is locally overlain by a thin cap carbonate bed with a highly negative C isotopic signature. Thin (1-15 cm) silicic ash beds are found interlayered with turbidites just below and above the glacial deposits and the glacial deposits locally contain volcanic bombs, pyroclastic debris, and lavas. U-Pb geochronology of zircons separated from ash-beds below, within, and above the glacial deposits indicates that they are ca 580 Ma. This is considerably younger than previous estimates and calls into question many of the global correlations with similar rocks. An ash-bed within the overlying Drook formation is preserved in depositional contact with spectacular surfaces exposing Ediacaran fossils. Zircons separated from it yield an age of 575 Ma

  19. Geochemical Signatures of Neoproterozoic Granites and Granitoid-gneisses from Angavo Belt, Central Madagascar

    Science.gov (United States)

    Raharimahefa, T.

    2015-12-01

    The basement rocks of Madagascar record high-grade metamorphism, magmatism, and contractional and extensional structures that accompanied the collision of the eastern and western Gondwana segments of the supercontinent followed by its collapse. In the eastern central Madagascar, granitoids dominate the landscape and occur in a large area near and within the N-S trending highly strained zone known as the Angavo Shear Zone or Angavo belt. The area is a key in understanding the evolution of basement of Madagascar and the reconstruction of the Gondwana supercontinent. These granitoids range from layered to massive and previously published U-Pb zircon dating yielded three distinctive Neoproterozoic magmatisms at 770 Ma to 820 Ma, ca. 660Ma, and ca 550Ma. However, it was unknown whether these ages represent distinct magmatic pulses or reflect a continuous granitoid emplacement. This work contributes to the knowledge of the Malagasy basement rocks and to explore and discuss the origin and petrotectonic evolution of the granites and granitoid-gneisses from this part of the Madagascar. The rock samples are placed into three groups: group A and B for granitoid-gneisses and a third group for the granite layers. Group A and B are metaluminous and slightly peraluminous, respectively. All rocks have typical subduction zone calc-alkaline signatures. Group A is characterized by enrichment in large ion lithophile elements (LILE) but low U, LREE enrichment, depletion in the high field strength elements (HFSE). In contrast, Group B has REE patterns closely similar to Archean sediments. The granite layers show fractionated REE patterns in which HREE patterns show strong correlation with Zr abundances. Trends in major element variation diagrams and the enrichment of incompatible elements could be explained by simple fractional crystallization, while the overall geochemical signatures reflect either (1) melting of ancient crust or (2) crustal contamination of a more evolved magmas that

  20. Geochronological Constraints on Neoproterozoic Glaciations, the first appearance of Metazoans, and the Cambrian Explosion.

    Science.gov (United States)

    Bowring, S.; Condon, D.; Ramezani, J.; Myrow, P.; Landing, E.

    2004-05-01

    Studies of Neoproterozoic climate fluctuations, plate reconstructions, biological evolution and their interrelationships have been hindered by a lack of high-precision geochronological constraints. The correlation and estimates of duration for Neoproterozoic glaciations has relied on physical/chemo-stratigraphy, and thermal subsidence models respectively. New geochronological constraints from Neoproterozoic successions worldwide have sharpened the debate as to the number, synchroneity, and duration of glacial episodes and the relationship, if any, between Metazoan evolution and global glaciation(s). Crucial to the debate are correct interpretation of geochronological data that range from U-Pb zircon studies of intercalated volcanic ash-beds, U-Pb detrital zircon studies, Re-Os from black shales, Rb-Sr from clay-rich rocks, U-Pb and Pb-Pb from carbonates and phosphates, and Lu-Hf from phosphates. Development of a highly resolved Neoproterozoic timescale will require integration and cross-calibration of multiple dating techniques and consideration of what is actually being recorded by each chronometer. A review of available geological and geochronological data indicate that there were at least three and perhaps as many as five periods of Neoproterozoic glacial deposition including rocks from United States (Idaho and Virginia), Newfoundland and the Northwest Territories of Canada, Namibia, and Oman. What must be evaluated is how the paleogeographic distribution of glaciated regions varied with time during the Neoproterozoic. Do Neoproterozoic glacial successions distributed worldwide record a small number of globally synchronous, long-lived glaciations, or numerous diachronous glacial epochs, or a combination of both? At present, the duration of only one glacial deposit, the ca 581 Ma Gaskiers Formation (Newfoundland), is known and it is on the order of 1 Ma, at odds with a long-lived global glaciation predicted by the snowball Earth hypothesis. Other major issues are

  1. Continental flood basalt weathering as a trigger for Neoproterozoic Snowball Earth

    Science.gov (United States)

    Cox, Grant M.; Halverson, Galen P.; Stevenson, Ross K.; Vokaty, Michelle; Poirier, André; Kunzmann, Marcus; Li, Zheng-Xiang; Denyszyn, Steven W.; Strauss, Justin V.; Macdonald, Francis A.

    2016-07-01

    Atmospheric CO2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720-635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13 C) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early-middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth.

  2. Neoproterozoic active continental margin in the southeastern Yangtze Block of South China: Evidence from the ca. 830-810 Ma sedimentary strata

    Science.gov (United States)

    Wang, Wei; Zhou, Mei-Fu; Zhao, Jun-Hong; Pandit, Manoj K.; Zheng, Jian-Ping; Liu, Ze-Rui

    2016-08-01

    The Jiangnan Fold Belt in the South China Block has been traditionally assumed to be Mesoproterozoic in age and related to the global Grenville orogeny. Sedimentary successions in the Jiangnan Fold Belt archive direct record of tectonic evolution; however, they have not yet been evaluated properly. The Lushan massif, comprising Kangwanggu and Xingzi groups, is the major basement complex in the Jiangnan Belt. Regional correlation of these two groups is poorly constrained, such as with the Shuangqiaoshan group, and thus their role in the regional tectonic evolution is not clear. Detrital zircon U-Pb ages suggest that the Xingzi and Kangwanggu groups were deposited at 820-810 and ca. 830 Ma, respectively. They are composed of dominantly felsic to intermediate volcanic detritus, as indicated by the relatively high Th/Cr (0.24-0.06) ratios and radiogenic Nd isotopes (εNd(t) values = + 1.5 to - 2.9) of the sedimentary rocks. An overwhelming abundance of Neoproterozoic (ca. 860-810 Ma) angular, detrital zircon grains in both the groups indicates derivation chiefly from locally distributed syn-sedimentary igneous rocks. A predominance of zircons with ages close to the time of deposition implies a convergent plate margin setting for Kangwanggu and Xingzi groups. Geochemical signatures, such as La-Th-Co and Th-Sc-Zr/10 plots for Xingzi and Kangwanggu sedimentary rocks also underline tectonically active settings, consistent with the arc affinity of the associated mafic and felsic volcanic rocks. In contrast to the dominant Neoproterozoic detritus in the Kangwanggu sandstone, argillaceous rocks of the Xingzi group received additional input of pre-Neoproterozoic detritus. Moreover, the Xingzi argillaceous rocks have εNd(t) values (+ 0.9 to - 2.9) slightly lower than those of the Kangwanggu sandstones (+ 1.5 to 0.0), indicating contribution from mature crustal materials exposed during progressive uplift of continental basement during orogenesis. These features suggest the

  3. Geochemistry and petrogenesis of Neoproterozoic Mylliem granitoids, Meghalaya Plateau, northeastern India

    Indian Academy of Sciences (India)

    Jyotisankar Ray; Abhishek Saha; Sohini Ganguly; V Balaram; A Keshav Krishna; Sampa Hazra

    2011-06-01

    The Mylliem granitoids of the Meghalaya Plateau, northeastern India, represent one of the disharmonic Neoproterozoic igneous plutons, which are intrusive into low-grade Shillong Group of metasediments. Field studies indicate that the Mylliem granitoids cover an area of about 40 km2 and is characterized by development of variable attitude of primary foliations mostly marked along the margin of the pluton. Xenoliths of both Shillong Group of metasediments and mafic rocks have been found to occur within Mylliem granitoids. Structural study of the primary foliation is suggestive of funnel-shaped intrusion of Mylliem granitoids with no appreciable evidence of shearing. Petrographically, Mylliem granitoids are characterized by pink to white phenocrysts of prismatic microcline/perthite and lath-shaped plagioclase (An20–An29). Groundmass material is characterized by quartz, microcline, plagioclase, muscovite and biotite. Sphene and apatite occur as accessory minerals. Petrographically Mylliem granitoids have been discriminated as granite and granodiorite according to IUGS system of classification. Critical evaluation of geochemical data and variation trends of major oxides/trace elements suggests a significant role of fractional crystallization in the evolution of Mylliem pluton. Th/U ratios (3.22–6.77) indicate a relatively higher abundance of Th over U. Chondrite-normalized REE diagram characteristically shows an enriched LREE pattern and prominent negative Eu anomaly (Eu/Eu* = 0.16–0.42) indicating the significant role of plagioclase fractionation from the parent magma. An overall strong REE fractionation pattern has been envisaged for Mylliem granitoids. The strong REE fractionation of the Mylliem granitoids is depicted by (Ce/Yb) values, which show a range of 1.39 to 1.65. The aluminium saturation index (ASI) (ranging from 1.0 to 1.3), A/CNK ratios (ranging from 1.4 to 2.11) and A/NK ratios (ranging from 1.75 to 2.43) provide evidences for the peraluminous, S

  4. Geology of East Egypt greenstone field in Neoproterozoic isoand arc: Reconstruction of Iron formation sedimentary environment.

    Science.gov (United States)

    Kiyokawa, S.; Suzuki, T.

    2015-12-01

    Geology of East Egypt greenstone-granit belt which is northern part of Nubia shield was identified neoproterozoic island arc amalgamated sections. There are several iron formation within these greenstone belt. Age data shows this iron formation may be overlaped during 700 Ma Snowball period, how ever, there is no detail report of well preserved ice related evidences. We now started detail field work for identified tectonic reconstruction, original stratigraphy around Iron formation and sedimentary environment during the iron formation sedimentation area. East Egyptian shield was divided three geology, Proterozoic greenstone complex, 700-600 Granitic domes and cover sequence (Hammamet Group). We focus three area to identified sedimentary environment of iron sedimentation. Along the north-south trend of Wadi EL Dabban area are, we named Wadi branch as West site is RW-0 ~ 12, East site is RE-0 ~ 12 from north to south. Northern area is structurally moderate, southern portion is north dipping. Southern portion was intruded by granite and several place contain granitic dikes. Northeast to eastern area are identified younger sedimentary sequence (Hammamat Group) which is unconformablly overlay on the other iron formation bearing greenstone belt. Structurally these area is divided four units. Wadi was divided by right-lateral strike-ship fault. The displacement are more than 3 km. Also north dipping faults are identified.East-West trend fault are divided two units. It is divided NE, SE, NW and NS units.SW unit is most well preserved thick sequence of the Iron formation. SW unit is well preserved iron formation sequence within thick volcaniclastics. This unit mostly north dipping around 40-60 degree. Structural repetition in not well understand. Reconstract stratigraphy in this unit is at least 4000m in thickness. 5 member is identified in this sequence. Several thin iron formations are observed with in pillow lava and volcaniclastic sequence. These very thick

  5. Discussion on the Neoproterozoic glaciations in the South China Block and their related paleolatitudes

    Institute of Scientific and Technical Information of China (English)

    ZHANG QiRui; CHU XueLei; FENG LianJun

    2009-01-01

    The Kaigas, Sturtian, Marinoan, and Gaskiers glaciations are widely recognized in Neoproterozoic. However, in the South China Block only the Jiangkou (Sturtian) and Nantuo (Marinoan) are symbolized by sedimentary records. The Kaigas, recorded by isotopic and chemical proxies, exhibited likely the nature of cold paleoclimate with local mountain glaciation. The correlation of the Doushantuo Forma-tion with the Gaskiers is indicated by the carbon isotope excursion and the dated age from the interval, however the South China Block was then under non-glacial weather. With no paleomagnetic data, the position of the South China Block during the Sturtian glaciation cannot be determined. The paleolati-tudes of the South China Block during the Kaigas and Nantuo glaciations are intermediate, even though the Nantuo was once rendered erratically deduced equatorial. In fact, the paleolatitudes of the South China Block during the Neoproterozoic glaciations are all likely at about 30°-40°.

  6. Isotopic evidence for two neoproterozoic high-grade metamorphic events in the Brazilia belt

    International Nuclear Information System (INIS)

    The Brasilia Belt is part of a Brasiliano/Pan African orogen developed between the Amazon and Sao Francisco cratons. The stabilization of the belt occurred after the last metamorphic event at ca. 620 Ma. There has been increasing geochronological evidence, however, for an older Neoproterozoic metamorphic event at ca. 780 Ma, observed mainly in high grade rocks of three large mafic-ultramafic complexes in the northern part of the belt. In this study we present: (i) new U-Pb and Sm-Nd geochronological data, (ii) a review of the existing metamorphic ages in the Brasilia Belt, and (iii) a discussion on the tectonic model to explain the two Neoproterozoic metamorphic ages (au)

  7. Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era

    OpenAIRE

    Lenton, TM; Boyle, RA; Poulton, SW; Shields-Zhou, GA; Butterfield, NJ

    2014-01-01

    The Neoproterozoic era (about 1,000 to 542 million years ago) was a time of turbulent environmental change. Large fluctuations in the carbon cycle were associated with at least two severe-possible Snowball Earth-glaciations. There were also massive changes in the redox state of the oceans, culminating in the oxygenation of much of the deep oceans. Amid this environmental change, increasingly complex life forms evolved. The traditional view is that a rise in atmospheric oxygen concentrations l...

  8. The Neoproterozoic and Early Paleozoic Tectonic and Environmental Evolution of Alaska and Northwest Canada

    OpenAIRE

    Strauss, Justin Vincent

    2015-01-01

    Neoproterozoic and early Paleozoic sedimentary deposits of the North American Cordillera record large fluctuations in global biogeochemical cycles, the establishment and diversification of multiple eukaryotic clades, the fragmentation of the supercontinent Rodinia, and the protracted development and subsequent demise of the western and northern Laurentian passive margins. Here, I put forth new tectono-, bio-, and chemo-stratigraphic models for the ~780-540 Ma Windermere Supergroup of western ...

  9. Microstructures in Metasedimentary Rocks from the Neoproterozoic Bonahaven Formation, Scotland: Microconcretions, Impact Spherules, or Microfossils?

    OpenAIRE

    Anderson, Ross P.; Fairchild, Ian J.; Tosca, Nicholas J.; Knoll, Andrew Herbert

    2013-01-01

    Microscopic spherules in relatively undeformed mudstones of the Neoproterozoic Bonahaven Formation, Islay, Scotland, are differentiated from their matrix by a sharp micron-scale, smoothly rounded boundary. These elongate spherules were earlier interpreted as hollow bodies filled penecontemporaneously by glauconite and subsequently metamorphosed to phengite, but their origin remains a matter of debate. Spherules observed in thin section are predominantly rounded (∼74%) but can exhibit a flat e...

  10. Methane seeps, methane hydrate destabilization, and the late Neoproterozoic postglacial cap carbonates

    Institute of Scientific and Technical Information of China (English)

    JIANG Ganqing; SHI Xiaoying; ZHANG Shihong

    2006-01-01

    Methane hydrates constitute the largest pool of readily exchangeable carbon at the Earth's sedimentary carapace and may destabilize, in some cases catastrophically, during times of global-scale warming and/or sea level changes. Given the extreme cold during Neoproterozoic ice ages, the aftermath of such events is perhaps amongst the most likely intervals in Earth history to witness a methane hydrate destabilization event. The coincidence of localized but widespread methane seep-like structures and textures, methane-derived isotopic signal,low sulfate concentration, marine barites, and a prominent, short-lived carbon isotope excursion (δ13C≤-5‰) from the post-Marinoan cap carbonates (~635 Ma) provides strong evidence for a methane hydrate destabilization event during the late Neoproterozoic postglacial warming and transgression. Methane release from hydrates could cause a positive feedback to global warming and oxidation of methane could result in ocean anoxia and fluctuation of atmospheric oxygen, providing an environmental force for the early animal evolution in the latest Neoproterozoic. The issues that remain to be clarified for this event include the trigger of methane hydrate destabilization, the time of initial methane release, the predicted ocean anoxia event and its relationship with the biological innovation, additional geochemical signals in response to methane release, and the regional and global synchrony of cap carbonate precipitation. The Doushantuo cap carbonate in South China provides one of the best examples of its age for a better understanding of these issues.

  11. Molar tooth structures in calcareous nodules, early Neoproterozoic Burovaya Formation, Turukhansk region, Siberia

    Science.gov (United States)

    Pope, Michael C.; Bartley, Julie K.; Knoll, Andrew H.; Petrov, Peter Yu.

    2003-05-01

    Molar tooth structures are abundant in large (1-2 m diameter) carbonate nodules within fine-grained, subtidal carbonates of the early Neoproterozoic (lower Upper Riphean) Burovaya Formation along the Sukhaya Tunguska River, Turukhansk Uplift, northwestern Siberia. Although molar tooth structures are regionally abundant in this unit, here they occur only within the nodules. Stable isotopic compositions of molar-tooth-filling dolomicrospar cements and of thinly bedded dolomicrite within and surrounding the nodules are indistinguishable from one another. The carbon isotopic compositions (mean δ13C=+2.8‰ PDB±0.4) reflect mean average oceanic surface water composition during their formation; the light oxygen isotopic compositions (mean δ18O=-6.4‰ PDB±2.2) are generally similar to those of other little-altered Meso- to Neoproterozoic limestones and dolostones. These molar tooth structures have no features that would support a tectonic origin; they more likely formed through bacterial processes. Carbonate cement filling of these voids occurred soon after their formation, but the mechanism responsible for this carbonate precipitation is currently uncertain. Local restriction of molar tooth structures to early diagenetic nodules suggests that penecontemporaneous lithification was required for the formation, or at least preservation, of these widespread Mesoproterozoic to Neoproterozoic features.

  12. Neoproterozoic Land Colonisation, Rising Oxygen, Global Cooling and the Cambrian Explosion

    Science.gov (United States)

    Lenton, T. M.; Watson, A. J.

    2004-12-01

    The Neoproterozoic (1000-542 Ma BP) was a time of severe glaciations and a major transition from microscopic to macroscopic life forms. We develop the hypothesis that a rise in atmospheric oxygen in the Neoproterozoic was driven by the biological colonization of the land surface. If early forms of photosynthetic land life selectively weathered continental rock in order to extract nutrients, this would have led to an increase in the flux of biologically available phosphorus to the ocean. We show that recent models for coupled biogeochemical cycles, despite differences in the feedback mechanisms represented, predict this would lead to a rise in atmospheric oxygen concentration, consistent with biological and geochemical evidence. Increased weathering of silicate rocks would also have caused a decline in atmospheric carbon dioxide, which could have been a causal factor in the Neoproterozoic glaciations. A rise in oxygen may have provided a necessary condition for the evolution of animals with hard skeletons seen in the Cambrian explosion. Furthermore, an increase in phosphorus supply to the ocean may have driven an increase in the phosphorus content of marine primary producers. This would have represented an increase in food quality for grazing animals, which have a high phosphorus requirement, and may thus have removed a further limitation on their evolutionary radiation.

  13. Evaluation of the Re-Os Geochronometer in Organic-rich Mudrocks as a Method for Constraining the Absolute Ages of Neoproterozoic Glaciogenic Deposits

    Science.gov (United States)

    Kendall, B. S.; Creaser, R. A.; Ross, G. M.

    2002-12-01

    Absolute-age constraints on the Neoproterozoic glaciations are generally poor due to a paucity of suitable plutonic and volcanic igneous rocks that are temporally and spatially related to Neoproterozoic glaciogenic deposits and are amenable to radiometric dating methods. In this study, the Re-Os isotope systematics of dark gray, sulfidic slates from the Old Fort Point Formation (OFP) of the Windermere Supergroup (near Jasper, Alberta) were examined to test the ability of the Re-Os geochronometer to provide an absolute age constraint for a Neoproterozoic glaciogenic deposit. The OFP has been interpreted as the deep water expression of post-glacial sea level rise and therefore is comparable stratigraphically to cap carbonates that immediately overlie glaciogenic deposits worldwide. Despite the relatively low Re (6-16 ppb) and Os (0.07-0.14 ppb) concentrations and total organic contents (~ 0.5% TOC) of the slates compared to other organic-rich mudrocks used in previous Re-Os isotope studies, precise well-fitted Re-Os isochrons have been obtained with two different dissolution methods. An age of 620.8 +/- 8.1 Ma (MSWD = 0.9; initial 187Os/188Os = 0.68 +/- 0.06) is obtained using conventional aqua regia dissolution. Using a method designed to selectively dissolve organic matter alone, an age of 609.0 +/- 8.3 Ma (MSWD = 1.5; initial 187Os/188Os = 0.62 +/- 0.05) is obtained. These absolute age results are in accord with existing age constraints (e.g., stratigraphically younger Hamill Group with a U-Pb zircon age of 569 Ma). The well-defined Re-Os systematics of the OFP slates demonstrates for the first time that the Re-Os system is not disturbed in organic-rich sediments during lower greenschist (-chlorite) grade metamorphic conditions. The whole-rock analysis of each individual sample yields consistently higher initial 187Os/188Os isotope ratios than the corresponding organic matter analysis and suggests that a significant radiogenic detrital Os component is present

  14. Implications for the Neoproterozoic Biological and Climatic History from Dating of the Doushantuo Phosphorites, S. China

    Science.gov (United States)

    Barfod, G. H.; Albarede, F.; Knoll, A. H.; Xiao, S.; Frei, R.; Baker, J.

    2002-12-01

    Models such as "Snowball Earth" suggest a link between Neoproterozoic glaciation events and the animal diversifications that preceded the Cambrian explosion. To evaluate such hypotheses, it is critical to resolve the precise chronology of the Neoproterozoic. As of now, ages of many Neoproterozoic sedimentary successions are only weakly constrained by bio- and chemostratigraphical correlation to successions that contain dated ash layers. Furthermore, attempts to radiometrically date sedimentary successions have had limited success. Pb-Pb and Lu-Hf dating of phosphates yield consistent ages close to 600 Ma for the Doushantuo phosphorites, South China. These age constraints are consistent with a depositional age estimate of 580 Ma +/- 20 Ma based on C-isotopic and biostratigraphic correlations (Knoll and Xiao, 1999, Acta Micropalaeontol. 16). The dates are however significantly younger than earlier reported Rb-Sr and Sm-Nd ages (610-700 Ma) for the Doushantuo sediments, which have been ascribed to the influence from detrital clay on the measured isotope compositions. The Lu-Hf and Pb-Pb ages indicate that the exquisitely preserved animal remains found in the Doushantuo Formation predate diverse Ediacaran fossil assemblages and thus represent the earliest animal ancestry assemblage known. The Doushantuo formation lies directly above the Nantuo Tillite deposits, which is generally correlated with the "Marinoan" glaciation - the younger of the two major Neoproterozoic ice ages. Age constraints for "Marinoan" glaciogenic deposits only exist in Newfoundland and Massachusetts, where radiometric dating constrain the glaciation to be younger than 595.5 +/- 2 Ma. Compared to this date, the Pb-Pb age of 599.3 +/- 4.2 Ma for the Doushantuo phosphorites indicates that the Nantuo glaciation predates the glaciation recorded in Eastern North America and therefore support the occurrence of a distinct post-Marinoan glaciation. The combination of Pb-Pb and Lu-Hf dating applied to

  15. The Neoproterozoic Drift History of Laurentia: a Critical Evaluation and new Palaeomagnetic Data from Northern and Eastern Greenland

    DEFF Research Database (Denmark)

    Christiansen, Jørgen Løye

    2008-01-01

    tillite yield a stable magnetization that passes fold and reversal tests and places this margin of Laurentia at a high palaeolatitude (~70°) during deposition &150; this result is being confirmed by analysis of a second suite of samples collected in 2007. Interestingly, this would suggest that late...... available poles. We present new palaeomagnetic data from the Neoproterozoic sucessions of northern and eastern Greenland that confirm that Laurentia drifted into high latitudes during the late Neoproterozoic. Detailed investigation of the uppermost Eleonore Bay Supergroup (Sturtian?), yields a stable...... Neoproterozoic glaciations encompassed a broad range of latitudes, but means that required palaeogeography for an ice-albedo catastrophe did not exist. Finally, six sites from the uppermost Precambrian units yield a stable magnetization that passes a fold and reversal test and place this part of the Laurentian...

  16. Constraining the margins of Neoproterozoic ice masses: depositional signature, palaeoflow and glaciodynamics

    Science.gov (United States)

    Busfield, Marie; Le Heron, Daniel

    2016-04-01

    The scale and distribution of Neoproterozoic ice masses remains poorly understood. The classic Snowball Earth hypothesis argues for globally extensive ice sheets, separated by small ocean refugia, yet the positions of palaeo-ice sheet margins and the extent of these open water regions are unknown. Abundant evidence worldwide for multiple cycles of ice advance and recession is suggestive of much more dynamic mass balance changes than previously predicted. Sedimentological analysis enables an understanding of the changing ice margin position to be gained through time, in some cases allowing it to be mapped. Where the maximum extent of ice advance varies within a given study area, predictions can also be made on the morphology of the ice margin, and the underlying controls on this morphology e.g. basin configuration. This can be illustrated using examples from the Neoproterozoic Kingston Peak Formation in the Death Valley region of western USA. Throughout the Sperry Wash, northern Kingston Range and southern Kingston Range study sites the successions show evidence of multiple cycles of ice advance and retreat, but the extent of maximum ice advance is extremely variable, reaching ice-contact conditions at Sperry Wash but only ice-proximal settings in the most distal southern Kingston Range. The overall advance is also much more pronounced at Sperry Wash, from ice-distal to ice-contact settings, as compared to ice-distal to ice-proximal settings in the southern Kingston Range. Therefore, the position of the ice margin can be located at the Sperry Wash study site, where the more pronounced progradation is used to argue for topographically constrained ice, feeding the unconstrained shelf through the northern into the southern Kingston Range. This raises the question as to whether Neoproterozoic ice masses could be defined as topographically constrained ice caps, or larger ice sheets feeding topographically constrained outlet glaciers.

  17. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic

    Science.gov (United States)

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li

    2016-06-01

    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and carbonatite reveal rift-related extensional tectonic settings with magma sources involving both mantle and crustal components during Paleoproterozoic. The late Neoproterozoic shoshonitic adakite-like syenite from KAC also formed in a rift-related setting. In both cases, intracontinental rifting associated with post-collisional extension is proposed.

  18. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    Science.gov (United States)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  19. Molecular Fossils for Understanding Biodiversity During the Neoproterozoic-Cambrian Transition in China

    Science.gov (United States)

    Pi, Y.; Tuo, J.; McFadden, K.; Xiao, S.; Zhang, C. L.

    2005-12-01

    Neoproterozoic-Cambrian rocks in South China contain an extraordinary fossil record, including exceptionally well preserved animal embryos, acritarchs, and multi-cellular algae. The goal of this study was to evaluate the microbial diversity associated with these remarkably preserved fossil assemblages at the Neoproterozoic-Cambrian transition. Rock samples of 520-632 Ma in age were collected in the Yangtze Gorges area and southern Anhui Province, China. Samples were powdered and extracted for organic biomarkers. The content of bitumen A accounted for 4-16% of the rock material and most of it (49-79%) was asphaltenes. Saturated and aromatic hydrocarbons accounted for 2-6% and 1-3%, respectively. Analysis using GC-MS indicated the predominance of n-alkanes and less abundant isoprenoid alkanes in the saturated fractions. The n-alkanes were characterized by homologues dominated by C15-C17, which is consistent with the result of high thermal-evolution (Brocks et al., 2003. GCA 67:4321-4335). Hopanoids were present in less abundance and ranged from C29 to C32. A smaller amount of heavy-molecular-weight n-alkanes (C23-C39) was also detected, which indicated a source of high plants and must be contamination from younger organic matter. Still, patterns of variation can be detected among these samples. For example, the ratio of pristane to phytane was all greater than 1.0 except for one sample (JLW9.3) from Yangtze Gorges area. The results indicate that sample JLW9.3 might have been deposited in a reducing environment whereas the other samples might have been formed in relatively oxidative environments. The overall results, however, suggest that rock samples from the Neoproterozoic-Cambrian transition in China have gone through significant metamorphism; thus, understanding of microbial communities using molecular biomarkers in such altered rocks needs to be cautiously executed.

  20. Geological setting and tectonic subdivision of the Neoproterozoic orogenic belt of Tuludimtu, western Ethiopia

    Science.gov (United States)

    Allen, Alistair; Tadesse, Gebremedhin

    2003-05-01

    The N-S trending Tuludimtu Belt in the extreme west of Ethiopia has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka domains. The Kemashi, Dengi and Sirkole Domains, forming the core of the belt, contain volcano-sedimentary successions, whilst the Didesa and Daka Domains are gneiss terranes, interpreted to represent the eastern and western forelands of the Tuludimtu Belt. The Kemashi Domain, which consists of an ophiolitic sequence of ultramafic and mafic volcanic and plutonic rocks together with sedimentary rocks of oceanic affinity, is interpreted as oceanic crust and is considered to represent an arc-continent suture zone. The Dengi Domain, composed of mafic to felsic volcanic and plutonic rocks, and a sequence of volcanoclastic, volcanogenic, and carbonate sediments, is interpreted as a volcanic arc. The Sirkole Domain consists of alternating gneiss and volcano-sedimentary sequences, interpreted as an imbricated basement-cover thrust-nappe complex. All the domains are intruded by syn- and post-kinematic Neoproterozoic granitoids. Structural analysis within the Didesa and Daka Domains indicate the presence of pre-Pan African structures, upon which Neoproterozoic deformation has been superimposed. The gneissic rocks of these two domains are regarded as pre-Pan African continental fragments amalgamated to West Gondwana during Neoproterozoic collision events. Unconformably overlying all of the above are a series of tilted but internally undeformed conglomerate-sandstone-shale sequences, regarded as post-accretionary molasse-type deposits, formed during gravitational collapse of the Tuludimtu Belt. The Tuludimtu Belt is interpreted as a collision orogenic belt formed during the assembly of West Gondwana prior to final closure of the Mozambique Ocean.

  1. THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their Ecosystems

    Science.gov (United States)

    Narbonne, Guy M.

    2005-01-01

    The Ediacara biota (575-542 Ma) marks the first appearance of large, architecturally complex organisms in Earth history. Present evidence suggests that the Ediacara biota included a mixture of stem- and crown-group radial animals, stem-group bilaterian animals, "failed experiments" in animal evolution, and perhaps representatives of other eukaryotic kingdoms. These soft-bodied organisms were preserved under (or rarely within) event beds of sand or volcanic ash, and four distinct preservational styles (Flinders-, Fermeuse-, Conception-, and Nama-style) profoundly affected the types of organisms and features that could be preserved. Even the earliest Ediacaran communities (575-565 Ma) show vertical and lateral niche subdivision of the sessile, benthic, filter-feeding organisms, which is strikingly like that of Phanerozoic and modern communities. Later biological and ecological innovations include mobility (>555 Ma), calcification (550 Ma), and predation (extinction andor biological interactions with the rapidly evolving animals of the Cambrian explosio

  2. Co-evolution of Eukaryotes and Ocean and Atmosphere Oxygenation in the Neoproterozoic and Paleozoic Eras

    Science.gov (United States)

    Lenton, T. M.; Daines, S. J.; Mills, B.; Boyle, R. A.

    2014-12-01

    The nature, timing and cause(s) of the Earth's second oxygenation event are widely debated. It has been argued that there was a single pronounced rise in atmospheric oxygen toward present levels in the Late Neoproterozoic, which in turn triggered the evolution of animals. Here we suggest a more complex co-evolutionary scenario, with fluctuations in ocean and atmosphere oxygenation in the Late Neoproterozoic and Early Paleozoic caused partly by the evolution of animals, followed by a pronounced rise of atmospheric oxygen to present levels later in the Paleozoic caused by the rise of land plants. Current geochemical evidence suggests some parts of the deep oceans became oxygenated during the Ediacaran, but there was subsequent de-oxygenation of the ocean during the Cambrian that may have persisted into the Ordovician. Only later in the Paleozoic is there evidence for widespread oxygenation of the deep ocean, together with charcoal indicating atmospheric oxygen had approached present levels. The limited Neoproterozoic oxygenation of the ocean could be explained by the evolution of filter-feeding sponges removing oxygen demand from the water column and encouraging a shift from cyanobacteria to faster-sinking eukaryotic algae, which transferred oxygen demand to greater depths and into sediments. The resulting oxygenation of shelf bottom waters would have increased phosphorus removal from the ocean thus lowering global productivity and oxygen demand in a positive feedback loop encouraging ocean oxygenation [1]. The subsequent Cambrian de-oxygenation of the ocean could be explained by the evolution of bioturbating animals oxygenating the sediments and thus lowering the C/P burial ratio of organic matter, reducing organic carbon burial and lowering atmospheric oxygen [2]. The later rise of land plants, selectively weathering phosphorus from continental rocks and producing recalcitrant high C/P biomass, increased organic carbon burial and atmospheric oxygen, finally

  3. Mid-Neoproterozoic ridge subduction and magmatic evolution in the northeastern margin of the Indochina block: Evidence from geochronology and geochemistry of calc-alkaline plutons

    Science.gov (United States)

    Qi, Xuexiang; Santosh, M.; Zhao, Yuhao; Hu, Zhaocuo; Zhang, Chao; Ji, Fengbao; Wei, Cheng

    2016-04-01

    The mid-Neoproterozoic medium- to high-K calc-alkaline magmatic rocks in the northeastern margin of the Indochina block, SW China, provide important insights into the relationship of the Indochina block with the Gondwana supercontinent. Here we report zircon LA-ICP-MS U-Pb data from the early and late stage plutons which yield weighted mean 206Pb/238U ages of 765 Ma and 732-739 Ma suggesting mid-Neoproterozoic emplacement. The zircon εHf(t) values show a range of - 3.2 to + 2.4 (average + 0.1 ± 0.9) with TDMC of 1510 to 1870 Ma for the early plutons, and - 5.4 to + 5.1 (average + 2.1 to - 3.9) with TDMC of 1366 to 1985 Ma for late plutons. Both groups show similar geochemical characteristics including high Mg#, enrichment of LILE and LREE, slight negative Eu anomalies, and strongly negative Nb, Ta and Ti anomalies, with all the samples falling within the continental/island arc field in tectonic discrimination diagrams. These features suggest that the early and late stage magmas were produced by the mixing of mantle-derived magma and crust-derived magma in different proportion within an active continental margin, in subduction-related continental-arc tectonic setting. The linear zoning and roughly parallel distribution of the two generations of intrusions with a hiatus of 20 Ma might suggest an episode of ridge subduction with asthenosphere upwelling through the slab window that generated the second phase of plutons.

  4. Late neoproterozoic igneous complexes of the western Baikal-Muya Belt: Formation stages

    Science.gov (United States)

    Fedotova, A. A.; Razumovskiy, A. A.; Khain, E. V.; Anosova, M. O.; Orlova, A. V.

    2014-07-01

    The paper presents new geological, geochemical, and isotopic data on igneous rocks from a thoroughly studied area in the western Baikal-Muya Belt, which is a representative segment of the Neoproterozoic framework of the Siberian Craton. Three rock associations are distinguished in the studied area: granulite-enderbite-charnockite and ultramafic-mafic complexes followed by the latest tonalite-plagiogranitegranite series corresponding to adakite in geochemical characteristics. Tonalites and granites intrude the metamorphic and gabbroic rocks of the Tonky Mys Point, as well as Slyudyanka and Kurlinka intrusions. The tonalites yielded a U-Pb zircon age of 595 ± 5 Ma. The geochronological and geological information indicate that no later than a few tens of Ma after granulite formation they were transferred to the upper lithosphere level. The Sm-Nd isotopic data show that juvenile material occurs in rocks of granitoid series (ɛNd(t) = 3.2-7.1). Ophiolites, island-arc series, eclogites, and molasse sequences have been reviewed as indicators of Neoproterozoic geodynamic settings that existed in the Baikal-Muya Belt. The implications of spatially associated granulites and ultramafic-mafic intrusions, as well as granitoids with adakitic geochemical characteristics for paleogeodynamic reconstructions of the western Baikal-Muya Belt, are discussed together with other structural elements of the Central Asian Belt adjoining the Siberian Platform in the south.

  5. Sedimentary and tectonic history of the Holowilena Ironstone, a Neoproterozoic iron formation in South Australia

    Science.gov (United States)

    Lechte, Maxwell Alexander; Wallace, Malcolm William

    2015-11-01

    The Holowilena Ironstone is a Neoproterozoic iron formation in South Australia associated with glacial deposits of the Sturtian glaciation. Through a comprehensive field study coupled with optical and scanning electron microscopy, X-ray fluorescence, and X-ray diffraction, a detailed description of the stratigraphy, sedimentology, mineralogy, and structure of the Holowilena Ironstone was obtained. The Holowilena Ironstone comprises ferruginous shales, siltstones, diamictites, and is largely made up of hematite and jasper, early diagenetic replacement minerals of precursor iron oxyhydroxides, and silica. These chemical precipitates are variably influenced by turbidites and debris flows contributing clastic detritus to the depositional system. Structural and stratigraphic evidence suggests deposition within a synsedimentary half-graben. A model for the Holowilena Ironstone is proposed, in which dense oxic fluids expelled during sea ice formation in the Cryogenian pool in the depression of the half-graben, allowing for long-lived mixing with the ferruginous seawater and the deposition of iron oxides. This combination of glacial dynamics, tectonism, and ocean chemistry may explain the return of iron formations in the Neoproterozoic.

  6. Timing and sources of pre-collisional Neoproterozoic sedimentation along the SW margin of the Congo Craton (Kaoko Belt, NWNamibia)

    Czech Academy of Sciences Publication Activity Database

    Konopásek, J.; Košler, J.; Sláma, Jiří; Janoušek, V.

    2014-01-01

    Roč. 26, č. 1 (2014), s. 386-401. ISSN 1342-937X Institutional support: RVO:67985831 Keywords : detrital zircons * protolith ages * geochronology * Neoproterozoic Kaoko Belt * geochronology (Namibia) Subject RIV: DB - Geology ; Mineralogy Impact factor: 8.235, year: 2014

  7. Two diamictites, two cap carbonates, two δ13C excursions, two rifts: The Neoproterozoic Kingston Peak Formation, Death Valley, California

    Science.gov (United States)

    Prave, A. R.

    1999-04-01

    Stratigraphic mapping of the Neoproterozoic glaciogenic Kingston Peak Formation (Death Valley, California) provides evidence for two temporally discrete extensional deformation episodes. These episodes are bracketed by the Sourdough Limestone and Noonday Dolomite, the facies characteristics and δ13C data (ranging between 2.15 and -2.56‰ and -1.88 and -4.86‰, respectively) of which make them equivalent to Sturtian and Varangian age cap carbonates, respectively. This constrains the two extensional episodes along the southwestern margin of Laurentia to ca. 700 Ma and ca. 600 Ma. These observations and data show that the field evidence for mid-Neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest Neoproterozoic breakup are both correct. Thus, Neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m.y. or more. Confining rifting to within the Kingston Peak Formation thereby places the younger Proterozoic rocks of the southwestern Great Basin in the rift to drift tectonic phase.

  8. GCM Simulations of Neoproterozoic "Snowball Earth" Conditions: Implications for the Environmental Limits on Terrestrial Metazoans and Their Extraterrestrial Analogues

    Science.gov (United States)

    Sohl, L. E.; Chandler, M. A.

    2001-01-01

    The Neoproterozoic Snowball Earth intervals provide excellent opportunities to examine the environmental limits on terrestrial metazoans. A series of GCM simulations was run in order to quantify climatic conditions during these intervals. Additional information is contained in the original extended abstract.

  9. Giant submarine landslide grooves in the Neoproterozoic/Lower Cambrian Phe Formation, northwest Himalaya: Mechanisms of formation and palaeogeographic implications

    Science.gov (United States)

    Draganits, E.; Schlaf, J.; Grasemann, B.; Argles, T.

    2008-04-01

    Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North-South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new "double provenance" model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible

  10. The Precambrian of Transangaria, Yenisei Ridge (Siberia): Neoproterozoic microcontinent, Grenville-age orogen, or reworked margin of the Siberian craton?

    Science.gov (United States)

    Kuzmichev, Alexander B.; Sklyarov, Eugene V.

    2016-01-01

    The Yenisei Ridge was traditionally perceived as an uplifted segment of the western Siberian craton affected by Neoproterozoic collision events. However, the suggestions for Archaean or Palaeoproterozoic ('Siberian') basement in Transangaria have not been confirmed by reliable geochronological data. A new view regards most of the Ridge, namely, its Transangarian segment, to be an exotic Neoproterozoic terrane that collided with Siberia in the late Neoproterozoic. This paper presents new U-Pb SHRIMP zircon ages demonstrating that Archaean rocks (2611 ± 12 Ma) actually exist in this territory. We also provide a review of published U-Pb zircon ages for igneous and metamorphic rocks of Transangaria together with our new age data. This geochronological dataset clarifies the geology of the Yenisei Ridge and leads to new conclusions, as follows. (1) It is likely that Transangaria was originally underlain by an Archaean-Palaeoproterozoic basement, similar to that of the Siberian craton. (2) Geochronological data do not confirm the idea of widespread "Greenvillian age" granitoides in Transangaria. (3) The Neoproterozoic evolution of the Yenisei Ridge segment of the Siberian craton margin includes the following events. (i) Collision of an unidentified terrane with the western margin (in recent coordinates) of the Siberian craton during 900-855 Ma. The colliding terrane is no longer present in the current structure. (ii) Dextral shearing during 830-800 Ma may have been caused by counter-clockwise rotation of the Siberian craton. (iii) Extensional conditions prevailed during 800-700 Ma. The Isakovka oceanic basin formed at this time interval. (iv) Thrusting of the Isakovka island arc and accretionary prism onto the Siberian margin occurred during the late Neoproterozoic (650-630 Ma) and caused high-pressure metamorphism.

  11. Carbon isotope fluctuations through the neoproterozoic-lower cambrian Birmania basin, Rajasthan, India

    International Nuclear Information System (INIS)

    The paleogeographic reconstruction of the end phase of Neoproterozoic assumes a significance due to the fact that the interactions between the biosphere and the atmosphere, hydrosphere and geosphere during this period of time strongly influenced the evolution of life and initiated a remarkable phase of organic evolution well documented in the rocks of this age (Banerjee and Majumdar, 1999). Time related changes in these carbon reservoirs and processes during the end Proterozoic have played an important role in the evolution of the environment and of life (Des Marais, 1997). Brasier (1992) discussed at length various factors that pushed shallow marine ecosystem of the late Neoproterozoic-Cambrian towards P-limitation and suggested that nitrate fixation, density stratification and massive removal of P in the sediments were responsible for the formation of phosphatic deposits within this time interval. East Gondwana assembly of continents provide fine examples of stratigraphic successions in which the ideas related to oceanic stratification, phosphate deposition, enhanced organic production and carbon isotope fluctuations can be verified and correlated from continent to continent (Banerjee and Majumdar, 1999). The Birmania basin is an oval shaped isolated remnant of the Marwar basin (Neo-proterozoic-Early Palaeozoic) located in the heart of the Thar desert of western Rajasthan, India. It is underlain by Malani Igneous Suite of rocks which range in age from 780 to 680Ma (Rathore et al., 1999).The Birmania basin comprises around 900 metre thick sedimentary sequence of siliciclastic, carbonate and phosphorite facies. These sequences are unconformably overlain by La-thi conglomerate of Jurassic age in north-ern flank of the basin. Global Neoproterozoic glacial activity in the western Rajasthan is also reported and is represented by Pokaran Boulder Bed, few kms away from study area. The Pokaran Boulder Bed overlies the Malani Igneous Suite and is mainly consist of boulders

  12. Late-Neoproterozoic hydrothermal fluid activity in the Tandilia belt, Argentina

    Directory of Open Access Journals (Sweden)

    Juan C Martínez

    2013-09-01

    Full Text Available In the Barker - Villa Cacique area, Tandilia belt, alteration mineral assemblages were studied by petrography, XRD and EMPA at three different stratigraphic levels: (1 a phyllic alteration at the unconformity palaeoproterozoic basement-neoproterozoic sedimentary succession (TLPU; (2 an advanced argillic alteration in the Las Águilas Formation (middle level; and (3 a phyllic alteration on pyroclastic rocks of the Olavarría Formation (upper level. Special emphasize was placed on the chemical characterization of K-white micas and chlorites. Secondary K-white micas of altered migmatites, from the Las Aguilas and Olavarría Formations have a low paragonite content (Na* 9.5 km for the entire sedimentary pile. Hot fluids would rise from deep-seated realms, metamorphic and/or hidden igneous sources. A correlation with a Brasiliano thermo-tectonic event is hypothesized.

  13. Understanding and modelling Neo-proterozoic glaciations and their associated phenomena

    International Nuclear Information System (INIS)

    The objective of this research thesis is to provide a consistent image of extreme glaciations which occurred during the Neo-proterozoic era. By using climate and carbon cycle models (or model of bio-geochemical cycles), the author aims at answering various scientific questions raised by the Snowball Earth hypothesis. After a description of the main geological features which characterize the Proterozoic, scientific problems are presented. The author then reports the study of carbon cycle during glaciation in order to understand its operation. Based on this constraint, a consistent scenario of exit from glaciation is defined. The physical-chemical evolution of the ocean during and after a global glaciation is then quantified in order to assess its potential effects on the environment and on the Precambrian biosphere. The last part focuses on the post-glacial evolution to establish the delay for a return to equilibrium of climate after such an extreme event

  14. Root zone of a continental rift: the Neoproterozoic Kebnekaise Intrusive Complex, northern Swedish Caledonides

    DEFF Research Database (Denmark)

    Kirsch, Moritz; Svenningsen, Olaf

    2016-01-01

    Mafic magmatic rocks formed between ca. 615 and 560 Ma along the Neoproterozoic margins of Baltica and Laurentia are classically attributed to continental rifting heralding the opening of the Iapetus Ocean. We report new data for the Kebnekaise Intrusive Complex (KIC) exposed in the Seve Nappes in...... northern Sweden. The KIC consists of sheeted dolerite dykes and gabbroic bodies with mutually intrusive relations. Major and trace element data exhibit a transitional- to normal-mid-ocean-ridge basalt-type geochemical signature. Differentiation processes and late-stage liquid immiscibility of a tholeiitic...... represent a high-level magma plumbing system in a late-stage continental rift. The composition and volume of rift-related igneous rocks in the Seve Nappes are inconsistent with a mantle plume origin, but are thought to record progressive lithospheric thinning and increasing involvement of an asthenospheric...

  15. Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    HARTMANN LÉO A.

    2003-01-01

    Full Text Available Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite or compositional (e.g. mantle spinel remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3 and narrow 1-3 m-wide shear zones (M4 containing asbestos.

  16. Global Neoproterozoic (Sturtian) post-glacial sulfide-sulfur isotope anomaly recognised in Namibia

    Science.gov (United States)

    Gorjan, Paul; Walter, Malcolm R.; Swart, Roger

    2003-02-01

    The Neoproterozoic Earth experienced at least two, probably global, glaciations. Each glaciation was superceded by deposition of a layer of carbonate ('cap-carbonate') that has a distinctive lithology and depletion in 13C ( δ13C carbonate ˜ -5‰). The ˜700 Ma Sturtian glaciation is followed by deposition of a cap-carbonate and post-glacial succession which contain bacterially produced sulfides extremely enriched in 34S (average δ34S sulfide ˜ +30‰) with maximum values up to +60‰. This level of 34S enrichment in sulfides is unique to the Sturtian post-glacial succession and recognised in Australia, Canada, and China. In the Neoproterozoic of the Nama Basin, Namibia, the Gobabis Member is the basal unit of the Court Formation, which overlies the glacial Blaubeker Formation. δ13C carbonate analyses from the Gobabis Member range from -5.2 to -2.2‰ (average = -3.7‰; n = 10). δ34S sulfide ranges from +16.1 to +61.1‰ (average = +37.6‰; n = 8). These results are consistent with a Sturtian age for the Blaubeker Formation and overlying Gobabis Member, which have previously been interpreted as Sturtian. The sulfur isotopic results are comparable with δ34S sulfide in Sturtian post-glacial units of Australia, Canada and China. This adds to the evidence for correlation of the Blaubeker Formation with Sturtian glaciations on other continents. The cause of such elevated δ34S sulfide is enigmatic. Geochemical evidence suggests the sulfide was not formed from low sulfate waters nor in euxinic conditions, which discounts any known modern analogue. 34S enrichment in sulfides is therefore postulated to be caused by enrichment of 34S in contemporaneous seawater ( δ34S sulfate up to +60‰?). The rise in seawater δ34S sulfate is considered to be the result of intense bacterial sulfate reduction in an anoxic ocean during the Sturtian glaciation.

  17. Organic Carbon Isotope Geochemistry of the Neoproterozoic Doushantuo Formation, South China

    Institute of Scientific and Technical Information of China (English)

    GUO Qingjun; LIU Congqiang; Harald STRAUSS; Tatiana GOLDBERG; ZHU Maoyan; PI Daohui; WANG Jian

    2006-01-01

    The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China,documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata,exquisitely preserved fossils have been discovered: the Weng'an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng'an section of a carbonate platform (shelf of the Yangtze Platform, Guizhou Province) from the Songtao section and Nanming section of a transition belt (slope of the Yangtze Platform, Guizhou Province) and from the Yanwutan section (basin area of the Yangtze Platform, Hunan Province). Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon (mean δ13Corg = -35.0%) from the uppermost Nantuo Formation are followed by an overall increase in δ13C up-section. Carbon isotope values vary between -9.9% and 3.6% for carbonate and between -35.6% and -21.5% for organic carbon, respectively. Heavier δ13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity (such as the Weng'an biota). The δ13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin,reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.

  18. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Gioia, Simone Maria Costa Lima [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: marcio@unb.br

    2000-03-01

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863{+-} 97 Ma and e{sub Nd} (T) of +4.1 T{sub D}M model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 {+-} 77 Ma and e{sub Nd} (T) of +2.9. T {sub DM} values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 {+-} 120 Ma and initial e{sub Nd} value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  19. Late Neoproterozoic to holocene thermal history of the precambrian Georgetown inlier, northeast Australia

    International Nuclear Information System (INIS)

    Carboniferous-Permian volcanic complexes and isolated patches of Upper Jurassic - Lower Cretaceous sedimentary units provide a means to qualitatively assess the exhumation history of the Georgetown Inlier since ca 350 Ma. However, it is difficult to quantify its exhumation and tectonic history for earlier times. Thermochronological methods provide a means for assessing this problem. Biotite and alkali feldspar 40Ar/39Ar and apatite fission track data from the inlier record a protracted and non-linear cooling history since ca 750 Ma. 40Ar/39Ar ages vary from 380 to 735 Ma, apatite fission track ages vary between 132 and 258 Ma and mean track lengths vary between 10.89 and 13.11 mm. These results record up to four periods of localised accelerated cooling within the temperature range of ∼ 320-60 deg C and up to ∼ 14 km of crustal exhumation in parts of the inlier since the Neoproterozoic, depending on how the geotherm varied with time. Accelerated cooling and exhumation rates (0.19-0.05 km/106 years) are observed to have occurred during the Devonian, late Carboniferous - Permian and mid-Cretaceous - Holocene periods. A more poorly defined Neoproterozoic cooling event was possibly a response to the separation of Laurentia and Gondwana. The inlier may also have been reactivated in response to Delamerian-age orogenesis. The Late Palaeozoic events were associated with tectonic accretion of terranes east of the Proterozoic basement. Post mid-Cretaceous exhumation may be a far-field response to extensional tectonism at the southern and eastern margins of the Australian plate. The spatial variation in data from the present-day erosion surface suggests small-scale fault-bounded blocks experienced variable cooling histories. This is attributed to vertical displacement of up to ∼2 km on faults, including sections of the Delaney Fault, during Late Palaeozoic and mid-Cretaceous times. Copyright (2001) Geological Society of Australia

  20. A model for Iapetan rifting of Laurentia based on Neoproterozoic dikes and related rocks

    Science.gov (United States)

    Burton, William C.; Southworth, Scott

    2010-01-01

    Geologic evidence of the Neoproterozoic rifting of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and rift-related clastic sedimentary sequences. The spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting. The most salient features include: (1) a rift-related magmatic event recorded in the French Broad massif and the southern and central Shenandoah massif that is distinctly older than that recorded in the northern Shenandoah massif and northward; (2) felsic volcanic centers at the north ends of both French Broad and Shenandoah massifs accompanied by dike swarms; (3) differences in volume between massifs of cover-sequence volcanic rocks and rift-related clastic rocks; and (4) WNW orientation of the Grenville dike swarm in contrast to the predominately NE orientation of other Neoproterozoic dikes. Previously proposed rifting mechanisms to explain these features include rift-transform and plume–triple-junction systems. The rift-transform system best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant rifting mechanism for most of the Laurentian margin. To explain feature 4, as well as magmatic ages and geochemical trends in the Northern Appalachians, we propose that a plume–triple-junction system evolved into the rift-transform system. A ca. 600 Ma mantle plume centered east of the Sutton Mountains generated the radial dike swarm of the Adirondack massif and the Grenville dike swarm, and a collocated triple junction generated the northern part of the rift-transform system. An eastern branch of this system produced the Long Range dike swarm in Newfoundland, and a subsequent western branch produced the ca. 554 Ma Tibbit Hill volcanics and the ca. 550 Ma rift-related magmatism of Newfoundland.

  1. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    International Nuclear Information System (INIS)

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863± 97 Ma and eNd (T) of +4.1 TDM model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 ± 77 Ma and eNd (T) of +2.9. T DM values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 ± 120 Ma and initial eNd value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  2. Biological feedbacks as cause and demise of the Neoproterozoic icehouse: astrobiological prospects for faster evolution and importance of cold conditions.

    Directory of Open Access Journals (Sweden)

    Pekka Janhunen

    Full Text Available Several severe glaciations occurred during the Neoproterozoic eon, and especially near its end in the Cryogenian period (630-850 Ma. While the glacial periods themselves were probably related to the continental positions being appropriate for glaciation, the general coldness of the Neoproterozoic and Cryogenian as a whole lacks specific explanation. The Cryogenian was immediately followed by the Ediacaran biota and Cambrian Metazoan, thus understanding the climate-biosphere interactions around the Cryogenian period is central to understanding the development of complex multicellular life in general. Here we present a feedback mechanism between growth of eukaryotic algal phytoplankton and climate which explains how the Earth system gradually entered the Cryogenian icehouse from the warm Mesoproterozoic greenhouse. The more abrupt termination of the Cryogenian is explained by the increase in gaseous carbon release caused by the more complex planktonic and benthic foodwebs and enhanced by a diversification of metazoan zooplankton and benthic animals. The increased ecosystem complexity caused a decrease in organic carbon burial rate, breaking the algal-climatic feedback loop of the earlier Neoproterozoic eon. Prior to the Neoproterozoic eon, eukaryotic evolution took place in a slow timescale regulated by interior cooling of the Earth and solar brightening. Evolution could have proceeded faster had these geophysical processes been faster. Thus, complex life could theoretically also be found around stars that are more massive than the Sun and have main sequence life shorter than 10 Ga. We also suggest that snow and glaciers are, in a statistical sense, important markers for conditions that may possibly promote the development of complex life on extrasolar planets.

  3. Possible Record of Neoproterozoic Ice Sheet Collapse: The Kapp Lyell Diamictite Sequence of southwest Spitsbergen, Svalbard

    Science.gov (United States)

    Bjornerud, M.

    2008-12-01

    The Late Proterozoic Kapp Lyell diamictites of northern Wedel Jarlsberg Land, southwest Spitsbergen, have long been recognized as ancient glacial deposits, but their place within the global stratigraphic framework of 'Snowball Earth' has remained unclear owing to the complexity of superimposed Caledonian deformation and to the inaccessible terrain in which they occur. Newly deglaciated exposures of the rocks now provide a more complete picture of the changing environment in which they were deposited and their place in the global chronostratigraphy. The Kapp Lyell Sequence (KLS) is the higher of two diamictic to conglomeratic Neoproterozoic units in SW Spitsbergen. The lower of these, the Konglomeratfjellet Formation, is not unambiguously glaciogenic, but it is topped by a carbonate sequence with textures similar to 'cap' carbonate units in other Neoproterozoic sequences. These carbonates are succeeded by ca. 2000 m of black phyllite with rare lone stones. The phyllite is overlain with apparent conformity by the 2000-3000 m thick KLS, which actually consists of three distinct types of diamictite, all apparently glaciomarine. The KLS begins with 500- 1000 m of finely laminated diamictite punctuated by pebble- to boulder-sized lone stones, presumably ice- rafted. The cm-scale laminae are defined by layers of sand-to-silt sized particles of detrital dolomite alternating with thin films of graphitic phyllite. Preliminary delta 13C values from this graphitic material are very negative, pointing to a biogenic origin. The extraordinary uniformity of the laminae indicates repetitive, possibly seasonal, depositional cycles, but the density of lone stones increases upsection, recording accelerating delivery of ice-rafted debris to the basin. Carbonate clasts predominate, and many have distinctive textures (cm-sized ooids, digitate stromatolites) that link them with the 'cap' carbonate unit lower in the section. The laminated diamictite interval ends abruptly with the

  4. The Jormungand Global Climate State and Implications for the Neoproterozoic Snowball Paradox (Invited)

    Science.gov (United States)

    Abbot, D. S.; Voigt, A.; Koll, D.; Pierrehumbert, R. T.

    2010-12-01

    We present a previously undescribed global climate state, the Jormungand state, that is nearly ice-covered with a narrow (~10-15 degrees of latitude) strip of open ocean near the equator. This state is sustained by internal dynamics of the hydrological cycle and the cryosphere. There is a new bifurcation in global climate climate associated with the Jormungand state that leads to significant hysteresis. We investigate the Jormungand state in a coupled ocean-atmosphere GCM, in multiple atmospheric GCMs coupled to a mixed layer ocean run in an idealized configuration, and we make a simple modification to the Budyko-Sellers model so that it produces Jormungand states. We suggest that the Jormungand state may be a better model for the Neoproterozoic glaciations (~635 Ma and ~715 Ma) than either the hard Snowball or the Slushball models. A Jormungand state would have a large enough region of open ocean near the equator to explain the micropaleontological and molecular clock evidence that photosynthetic eukaryotes thrived both before and immediately after the Neoproterozoic episodes. Additionally, since there is significant hysteresis associated with the Jormungand state, it can explain the cap carbonate sequences, the oxygen isotopic evidence that suggests high CO2 values, and the various evidence that suggests lifetimes for the glaciations of 1 Myrs or more. Since there is not significant hysteresis associated with the Slushball model, the Slushball model cannot explain these observations. Finally, we note that although the Slushball and Jormungand models share the characteristic of open ocean in the tropics, the Jormungand state is produced by entirely different physics, is entered through a new bifurcation in global climate, and is associated with significant hysteresis. Bifurcation diagram of global climate in the CAM global climate model, run with no continents, a 50 m mixed layer with no ocean heat transport, an eccentricity of zero, and annually and diurnally

  5. Gammaspectrometry identification covering Neoproterozoic supracrustal sequences in the Serido Belt , northeastern Brazil; Identificacao gamaespectrometrica de placeres rutilo-monaziticos neoproterozoicos no sul da Faixa Serido, nordeste do Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Sebastiao Milton P. da, E-mail: smpsilva@cchla.ufrn.br, E-mail: sebastiaomilton@gmail.com [Laboratorio de Geoprocessamento, Departamento de Geografia, Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil); Crosta, Alvaro P., E-mail: alvaro@ige.unicamp.br [Instituto de Geociencias, Universidade Estadual de Campinas (Unicamp), SP (Brazil); Ferreira, Francisco J.F., E-mail: francisco.ferreira@ufpr.br [Laboratorio de Pesquisas em Geofisica Aplicada- LPGA, Departamento de Geologia, Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil); Beurlen, Hartmut, E-mail: beurlen@terra.com.br [Programa de Pos-Graduacao em Geociencias, Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil); Silva, Adalene M., E-mail: adalene@unb.br [Laboratorio de Geofisica Aplicada, Instituto de Geociencias da Universidade de Brasilia (UnB), DF (Brazil); Silva, Marcelo R.R. da, E-mail: marcelor@ufpe.br [Departamento de Geologia, Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil)

    2010-01-15

    Aerial gamma-ray survey data covering Neoproterozoic supracrustal sequences in the Serido Belt were processed and analyzed together with ground gamma-ray data, air photos and geological data for lithogeophysical characterization and mapping of granitic rocks, related pegmatites fields and lithological units of Serido Group. Interpretation was based on individual and ternary images of the three radio-elements and the eU/eTh and eTh/K ratios, and allowed the discovery of thorium anomalies associated with coarse-grained metarenites and metaconglomerates facies intercalated with quartzites of the Equador Formation. High contents of iron oxides, ilmenite, monazite, rutile, titanite and zircon were identified by ore microscopy of polished sections in the metaconglomerate's matrix. Semiquantitative scanning electron microscopy (SEM) analyses in minerals of two samples revealed up to 79.4% of Th0{sub 2} and 87.7% of REE in monazites; up to 99.2% of Ti0{sub 2} in ilmenite and rutile and up to 1.81 % of HfO{sub 2} in zircon. Gamma-ray anomalies due to thorium were also identified in association with sediments of Cenozoic age in the region. (author)

  6. Concordant paleolatitudes for Neoproterozoic ophiolitic rocks of the Trinity Complex, Klamath Mountains, California

    Science.gov (United States)

    Mankinen, E.A.; Lindsley-Griffin, N.; Griffin, J.R.

    2002-01-01

    New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel to paleolatitude in the basin between Laurasia and Australia-East Antarctica as the Rodinian supercontinent began to break up. It then continued to move parallel to paleolatitude at least through Middle Devonian time. Although the eastern Klamath plate served as a nucleus against which more western components of the Klamath Mountains province amalgamated, the Klamath superterrane was not accreted to North America until Early Cretaceous time.

  7. Developmental modes of the Neoproterozoic-Lower Paleozoic marine hydrocarbon source rocks in China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the researches on rock type, the mode of occurrence, diagnostic minerals and creatures, the sedimentary geochemistry and organic facies of Chinese marine source rocks from wells and outcrops,and on the research findings of developmental modes of foreign marine source rock, the authors consider that it is impossible to objectively make clear the formation mechanism of hydrocarbon source rock with high organic matter abundance by either single mode of preservation or high organic matter productivity. According to the Chinese geological features, the formation mechanism of the Neoproterozoic-Lower Paleozoic marine source rock is generalized into four modes, namely, thermal water activity-upwelling flow-anoxic; carbonate gentle slope-upwelling flow; xerothermic climate-brine euxinic milieu; and humid climate-retained euxinic milieu; as the Lower Cambrian undercompensation basin organic facies (the Tarim Basin, South China and southwestern margin of North China), carbonate gentle lime mud bound organic facies (the Upper Ordovician in Tazhong region of the Tarim Basin and the Lower Silurian in the Upper Yangtze Platform), the Middle Cambrian evaporation laggon organic facies (the Tarim Basin and the Upper Yangtze Platform), enclosed undercompensation terrigenous bay organic facies (the Middle-Upper Ordovician in the west of the Tarim Basin, the Lower Silurian Longmaxi Formation in the Upper Yangtze platform). Chinese marine sedimentations with lower organic matter abundance are generalized into two modes of consumption-dilution mode of open epicontinental sea and depletion-dilution mode of supercompensation basin.

  8. Stratigraphical analysis of the neoproterozoic sedimentary sequences of the Sao Francisco Basin

    International Nuclear Information System (INIS)

    A stratigraphic analysis was performed under the principles of Sequence Stratigraphy on the neoproterozoic sedimentary sequences of the Sao Francisco Basin (Central Brazil). Three periods of deposition separated by unconformities were recognized in the Sao Francisco Megasequence: (1) Sequences 1 and 2, a cryogenian glaciogenic sequence, followed by a distal scarp carbonate ramp, developed during stable conditions, (2) Sequence 3, a Upper Cryogenian stack homoclinal ramps with mixed carbonate-siliciclastic sedimentation, deposited under a progressive influence of compressional stresses of the Brasiliano Cycle, (3) Sequence 4, a Lower Ediacaran shallow platform dominated by siliciclastic sedimentation of molassic nature, the erosion product of the nearby uplifted thrust sheets. Each of the carbonate-bearing sequences presents a distinct δ13C isotopic signature. The superposition to the global curve for carbon isotopic variation allowed the recognition of a major depositional hiatus between the Paranoa and Sao Francisco Megasequences, and suggested that the glacial diamictite deposition (Jequitai Formation) took place most probably around 800 Ma. This constrains the Sao Francisco Megasequence deposition to the interval between 800 and 600 Ma (the known ages of the Brasiliano Orogeny defines the upper limit). A minor depositional hiatus (700.680 Ma) was also identified separating sequences 2 and 3. Isotopic analyses suggest that from then on, more restricted environmental conditions were established in the basin, probably associated with a first order global event, which prevailed throughout deposition of the Sequence 3. (author)

  9. Microorganisms Linked to Neoproterozoic Microspar Carbonate Sedimentation in the Jilin-Liaoning Area

    Institute of Scientific and Technical Information of China (English)

    GE Ming; KUANG Hongwei; MENG Xianghua; George FURNISS

    2004-01-01

    Molar-tooth carbonate refers to a sort of rock that has ptygmatical folded structure comparable to the ivory. This kind of carbonate exists in a special time range (from Middle to Neoproterozoic). Its origin and the possibility to use it in stratigraphic correlation of the paleocontinent is the key task of the IGCP447, a project on Proterozoic molar tooth carbonates and the evolution of the earth (2001-2005). The importance lies in that the molar-tooth structure is the key to solving problems related to Precambrian biological and global geochemical events. The molar-tooth structure is associated with microorganisms.Development and recession of such carbonates have relations with the evolution process of early lives and abrupt changes in sea carbonate geochemistry. In recent years, based on researches on petrology,geochemistry and Sr isotope of molar-tooth carbonate in the Jilin-Liaoning and Xuzhou-Huaiyang area, the authors hold that it can be used as a marker for stratigraphic sequence and sedimentary facies analyses.

  10. Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era

    Science.gov (United States)

    Lenton, Timothy M.; Boyle, Richard A.; Poulton, Simon W.; Shields-Zhou, Graham A.; Butterfield, Nicholas J.

    2014-04-01

    The Neoproterozoic era (about 1,000 to 542 million years ago) was a time of turbulent environmental change. Large fluctuations in the carbon cycle were associated with at least two severe -- possible Snowball Earth -- glaciations. There were also massive changes in the redox state of the oceans, culminating in the oxygenation of much of the deep oceans. Amid this environmental change, increasingly complex life forms evolved. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. We argue instead that the evolution of increasingly complex eukaryotes, including the first animals, could have oxygenated the ocean without requiring an increase in atmospheric oxygen. We propose that large eukaryotic particles sank quickly through the water column and reduced the consumption of oxygen in the surface waters. Combined with the advent of benthic filter feeding, this shifted oxygen demand away from the surface to greater depths and into sediments, allowing oxygen to reach deeper waters. The decline in bottom-water anoxia would hinder the release of phosphorus from sediments, potentially triggering a potent positive feedback: phosphorus removal from the ocean reduced global productivity and ocean-wide oxygen demand, resulting in oxygenation of the deep ocean. That, in turn, would have further reinforced eukaryote evolution, phosphorus removal and ocean oxygenation.

  11. Finding of Neoproterozoic low-18O igneous rocks in the northern margin of the Dabie orogen

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yongfei; WU Yuanbao; ZHAO Zifu; GONG Bing

    2004-01-01

    @@ It has been one of the most intriguing questions in the earth sciences whether the snowball Earth event is genetically associated with mantle superwelling, supercontinent assemblage and breakup, and rift magmatism during the Neoproterozoic[1-4]. In order to demonstrate the occurrence of significant interaction in energy and matter between the earth's interior and exterior in this period, it is critical to find coeval igneous rocks that contain the signature of surface water and thus form low-18O magma.Several investigations of U-Pb dating and O isotope analysis were carried out for zircons from ultrahigh pressure (UHP) metamorphic rocks in the Dabie-Sulu orogen,east-central China[5-8]. The results indicate that low δ18O zircons have U-Pb ages of 700-800 Ma as dated by either TIMS discordia upper-intercept or SIMS in-situ magmatic core, and the origin of low δ18O water is related to cold paleoclimate during the Sturtian ice age.

  12. Generation of continental crust in the northern part of the Borborema Province, northeastern Brazil, from Archaean to Neoproterozoic

    Science.gov (United States)

    de Souza, Zorano Sérgio; Kalsbeek, Feiko; Deng, Xiao-Dong; Frei, Robert; Kokfelt, Thomas Find; Dantas, Elton Luiz; Li, Jian-Wei; Pimentel, Márcio Martins; Galindo, Antonio Carlos

    2016-07-01

    (TZ). Early Neoproterozoic volcanism at 1091 Ma, and A-type plutonism, from 920 to 775 Ma, mark the intracontinental magmatism in the TZ. In the Seridó Domain, the Late Neoproterozoic registers several events of plutonism, at 600-593, 575-560, 548-533, 528-510, 495-450 Ma. These rocks cover ca. 15% of the area, while Neoproterozoic supracrustal rocks cover ca. 30%. The most important magmatic event is that at 575 Ma, consistent with the peak of widespread transpression and synchronous high temperature metamorphism. The Neoproterozoic rocks are mostly K-enriched alkaline or transitional to calc-alkaline. Inherited Archaean and Palaeoproterozoic zircons and Nd model ages, as well as moderate to strongly negative (-21 to -9) epsilon Nd, and persistent negative anomalies for Ta-Nb, Ti and P indicate significant crustal contributions in their genesis. While a convergent setting (subduction zone) could explain the Archaean and Palaeoproterozoic units, this is not so for the Neoproterozoic rocks which mimic the geochemical and isotopic features of the older sources. In the study area, the peak of juvenile accretion (mantle derived magmas) took place in the Archaean (3.4-2.7 Ga) and Palaeproterozoic (2.4-2.11 Ga), whereas crustal recycling predominated in the Neoproterozoic.

  13. Is high obliquity a still plausible explanation for Neoproterozoic low-latitude glaciations ?

    Science.gov (United States)

    Levrard, B.; Laskar, J.

    2003-04-01

    The observations of enigmatic low-latitude glaciogenic sequences during the Sturtian (˜ 750-700 Ma) and the Varanger (˜ 620-570 Ma) glacial intervals of the Neopropterozo& uml;i c era remain the subject of controversial debates concerning possible scenarii. Of the many models that have been proposed to account for theses paradoxical features, the high-obliquity scenario invoked by G.E. Williams (1975) appears to be still largely considered. However, a such scenario requires a dissipative mechanism to bring back the Earth's obliquity from a value higher than 55o to the present value (˜ 23.5o) in less than 200 Ma. Williams (1993) suggested that core-mantle friction could have explained this substantial decrease. However, it was demonstrated by Néron de Surgy and Laskar (1997) and confirmed by Pais et al. (1999) that, not only it requires abnormal values of effective viscosity, but due to the conservation of the angular momentum, it is also largely conflicting with the paleorotation data. D.M Williams et al. (Nature, 1998) recently proposed that ``climate friction" could have produced this decrease in less than 100 Ma between ˜ 600 Ma and 500 Ma. We have revisited in details this mecanism (Levrard and Laskar, submitted to Geo. J. Int., 2002) for the Neoproterozoic glaciations. In response to periodic variations in the obliquity, the redistribution of ice/water mass and the isostatic adjusment to the surface loading affect the dynamical ellipticity of the Earth. Delayed responses in the mass redistribution may introduce a secular term in the obliquity evolution (Bills, 1994; Rubincam, 1995; Ito et al, 1995). We analyze the obliquity-oblateness feedback using non-linear response of ice sheets (Imbrie and Imbrie, 1980) to insolation forcing and layered models with Maxwell visco-elastic rheology. Possible increase in the non-linear response of ice sheets to insolation forcing and latitudinal changes in this forcing strongly limit the contribution of the obliquity

  14. Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

    Science.gov (United States)

    Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

    2013-08-01

    The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

  15. Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review

    Science.gov (United States)

    Küster, Dirk; Harms, Ulrich

    1998-12-01

    Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite-granite, biotite-hornblende-granite, quartz-monzonite and quartz-syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sr i-ratios between 0.7060 and 0.7236 and ɛNd( t) values between -15.8 and -5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sr i-ratios (0.7036-0.7075) and positive ɛNd( t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities

  16. Late Neoproterozoic Nuqara Dokhan Volcanics, Central Eastern Desert, Egypt: Geochemistery and petrogenesis

    Science.gov (United States)

    Hassan, Tharwat; Asran, Asran; Amron, Taha; Natflos, Theo

    2014-05-01

    The Nuqara volcanic is one of the northernmost outcrops of the Arabian-Nubian Shield Dokhan volcanics. The origin and tectonic setting of the late Neoproterozoic Dokhan volcanics (ca. 610-560 Ma) in the Egyptian Eastern Desert is highly debated. The debate concerns the tectonic setting where they formed during transition between convergent to extensional regime or after the East- and the West-Gondwana collision (~600Ma). In order to solve this problem, lavas from Nuqara area were studied geologically and geochemically. Nuqara Dokhan volcanics comprises two main rock suites: (a) an intermediate volcanic suite, consisting of basaltic andesite, andesite and their associated pyroclastics rocks; and (b) a felsic volcanic suite composed of dacite, rhyolite and ignimbrites. The two suites display well-defined major and trace element trends and continuum in composition with wide ranges in SiO2 (52-75.73%), CaO (9.19-0.22%), MgO (5.29-0.05%), Sr (1367-7.4 ppm), Zr (688.5-172.7 ppm), Cr (207-0.4 ppm), and Ni (94.3-0.2 ppm). The Nuqara Dokhan volcanics are characterized by strong enrichment in LILE relative to HFSE and affiliated to the calc-alkaline subducted - related magmatism. Geochemical Modeling displays that the evolution of these rocks was governed by fractional crystallization of plagioclase, amphiboles, pyroxene, magnetite and apatite in the intermediate varieties and plagioclase, amphibole, magnetite, apatite and zircon in the felsic varieties. The obtained mineral chemistry of these volcanics reveals: (a) Plagioclase range in composition from An55 to An40 in basaltic andesite and from An39 to An24 in andesite. (b) Alkali feldspars have sanidine composition. (c) Clinopyroxenes have augite composition. The low Al2O3 contents (1.94-5.588 wt %) indicate that clinopyroxene crystallized at low - pressure conditions. (d) Amphiboles have magnesio- hornblende composition.

  17. Petrogenesis and tectonic implications of the Neoproterozoic Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China

    Science.gov (United States)

    Yang, Yi-Jin; Zhu, Wei-Guang; Bai, Zhong-Jie; Zhong, Hong; Ye, Xian-Tao; Fan, Hong-Peng

    2016-03-01

    Mafic-ultramafic dykes are important geological markers that can punctuate the onset of crustal extension during the breakup of a continent and provide valuable information on the mantle source. This study reports secondary ion mass spectroscopy zircon and baddeleyite U-Pb ages, elemental and Nd isotopic data for the Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China. Two kinds of rocks are confirmed: the picritic rock and the dolerite. Based on petrographic and geochemical features, the dolerite dykes are further subdivided into two groups: Group I mafic and Group II mafic dykes, which emplaced at ~760 Ma (zircon U-Pb) and ~800 Ma (zircon and baddeleyite U-Pb), respectively. All samples from the picritic rocks and the Group I mafic rocks show the features of high-Ti and alkaline basaltic magma in composition as well as "humped" trace element patterns, which are similar to those of typical alkaline basalts associated with continental rifts except for the slightly negative Nb-Ta anomalies. The Group II mafic rocks display the features of low-Ti and tholeiitic magma, moderately enriched in LILE and LREE, and characterized by distinctively negative Nb-Ta anomalies. The primary magmas of the picritic rocks and the Group I mafic rocks were generated from ca 25 % partial melting of an OIB-like, Nd isotopically depleted but incompatible elements relatively enriched mantle source within a garnet stable field. The Group II mafic rocks crystallized from crustal contaminated mafic magmas that were derived from a spinel-bearing sub-continental lithospheric mantle source, because of low ratios of La/Yb, Ti/Y and Sm/Yb. Geochemical features suggest that these groups of mafic-ultramafic dykes were formed in a continental rift setting, but derived from different mantle sources. In combination with other Neoproterozoic igneous rocks in the western margin of Yangtze Block, it is suggested that the Datian mafic-ultramafic dykes in the Panzhihua area

  18. Molecular composition and indigenity of organic matter in Late Neoproterozoic sedimentary rocks from the Yangtze region, South China

    Institute of Scientific and Technical Information of China (English)

    LI Meijun; WANG Tieguan; WANG Chunjiang; ZHANG Weibiao

    2006-01-01

    Diamictites from Late Neoproterozoic Nantuo tillites (~600 Ma), and dolomites from the overlying Dousantuo and Dengying formations in the Yangtze region, southern China, were analyzed for solvent extractable hydrocarbons. Even though all these samples have low contents of TOC and have undergone overmature thermal evolution, there has been still preserved quite a large amount of hydrocarbons. Analysis of the extracts by gas chromatography-mass spectrometry (GC-MS) revealed the presence of n-alkanes, regular acyclic isoprenoids, tricyclic terpanes, hopanes, gammacerane, steranes, and polyaromatic hydrocarbons. Strict experimental measurements were performed in the analytical procedure to prevent any potential contaminants from being introduced. All these bitumens have molecular markers of Precambrian characteristics and no external organics derived from current contamination events or migrated hydrocarbons from younger strata. The maturity parameters for bitumens indicate that the hydrocarbons are of over-maturity, which is consistent with the thermal maturity of the host rocks. Consequently, it is concluded that the Late Neoproterozoic bitumens in the Yangtze region, South China, are indigenous to their host rocks, which provides the basis for our organic geochemical research on "Snowball Earth" and "Cambrian Explosion."

  19. The initiation of Neoproterozoic "snowball" climates in CCSM3: the influence of paleo-continental configuration

    Directory of Open Access Journals (Sweden)

    Y. Liu

    2013-07-01

    Full Text Available We identify the "hard snowball" bifurcation point at which total sea ice cover of the oceans is expected by employing the comprehensive coupled climate model CCSM3 for two realistic Neoproterozoic continental configurations, namely a low-latitude configuration appropriate for the 720 Ma Sturtian glaciation and a higher southern latitude configuration more appropriate for the later 635 Ma Marinoan glaciation. We find that for the same total solar insolation (TSI and atmospheric CO2 concentration (pCO2, the most recent continental configuration is characterized by colder climate than the 720 Ma continental configuration and enters the hard snowball state more easily on account of the following four factors: the low heat capacity of land in the south polar region, the higher albedo of the snow covered land compared to that of sea ice, the more negative net cloud forcing near the ice front in the Northern Hemisphere (NH, and more importantly, the more efficient sea ice transport towards the equator in the NH due to the absence of blockage by continents. Beside the paleogeography, we also find the optical depth of aerosol to have a significant influence on this important bifurcation point. When the high value (recommended by CCSM3 but demonstrated to be a significant overestimate is employed, the critical values of pCO2, beyond which a hard snowball will be realized, are between 80–90 ppmv and 140–150 ppmv for the Sturtian and Marinoan continental configurations, respectively. However, if a lower value is employed that enables the model to approximately reproduce the present-day climate, then the critical values of pCO2 become 50–60 ppmv and 100–110 ppmv for the two continental configurations, respectively. All of these values are higher than previously obtained for the present-day geography (17–35 ppmv using the same model, primarily due to the absence of vegetation, but are much lower than that obtained previously for the 635 Ma

  20. Tidal shelf sedimentation in the Neoproterozoic Chattisgarh succession of central India

    Indian Academy of Sciences (India)

    Sarbani Patranabis Deb

    2005-06-01

    The Neoproterozoic Kansapathar Sandstone of the Chattisgarh basin, a shallow marine shelf bar sequence, consists of mineralogically and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. The sediments were transported, reworked and deposited in subtidal environments by strong tidal currents of macrotidal regime as well as storms, and accumulated as discrete shoaling-upward features, separated from each other by muddy to low-energy sandy deposits. The sandbodies developed into shoaling up linear bars, often more than a kilometre in length, through accretion of thick cross-stratified units in transverse directions under the influence of ebb and flood tidal currents, as well as in longitudinal direction affected by southeasterly flowing along-shore currents. The aggrading upper surfaces of the bars experienced protracted reworking by strong oscillatory wave currents leading to extensive development of subaqueous 2D or 3D dunes mantled with lag pebble deposits at different points. With continued shoaling and progradation, thebars amalgamated into large sandstone sheets with the development of high energy beach depositsand coastal sand flats in the uppermost part of the sequence. The presence of rill marks, flat-topped ripples, wrinkle marks, desiccation cracks and adhesion warts point to intertidal conditions with intermittent exposure. The high energy sandstone bars overlie a thick mudstone-dominated shelf sequence across a sharp interface indicating rapid change in the sea-level, provenance, rate of sediment generation and sediment input, and circulation condition in the shelf. A quiet muddy shelf was replaced by a major sand-depositing environment with strong, open marine circulation. An interplay of tidal currents, oscillatory wave currents and storm currents generated a complex flow pattern that varied in time and space from bimodal-bipolar to strongly unimodal flows. Close parallelism of wave ripple crests, trend of linear bars

  1. The Neoproterozoic-Cambrian Paraguay Belt, central Brazil: Part I - New structural data and a new approach on the regional implications

    Science.gov (United States)

    Silva, Luiz José Homem D'el-Rey; Walde, Detlef Hans-Gerd; Saldanha, Davi Oliveira

    2016-04-01

    Together with the Araguaia and Brasília belts, the Paraguay belt forms in central Brazil, the Tocantins Province that is one of the largest orogens of western Gondwana. The Corumbá area occupies the site where the northern and southern parts of the Paraguay belt form, together with the Chiquitos-Tucavaca aulacogen (stretching E-W in the adjacent Bolivian territory) an R-R-R basin system opened-filled in the ~ 700/650-540 Ma interval within the Amazon-Rio Apa paleo-continent. The sedimentary (volcanic) rocks of the Jacadigo and Corumbá Groups found around the Corumbá city record part of the Neoproterozoic-Cambrian passive margin precursor of the Paraguay belt. Our pioneer structural analysis reveals that these rocks experienced progressive deformation (phases D1-D2-D3) and low-grade metamorphism during the Brasiliano Cycle (540-513 Ma). The crystalline basement was also involved, according to structural data and K-Ar ages in the literature. The paleo-passive margin was thickened during the D1-D2 deformation and was lately shortened (D3) in two orthogonal directions, SE-NW (D3P) and SW-NE (D3T). Developed co-axially and verging to NW, D1-D2-D3P structures record the closure of the basin precursor of the Paraguay belt, whereas D3T structures seem related to the inversion of the aulacogen. Although the tectonic transport to NW, as observed in the Corumbá area, matches the reported transport of Paraguay belt's supracrustal rocks towards the eastern margin of the Rio Apa block and Araguaia belt's rocks towards the Amazon craton, the transport direction is opposite in other parts of the Paraguay belt. Our comprehensive discussion of these facts brings to light profound regional implications.

  2. Neoproterozoic geodynamic evolution of SW-Gondwana: a southern African perspective

    Science.gov (United States)

    Frimmel, H. E.; Basei, M. S.; Gaucher, C.

    2011-04-01

    Our current understanding of the tectonic history of the principal Pan-African orogenic belts in southwestern Africa, reaching from the West Congo Belt in the north to the Lufilian/Zambezi, Kaoko, Damara, Gariep and finally the Saldania Belt in the south, is briefly summarized. On that basis, possible links with tectono-stratigraphic units and major structures on the eastern side of the Río de la Plata Craton are suggested, and a revised geodynamic model for the amalgamation of SW-Gondwana is proposed. The Río de la Plata and Kalahari Cratons are considered to have become juxtaposed already by the end of the Mesoproterozoic. Early Neoproterozoic rifting led to the fragmentation of the northwestern (in today's coordinates) Kalahari Craton and the splitting off of several small cratonic blocks. The largest of these ex-Kalahari cratonic fragments is probably the Angola Block. Smaller fragments include the Luis Alves and Curitiba microplates in eastern Brazil, several basement inliers within the Damara Belt, and an elongate fragment off the western margin, named Arachania. The main suture between the Kalahari and the Congo-São Francisco Cratons is suspected to be hidden beneath younger cover between the West Congo Belt and the Lufilian/Zambezi Belts and probably continues westwards via the Cabo Frío Terrane into the Goiás magmatic arc along the Brasilia Belt. Many of the rift grabens that separated the various former Kalahari cratonic fragments did not evolve into oceanic basins, such as the Northern Nosib Rift in the Damara Belt and the Gariep rift basin. Following latest Cryogenian/early Ediacaran closure of the Brazilides Ocean between the Río de la Plata Craton and the westernmost fragment of the Kalahari Craton, the latter, Arachania, became the locus of a more than 1,000-km-long continental magmatic arc, the Cuchilla Dionisio-Pelotas Arc. A correspondingly long back-arc basin (Marmora Basin) on the eastern flank of that arc is recognized, remnants of which

  3. Geochemistry of metavolcanics from the Neoproterozoic Tuludimtu orogenic belt, western Ethiopia

    Science.gov (United States)

    Tadesse, Gebremedhin; Allen, Alistair

    2004-06-01

    The 200 km wide Tuludimtu Belt of Western Ethiopia is one of a series of N-S trending Neoproterozoic orogenic belts of the East African Orogenic Province in southeastern Sudan and western and southern Ethiopia. The Tuludimtu Belt consists of deformed greenschist facies metasediments and metavolcanics, flanked to the east and west by gneissic terranes, all of which are invaded by pre-, syn- and post-tectonic intrusives ranging from ultramafic to felsic in composition. The Tuludimtu Belt has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka Domains. On the basis of lithological associations, the three domains in the core of the belt, the Kemashi, Dengi and Sirkole Domains, are respectively interpreted to represent an ophiolitic terrane of oceanic crustal origin, a volcanic arc, and a fold-thrust terrane composed of interleaved thrust sheets of gneissic basement and cover strata. The Didesa and Daka Domains are composed of moderate- to high-grade gneisses, possibly representing the basement forelands to the belt. Major and trace element geochemistry for metavolcanics of predominantly basaltic and andesitic composition from the Kemashi, Dengi and Didesa Domains, are presented, and a preliminary analysis of the data undertaken. Two suites of metavolcanics are clearly differentiated by the discrimination diagrams. The samples from all three domains are predominantly tholeiitic, subalkaline basalts and andesites. Bivariate plots reveal weak negative correlations of SiO 2 and Al 2O 3 with MgO, and a positive correlation of CaO with MgO, indicating that magmas evolved by fractionation of clinopyroxene, orthopyroxene and olivine from the parent liquids. Trace element spider diagrams show a tight coherence of patterns for the Dengi and Sirkole samples, suggestive that alteration did not accompany metamorphic processes to any great extent, and a slight depletion of HFS elements possibly due to fractionation

  4. High-pressure thermal aureoles around two Neoproterozoic synorogenic magmatic epidote-bearing granitoids, Northeastern Brazil

    Science.gov (United States)

    Caby, Renaud; Sial, Alcides N.; Ferreira, Valderez P.

    2009-02-01

    Unusual high-pressure inner thermal aureoles are described from the Minador and Angico Torto epidote-bearing tonalitic plutons that emplaced into greenschist-facies metasedimentary rocks of the Neoproterozoic Cachoeirinha-Salgueiro belt, northeastern Brazil. The foliated pelitic hornfelses display the mineral assemblage garnet, kyanite, staurolite, muscovite, biotite, plagioclase ± quartz. Rare fibrolite is only found very close to the contacts. Hornfelses display steep mineral lineations and steeply-dipping foliations concordant with magmatic contacts. Leucocratic veinlets containing quartz, oligoclase, garnet, kyanite, staurolite, rutile and ilmenite suggest that limited melting conditions were reached very close to magmatic contacts ( T ⩾ 650 °C, P around 8 kbar). These high-pressure hornfelses form a few meters thick, rigid envelopes around the two plutons. Contrary to known examples of kyanite-bearing hornfelses that recorded high-temperature decompression, the nearly isobaric cooling down to ca. 450 °C is constrained by 3.20-3.30 Si contents of retrogressive phengites from both inner hornfelses and ductilely-deformed tonalite at the pluton margins. Isograds and bathograds are, therefore, apparently telescoped due to HP/LT shearing, possibly caused by subsequent differential vertical movements affecting these two solidified plutons. The unusual depth of emplacement of these syn-kinematic calc-alkaline plutons is explained by a tentative geodynamic model involving a pre-620 Ma-subduction setting. Resumen Las aureolas internas que rodean dos plutones tonalíticos emplazados dentro de rocas cajas en facies esquistos verdes del Cinturón-plegado Cachoeirinha-Salgueiro al noreste de Brasil, contienen hornfelses pelíticos foliados con granate, kyanita, estaurolita, muscovita, biotita, plagioclasa ± cuarzo. Fibrolita es rara ó es encontrada solamente cerca de las zonas de contacto. Los hornfelses desarrollaron foliaciones concordantes con buzamiento fuerte

  5. Deep inside a neoproterozoic intra-oceanic arc: growth, differentiation and exhumation of the Amalaoulaou complex (Gourma, Mali)

    Science.gov (United States)

    Berger, Julien; Caby, Renaud; Liégeois, Jean-Paul; Mercier, Jean-Claude C.; Demaiffe, Daniel

    2011-10-01

    We show here that the Amalaoulaou complex, in the Pan-African belt of West Africa (Gourma, Mali), corresponds to the lower and middle sections of a Neoproterozoic intra-oceanic arc. This complex records a 90-130-Ma-long evolution of magmatic inputs and differentiation above a subducting oceanic slab. Early c. 793 Ma-old metagabbros crystallised at lower crustal or uppermost mantle depths (25-30 km) and have geochemical characteristic of high-alumina basalts extracted from a depleted mantle source slightly enriched by slab-derived sedimentary components ((La/Sm)N West African craton belong to the life and closure of the Pharusian Ocean that eventually led to the formation of the Greater Gondwana supercontinent, a similar story having occurred on the other side of the Sahara with the Mozambique Ocean.

  6. Macroalgal holdfasts and their interaction with environments from the Neoproterozoic Doushantuo Formation in Guizhou,South China

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Numerous macro-organisms of the Doushantuo macrobiota, which were found in the black carbonaceous mudstone of the upper Neoproterozoic Ediacraan Doushan-tuo Formation in Jiangkou County, Guizhou Province, China, are considered to live on sea floor by their holdfasts. The appearance and preserved forms of the macroalgal holdfasts may provide some data to the study of the living and buried environments ofmacrobiota. They lived in the lower energy and clear environment, and fixed on a soupground with rich water (about 79% water). Currents, possibly ocean currents, could pull out the macroalgal holdfasts from the soupground and break off the macroalgal foliations. After such events, the corpses of macro-organisms would be covered in a reduced environment by the deposits. Afterwards, a new community, including regenerating and undying macro-organisms, lived continuously on a new deposit.

  7. 'Zipper-rift': a tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma

    Science.gov (United States)

    Eyles, Nicholas; Januszczak, Nicole

    2004-03-01

    The 'Snowball Earth' model of Hoffman et al. [Science 281 (1998) 1342] has stimulated renewed interest in the causes of glaciation in Earth history and the sedimentary, stratigraphic and geochemical response. The model invokes catastrophic global Neoproterozoic refrigerations when oceans froze, ice sheets covered the tropics and global temperatures plummeted to -50 °C. Each event is argued to be recorded by tillites and have lasted up to 10 million years. Planetary biological activity was arrested only to resume in the aftermath of abrupt and brutal volcanically generated 'greenhouse' deglaciations when global temperatures reached +50 °C. The 'Cambrian explosion' is regarded by some as a consequence of post-Snowball glacioeustatic flooding of continental shelves. We shall show by a systematic review of the model that it is based on many long standing assumptions of the character and origin of the Neoproterozoic glacial record, in particular, 'tillites', that are no longer valid. This paper focusses on the sedimentological and stratigraphic evidence for glaciation in the light of current knowledge of glacial depositional systems. By integrating this analysis with recent understanding of the tectonic setting of Neoproterozoic sedimentary basins, an alternative 'Zipper-rift' hypothesis for Neoproterozoic glaciations is developed. The 'Zipper-rift' model emphasises the strong linkage between the first-order reorganisation of the Earth's surface created by diachronous rifting of the supercontinent Rodinia, the climatic effects of uplifted rift flanks and the resulting sedimentary record deposited in newly formed rift basins. Initial fragmentation of Rodinia commenced after about 750 Ma (when the paleo-Pacific Ocean started to form along the western margin of Laurentia) and culminated sometime after 610 Ma (with the opening of the paleo-Atlantic Ocean on the eastern margin of Laurentia). Breakup is recorded by well-defined 'tectonostratigraphic' successions that were

  8. Detrital zircon geochronology of some neoproterozoic to triassic rocks in interior alaska

    Science.gov (United States)

    Bradley, D.C.; McClelland, W.C.; Wooden, J.L.; Till, A.B.; Roeske, S.M.; Miller, M.L.; Karl, S.M.; Abbott, J.G.

    2007-01-01

    We report 777 U-Pb SHRIMP detrital zircon ages from thirteen sandstones and metasandstones in interior Alaska. About sixty grains per sample were analyzed; typically, half to three-fourths of these were concordant within ?? 10%. Farewell terrane. Two quartzites were collected from Ruby quadrangle and a third from Taylor Mountains quadrangle. All three are interpreted to represent a low stratigraphic level in the Nixon Fork platform succession; the samples from Ruby quadrangle are probably late Neoproterozoic, and the sample from Taylor Mountains quadrangle is probably Cambrian in age. The youngest detrital zircon in any of the three is 851 Ma. The two Ruby quadrangle samples area almost identical: one has a major age cluster at 1980-2087 and minor age clusters at 944-974 and 1366-1383 Ma; the other has a major age cluster at 1993-2095 Ma and minor age clusters at 912-946 and 1366-1395 Ma. The Taylor Mountains sample shows one dominant peak at 1914-2057 Ma. Notably absent are zircons in the range 1800-1900 Ma, which are typical of North American sources. The detrital zircon populations are consistent with paleontological evidence for a peri- Siberian position of the Farewell terrane during the early Paleozoic. Mystic subterrane of the Farewell terrane. Three graywackes from flysch of the Mystic subterrane, Talkeetna quadrangle, were sampled with the expectation that all three were Pennsylvanian. Asample from Pingston Creek is Triassic (as revealed by an interbedded ash dated at ca. 223 Ma) and is dominated by age clusters of 341-359 and 1804-1866 Ma, both consistent with a sediment source in the Yukon-Tanana terrane. Minor age clusters at 848-869 and 1992-2018 Ma could have been sourced in the older part of the Farewell terrane. Still other minor age clusters at 432-461, 620-657, 1509-1536, and 1627-1653 Ma are not readily linked to sources that are now nearby. Asample from Surprise Glacier is mid-Mississippian or younger. Adominant age cluster at 1855-1883 and a

  9. Stratigraphic architecture of the Neoproterozoic glacial rocks in the "Xiang-Qian-Gui" region of the central Yangtze Block, South China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Qirui; CHU Xuelei; Heinrich BAHLBURG; FENG Lianjun; Nicole DOBRZINSKI; ZHANG Tonggang

    2003-01-01

    The Yangtze Block in South China is one of the important regions where Neoproterozoic glacial rocks are well developed and studied. However, the classification and correlation of the Neoproterozoic glacial sequences in the central Yangtze Block still remain controversial among Chinese geologists. The original Sinian sections around the Yangtze Gorges Region became an official standard for classification and correlation since the 1950s. Subsequent regional geologic studies, however, resulted in different classification and correlation, because of its incompleteness. We select one of the complete sections in the bordering areas of Xiang (Hunan), Qian (Guizhou) and Gui (Guangxi), as a standard of classification and correlation. The temporal and spatial distribution, i.e. the stratigraphic architecture, of the glacial rocks in the central Yangtze Block is suggested. Our results indicate that the glacial sequence on the Yangtze Block was deposited during the Nantuo Ice-age, the Datangpo Interglacial-age and Jiangkou Ice-age, in descending order.

  10. The Apparent Polar Wander Path of the Tarim block (NW China) since the Neoproterozoic and its implications for a long-term Tarim-Australia connection

    OpenAIRE

    Zhao, Pan; Yan CHEN; Zhan, Sheng; Xu, Bei; Faure, Michel

    2014-01-01

    In order to better understand the kinematic history of the Tarim block after the breakup of the Rodinia supercontinent, paleomagnetic studies have been carried out on Neoproterozoic strata from the Quruqtagh and Yecheng areas in the northeastern and southwestern Tarim block (NW China), respectively. Totally, 547 sedimentary and volcanic samples were collected from 64 sites. Magnetic mineralogical studies show that titanium-poor magnetite and hematite are the principal magnetic remanent carrie...

  11. Tectonic model for development of the Byrd Glacier discontinuity and surrounding regions of the Transantarctic Mountains during Neoproterozoic-Early Paleozoic

    OpenAIRE

    Stump, E.; Gootee, B.; Talarico, F.

    2006-01-01

    The Byrd Glacier discontinuity us a major boundary crossing the Ross Orogen, with crystalline rocks to the north and primarily sedimentary rocks to the south. Most models for the tectonic development of the Ross Orogen in the central Transantarctic Mountains consits of two-dimensional transects across the belt, but do not adress the major longitudinal contrast at Byrd Glacier. This paper presents a tectonic model centering on the Byrd Glacier discontinuity. Rifting in the Neoproterozoic produ...

  12. Paleomagnetic study on the Neoproterozoic mafic dikes and Early Permian volcanic-sedimentary rocks from NW Yili Block (NW China): Implications for post-orogenic kinematic evolution of the SW CAOB

    Science.gov (United States)

    Zhu, Xin; Wang, Bo; Chen, Yan; Liu, Hongsheng; Shu, Liangshu; Faure, Michel

    2016-04-01

    As one of the largest accretionary orogens of the world, the Central Asian Orogenic Belt (CAOB) has been the focus of geological studies in the last decades. However, several key points are still in hot debate, such as the formation process of the Paleo-Asian Ocean, the intracontinental movements among constituent blocks of the CAOB. In order to better understand these questions, we conducted a paleomagnetic study on the Neoproterozoic (ca. 780 Ma) mafic dikes and Early Permian (ca. 268 Ma) volcanic and sedimentary rocks from NW of the Yili Block (NW China). Ten sites have been sampled from three mafic dikes. The thickness of dikes varies from 10 to 40 meters. At about 15 km west of the mafic dikes, 4 sites were drilled in the Lower Permian basalts and limestones that unconformably overlay the Neoproterozoic mafic dikes. Mineralogical investigations show the titanium-poor magnetite as the major magnetic remanence carrier. Stepwise alternating field (AF) and thermal demagnetizations reveal two-component magnetizations. The low temperature (coercivity) component shows a viscous and unstable magnetic remanence, whereas the high temperature (coercivity) component stably decays toward to the origin and is considered as the characteristic remanent magnetization (ChRM). All ChRMs isolated from both the mafic dikes and volcanic-sedimentary samples exclusively show a reversed magnetic polarity. Based on the following 3 arguments, we suggest that the Neoprotozoic mafic dikes have been remagnetized in the Early Permian. 1. International reference of magnetostratigraphic polarity shows a dominance of the normal polarity for the Neoproterozoic period and a superchron of the reversed polarity for the late Carboniferous-Permian; 2. Two groups of sampling show coherent paleomagnetic poles with an undistinguishable angular difference; and 3. The widespread Early Permian magmatism in the sampling area could be the cause of the remagnetization. Consequently, an Early Permian

  13. Petrogenesis and LA-ICP-MS zircon U-Pb dating of Late Neoproterozoic granitic gneisses in western Qilian Mountain%祁连山西段新元古代晚期花岗质片麻岩成因及LA-ICP-MS锆石U-Pb定年

    Institute of Scientific and Technical Information of China (English)

    李猛; 王超; 李荣社; 彭岩

    2015-01-01

    Neoproterozoic granitic gneisses from the Diaodaban area of the western Qilian Mountain outcrop in two-mica gneiss of the Beidahei Group. The granitic gneisses are mainly alkaline and peraluminous, with A/CNK values of 1.04~1.12. Their low Rb values and high Sr and Ba values as well as K/Rb ratios of 179~225 show that the rocks are not highly fractionated granite;nev⁃ertheless, the rocks have obvious negative Eu anomaly (Eu/Eu∗=0.25~0.35), indicating that the magma experienced weak fraction⁃ation crystallization. The diagram of (Al2O3+TFeO+MgO+TiO2)-Al2O3/(TFeO+MgO+TiO2) suggests that the protolith of the rocks was sourced from graywacke or mafic-intermediate igneous rocks. Samples are enriched in incompatible elements and have geochemical characteristics of the intraplate granite in Y-Nb and (Y+Nb)-Rb diagrams. LA-ICP-MS zircon U-Pb dating of the granitic rocks yielded a weighted mean age of 736 ± 5Ma, suggesting that there is a magmatic record of 750~730Ma in the Qilian Mountain, probably resulting from intraplate extension in the late Neoproterozoic. The Neoproterozoic magmatic activities in the Qilian Mountain recorded a long-term evolution history from early Neoproterozoic convergence through Late Neoproterozoic ex⁃tension to breakup.%祁连山西段吊大坂新元古代花岗质片麻岩出露于北大河岩群二云母片麻岩中。地球化学特征显示,吊大坂新元古代花岗质片麻岩主要为碱性、弱过铝质花岗岩(A/CNK=1.04~1.12)。岩石主体Rb含量较低,Sr和Ba含量高,K/Rb值介于179~225之间,说明吊大坂新元古代花岗质片麻岩不是高分异花岗岩,但明显的负Eu异常(Eu/Eu∗=0.25~0.35),说明该岩浆经历了弱的分离结晶作用。在(Al2O3+TFeO+MgO+TiO2)-Al2O3/(TFeO+MgO+TiO2)图解中,未经历强烈分异的花岗质岩石样品点落入地壳杂砂岩或中性岩浆岩源区。未经历强烈分异的样品富集强不相容元素,并且在Y-Nb和(Y+Nb)-Rb图解中,主

  14. Vestiges of an Iapetan rift basin in the New Jersey Highlands: Implfications for the Neoproterozoic Laurentian margin

    Science.gov (United States)

    Gates, A.E.; Volkert, R.A.

    2004-01-01

    Thin, discontinuous remnants of Neoproterozoic intracratonic rift-basin deposits of the Chestnut Hill Formation occur in the western New Jersey Highlands. These deposits form an important link between well-documented Iapetan rift-basins in both the northern and southern Appalachians. The close spatial relations of Chestnut Hill rocks to Paleozoic sedimentary rocks open the possibility that additional Iapetan rift-basins could be concealed beneath the rocks of the Valley and Ridge Province to the west indicating a much broader zone of rifting than has been previously proposed. The Chestnut Hill Formation is intermittently exposed along a 100 km-long band that extends northeast from Pennsylvania nearly to New York State. The lower part of the Chestnut Hill Formation is composed of interbedded lithic pebble- to boulder-conglomerate and feldspathic sandstone grading upward into interbedded phyllite, feldspathic and quartz sandstone, local paleosaprolite, quartz-pebble conglomerate, thin limestone lenses, volcanic, and volcaniclasic rocks, abundant bedded ironstone (hematite ore), and ultimately into diamictites that are interpreted as possible tilloids and containing rounded intra and extrabasinal clasts of the other lithologies. Extensive soft-sediment deformation, cross bedding, and clastic dikes are common in all but the lowest and upper facies. Banded hematite layers occur preferentially in fine-grained tuffs and tuffaceous sediments, but hematitization has affected most lithologies. Volcanic rocks consist of altered rhyolitic tuffs and lapilli tuffs that are interbedded with sediments. The Chestnut Hill Formation is interpreted to have been deposited in early alluvial, and later a complex of fluvial, lacustrine and deltaic environments. Provenance studies based upon petrographic and geochemical analysis of clastic rocks indicate that the sediments are predominantly immature and reflect derivation from local uplifted felsic basement sources in a rifted

  15. Late Paleoproterozoic-Neoproterozoic multi-rifting events in the North China Craton and their geological significance: A study advance and review

    Science.gov (United States)

    Zhai, Mingguo; Hu, Bo; Zhao, Taiping; Peng, Peng; Meng, Qingren

    2015-11-01

    An important Paleoproterozoic mobile belt event took place in the North China Craton (NCC), termed the Hutuo Movement. This event has been interpreted to represent cratonic reworking characterized by rifting-subduction-collision processes. The NCC then evolved into a stable platform or para-platform tectonic setting in Earth's middle age period more than ~ 1.0 Ga. Thick Late Paleoproterozoic-Neoproterozoic sedimentary sequences were extensively deposited on the early metamorphic basement. The major sedimentary basins include the Xiong'er aulacogen system in the south-central NCC, the Yan-Liao aulacogen system in the north-central NCC, the Northern marginal rift system in the northwestern NCC and the Eastern marginal rift system in the eastern NCC. The following four stages of magmatic activity are recognized in the Late Paleoproterozoic to Neoproterozoic interval: (1) ~ 1800 to 1780 Ma Xiong'er igneous province (XIP), (2) ~ 1720 to 1620 Ma anorogenic magmatic association, (3) ~ 1350 to 1320 Ma diabase sill swarms, and (4) ~ 900 Ma mafic dyke swarms. These four magmatic events suggest that the NCC was situated in an intra-plate setting for a long time from ~ 1.8 Ga to ~ 0.7 Ga or even younger, and the magmatic events were associated with multi-stage rifting activities. We document that the NCC was in a long-term extensional tectonic setting during Late Paleoproterozoic-Neoproterozoic era. The main ore deposits in this period are magmatic type iron deposits related to anorthosite-gabbro bodies, REE-Nb-Fe and Pb-Zn-Cu-Fe deposits related to Mesoproterozoic-Neoproterozoic rifts. Orogenic metal deposits are absent. There is no evidence indicating that the Grenville or other orogenic events affected the NCC. The reason for the absence of Grenvillian aged events in the NCC is probably because it was far from the edge of the Nuna supercontinent, if such a supercontinent did exist. There is another possibility that the Earth's middle age represented a particular tectonic

  16. 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

  17. Pedogenic calcretes within fracture systems and beddings in Neoproterozoic limestones of the Irecê Basin, northeastern Brazil

    Science.gov (United States)

    Borges, S. V. F.; Balsamo, F.; Vieira, M. M.; Iacumin, P.; Srivastava, N. K.; Storti, F.; Bezerra, F. H. R.

    2016-07-01

    Calcretes or caliches are continental limestones developed by surficial weathering process that takes place mostly in arid and semi-arid regions. In the Irecê Basin, northeastern Brazil, in addition to the regular occurrence of pedogenic calcretes, a peculiar type of structurally controlled calcretes occurs on Neoproterozoic limestones. These peculiar calcretes developed near the surface and occur (1) between layers, (2) inside fractures and (3) within major thrust faults. Fieldwork on selected outcrops was integrated with petrographic, mineralogic, geochemical, density and mercury intrusion porosity analyses to constrain the environment of formation and their petrophysical properties. The results revealed that this type of calcrete is the product of multiepisodic events of dissolution and precipitation occurring during the wet and dry seasons in the region along fractures and beddings. Based on the petrophysical results, we suggest that these calcretes may have an important role in the migration of fluids through the impermeable host carbonate rock and that they act as a conduit for fluid flow, as revealed by their high porosity (mean value = 26%) and remarkable pore connectivity.

  18. Evidence for Palaeozoic magmatism recorded in the Late Neoproterozoic Marlborough ophiolite, New England Fold Belt, central Queensland

    International Nuclear Information System (INIS)

    The ultramafic-mafic complex in the Marlborough terrane of the northern New England Fold Belt is dominated by members of a Neoproterozoic (ca 560 Ma) ophiolite (V1). The ophiolite has been intruded by the products of three Palaeozoic tectonomagmatic episodes (V2, V3 and V4). The V2 magmatic episode is represented by tholeiitic and calc-alkaline basalts and gabbros of island-arc affinities. Sm/Nd isotopes give a whole-rock isochron age of 380 ± 19 Ma (2σ) to this episode, some 180 million years younger than the V1 ophiolitic rocks. The V3 magmatic episode includes tholeiitic and alkali basalts with enriched geochemical signatures characteristic of intraplate volcanism. A whole-rock Sm/Nd isochron age of 293 ± 35 Ma is obtained for this event. A fourth magmatic event (V4) is represented by basaltic andesites and siliceous intrusives with geochemical features similar to modern adakites. This event has its type locality in the Percy Isles. These data provide tectonic and geochronological constraints for the previously enigmatic Marlborough terrane and as such contribute to the ever-evolving understanding of New England Fold Belt development. Copyright (1999) Geological Society of Australia

  19. 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.

  20. Newly discovered Cryogenenian Diamicties and Cap-carbonate in the Neoproterozoic successions from the Tarim Craton, NW China

    Science.gov (United States)

    Wen, B.; Evans, D. A.; Li, Y.; Wang, Z.

    2014-12-01

    Neoproterozoic cap carbonates associated with glacial deposits have been the unique lithofacies for establishing regional or interregional correlations and understanding the environmental conditions in the postglacial oceans. Here, we report a newly discovered Cryogenian tillite (in Aksu section), and a diamictite and cap-carbonate couplet (DCC) (in Wushi section) from the northwestern margin of Tarim Craton, NW China. The Aksu tillite is represented by reddish conglomerates, comprising angular to subrounded, poorly sorted clasts with diameters of 5-30 cm. Notably, the glaciogenic features, such as striations on clasts can be observed. The DCC member in Wushi section, sits atop an angular unconformity, and represents the end-Cryogenian strata according to the regional sequence stratigraphy (at the base of the Sugetbrak Fm, redbeds with interbedded 615-Ma mafic magmatism). The upper cap-carbonate of the DCC member consists of a leaching technique was employed to extract the information about the chemical compositions of post-glacial ocean water. The δ13CPDB results consistently show moderate negative values of ca. -2.5‰. The minimum 87Sr/86Sr ratio from the leachates of each sample defines the contemporaneous seawater value, with the Mg/Ca ratio close to 1 (0.8). The 87Sr/86Sr ratios of all representative samples vary from 0.70680 to 0.70855. All the chemostratigraphic and cap-dolomite characteristics may suggest that our newly discovered Aksu diamictite and the Wushi DCC member represent the ending of the Cryogenian Marinoan glaciation.

  1. Isotopic evolution of the terminal Neoproterozoic and early Cambrian carbon cycle on the northern Yangtze Platform, South China

    Institute of Scientific and Technical Information of China (English)

    GUO Qingjun; LIU Congqiang; Harald STRAUSS; Tatiana GOLDBERG

    2003-01-01

    Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform, Sichuan Province of China. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian Guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow-water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between -35.8‰ and -30.1‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between -3.5‰ and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle, specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.

  2. Volcanosedimentary Basins in the Arabian-Nubian Shield: Markers of Repeated Exhumation and Denudation in a Neoproterozoic Accretionary Orogen

    Directory of Open Access Journals (Sweden)

    Victoria Pease

    2013-07-01

    Full Text Available The Arabian-Nubian Shield (ANS includes Middle Cryogenian-Ediacaran (790–560 Ma sedimentary and volcanic terrestrial and shallow-marine successions unconformable on juvenile Cryogenian crust. The oldest were deposited after 780–760 Ma shearing and suturing in the central ANS. Middle Cryogenian basins are associated with ~700 Ma suturing in the northern ANS. Late Cryogenian basins overlapped with and followed 680–640 Ma Nabitah orogenesis in the eastern ANS. Ediacaran successions are found in pull-apart and other types of basins formed in a transpressive setting associated with E-W shortening, NW-trending shearing, and northerly extension during final amalgamation of the ANS. Erosion surfaces truncating metamorphosed arc rocks at the base of these successions are evidence of periodic exhumation and erosion of the evolving ANS crust. The basins are evidence of subsequent subsidence to the base level of alluvial systems or below sea level. Mountains were dissected by valley systems, yet relief was locally low enough to allow for seaways connected to the surrounding Mozambique Ocean. The volcanosedimentary basins of the ANS are excellently exposed and preserved, and form a world-class natural laboratory for testing concepts about crustal growth during the Neoproterozoic and for the acquisition of data to calibrate chemical and isotopic changes, at a time in geologic history that included some of the most important, rapid, and enigmatic changes to Earth’s environment and biota.

  3. Depositional tracts and stratigraphic architecture of the Itajaí Basin sedimentary sucessions (Neoproterozoic, northeastern Santa Catarina, Brazil

    Directory of Open Access Journals (Sweden)

    Michel Silva Costa

    2015-06-01

    Full Text Available Neoproterozoic sedimentary successions of the Itajaí Basin show depositional trends and a stratigraphic framework characteristics of foreland basin system. The sedimentary environments have developed in basin conditions ranging from deep marine context, transitional shallow marine, to continental. Stratigraphic architecture comprises three depositional tracts (DT: DTI - submarine fans system that records the initial basin sedimentation and involves frontal and distal turbiditic deposits; DTII - transitional to shallow marine depositional system that represents the efective infill fase of basin, and includes deltaic succession with braided channels dominated plain; and DTIII - fluvial braided and alluvial fan depositional system that comprises the final stage of basin sedimentation. Arkoses and greywacke of the DTI present paleocurrent unimodals patterns and general trend to south-southeast, suggesting source area from Santa Catarina Granulitic Complex. The sandstones and conglomerates of DTII and DTIII have opposite paleocurrent pattern, indicating source area from both Metamorphic Brusque Complex and Florianópolis Batolith. Integration of paleoenvironmental and stratigraphic data, with previous information (U-Pb in detrital zircon, allowed a consistent interpretation on the sedimentary evolution and detrital sources of the basin and represent a progress on the discussions on the knowledge of the Itajaí Basin and its significance in the evolutionary context of the Dom Feliciano Belt.

  4. The importance of XRD analysis in provenance and palaeoenvironmental studies of the Piedras de Afilar Formation, Neoproterozoic of Uruguay

    Science.gov (United States)

    Pamoukaghlian, K.; Poiré, D. G.; Gaucher, C.; Uriz, N.; Cingolani, C.; Frigeiro, P.

    2009-04-01

    The Piedras de Afilar Formation crops out in the southeast part of Uruguay, forming part of the Tandilia Terrane (sensu Bossi et al. 2005). Pamoukaghlian et al. (2006) and Gaucher et al. (2008) have published δ13C, δ18O and U/Pb SHRIMP results, which indicate a Neoproterozoic age for this formation. The palaeoenvironment has been defined as a shallow marine platform based on the presence of interference ripples, hummocky and mega-hummocky cross-stratification. X-ray diffraction (XRD) analyses help to better constrain the palaeoenvironment: the presence of chlorite/smectite found in black shales, suggest a reducing environment, and abundant illite indicates a cold to temperate climate. Provenance studies have been undertaken that utilise a combination of detailed palaeocurrent measurements, petrographic descriptions, XRD analyses, and geochemical isotopic analyses, including U/Pb SHRIMP determinations. Mineral compositional diagrams for sandstones suggest a stable cratonic provenance. Palaeocurrents are mainly from the NNE, indicating a provenance from the cratonic areas of the Tandilia Terrane. The illite crystal index indicates diagenetic to low-metamorphic conditions for the sequence; this is important to confirm that the identified minerals are authigenic. Clay minerals identified by XRD analysis of sandstones from the siliciclastic member are illite (80 - 90%), kaolinite (5 - 10%), and chlorite (5 - 10%). This is consistent with a provenance from the cratonic areas (quartz-feldspar dominated rock types). Isotopic analyses have been undertaken to provide better constraints on the tectonic setting. U/Pb SHRIMP ages for the youngest zircons are 990 Ma (Gaucher et al. 2008), and the basal granite (Granito de la Paz) is 2056 ± 11 Ma (Hartmann et al. 2001), suggesting a provenance from the Archaean basement for the Piedras de Afilar Formation, like its counterparts in the Rio de la Plata Craton. References Bossi, J., Piñeyro, D., Cingolani, C. (2005). El l

  5. Mid-Neoproterozoic (ca. 830-800 Ma) metamorphic P-T paths link Tarim to the circum-Rodinia subduction-accretion system

    Science.gov (United States)

    Ge, Rongfeng; Zhu, Wenbin; Wilde, Simon A.

    2016-06-01

    Long-lived exterior accretionary orogeny shapes tectonothermal evolution of the peripheral building blocks of supercontinents and leads to considerable crustal growth. However, such accretionary orogeny has only been locally recognized for the Rodinia supercontinent. Here a suite of newly discovered mid-Neoproterozoic high-grade metamorphic rocks in the northern Tarim Craton, NW China, are used to test the exterior accretion hypothesis for Rodinia. These rocks occur as dark-colored mafic and calc-silicate boudins in impure marbles and mica schists. Geochemical data suggest a protolith of arc-related basalts metasomatized by Ca-rich fluids. Mineral assemblages, phase diagram modeling, and mineral compositions for a garnet pyroxenite and a garnet clinopyroxene gneiss reveal upper amphibolite to high-pressure granulite facies peak metamorphism (660-700°C, 11-12 kbar) following a counterclockwise P-T path, which is characterized by prograde burial and heating, followed by near-isothermal burial and retrograde exhumation and cooling. This P-T path is interpreted to have recorded crustal thickening of an earlier magmatic arc transformed to a fore arc by subduction erosion and subsequent burial along bent isotherms near the subduction channel. All studied samples record ca. 830-800 Ma metamorphic zircon U-Pb ages, which probably date the early exhumation and cooling according to Ti-in-zircon temperatures, zircon rare earth element patterns, and Hf isotopes. This is the first mid-Neoproterozoic P-T-t path in Tarim, and it provides metamorphic evidence for a mid-Neoproterozoic advancing-type accretionary orogeny, which is coeval with the initial breakup events of Rodinia and thus links Tarim to the circum-Rodinia accretion system, supporting the peripheral subduction model.

  6. Zircon (U-Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

    Science.gov (United States)

    Powell, Jeremy; Schneider, David; Stockli, Daniel; Fallas, Karen

    2016-03-01

    Sedimentary strata of the Neoproterozoic Mackenzie Mountains Supergroup (MMSG) and Windermere Supergroup (WSG) occupy the cores of anticlines in the Mackenzie Mountains of the Canadian Cordilleran Foreland Belt. Stratigraphic and structural evidence suggest that these rocks have undergone several episodes of burial and unroofing relatively intact. We report single-grain detrital muscovite 40Ar/39Ar and zircon (U-Th)/He (ZHe) data from a suite of samples across the fold-thrust belt and the Neoproterozoic stratigraphic record. The strata have not reached high enough temperatures to reset the muscovite 40Ar/39Ar system, and instead our detrital muscovite data refine Tonian-Cryogenian depositional ages. Single-crystal ZHe dates range from 432 ± 35 to 46 ± 4 Ma, indicating that MMSG and WSG strata have not been heated sufficiently to fully reset the ZHe system. These factors make the Neoproterozoic strata an attractive natural laboratory to test the utility of the zircon radiation damage and annealing model on the quantification of thermal histories from detrital zircon populations that have accumulated radiation damage over long geologic timescales. Thermal modeling reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo-Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75-67 Ma in the southwest and 60-55 Ma at the deformation front. Ultimately, relationships between radiation damage and helium diffusion kinetics in zircon explain substantial ZHe date dispersion and elucidate the temperature-time history of the northern Canadian Cordillera.

  7. Iso-Naakkima, a circular structure filled with Neoproterozoic sediments, Pieksämäki, southeastern Finland

    Directory of Open Access Journals (Sweden)

    Elo, S.

    1993-06-01

    Full Text Available A circular Bouguer gravity anomaly with a minimum of -4.0 mGal and halfamplitude width of 2 km was recognized at Lake Iso-Naakkima (62°11'N, 27°09'E, southeastern Finland. The gravity low is associated with subdued aeromagnetic signature and notable airborne and ground electromagnetic anomalies that indicate low bedrock resistivity. The drilling record beneath the recent (Quaternary glacial sediments, 25-40 m thick, reveals a 100 m thick sequence of unmetamorphosed shale, siltstone, quartz sandstone, kaolinitic clay and conglomeratic sandstone that rest on a weathered mica gneiss basement. The upward fining sequence is characterized by red colour, high kaolinite content, and tilted, distorted and brecciated beds. According to the geophysical modelling the diameter of the whole basin is 3 km and that of the sedimentary rocks 2 km, and the depth is 160 m. Shock lamellas in quartz clasts of the basal conglomeratic sandstone, almost omnipresent kink banding in micas of the rocks beneath the basin floor and the occurrence of polymictic dike breccia in the underlying mica gneiss suggest shock metamorphism. It was concluded that the basin originated by a meteorite impact. However, the impact-generated rocks were subsequently eroded before the sedimentation and only minor marks of shock metamorphism were preserved. Lateritic weathering took place prior to deposition of the sediments. Quartz sandstone and siltstone are interpreted as fluvial deposits and the thinly laminated shales as transgressi ve lacustrine or lagoonal deposits. The microfossil assemblage in the shale includes sphaeromorphs of acritarchs from Late Riphean (Neoproterozoic. Postdepositional subsidence of the Iso-Naakkima basin, shown by tilted sediments, preserved the sequence from further erosion.

  8. Superposed folding and associated fracturing influence hypogene karst development in Neoproterozoic carbonates, São Francisco Craton, Brazil

    Science.gov (United States)

    Ennes-Silva, Renata A.; Bezerra, Francisco H. R.; Nogueira, Francisco C. C.; Balsamo, Fabrizio; Klimchouk, Alexander; Cazarin, Caroline L.; Auler, Augusto S.

    2016-01-01

    Porosity and permeability along fractured zones in carbonates could be significantly enhanced by ascending fluid flow, resulting in hypogene karst development. This work presents a detailed structural analysis of the longest cave system in South America to investigate the relationship between patterns of karst conduits and regional deformation. Our study area encompasses the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves, which are ca. 107 km and 34 km long, respectively. This cave system occurs in Neoproterozoic carbonates of the Salitre Formation in the northern part of the São Francisco Craton, Brazil. The fold belts that are around and at the craton edges were deformed in a compressive setting during the Brasiliano orogeny between 750 and 540 Ma. Based on the integrated analysis of the folds and brittle deformation in the caves and in outcrops of the surrounding region, we show the following: (1) The caves occur in a tectonic transpressive corridor along a regional thrust belt; (2) major cave passages, at the middle storey of the system, considering both length and frequency, developed laterally along mainly (a) NE-SW to E-W and (b) N to S oriented anticline hinges; (3) conduits were formed by dissolutional enlargement of subvertical joints, which present a high concentration along anticline hinges due to folding of competent grainstone layers; (4) the first folding event F1 was previously documented in the region and corresponds with NW-SE- to N-S-trending compression, whereas the second event F2, documented for the first time in the present study, is related to E-W compression; and (5) both folding events occurred during the Brasiliano orogeny. We conclude that fluid flow and related dissolution pathways have a close relationship with regional deformation events, thus enhancing our ability to predict karst patterns in layered carbonates.

  9. Mineralogy and geochemistry of the Late Neoproterozoic rare metal granitoids of Gabal El-Ineigi pluton, Northern Arabian-Nubian Shield, Egypt

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Mohamed, Haroun A.; Farahat, Esam S.; Ahmed, Awaad F.

    2016-04-01

    Gabal El-Ineigi granitoid pluton is situated in the Central Eastern Desert of Egypt and is considered as one of the good examples of the fluorite bearing rare metal granites in the Arabian Nubian Shield (ANS). It constitutes a multiphase pluton consists of porphyritic syenogranites (SG) and coarse to medium grained highly evolved alkali-feldspar granites (AFG) intruded into the older granodiorites and metagabbro-diorite rocks. Petrographic features indicate that quartz, K-feldspar (perthite, Or97‑99), plagioclase (albite, An0‑6) and biotite are the major mineral phases of both granitic types with subordinate muscovite that is observed only in the AFG. Columbite, rutile, fluorite, zircon and thorite are the significant accessory minerals in the AFG while, allanite is exclusively encountered in the SG. Mineral chemistry study reveals that Nb-Ta-Ti-bearing oxides [columbite-group minerals (CGM)] and Nb-bearing oxides (ilmenorutile) represent the most common Nb-Ta host in the AFG. The CGM are represented mostly by complex zoned columbite-(Fe) and rarely by yttrocolumbite-(Y), with Mn/(Mn+Fe) ratios ranging from 0.17 to 0.31. Xenomorphic fluorite (F=46-51 wt%) is commonly filling the spaces between the major mineral phases and sometimes host rare metal minerals, e.g. columbite and thorite. Euhedral zoned allanite (Ce-Nd) is the common REE bearing mineral encountered in the SG. Geochemically, Gabal El-Ineigi granitoids are metaluminous (A/CNK= 0.95-0.99) related to post-collosional A2-type granites. The late phase AFG have distinctive geochemical features typical of rare-metal granites. They are highly fractionated calc-alkaline granitoids characterized by high Rb, Nb, Y, U and many HFSE contents, and extremely low Sr and Ba contents (4-35 and 13-18 ppm, respectively). Moreover, their REE patterns show pronounced negative Eu anomalies (Eu/Eu*=0.03 - 0.05) and tetrad effect (TE1,3=1.16 and 1.42), implying extensive fractionation via fluid-rock interaction that

  10. A comparison of the biological,geological events and environmental backgrounds between the Neoproterozoic-Cambrian and Permian-Triassic transitions

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The Neoproterozoic-Cambrian(N-C) and Permian-Triassic(P-T) transitions have been regarded the two most critical transitions in earth history because of the explosive biological radiation in the early Cambrian(the Cambrian Explosion) and the largest mass extinction at the end-Permian.Previous studies suggest that these two critical transitions showed certain comparability in major evolutionary events.In other words,a series of biological,geological,and geochemical events that had happened in the N-C transition occurred repeatedly during the P-T transition.Those events included continental re-configuration related to the deep mantle dynamics,global-scale glaciations,large C-,Sr-,and S-isotope perturbations indicating atmospheric and oceanic changes,abnormal precipitation of carbonates,and associated multiple biological radiations and mass extinctions.The coupling of those events in both N-C and P-T transitions suggests that deep mantle dynamics could be a primary mechanism driving dramatic changes of environment on the earth’s surface,which in turn caused major biological re-organizations.A detailed comparison of those events during the two critical transitions indicates that despite their general comparability,significant differences do exist in magnitude,duration,and frequency.The supercontinent Rodinia began to rift before the Snowball Earth time.By contrast,the supercontinent Pangea entered the dispersal stage after the greatest glaciation from the Late Carboniferous to Cisuralian.Quantitative data and qualitative analyses of different fossil groups show a more profound mass extinction during the N-C transition than at the end-Permian in terms of ecosystem disruption.This is indicated by the disappearance of the whole Ediacaran biota at the N-C boundary.The subsequent appearances of many new complex animals at phylum level in the early Cambrian mark the establishment of a brand new ecosystem.However,the end-Permian mass extinction is manifested mainly by the

  11. Petrological, geochemical and geochronological evidence for a Neoproterozoic ocean basin recorded in the Marlborough terrane of the northern New England Fold Belt

    International Nuclear Information System (INIS)

    Petrological, geochemical and radiogenic isotopic data on ophiolitic-type rocks from the Marlborough terrane, the largest (∼700 km2) ultramafic-mafic rock association in eastern Australia, argue strongly for a sea-floor spreading centre origin. Chromium spinel from partially serpentinised mantle harzburgite record average Cr/(Cr + Al) = 0.4 with associated mafic rocks displaying depleted MORB-like trace-element characteristics. A Sm/Nd isochron defined by whole-rock mafic samples yields a crystallisation age of 562 ± 22 Ma (2σ). These rocks are thus amongst the oldest rocks so far identified in the New England Fold Belt and suggest the presence of a late Neoproterozoic ocean basin to the east of the Tasman Line. The next oldest ultramafic rock association dated from the New England Fold Belt is ca 530 Ma and is interpreted as backarc in origin. These data suggest that the New England Fold Belt may have developed on oceanic crust, following an oceanward migration of the subduction zone at ca 540 Ma as recorded by deformation and metamorphism in the Anakie Inlier. Fragments of late Neoproterozoic oceanic lithosphere were accreted during progressive cratonisation of the east Australian margin. Copyright (1999) Geological Society of Australia

  12. The Jebel Ohier deposit—a newly discovered porphyry copper-gold system in the Neoproterozoic Arabian-Nubian Shield, Red Sea Hills, NE Sudan

    Science.gov (United States)

    Bierlein, F. P.; McKeag, S.; Reynolds, N.; Bargmann, C. J.; Bullen, W.; Murphy, F. C.; Al-Athbah, H.; Brauhart, C.; Potma, W.; Meffre, S.; McKnight, S.

    2016-08-01

    Ongoing exploration in the Red Sea Hills of NE Sudan has led to the identification of a large alteration-mineralization system within a relatively undeformed Neoproterozoic intrusive-extrusive succession centered on Jebel Ohier. The style of mineralization, presence of an extensive stockwork vein network within a zoned potassic-propylitic-argillic-advanced argillic-altered system, a mineralization assemblage comprising magnetite-pyrite-chalcopyrite-bornite (±gold, silver and tellurides), and the recurrence of fertile mafic to intermediate magmatism in a developing convergent plate setting all point to a porphyry copper-gold association, analogous to major porphyry Cu-Au-Mo deposits in Phanerozoic supra-subduction settings such as the SW Pacific. Preliminary U-Pb age dating yielded a maximum constraint of c. 730 Ma for the emplacement of the stockwork system into a significantly older ( c. 800 Ma) volcanic edifice. The mineralization formed prior to regional deformation and accretion of the host terrane to a stable continental margin at by c. 700 Ma, thus ensuring preservation of the deposit. The Jebel Ohier deposit is interpreted as a relatively well-preserved, rare example of a Neoproterozoic porphyry Cu-Au system and the first porphyry Cu-Au deposit to be identified in the Arabian-Nubian Shield.

  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. Le magmatisme basique filonien néoprotérozoïque de la boutonnière de Zenaga, Anti-Atlas central, Maroc: pétrologie, géochimie et signification géodynamiqueNeoproterozoic basic dykes of the Zenaga Inlier, central Anti-Atlas, Morocco: petrology, geochemistry and geodynamic significance

    Science.gov (United States)

    Hafid, A.; Sagon, J. P.; Julivert, M.; Arboleya, M. L.; Saquaque, A.; El-Boukhari, A.; Saidi, A.; Soler, J. M. F.

    2001-05-01

    Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P 2O 5, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding.

  15. Volcanism and stratigraphy of the Neoproterozoic Campo Alegre Basin, SC, Brazil

    Directory of Open Access Journals (Sweden)

    SERGIO B. CITRONI

    2001-12-01

    Full Text Available The depositional succession of the Campo Alegre Basin (Santa Catarina - southern Brazil was investigated having the evolution of the volcanic activity as background. The different stratigraphic units are interpreted as belonging to different volcanic stages: Bateias Formation, conglomerates and sandstones, related with a pre-volcanic stage; Campo Alegre Group, at the main volcanic stage, with each different formation corresponding to different episodes of volcanism - Rio Negrinho Formation, corresponding to the basic volcanism, Avenca Grande Formation to ignimbritic event, Serra de São Miguel Formation to the acid volcanism and Fazenda Uirapuru Formation, related to an explosive event; Rio Turvo and Arroio Água Fria formations correspond respectively to inner and extra-caldera deposits.A sucessão deposicional das rochas vulcânicas e sedimentares da Bacia de Campo Alegre (Santa Catarina - sul do Brasil foi estabelecida tendo como "background" a evolução da atividade vulcânica. As diferentes unidades estratigráficas são consideradas como pertencentes a diferentes estágios do vulcanismo: Formação Bateias, constituída por conglomerados e arenitos, é relacionada a um estágio pré-vulcânico; Grupo Campo Alegre, depositado durante o estágio vulcânico principal, é constituído de diferentes formações que refletem os diversos momentos desse vulcanismo - Formação Rio Negrinho, relacionada ao vulcanismo básico, Formação Avenca Grande a eventos ignimbríticos, Formação Serra de São Miguel ao vulcanismo ácido e a Formação Fazenda Uirapuru a um evento explosivo; as formações Rio Turvo e Arroio Água Fria correspondem respectivamente a depósitos do interior e do exterior de uma caldeira abatida.

  16. Chuar Group of the Grand Canyon: record of breakup of Rodinia, associated change in the global carbon cycle, and ecosystem expansion by 740 Ma

    Science.gov (United States)

    Karlstrom, K. E.; Bowring, S. A.; Dehler, C. M.; Knoll, A. H.; Porter, S. M.; Des Marais, D. J.; Weil, A. B.; Sharp, Z. D.; Geissman, J. W.; Elrick, M. B.; Timmons, J. M.; Crossey, L. J.; Davidek, K. L.

    2000-01-01

    The Chuar Group (approximately 1600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at low latitudes during extension on the north-trending Butte fault system and is inferred to record rifting during the breakup of Rodinia. Shallow-marine deposition is documented by tide- and wave-generated sedimentary structures, facies associations, and fossils. C isotopes in organic carbon show large stratigraphic variations, apparently recording incipient stages of the marked C isotopic fluctuations that characterize later Neoproterozoic time. Upper Chuar rocks preserve a rich biota that includes not only cyanobacteria and algae, but also heterotrophic protists that document increased food web complexity in Neoproterozoic ecosystems. The Chuar Group thus provides a well-dated, high-resolution record of early events in the sequence of linked tectonic, biogeochemical, environmental, and biological changes that collectively ushered in the Phanerozoic Eon.

  17. Derivation of S and Pb in phanerozoic intrusion-related metal deposits from neoproterozoic sedimentary pyrite, Great Basin, United States

    Science.gov (United States)

    Vikre, P.G.; Poulson, S.R.; Koenig, A.E.

    2011-01-01

    The thick (???8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high d34S values (-11.6 to 40.8%, Pb isotopes ( 207Pb/204Pb Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb from sedimentary pyrite, and volatiles acquired from deeper crustal or mantle sources. In the central and eastern Great Basin, the wide distribution and high density of small to mid-sized vein, replacement, and skarn intrusion-related metal deposits

  18. Transition from island-arc to passive setting on the continental margin of Gondwana: U-Pb zircon dating of Neoproterozoic metaconglomerates from the SE margin of the Teplá-Barrandian Unit, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Dunkley, D. J.; Kachlík, V.; Kusiak, M. A.

    2008-01-01

    Roč. 461, 1-4 (2008), s. 44-59. ISSN 0040-1951 Institutional research plan: CEZ:AV0Z30130516 Keywords : Bohemian Massif * Teplá–Barrandian Unit * Neoproterozoic * Armorican Terrane Assemblage * Gondwana * zircon dating Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.677, year: 2008

  19. Neoproterozoic diamictite-bearing sedimentary rocks in the northern Yili Block and their constraints on the Precambrian evolution of microcontinents in the Western Central Asian Orogenic Belt

    Science.gov (United States)

    He, Jingwen; Zhu, Wenbin; Zheng, Bihai; Wu, Hailin; Cui, Xiang; Lu, Yuanzhi

    2015-12-01

    The origin and tectonic setting of Precambrian sequences in the Central Asian Orogenic Belt (CAOB) have been debated due to a lack of high resolution geochronological data. Answering this question is essential for the understanding of the tectonic framework and Precambrian evolution of the blocks within the CAOB. Here we reported LA-ICP-MS detrital zircon U-Pb ages and in-situ Hf isotopic data for Neoproterozoic sedimentary cover in the northern Yili Block, an important component of the CAOB, in order to provide information on possible provenance and regional tectonic evolution. A total of 271 concordant U-Pb zircon ages from Neoproterozoic sedimentary cover in the northern Yili Block define three major age populations of 1900-1400 Ma, 1300-1150 Ma and 700-580 Ma, which are quite different from cratons and microcontinents involved in the CAOB. Although it is not completely consistent with the local basement ages, an autochthonous provenance interpretation is more suitable. Some zircon grains show significant old Hf model ages (TDMC; 3.9-2.4 Ga) and reveal continental crust as old as Paleoarchean probably existed. Continuous Mesoproterozoic zircon age populations exhibit large variations in the εHf(t) ratios, suggesting the long-time involvement of both reworked ancient crust and juvenile material. Similar Mesoproterozoic evolution pattern is identified in many continental terranes involved in the CAOB that surround the Tarim Craton. Based on our analysis and published research, we postulate that the northern Yili Block, together with Chinese Central Tianshan, Kyrgyz North Tianshan and some other microcontinents surrounding the Tarim Craton, once constituted the continental margin of the Tarim Craton in the Mesoproterozoic, formed by long-lived accretionary processes. Most of the late Neoproterozoic zircons exhibit significant positive εHf(t) ratios, suggesting the addition of juvenile crust. It is consistent with the tectonic event related to the East Africa

  20. Towards a new understanding of the Neoproterozoic-early palæozoic Lufilian and northern Zambezi belts in Zambia and the Democratic Republic of Congo

    Science.gov (United States)

    Porada, Hubertus; Berhorst, Volker

    2000-04-01

    The Lufilian Belt is of geological significance and economic importance due to rich CuCo mineralisation in the Katanga Province of the Democratic Republic of Congo and the Copperbelt of Zambia. Though thorough exploration has yielded much information on the mines districts, the understanding of the belt as a whole appears, to some extent, historically charged and confused. In the first part of this article, basic knowledge and assumptions are reviewed and existing models critically assessed. Results include recognition of standard lithostratigraphies of the Katanga Supergroup comprising the Roan, Mwashia, Lower and Upper Kudelungu Groups in the Copperbelt and Katanga, a lower limit for the onset of deposition at about 880 Ma, and a major orogenetic event involving northeast directed thrusting (Lufilian Orogeny) at 560-550 Ma. The depositional history of the Lufilian Belt was controlled by continental rifting leading to formation of a passive continental margin. Continental rifting related to the dispersal of Rodinia began ca 880 Ma ago and was accompanied by magmatism (Kafue rhyolites: 879 Ma; Nchanga Granite: 877 Ma; Lusaka Granite: 865 Ma). Differential subsidence of the northwestward propagating rift soon allowed invasion by the sea advancing from the southeast, and subsequent development of marine rift-basin and platform domains. The standard stratigraphies for the Roan Group are restricted to the platform domain that bordered the rift-basin on its northeastern side. This domain included the Domes region of the Lufilian Belt and extended southeastwards into the northern Zambezi Belt. The platform was differentiated into a carbonate platform (barrier) represented by the Bancroft Subgroup (previously 'Upper Roan') in Zambia and Kambove Dolomite Formation in Katanga and a lagoon-basin (lower Kitwe Subgroup/Zambia; Dolomitic Shale Formation/Katanga) with mudflats (R.A.T. Subgroup/Katanga) and a siliciclastic margin towards the hinterland. The mineralised

  1. Fluctuations in late Neoproterozoic atmospheric oxidation - Cr isotope chemostratigraphy and iron speciation of the late Ediacaran lower Arroyo del Soldado Group (Uruguay)

    DEFF Research Database (Denmark)

    Frei, Robert; Gaucher, Claudio; Stolper, Daniel;

    2013-01-01

    -Cambrian boundary, paleoceanographic conditions resembled more those of Paleoproterozoic oceans than Phanerozoic and present oceans. This highlights the sheer magnitude of ecological changes at the Precambrian-Cambrian transition, changes which ultimately led to the demise of the Precambrian world and the birth of...

  2. 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

  3. Neoproterozoic Western Gondwana assembly and subduction-related plutonism: the role of the Rio Negro Complex in the Ribeira Belt, Brazil

    International Nuclear Information System (INIS)

    The assembly of Western Gondwana, during the Neoproterozoic, involved the Sao Francisco/West Congo Craton and its passive margins. The Ribeira Belt lies along the Brazilian Atlantic Coast and is one of the products of the super continent amalgamation. Collisional processes were preceded by subduction, recorded by the Rio Negro Complex orthogneisses at the Ribeira Belt. Its plutonites represent a gabbro-diorite-tonalite-throndhjemite plutonic series that evolved from 637 Ma (U-Pb zircon age of the tonalite gneiss) to nearly 600 Ma, at the beginning of the collisional event. Field, petrographic, litogeochemical, and isotopic characteristics of the Rio Negro Complex point to magmatism at a very mature oceanic arc or an immature continental crust as seen along attenuated passive margins. in the latter hypothesis, the margin could be related to a microplate or to the Congo/Angola Craton. (author)

  4. A normalised seawater strontium isotope curve: possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

    Directory of Open Access Journals (Sweden)

    G. A. Shields

    2007-07-01

    Full Text Available The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87Sr/86Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87Sr/86Sr is also influenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawater 87Sr/86Sr curve to plausible trends in the 87Sr/86Sr ratios of the three major Sr sources: carbonate dissolution, silicate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influence, indicating that this interval was characterised by a transient increase in global weathering rates and/or by the weathering of unusually radiogenic crustal rocks. Close correlation between the normalised 87Sr/86Sr curve, a published seawater δ34S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a major contributing factor to the steep rise in seawater 87Sr/86Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutrient availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87Sr/86Sr curves will, it is hoped, help to improve future geochemical models of Earth System dynamics.

  5. Geochemical and isotopic composition of Pan-African metabasalts from southwestern Gondwana: Evidence of Cretaceous South Atlantic opening along a Neoproterozoic back-arc

    Science.gov (United States)

    Will, Thomas M.; Frimmel, Hartwig E.; Gaucher, Claudio; Bossi, Jorge

    2014-08-01

    A lithogeochemical and Sr-Nd-Pb isotope study of former oceanic crustal rocks from the Cuchilla Dionisio Terrane in the southern Dom Feliciano Belt, Uruguay (La Tuna amphibolites) and metabasites in the Chameis Subterrane of the Marmora Terrane in the Gariep Belt, Namibia/South Africa shows that these rocks are compositionally very similar and probably represent the same unit on opposite sides of the modern South Atlantic. The mafic rocks from both terranes are tholeiitic metabasalts and -andesites and have depleted rare earth element patterns, generally low TiO2 (basin basalts (BABB). In addition, both rock suites have extremely depleted Nd isotope compositions (εNd630 Ma = 6.7-9.4), superchondritic 147Sm/144Nd ratios, and low 206Pb/204Pb and 207Pb/204Pb initial ratios. The 87Sr/86Sr initial ratios of the La Tuna mafic rocks are low, whereas the Chameis metagabbro samples have higher, possibly alteration-related ratios. The geochemical and isotopic signatures are consistent with the formation of both rock suites in the same mature Neoproterozoic back-arc basin (Marmora Basin), supporting conclusions drawn from earlier provenance studies of metasedimentary units from these terranes. Other mafic rocks from the Marmora Terrane are interpreted as ocean island basalts that formed in a within-plate setting. A corollary of the conclusion that the mafic rocks in the Cuchilla Dionisio and Marmora Terranes formed in the same back-arc basin is (1) that the main Pan-African suture between the Río de la Plata Craton and the Kalahari Craton lies to the west of the Dom Feliciano Belt in South America, and (2) that the opening of the modern South Atlantic did not occur along that suture but along the axis of the Neoproterozoic Marmora back-arc basin.

  6. Detrital zircon analysis of Mesoproterozoic and neoproterozoic metasedimentary rocks of northcentral idaho: Implications for development of the Belt-Purcell basin

    Science.gov (United States)

    Lewis, R.S.; Vervoort, J.D.; Burmester, R.F.; Oswald, P.J.

    2010-01-01

    The authors analyzed detrital zircon grains from 10 metasedimentary rock samples of the Priest River complex and three other amphibolite-facies metamorphic sequences in north-central Idaho to test the previous assignment of these rocks to the Mesoproterozoic Belt-Purcell Supergroup. Zircon grains from two samples of the Prichard Formation (lower Belt) and one sample of Cambrian quartzite were also analyzed as controls with known depositional ages. U-Pb zircon analysis by laser ablation - inductively coupled plasma - mass spectrometry reveals that 6 of the 10 samples contain multiple age populations between 1900 and 1400 Ma and a scatter of older ages, similar to results reported from the Belt- Purcell Supergroup to the north and east. Results from the Priest River metamorphic complex confirm previous correlations with the Prichard Formation. Samples from the Golden and Elk City sequences have significant numbers of 1500-1380 Ma grains, which indicates that they do not predate the Belt. Rather, they are probably from a relatively young, southwestern part of the Belt Supergroup (Lemhi subbasin). Non-North American (1610-1490 Ma) grains are rare in these rocks. Three samples of quartzite from the Syringa metamorphic sequence northwest of the Idaho batholith contain zircon grains younger than the Belt Supergroup and support a Neoproterozoic age. A single Cambrian sample has abundant 1780 Ma grains and none younger than ~1750 Ma. These results indicate that the likely protoliths of many high-grade metamorphic rocks in northern Idaho were strata of the Belt-Purcell Supergroup or overlying rocks of the Neoproterozoic Windermere Supergroup and not basement rocks.

  7. 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.

  8. Tethyan, Mediterranean, and Pacific analogues for the Neoproterozoic Paleozoic birth and development of peri-Gondwanan terranes and their transfer to Laurentia and Laurussia

    Science.gov (United States)

    Keppie, J. Duncan; Nance, R. Damian; Murphy, J. Brendan; Dostal, J.

    2003-04-01

    Modern Tethyan, Mediterranean, and Pacific analogues are considered for several Appalachian, Caledonian, and Variscan terranes (Carolina, West and East Avalonia, Oaxaquia, Chortis, Maya, Suwannee, and Cadomia) that originated along the northern margin of Neoproterozoic Gondwana. These terranes record a protracted geological history that includes: (1) ˜1 Ga (Carolina, Avalonia, Oaxaquia, Chortis, and Suwannee) or ˜2 Ga (Cadomia) basement; (2) 750-600 Ma arc magmatism that diachronously switched to rift magmatism between 590 and 540 Ma, accompanied by development of rift basins and core complexes, in the absence of collisional orogenesis; (3) latest Neoproterozoic-Cambrian separation of Avalonia and Carolina from Gondwana leading to faunal endemism and the development of bordering passive margins; (4) Ordovician transport of Avalonia and Carolina across Iapetus terminating in Late Ordovician-Early Silurian accretion to the eastern Laurentian margin followed by dispersion along this margin; (5) Siluro-Devonian transfer of Cadomia across the Rheic Ocean; and (6) Permo-Carboniferous transfer of Oaxaquia, Chortis, Maya, and Suwannee during the amalgamation of Pangea. Three potential models are provided by more recent tectonic analogues: (1) an "accordion" model based on the orthogonal opening and closing of Alpine Tethys and the Mediterranean; (2) a "bulldozer" model based on forward-modelling of Australia during which oceanic plateaus are dispersed along the Australian plate margin; and (3) a "Baja" model based on the Pacific margin of North America where the diachronous replacement of subduction by transform faulting as a result of ridge-trench collision has been followed by rifting and the transfer of Baja California to the Pacific Plate. Future transport and accretion along the western Laurentian margin may mimic that of Baja British Columbia. Present geological data for Avalonia and Carolina favour a transition from a "Baja" model to a "bulldozer" model. By

  9. 900 Ma Pole from the Bjerkreim-Sokndal Layered Intrusion, Rogaland Igneous Complex, Norway: Where Was Baltica in the Early Neoproterozoic?

    Science.gov (United States)

    Brown, L. L.; McEnroe, S. A.

    2014-12-01

    of a contact aureole around the intrusion. Comparison to other early Neoproterozoic paleomagnetic poles from southern Scandinavia confirms the high southern latitude position of Baltica at this time. A paucity of ~900 Ma poles from other ancient cratons precludes a more detailed picture of Rodinia in the early Neoproterozoic.

  10. Tectonic evolution of the Brusque Group, Dom Feliciano belt, Santa Catarina, Southern Brazil

    Science.gov (United States)

    Basei, M. A. S.; Campos Neto, M. C.; Castro, N. A.; Nutman, A. P.; Wemmer, K.; Yamamoto, M. T.; Hueck, M.; Osako, L.; Siga, O.; Passarelli, C. R.

    2011-12-01

    The Dom Feliciano Belt constitutes the main geotectonic unit of the southeastern portion of Brazil and Uruguay. It was formed by the end of the Neoproterozoic as a result of the interaction among the Rio de La Plata, Paranapanema, Congo and Kalahari cratons during the formation of Western Gondwana. The Brusque Group represents the supracrustal units of the Dom Feliciano Belt that occur in its northernmost part, which ends in the Brazilian coast and probable continuity in the Kaoko Belt in southwestern Africa. It is possible to constrain the evolution of the Brusque Group paleobasin to the Neoproterozoic, with the rift phase starting in the Tonian (940-840 Ma) and the main sedimentation occurring until 640 Ma, as indicated by the ages of the acid volcanic rocks intercalated with the metasedimentary sequence. The supracrustal rocks can be grouped in three main units lithostratigraphically organized from the oldest to the youngest: Rio Oliveira Formation (rift phase, predominating metavolcanic units), Botuverá Formation (metasedimentary) and Rio da Areia Formation (metavolcano-carbonatic). Between 640 and 600 Ma several metamorphism and deformation phases affected the Brusque Group. Around 600 ± 10 Ma the three granitic suites (São João Batista, Valsungana and Nova Trento) were emplaced within regional metamorphites, producing post-foliation S2 metamorphic aureoles. S2 represents the main foliation observed in the metavolcanosedimentary rocks that constitute the Brusque Group. The tectonic model for the evolution of Brusque Group can be better achieved only when the geochemical, isotopic and geochronologic information available for the Dom Feliciano Belt in Santa Catarina, is considered as a whole. Therefore it is here suggested that the Brusque Group initially evolved in an independent peri-cratonic basin setting separated from the Florianópolis - Pelotas-Aiguá magmatic arc by the Adamastor ocean, having been juxtaposed to it only around 600 Ma, when Brusque

  11. Geochemistry of Precambrian sedimentary rocks used to solve stratigraphical problems: An example from the Neoproterozoic Volta basin, Ghana

    DEFF Research Database (Denmark)

    Kalsbeek, F.; Frei, Robert

    2010-01-01

    siltstones and mudstones, intercalated with the sandstones from the different units, were used in an attempt to solve some of these problems. Siltstones and mudstones from the Bombouaka Group can be unequivocally distinguished from similar rocks from the Oti and Obosum Groups by higher K2O and Rb, larger Eu...... anamalies, higher 87Sr/86Sr, and more negative var epsilonNd values. Geochemical distinction between samples from the Oti and Obosum Groups is ambiguous because published geological maps differ with respect to the relative extents of the Oti and Obosum Groups. Rb–Sr isotope data, combined with high degrees...... from the Oti and Obosum Groups is used to solve one of the outstanding controversies regarding the stratigraphy of the Volta basin....

  12. Geochemistry and zircon ages of mafic dikes in the South Qinling, central China: evidence for late Neoproterozoic continental rifting in the northern Yangtze block

    Science.gov (United States)

    Zhu, Xiyan; Chen, Fukun; Liu, Bingxiang; Zhang, He; Zhai, Mingguo

    2015-01-01

    Neoproterozoic volcanic-sedimentary sequences of the southern Qinling belt, central China, were intruded by voluminous mafic dikes. secondary ion mass spectrometry zircon U-Pb dating indicates that these dikes were emplaced at 650.8 ± 5.2 Ma, coeval with mafic rocks occurring at the northern margin of the Yangtze block. The dikes are characterized by enrichment of large ion lithophile elements, high Ti contents (up to 3.73 wt%) and Nb/Ta ratios between 14.5 and 19.6, suggesting a mantle source of oceanic island basalt affinity. Initial 87Sr/86Sr ratios show positive correlation with SiO2 contents and negative correlation with Zr/Nb ratios, implying that these rocks were affected by crustal contamination during the magma ascend and emplacement process. The dikes have initial ɛ Nd values of +0.2 to +3.3, low 206Pb/204Pb ratios of 16.96-17.45, and moderate 87Sr/86Sr ratios of 0.7043-0.7076, likely pointing to the involvement of an enriched mantle source. The mafic dikes and coeval mafic volcanic equivalents in the South Qinling and the northern Yangtze are hypothesized to be related with the prolonged breakup of the supercontinent Rodinia, suggesting that continental rifting lasted until ca. 650 Ma.

  13. Rapid adaptation of phytoplankters to geothermal waters is achieved by single mutations: were extreme environments 'Noah's Arks' for photosynthesizers during the Neoproterozoic 'snowball Earth'?

    Science.gov (United States)

    Costas, Eduardo; Flores-Moya, Antonio; López-Rodas, Victoria

    2008-01-01

    Geothermal waters often support remarkable communities of microalgae and cyanobacteria apparently living at the extreme limits of their tolerance. Little is known about the mechanisms allowing adaptation of mesophilic phytoplankters to such extreme conditions, but recent studies are challenging many preconceived notions about this. The aim of this study was to analyse mechanisms allowing adaptation of mesophilic microalgae and cyanobacteria to stressful geothermal waters. To distinguish between the pre-selective or post-selective origin of adaptation processes allowing the proliferation of mesophilic phytoplankters in geothermal waters, several Luria-Delbrück fluctuation analysis were performed with the microalga Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa, both isolated from nonextreme waters. Geothermal waters from seven places in Italy and five icebound places at Los Andes in Argentina were used as selective agents. Physiological adaptation was achieved in the least toxic waters. In contrast, rapid genetic adaptation was observed in waters ostensibly lethal for the experimental organisms. This adaptation was achieved as consequence of single mutations at one locus. It was hypothesized that a similar mechanism of rapid genetic adaptation could explain the survival of photosynthetic life during the Neoproterozoic 'snowball Earth,' where geothermal refuges such as those studied could have been 'Noah's Arks' for microalgae and cyanobacteria. PMID:18803596

  14. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

    Directory of Open Access Journals (Sweden)

    Sommer Carlos A.

    2006-01-01

    Full Text Available The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

  15. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins.

    Science.gov (United States)

    Sommer, Carlos A; Lima, Evandro F; Nardi, Lauro V S; Liz, Joaquim D; Waichel, Breno L

    2006-09-01

    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources. PMID:16936944

  16. 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.

  17. Group cubization

    OpenAIRE

    Osajda, Damian

    2016-01-01

    We present a procedure of group cubization: It results in a group whose some features resemble the ones of a given group, and which acts without fixed points on a CAT(0) cubical complex. As a main application we establish lack of Kazhdan's property (T) for Burnside groups. Other applications include new constructions of non-exact groups.

  18. The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

    Science.gov (United States)

    Hofmann, Mandy; Linnemann, Ulf; Hoffmann, Karl-Heinz; Gerdes, Axel; Eckelmann, Katja; Gärtner, Andreas

    2014-07-01

    This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203-2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323-354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0-1.4 Ga Namaqua Province, 1.7-2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu-Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. ɛHf( t) signatures range between -24 and +14.8, which relate to TDM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from

  19. Group X

    Energy Technology Data Exchange (ETDEWEB)

    Fields, Susannah

    2007-08-16

    This project is currently under contract for research through the Department of Homeland Security until 2011. The group I was responsible for studying has to remain confidential so as not to affect the current project. All dates, reference links and authors, and other distinguishing characteristics of the original group have been removed from this report. All references to the name of this group or the individual splinter groups has been changed to 'Group X'. I have been collecting texts from a variety of sources intended for the use of recruiting and radicalizing members for Group X splinter groups for the purpose of researching the motivation and intent of leaders of those groups and their influence over the likelihood of group radicalization. This work included visiting many Group X websites to find information on splinter group leaders and finding their statements to new and old members. This proved difficult because the splinter groups of Group X are united in beliefs, but differ in public opinion. They are eager to tear each other down, prove their superiority, and yet remain anonymous. After a few weeks of intense searching, a list of eight recruiting texts and eight radicalizing texts from a variety of Group X leaders were compiled.

  20. Group Flow and Group Genius

    Science.gov (United States)

    Sawyer, Keith

    2015-01-01

    Keith Sawyer views the spontaneous collaboration of group creativity and improvisation actions as "group flow," which organizations can use to function at optimum levels. Sawyer establishes ideal conditions for group flow: group goals, close listening, complete concentration, being in control, blending egos, equal participation, knowing…

  1. Redox condition of the late Neoproterozoic pelagic deep ocean: 57Fe Mössbauer analyses of pelagic mudstones in the Ediacaran accretionary complex, Wales, UK

    Science.gov (United States)

    Sato, Tomohiko; Sawaki, Yusuke; Asanuma, Hisashi; Fujisaki, Wataru; Okada, Yoshihiro; Maruyama, Shigenori; Isozaki, Yukio; Shozugawa, Katsumi; Matsuo, Motoyuki; Windley, Brian F.

    2015-11-01

    We report geological and geochemical analysis of Neoproterozoic pelagic deep-sea mudstones in an accretionary complex in Lleyn, Wales, UK. Ocean plate stratigraphy at Porth Felen, NW Lleyn, consists of mid-ocean ridge basalt (> 4 m), bedded dolostone (2 m), black mudstone (5 m), hemipelagic siliceous mudstone (1 m,) and turbiditic sandstone (15 m), in ascending order. The absence of terrigenous clastics confirms that the black and siliceous mudstone was deposited in a pelagic deep-sea. Based on the youngest U-Pb age (564 Ma) of detrital zircons separated from overlying sandstone, the deep-sea black mudstone was deposited in the late Ediacaran. The 5 m-thick black mudstone contains the following distinctive lithologies: (i) black mudstone with thin pyritic layers (0.8 m), (ii) alternation of black mudstone and gray/dark gray siliceous mudstone (2.4 m), (iii) thinly-laminated dark gray shale (1 m), and (iv) black mudstone with thin pyritic layers (1 m). 57Fe Mössbauer spectroscopy confirms that these black mudstones contain pyrite without hematite. In contrast, red bedded claystones (no younger than 542 Ma) in the neighboring Braich section contain hematite as their main iron mineral. These deep-sea mudstones in the Lleyn Peninsula record a change of redox condition on the pelagic deep-sea floor during the Ediacaran. The black mudstone at Porth Felen shows that deep-sea anoxia existed in the late Ediacaran. The eventual change from a reducing to an oxidizing deep-sea environment likely occurred in the late Ediacaran (ca. 564-542 Ma).

  2. Regional setting and characteristics of the Neoproterozoic Wadi Hamama Zn-Cu-Ag-Au prospect: evidence for an intra-oceanic island arc-hosted volcanogenic hydrothermal system

    Science.gov (United States)

    Abd El-Rahman, Yasser; Surour, Adel A.; El-Manawi, Abdel Hamid W.; El-Dougdoug, Abdel-Monem A.; Omar, Sayed

    2015-04-01

    The Wadi Hamama area is a volcanogenic Zn-Cu-Au-Ag prospect. It is hosted by a Neoproterozoic bimodal-mafic sequence, which comprises basalt, dacite and rhyolite along with volcaniclastic rocks. The rocks have a low-K tholeiitic affinity and are enriched in large ion lithophile elements over high field strength elements, which indicated their formation in an intra-oceanic island arc tectonic setting. The area was intruded by a tonalite-trondhjemite body, which has an intra-oceanic island arc affinity and later by diorite, which has a cordilleran-margin geochemical affinity. These rock units were intruded by post-tectonic granite dykes, which have a within-plate geochemical signature. There is a quartz-carbonate horizon extending along the contact between the basalt and the volcaniclastic rocks, mainly banded and lapilli tuffs. This horizon is of exhalative origin and is underlain by a mushroom-shaped alteration zone extending from the horizon down to the massive basalt. The footwall alteration is characterized by a silica-rich core surrounded by a thick chlorite sheath. Both the quartz-carbonate horizon and the footwall-altered rocks enclose historical trenches and pits. Sulfide-rich core samples are enriched in Zn, relative to Cu, and in Ag, which indicates the low-temperature nature of the hydrothermal system. The prospect was affected by supergene processes, which led to the widespread occurrence of secondary copper minerals and gold enrichment relative to the leached base metals, especially Zn. The prospect formed through a limited rifting of an intra-oceanic island arc which resulted in the formation of a small-scale volcanogenic Zn-Cu-Ag-Au prospect.

  3. Replacement of benthic communities in two Neoproterozoic-Cambrian subtropical-to-temperate rift basins, High Atlas and Anti-Atlas, Morocco

    Science.gov (United States)

    Clausen, Sébastien; Álvaro, J. Javier; Zamora, Samuel

    2014-10-01

    The ‘Cambrian explosion’ is often introduced as a major shift in benthic marine communities with a coeval decline of microbial consortia related to the diversification of metazoans and development of bioturbation (‘Agronomic Revolution’). Successive community replacements have been reported along with ecosystem diversification and increase in guild complexity from Neoproterozoic to Cambrian times. This process is recorded worldwide but with regional diachroneities, some of them directly controlled by the geodynamic conditions of sedimentary basins. The southern High Atlas and Anti-Atlas of Morocco record development of two rifts, Tonian (?) - early Cryogenian and latest Ediacarian-Cambrian in age, separated by the onset of the Pan-African Orogeny. This tectonically controlled, regional geodynamic change played a primary control on pattern and timing of benthic ecosystem replacements. Benthic communities include microbial consortia, archaeocyathan-thromboid reefal complexes, chancelloriid-echinoderm-sponge meadows, and deeper offshore echinoderm-dominated communities. Microbial consortia appeared in deeper parts of the Tonian (?) - early Cryogenian fluvio-deltaic progradational rift sequences, lacustrine environments of the Ediacaran Volcanic Atlasic Chain (Ouarzazate Supergroup) and the Ediacaran-Cambrian boundary interval, characterized by the peritidal-dominated Tifnout Member (Adoudou Formation). They persisted and were largely significant until Cambrian Age 3, as previous restricted marine conditions precluded the immigration of shelly metazoans in the relatively shallow epeiric parts of the Cambrian Atlas Rift. Successive Cambrian benthic communities were replaced as a result of distinct hydrodynamic and substrate conditions, which allow identification of biotic (e.g., antagonistic relationships between microbial consortia and echinoderms, and taphonomic feedback patterns in chancelloriid-echinoderm-sponge meadows) and abiotic (e.g., rifting

  4. 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).

  5. Geochemistry and detrital zircon geochronology of Neoproterozoic sedimentary rocks in eastern Hunan Province and their tectonic significance%湘东新元古代沉积岩的地球化学和碎屑锆石年代学特征及其构造意义

    Institute of Scientific and Technical Information of China (English)

    王鹏鸣; 于津海; 孙涛; 凌洪飞; 陈培荣; 赵葵东; 陈卫峰; 刘潜

    2012-01-01

    This study presents new geochemical and zircon U-Pb and Lu-Hf isutopic data for Neoproterozoic meta-sedimentary rocks in the Xiangxiang-Liling area, eastern Hunan Province and Guiyang area, southeastern Hunan Province. Geochemical data show that the sedimentary rocks from these two areas have similar and moderate composition maturity. However, large K2O/Na2O variations suggest that these sedimentary rocks experienced different degree of the eluviation. Rare earth element ( REE) patterns of these sedimentary rocks from two areas are similar to those of post-Archean Australian shales (PAAS) with slightly high concentrations, especially for heavy REEs. The sedimentary rocks of the Banxi Group in the eastern Hunan Province have higher compatible elements (e. G. Sc, Cr, Ni) than the Sinian sedimentary rocks in the southeastern Province, implying that provenance of the former has more intermediate to mafic rocks than the later. U-Pb dating results of detrital zircons from two sedimentary rocks indicate that a Neoproterozoic sedimentary rock in eastern Hunan Province has abundant 850 ~800Ma detritus without ~ 1000Ma ones, suggesting its affinity with the Yangtze Block. However, a Neoproterozoic sedimentary rock in southeastern Hunan Province contains many Grenvillian detrital zircons and less ~ 2. 5Ga ones without - 800Ma elastic materials, similar to those in the Cathaysia Block. This difference suggests that the boundary between the Yangtze and Cathaysia blocks probably pass between the Xiangxiang-Liling area, eastern Hunan Province and Guiyang area, southeastern Hunan Province. Previous study (Wang et al. , 2010a) has indicated that Early Paleozoic sedimentary rocks in these two areas have detritus similar to the Cathaysia Block, suggesting that their provenances are in the Cathaysia Block. Consequently, the sediments in the eastern Hunan Province change significantly from Late Neoproterozoic (Sinian) to Early Paleozoic time (Middle Cambrian) , suggesting a tectonic

  6. Corrigendum to "Climate simulations of Neoproterozoic snowball Earth events: Similar critical carbon dioxide levels for the Sturtian and Marinoan glaciations" [Earth Planet. Sci. Lett. 404 (2014) 200-205

    Science.gov (United States)

    Feulner, Georg; Kienert, Hendrik

    2015-11-01

    In Fig. 4 of our article, the colours of the curves representing the Neoproterozoic climate states at 720 Ma (1 Ma = 1 million years ago) and 650 Ma were inadvertently interchanged. The blue lines refer to the 720 Ma (Sturtian) state, the red lines to the 650 Ma (Marinoan) state. Both the description in the figure legend and the discussion in the text are correct, so the conclusions in the article are not affected. The corrected Fig. 4 with the full legend appears below for the readers' convenience.

  7. Group morphology

    NARCIS (Netherlands)

    Roerdink, Jos B.T.M.

    2000-01-01

    In its original form, mathematical morphology is a theory of binary image transformations which are invariant under the group of Euclidean translations. This paper surveys and extends constructions of morphological operators which are invariant under a more general group TT, such as the motion group

  8. Abelian Groups

    Energy Technology Data Exchange (ETDEWEB)

    Mishina, A.P.

    1995-10-15

    This fifth survey of reviews on abelian groups comprises papers reviewed in 1985-1992. Just as in the preceding surveys, the issues concerning finite abelian groups, topological groups, ordered groups, group algebras, modules (with rare exceptions), and topics on logic are not considered. The issues on the lattice of subgroups of an abelian group are included in Section 11. In contrast to the fourth survey, this one does not contain Sections 6 (N-high subgroups), 9 (rings with a given additive group), and 10 (valuated groups); since only a few papers treated these topics, the material discussed earlier in Sections 9, and 10 is now included in Section 11 and the material of the former Section 6 will be found in Sections 1, 7, 8, and 11 of this survey. On the other hand, the fifth survey has three new sections devoted to separable groups (a new Sect. 5), Butler groups (a new Sect. 6), and the endormorphism rings and automorphism groups of abelian groups (a new Sect. 9).

  9. Permutation groups

    CERN Document Server

    Passman, Donald S

    2012-01-01

    This volume by a prominent authority on permutation groups consists of lecture notes that provide a self-contained account of distinct classification theorems. A ready source of frequently quoted but usually inaccessible theorems, it is ideally suited for professional group theorists as well as students with a solid background in modern algebra.The three-part treatment begins with an introductory chapter and advances to an economical development of the tools of basic group theory, including group extensions, transfer theorems, and group representations and characters. The final chapter feature

  10. Galaxy Groups

    Science.gov (United States)

    Tully, R. Brent

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times {{10}12}{{M}⊙ } are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of {{Ω}matter}˜ 0.15 in a flat topology, with a 68% probability of being less than 0.44.

  11. Galaxy groups

    Energy Technology Data Exchange (ETDEWEB)

    Brent Tully, R. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10{sup 12}M{sub ⊙} are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of Ω{sub matter}∼0.15 in a flat topology, with a 68% probability of being less than 0.44.

  12. Lead isotope evidence for recent uranium mobility in geological formations of Brazil: implications for radioactive waste disposal

    International Nuclear Information System (INIS)

    Lead-lead isotope data from whole rock samples are used to investigate the recent (last few million years) mobility of U and Th. The method is based on the comparison of the calculated present day U and Th concentrations required to yield the Pb isotope composition in the samples with the actual present day concentrations of U and Th obtained by direct measurement. The geological formations studied include the Neoproterozoic carbonate sediments of the Bambui Group, Archean/Paleoproterozoic granite-greenstone terrain of the Contendas-Mirante Complex and a Proterozoic ortho-gneisses hosting U deposit in Lagoa Real. All these formations are in the Sao Francisco Craton, Brazil. The data show high U mobility in the carbonate sediments and in the deformed ortho-gneisses set in a ductile shear zone. Infiltration of groundwater through fault zones seems to have facilitated the U mobility. The Pb isotope approach is a useful technique complementing U-series disequilibrium studies and may be included for site characterization studies for radioactive waste disposal. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  13. Galaxy Groups

    CERN Document Server

    Tully, R Brent

    2014-01-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10^12 Msun are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosi...

  14. Geochemical characteristics of Bikou volcanic group and Sr-Nd-Pb isotopic composition: Evidence for breakup event in the north margin of Yangtze plate, Jining era

    Institute of Scientific and Technical Information of China (English)

    LI; YongFei; LAI; ShaoCong; QIN; JiangFeng; LIU; Xin; WANG; Juan

    2007-01-01

    The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is composed of several residual oceanic crust units: MORB (mid-ocean ridge basalt), Alk-OIB (alkaline ocean island basalt) and Th-OIB (tholeiitic ocean island basalt) as well as subduction-related volcanic rocks. According to field observation, those distinct rocks occurred collectively in form of tectonic contact, implying that the Bikou volcanic group was an ophiolitic mélange. Coupled with geochronological data, a perished oceanic basin at the northern margin of the Yangtze block during Neoproterozoic was tested by this ophiolitic mélange. Meanwhile, the isogeochemical data suggest that the ocean occurred in the Southern Hemisphere identical to Indian, South Atlantic and South Pacific oceans in terms of their Dupal anomalies, and the original source of the rocks could be probably mixing by EMⅠand EMⅡ component caused by dehydration melting of subducting oceanic crust during subduction process. On the basis of geochemical characteristics of the studied rocks, the Bikou volcanic group could imply that a partial breakup event occurred in the northern margin of Yangtze plate during the Neoproterozoic era.

  15. Mineral chemistry and geochemistry of the Late Neoproterozoic Gabal Abu Diab granitoids, Central Eastern Dessert, Egypt: Implications for the origin of rare metal post-orogenic A-type granites

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Ahmed, Awaad F.; Mohamed, Haroun A.

    2015-04-01

    The Neoproterozoic Gabal Abu Diab pluton is a part of the Arabian Nubian shield (ANS) continental crust and located in the Central Eastern Desert (CED) of Egypt. It constitutes multiphase granitic pluton intruded into granodiorite and metagabbro-diorite rocks with sharp and nonreactive contacts. Based on field observations, colors, structural variations and petrographic investigations, this granitic outcrop consists of an inner core of two-mica granite (TMG) followed outward by garnet bearing muscovite granite (GBMG) and albite granite (AG). Petrographical study indicated that medium to coarse-grained TMG is dominated by K-feldspar (Or88-98), quartz, plagioclase (albite, An0-7), muscovite and biotite with hypidiomorphic texture. With exception the appearance of garnet and the disappearance of biotite the GBMG resembles the TGM, while AG is leucocratic without any mafic mineral. The main accessories are zircon, Nb and Ta-bearing rutile, columbite, ilmenorutile, ilmenite, magnetite and apatite. This mineralogical similarity and the existence of columbite group minerals (CGM) in all granitoids, indicates a cogenetic relationship. Microprobe analyses reveal that, besides the CGM, rutile and ilmenite are the main repository phases for Nb-Ta-Ti. Columbite-(Mn) exists as individual subhedral crystals (up to 100μm in size) or intimate intergrowth with Nb-bearing rutile and/or ilmenite. The CGM are represented mostly by columbite-(Mn) with Ta/(Ta+Nb) and Mn/(Mn+Fe) ratio ranging from 0.02-0.08 and 0.4-0.9, respectively suggesting extreme degree of magmatic fractionation. Rutile contains significant amounts of Ta (up to 4 wt.% Ta2O5) and Nb (up to 22 wt.% Nb2O5). Biotites are phlogopite-annite in composition (Ann47-60Phlog40-53,on average) and are enriched with AlIV that characterize peraluminous granites. Garnets contain 60-69 mol.% spessartine and 28-36 mol.% almandine where, the ratio of spessartine and almandine together exceeds 95 mole percent, similar to garnet occur

  16. Hydra groups

    CERN Document Server

    Dison, Will

    2010-01-01

    We give examples of CAT(0), biautomatic, free-by-cyclic, one-relator groups which have finite-rank free subgroups of huge (Ackermannian) distortion. This leads to elementary examples of groups whose Dehn functions are similarly extravagant. This behaviour originates in manifestations of Hercules-versus-the-hydra battles in string-rewriting.

  17. Reflection groups

    International Nuclear Information System (INIS)

    In 2005, PISA organised proactive meetings of reflection groups on involvement in decision making, expert culture and ethical aspects of radiation protection.All reflection group meetings address particular targeted audiences while the output publication in book form is put forward

  18. W-Au skarns in the Neo-Proterozoic Seridó Mobile Belt, Borborema Province in northeastern Brazil: an overview with emphasis on the Bonfim deposit

    Science.gov (United States)

    Souza Neto, João Adauto; Legrand, Jean Michel; Volfinger, Marcel; Pascal, Marie-Lola; Sonnet, Philippe

    2008-02-01

    The Seridó Mobile Belt (SMB) is located in the Borborema Province in northeastern Brazil and consists of a gneiss basement (Archean to Paleo-Proterozoic), a metasedimentary sequence (marble, quartzites, and schists), and the Brasiliano igneous suite (both of Neo-Proterozoic age). In this region, skarns occur within marble and at the marble-schist contact in the metasedimentary sequence. Most of the skarn deposits have been discovered in the early 1940s, and since then, they have been exploited for tungsten and locally gold. Recently, the discovery of gold in the Bonfim tungsten skarn has resulted in a better understanding of the skarn mineralization in this region. The main characteristics of the SMB skarns are that they are dominantly oxidized tungsten skarns, with the exception of the Itajubatiba and Bonfim gold-bearing skarns, which are reduced based on pyrrhotite as the dominant sulfide, garnet with high almandine and spessartine component, and elevated gold contents. In the Bonfim deposit, pressure estimates indicate that the skarns formed at 10- to 15-km depth. The mineralized skarns present the prograde stage with almandine, diopside, anorthite, and actinolite-magnesio-hornblende, and titanite, apatite, allanite, zircon, and monazite as accessory minerals. The retrograde stage is characterized by alkali feldspar, clinozoisite-zoisite-sericite, calcite, and quartz. Scheelite occurs in four ore-shoots distributed within the marble and at the marble-schist contact. The main ore body is 5-120 cm wide and contains an average of 4.8-wt.% WO3, which occurs in the basal marble-schist contact. Fold hinges appear to control the location of high-grade scheelite. The late-stage gold mineralization contains bismite (Bi2O3), fluorine-bearing bismite, native bismuth, bismuthinite (Bi2S3), and joseite [Bi4(Te,S)3], and also chlorite, epidote, prehnite, chalcopyrite, and sphalerite. This gold-bismuth-tellurium mineralization exhibits a typical late character and occurs as a

  19. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry

    Science.gov (United States)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa

    2016-07-01

    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  20. Neoproterozoic A-type granitoids of the central and southern Appalachians: Intraplate magmatism associated with episodic rifting of the Rodinian supercontinent

    Science.gov (United States)

    Tollo, R.P.; Aleinikoff, J.N.; Bartholomew, M.J.; Rankin, D.W.

    2004-01-01

    Emplacement of compositionally distinctive granitic plutons accompanied two pulses (765-680 and 620-550Ma) of crustal extension that affected the Rodinian craton at the present location of the central Appalachians during the Neoproterozoic. The dominantly metaluminous plutons display mineralogical and geochemical characteristics of A-type granites including high FeO t/MgO ratios, high abundances of Nb, Zr, Y, Ta, and REE (except Eu), and low concentrations of Sc, Ba, Sr, and Eu. These dike-like, sheet complexes occur throughout the Blue Ridge province of Virginia and North Carolina, and were emplaced at shallow levels in continental crust during active extension, forming locally multiple-intrusive plutons elongated perpendicular to the axis of extension. New U-Pb zircon ages obtained from the Polly Wright Cove (706??4Ma) and Suck Mountain (680??4Ma) plutons indicate that metaluminous magmas continued to be replenished near the end of the first pulse of rifting. The Suck Mountain body is presently the youngest known igneous body associated with earlier rifting. U-Pb zircon ages for the Pound Ridge Granite Gneiss (562??5Ma) and Yonkers Gneiss (563??2Ma) in the Manhattan prong of southeastern New York constitute the first evidence of plutonic felsic activity associated with the later period of rifting in the U.S. Appalachians, and suggest that similar melt-generation processes were operative during both intervals of crustal extension. Fractionation processes involving primary minerals were responsible for much of the compositional variation within individual plutons. Compositions of mapped lithologic units in a subset of plutons studied in detail define overlapping data arrays, indicating that, throughout the province, similar petrologic processes operated locally on magmas that became successively more chemically evolved. Limited variation in source-sensitive Y/Nb and Yb/Ta ratios is consistent with results of melting experiments and indicates that metaluminous

  1. Methanogenesis produces strong 13C-enrichment in stromatolites of Lagoa Salgada, Brazil: A modern analogue for Palaeo-/Neoproterozoic stromatolites?

    Science.gov (United States)

    Meister, Patrick; Birgel, Daniel; Lundberg, Rebecca; Horat, Thomas; Bontognali, Tomaso; Bahniuk Rumbelsperger, Anelize; Rezende, Carlos; Vásconcelos, Crisógono; McKenzie, Judith A.

    2015-04-01

    methanogenesis. Radiogenic Sr-isotope compositions support a mixed water scenario with continental ground or surface water as additional source of alkalinity. Evaporative concentration during dry periods increased the carbonate saturation state in the brine inducing spontaneous or perhaps microbially catalysed precipitation of carbonate. Unusually 13C-enriched stomatolitic deposits also appear in the geological record during prolonged periods in the Palaeo- and Neoproterozoic. Thus, Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in seawater allowed methanogens to prevail over sulphate-reducing bacteria.

  2. Algebraic Groups

    DEFF Research Database (Denmark)

    2007-01-01

    The workshop continued a series of Oberwolfach meetings on algebraic groups, started in 1971 by Tonny Springer and Jacques Tits who both attended the present conference. This time, the organizers were Michel Brion, Jens Carsten Jantzen, and Raphaël Rouquier. During the last years, the subject of...... algebraic groups (in a broad sense) has seen important developments in several directions, also related to representation theory and algebraic geometry. The workshop aimed at presenting some of these developments in order to make them accessible to a "general audience" of algebraic group-theorists, and to...

  3. Group Grammar

    Science.gov (United States)

    Adams, Karen

    2015-01-01

    In this article Karen Adams demonstrates how to incorporate group grammar techniques into a classroom activity. In the activity, students practice using the target grammar to do something they naturally enjoy: learning about each other.

  4. Abelian groups

    CERN Document Server

    Fuchs, László

    2015-01-01

    Written by one of the subject’s foremost experts, this book focuses on the central developments and modern methods of the advanced theory of abelian groups, while remaining accessible, as an introduction and reference, to the non-specialist. It provides a coherent source for results scattered throughout the research literature with lots of new proofs. The presentation highlights major trends that have radically changed the modern character of the subject, in particular, the use of homological methods in the structure theory of various classes of abelian groups, and the use of advanced set-theoretical methods in the study of undecidability problems. The treatment of the latter trend includes Shelah’s seminal work on the undecidability in ZFC of Whitehead’s Problem; while the treatment of the former trend includes an extensive (but non-exhaustive) study of p-groups, torsion-free groups, mixed groups, and important classes of groups arising from ring theory. To prepare the reader to tackle these topics, th...

  5. Group dynamics.

    Science.gov (United States)

    Scandiffio, A L

    1990-12-01

    Group dynamics play a significant role within any organization, culture, or unit. The important thing to remember with any of these structures is that they are made up of people--people with different ideas, motivations, background, and sometimes different agendas. Most groups, formal or informal, look for a leader in an effort to maintain cohesiveness of the unit. At times, that cultural bond must be developed; once developed, it must be nurtured. There are also times that one of the group no longer finds the culture comfortable and begins to act out behaviorally. It is these times that become trying for the leader as she or he attempts to remain objective when that which was once in the building phase of group cohesiveness starts to fall apart. At all times, the manager must continue to view the employee creating the disturbance as an integral part of the group. It is at this time that it is beneficial to perceive the employee exhibiting problem behaviors as a special employee, as one who needs the benefit of your experience and skills, as one who is still part of the group. It is also during this time that the manager should focus upon her or his own views in the area of power, communication, and the corporate culture of the unit that one has established before attempting to understand another's point of view. Once we understand our own motivation and accept ourselves, it is then that we may move on to offer assistance to another. Once we understand our insecurities recognizing staff dysfunction as a symptom of system dysfunction will not be so threatening to the concept of the manager that we perceive ourselves to be. It takes a secure person to admit that she or he favors staff before deciding to do something to change things. The important thing to know is that it can be done. The favored staff can find a new way of relating to others, the special employee can find new modes of behavior (and even find self-esteem in the process), the group can find new ways

  6. Group representations

    CERN Document Server

    Karpilovsky, G

    1994-01-01

    This third volume can be roughly divided into two parts. The first part is devoted to the investigation of various properties of projective characters. Special attention is drawn to spin representations and their character tables and to various correspondences for projective characters. Among other topics, projective Schur index and projective representations of abelian groups are covered. The last topic is investigated by introducing a symplectic geometry on finite abelian groups. The second part is devoted to Clifford theory for graded algebras and its application to the corresponding theory

  7. Group Anonymity

    CERN Document Server

    Chertov, Oleg; 10.1007/978-3-642-14058-7_61

    2010-01-01

    In recent years the amount of digital data in the world has risen immensely. But, the more information exists, the greater is the possibility of its unwanted disclosure. Thus, the data privacy protection has become a pressing problem of the present time. The task of individual privacy-preserving is being thoroughly studied nowadays. At the same time, the problem of statistical disclosure control for collective (or group) data is still open. In this paper we propose an effective and relatively simple (wavelet-based) way to provide group anonymity in collective data. We also provide a real-life example to illustrate the method.

  8. Tectaria group

    NARCIS (Netherlands)

    Holttum, R.E.

    1991-01-01

    Polypodiaceae subfam. Dryopteridoideae section A, auct.: C. Chr. in Verdoorn, Man. Pteridol. (1938) 543, p.p. Aspidiaceae tribe Aspidieae auct.: Ching, Sunyatsenia 5 (1940) 250, excl. Lomariopsis and related genera. — Aspidiaceae, group of Ctenitis Copel., Gen. Fil. (1947) 153. Aspidiaceae auct.: Pi

  9. Group Learning.

    Science.gov (United States)

    Black, Susan

    1992-01-01

    Research suggests that cooperative learning works best when students are first taught group-processing skills, such as leadership, decision making, communication, trust building, and conflict management. Inadequate teacher training and boring assignments can torpedo cooperative learning efforts. Administrators should reassure teachers with…

  10. Group play

    DEFF Research Database (Denmark)

    Tychsen, Anders; Hitchens, Michael; Brolund, Thea;

    2008-01-01

    Role-playing games (RPGs) are a well-known game form, existing in a number of formats, including tabletop, live action, and various digital forms. Despite their popularity, empirical studies of these games are relatively rare. In particular there have been few examinations of the effects of the...... various formats used by RPGs on the gaming experience. This article presents the results of an empirical study, examining how multi-player tabletop RPGs are affected as they are ported to the digital medium. Issues examined include the use of disposition assessments to predict play experience, the effect...... of group dynamics, the influence of the fictional game characters and the comparative play experience between the two formats. The results indicate that group dynamics and the relationship between the players and their digital characters, are integral to the quality of the gaming experience in...

  11. Group therapy

    International Nuclear Information System (INIS)

    Full text: In his review 'Genesis of Unified Gauge Theories' at the symposium in Honour of Abdus Salam (June, page 23), Tom Kibble of Imperial College, London, looked back to the physics events around Salam from 1959-67. He described how, in the early 1960s, people were pushing to enlarge the symmetry of strong interactions beyond the SU(2) of isospin and incorporate the additional strangeness quantum number. Kibble wrote - 'Salam had students working on every conceivable symmetry group. One of these was Yuval Ne'eman, who had the good fortune and/or prescience to work on SU(3). From that work, and of course from the independent work of Murray Gell- Mann, stemmed the Eightfold Way, with its triumphant vindication in the discovery of the omega-minus in 1964.' Yuval Ne'eman writes - 'I was the Defence Attaché at the Israeli Embassy in London and was admitted by Salam as a part-time graduate student when I arrived in 1958. I started research after resigning from the Embassy in May 1960. Salam suggested a problem: provide vector mesons with mass - the problem which was eventually solved by Higgs, Guralnik, Kibble,.... (as described by Kibble in his article). I explained to Salam that I had become interested in symmetry. Nobody at Imperial College at the time, other than Salam himself, was doing anything in groups, and attention further afield was focused on the rotation - SO(N) - groups. Reacting to my own half-baked schemes, Salam told me to forget about the rotation groups he taught us, and study group theory in depth, directing me to Eugene Dynkin's classification of Lie subalgebras, about which he had heard from Morton Hamermesh. I found Dynkin incomprehensible without first learning about Lie algebras from Henri Cartan's thesis, which luckily had been reproduced by Dynkin in his 1946 thesis, using his diagram method. From a copy of a translation of Dynkin's thesis which I found in the British Museum Library, I

  12. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2011-01-01

    The CMS Communications Group, established at the start of 2010, has been busy in all three areas of its responsibility: (1) Communications Infrastructure, (2) Information Systems, and (3) Outreach and Education. Communications Infrastructure There are now 55 CMS Centres worldwide that are well used by physicists working on remote CMS shifts, Computing operations, data quality monitoring, data analysis and outreach. The CMS Centre@CERN in Meyrin, is the centre of the CMS offline and computing operations, hosting dedicated analysis efforts such as during the CMS Heavy Ion lead-lead running. With a majority of CMS sub-detectors now operating in a “shifterless” mode, many monitoring operations are now routinely performed from there, rather than in the main Control Room at P5. The CMS Communications Group, CERN IT and the EVO team are providing excellent videoconferencing support for the rapidly-increasing number of CMS meetings. In parallel, CERN IT and ...

  13. Timing of maturation of a Neoproterozoic oceanic arc during Pan-African Orogeny: the Asmlil complex (Anti-Atlas, South Morocco)

    Science.gov (United States)

    Triantafyllou, Antoine; Berger, Julien; Baele, Jean-Marc; Bruguier, Olivier; Diot, Hervé; Ennih, Nasser; Plissart, Gaëlle; Monnier, Christophe; Watlet, Arnaud; Vandycke, Sara

    2016-04-01

    Many intra-oceanic paleo-arcs are exposed in the Pan-African belt surrounding the West African Craton. In the Moroccan Anti-Atlas, remnants of Intra-Oceanic Subduction Zone (IOSZ) are preserved in few erosional windows moulded along the Anti-Atlas Major fault. These complexes highlight a Neoproterozoic paleo-suture made of 760 My back-arc ophiolites thrusted to the south onto a dismembered band of oceanic arc relics. The Asmlil arc complex, located in the southern part of the Bou Azzer inlier, is made of (i) 755 to 745 My- intermediate banded gneiss interpreted as metavolcanic products of a juvenile oceanic arc. This latter has been intruded by (ii) medium-grained hornblende-gabbro and dioritic magmas, in turn intruded by (iii) medium- to coarse grained hornblenditic-granodioritic decametric intrusions under sub-magmatic HT conditions. Hornblende-gabbros are made of garnet + amphibole/cpx relics + epidote + rutile paragenesis. Calculated pseudosections yielded P ~ 11-12 kbar for T ranging between 600 and 720°C for garnet growth. Measured Zr-in-rutile thermometer gave slightly higher temperature ranging between 710-790°C. On the field, garnet-rich leucocratic veinlets suggest that moderate partial melting of the mafic rock or localized dehydration reactions took place under garnet-granulite conditions (>800°C for hydrated chemical system). New geochronological data on garnet-bearing leucogabbros constrain their emplacement at 700 ±7 My (U-Pb zircon with low Th/U age (age of 654 ±7 My (U-Pb method on rutile). Geochemical data of each mafic and ultramafic facies (hornblende gabbro, garnet-bearing facies and hornblendite) show typical arc signature (marked by e.g. Nb-Ta anomaly, (La/Sm)N: 0.8-1.6 ; (Nb/La) < 0.46 ; high Nb/Ba ratio ; 0.4 < K2O < 2.1 wt%). Intrusive granodioritic magmas show depleted HREE trend similar to granitoids in the Kohistan paleo-arc. Melting modeling suggests they are produced by partial melting of a REE-depleted gabbronorite with cpx

  14. Zircon dating of Neoproterozoic and Cambrian ophiolites in West Mongolia and implications for the timing of orogenic processes in the central part of the Central Asian Orogenic Belt

    Science.gov (United States)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Tomurhuu, Dondov; Liu, Dunyi

    2014-06-01

    , we re-subdivide West Mongolia into: a latest Neoproterozoic-early Cambrian, arc-microcontinent collision zone north of the MML; a Cambrian Gobi Altai ophiolite-microcontinent collision zone and a Cambrian Trans-Altai forearc complex south of the MML. The central CAOB evolved in five phases: subduction initiation and arc formation (ca. 573 to > ca. 540 Ma); arc-microcontinent collision (ca. 535-524 Ma); a continuum of slab delamination, overthrusting, crustal thickening and surface uplift (ca. 519-482 Ma) in Northwest Mongolia; initiation of new subduction zones in South Mongolia (ca. 523-511 Ma); and continuing orogeny with local surface uplift. Overall, the current, documented timing of orogenic development in the central CAOB is largely consistent with a W/SW-Pacific style of evolution in terms of subduction initiation, short timescales of individual orogenies, and episodic subduction-collision during a continuing migration of subduction zones.

  15. C- and Sr-isotope stratigraphy of the São Caetano complex, Northeastern Brazil: a contribution to the study of the Meso-Neoproterozoic seawater geochemistry

    Directory of Open Access Journals (Sweden)

    Juan C. Silva

    2005-03-01

    Full Text Available C-isotope and 87Sr/86Sr values for five carbonate successions from the São Caetano Complex, northeastern Brazil, were used to constrain their depositional age and to determine large variations in the C- and Sr-isotopic composition of seawater under the framework of global tectonic events. Three C-isotope stages were identified from base to top in a composed chemostratigraphic section: (1 stage in which delta13C values vary from +2 to +3.7‰ PDB and average 3‰ PDB, (2 stage with delta13C values displaying stronger oscillations (from -2‰ to +‰ PDB, and (3 stage with an isotopic plateau with values around +3.7‰ PDB. Constant 87Sr/86Sr values (~ 0.70600 characterize C-isotope stage 1, whereas slightly fluctuating values (from 0.70600 to 0.70700 characterize C-isotope stage 2. Finally, 87Sr/86Sr values averaging 0.70600 characterize C-isotope stage 3. The C- and Sr- chemostratigraphic pathways permit to state: (a the C- and Sr-isotope secular curves registered primary fluctuations of the isotope composition of seawater during late Mesoproterozoic- early Neoproterozoic transition in the Borborema Province, and (b onset of the Cariris Velhos/Greenville cycle, widespread oceanic rifting, continental magmatic arc formation and onset of the agglutination of Rodinia supercontinent, mostly controlled the C- and Sr-isotope composition of seawater during the C-isotope stages 1, 2 and 3.Valores de isótopos de C e 87Sr/86Sr de cinco seqüências de carbonatos do Complexo São Caetano, nordeste do Brasil; foram usados para estimar a sua idade de deposição e relacionar variações da composição isotópica na água do mar com eventos tectônicos globais. Três estágios de variação de isótopos de carbono foram identificados de base para o topo numa seção quimioestratigráfica composta: (1 estágio em que delta13C varia de +2 a +3.7‰PDB (media 3‰PDB, (2 estágio no qual delta13C varia consideravelmente (de -2 a +3‰PDB e (3 est

  16. Gold and uranium metallogenesis in the framework of Neo-proterozoic crust growth and differentiation: example of the Mayo-Kebbi Massif (Chad) in the Central Africa Orogenic belt

    International Nuclear Information System (INIS)

    The Mayo Kebbi massif located in southwestern Chad between the Congo craton in the South, the West African craton in the west and the Sahara meta-craton to the east exposes a segment of Neo-proterozoic juvenile crust accreted in the Central African orogenic belt during the Pan African orogeny. It consists of two greenstone belts (Zalbi and Goueygoudoum) separated by the May Kebbi calc-alkaline batholith complexes and intruded by calc-alkaline high-K granitic plutons. The whole is covered by Phanerozoic sedimentary formations. The greenstone belts contain sulphide zones hosted mainly by meta-plutonic rocks (granodiorites) and meta-basalts and meta-volcaniclastics. The mineralization comprises pyrite, pyrrhotite, arsenopyrite, chalcopyrite, pentlandite, pentlandite silver, pentlandite cobaltiferous, sphalerite, cobaltite. These sulphides are disseminated, aggregated in form of layers or are filling veins and cracks. The greenstones also contain quartz veins with calcite and chlorite comprising a mineralization made of pyrite, chalcopyrite, galena and gold. Gold is present both as native crystals and as electrum. The high-K calc-alkaline Zabili granitic pluton hosts uranium mineralization related to a superposition of: (1) ductile deformation and metasomatic alteration implying the interaction between magmatic minerals with a Na-rich fluid, of potential magmatic origin, coeval to the main deposition of uranium oxides, followed by (2) brittle deformation and deposition of secondary hydrated uranium silicates involving a Na-Ca-rich fluid. We propose that these uranium mineralizations represent the extreme expression of crustal differentiation as a result of Pan-African reworking of a Neo-proterozoic juvenile crustal segment. (author)

  17. 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

    Directory of Open Access Journals (Sweden)

    Márcio Martins Pimentel

    2003-08-01

    Full Text Available 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 indicates an Archean age for the recrystallization episode (2793 ± 3 Ma and one inherited grain with an age of 3092 ± 9suggests, together with negative values of eNd(T (+0.4 and –4.6, that the magma was contaminated with older crust. Oneleucocratic granite (GOV-1 exposed north of the Goiás greenstone belt crystallized at 626 ± 7 Ma, as indicated by theigneous overgrowths surrounding older inherited cores. The latter indicate a crystallization age of 2893 ± 12 Ma. This rockis interpreted therefore as the product of Neoproterozoic anatexis of ca. 2.89 Ga-old rocks of the Caiçara Complex. This isreinforced by strongly negative eNd(T = 626 values of – 28.0 and –29.0. Its crystallization age is identical to the U-Pb agesof the Itapuranga granite and Uruana quartz syenite, which are exposed to the north of the investigated area and interpretedas syn-tectonic intrusions in relation to the main Brasiliano tectonic event. This represents, therefore, the first evidence ofNeoproterozoic magmatism within the Goiás Archean Block and raises the possibility that other leucogranite dykes andstocks identified regionally may also have been formed during the Brasiliano orogeny.

  18. Lego Group

    DEFF Research Database (Denmark)

    Møller Larsen, Marcus; Pedersen, Torben; Slepniov, Dmitrij

    2010-01-01

    The last years’ rather adventurous journey from 2004 to 2009 had taught the fifth-largest toy-maker in the world - the LEGO Group - the importance of managing the global supply chain effectively. In order to survive the largest internal financial crisis in its roughly 70 years of existence, the...... phase out the entire sourcing collaboration with Flextronics. This sudden change in its sourcing strategy posed LEGO management with a number of caveats. Despite the bright forecasts, the collaboration did not fulfill the initial expectations, and the company needed to understand why this had happened...

  19. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2011-01-01

    The CMS Communications Group has been busy in all three areas of its responsibility: (1) Communications Infrastructure, (2) Information Systems, and (3) Outreach and Education. Communications Infrastructure The 55 CMS Centres worldwide are well used by physicists working on remote CMS shifts, Computing operations, data quality monitoring, data analysis and outreach. The CMS Centre@CERN in Meyrin, is the centre of the CMS Offline and Computing operations, and a number of subdetector shifts can now take place there, rather than in the main Control Room at P5. A new CMS meeting room has been equipped for videoconferencing in building 42, next to building 40. Our building 28 meeting room and the facilities at P5 will be refurbished soon and plans are underway to steadily upgrade the ageing equipment in all 15 CMS meeting rooms at CERN. The CMS evaluation of the Vidyo tool indicates that it is not yet ready to be considered as a potential replacement for EVO. The Communications Group provides the CMS-TV (web) cha...

  20. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2010-01-01

    The CMS Communications Group, established at the start of 2010, has been strengthening the activities in all three areas of its responsibility: (1) Communications Infrastructure, (2) Information Systems, and (3) Outreach and Education. Communications Infrastructure The Communications Group has invested a lot of effort to support the operations needs of CMS. Hence, the CMS Centres where physicists work on remote CMS shifts, Data Quality Monitoring, and Data Analysis are running very smoothly. There are now 55 CMS Centres worldwide, up from just 16 at the start of CMS data-taking. The latest to join are Imperial College London, the University of Iowa, and the Università di Napoli. The CMS Centre@CERN in Meyrin, which is now full repaired after the major flooding at the beginning of the year, has been at the centre of CMS offline and computing operations, most recently hosting a large fraction of the CMS Heavy Ion community during the lead-lead run. A number of sub-detector shifts can now take pla...

  1. Cardiovascular group

    Science.gov (United States)

    Blomqvist, Gunnar

    1989-01-01

    As a starting point, the group defined a primary goal of maintaining in flight a level of systemic oxygen transport capacity comparable to each individual's preflight upright baseline. The goal of maintaining capacity at preflight levels would seem to be a reasonable objective for several different reasons, including the maintenance of good health in general and the preservation of sufficient cardiovascular reserve capacity to meet operational demands. It is also important not to introduce confounding variables in whatever other physiological studies are being performed. A change in the level of fitness is likely to be a significant confounding variable in the study of many organ systems. The principal component of the in-flight cardiovascular exercise program should be large-muscle activity such as treadmill exercise. It is desirable that at least one session per week be monitored to assure maintenance of proper functional levels and to provide guidance for any adjustments of the exercise prescription. Appropriate measurements include evaluation of the heart-rate/workload or the heart-rate/oxygen-uptake relationship. Respiratory gas analysis is helpful by providing better opportunities to document relative workload levels from analysis of the interrelationships among VO2, VCO2, and ventilation. The committee felt that there is no clear evidence that any particular in-flight exercise regimen is protective against orthostatic hypotension during the early readaptation phase. Some group members suggested that maintenance of the lower body muscle mass and muscle tone may be helpful. There is also evidence that late in-flight interventions to reexpand blood volume to preflight levels are helpful in preventing or minimizing postflight orthostatic hypotension.

  2. Group evaporation

    Science.gov (United States)

    Shen, Hayley H.

    1991-01-01

    Liquid fuel combustion process is greatly affected by the rate of droplet evaporation. The heat and mass exchanges between gas and liquid couple the dynamics of both phases in all aspects: mass, momentum, and energy. Correct prediction of the evaporation rate is therefore a key issue in engineering design of liquid combustion devices. Current analytical tools for characterizing the behavior of these devices are based on results from a single isolated droplet. Numerous experimental studies have challenged the applicability of these results in a dense spray. To account for the droplets' interaction in a dense spray, a number of theories have been developed in the past decade. Herein, two tasks are examined. One was to study how to implement the existing theoretical results, and the other was to explore the possibility of experimental verifications. The current theoretical results of group evaporation are given for a monodispersed cluster subject to adiabatic conditions. The time evolution of the fluid mechanic and thermodynamic behavior in this cluster is derived. The results given are not in the form of a subscale model for CFD codes.

  3. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2010-01-01

    The recently established CMS Communications Group, led by Lucas Taylor, has been busy in all three of its main are areas of responsibility: Communications Infrastructure, Information Systems, and Outreach and Education Communications Infrastructure The damage caused by the flooding of the CMS Centre@CERN on 21st December has been completely repaired and all systems are back in operation. Major repairs were made to the roofs, ceilings and one third of the floor had to be completely replaced. Throughout these works, the CMS Centre was kept operating and even hosted a major press event for first 7 TeV collisions, as described below. Incremental work behind the scenes is steadily improving the quality of the CMS communications infrastructure, particularly Webcasting, video conferencing, and meeting rooms at CERN. CERN/IT is also deploying a pilot service of a new videoconference tool called Vidyo, to assess whether it might provide an enhanced service at a lower cost, compared to the EVO tool currently in w...

  4. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2011-01-01

    Communications Infrastructure The 55 CMS Centres worldwide are well used by physicists working on remote CMS shifts, Computing operations, data quality monitoring, data analysis and outreach. The CMS Centre@CERN in Meyrin is particularly busy at the moment, hosting about 50 physicists taking part in the heavy-ion data-taking and analysis. Three new CMS meeting room will be equipped for videoconferencing in early 2012: 40/5B-08, 42/R-031, and 28/S-029. The CMS-TV service showing LHC Page 1, CMS Page 1, etc. (http://cmsdoc.cern.ch/cmscc/projector/index.jsp) is now also available for mobile devices: http://cern.ch/mcmstv. Figure 12: Screenshots of CMS-TV for mobile devices Information Systems CMS has a new web site: (http://cern.ch/cms) using a modern web Content Management System to ensure content and links are managed and updated easily and coherently. It covers all CMS sub-projects and groups, replacing the iCMS internal pages. It also incorporates the existing CMS public web site (http:/...

  5. COMMUNICATIONS GROUP

    CERN Multimedia

    L. Taylor

    2012-01-01

      Outreach and Education We are fortunate that our research has captured the public imagination, even though this inevitably puts us under the global media spotlight, as we saw with the Higgs seminar at CERN in December, which had 110,000 distinct webcast viewers. The media interest was huge with 71 media organisations registering to come to CERN to cover the Higgs seminar, which was followed by a press briefing with the DG and Spokespersons. This event resulted in about 2,000 generally positive stories in the global media. For this seminar, the CMS Communications Group prepared up-to-date news and public material, including links to the CMS results, animations and event displays [http://cern.ch/go/Ch8thttp://cern.ch/go/Ch8t]. There were 44,000 page-views on the CMS public website, with the Higgs news article being by far the most popular item. CMS event displays from iSpy are fast becoming the iconic media images, featuring on numerous major news outlets (BBC, CNN, MSN...) as well as in the sci...

  6. 皖南新元古代花岗闪长岩地球化学特征及构造环境%Geochemical characteristics and tectonic setting of Neoproterozoic granodiorites in South Anhui Province

    Institute of Scientific and Technical Information of China (English)

    翁望飞; 支利庚; 蔡连友; 李永成; 徐生发; 王邦民

    2012-01-01

    皖南新元古代花岗闪长岩沿祁门-歙县-三阳深断裂呈串珠状出露。本文在对其岩石学、地球化学细致分析的基础上,探讨了岩体的岩石成因和产出环境。皖南新元古代花岗闪长岩主要由石英、钾长石和斜长石组成,普遍含富铝矿物黑云母和堇青石,副矿物包括锆石、磷灰石、钛铁矿、独居石、磷钇矿、极少的磁铁矿等。地球化学分析数据显示,岩石总体具高硅、高钾、高铝和低钠、低镁、低钙的特征;岩石富碱(ALK=6.63%),高K2O/Na2O比值(1.33)。里特曼指数δ为0.8~2.91,碱度率AR为1.56~3.14,属高钾钙碱性系列。岩石铝饱和指数(A/CNK-1.31)大于1.1,具强过铝质S型花岗岩的特征。岩石稀土元素呈轻稀土富集、重稀土亏损的特征,∑LREE/∑HREE比值为5.36~8.36,具较强的负铕异常(δEu=0.39~0.7),配分模式为右倾“V”字形态;微量元素明显富集Rb、Th而亏损Ba、Nb、Ta、Sr等,为低Sr高Yb型花岗岩。地球化学特征显示其岩浆源于围岩-中元古代牛屋组浅变质千枚岩的部分熔融,反映陆-陆碰撞挤压造山环境,为晋宁运动晚期华夏板块向北俯冲与扬子板块碰撞造山的火山弧产物。%Neoproterozoic granodiorites in South Anhui Province are developed along Qimen-Shexian-Sanyang deep fracture and outcropped in the form of beaded veins. This paper studied petrographical and geochemi- cal characteristics of these granodiorites as well as its petrogenesis and tectonic setting. These granodior- ites mainly consist of quartz, potash feldspar, plagioelase, biotite and cordierite with minor accessory min- erals of zircon, apatite, ilmenite, monazite, xenotime. Geochemical analyses show that the granodiorites have high contents of SiO2, K2O, Al2O3 and total alkal (ALK=6.63%), but relatively low contents of Na2O, MgO, CaO. The ratios of K2O/Na2O (1.33

  7. From mapping class groups to automorphism groups of free groups

    DEFF Research Database (Denmark)

    Wahl, Nathalie

    2005-01-01

    We show that the natural map from the mapping class groups of surfaces to the automorphism groups of free groups, induces an infinite loop map on the classifying spaces of the stable groups after plus construction. The proof uses automorphisms of free groups with boundaries which play the role of...... mapping class groups of surfaces with several boundary components....

  8. Tectonostratigraphy and depositional history of the Neoproterozoic volcano-sedimentary sequences in Kid area, southeastern Sinai, Egypt: Implications for intra-arc to foreland basin in the northern Arabian-Nubian Shield

    Science.gov (United States)

    Khalaf, E. A.; Obeid, M. A.

    2013-09-01

    This paper presents a stratigraphic and sedimentary study of Neoproterozoic successions of the South Sinai, at the northernmost segment of the Arabian-Nubian Shield (ANS), including the Kid complex. This complex is composed predominantly of thick volcano-sedimentary successions representing different depositional and tectonic environments, followed by four deformational phases including folding and brittle faults (D1-D4). The whole Kid area is divisible from north to south into the lower, middle, and upper rock sequences. The higher metamorphic grade and extensive deformational styles of the lower sequence distinguishes them from the middle and upper sequences. Principal lithofacies in the lower sequence include thrust-imbricated tectonic slice of metasediments and metavolcanics, whereas the middle and upper sequences are made up of clastic sediments, intermediate-felsic lavas, volcaniclastics, and dike swarms. Two distinct Paleo- depositional environments are observed: deep-marine and alluvial fan regime. The former occurred mainly during the lower sequence, whereas the latter developed during the other two sequences. These alternations of depositional conditions in the volcano-sedimentary deposits suggest that the Kid area may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions. Geochemical and petrographical data, in conjunction with field relationships, suggest that the investigated volcano-sedimentary rocks were built from detritus derived from a wide range of sources, ranging from Paleoproterozoic to Neoproterozoic continental crust. Deposition within the ancient Kid basin reflects a complete basin cycle from rifting and passive margin development, to intra-arc and foreland basin development and, finally, basin closure. The early phase of basin evolution is similar to various basins in the Taupo volcanics, whereas the later phases are similar to the Cordilleran-type foreland basin. The

  9. EVIDENCE FOR POSSIBLE METAZOAN ACTIVITY IN NEOPROTEROZOIC ABERRANT STROMATOLITES AND THROM-BOLITE STRUCTURES%新元古代奇异叠层石和凝块石中可疑的动物活动证据

    Institute of Scientific and Technical Information of China (English)

    曹瑞骥

    1999-01-01

    The Neoproterozoic Shijiachong Formation contains a well preserved suite of aberrant stromatolites with graze-like and burrow -like scar structures,thrombolite structures and stromatolite-thrombolite structure unities.Analysis of their morphologies and features leads to the conclusi on that these structures might have been in connection with metazoan activity, but the possibility of their abiotic origin can not be ruled out.As aguess these metazoans seem already to show highly developed behaviour.A close relationship might exist between the thrombolite structure and ecological effects of grazing and burrowing metazoans.The Cambrian life explosion seems to be more apparent tha nreal in evolutionary history because older metazoans in Neoproterozoic were not capable of preservation due to lack of hard parts and suitable embedding sediments.%在湖北保康马桥地区,新元古代神农架群石家冲组中产出一套奇异的叠层石、凝块石和叠层石-凝块石联合体.其中叠层石具有类似于食草和钻孔动物破坏的疤痕.通过对上述构造形态和特征分析,这些构造可能与后生动物的活动有关,但也不排除它们是非生物成因的可能.这些后生动物似乎已显示高度发育的行为.当前的资料表明,在凝块石构造与食草和钻孔动物生态效应之间似乎存在着一种紧密的联系.在生物进化史上,寒武纪生命大爆发似乎仅是一种表面现象,因为较古老的后生动物由于缺少硬壳部分和合适的埋藏条件,而无保存能力.

  10. 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.

  11. 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)

  12. 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)

  13. 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.

  14. 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)

  15. Integrated Groups and Smooth Distribution Groups

    Institute of Scientific and Technical Information of China (English)

    Pedro J. MIANA

    2007-01-01

    In this paper, we prove directly that α-times integrated groups define algebra homo-morphisms. We also give a theorem of equivalence between smooth distribution groups and α-times integrated groups.

  16. Which finite simple groups are unit groups?

    DEFF Research Database (Denmark)

    Davis, Christopher James; Occhipinti, Tommy

    2014-01-01

    We prove that if G is a finite simple group which is the unit group of a ring, then G is isomorphic to either (a) a cyclic group of order 2; (b) a cyclic group of prime order 2^k −1 for some k; or (c) a projective special linear group PSLn(F2) for some n ≥ 3. Moreover, these groups do all occur as...... unit groups. We deduce this classification from a more general result, which holds for groups G with no non-trivial normal 2-subgroup....

  17. Group Work Publication-1991.

    Science.gov (United States)

    Zimpfer, David G.

    1992-01-01

    Lists 21 new publications in group work, of which 9 are reviewed. Those discussed include publications on group counseling and psychotherapy, structured groups, support groups, psychodrama, and social group work. (Author/NB)

  18. Group Composition, Group Interaction and Achievement in Cooperative Small Groups.

    Science.gov (United States)

    Webb, Noreen M.

    This study investigated interaction and achievement in cooperative small groups in four junior high school mathematics classrooms. Ninety-six students learned a one-week unit on consumer mathematics in mixed-ability or uniform-ability groups. Students in mixed-ability groups scored higher on a problem-solving test than students in uniform-ability…

  19. Group dynamic processes in email groups

    OpenAIRE

    Alpay, Esat

    2005-01-01

    Abstract Discussion is given on the relevance of group dynamic processes in promoting decision-making in email discussion groups. General theories on social facilitation and social loafing are considered in the context of email groups, as well as the applicability of psychodynamic and interaction-based models. It is argued that such theories may indeed provide insight into email group interactions, but that...

  20. Group Cohesion in Experiential Growth Groups

    Science.gov (United States)

    Steen, Sam; Vasserman-Stokes, Elaina; Vannatta, Rachel

    2014-01-01

    This article explores the effect of web-based journaling on changes in group cohesion within experiential growth groups. Master's students were divided into 2 groups. Both used a web-based platform to journal after each session; however, only 1 of the groups was able to read each other's journals. Quantitative data collected before and…

  1. Probability groups as orbits of groups

    International Nuclear Information System (INIS)

    The set of double cosets of a group with respect to a subgroup and the set of orbits of a group with respect to a group of automorphisms have structures which can be studied as multigroups, hypergroups or Pasch geometries. When the subgroup or the group of automorphisms are finite, the multivalued products can be provided with some weightages forming so-called Probability Groups. It is shown in this paper that some abstract probability groups can be realized as orbit spaces of groups. (author)

  2. Group theories: relevance to group safety studies.

    Science.gov (United States)

    Benevento, A L

    1998-01-01

    Promoting safety in the workplace has been attempted in a variety of ways. Increasingly, industries are using groups such as safety teams and quality circles to promote worker safety. Group influences on individual behavior and attitudes have long been studied in the social psychology literature, but the theories have not been commonly found outside the psychology arena. This paper describes the group theories of group polarization, risky shift, social loafing, groupthink and team think and attempts to apply these theories to existing studies that examine work group influences on safety. Interesting parallels were found but only one study examined group influences as their primary focus of research. Since groups are increasingly used for safety promotion, future research on safety that studies group influences with respect to current group theories is recommended. PMID:24441299

  3. The Tectonic Cycle of Neoproterozoic in Tarim Basin and its Hydrocarbon Implications%塔里木盆地新元古代伸展-挤压构造旋回

    Institute of Scientific and Technical Information of China (English)

    郭群英; 邬光辉; 冯晓军; 何曙

    2015-01-01

    Based on the analysis of chronology data,drilling and seismic data,it is showed that the tectonic characteris-tics is totally different from that of Cambrian in Tarim basin. There is strong intraplate extension activity and magmatism with the peak ~770 Ma,the same tectonothermal events as the breakup of the Rodinia supercontinent in Nanhua Period, which resulted in a serial of E-W trend discontinuous rift system in Tarim craton.In the end of Sinian Period,there is far-ranging uplift and denudation related to Pan-African orogenic with a large regional unconformity,which caused the north-south zonation tectonic regime different with the east-west zonation in Cambrian.It undergone 4 stages evolution in Neo-proterozoic with the rifting stage- the faulting depression stage in Nanhua Period,the depression stage and compression uplift stage in Sinian Period,indicated an integrated intense extension-compression tectonic cycle.It is demonstrated that the tectonic evolution in Neoproterozoic is much different from that in Phanerozoic with large-scale unconformity be-tween them.%塔里木盆地新元古代构造演化对显生宙成盆成烃作用研究具重要意义。通过锆石年代学研究结合新的钻探与地震资料进行构造解析,结果发现:①塔里木盆地内部发育峰值约770 Ma的与超大陆裂解相关的强伸展构造活动,南华纪可能存在一系列近EW向展布的不连续断陷系统;②震旦纪晚期存在与“泛非运动”相关的广泛抬升剥蚀,与寒武纪存在大型的区域不整合,南北分带的构造体制不同。综合分析表明,塔里木盆地新元古代经历南华纪大陆裂谷-断陷期、震旦纪坳陷-挤压抬升期等4期构造演变,发育完整的强伸展-挤压构造旋回;新元古代具与显生宙显著不同的构造演化特征,震旦—寒武系间存在大规模构造-沉积间断。

  4. Paleoenvironments in Meso-Neoproterozoic carbonates of the Mbuji-Mayi Supergroup (Democratic Republic of Congo) - Microfacies analysis combined with C-O-Sr isotopes, major-trace elements and REE + Y distributions

    Science.gov (United States)

    Delpomdor, F.; Blanpied, C.; Virgone, A.; Préat, A.

    2013-12-01

    The Meso- and Neoproterozoic Mbuji-Mayi Supergroup (1155 Ma to ca. 800 Ma) was deposited in the SE-NW trending siliciclastic-carbonate failed-rift in the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. Drillcore- and outcrop-derived microfacies, isotope (C, O and Sr) compositions of carbonates and REE + Y distributions are integrated to unravel the paleoenvironmental and chemical conditions prevailing during deposition and alteration (or contamination) of the Mbuji-Mayi carbonates. The carbonate succession (BIe subgroup and BIIa to BIIe subgroups), composed of 11 microfacies (MF), records the evolution of a marine ramp submitted to evaporation, with basinal and low-energy outer-ramp environments (MF1-MF5), biohermal mid-ramp (MF6) and restricted tide-dominated lagoon inner-ramp (MF7-MF9) settings, overlain by lacustrine (MF10) and sabkha (MF11) environments. The ramp margin is characterized by thick stacks of stromatolitic bioherms. δ13C and δ18O relationships in the Mbuji-Mayi carbonates allow discrimination between meteoric (δ13C: -7.5‰ to +0.0‰, δ18O: -7.0‰ to -1.0‰) and burial lithifications (δ13C: -1.5‰ to +0.0‰, δ18O: -15.1‰ to -7.0‰), that overprinted a primary marine signal (δ13C: -1.5‰ to +2.0‰, δ18O: -3.0‰ to +0.5‰) partially preserved in the subgroups. Unaltered pristine signals are found in the Mbuji-Mayi carbonates with 87Sr/86Sr ratios (0.7065-0.7082) similar to those of the marine-preserved strontium signatures of the early Neoproterozoic oceans. The PAAS-normalized REE + Y distributions indicate that the BIe carbonates were altered by Fe-oxide-rich hydrothermal fluids. BIIb and BIIe carbonates exhibit uniform light REE depleted patterns suggesting inputs of detrital river material whereas a marine seawater, highlighted by the REE + Y distributions is preserved in BIIc and BIId carbonates. The pattern of carbon, oxygen and strontium isotopic variations in the Mbuji-Mayi carbonates reflects deposition and early diagenesis in

  5. Possible Pre-Cryogenian Eutrophication Event Recorded In ~770-742 Ma Strata Of The Uinta Mountain Group, Utah, USA

    Science.gov (United States)

    Dehler, C. M.; Hayes, D. S.; Nagy, R. M.

    2011-12-01

    Previous mid-Neoproterozoic microfossil diversity studies yield evidence for a relatively sudden biotic change prior to the Cryogenian (Sturtian) glaciations. In an event interpreted as a mass extinction of eukaryotic phytoplankton followed by bacterial dominance, diverse assemblages of complex acritarchs are replaced by more uniform assemblages consisting of simple leiosphaerid acritarchs and bacteria. Recent data from the Chuar Group of the Grand Canyon (770-742 Ma) suggest this biotic change was caused by eutrophication rather than the previous idea that this change was due to the direct effects of Sturtian glaciation. Evidence includes total organic carbon increases indicative of increasing primary productivity followed by iron speciation values that suggest sustained water column anoxia. A new data set (this study) suggests that this same eutrophication event may be recorded in shale units of the formation of Hades Pass and the Red Pine Shale of Utah's Neoproterozoic Uinta Mountain Group (770-742 Ma). Preliminary results of this study include a significant shift in microfossil assemblage from a higher-diversity (H'= 0.60) fauna that includes some ornamented acritarchs to a lower-diversity (H' = 0.11) fauna dominated by smooth leiosphaerids and microfossils of a bacterial origin (Ba|lla/ Sphaerocongregus sp.). This biotic change co-occurs with a significant increase in total organic carbon values that directly follows a positive carbon-isotopic excursion, suggesting increased primary productivity that may have been the result of elevated sediment influx and nutrient availability. Both the biotic change and period of increased total organic carbon values correspond with the onset of an interval of anoxia (indicated by total iron to aluminum ratios above 0.60) and a spike in sulfur concentration. Thus far, these findings support 1) correlations between the Uinta Mountain and Chuar groups, 2) the idea that the biotic turnover preserved in both strata was at least

  6. A neoproterozoic age for the chromitite and gabbro of the Tapo Ultramafic Massif, Eastern Cordillera, Central Peru, and its tectonic implications

    OpenAIRE

    Tassinari, Colombo G.; Castroviejo Bolibar, Ricardo; Rodrigues, Jose F.; Acosta, Jorge; Pereira, Eurico

    2011-01-01

    The ultramafic-mafic rocks of the Tapo Complex are exposed in the Eastern Cordillera of the Central Peruvian Andes. This complex is composed of serpentinised peridotites and metabasites with some podiform chromitite lenses and chromite disseminations and overlies the sandstones, conglomerates, and tuffs of the Carboniferous Ambo Group. The metagabbros and amphibolites showa tholeiitic affiliation and a flat REE spider diagram, with a slight LREE depletion and a positive Eu anomaly suggesting ...

  7. AREVA group overview; Presentation du groupe AREVA

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2002-02-08

    This document presents the Group Areva, a world nuclear industry leader, from a financial holding company to an industrial group, operating in two businesses: the nuclear energy and the components. The structure and the market of the group are discussed, as the financial assets. (A.L.B.)

  8. Group Dynamic Processes in Email Groups

    Science.gov (United States)

    Alpay, Esat

    2005-01-01

    Discussion is given on the relevance of group dynamic processes in promoting decision-making in email discussion groups. General theories on social facilitation and social loafing are considered in the context of email groups, as well as the applicability of psychodynamic and interaction-based models. It is argued that such theories may indeed…

  9. Interagency mechanical operations group numerical systems group

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-09-01

    This report consists of the minutes of the May 20-21, 1971 meeting of the Interagency Mechanical Operations Group (IMOG) Numerical Systems Group. This group looks at issues related to numerical control in the machining industry. Items discussed related to the use of CAD and CAM, EIA standards, data links, and numerical control.

  10. Introduction to Sporadic Groups

    CERN Document Server

    Boya, Luis J

    2011-01-01

    This is an introduction to finite simple groups, in particular sporadic groups, intended for physicists. After a short review of group theory, we enumerate the $1+1+16=18$ families of finite simple groups, as an introduction to the sporadic groups. These are described next, in three levels of increasing complexity, plus the six isolated "pariah" groups. The (old) five Mathieu groups make up the first, smallest order level. The seven groups related to the Leech lattice, including the three Conway groups, constitute the second level. The third and highest level contains the Monster group $\\mathbb M$, plus seven other related groups. Next a brief mention is made of the remaining six pariah groups, thus completing the $5+7+8+6=26$ sporadic groups. The review ends up with a brief discussion of a few of physical applications of finite groups in physics, including a couple of recent examples which use sporadic groups.

  11. Introduction to Sporadic Groups

    Directory of Open Access Journals (Sweden)

    Luis J. Boya

    2011-01-01

    Full Text Available This is an introduction to finite simple groups, in particular sporadic groups, intended for physicists. After a short review of group theory, we enumerate the 1+1+16=18 families of finite simple groups, as an introduction to the sporadic groups. These are described next, in three levels of increasing complexity, plus the six isolated ''pariah'' groups. The (old five Mathieu groups make up the first, smallest order level. The seven groups related to the Leech lattice, including the three Conway groups, constitute the second level. The third and highest level contains the Monster group M, plus seven other related groups. Next a brief mention is made of the remaining six pariah groups, thus completing the 5+7+8+6=26 sporadic groups. The review ends up with a brief discussion of a few of physical applications of finite groups in physics, including a couple of recent examples which use sporadic groups.

  12. Experience with Group Supervision

    OpenAIRE

    Chen, Weiqin

    2006-01-01

    Supervision can take a few different forms. For example, it can be one-to-one supervision and it can also be group supervision. Group supervision is an important process within the scientific community. Many research groups use this form to supervise doctoral- and master students in groups. Some efforts have been made to study this process. For example, Samara (2002) studied the group supervision process in group writing. However, group supervision has not been studied thorough...

  13. SHRIMP zircon U-Pb dating of ;Neoproterozoic Chencai Complex in Jiangshan-Shaoxing fault zone and its implications%江山-绍兴断裂带陈蔡岩群片麻岩SHRIMP锆石U-Pb年龄及其地质意义

    Institute of Scientific and Technical Information of China (English)

    高林志; 丁孝忠; 刘燕学; 张传恒; 张恒; 黄志忠; 许兴苗; 周宗尧

    2014-01-01

    A series of parametamorphic rocks, as the oldest metamorphosed basement in the Jiangshan-Shaoxing fault zone, consist of gneiss, schist and marble of medium-deep metamorphism and are in fault contact with the Shuangxiwu Group in Chencai area, Zhu-ji County, Zhejiang Province. Because the Chencai Group which suffered deep metamorphism and deformation is developed in the southern part of the Jiangshan-Shaoxing fault zone, most Chinese geologists assign the group to the small patch of the Cathysia Plate and make correlation with Paleoproterozoic Mayuan Group in Fujian Province or the Badu Group in Zhejiang Province and the Me-soproterozoic Tieshajie Foramtion in Jiangxi Province. Lots of zircons were collected from garnet sillimanite biotite plagiogneiss and sillimanite garnet biotite gneiss in the Xiawuzhai Formation of the Chencai Group. The zircons have a typical core, mantle and edge structure, the age of the core is usually in the range of 848~845Ma and the age of the late accretion edge is Caledonian (431Ma). Ac-cording to the zircon dating of the plagioclase gneiss of the Chencai Group, the authors consider that the Chencai Group can not on-ly be correlated with the Paleoproterozoic Mayuan Group of Fujian Province, but also with Mesoproterozoic Tieshajie Formation of Jiangxi Province. The protolith age of the Chencai Group suggests Neoproterozoic ( 848~845Ma), which is younger than that of the Shuangxiwu Group (905~877Ma) in the stratigraphic column and the stratigraphic division, and the age belongs to the domain of the Jiangnan Orogenic Belt. However, this age has an important significance in the correlation of metamorphosed provinces in the Jiang-Shan-ShaoXing fault zone and the study of its tectonic evolution.%浙江诸暨陈蔡地区发育一套副变质岩层,由中深度变质的片麻岩、片岩和大理岩组成,与双溪坞群为断层接触,其地质时代多被视为与江山-绍兴断裂带南东侧的华夏地块古老变质基底相同。

  14. Small Group Research

    Science.gov (United States)

    McGrath, Joseph E.

    1978-01-01

    Summarizes research on small group processes by giving a comprehensive account of the types of variables primarily studied in the laboratory. These include group structure, group composition, group size, and group relations. Considers effects of power, leadership, conformity to social norms, and role relationships. (Author/AV)

  15. Group B Strep Infection

    Science.gov (United States)

    MENU Return to Web version Group B Strep Infection Overview What is group B strep? Group B streptococcus, or group B strep for short, is a certain kind ... in the intestine, rectum, and vagina (in women). Group B strep doesn’t usually cause problems in ...

  16. Structural analysis of the Rio Pardo Group - southeast of Bahia state

    Directory of Open Access Journals (Sweden)

    Marcos Egydio-Silva

    2011-12-01

    Full Text Available The Meso- to Neoproterozoic Rio Pardo Group is located in the southeastern region of the Bahia State and consistsof low-grade metasedimentary rocks deposited on Paleoproterozoic to Archean basement. From the base to the top, themetasedimentary rocks are grouped into the following sequences: Panelinha Formation consisting of coarse-grainedimmature clastics; the overlying Itaimbé Subgroup which is made up of the Camacã Formation (metapelites with localcarbonates, the Água Preta Formation (fi ne-grained metapsamites and local carbonate lenses, Serra do Paraíso Formation(metacarbonates and quartzites and the Santa Maria Eterna Formation (metaconglomerates and metacarbonates. TheSalobro Formation was deposited unconformably on this sequence and consists of coarse-grained immature and local fi negrainedclastic rocks. The Rio Pardo Group was affected by three successive folding events, which were recorded in twolitho-structural units. The litho-structural unit 1 is located in the northeastern part of the basin, and the litho-structural unit2, in the southwestern part of the basin. These units are separated by the Rio Pardo-Água Preta inverse fault, trending NWSEand dipping SW. The fi rst unit is autochthonous and monophasic and displays open folds and slaty cleavage, changinggradually towards southwest into large overturned folds with axial plane schistosity. The second unit is polyphasic andshows large folds with NE vergence. A third folding is represented by folds and foliations present at the western marginof the basin. The NE vergence of the Rio Pardo Group can be explained by changes in the deformation regime and in thedirection of the principal axis of deformation in the north sector of the Araçuaí belt during the Brasiliano collision orogen.The tectonic transport to the north could be the cause of deformation of the Rio Pardo Group.

  17. Redefining Cohesiveness in Groups.

    Science.gov (United States)

    Keyton, Joann; Springston, Jeff

    1990-01-01

    Attempted to replicate and extend research on work of Kelly and Duran in assessing relationship of group member perceptions of group interaction to group effectiveness. Concludes perceived similarity may not always align with perceptions of cohesiveness. (Author/ABL)

  18. Geochemistry and U-Pb geochronology of the Neoproterozoic-Cambrian Koettlitz Glacier Alkaline Province, Royal Society Range, Transantarctic Mountains, Antarctica

    International Nuclear Information System (INIS)

    In the southeastern foothills of the Royal Society Range, southern Victoria Land, a diverse array of gabbroic to granitic rocks intrude marbles and schists of the late Proterozoic Skelton Group. A-type characteristics include abundant fluorite, high SiO2, Na2O, K2O, Ga/Al, Y and Nb with low Sr and CaO. A monzogabbro and a monzonite have identical 539 ± 4 Ma ages and a quartz-monzonite is 534 ± 3 Ma. Nearby is a 517 ± 4 Ma A-type granite pluton with more extreme A-type geochemical characteristics. This is the first report of A-type granites from anywhere in the Transantarctic Mountains. The presence of these A-type granitoids in close proximity to contemporaneous nepheline syenites and carbonatites suggests strongly that this area was undergoing extension during pluton emplacement. The occurrence of A-type granitoids at least as far south as the Skelton Glacier suggests that the atypical, extensional province, herein referred to as the Koettlitz Glacier Alkaline Province, extends for at least 60 km parallel to the Transantarctic Mountains. Alkaline magmatism in the Koettlitz Glacier Alkaline Province initiated before the generation of voluminous subduction-related calc-alkaline magmas related to the Ross Orogeny. (author). 38 refs., 7 figs., 2 tabs

  19. A Neoproterozoic age for the chromitite and gabbro of the Tapo ultramafic Massif, Eastern Cordillera, Central Peru and its tectonic implications

    Science.gov (United States)

    Tassinari, Colombo C. G.; Castroviejo, Ricardo; Rodrigues, Jose F.; Acosta, Jorge; Pereira, Eurico

    2011-12-01

    The ultramafic-mafic rocks of the Tapo Complex are exposed in the Eastern Cordillera of the Central Peruvian Andes. This complex is composed of serpentinised peridotites and metabasites with some podiform chromitite lenses and chromite disseminations and overlies the sandstones, conglomerates, and tuffs of the Carboniferous Ambo Group. The metagabbros and amphibolites show a tholeiitic affiliation and a flat REE spider diagram, with a slight LREE depletion and a positive Eu anomaly suggesting magmatic accumulation of plagioclase, in an ocean ridge or ocean island environment. Sm-Nd isotopic analyses were performed on chromite as well as on whole rock from the gabbro. All samples yielded an Sm-Nd isochrone age of 718 ± 47 Ma with an initial 143Nd/ 144Nd of 0.51213 ± 0.00005. The ɛNd (718 Ma) values calculated for both chromite and gabbro are in close agreement, around 8.0, implying that they were formed at the same time from the same mantelic magma source. Furthermore a K-Ar age on amphibole of 448 ± 26 Ma was obtained, interpreted as the cooling age of a younger orogenic event. These rocks represent slices of oceanic crust (from a dismembered ophiolitic complex), metamorphosed and later overthrust on upper Palaeozoic continental formations.

  20. Higher arithmetic Chow groups

    OpenAIRE

    Burgos Gil, José Ignacio; Feliu, E.

    2009-01-01

    We give a new construction of higher arithmetic Chow groups for quasi-projective arithmetic varieties over a field. Our definition agrees with the higher arithmetic Chow groups defined by Goncharov for projective arithmetic varieties over a field. These groups are the analogue, in the Arakelov context, of the higher algebraic Chow groups defined by Bloch. The degree zero group agrees with the arithmetic Chow groups of Burgos. Our new construction is shown to be a contravariant functor and is ...

  1. Mineral chemistry of radioactive and associated phases from neoproterozoic unconformity related uranium deposits from Koppunuru, Palnad sub-basin, Guntur District, Andhra Pradesh, India

    International Nuclear Information System (INIS)

    Unconformity proximal uranium mineralization at Koppunuru occurs in basement granitoids and the overlying Banganalapalle Formation of Kurnool Group in Palnad sub-basin. The U-mineralization transgresses the unconformity both above and below. Later remobilization of uranium is evident, as they are intermittently intercepted within the sediments overlying the unconformity. Subsurface exploration by drilling intercepted three mineralization bands, viz. Band A and B upto 80m above the unconformity in the overlying Banganapalle quartzite and Band C, mostly sub-parallel to the unconformity and confined to basal conglomerate/grit horizon except a few boreholes where it is transgressing to granitic horizon (2 (upto 2.00 %), ThO2 (0.03 to 1.51 %) and RE2O3 (0.12 to 3.56 %). Such activities signify the processes of epigenetic fluid/gel related to U-concentration. At increasing depths, possibility of AI- bearing radioactive phases is also envisaged. The radioactive phases present in the samples reveal negligible to low thorium indicating low temperature phenomena. They are likely to be emplaced by the epigenetic solution/gel rich in U, Ti, Si, AI, Ca, P and Pb, preferably along available spaces as vein, cavity and grain boundary. U-associated sulphides occurring as veins and fracture fills, essentially comprise pyrite, pyrrhotite, chalcopyrite, pentlandite and galena. They have normal chemistry but for subtle variations in minor elements. The pyrite and pyrrhotite are invariably arseniferous and they dominate the sulphides. Thus, it is concluded that the area has potential for multi-episodic epigenetic U-mineralization

  2. Syn-collisional peraluminous magmatism in the Rio Doce region: mineralogy, geochemistry and isotopic data of the Neoproterozoic Urucum Suite (eastern Minas Gerais State, Brazil)

    Energy Technology Data Exchange (ETDEWEB)

    Nalini Junior, Herminio Arias [Ouro Preto Univ., MG (Brazil). Escola de Minas. Dept. de Geologia]. E-mail: nalini@degeo.ufop.br; Bilal, Essaid [Ecole de Mines de Saint Etienne (France); Neves, Jose Marques Correia [Minas Gerais Univ., Belo Horizonte, MG (Brazil). Inst. de Geociencias

    2000-03-01

    The Urucum Suite granitoids (Rio Doce region southeastern Brazil) contains four main facies: megafeldspar granites, deformed medium-to-coarse-grained granites, tourmaline, and pegmatitic facies. they intrude both the staurolite-garnet-muscovite-biotite schist of the Sao Tome formation (Rio Doce Group) and the Galileia metaluminous suite (596{+-}4 Ma). Detailed structural studies suggest that the Urucum Suite emplaced during an important dextral strike-slip movement (D{sub 1} phase) of the Brasiliano orogeny (650-450 Ma). Modal and chemical mineralogical variations suggest an evolution from the megafeldspar facies to the pegmatitic facies. Whole-rock geochemistry indicates the peraluminous character of the Urucum suite granitoids, the evolution from the megafeldspar facies granites to pegmatite facies granites to pegmatitic facies granites and suggests the syn-collisional character of this suite. U-Pb zircon (582{+-} 2 Ma) and monazite (576-573 {+-}4 Ma) data indicate that the Urucum Suite emplaced during the Brasiliano orogeny. The peraluminous nature of the Suite and isotopic rich character in the Rb-Sr ({sup 87} Sr/{sup 86} Sr = 0.7114 to 0.7165) and Sm Nd (eNd{sub (T)} = -7.4 and -8.2) systems indicate that it formed by partial melting of older intermediate to felsic crustal sources. Based on early Proterozoic model-ages (2.3 to 1.8 Ga) and on 2.0 ga U-Pb inherited signature, granitoids of the Suite are probably derived from a rocks with a long crustal residence (Transamazonian basement), without extensive mantle contribution. (author)

  3. Syn-collisional peraluminous magmatism in the Rio Doce region: mineralogy, geochemistry and isotopic data of the Neoproterozoic Urucum Suite (eastern Minas Gerais State, Brazil)

    International Nuclear Information System (INIS)

    The Urucum Suite granitoids (Rio Doce region southeastern Brazil) contains four main facies: megafeldspar granites, deformed medium-to-coarse-grained granites, tourmaline, and pegmatitic facies. they intrude both the staurolite-garnet-muscovite-biotite schist of the Sao Tome formation (Rio Doce Group) and the Galileia metaluminous suite (596±4 Ma). Detailed structural studies suggest that the Urucum Suite emplaced during an important dextral strike-slip movement (D1 phase) of the Brasiliano orogeny (650-450 Ma). Modal and chemical mineralogical variations suggest an evolution from the megafeldspar facies to the pegmatitic facies. Whole-rock geochemistry indicates the peraluminous character of the Urucum suite granitoids, the evolution from the megafeldspar facies granites to pegmatite facies granites to pegmatitic facies granites and suggests the syn-collisional character of this suite. U-Pb zircon (582± 2 Ma) and monazite (576-573 ±4 Ma) data indicate that the Urucum Suite emplaced during the Brasiliano orogeny. The peraluminous nature of the Suite and isotopic rich character in the Rb-Sr (87 Sr/86 Sr = 0.7114 to 0.7165) and Sm Nd (eNd(T) = -7.4 and -8.2) systems indicate that it formed by partial melting of older intermediate to felsic crustal sources. Based on early Proterozoic model-ages (2.3 to 1.8 Ga) and on 2.0 ga U-Pb inherited signature, granitoids of the Suite are probably derived from a rocks with a long crustal residence (Transamazonian basement), without extensive mantle contribution. (author)

  4. Higher arithmetic Chow groups

    DEFF Research Database (Denmark)

    Gil, J. I. Burgos; Feliu, Elisenda

    2012-01-01

    context, of the higher algebraic Chow groups defined by Bloch. For projective varieties the degree zero group agrees with the arithmetic Chow groups defined by Gillet and Soulé, and in general with the arithmetic Chow groups of Burgos. Our new construction is shown to be a contravariant functor and is...... endowed with a product structure, which is commutative and associative....

  5. Assertive Training in Groups

    Science.gov (United States)

    Sansbury, David L.

    1974-01-01

    This article describes a group approach to helping the nonassertive client. After describing the group composition and goals, he presents a session by session description for conducting the assertive training group. In addition, he presents suggestions based on experiences in leading the group. (Author)

  6. Robust Group Linkage

    OpenAIRE

    Li, Pei; Dong, Xin Luna; Guo, Songtao; Maurino, Andrea; Srivastava, Divesh

    2015-01-01

    We study the problem of group linkage: linking records that refer to entities in the same group. Applications for group linkage include finding businesses in the same chain, finding conference attendees from the same affiliation, finding players from the same team, etc. Group linkage faces challenges not present for traditional record linkage. First, although different members in the same group can share some similar global values of an attribute, they represent different entities so can also...

  7. Neoproterozoic-Paleozoic Sedimentary Basins Evolution of Xing-Meng Orogenic Belt%兴蒙造山系新元古代-古生代沉积盆地演化

    Institute of Scientific and Technical Information of China (English)

    杨文麟; 骆满生; 王成刚; 徐增连

    2014-01-01

    Based on comprehensive analysis of the type,sedimentary formation,biostratigraphy and chronostratigraphy for 24 main sedimentary basins,we study the evolution of sedimentary basins of Xing-Meng orogenic belt in the Neoproterozoic-Paleo-zoic,dividing it into six phases as follows.(1)The epicontinental accretion in the Neoproterozoic to Early Cambrian character-ized by the assembly of Ergun and Xingan blocks,as Huanyu-Xinlin ophiolite accreted to margin of southern Ergun blocks;(2)The stable epicontinental sediment in the Terreneuvian-Serises 2,with the feature of a relatively stable clastic-calciclastic sediment around the blocks while Jiamusi massif affected by Late Pan-African metamorphic event;(3)The formation of archi-pelagic arc-basin systems in the Early and Middle Ordovician,marked by the distribution of arc-basin in the margin of Duobaoshan and the different levels oceanic crust subduction effect among other land masses;(4)The development of archipe-lagic arc-basin systems in the Late Ordovician to Pridoli,as the erosion of the uplifted land masses;(5)The subduction of ar-chipelagic arc-basin systems in the Early Devonian to Early Carboniferous,characterized by the collage of Ergun-Xingan and Songnen blocks and the transformation of western margin of Jiamusi massif from passive to active in the late Early Carbonifer-ous;(6)The oceanic-continental transition in the Late Carboniferous-Lopingian,characterized by the assembly of Jiamusi mas-sif,Songnen massif,and Khanka massif.Massifs of Northeast China completely collaged to a whole.%在系统分析兴蒙造山系新元古代-古生代24个沉积盆地类型、沉积建造、生物地层与年代地层等特征的基础上,划分了6个沉积大地构造演化阶段并对其进行讨论:(1)新元古代-寒武纪早期陆缘增生阶段:额尔古纳地块向南增生并与兴安地块拼贴,形成环宇-新林蛇绿岩拼合带;(2)寒武纪纽芬兰世-第二世陆缘稳定沉积阶段:各地块边

  8. First evidence for expressive neoproterozoic intraplated mafic rocks and magma mixing in post-collisional A-PA type granites, Southern Brazil: Geochemistry and U-Pb (zircon), Nd-Sr-18O(zircon) isotope investigations

    International Nuclear Information System (INIS)

    New and recent geological investigations around Pien-Tijucas suture zone, between Luis Alves and Curitiba Microplates (Basei et al.2000) led to mapping of Palermo, Agudos do Sul and Rio Negro A-PA type Granites with expressive expositions of alkaline felsic ans mafic rocks and, associated mafic and felsic hybrid rocks. The suture zone is formed by subduction arc-related Pien-Mandirituba deformed calc-alkaline I-type granite belt and serpentinized supra subduction zone (SSZ) obducted mantle rocks with intrusive Neoproterozoic (650-630 Ma) very high Cr and Ni tholeitic gabbros. The Pien-Mandirituba calc-alkaline I-type Granite Belt is constituted by three main granite suites. The older emplaced pre-collisional suite is constituted by deformed to highly deformed amphibole and biotite-rich, magmatic epidote-absent quartz-monzodiorites and granodiorites formed between 620 and 610 Ma. The second sincollisional granite suite is constituted by deformed and slightly deformed low content amphibole-biotite-magmatic epidote-bearing, quartz-monzodiorites, granodiorites and leucogranodiorites emplaced between 605 and 595 Ma. The third, also sincollisional, granite suite is deformed to highly deformed biotite ± amphibole monzogranites. The deformation age of the three non-cogenetic granite suites of this granite belt is between 605-595 Ma. The granite rocks of the Pien-Mandirituba Granite Belt are meta-aluminous to slightly peraluminous, high K calc-alkaline, generally with high Ba, high Sr and low Rb contents. Palermo, Agudos do Sul and Rio Negro Granites are components of the expressive Neoproterozoic volcanic and plutonic alkaline-peralkaline Serra do Mar Suite (Kaul 1997), emplaced in extensional post-collisional and anorogenic settings along the central portion and northern border of the Luis Alves Microplate and southern border of the Curitiba Microplate. Magma mixing evidence is rare ou absent in the other components of the Serra do Mar volcanic and plutonic suite. The

  9. Pretty Private Group Management

    CERN Document Server

    Heen, Olivier; Neumann, Christoph; Onno, Stéphane

    2011-01-01

    Group management is a fundamental building block of today's Internet applications. Mailing lists, chat systems, collaborative document edition but also online social networks such as Facebook and Twitter use group management systems. In many cases, group security is required in the sense that access to data is restricted to group members only. Some applications also require privacy by keeping group members anonymous and unlinkable. Group management systems routinely rely on a central authority that manages and controls the infrastructure and data of the system. Personal user data related to groups then becomes de facto accessible to the central authority. In this paper, we propose a completely distributed approach for group management based on distributed hash tables. As there is no enrollment to a central authority, the created groups can be leveraged by various applications. Following this paradigm we describe a protocol for such a system. We consider security and privacy issues inherently introduced by rem...

  10. Groups as Graphs

    CERN Document Server

    Kandasamy, W B Vasantha

    2009-01-01

    For the first time we represent every finite group in the form of a graph in this book. The authors choose to call these graphs as identity graph, since the main role in obtaining the graph is played by the identity element of the group. This study is innovative because through this description one can immediately look at the graph and say the number of elements in the group G which are self-inversed. Also study of different properties, like the subgroups of a group, normal subgroups of a group, p-sylow subgroups of a group and conjugate elements of a group are carried out using the identity graph of the group in this book. This book has four chapters. The first chapter is introductory. The second chapter represents groups as graphs. In the third chapter, we have defined similar types of graphs for algebraic structures like commutative semigroups, loops, commutative groupoids and commutative rings. The final chapter poses 52 problems.

  11. Occurrence of helically coiled microfossil Obruchevella in the Owk Shale of the Kurnool Group and its significance

    Indian Academy of Sciences (India)

    Mukund Sharma; Yogmaya Shukla

    2012-06-01

    The present study reports occurrence of helically coiled microfossil Obruchevella Reitlinger from the Owk Shale of the Kurnool Group from the peninsular India. The age of the Kurnool Group is poorly constrained due to the absence of direct radiometric dating and meager palaeobiological data. Occurrence of Obruchevella is considered as a typical Vendian marker genus recorded mostly from close to the Precambrian–Cambrian boundary successions. Hence, the present assemblage is important to ascertain the age of the basin. In the Owk Shale, four species of Obruchevella, viz., O. delicata, O. parva, O. minor and O. valdaica are recorded as organic walled microfossils. Among them O. valdaica is the largest in terms of size parameters. On the global scale, the recovered species occur in the Late Neoproterozoic to Early Cambrian sediments. Therefore, the occurrence of microfossil Obruchevella in the Owk Shale and known burrow structures in the Narji Limestone suggest Ediacaran age close to the Cambrian for the Kurnool Basin and challenges the recently assigned esoproterozoic age of the basin.

  12. The Araxá Group in the South-Southwest Region of the Goiás State

    Directory of Open Access Journals (Sweden)

    Guillermo Rafael Beltran Navarro

    2013-06-01

    Full Text Available In the S – SW region of Goiás State, Brazil, the Araxá Group is constituted of a metasedimentary sequence containing schistoseand gneissic (garnet-biotite-quartz schists, feldspatic garnet-biotite-quartz schists, garnet-biotite-quartz paragneisses,with muscovite and locally amphibole, epidote, kyanite and staurolite. This sequence presents intercalations of metaultramaficrocks (serpentinite, actinolite schist, talc schist, chlorite schist, metamafic ones (amphibolite, amphibole schistcontaining or not garnet, garnet amphibolite and associated granitic bodies. Chemically, the Araxá Group metasedimentspresent peraluminous composition, showing enrichment in LILE, when compared with HFSE and REE, and displayingnegative anomalies of Nb, Ta, Sr, P and Ti. Their chemical composition is that of greywake and the chemical characteristicsof the sediments are generated in magmatic arcs. Isotopic data for Sm/Nd – model ages (TDM between 1,04 – 1,51 and1,76 – 2,26 Ga – and U/Pb (predominance of zircon with ages < 900 Ma suggest that these metasediments have Neoproterozoicrocks as the source rocks. Chemical and isotopic characteristics of the studied metasediments suggest that theirsource are rocks originated in magmatic arcs and that they were deposited in a fore arc basin developed in the margins ofNeoproterozoic island arcs.

  13. Magnetotelluric investigation of the Vestfold Hills and Rauer Group, East Antarctica

    Science.gov (United States)

    Peacock, J. R.; Selway, K.

    2016-04-01

    The Vestfold Hills and Rauer Group in East Antarctica have contrasting Archean to Neoproterozoic geological histories and are believed to be juxtaposed along a suture zone that now lies beneath the Sørsdal Glacier. Exact location and age of this suture zone are unknown, as is its relationship to regional deformation associated with the amalgamation of East Gondwana. To image the suture zone, magnetotelluric (MT) data were collected in Prydz Bay, East Antarctica, mainly along a profile crossing the Sørsdal Glacier and regions inland of the Vestfold Hills and Rauer Group islands. Time-frequency analysis of the MT time series yielded three important observations: (1) Wind speeds in excess of ˜8 m/s reduce coherence between electric and magnetic fields due to charged wind-blown particles of ice and snow. (2) Estimation of the MT transfer function is best between 1000 and 1400 UT when ionospheric Hall currents enhance the magnetic source field. (3) Nonplanar source field effects were minimal but detectable and removed from estimation of the MT transfer function. Inversions of MT data in 2-D and 3-D produce similar resistivity models, where structures in the preferred 3-D resistivity model correlate strongly with regional magnetic data. The electrically conductive Rauer Group is separated from the less conductive Vestfold Hills by a resistive zone under the Sørsdal Glacier, which is interpreted to be caused by oxidation during suturing. Though a suture zone has been imaged, no time constrains on suturing can be made from the MT data.

  14. The Bambui Health and Aging Study (BHAS: factors associated with the treatment of hypertension in older adults in the community

    Directory of Open Access Journals (Sweden)

    Firmo Josélia Oliveira Araújo

    2003-01-01

    Full Text Available The objective of this study was to investigate the factors associated with the treatment of hypertension among older adults living in the community. All residents (n = 1,742 of Bambuí, Minas Gerais State, Brazil (15,000 inhabitants aged superscript three 60 years were selected, and 1494 (85.8% were interviewed and examined. Of these, 919 (61.5% were hypertensive, 704 were aware of their condition (study population, and 578 were under treatment. Only 38.8% of the individuals under treatment presented controlled systolic and diastolic pressures (< 140 and < 90mmHg, respectively. Independent associations with treatment of hypertension were found for, in decreasing order of magnitude: less time elapsed since the last blood pressure measurement, greater number of physician visits in the past 12 months, higher body mass index, female gender, history of coronary disease, changes in diet due to arterial hypertension, and higher family income. Our results show that the factors most strongly associated with treatment of hypertension (use of health services could be modified through adequate health policies for older adults.

  15. Fast Overlapping Group Lasso

    CERN Document Server

    Liu, Jun

    2010-01-01

    The group Lasso is an extension of the Lasso for feature selection on (predefined) non-overlapping groups of features. The non-overlapping group structure limits its applicability in practice. There have been several recent attempts to study a more general formulation, where groups of features are given, potentially with overlaps between the groups. The resulting optimization is, however, much more challenging to solve due to the group overlaps. In this paper, we consider the efficient optimization of the overlapping group Lasso penalized problem. We reveal several key properties of the proximal operator associated with the overlapping group Lasso, and compute the proximal operator by solving the smooth and convex dual problem, which allows the use of the gradient descent type of algorithms for the optimization. We have performed empirical evaluations using the breast cancer gene expression data set, which consists of 8,141 genes organized into (overlapping) gene sets. Experimental results demonstrate the eff...

  16. Multicultural group work

    DEFF Research Database (Denmark)

    Hansen, Annette Skovsted

    2014-01-01

    Motivation for the activity I use this strategy for forming groups to ensure diverse/multicultural groups that combine a variety of different strengths and resources based on student's academic, disciplinary, linguistic, national, personal and work backgrounds....

  17. Group B streptococcus - pregnancy

    Science.gov (United States)

    Group B streptococcus (GBS) is a type of bacteria that some women carry in their intestines and ... Mosby; 2015:chap 55. Pannaraj PS, Baker CJ. Group B streptococcal infections. In: Cherry J, Harrison GJ, ...

  18. Group Decision Process Support

    DEFF Research Database (Denmark)

    Gøtze, John; Hijikata, Masao

    1997-01-01

    Introducing the notion of Group Decision Process Support Systems (GDPSS) to traditional decision-support theorists.......Introducing the notion of Group Decision Process Support Systems (GDPSS) to traditional decision-support theorists....

  19. Group B streptococcus - pregnancy

    Science.gov (United States)

    ... page: //medlineplus.gov/ency/patientinstructions/000511.htm Group B streptococcus - pregnancy To use the sharing features on this page, please enable JavaScript. Group B streptococcus (GBS) is a type of bacteria that ...

  20. SUPPORT GROUPS IN ICEHEARTS

    OpenAIRE

    Cacho, Corey

    2016-01-01

    ABSTRACT Cacho, Corey Support groups in Icehearts. 33 p., 0 appendices. Language: English. Spring 2016. Diaconia University of Applied Sciences. Degree Programme in Social Services, Bachelor of Social Services. The purpose of my thesis is to provide a social support group model for the employees of Icehearts. The social support group model covers the mental health and wellbeing of the employees. The aim of the support group model is to give the employees a creative way of ...

  1. Group Wage Curves

    OpenAIRE

    Bartik, Timothy J.

    2000-01-01

    Using panel data on U.S. MSAs, this paper estimates how a typical MSA's wages of different demographic groups, and prices, are affected by overall MSA unemployment, the distribution of unemployment among different groups, and national prices and wages. MSA unemployment has strong effects on MSA wages and prices, but the distribution of unemployment among different groups has weak effects on wages and prices. Using these estimates, simulations show that targeting high-unemployment groups for u...

  2. Introduction to quantum groups

    OpenAIRE

    Podles, P.; Muller, E.

    1997-01-01

    We give an elementary introduction to the theory of algebraic and topological quantum groups (in the spirit of S. L. Woronowicz). In particular, we recall the basic facts from Hopf (*-) algebra theory, theory of compact (matrix) quantum groups and the theory of their actions on compact quantum spaces. We also provide the most important examples, including the classification of quantum SL(2)-groups, their real forms and quantum spheres. We also consider quantum SL_q(N)-groups and quantum Loren...

  3. Graphical Cyclic Permutation Groups

    OpenAIRE

    Grech, Mariusz

    2012-01-01

    We establish conditions for a permutation group generated by a single permutation of a prime power order to be an automorphism group of a graph or an edge-colored graph. This corrects and generalizes the results of the two papers on cyclic permutation groups published in 1978 and 1981 by S. P. Mohanty, M. R. Sridharan, and S. K. Shukla.

  4. Change through Group Work.

    Science.gov (United States)

    McAllan, Les; Friedman, Amy; Spears, Evans

    Perhaps the most well known treatment modalities in the field of prevention and treatment of addiction are groups. Group settings serve to bring individuals with addictions together at one time in one place to work on relevant issues together. Groups may serve as a safe environment for learning new social and relationship skills, gaining…

  5. AREVA group overview

    International Nuclear Information System (INIS)

    This document presents the Group Areva, a world nuclear industry leader, from a financial holding company to an industrial group, operating in two businesses: the nuclear energy and the components. The structure and the market of the group are discussed, as the financial assets. (A.L.B.)

  6. Groups, combinatorics and geometry

    CERN Document Server

    Ivanov, A A; Saxl, J

    2003-01-01

    Over the past 20 years, the theory of groups in particular simplegroups, finite and algebraic has influenced a number of diverseareas of mathematics. Such areas include topics where groups have beentraditionally applied, such as algebraic combinatorics, finitegeometries, Galois theory and permutation groups, as well as severalmore recent developments.

  7. Microscopic group constants determination

    International Nuclear Information System (INIS)

    The method of microscopic group constants determination for nuclear reactor calculations is described in this paper. The principle of this method is group averaging of microscopic cross sections with respect to the standard spectrum. The group cross sections obtained are used for the calculation of fast critical assembly Jezebel. (author)

  8. Group I intron ribozymes

    DEFF Research Database (Denmark)

    Nielsen, Henrik

    2012-01-01

    Group I intron ribozymes constitute one of the main classes of ribozymes and have been a particularly important model in the discovery of key concepts in RNA biology as well as in the development of new methods. Compared to other ribozyme classes, group I intron ribozymes display considerable...... intronic products of these pathways have the potential to integrate into targets and to form various types of circular RNA molecules. Thus, group I intron ribozymes and associated elements found within group I introns is a rich source of biological phenomena. This chapter provides a strategy and protocols...... for initial characterization of new group I intron ribozymes....

  9. Group theory I essentials

    CERN Document Server

    Milewski, Emil G

    2012-01-01

    REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Group Theory I includes sets and mapping, groupoids and semi-groups, groups, isomorphisms and homomorphisms, cyclic groups, the Sylow theorems, and finite p-groups.

  10. Splittings of knot groups

    OpenAIRE

    Friedl, Stefan; Silver, Daniel S.; Williams, Susan G.

    2013-01-01

    Let K be a knot of genus g. If K is fibered, then it is well known that the knot group pi(K) splits only over a free group of rank 2g. We show that if K is not fibered, then pi(K) splits over non-free groups of arbitrarily large rank. Furthermore, if K is not fibered, then pi(K) splits over every free group of rank at least 2g. However, pi(K) cannot split over a group of rank less than 2g. The last statement is proved using the recent results of Agol, Przytycki-Wise and Wise.

  11. Grouped exposed metal heaters

    Energy Technology Data Exchange (ETDEWEB)

    Vinegar, Harold J. (Bellaire, TX); Coit, William George (Bellaire, TX); Griffin, Peter Terry (Brixham, GB); Hamilton, Paul Taylor (Houston, TX); Hsu, Chia-Fu (Granada Hills, CA); Mason, Stanley Leroy (Allen, TX); Samuel, Allan James (Kular Lumpar, MY); Watkins, Ronnie Wade (Cypress, TX)

    2010-11-09

    A system for treating a hydrocarbon containing formation is described. The system includes two or more groups of elongated heaters. The group includes two or more heaters placed in two or more openings in the formation. The heaters in the group are electrically coupled below the surface of the formation. The openings include at least partially uncased wellbores in a hydrocarbon layer of the formation. The groups are electrically configured such that current flow through the formation between at least two groups is inhibited. The heaters are configured to provide heat to the formation.

  12. Grouped exposed metal heaters

    Energy Technology Data Exchange (ETDEWEB)

    Vinegar, Harold J. (Bellaire, TX); Coit, William George (Bellaire, TX); Griffin, Peter Terry (Brixham, GB); Hamilton, Paul Taylor (Houston, TX); Hsu, Chia-Fu (Granada Hills, CA); Mason, Stanley Leroy (Allen, TX); Samuel, Allan James (Kular Lumpar, ML); Watkins, Ronnie Wade (Cypress, TX)

    2012-07-31

    A system for treating a hydrocarbon containing formation is described. The system includes two or more groups of elongated heaters. The group includes two or more heaters placed in two or more openings in the formation. The heaters in the group are electrically coupled below the surface of the formation. The openings include at least partially uncased wellbores in a hydrocarbon layer of the formation. The groups are electrically configured such that current flow through the formation between at least two groups is inhibited. The heaters are configured to provide heat to the formation.

  13. CHAOTIC GROUP ACTIONS

    Institute of Scientific and Technical Information of China (English)

    ShiEnhui; ZhouLizhen; ZhouYoucheng

    2003-01-01

    It is proved that there is no chaotic group actions on any topological space with free arc.In this paper the chaotic actions of the group like G×F,where F is a finite group,are studied.In particular,under a suitable assumption ,if F is a cyclic group,then the topological space which admits a chaotic action of Z×F must admit a chatotic homeomorphism.A topological space which admits a chaotic group action but admits no chaotic horneomorphism is constructed.

  14. On -nilpotent abelian groups

    Indian Academy of Sciences (India)

    Mohammad Mehdi Nasrabadi; Ali Gholamian

    2014-11-01

    Let be a group and $A = \\text{Aut}(G)$ be the group of automorphisms of . Then, the element $[g, ] = g^{-1}(g)$ is an autocommutator of $g \\in G$ and $ \\in A$. Hence, for any natural number the -th autocommutator subgroup of is defined as $K_{m}(G)=\\langle [g,_{1},\\ldots,_{m}]|g\\in G,_{1},\\ldots,_{m}\\in A\\rangle$, where $[g, _{1}, _{2},\\ldots, _{m}] = [[g,_{1},\\ldots,_{m−1}], _{m}]$. In this paper, we introduce the new notion of -nilpotent groups and classify all abelian groups which are -nilpotent groups.

  15. Perfect numbers and groups

    OpenAIRE

    Leinster, Tom

    2001-01-01

    A number is perfect if it is the sum of its proper divisors; here we call a finite group `perfect' if its order is the sum of the orders of its proper normal subgroups. (This conflicts with standard terminology but confusion should not arise.) The notion of perfect group generalizes that of perfect number, since a cyclic group is perfect exactly when its order is perfect. We show that, in fact, the only abelian perfect groups are the cyclic ones, and exhibit some non-abelian perfect groups of...

  16. Group Psychotherapy in Denmark.

    Science.gov (United States)

    Jørgensen, Lars Bo; Thygesen, Bente; Aagaard, Søren

    2015-10-01

    This is a short article on the history and training standards in the Institute of Group Analysis in Copenhagen (IGA-CPH). We describe theoretical orientations and influences in the long-term training program and new initiatives, like courses in mentalization-based group treatment and a dynamic short-term group therapy course, as well as research in group psychotherapy in Denmark. Some group analytic initiatives in relation to social issues and social welfare are presented, as well as initiatives concerning the school system and unemployment. PMID:26401798

  17. E-groups training

    CERN Multimedia

    HR Department

    2012-01-01

    There will be an e-groups training course on 16 March 2012 which will cover the main e-groups functionalities i.e.: creating and managing e-groups, difference between static and dynamic e-groups, configuring posting restrictions and archives, examples of where e-groups can be used in daily work. Even if you have already worked with e-groups, this may be a good opportunity to learn about the best practices and security related recommendations when using e-groups. You can find more details as well as enrolment form for the training (it’s free) here. The number of places is limited, so enrolling early is recommended.   Technical Training Tel. 72844

  18. Toleration, Groups, and Multiculturalism

    DEFF Research Database (Denmark)

    Lægaard, Sune

    The chapter considers how groups might be relevant as objects of policies of toleration and the different senses 'group' might have in relation to questions of toleration. The chapter argues that groups can be relevant to toleration in several different ways as objects of toleration. Toleration is...... routinely defined as involving an objection component, a power requirement and an acceptance component. The objection and acceptance components refer to reasons or dispositions of the subjects of toleration, e.g. public authorities deciding how to act in relation to groups. The power condition refers to the...... toleration allows receivers of toleration to enjoy. The chapter shows how groups may be objects of toleration in different ways in relation to each of these components or conditions of toleration. The sense of 'group' relevant to toleration may differ when the group is an object of power, i.e. when others...

  19. Alternatives for pseudofinite groups

    CERN Document Server

    Houcine, Abderezak Ould

    2012-01-01

    The famous Tits' alternative states that a linear group either contains a nonabelian free group or is soluble-by-(locally finite). We study in this paper similar alternatives in pseudofinite groups. We show for instance that an $\\aleph_{0}$-saturated pseudofinite group either contains a subsemigroup of rank $2$ or is nilpotent-by-(uniformly locally finite). We call a class of finite groups $G$ weakly of bounded rank if the radical $rad(G)$ has a bounded Pr\\"ufer rank and the index of the sockel of $G/rad(G)$ is bounded. We show that an $\\aleph_{0}$-saturated pseudo-(finite weakly of bounded rank) group either contains a nonabelian free group or is nilpotent-by-abelian-by-(uniformly locally finite). We also obtain some relations between this kind of alternatives and amenability.

  20. Ocean chemistry: Neoproterozoic glass-bleeding

    Science.gov (United States)

    Fairchild, Ian J.

    2016-03-01

    Volcanic eruptions at ocean ridges produce large volumes of glass that is rapidly leached by seawater. Geochemical calculations suggest that this process helps to explain the deposition of carbonates at the end of extreme ice ages.

  1. The evolution of the neoproterozoic São Gabriel juvenile terrane, southern Brazil based on SHRIMP and LA-ICP-MS U-Pb ages and ?18O data on detrital zircon

    Science.gov (United States)

    Lena, L. O.; Pimentel, M. M.; Philipp, R. P.; Armstrong, R. A.; Sato, K.

    2013-12-01

    . This is explained by the installation of a continental magmatic arc along the western margin of the Rio de La Plata Craton. Period III took place between ca. 690-650 represented by the accretion of the arc system to the Rio de La Plata Craton. In this timeframe only continental crust-derived magmas are recognized and no mantle δ18O values are observed. In summary, our data provides an insight into the progressive evolution of the São Gabriel terrane from an intra-oceanic subduction zone at ca. 879-750 Ma to a continental arc setting (ages < 690 Ma) into three distinct periods, which preceded ocean closure and continental collision at the end of the Neoproterozoic.

  2. Group Psychotherapy in Italy.

    Science.gov (United States)

    Giannone, Francesca; Giordano, Cecilia; Di Blasi, Maria

    2015-10-01

    This article describes the history and the prevailing orientations of group psychotherapy in Italy (psychoanalytically oriented, psychodrama, CBT groups) and particularly group analysis. Provided free of charge by the Italian health system, group psychotherapy is growing, but its expansion is patchy. The main pathways of Italian training in the different group psychotherapy orientations are also presented. Clinical-theoretical elaboration on self development, psychopathology related to group experiences, and the methodological attention paid to objectives and methods in different clinical groups are issues related to group therapy in Italy. Difficulties in the relationship between research and clinical practice are discussed, as well as the empirical research network that tries to bridge the gap between research and clinical work in group psychotherapy. The economic crisis in Italy has led to massive cuts in health care and to an increasing demand for some forms of psychological treatment. For these reasons, and because of its positive cost-benefit ratio, group psychotherapy is now considered an important tool in the national health care system to expand the clinical response to different forms of psychological distress. PMID:26401793

  3. Géochimie et cadre géodynamique du volcanisme néoprotérozoïque terminal (vendien) du Haut Atlas occidental, Maroc(Geochemical features and tectonic setting of late Neoproterozoic Vendian volcanism in the western High Atlas, Morocco)

    Science.gov (United States)

    Jouhari, A.; El-Archi, A.; Aarab, M.; El-Attari, A.; Ennih, N.; Laduron, D.

    2001-05-01

    Late Neoproterozoic Vendian volcanic and volcaniclastic rocks are widely distributed in the western High Atlas. They are located north of the Tizi n'Test Fault, separating the West African Craton from a northerly adjacent craton. These volcanic rocks overlie a semipelitic formation, which represents the equivalent of the Tidilline and Anzi Formations of the Anti-Atlas. The geochemical characteristics of these volcanic rocks suggest a calc-alkaline active margine environment associated with the post Pan-African tectonics. They differ from those of the Anti-Atlas by their lower content of K 2O. The later rock type was generated by a melting process of the crust subducted beneath the northern craton. A carbonate-shale unit, which contains examples of interstratified calc-alkaline dacite, overlies the volcanic succession, demonstrating that the volcanic activity continued sporadically until Early Cambrian times.

  4. Les granitoïdes néoprotérozoïques de Khzama, Anti-Atlas central, Maroc: marqueurs de l'évolution d'un magmatisme d'arc à un magmatisme alcalineNeoproterozoic granitoids from Khzama, central Anti-Atlas, Morocco: evolution markers from arc magmatism to alkaline magmatism

    Science.gov (United States)

    El-Khanchaoui, T.; Lahmam, M.; El-Boukhari, A.; El-Beraaouz, H.

    2001-05-01

    Petrological study and zircon typology provide important information that is related to the classification and genesis of Neoproterozoic granitoids in the Khzama area (northeast Siroua). The Pan-African granitoids show a transition from island-arc magmatism to alkaline magmatism. A space and time zonation of magmatism from the north to the south is evident. Early Pan-African granitoids were generated from various magma sources through different petrogenetic mechanisms. The first association corresponds to the low-K calc-alkaline plutons of Ait Nebdas, the second one correponds to high-K calc-alkaline post-collisional granites (Tamassirte-Tiferatine and Ifouachguel). Finally, shoshonitic magmatism (Irhiri) ends the magmatic evolution of the region. Thus, the late Pan-African granitic plutonism began with calc-alkaline associations and ended with K-alkaline magmatism in a transtensional setting, heralding the onset of the Moroccan Palæozoic cycle.

  5. Blood groups systems

    Directory of Open Access Journals (Sweden)

    Ranadhir Mitra

    2014-01-01

    Full Text Available International Society of Blood Transfusion has recently recognized 33 blood group systems. Apart from ABO and Rhesus system, many other types of antigens have been noticed on the red cell membranes. Blood grouping and cross-matching is one of the few important tests that the anaesthesiologist orders during perioperative period. Hence, a proper understanding of the blood group system, their clinical significance, typing and cross-matching tests, and current perspective are of paramount importance to prevent transfusion-related complications. Nonetheless, the knowledge on blood group system is necessary to approach blood group-linked diseases which are still at the stage of research. This review addresses all these aspects of the blood groups system.

  6. Blood groups systems.

    Science.gov (United States)

    Mitra, Ranadhir; Mishra, Nitasha; Rath, Girija Prasad

    2014-09-01

    International Society of Blood Transfusion has recently recognized 33 blood group systems. Apart from ABO and Rhesus system, many other types of antigens have been noticed on the red cell membranes. Blood grouping and cross-matching is one of the few important tests that the anaesthesiologist orders during perioperative period. Hence, a proper understanding of the blood group system, their clinical significance, typing and cross-matching tests, and current perspective are of paramount importance to prevent transfusion-related complications. Nonetheless, the knowledge on blood group system is necessary to approach blood group-linked diseases which are still at the stage of research. This review addresses all these aspects of the blood groups system. PMID:25535412

  7. Stochastic Lie group integrators

    CERN Document Server

    Malham, Simon J A

    2007-01-01

    We present Lie group integrators for nonlinear stochastic differential equations with non-commutative vector fields whose solution evolves on a smooth finite dimensional manifold. Given a Lie group action that generates transport along the manifold, we pull back the stochastic flow on the manifold to the Lie group via the action, and subsequently pull back the flow to the corresponding Lie algebra via the exponential map. We construct an approximation to the stochastic flow in the Lie algebra via closed operations and then push back to the Lie group and then to the manifold, thus ensuring our approximation lies in the manifold. We call such schemes stochastic Munthe-Kaas methods after their deterministic counterparts. We also present stochastic Lie group integration schemes based on Castell--Gaines methods. These involve using an underlying ordinary differential integrator to approximate the flow generated by a truncated stochastic exponential Lie series. They become stochastic Lie group integrator schemes if...

  8. Presentations of groups

    CERN Document Server

    Johnson, D L

    1997-01-01

    The aim of this book is to provide an introduction to combinatorial group theory. Any reader who has completed first courses in linear algebra, group theory and ring theory will find this book accessible. The emphasis is on computational techniques but rigorous proofs of all theorems are supplied. This new edition has been revised throughout, including new exercises and an additional chapter on proving that certain groups are infinite.

  9. Group Problem Solving

    CERN Document Server

    Laughlin, Patrick R

    2011-01-01

    Experimental research by social and cognitive psychologists has established that cooperative groups solve a wide range of problems better than individuals. Cooperative problem solving groups of scientific researchers, auditors, financial analysts, air crash investigators, and forensic art experts are increasingly important in our complex and interdependent society. This comprehensive textbook--the first of its kind in decades--presents important theories and experimental research about group problem solving. The book focuses on tasks that have demonstrably correct solutions within mathematical

  10. Blood groups systems

    OpenAIRE

    Ranadhir Mitra; Nitasha Mishra; Girija Prasad Rath

    2014-01-01

    International Society of Blood Transfusion has recently recognized 33 blood group systems. Apart from ABO and Rhesus system, many other types of antigens have been noticed on the red cell membranes. Blood grouping and cross-matching is one of the few important tests that the anaesthesiologist orders during perioperative period. Hence, a proper understanding of the blood group system, their clinical significance, typing and cross-matching tests, and current perspective are of paramount importa...

  11. Incentives and group identity

    OpenAIRE

    MASELLA, Paolo; Meier, Stephan; Zahn, Philipp

    2012-01-01

    This paper investigates in a principal-agent environment whether and how group membership influences the effectiveness of incentives and when incentives can have “hidden costs”, i.e., a detrimental effect. We show experimentally that in all interactions control mechanisms can have hidden costs for reasons specific to group membership. In within-group interactions control has detrimental effects because the agent does not expect to be controlled and reacts negatively when being controlled. In ...

  12. Group therapy for adolescents

    OpenAIRE

    Nada Hribar

    2001-01-01

    The group included adolescents from secondary school and some students. The group had weekly sessions or twice on mounth. The adolescents had varied simptoms: depressive, anxiety, psychosomatic disorders, learning difficulties, cunduct problems. All of adolescents were common on many problems in social interactions. The goal of therapeutic work were: to increase assertiveness skills and to reduce the anxious in social situations. The adolescents in group raised a self-esteem and developed som...

  13. Bayesian Group Factor Analysis

    OpenAIRE

    Virtanen, Seppo; Klami, Arto; Khan, Suleiman A; Kaski, Samuel

    2011-01-01

    We introduce a factor analysis model that summarizes the dependencies between observed variable groups, instead of dependencies between individual variables as standard factor analysis does. A group may correspond to one view of the same set of objects, one of many data sets tied by co-occurrence, or a set of alternative variables collected from statistics tables to measure one property of interest. We show that by assuming group-wise sparse factors, active in a subset of the sets, the variat...

  14. Semisimple Metacyclic Group Algebras

    Indian Academy of Sciences (India)

    Gurmeet K Bakshi; Shalini Gupta; Inder Bir S Passi

    2011-11-01

    Given a group of order $p_1p_2$, where $p_1,p_2$ are primes, and $\\mathbb{F}_q$, a finite field of order coprime to $p_1p_2$, the object of this paper is to compute a complete set of primitive central idempotents of the semisimple group algebra $\\mathbb{F}_q[G]$. As a consequence, we obtain the structure of $\\mathbb{F}_q[G]$ and its group of automorphisms.

  15. Explosive Technology Group

    Data.gov (United States)

    Federal Laboratory Consortium — The Explosive Technology Group (ETG) provides diverse technical expertise and an agile, integrated approach to solve complex challenges for all classes of energetic...

  16. Factoring groups into subsets

    CERN Document Server

    Szabo, Sandor

    2009-01-01

    Decomposing an abelian group into a direct sum of its subsets leads to results that can be applied to a variety of areas, such as number theory, geometry of tilings, coding theory, cryptography, graph theory, and Fourier analysis. Focusing mainly on cyclic groups, Factoring Groups into Subsets explores the factorization theory of abelian groups. The book first shows how to construct new factorizations from old ones. The authors then discuss nonperiodic and periodic factorizations, quasiperiodicity, and the factoring of periodic subsets. They also examine how tiling plays an important role in n

  17. Study Groups in Denmark

    DEFF Research Database (Denmark)

    Hjorth, Poul G.

    2007-01-01

    Since 1998 European Study Groups have been held in Denmark, and Danish companies from LEGO and NOVO to very small high-tech firms have participated. I briefly describe the history, the organisation and the format of the Danish Study Groups, and highlight a few problem solutions.......Since 1998 European Study Groups have been held in Denmark, and Danish companies from LEGO and NOVO to very small high-tech firms have participated. I briefly describe the history, the organisation and the format of the Danish Study Groups, and highlight a few problem solutions....

  18. Lie groups for pedestrians

    CERN Document Server

    Lipkin, Harry J

    2002-01-01

    According to the author of this concise, high-level study, physicists often shy away from group theory, perhaps because they are unsure which parts of the subject belong to the physicist and which belong to the mathematician. However, it is possible for physicists to understand and use many techniques which have a group theoretical basis without necessarily understanding all of group theory. This book is designed to familiarize physicists with those techniques. Specifically, the author aims to show how the well-known methods of angular momentum algebra can be extended to treat other Lie group

  19. Weyl group invariants

    CERN Document Server

    Kameko, Masaki

    2012-01-01

    For any odd prime $p$, we prove that the induced homomorphism from the mod $p$ cohomology of the classifying space of a compact simply-connected simple connected Lie group to the Weyl group invariants of the mod $p$ cohomology of the classifying space of its maximal torus is an epimorphism except for the case $p=3$, $G=E_8$.

  20. Introduction to quantum groups

    International Nuclear Information System (INIS)

    These pedagogical lectures contain some motivation for the study of quantum groups; a definition of ''quasi triangular Hopf algebra'' with explanations of all the concepts required to build it up; descriptions of quantised universal enveloping algebras and the quantum double; and an account of quantised function algebras and the action of quantum groups on quantum spaces. (author)

  1. Topologies on Abelian Groups

    Science.gov (United States)

    Zelenyuk, E. G.; Protasov, I. V.

    1991-04-01

    A filter phi on an abelian group G is called a T-filter if there exists a Hausdorff group topology under which phi converges to zero. G{phi} will denote the group G with the largest topology among those making phi converge to zero. This method of defining a group topology is completely equivalent to the definition of an abstract group by defining relations. We shall obtain characterizations of T-filters and of T-sequences; among these, we shall pay particular attention to T-sequences on the integers. The method of T-sequences will be used to construct a series of counterexamples for several open problems in topological algebra. For instance there exists, on every infinite abelian group, a topology distinguishing between sequentiality and the Fréchet-Urysohn property (this solves a problem posed by V.I. Malykhin) we also find a topology on the group of integers admitting no nontrivial continuous character, thus solving a problem of Nienhuys. We show also that on every infinite abelian group there exists a free ultrafilter which is not a T-ultrafilter.

  2. Study Groups in Denmark

    DEFF Research Database (Denmark)

    Hjorth, Poul G.

    2007-01-01

    Since 1998 European Study Groups have been held in Denmark, and Danish companies from LEGO and NOVO to very small high-tech firms have participated. I briefly describe the history, the organisation and the format of the Danish Study Groups, and highlight a few problem solutions....

  3. 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.

  4. Natural analogue working group

    International Nuclear Information System (INIS)

    A Natural Analogue Working Group was established by the Commission of the European Communities in 1985. The purpose of this group is to bring together modellers with earth scientists and others, so that maximum benefit can be obtained from natural analogue studies with a view to safe geological disposal of radioactive waste. The first meeting of this group was held in Brussels from November 5 to 7, 1985. The discussions mainly concerned the identification of the modellers' needs and of the earth scientists' capacity to provide for them. Following the debates, a written statement was produced by the Group; this document forms the core of the present Report. Notes and outlines of many of the presentations made are grouped in four appendixes. The valuable contribution of all those involved in the meeting is gratefully acknowledged

  5. Isotropy in group cohomology

    DEFF Research Database (Denmark)

    Ben David, Nir; Ginosar, Yuval; Meir, Ehud

    2014-01-01

    The analog of Lagrangians for symplectic forms over finite groups is studied, motivated by the fact that symplectic G  -forms with a normal Lagrangian N◃G  are in one-to-one correspondence, up to inflation, with bijective 1-cocycle data on the quotients G/N  . This yields a method to construct...... groups of central type from such quotients, known as Involutive Yang–Baxter groups. Another motivation for the search of normal Lagrangians comes from a non-commutative generalization of Heisenberg liftings that require normality. Although it is true that symplectic forms over finite nilpotent groups...... always admit Lagrangians, we exhibit an example where none of these subgroups is normal. However, we prove that symplectic forms over nilpotent groups always admit normal Lagrangians if all their p  -Sylow subgroups are of order less than p 8   ....

  6. Cyclic Soft Groups and Their Applications on Groups

    Directory of Open Access Journals (Sweden)

    Hacı Aktaş

    2014-01-01

    Full Text Available In crisp environment the notions of order of group and cyclic group are well known due to many applications. In this paper, we introduce order of the soft groups, power of the soft sets, power of the soft groups, and cyclic soft group on a group. We also investigate the relationship between cyclic soft groups and classical groups.

  7. Critical groups - basic concepts

    International Nuclear Information System (INIS)

    The potential exposure pathways from the land application site to man are presented. It is emphasised that the critical group is not necessary the population group closest to the source. It could be the group impact by the most significant pathways(s). Only by assessing the importance of each of these pathways and then combining them can a proper choice of critical group be made. It would be wrong to select a critical group on the basis that it seems the most probable one, before the pathways have been properly assessed. A calculation in Carter (1983) suggested that for the operating mine site, the annual doses to an Aboriginal person, a service worker and a local housewife, were all about the same and were in the range 0.1 to 0.2 mSv per year. Thus it may be that for the land application area, the critical group turns out to be non-Aboriginal rather than the expected Aboriginal group. 6 refs., 3 figs

  8. Quantum group connections

    OpenAIRE

    Lewandowski, Jerzy; Okolow, Andrzej

    2008-01-01

    The Ahtekar-Isham C*-algebra known from Loop Quantum Gravity is the algebra of continuous functions on the space of (generalized) connections with a compact structure Lie group. The algebra can be constructed by some inductive techniques from the C*-algebra of continuous functions on the group and a family of graphs embedded in the manifold underlying the connections. We generalize the latter construction replacing the commutative C*-algebra of continuous functions on the group by a non-commu...

  9. Group therapy for adolescents

    Directory of Open Access Journals (Sweden)

    Nada Hribar

    2001-03-01

    Full Text Available The group included adolescents from secondary school and some students. The group had weekly sessions or twice on mounth. The adolescents had varied simptoms: depressive, anxiety, psychosomatic disorders, learning difficulties, cunduct problems. All of adolescents were common on many problems in social interactions. The goal of therapeutic work were: to increase assertiveness skills and to reduce the anxious in social situations. The adolescents in group raised a self-esteem and developed some assertiveness skills: eye contact" and effective communication skills, persistence, refusing and requesting, giving and receiving critism, etc. The methods of work and techniques were based on principles of cognitive-behaviour therapy.

  10. Group ring cryptography

    CERN Document Server

    Hurley, Barry

    2011-01-01

    Cryptographic systems are derived using units in group rings. Combinations of types of units in group rings give units not of any particular type. This includes cases of taking powers of units and products of such powers and adds the complexity of the {\\em discrete logarithm} problem to the system. The method enables encryption and (error-correcting) coding to be combined within one system. These group ring cryptographic systems may be combined in a neat way with existing cryptographic systems, such as RSA, and a combination has the combined strength of both systems. Examples are given.

  11. Group key management

    Energy Technology Data Exchange (ETDEWEB)

    Dunigan, T.; Cao, C.

    1997-08-01

    This report describes an architecture and implementation for doing group key management over a data communications network. The architecture describes a protocol for establishing a shared encryption key among an authenticated and authorized collection of network entities. Group access requires one or more authorization certificates. The implementation includes a simple public key and certificate infrastructure. Multicast is used for some of the key management messages. An application programming interface multiplexes key management and user application messages. An implementation using the new IP security protocols is postulated. The architecture is compared with other group key management proposals, and the performance and the limitations of the implementation are described.

  12. Homogenous finitary symmetric groups

    Directory of Open Access Journals (Sweden)

    Otto‎. ‎H‎. Kegel

    2015-03-01

    Full Text Available We characterize strictly diagonal type of embeddings of finitary symmetric groups in terms of cardinality and the characteristic. Namely, we prove the following. Let kappa be an infinite cardinal. If G=underseti=1stackrelinftybigcupG i , where G i =FSym(kappan i , (H=underseti=1stackrelinftybigcupH i , where H i =Alt(kappan i , is a group of strictly diagonal type and xi=(p 1 ,p 2 ,ldots is an infinite sequence of primes, then G is isomorphic to the homogenous finitary symmetric group FSym(kappa(xi (H is isomorphic to the homogenous alternating group Alt(kappa(xi , where n 0 =1,n i =p 1 p 2 ldotsp i .

  13. RAS Laboratory Groups

    Science.gov (United States)

    The RAS Initiative uses multiple technologies to attack RAS-driven cancers. The resources of the Frederick National Lab allocated to the RAS Hub are organized into seven laboratory groups, each contributing to the collaborative effort.

  14. Homogeneous group, research, institution

    Directory of Open Access Journals (Sweden)

    Francesca Natascia Vasta

    2014-09-01

    Full Text Available The work outlines the complex connection among empiric research, therapeutic programs and host institution. It is considered the current research state in Italy. Italian research field is analyzed and critic data are outlined: lack of results regarding both the therapeutic processes and the effectiveness of eating disorders group analytic treatment. The work investigates on an eating disorders homogeneous group, led into an eating disorder outpatient service. First we present the methodological steps the research is based on including the strong connection among theory and clinical tools. Secondly clinical tools are described and the results commented. Finally, our results suggest the necessity of validating some more specifical hypothesis: verifying the relationship between clinical improvement (sense of exclusion and painful emotions reduction and specific group therapeutic processes; verifying the relationship between depressive feelings, relapses and transition trough a more differentiated groupal field.Keywords: Homogeneous group; Eating disorders; Institutional field; Therapeutic outcome

  15. Group Support Systems (GSS)

    Science.gov (United States)

    Hamel, Gary P.; Wijesinghe, R.

    1996-01-01

    Groupware is a term describing an emerging computer software technology enhancing the ability of people to work together as a group, (a software driven 'group support system'). This project originated at the beginning of 1992 and reports were issued describing the activity through May 1995. These reports stressed the need for process as well as technology. That is, while the technology represented a computer assisted method for groups to work together, the Group Support System (GSS) technology als required an understanding of the facilitation process electronic meetings demand. Even people trained in traditional facilitation techniques did not necessarily aimlessly adopt groupware techniques. The latest phase of this activity attempted to (1) improve the facilitation process by developing training support for a portable groupware computer system, and (2) to explore settings and uses for the portable groupware system using different software, such as Lotus Notes.

  16. UnitedHealth Group

    Science.gov (United States)

    UnitedHealth Group provides accessible and affordable services, improved quality of care, coordinated health care efforts, and a supportive environment for shared decision making between patients and their physicians.

  17. Groups – Additive Notation

    Directory of Open Access Journals (Sweden)

    Coghetto Roland

    2015-06-01

    Full Text Available We translate the articles covering group theory already available in the Mizar Mathematical Library from multiplicative into additive notation. We adapt the works of Wojciech A. Trybulec [41, 42, 43] and Artur Korniłowicz [25].

  18. Radiation Protection Group

    CERN Multimedia

    2006-01-01

    The Radioactive Waste Section of the Radiation Protection Group wishes to inform you that the Radioactive Waste Treatment Centre will be closed on the afternoon of Tuesday 19 December 2006. Thank-you for your understanding.

  19. Anxiety Disorders: Support Groups

    Science.gov (United States)

    ... Guidelines Scientific Council Special Interest Groups Child & Adolescent Anxiety SIG Peer Consultation OCD & Related Disorders SIG Peer ... Jobs and Fellowships Journal & Multimedia Announcements Depression and Anxiety Podcasts & Videos Resources Clinical Practice Reviews & Teaching Tools ...

  20. Group Capability Model

    Science.gov (United States)

    Olejarski, Michael; Appleton, Amy; Deltorchio, Stephen

    2009-01-01

    The Group Capability Model (GCM) is a software tool that allows an organization, from first line management to senior executive, to monitor and track the health (capability) of various groups in performing their contractual obligations. GCM calculates a Group Capability Index (GCI) by comparing actual head counts, certifications, and/or skills within a group. The model can also be used to simulate the effects of employee usage, training, and attrition on the GCI. A universal tool and common method was required due to the high risk of losing skills necessary to complete the Space Shuttle Program and meet the needs of the Constellation Program. During this transition from one space vehicle to another, the uncertainty among the critical skilled workforce is high and attrition has the potential to be unmanageable. GCM allows managers to establish requirements for their group in the form of head counts, certification requirements, or skills requirements. GCM then calculates a Group Capability Index (GCI), where a score of 1 indicates that the group is at the appropriate level; anything less than 1 indicates a potential for improvement. This shows the health of a group, both currently and over time. GCM accepts as input head count, certification needs, critical needs, competency needs, and competency critical needs. In addition, team members are categorized by years of experience, percentage of contribution, ex-members and their skills, availability, function, and in-work requirements. Outputs are several reports, including actual vs. required head count, actual vs. required certificates, CGI change over time (by month), and more. The program stores historical data for summary and historical reporting, which is done via an Excel spreadsheet that is color-coded to show health statistics at a glance. GCM has provided the Shuttle Ground Processing team with a quantifiable, repeatable approach to assessing and managing the skills in their organization. They now have a common

  1. Genomics Research Group Session

    OpenAIRE

    Baldwin, D.; Chittur, S.V.; Raghavachari, N.; N Jafari; Aquino, C.; Perera, A; Reyero, N.G.

    2014-01-01

    The Genomics Research Group (GRG) presentation is intended to describe the current activities of the group in applying the latest tools and technologies for transcriptome analysis to determine the advantages and disadvantages of each of the platforms. We will present three ongoing projects. In the first project, we specifically evaluated microarrays, QPCR and Next Generation Sequencing (NGS) platforms for examining the sensitivity and specificity of microRNA detection using synthetic miRNA st...

  2. Reactivity of nitrosyl group

    International Nuclear Information System (INIS)

    Reactivity of ruthenium nitrosyl complexes is considered. According to X-ray structure analysis data nitrogen oxide interaction with metals results in formation of two complexes. The first ones contain linear nitrosyls (valence bond angle 180 deg in M-NO grouping), the second ones - bend nitrosyls (the bond angle in M-N-O grouping 120-130 deg). The first type complexes react primarily with nucleophilic reagents (OH-, N3-), the second ones - with electrophilic reagents

  3. Introduction to group theory

    Directory of Open Access Journals (Sweden)

    Canals B.

    2012-03-01

    Full Text Available This chapter is a concise mathematical introduction into the algebra of groups. It is build up in the way that definitions are followed by propositions and proofs. The concepts and the terminology introduced here will serve as a basis for the following chapters that deal with group theory in the stricter sense and its application to problems in physics. The mathematical prerequisites are at the bachelor level.1

  4. Arithmetic Cohomology Groups

    OpenAIRE

    Sugahara, K.; Weng, L

    2015-01-01

    We first introduce global arithmetic cohomology groups for quasi-coherent sheaves on arithmetic varieties, adopting an adelic approach. Then, we establish fundamental properties, such as topological duality and inductive long exact sequences, for these cohomology groups on arithmetic surfaces. Finally, we expose basic structures for ind-pro topologies on adelic spaces of arithmetic surfaces. In particular, we show that these adelic spaces are topologically self-dual.

  5. Fuzzy Soft Topological Groups

    Directory of Open Access Journals (Sweden)

    S. Nazmul

    2014-03-01

    Full Text Available Notions of Lowen type fuzzy soft topological space are introduced and some of their properties are established in the present paper. Besides this, a combined structure of a fuzzy soft topological space and a fuzzy soft group, which is termed here as fuzzy soft topological group is introduced. Homomorphic images and preimages are also examined. Finally, some definitions and results on fuzzy soft set are studied.

  6. Email Grouping Method

    OpenAIRE

    Taiwo Ayodele; Shikun Zhou; Rinat Khusainov

    2010-01-01

    In this paper we presents a neural network based system for automated email grouping into activities found in the email message- Email Grouping Method (EGM). Email users spend a lot of time reading, replying and organizing their emails and this seems to be time consuming and sometimes can resolves to less performance of daily duty, and un-necessary distractions. A new system that can manage mails on our behalf is required. EGM is developed to help organise email messages, intelligently struct...

  7. Membership in citizen groups

    OpenAIRE

    Barbieri, Stefano; Mattozzi, Andrea

    2009-01-01

    We analyze the coordination problem of agents deciding to join a group that uses membership revenues to provide a discrete public good and excludable benefits. The public good and the benefits are jointly produced, so that benefits are valued only if the group succeeds in providing the public good. With asymmetric information about the cost of provision, the static membership game admits a unique equilibrium and we characterize the optimal membership fee. We show that heterogeneity in valuati...

  8. Group Factor Analysis

    OpenAIRE

    Klami, Arto; Virtanen, Seppo; Leppäaho, Eemeli; Kaski, Samuel

    2014-01-01

    Factor analysis provides linear factors that describe relationships between individual variables of a data set. We extend this classical formulation into linear factors that describe relationships between groups of variables, where each group represents either a set of related variables or a data set. The model also naturally extends canonical correlation analysis to more than two sets, in a way that is more flexible than previous extensions. Our solution is formulated as variational inferenc...

  9. Interocular grouping without awareness.

    Science.gov (United States)

    Lin, San-Yuan; Yeh, Su-Ling

    2016-04-01

    Interocular grouping occurs when different parts of an image presented to each eye bound into a coherent whole. Previous studies anticipated that these parts are visible to both eyes simultaneously (i.e., the images altered back and forth). Although this view is consistent with the general consensus of binocular rivalry (BR) that suppressed stimuli receive no processing beyond rudimentary level (i.e., adaptation), it is actually inconsistent with studies that use continuous flash suppression (CFS). CFS is a form of interocular suppression that is more stable and causes stronger suppression of stimuli than BR. In the present study, we examined whether or not interocular grouping needs to occur at a conscious level as prior studies suggested. The modified double-rectangle paradigm used by Egly, Driver, and Rafal (1994) was adopted, and object-based attention was directed for successful grouping. To induce interocular grouping, we presented complementary parts of two rectangles dichoptically for possible interocular grouping and a dynamic Mondrian in front of one eye (i.e., CFS). Two concurrent targets were presented after one of the visible parts of the rectangles was cued. Participants were asked to judge which target appeared first. We found that the target showed on the cued rectangle after interocular grouping was reported to appear first more frequently than the target on the uncued rectangle. This result was based on the majority of trials where the suppressed parts of the objects remained invisible, which indicates that interocular grouping can occur without all the to-be-grouped parts being visible and without awareness. PMID:26851342

  10. Groups, rings, modules

    CERN Document Server

    Auslander, Maurice

    2014-01-01

    This classic monograph is geared toward advanced undergraduates and graduate students. The treatment presupposes some familiarity with sets, groups, rings, and vector spaces. The four-part approach begins with examinations of sets and maps, monoids and groups, categories, and rings. The second part explores unique factorization domains, general module theory, semisimple rings and modules, and Artinian rings. Part three's topics include localization and tensor products, principal ideal domains, and applications of fundamental theorem. The fourth and final part covers algebraic field extensions

  11. N-ary Groups

    CERN Document Server

    Gal'mak, Alexander M

    2011-01-01

    The book "N-ary Groups" (in Russian) consists of two Parts. It is intended on the one hand as an initial introduction to the theory of n-ary groups, and on the other hand it contains the published results by the author on this subject. At present, the theory of n-ary groups developing but slowly from group theory. Nonetheless, ternary and n-ary structures have recently been applied to modern models of elementary particle physics. One of the author's goals in this book is to draw the attention of mathematicians and theoretical physicists to the theory of n-ary groups, to some of its distinguishing features, and to details relevant to its further development and application. Part I: Theorems of Post and Gluskin-Hosszu. 1.1. Classical definitions of n-ary groups. Examples. 1.2. Analogies of identity and inverse elements. 1.3. Equivalent sequences. 1.4. Post's coset theorem. 1.5. Theorem of Gluskin-Hosszu. 1.6. Connection between the Post's coset theorem and theorem of Gluskin-Hosszu. Addition and comments. Part ...

  12. Group 2. Grouting

    International Nuclear Information System (INIS)

    This paper summarizes the findings of the Grouting Working Group which met during the Workshop on Radioactive, Hazardous, and/or Mixed Waste Sludge Management. The scope of this working group was to identify issues related to laboratory-scale experimentation in support of operation and design of an actual plant. The group recognizes that several stabilization/solidification (S/S) host media are available and, whichever is chosen, must be proven appropriate for the specific disposal scenario. However, the group focused on developing a systematic approach for the selection of cement-based grouting as an option, because of the prevalence of its application. It should be recognized that many of the issues will be generic to any stabilization process. Prior to the workshop, this group's members identified over 30 issues for discussion. At a previous informal session, the group distilled these to four issues that are believed to be at the heart of the 30 considered. The four issues were: (1) that both standard and site process-specific performance criteria must be identified, (2) that the waste-binder chemical interactions and the subsequent effect of these interactions on the chemical and physical properties of the resulting waste form must be better understood, (3) that scale-up factors must be considered in order to improve the probability of successfully developing waste-form products, and (4) that if S/S technology is to remain a widely used treatment option, product quality and performance must be confirmed over time

  13. Independents' group posts loss

    International Nuclear Information System (INIS)

    Low oil gas prices and special charges caused the group of 50 U.S. independent producers Oil and Gas Journal tracks to post a combined loss in first half 1992. The group logged a net loss of $53 million in the first half compared with net earnings of $354 million in first half 1991, when higher oil prices during the Persian Gulf crisis buoyed earnings in spite of crude oil and natural gas production declines. The combined loss in the first half follows a 45% drop in the group's earnings in 1991 and compares with the OGJ group of integrated oil companies whose first half 1992 income fell 47% from the prior year. Special charges, generally related to asset writedowns, accounted for most of the almost $560 million in losses posted by about the third of the group. Nerco Oil and Gas Inc., Vancouver, Wash., alone accounted for almost half that total with charges related to an asset writedown of $238 million in the first quarter. Despite the poor first half performance, the outlook is bright for sharply improved group earnings in the second half, assuming reasonably healthy oil and gas prices and increased production resulting from acquisitions and in response to those prices

  14. Coordinating Group report

    International Nuclear Information System (INIS)

    In December 1992, western governors and four federal agencies established a Federal Advisory Committee to Develop On-site Innovative Technologies for Environmental Restoration and Waste Management (the DOIT Committee). The purpose of the Committee is to advise the federal government on ways to improve waste cleanup technology development and the cleanup of federal sites in the West. The Committee directed in January 1993 that information be collected from a wide range of potential stakeholders and that innovative technology candidate projects be identified, organized, set in motion, and evaluated to test new partnerships, regulatory approaches, and technologies which will lead to improve site cleanup. Five working groups were organized, one to develop broad project selection and evaluation criteria and four to focus on specific contaminant problems. A Coordinating Group comprised of working group spokesmen and federal and state representatives, was set up to plan and organize the routine functioning of these working groups. The working groups were charged with defining particular contaminant problems; identifying shortcomings in technology development, stakeholder involvement, regulatory review, and commercialization which impede the resolution of these problems; and identifying candidate sites or technologies which could serve as regional innovative demonstration projects to test new approaches to overcome the shortcomings. This report from the Coordinating Group to the DOIT Committee highlights the key findings and opportunities uncovered by these fact-finding working groups. It provides a basis from which recommendations from the DOIT Committee to the federal government can be made. It also includes observations from two public roundtables, one on commercialization and another on regulatory and institutional barriers impeding technology development and cleanup

  15. Facilities removal working group

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-03-01

    This working group`s first objective is to identify major economic, technical, and regulatory constraints on operator practices and decisions relevant to offshore facilities removal. Then, the group will try to make recommendations as to regulatory and policy adjustments, additional research, or process improvements and/or technological advances, that may be needed to improve the efficiency and effectiveness of the removal process. The working group will focus primarily on issues dealing with Gulf of Mexico platform abandonments. In order to make the working group sessions as productive as possible, the Facilities Removal Working Group will focus on three topics that address a majority of the concerns and/or constraints relevant to facilities removal. The three areas are: (1) Explosive Severing and its Impact on Marine Life, (2) Pile and Conductor Severing, and (3) Deep Water Abandonments This paper will outline the current state of practice in the offshore industry, identifying current regulations and specific issues encountered when addressing each of the three main topics above. The intent of the paper is to highlight potential issues for panel discussion, not to provide a detailed review of all data relevant to the topic. Before each panel discussion, key speakers will review data and information to facilitate development and discussion of the main issues of each topic. Please refer to the attached agenda for the workshop format, key speakers, presentation topics, and panel participants. The goal of the panel discussions is to identify key issues for each of the three topics above. The working group will also make recommendations on how to proceed on these key issues.

  16. Linear algebraic groups

    CERN Document Server

    Springer, T A

    1998-01-01

    "[The first] ten chapters...are an efficient, accessible, and self-contained introduction to affine algebraic groups over an algebraically closed field. The author includes exercises and the book is certainly usable by graduate students as a text or for self-study...the author [has a] student-friendly style… [The following] seven chapters... would also be a good introduction to rationality issues for algebraic groups. A number of results from the literature…appear for the first time in a text." –Mathematical Reviews (Review of the Second Edition) "This book is a completely new version of the first edition. The aim of the old book was to present the theory of linear algebraic groups over an algebraically closed field. Reading that book, many people entered the research field of linear algebraic groups. The present book has a wider scope. Its aim is to treat the theory of linear algebraic groups over arbitrary fields. Again, the author keeps the treatment of prerequisites self-contained. The material of t...

  17. Illinois Wind Workers Group

    Energy Technology Data Exchange (ETDEWEB)

    David G. Loomis

    2012-05-28

    The Illinois Wind Working Group (IWWG) was founded in 2006 with about 15 members. It has grown to over 200 members today representing all aspects of the wind industry across the State of Illinois. In 2008, the IWWG developed a strategic plan to give direction to the group and its activities. The strategic plan identifies ways to address critical market barriers to the further penetration of wind. The key to addressing these market barriers is public education and outreach. Since Illinois has a restructured electricity market, utilities no longer have a strong control over the addition of new capacity within the state. Instead, market acceptance depends on willing landowners to lease land and willing county officials to site wind farms. Many times these groups are uninformed about the benefits of wind energy and unfamiliar with the process. Therefore, many of the project objectives focus on conferences, forum, databases and research that will allow these stakeholders to make well-educated decisions.

  18. Financial Lie groups

    CERN Document Server

    carfí, David

    2011-01-01

    In this paper we see the evolution of a capitalized financial event e, with respect to a capitalization factor f, as the exponential map of a suitably defined Lie group G(f,e), supported by the half-space of capitalized financial events having the same capital sign of e. The Lie group G(f,e) depends upon the capitalization factor f and on the event e itself. After the extension of the definition of exponential map of a Lie group, we shall eliminate the dependence on the financial event e, recognizing the presence of essentially one unique financial Lie semigroup, supported by the entire space of capitalized financial events, determined by the capitalization factor f.

  19. Instructions to working groups

    Science.gov (United States)

    Foushee, H. Clayton

    1987-01-01

    The key to the success of this workshop is your active participation in the working group process. The goals of this workshop are to address four major questions regarding Cockpit Resource Management (CRM) Training. To some extent the working group topic areas parallel these issues, but in some cases they do not. However, it is important for all of the working groups to keep these general questions in mind during their deliberations: (1) What are the essential elements of an optimal CRM Training program; (2) What are the strengths and weaknesses of current approaches to CRM Training; (3) How can CRM Training best be implemented, and what barriers exist; and (4) Is CRM Training effective, do we know, and if not, how can we find out.

  20. Group Psychotherapy in Sweden.

    Science.gov (United States)

    Ahlin, Göran

    2015-10-01

    The paper presents an overview of the national developments of group psychotherapy (GPS) in Sweden during the period from World War II until the present time. Methods and concepts, imported primarily from England and the United States, inspired trainings and widespread psychodynamic and group analytic applications in schools, health treatment, and social care. Education in psychotherapy and GPS at universities opened new therapeutic and vocational areas during the period 1970-2005. Increasing criticism of psychodynamics, as in other Western societies, but more radical in Sweden, has in the last decades made group analytic GPS diminish in favor of cognitive behavioral therapy models. Prospects for GPS further development may presently look bleak but, in a longer perspective, are promising. PMID:26401795

  1. Quantum threshold group signature

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In most situations, the signer is generally a single person. However, when the message is written on behalf of an organization, a valid message may require the approval or consent of several persons. Threshold signature is a solution to this problem. Generally speaking, as an authority which can be trusted by all members does not exist, a threshold signature scheme without a trusted party appears more attractive. Following some ideas of the classical Shamir’s threshold signature scheme, a quantum threshold group signature one is proposed. In the proposed scheme, only t or more of n persons in the group can generate the group signature and any t-1 or fewer ones cannot do that. In the verification phase, any t or more of n signature receivers can verify the message and any t-1 or fewer receivers cannot verify the validity of the signature.

  2. Focus group discussions

    CERN Document Server

    Hennink, Monique M

    2014-01-01

    The Understanding Research series focuses on the process of writing up social research. The series is broken down into three categories: Understanding Statistics, Understanding Measurement, and Understanding Qualitative Research. The books provide researchers with guides to understanding, writing, and evaluating social research. Each volume demonstrates how research should be represented, including how to write up the methodology as well as the research findings. Each volume also reviews how to appropriately evaluate published research. Focus Group Discussions addresses the challenges associated with conducting and writing focus group research. It provides detailed guidance on the practical and theoretical considerations in conducting focus group discussions including: designing the discussion guide, recruiting participants, training a field team, moderating techniques and ethical considerations. Monique Hennink describes how a methodology section is read and evaluated by others, such as journal reviewers or ...

  3. Colored Group Field Theory

    CERN Document Server

    Gurau, Razvan

    2009-01-01

    Group field theories are higher dimensional generalizations of matrix models. Their Feynman graphs are fat and in addition to vertices, edges and faces, they also contain higher dimensional cells, called bubbles. In this paper, we propose a new, fermionic Group Field Theory, posessing a color symmetry, and take the first steps in a systematic study of the topological properties of its graphs. Unlike its bosonic counterpart, the bubbles of the Feynman graphs of this theory are well defined and readily identified. We prove that this graphs are combinatorial cellular complexes. We define and study the cellular homology of this graphs. Furthermore we define a homotopy transformation appropriate to this graphs. Finally, the amplitude of the Feynman graphs is shown to be related to the fundamental group of the cellular complex.

  4. Supervision and group dynamics

    DEFF Research Database (Denmark)

    Hansen, Søren; Jensen, Lars Peter

    2004-01-01

     An important aspect of the problem based and project organized study at Aalborg University is the supervision of the project groups. At the basic education (first year) it is stated in the curriculum that part of the supervisors' job is to deal with group dynamics. This is due to the experience...... that many students are having difficulties with practical issues such as collaboration, communication, and project management. Most supervisors either ignore this demand, because they do not find it important or they find it frustrating, because they do not know, how to supervise group dynamics. This...... problem is not only found at Aalborg University but also at the engineering colleges in Denmark. For that reason a course was developed with the aim of addressing the problem and showing, how it can be dealt with. So far the course has been offered several times to supervisors at the engineering colleges...

  5. Fourier Analysis on Groups

    CERN Document Server

    Rudin, Walter

    2011-01-01

    In the late 1950s, many of the more refined aspects of Fourier analysis were transferred from their original settings (the unit circle, the integers, the real line) to arbitrary locally compact abelian (LCA) groups. Rudin's book, published in 1962, was the first to give a systematic account of these developments and has come to be regarded as a classic in the field. The basic facts concerning Fourier analysis and the structure of LCA groups are proved in the opening chapters, in order to make the treatment relatively self-contained.

  6. A Quantum Groups Primer

    Science.gov (United States)

    Majid, Shahn

    2002-05-01

    Here is a self-contained introduction to quantum groups as algebraic objects. Based on the author's lecture notes for the Part III pure mathematics course at Cambridge University, the book is suitable as a primary text for graduate courses in quantum groups or supplementary reading for modern courses in advanced algebra. The material assumes knowledge of basic and linear algebra. Some familiarity with semisimple Lie algebras would also be helpful. The volume is a primer for mathematicians but it will also be useful for mathematical physicists.

  7. Group theory and chemistry

    CERN Document Server

    Bishop, David M

    1993-01-01

    Group theoretical principles are an integral part of modern chemistry. Not only do they help account for a wide variety of chemical phenomena, they simplify quantum chemical calculations. Indeed, knowledge of their application to chemical problems is essential for students of chemistry. This complete, self-contained study, written for advanced undergraduate-level and graduate-level chemistry students, clearly and concisely introduces the subject of group theory and demonstrates its application to chemical problems.To assist chemistry students with the mathematics involved, Professor Bishop ha

  8. Hierarchies in student groups

    OpenAIRE

    Güntert, Manuel

    2008-01-01

    This is a research about hierarchies in student groups. It shows how they are built und what sense they have. The position of a student in his student peer group is evaluated. The influence of the look, the style, the behaviour of the other sex, the gender, the origin, the prehistory, the appearance, achievement and their effect on hierarchies is analysed and the impact of charisma and organisation are compared. The meaning of this research is to indicate how a student must be to get the lead...

  9. Bell, group and tangle

    International Nuclear Information System (INIS)

    The 'Bell' of the title refers to bipartite Bell states, and their extensions to, for example, tripartite systems. The 'Group' of the title is the Braid Group in its various representations; while 'Tangle' refers to the property of entanglement which is present in both of these scenarios. The objective of this note is to explore the relation between Quantum Entanglement and Topological Links, and to show that the use of the language of entanglement in both cases is more than one of linguistic analogy.

  10. FAW Group Gorporation

    Institute of Scientific and Technical Information of China (English)

    Yan Feng

    2007-01-01

    @@ As the founder of China's automobile industry, FAW Group Corporation (FAW) has maintained a dominant position in the automotive industry since its founding in 1953 in terms of its total assets, Production capacity, domestic and international sales, market share, and brand recognition.

  11. Group theory in cryptography

    CERN Document Server

    Blackburn, Simon R; Mullan, Ciaran

    2009-01-01

    This paper is a guide for the pure mathematician who would like to know more about cryptography based on group theory. The paper gives a brief overview of the subject, and provides pointers to good textbooks, key research papers and recent survey papers in the area.

  12. Group theory in physics

    CERN Document Server

    Cornwell, J F

    1989-01-01

    Recent devopments, particularly in high-energy physics, have projected group theory and symmetry consideration into a central position in theoretical physics. These developments have taken physicists increasingly deeper into the fascinating world of pure mathematics. This work presents important mathematical developments of the last fifteen years in a form that is easy to comprehend and appreciate.

  13. Space Systems Academic Group

    OpenAIRE

    2006-01-01

    The Space Systems Academic Group (SSAG) along with eight academic departments is an integral part of the Graduate School of Engineering and Applied Sciences. As an interdisciplinary association of professors it provides direction and guidance for two curricula: Space Systems Engineering and Space Systems Operations.

  14. Teaching Badminton to Groups.

    Science.gov (United States)

    Nelson, Jonathan E.

    1980-01-01

    Numerous ideas for teaching badminton to large groups are presented. The focus is on drills and techniques for off the court instructional stations. Instead of having students waiting their turn to play, more students can participate actively as they rotate from one station to another. (JN)

  15. Unclonable Group Identification

    DEFF Research Database (Denmark)

    Damgård, Ivan Bjerre; Dupont, Kasper; Pedersen, Michael Østergaard

    We introduce and motivate the concept of unclonable group identification, that provides maximal protection against sharing of identities while still protecting the anonymity of users. We prove that the notion can be realized from any one-way function and suggest a more efficient implementation...

  16. Group B Streptococcus

    Directory of Open Access Journals (Sweden)

    Albert H. Adriaanse

    1995-01-01

    Full Text Available Objective: Group B streptococcus (GBS, Streptococcus agalactiae is an important cause of neonatal sepsis. Prevention is possible by intrapartum screening for maternal GBS carriership and antimicrobial treatment of colonized women with risk factors during labor. The conflicting results of diagnostic performance are reported both for the newly developed rapid GBS antigen tests and Gram's stain.

  17. Cohomology of quantum groups

    CERN Document Server

    Frønsdal, Christian

    1995-01-01

    Lecture notes. Introduction to the cohomology of algebras, Lie algebras, Lie bialgebras and quantum groups. Contains a new derivation of the classification of classical r-matrices in terms of deformation cohomology, and a calculation of the esoteric forms of quantum gl(N) by deformation theory.

  18. End Group Modification

    DEFF Research Database (Denmark)

    Jahnsen, Rasmus O; Sandberg-Schaal, Anne; Frimodt-Møller, Niels; Nielsen, Hanne Mørck; Franzyk, Henrik

    , the most favorable hydrophobic activity-inducing moieties were found to be cyclohexylacetyl and pentafluorophenylacetyl groups, while the presence of a short PEG-like chain had no significant effect on activity. Introduction of cationic moieties conferred no effect or merely a moderate activity...

  19. Abandoning wells working group

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-03-01

    The primary objective of this working group is to identify major technical, regulatory, and environmental issues that are relevant to the abandonment of offshore wellbores. Once the issues have been identified, the working group also has the objective of making recommendations or providing potential solutions for consideration. Areas for process improvement will be identified and {open_quotes}best practices{close_quotes} will be discussed and compared to {open_quotes}minimum standards.{close_quotes} The working group will primarily focus on wellbore abandonment in the Gulf of Mexico. However, workshop participants are encouraged to discuss international issues which may be relevant to wellbore abandonment practices in the Gulf of Mexico. The Abandoning Wells Group has identified several major areas for discussion that have concerns related to both operators and service companies performing wellbore abandonments in the Gulf of Mexico. The following broad topics were selected for the agenda: (1) MMS minimum requirements and state regulations. (2) Co-existence of best practices, new technology, and P & A economics. (3) Liability and environmental issues relating to wellbore abandonment.

  20. Geodesic Renormalisation Group Flow

    OpenAIRE

    Dolan, Brian P

    1995-01-01

    It is shown that the renormalisation group flow in coupling constant space can be interpreted in terms of a dynamical equation for the couplings analogous to viscous fluid flow under the action of a potential. For free scalar field theory the flow is geodesic in two dimensions, while for $D \

  1. Teaching the renormalization group

    International Nuclear Information System (INIS)

    The renormalization group theory of continuous phase transitions is described with the use of a hands on model suitable for presentation as part of an undergraduate thermal physics course. It is an extension of the work of Maris and Kadanoff in that key concepts such as universality fixed points and critical surface are introduced

  2. With the Radiobiology Group

    CERN Multimedia

    1980-01-01

    The Radiobiology Group carries out experiments to study the effect of radiation on living cells. The photo shows the apparatus for growing broad beans which have been irradiated by 250 GeV protons. The roots are immersed in a tank of running water (CERN Weekly Bulletin 26 January 1981 and Annual Report 1980 p. 160). Karen Panman, Marilena Streit-Bianchi, Roger Paris.

  3. Cohomology of kleinian groups.

    Science.gov (United States)

    Kra, I

    1969-07-01

    Let [unk] be a (nonelementary) Kleinian group and q >/= 2 an integer. The group [unk] acts in a natural way on the vector space II(2q-2) of complex polynomials in one variable of degree group of [unk] with coefficients in II(2q-2). There are essentially two ways of constructing cohomology classes. One construction originated with Eichler and has recently been extended by Ahlfors. Another construction is due to Bers. We show that for finitely generated [unk], every cohomology class pepsilon H(1)([unk],II(2q-2)) can be written uniquely (if one chooses an invariant union of components of [unk]) as a sum of a Bers cohomology class and an Eichler cohomology class. Similar decompositions are obtained for the subgroups of parabolic cohomology classes introduced by Ahlfors. Some information on the structure of H(1)([unk],II(2q-2)) for infinitely generated groups [unk] is also obtained. PMID:16591774

  4. Anti- CC-Groups and Anti-PC-Groups

    Directory of Open Access Journals (Sweden)

    Francesco Russo

    2007-01-01

    subgroup H of G. An anti-PC group G is a group in which each nonfinitely generated subgroup K has the quotient group G/coreG(NG(K which is a polycyclic-by-finite group. Anti-CC groups and anti-PC groups are the subject of the present article.

  5. Nonequilibrium Renormalization Group

    International Nuclear Information System (INIS)

    Thermal equilibrium properties of many-body or field theories are known to be efficiently classified in terms of renormalization group fixed points. A particularly powerful concept is the notion of infrared fixed points, which are characterized by universality. These correspond to critical phenomena in thermal equilibrium, where a characteristic large correlation length leads to independence of long-distance properties from details of the underlying microscopic theory. In contrast, a classification of properties of theories far from thermal equilibrium in terms of renormalization group fixed points is much less developed. The notion of universality or critical phenomena far from equilibrium is to a large extent unexplored, in particular, in relativistic quantum field theories. Here the strong interest is mainly driven by theoretical and experimental advances in our understanding of early universe cosmology as well as relativistic collision experiments of heavy nuclei in the laboratory. In these lectures I will introduce the functional renormalization group for the effective average action out of equilibrium. While in equilibrium typically a Euclidean formulation is adequate, nonequilibrium properties require real-time descriptions. For quantum systems a generating functional for nonequilibrium correlation functions with given density matrix at initial time can be written down using the Schwinger-Keldysh closed time path contour. In principle, this can be used to construct a nonequilibrium functional renormalization group along similar lines as for Euclidean field theories in thermal equilibrium. However, important differences include the absence of time-translation invariance for general out-of-equilibrium situations. The nonequilibrium renormalization group takes on a particularly simple form at a fixed point, since it becomes independent of the initial density matrix. I will discuss some simple examples for which I derive a hierarchy of fixed point solutions

  6. Inversión y reactivación tectónicas cretácicocenozoicas en el Noroeste Argentino: influencia de las heterogeneidades del basamento neoproterozoico-paleozoico inferior Cretaceous-Cenozoic tectonic inversion and reactivation in Northwestern Argentina: Influence of Neoproterozoic-Lower Paleozoic basement heterogeneities

    Directory of Open Access Journals (Sweden)

    Fernando Hongn

    2010-03-01

    Full Text Available Los rasgos estructurales del basamento neoproterozoico-paleozoico inferior (Cámbrico- Ordovícico del noroeste argentino han controlado en diferentes grados el desarrollo de las estructuras posteriores, principalmente las vinculadas con la extensión cretácica y el acortamiento andino. La inversión tectónica de fallas normales relacionadas con el rift cretácico ha sido frecuentemente invocada entre los mecanismos que influyen en la definición de las zonas de doble vergencia y retrovergencia que muestra el orógeno andino en el noroeste argentino. En esta contribución proponemos que las estructuras del basamento jugaron un papel primario en la localización tanto de las fallas normales cretácicas posteriormente reactivadas como de las fallas inversas andinas. Una sección estructural regional entre la Cordillera de Domeyko (Chile y el Sistema de Santa Bárbara (aproximadamente 24º-25ºLS muestra segmentos con vergencias cenozoicas opuestas, en la que cada porción responde a diferentes controles ejercidos por estructuras previas. La inversión de fallas normales asociadas a sistemas de rift fue el principal control de la geometría y vergencia de las estructuras cenozoicas vinculadas al acortamiento andino en la Cordillera de Domeyko, en los Valles Calchaquíes y en el Sistema de Santa Bárbara. La reactivación de las estructuras y heterogeneidades originadas durante la evolución neoproterozoico-paleozoica del basamento controlaron el desarrollo de las estructuras cenozoicas en la Puna. La reactivación de las heterogeneidades no sólo influyó en los cambios de orientación y vergencia, sino también en la distribución temporal compleja que muestra el acortamiento andino. La reactivación múltiple de algunas estructuras del basamento neoproterozoico-paleozoico inferior ocurrió en diferentes etapas de su historia incluyendo inversiones positivas y negativas entre el Cretácico y el Cuaternario.The Neoproterozoic-Lower Paleozoic

  7. Ignimbritas riolíticas neoproterozoicas en la Sierra Norte de Córdoba: ¿evidencia de un arco magmático temprano en el ciclo Pampeano? Neoproterozoic rhyolite ignimbrites in the Sierra Norte de Córdoba: evidence of an early magmatic arc in the Pampean cycle?

    Directory of Open Access Journals (Sweden)

    EJ Llambías

    2003-12-01

    granodioritic and monzogranitic plutons of the Sierra Norte-Ambargasta batholtih, of Cambrian age. Dacitic to rhyolitic domes and dikes were intruded during the last stages of the batholith. In this paper we describe rhyolitic ignimbrite sheets within the metaconglomerates of the La Lidia Formation. The ignimbrites are moderately welded and consist of about 15 % of quartz, K-feldspar and entirely altered plagioclase porhyroclasts. Groundmass consists of devitrified glass shards. The conventional U/Pb zircon age is 584+22/-14 Ma and it is considered as the crystallization age. Very low grade metamorphism of the prehnite-pumpellyte facies altered the plagioclase to zoicite, sericite and pumpellyte. The Neoproterozoic silicic ignimbrites, together with the Cambrian calc-alkaline batholith and the related volcanics indicate the existence of a magmatic arc associated with the active margin of the Gondwana continent. This arc was active since Neoproterozoic times, with a duration of more than 60 Ma. Correlation of the Neoproterozoic metasedimentary and volcanics of Sierra Norte with the Puncoviscana Formation of Northwestern Argentina is considered.

  8. Mindfulness for group facilitation

    DEFF Research Database (Denmark)

    Adriansen, Hanne Kirstine; Krohn, Simon

    2014-01-01

    In this paper, we argue that mindfulness techniques can be used for enhancing the outcome of group performance. The word mindfulness has different connotations in the academic literature. Broadly speaking there is ‘mindfulness without meditation’ or ‘Western’ mindfulness which involves active...... thinking and ‘Eastern’ mindfulness which refers to an open, accepting state of mind, as intended with Buddhist-inspired techniques such as meditation. In this paper, we are interested in the latter type of mindfulness and demonstrate how Eastern mindfulness techniques can be used as a tool for facilitation....... A brief introduction to the physiology and philosophy of Eastern mindfulness constitutes the basis for the arguments of the effect of mindfulness techniques. The use of mindfulness techniques for group facilitation is novel as it changes the focus from individuals’ mindfulness practice to that of...

  9. Working group 4: Terrestrial

    International Nuclear Information System (INIS)

    A working group at a Canada/USA symposium on climate change and the Arctic identified major concerns and issues related to terrestrial resources. The group examined the need for, and the means of, involving resource managers and users at local and territorial levels in the process of identifying and examining the impacts and consequences of climatic change. Climatic change will be important to the Arctic because of the magnitude of the change projected for northern latitudes; the apparent sensitivity of its terrestrial ecosystems, natural resources, and human support systems; and the dependence of the social, cultural, and economic welfare of Arctic communities, businesses, and industries on the health and quality of their environment. Impacts of climatic change on the physical, biological, and associated socio-economic environment are outlined. Gaps in knowledge needed to quantify these impacts are listed along with their relationships with resource management. Finally, potential actions for response and adaptation are presented

  10. Two Abelian group constructions

    International Nuclear Information System (INIS)

    Let A be an Abelian group and n an integer >1. Let D be a divisible hull of A. Define A0sup((D))=A,Asub(r)sup((D)) = set containing x is an element of D|nx=y, for some y is an element of Asub(r=1)sup((D)), r=1,2,3,..., and Asub([n])sup((D))=Usub(r=0)sup(infinity)Asub(r)sup((D)). Then each Asub(r)sup((D)) is a subgroup of D and Asub([n])sup((D)) is the smallest n-divisible subgroup of D which contains A. Define Asub((D))sup([n])=Asub([n])sup((D))/A. A number of theorems and propositions are proved for the groups Asub([n])sup((D)) and Asub((D))sup([n])

  11. Group Formation in Economics

    Science.gov (United States)

    Demange, Gabrielle; Wooders, Myrna

    2005-01-01

    Broad and diverse ranges of activities are conducted within and by organized groups of individuals, including political, economic and social activities. These activities have recently become a subject of intense interest in economics and game theory. Some of the topics investigated in this collection are models of networks of power and privilege, trade networks, co-authorship networks, buyer-seller networks with differentiated products, and networks of medical innovation and the adaptation of new information. Other topics are social norms on punctuality, clubs and the provision of club goods and public goods, research and development and collusive alliances among corporations, and international alliances and trading agreements. While relatively recent, the literature on game theoretic studies of group formation in economics is already vast. This volume provides an introduction to this important literature on game-theoretic treatments of situations with networks, clubs, and coalitions, including some applications.

  12. ST Quality Working Group

    CERN Document Server

    Akhtar, S

    2000-01-01

    When CERN engages contractors or outside enterprises for supply and service contracts, a Quality certification is requested. CERN itself has no global certification. Nor are quality assurance systems well understood by the majority of CERN staff. This has not precluded successful activity but it is felt that a structured approach would have some benefits: elimination of occasional accelerator perturbations, improved documentation, efficient use of existing resources, enhanced sharing of experience and knowledge, avoidance of improper handover periods when staff leave CERN. In some cases talented staff spend too much time doing remedial jobs when they are capable of achieving much more. The ST quality working group was formed to address these problems. The goal of this quality working group is to help ST division maintain and continuously improve the quality of its services and operations, and give confidence to ST staff and clients that the requirements for quality are being fulfilled, maintained and improved...

  13. Communication from ST Group

    CERN Multimedia

    TS Department

    2008-01-01

    Please note that owing the preparations for the Open Days, the FM Group will not able to handle specific requests for waste collection from 2nd to 6th of April, nor removal or PC transport requests between the 31 March and 11 April. We kindly ask you to plan the collection of all types of waste and any urgent transport of office furniture or PCs before 31 March. Waste collection requests must be made by contacting FM Support on 77777 or at the e-mail address mailto:Fm.Support@cern.ch; removal of office furniture or PC transport requests must be made using the EDH ‘Transport request’ form (select "Removals" or "PC transport" from the drop-down menu). For any question concerning the sorting of waste, please consult the following web site: http://dechets-waste.web.cern.ch/dechets-waste/ Thank you for your understanding and collaboration. TS/FM Group

  14. The Ombudperson Initiative Group

    CERN Multimedia

    Laura Stewart

    Following many discussions that took place at some of the ATLAS Women's Network lunch gatherings, a few ATLAS women joined forces with similarly concerned CERN staff women to form a small group last Fall to discuss the need for a CERN-wide Ombudsperson. This has since evolved into the Ombudsperson Initiative Group (OIG) currently composed of the following members: Barbro Asman, Stockholm University; Pierre Charrue, CERN AB; Anna Cook, CERN IT; Catherine Delamare, CERN and IT Ombudsperson; Paula Eerola, Lund University; Pauline Gagnon, Indiana University; Eugenia Hatziangeli, CERN AB; Doreen Klem, CERN IT; Bertrand Nicquevert, CERN TS and Laura Stewart, CERN AT. On June 12, members of the OIG met with representatives of Human Resources (HR) and the Equal Opportunity Advisory Panel (EOAP) to discuss the proposal drafted by the OIG. The meeting was very positive. Everybody agreed that the current procedures at CERN applicable in the event of conflict required a thorough review, and that a professionnally trai...

  15. The Areva Group

    International Nuclear Information System (INIS)

    This document provides information on the Areva Group, a world nuclear industry leader, offering solutions for nuclear power generation, electricity transmission and distribution and interconnect systems to the telecommunications, computer and automotive markets. It presents successively the front end division including the group business lines involved in producing nuclear fuel for electric power generation (uranium mining, concentration, conversion and enrichment and nuclear fuel fabrication); the reactors and services division which designs and builds PWR, BWR and research reactors; the back end division which encompasses the management of the fuel that has been used in nuclear power plants; the transmission and distribution division which provides products, systems and services to the medium and high voltage energy markets; the connectors division which designs and manufactures electrical, electronic and optical connectors, flexible micro circuitry and interconnection systems. Areva is implemented in Europe, north and south america, africa and asia-pacific. (A.L.B.)

  16. Working group 2: Freshwater

    International Nuclear Information System (INIS)

    A working group at a Canada-USA symposium on climate change in the Arctic addressed freshwater issues from the perspective of water resource planning and management. Two issues were selected for discussion and identification of relationships with resource management: hydroelectric production and waste disposal. Gaps in knowledge about climate and water resources were identified along with potential actions for response and adaptation to climate change. Recommendations are offered to improve knowledge of Arctic climate and hydrology

  17. Combinatorial group theory

    CERN Document Server

    Lyndon, Roger C

    2001-01-01

    From the reviews: "This book (...) defines the boundaries of the subject now called combinatorial group theory. (...)it is a considerable achievement to have concentrated a survey of the subject into 339 pages. This includes a substantial and useful bibliography; (over 1100 ÄitemsÜ). ...the book is a valuable and welcome addition to the literature, containing many results not previously available in a book. It will undoubtedly become a standard reference." Mathematical Reviews, AMS, 1979.

  18. Equity valuation : Eurocash Group

    OpenAIRE

    Branco, Ana Isabel Antunes de Azevedo

    2015-01-01

    Equity valuation is an extremely complex and subjective process, it depends not only on the theoretical models but also on the analysis and assumptions used by the analyst. This thesis focuses on the valuation of Eurocash Group, a leading wholesale distributor of fast moving consumer goods (FMCG) in Poland. In order to present stronger conclusions we decided to use two different models: the discounted cash-flow (DCF) model and the multiples method as a complement. The combination of both l...

  19. KKG Group Paraffin Removal

    Energy Technology Data Exchange (ETDEWEB)

    Schulte, Ralph

    2001-12-01

    The Rocky Mountain Oilfield Testing Center (RMOTC) has recently completed a test of a paraffin removal system developed by the KKG Group utilizing the technology of two Russian scientists, Gennady Katzyn and Boris Koggi. The system consisting of chemical ''sticks'' that generate heat in-situ to melt the paraffin deposits in oilfield tubing. The melted paraffin is then brought to the surface utilizing the naturally flowing energy of the well.

  20. Holonomy groups and spacetimes

    OpenAIRE

    Hall, G. S.; Lonie, D. P.

    2003-01-01

    A study is made of the possible holonomy group types of a space-time for which the energy-momentum tensor corresponds to a null or non-null electromagnetic field, a perfect fluid or a massive scalar field. The case of an Einstein space is also included. The techniques developed are also applied to vacuum and conformally flat space-times and contrasted with already known results in these two cases. Examples are given.

  1. Holonomy groups and spacetimes

    CERN Document Server

    Hall, G S

    2000-01-01

    A study is made of the possible holonomy group types of a space-time for which the energy-momentum tensor corresponds to a null or non-null electromagnetic field, a perfect fluid or a massive scalar field. The case of an Einstein space is also included. The techniques developed are also applied to vacuum and conformally flat space-times and contrasted with already known results in these two cases. Examples are given.

  2. Hadron hadron collider group

    International Nuclear Information System (INIS)

    The objective of this group was to make a rough assessment of the characteristics of a hadron-hadron collider which could make it possible to study the 1 TeV mass scale. Since there is very little theoretical guidance for the type of experimental measurements which could illuminate this mass scale, we chose to extend the types of experiments which have been done at the ISR, and which are in progress at the SPS collider to these higher energies

  3. Heavy flavors study group

    International Nuclear Information System (INIS)

    The heavy flavor study group concentrated on three issues. First the investigation of an energy transverse trigger to be used to select out charm and beauty events. Second, in a dedicated high sensitivity two-body B experiment is it possible to ''tag'' the beauty particle. Third, the design of a photoproduction experiment that could accumulate 108 charm particles in a single Fermilab running period

  4. Ocenenie Volkswagen Group

    OpenAIRE

    Šusták, Tomáš

    2010-01-01

    Objective of the thesis is determination of Volkswagen Group's equity intrinsic value. Basic starting point of the analysis is seggregation of consolidated financial statements into financial and production division, which are valuated separately. The production division is valuated using both enterprise discounted cashflow and discounted economic profit analysis. Equity cashflow valuation is used to derive value of the financial division. Results of valuation implied by income approach are t...

  5. Multibunch working group

    International Nuclear Information System (INIS)

    The goal of this working group was to foment discussions about the use and limitations of multi-bunch, representatives from most operating or in-project synchrotron radiation sources (ALS, SPEAR, BESSY-2, SPRING-8, ANKA, DELTA, PEP-2, DIAMOND, ESRF...) have presented their experience. The discussions have been led around 3 topics: 1) resistive wall instabilities and ion instabilities, 2) higher harmonic cavities, and 3) multibunch feedback systems

  6. Mixed carbonate-siliciclastic sedimentation in forebulge grabens: An example from the Ediacaran Bambuí Group, São Francisco Basin, Brazil

    Science.gov (United States)

    Reis, Humberto L. S.; Suss, João F.

    2016-06-01

    Mixed carbonate-siliciclastic successions have been described in multiple Phanerozoic sedimentary settings recording the dynamic interplay of tectonics, eustasy, climate, in situ carbonate production, and variations in siliciclastic sediment supply. The Ediacaran Bambuí 1st-order sequence (i.e., Bambuí Group) covers most of the intracratonic São Francisco basin (southeast Brazil) and encompasses thick packages of carbonate and fine- to coarse-grained siliciclastic strata. Recording a marine foreland basin stage that developed in the São Francisco plate during the Neoproterozoic-early Paleozoic West Gondwana assembly, the Ediacaran deposits unconformably overlie Archean-Paleoproterozoic metamorphic assemblages of the Sete Lagoas basement high and fill a series of kilometer-long grabens in the southern São Francisco basin. Seismic data reveal that these troughs developed through the extensional reactivation of ancient basement structures along with the tectonically driven forebulge uplift of the Sete Lagoas high, in the early evolutionary stages of the Bambuí basin cycle. Based on the detailed description of continuous drill cores of a well recently drilled during hydrocarbon exploration campaigns, we recognized two transgressive-regressive 2nd-order sequences preserved within one of the focused grabens: (i) Sequence 1 includes the glaciogenic deposits of the basal Carrancas Formation that grade upward into the carbonate ramp successions of the Sete Lagoas Formation; (ii) Sequence 2 contains the siliciclastic-dominated and deep water to deltaic strata of the Serra de Santa Helena Formation and passes upward into peritidal carbonates of the Lagoa do Jacaré Formation. These sedimentary successions encompass suites of retrogradational, aggradational, and progradational lower-rank cycles and are bounded by erosional surfaces. Regional seismic interpretation, well data, and the available literature indicate that most of these deposits and their correlatives are

  7. Group process and group phenomena on the Internet.

    Science.gov (United States)

    Weinberg, H

    2001-07-01

    This article identifies group processes and group phenomena in discussion lists on the Internet and examines the differences and similarities with the processes in small and large groups. Group dynamics and phenomena, such as boundaries, cohesion, transference, scapegoating, and the leader's role are addressed. Large group features, such as alienation, vulnerability, and the vast amount of issues discussed in parallel are described. There are similarities between the discussion list and small groups on issues of cohesion and group norms, and in the psychological mechanisms of transference and scapegoating. There are differences regarding the contract, boundaries, leaving the group, and extra-group socialization. Although many of the phenomena described resemble a large group, a discussion list on the Internet maintains the illusion of being a small group and frequently acts like one. While a virtual therapy group would be somewhat different from a real group, it could nonetheless be useful. PMID:11447785

  8. Outer automorphism groups of certain 1-relator groups

    Institute of Scientific and Technical Information of China (English)

    KIM; Goansu

    2010-01-01

    Grossman first showed that outer automorphism groups of 1-relator groups given by orientable surface groups are residually finite,whence mapping class groups of orientable surfaces are residually finite.Allenby,Kim and Tang showed that outer automorphism groups of cyclically pinched 1-relator groups are residually finite,whence mapping class groups of orientable and non-orientable surfaces are residually finite.In this paper we show that outer automorphism groups of certain conjugacy separable 1-relator groups are residually finite.

  9. Countable groups are mapping class groups of hyperbolic 3-manifolds

    OpenAIRE

    Frigerio, Roberto; Martelli, Bruno

    2005-01-01

    We prove that for every countable group G there exists a hyperbolic 3-manifold M such that the isometry group of M, the mapping class group of M, and the outer automorphism group of the fundamental group of M are isomorphic to G.

  10. Quality of Group Member Agendas and Group Session Climate.

    Science.gov (United States)

    Kivlighan, Dennis M., Jr.; Jauquet, Carol A.

    1990-01-01

    Examined relationship between group members' (N=36) approach to group sessions and group session climate and relationship between length of time in group and agenda quality. Found average ratings of interpersonal and here-and-now dimensions of agendas were significantly related to average perception of group climate as more engaged and less…

  11. Technology working group

    International Nuclear Information System (INIS)

    The workshop of 26-27 june 2000, on nuclear power Plant LIfe Management (PLIM), also included working groups in which major issues facing PLIM activities for nuclear power plants were identified and discussed. The first group was on Technology. Utilities should consider required provisions capacity by properly maintaining and preserving the existing power plants to the extent practicable and taking into account growing demand, limits of energy conservation, and difficulties in finding new power plant sites. Generally, the extension of the life of nuclear power plant (e.g. from 40 years to 60 years) is an attractive option for utilities, as the marginal cost of most existing nuclear power plants is lower than that of almost all other power sources. It is also an attractive option for environmental protection. Consequently, PLIM has become an important issue in the context of the regulatory reform of the electricity markets. Therefore, the three main objectives of the Technology working group are: 1) Documenting how the safety of nuclear power plants being operated for the long-term has been confirmed, and suggesting ways of sharing this information. 2) Addressing development of advanced maintenance technologies necessary over the plant lifetime, and clarifying their technical challenges. 3) Suggesting potential areas of research and development that might, be necessary. Some potential examples of such research include: - improving the effectiveness of maintenance methods to assure detection of incipient faults; - providing cost effective preventive maintenance programmes; - furnishing systematic, cost-effective refurbishment programmes framed to be consistent with efforts to extend the time between re-fuelling; - developing a methodology that moves routine maintenance on-line without compromising safety. (author)

  12. Unilever Group : equity valuation

    OpenAIRE

    Pires, Susana Sofia Castelo

    2014-01-01

    The following dissertation has the purpose to value the Unilever Group, but more specifically Unilever N.V. being publicly traded in the Amsterdam Exchange Index. Unilever is seen as a global player and one of most successful and competitive fast-moving consumer goods companies. In order to valuate Unilever’s equity, a Discounted Cash Flow (DCF) approach is first carried out, since it is believed to be the most reliable methodology. The value estimated was €36.39, advising one to buy its s...

  13. Statistical Group Comparison

    CERN Document Server

    Liao, Tim Futing

    2011-01-01

    An incomparably useful examination of statistical methods for comparisonThe nature of doing science, be it natural or social, inevitably calls for comparison. Statistical methods are at the heart of such comparison, for they not only help us gain understanding of the world around us but often define how our research is to be carried out. The need to compare between groups is best exemplified by experiments, which have clearly defined statistical methods. However, true experiments are not always possible. What complicates the matter more is a great deal of diversity in factors that are not inde

  14. Bevalac computer support group

    International Nuclear Information System (INIS)

    During the past year, a group was created and placed under the leadership of Charles McParland. This is an expansion of previous Bevalac software efforts and has responsibilities in three major hardware and software areas. The first area is the support of the existing data acquisition/analysis VAX 11/780s at the Bevalac. The second area is the continued support of present data acquisition programs. The third principal area of effort is the development of new data acquisition systems to meet the increasing needs of the Bevalac experimental program

  15. Theory and modeling group

    Science.gov (United States)

    Holman, Gordon D.

    The primary purpose of the Theory and Modeling Group meeting was to identify scientists engaged or interested in theoretical work pertinent to the Max '91 program, and to encourage theorists to pursue modeling which is directly relevant to data which can be expected to result from the program. A list of participants and their institutions is presented. Two solar flare paradigms were discussed during the meeting -- the importance of magnetic reconnection in flares and the applicability of numerical simulation results to solar flare studies.

  16. Arithmetic of Quaternion Groups

    OpenAIRE

    Jahangiri, Majid

    2009-01-01

    Let $p$ be a prime and $a$ a quadratic non-residue $\\bmod p$. Then the set of integral solutions of the diophantine equation $x_0^2 - ax_1^2 -px_2^2 + apx_3^2=1$ form a cocompact discrete subgroup $\\Gamma_{p,a}\\subset SL(2,\\mathbb{R})$ and is commensurable with the group of units of an order in a quaternion algebra over $\\mathbb{Q}$. The problem addressed in this paper is an estimate for the traces of a set of generators for $\\Gamma_{p,a}$. Empirical results summarized in several tables show ...

  17. GroupFinder

    DEFF Research Database (Denmark)

    Bøgh, Kenneth Sejdenfaden; Skovsgaard, Anders; Jensen, Christian S.

    2013-01-01

    The notion of point-of-interest (PoI) has existed since paper road maps began to include markings of useful places such as gas stations, hotels, and tourist attractions. With the introduction of geopositioned mobile devices such as smartphones and mapping services such as Google Maps, the retrieval...... existing proposals retrieve results at single-PoI granularity. We assume that a mobile device user issues queries consisting of keywords and an automatically supplied geo-position, and we target the common case where the user wishes to find nearby groups of PoIs that are relevant to the keywords. Such...

  18. Social group utility maximization

    CERN Document Server

    Gong, Xiaowen; Yang, Lei; Zhang, Junshan

    2014-01-01

    This SpringerBrief explains how to leverage mobile users' social relationships to improve the interactions of mobile devices in mobile networks. It develops a social group utility maximization (SGUM) framework that captures diverse social ties of mobile users and diverse physical coupling of mobile devices. Key topics include random access control, power control, spectrum access, and location privacy.This brief also investigates SGUM-based power control game and random access control game, for which it establishes the socially-aware Nash equilibrium (SNE). It then examines the critical SGUM-b

  19. The technical review group

    International Nuclear Information System (INIS)

    This paper describes the formation of a technical review group (TRG) as an early application of the quality assurance program for high-level waste processing. The objectives and functions for a TRG are summarized. Organizational structure is presented. Interfaces for the TRG are described by a flow diagram following the review process from the originator's document submittal to the final approval. Interfacing organizations and their responsibilities during the review are shown. Experience to date with TRG activities are described and QA interaction is discussed

  20. Grouping Synonyms by Definitions

    OpenAIRE

    Falk, Ingrid; Gardent, Claire; Jacquey, Evelyne; Venant, Fabienne

    2009-01-01

    We present a method for grouping the synonyms of a lemma according to its dictionary senses. The senses are defined by a large machine readable dictionary for French, the TLFi (Tr\\'esor de la langue fran\\c{c}aise informatis\\'e) and the synonyms are given by 5 synonym dictionaries (also for French). To evaluate the proposed method, we manually constructed a gold standard where for each (word, definition) pair and given the set of synonyms defined for that word by the 5 synonym dictionaries, 4 ...

  1. Quantum Group $\\sigma$ Models

    CERN Document Server

    Frishman, Yitzhak; Zakrzewski, W J

    1993-01-01

    Field-theoretic models for fields taking values in quantum groups are investigated. First we consider $SU_q(2)$ $\\sigma$ model ($q$ real) expressed in terms of basic notions of noncommutative differential geometry. We discuss the case in which the $\\sigma$ models fields are represented as products of conventional $\\sigma$ fields and of the coordinate-independent algebra. An explicit example is provided by the $U_q(2)$ $\\sigma$ model with $q\\sp{N}=1$, in which case quantum matrices $U_q(2)$ are realised as $2N\\times 2N$ unitary matrices. Open problems are pointed out.

  2. Quantum Group $\\sigma$ Models

    OpenAIRE

    Frishman, Y.; Lukierski, J.; Zakrzewski, W. J.

    1992-01-01

    Field-theoretic models for fields taking values in quantum groups are investigated. First we consider $SU_q(2)$ $\\sigma$ model ($q$ real) expressed in terms of basic notions of noncommutative differential geometry. We discuss the case in which the $\\sigma$ models fields are represented as products of conventional $\\sigma$ fields and of the coordinate-independent algebra. An explicit example is provided by the $U_q(2)$ $\\sigma$ model with $q\\sp{N}=1$, in which case quantum matrices $U_q(2)$ ar...

  3. Representation Theory of Algebraic Groups and Quantum Groups

    CERN Document Server

    Gyoja, A; Shinoda, K-I; Shoji, T; Tanisaki, Toshiyuki

    2010-01-01

    Invited articles by top notch expertsFocus is on topics in representation theory of algebraic groups and quantum groupsOf interest to graduate students and researchers in representation theory, group theory, algebraic geometry, quantum theory and math physics

  4. Quantum group gauge fields

    International Nuclear Information System (INIS)

    This paper reports on a kind of solution in the effective theory of superstring. It was shown that extra time-like coordinates can solve the cosmological constant problem. To avoid the appearance of massless ghost we had to put some topological restrictions on the internal space K. One of this restriction is that K has no Killings vectors at all. Equation of motion got us that K has negative curvature. The simplest example of a manifold with negative curvature is an hyperboloid which is non-compact. In the σ-model approach this means that we have to deal with non-compact σ-models. Namely such type of σ-models is a subject of recent investigations in the context of the 2-dim gravity coupled with c=1 matter. However one can assume that K is a compact hyperbolic manifold. Such manifolds have rather complicated topology. In the usually adopted field theories fields take values in the simplest manifolds (line, plane, sphere, group, coset space, etc.). However adopted the possibility for signature to be the dynamical variable we have to deal with fields taken values in manifolds with complicate topology. One can go one step forward and try to consider field theories in which fields are more complicate objects, for example, are elements of quantum plane or quantum group

  5. ATLAS Detector Interface Group

    CERN Multimedia

    Mapelli, L

    Originally organised as a sub-system in the DAQ/EF-1 Prototype Project, the Detector Interface Group (DIG) was an information exchange channel between the Detector systems and the Data Acquisition to provide critical detector information for prototype design and detector integration. After the reorganisation of the Trigger/DAQ Project and of Technical Coordination, the necessity to provide an adequate context for integration of detectors with the Trigger and DAQ lead to organisation of the DIG as one of the activities of Technical Coordination. Such an organisation emphasises the ATLAS wide coordination of the Trigger and DAQ exploitation aspects, which go beyond the domain of the Trigger/DAQ project itself. As part of Technical Coordination, the DIG provides the natural environment for the common work of Trigger/DAQ and detector experts. A DIG forum for a wide discussion of all the detector and Trigger/DAQ integration issues. A more restricted DIG group for the practical organisation and implementation o...

  6. Biology task group

    International Nuclear Information System (INIS)

    The accomplishments of the task group studies over the past year are reviewed. The purposes of biological investigations, in the context of subseabed disposal, are: an evaluation of the dose to man; an estimation of effects on the ecosystem; and an estimation of the influence of organisms on and as barriers to radionuclide migration. To accomplish these ends, the task group adopted the following research goals: (1) acquire more data on biological accumulation of specific radionuclides, such as those of Tc, Np, Ra, and Sr; (2) acquire more data on transfer coefficients from sediment to organism; (3) Calculate mass transfer rates, construct simple models using them, and estimate collective dose commitment; (4) Identify specific pathways or transfer routes, determine the rates of transfer, and make dose limit calculations with simple models; (5) Calculate dose rates to and estimate irradiation effects on the biota as a result of waste emplacement, by reference to background irradiation calculations. (6) Examine the effect of the biota on altering sediment/water radionuclide exchange; (7) Consider the biological data required to address different accident scenarios; (8) Continue to provide the basic biological information for all of the above, and ensure that the system analysis model is based on the most realistic and up-to-date concepts of marine biologists; and (9) Ensure by way of free exchange of information that the data used in any model are the best currently available

  7. Business working group

    International Nuclear Information System (INIS)

    The workshop of 26-27 june 2000, on nuclear power Plant LIfe Management (PLIM), also included working groups in which major issues facing PLIM activities for nuclear power plants were identified and discussed. The third group was on Business. The discussion concerned the following points: There are concerns about retaining experienced/trained personnel, and maintaining a good working relationship among them, as well as about the closure of research facilities, the reduction in staff numbers under increasing economic pressure and the lack of new nuclear power plant constructions. The marginal cost of producing electricity is lower for most existing nuclear power plants than for almost all other energy sources. Refurbishment costs are usually relatively small compared with new investments. The ongoing regulatory reform of the electricity market will bring increasing competition. Although PLIM has been carried out in many countries with favourable results, there are still uncertainties which affect business decisions regarding financial and market risks in PLIM activities. Recommendations were made. (author)

  8. Group Life Insurance

    CERN Multimedia

    2013-01-01

    The CERN Administration would like to remind you that staff members and fellows have the possibility to take out a life insurance contract on favourable terms through a Group Life Insurance.   This insurance is provided by the company Helvetia and is available to you on a voluntary basis. The premium, which varies depending on the age and gender of the person insured, is calculated on the basis of the amount of the death benefit chosen by the staff member/fellow and can be purchased in slices of 10,000 CHF.    The contract normally ends at the retirement age (65/67 years) or when the staff member/fellow leaves the Organization. The premium is deducted monthly from the payroll.   Upon retirement, the staff member can opt to maintain his membership under certain conditions.   More information about Group Life Insurance can be found at: Regulations (in French) Table of premiums The Pension Fund Benefit Service &...

  9. Communication from ST Group

    CERN Multimedia

    TS Department

    2008-01-01

    In order to prepare the organization of the Open Days, please note that FM Group will not able to take into account either specific requests for waste collection from 2nd to 6th of April, either removal or PC transport requests between the 31st and the 11th of March. We kindly ask you to plan the collection of any type of waste and the urgent transport of office furniture or PC before the 31st of March. Waste collection requests shall be formulated contacting FM Support at 77777 or at the email address mailto:Fm.Support@cern.ch; removal of office furniture or PC transport requests must be made using the EDH ‘Transport request’ form selecting the "Removals" or the "PC transport" category from the drop-down menu. For any question concerning the waste sorting, please consult the following web address: http://dechets-waste.web.cern.ch/dechets-waste/. Thank you for your understanding and collaboration. TS/FM Group

  10. On the Brauer group

    International Nuclear Information System (INIS)

    For an arithmetic model X of a Fermat surface or a hyperkahler variety with Betti number b2(V otimes k-bar)>3 over a purely imaginary number field k, we prove the finiteness of the l-components of Br'(X) for all primes l>>0. This yields a variant of a conjecture of M. Artin. If V is a smooth projective irregular surface over a number field k and V(k)≠ nothing, then the l-primary component of Br(V)/Br(k) is an infinite group for every prime l. Let A1→M1 be the universal family of elliptic curves with a Jacobian structure of level N>=3 over a number field k supset of Q(e2πi/N). Assume that M1(k) ≠ nothing. If V is a smooth projective compactification of the surface A1, then the l-primary component of Br(V)/Br(M-bar1) is a finite group for each sufficiently large prime l

  11. Social group and mobbing

    Directory of Open Access Journals (Sweden)

    Baltezarević Vesna

    2009-01-01

    Full Text Available Our reality, having been subject to the numerous social crises during the last decades of the 20th century, is characterized by frequent incidences of powerlessness and alienation. The man is more frequently a subject to loneliness and overcomes the feeling of worthlessness, no matter whether he considers himself an individual or a part of a whole larger social. Such an environment leads to development of aggression in all fields of ones life. This paper has as an objective the pointing out of the mental harassment that is manifested in the working environment. There is a prevalence of mobbing cases, as a mode of pathological communication. The result of this is that a person, subjected to this kind of abuse, is soon faced with social isolation. This research also aspires to initiate the need for social groups self-organization of which victims are part of. The reaction modality of a social group directly conditions the outcome of the deliberate social drama, one is subjected to it as a result of mobbing.

  12. On Generalized PST-groups

    Institute of Scientific and Technical Information of China (English)

    WANG JUN-XIN; Du Xian-kun

    2011-01-01

    A finite group G is called a generalized PST-group if every subgroup contained in F(G) permutes all Sylow subgroups of G,where F(G) is the Fitting subgroup of G.The class of generalized PST-groups is not subgroup and quotient group closed,and it properly contains the class of PST-groups.In this paper,the structure of generalized PST-groups is first investigated.Then,with its help,groups whose every subgroup (or every quotient group) is a generalized PST-group are determined,and it is shown that such groups are precisely PST-groups.As applications,T-groups and PT-groups are characterized.

  13. Braided C*-quantum groups

    OpenAIRE

    Roy, Sutanu

    2016-01-01

    We propose a general theory of braided quantum groups in the C*-algebraic framework. More precisely, we construct braided quantum groups using manageable braided multiplicative unitaries over a regular C*-quantum group. We show that braided C*-quantum groups are equivalent to C*-quantum groups with projection.

  14. CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY

    International Nuclear Information System (INIS)

    In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit Mr = –18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.

  15. Group and ring theoretic properties of polycyclic groups

    CERN Document Server

    Wehrfritz, BAF

    2009-01-01

    Polycyclic groups are built from cyclic groups in a specific way. They arise in many contexts within group theory itself but also more generally in algebra, for example in the theory of Noetherian rings. The first half of this book develops the standard group theoretic techniques for studying polycyclic groups and the basic properties of these groups. The second half then focuses specifically on the ring theoretic properties of polycyclic groups and their applications, often to purely group theoretic situations. The book is intended to be a study manual for graduate students and researchers co

  16. 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

    Directory of Open Access Journals (Sweden)

    Eduardo O Zappetini

    2010-03-01

    , equivalente al magmatismo precolisional de los orógenos Juruena y Sunsas, se habría acrecionado al borde sudoccidental del cratón del Río de la Plata y formaría parte actualmente del sustrato de su borde paleoproterozoico sudoccidental y del sustrato del terreno para-autóctono Pampia. Este mecanismo acrecional sería similar al observado en otros núcleos cratónicos arqueanos-paleoproterozoicos, tales como los de Amazonas, Kalahari y Congo. Finalmente, la otra fuente importante de aporte de los Esquistos Santa Helena indica la existencia de una faja de rocas magmáticas neoproterozoicas que correspondería a un arco desarrollado sobre el margen oriental de Pampia.The Santa Helena Schists comprise biotite-garnet schists and minor sillimanite-garnet gneissoid lenses, reaching the higher amphibolite to lower granulite facies metamorphism . Suboutcrops of the schists occur at Estancia Santa Helena. U-Pb SHRIMP dating of the Santa Elena Schists detrital zircon yielded mostly Mesoproterozoic and Neoproterozoic ages, with a small number of Paleoproterozoic grains. Almost all the Mesoproterozoic and Neoproterozoic grains are magmatic and crystallized from a juvenile source (positive εHf, with TDM (Hf ranging 1127 to 1625 Ma, and 948 to 1274 Ma, respectively. The Paleoproterozoic zircons are also magmatic, with a TDM (Hf of 2310 Ma. The age of the youngest detrital zircon is 556 Ma, which corresponds to the maximum age for the onset of sedimentation, indicating that deposition probably started by Neoproterozoic times. The absolute absence of metamorphic zircons of Pampean age suggests that during the time of deposition of the schists, the metamorphic nucleous of the Pampean orogen was still not formed and exposed. This implies a great contrast with the provenance pattern of the nearby Green Schists, dominated by Cambrian metamorphic zircons, deposited between ca. 500 Ma and ca. 465 Ma, when the Pampean orogen was already exhumed and subject to denudation. It is interpreted

  17. Gutzwiller renormalization group

    Science.gov (United States)

    Lanatà, Nicola; Yao, Yong-Xin; Deng, Xiaoyu; Wang, Cai-Zhuang; Ho, Kai-Ming; Kotliar, Gabriel

    2016-01-01

    We develop a variational scheme called the "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method exploits the low-entanglement property of the ground state of local Hamiltonians in combination with the framework of the Gutzwiller wave function and indicates that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a surprisingly small number of variational parameters. We perform benchmark calculations of the single-band AIM that validate our theory and suggest that the GRG might enable us to study complex systems beyond the reach of the other methods presently available and pave the way to interesting generalizations, e.g., to nonequilibrium transport in nanostructures.

  18. Group life insurance

    CERN Multimedia

    2013-01-01

    The CERN Administration wishes to inform staff members and fellows having taken out optional life insurance under the group contract signed by CERN that the following changes to the rules and regulations entered into force on 1 January 2013:   The maximum age for an active member has been extended from 65 to 67 years. The beneficiary clause now allows insured persons to designate one or more persons of their choice to be their beneficiary(-ies), either at the time of taking out the insurance or at a later date, in which case the membership/modification form must be updated accordingly. Beneficiaries must be clearly identified (name, first name, date of birth, address).   The membership/modification form is available on the FP website: http://fp.web.cern.ch/helvetia-life-insurance For further information, please contact: Valentina Clavel (Tel. 73904) Peggy Pithioud (Tel. 72736)

  19. Doing focus group research

    DEFF Research Database (Denmark)

    Lindegaard, Laura Bang

    2014-01-01

    interview data can be of some use if the distinction between natural and contrived data is given up and replaced with a distinction between interview data as topic or as resource. In greater detail, such scholars argue that interview data are perfectly adequate if the researcher wants to study the topic of......Scholars of ethnomethodologically informed discourse studies are often sceptical of the use of interview data such as focus group data. Some scholars quite simply reject interview data with reference to a general preference for so-called naturally occurring data. Other scholars acknowledge that...... interview interaction, but inadequate as data for studying phenomena that go beyond the phenomenon of interview interaction. Neither of these more and less sceptical positions are, on the face of it, surprising due to the ethnomethodological commitment to study social order as accomplished in situ, not as...

  20. Working Group Report: Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Artuso, M.; et al.,

    2013-10-18

    Sensors play a key role in detecting both charged particles and photons for all three frontiers in Particle Physics. The signals from an individual sensor that can be used include ionization deposited, phonons created, or light emitted from excitations of the material. The individual sensors are then typically arrayed for detection of individual particles or groups of particles. Mounting of new, ever higher performance experiments, often depend on advances in sensors in a range of performance characteristics. These performance metrics can include position resolution for passing particles, time resolution on particles impacting the sensor, and overall rate capabilities. In addition the feasible detector area and cost frequently provides a limit to what can be built and therefore is often another area where improvements are important. Finally, radiation tolerance is becoming a requirement in a broad array of devices. We present a status report on a broad category of sensors, including challenges for the future and work in progress to solve those challenges.

  1. Graphs, groups and surfaces

    CERN Document Server

    White, AT

    1985-01-01

    The field of topological graph theory has expanded greatly in the ten years since the first edition of this book appeared. The original nine chapters of this classic work have therefore been revised and updated. Six new chapters have been added, dealing with: voltage graphs, non-orientable imbeddings, block designs associated with graph imbeddings, hypergraph imbeddings, map automorphism groups and change ringing.Thirty-two new problems have been added to this new edition, so that there are now 181 in all; 22 of these have been designated as ``difficult'''' and 9 as ``unsolved''''. Three of the four unsolved problems from the first edition have been solved in the ten years between editions; they are now marked as ``difficult''''.

  2. Tiny vampires in ancient seas: evidence for predation via perforation in fossils from the 780-740 million-year-old Chuar Group, Grand Canyon, USA.

    Science.gov (United States)

    Porter, Susannah M

    2016-05-25

    One explanation for the Early Neoproterozoic expansion of eukaryotes is the appearance of eukaryovorous predators-i.e. protists that preyed on other protists. Evidence for eukaryovory at this time, however, is indirect, based on inferences from character state reconstructions and molecular clocks, and on the presence of possible defensive structures in some protistan fossils. Here I describe 0.1-3.4 µm circular holes in seven species of organic-walled microfossils from the 780-740 million-year-old Chuar Group, Grand Canyon, Arizona, USA, that are similar to those formed today by predatory protists that perforate the walls of their prey to consume the contents inside. Although best known in the vampyrellid amoebae, this 'vampire-like' behaviour is widespread among eukaryotes, making it difficult to infer confidently the identity of the predator. Nonetheless, the identity of the prey is clear: some-and perhaps all-of the fossils are eukaryotes. These holes thus provide the oldest direct evidence for predation on eukaryotes. Larger circular and half-moon-shaped holes in vase-shaped microfossils from the upper part of the unit may also be the work of 'tiny vampires', suggesting a diversity of eukaryovorous predators lived in the ancient Chuar sea. PMID:27194696

  3. Introduction to complex reflection groups and their braid groups

    CERN Document Server

    Broué, Michel

    2010-01-01

    Weyl groups are particular cases of complex reflection groups, i.e. finite subgroups of GLr(C) generated by (pseudo)reflections. These are groups whose polynomial ring of invariants is a polynomial algebra. It has recently been discovered that complex reflection groups play a key role in the theory of finite reductive groups, giving rise as they do to braid groups and generalized Hecke algebras which govern the representation theory of finite reductive groups. It is now also broadly agreed upon that many of the known properties of Weyl groups can be generalized to complex reflection groups. The purpose of this work is to present a fairly extensive treatment of many basic properties of complex reflection groups (characterization, Steinberg theorem, Gutkin-Opdam matrices, Solomon theorem and applications, etc.) including the basic findings of Springer theory on eigenspaces. In doing so, we also introduce basic definitions and properties of the associated braid groups, as well as a quick introduction to Bessis' ...

  4. Harmonic Analysis and Group Representation

    CERN Document Server

    Figa-Talamanca, Alessandro

    2011-01-01

    This title includes: Lectures - A. Auslander, R. Tolimeri - Nilpotent groups and abelian varieties, M Cowling - Unitary and uniformly bounded representations of some simple Lie groups, M. Duflo - Construction de representations unitaires d'un groupe de Lie, R. Howe - On a notion of rank for unitary representations of the classical groups, V.S. Varadarajan - Eigenfunction expansions of semisimple Lie groups, and R. Zimmer - Ergodic theory, group representations and rigidity; and, Seminars - A. Koranyi - Some applications of Gelfand pairs in classical analysis.

  5. Working Group Versus Team Work

    OpenAIRE

    Valentina-Vasilica Zaharia; Mirela-Mihaela Dogaru; Dan-Marin Boaja

    2014-01-01

    The cell organization is represented by the working group and not the individual, groups that are a major feature of life organization. Quality circles were designed as tools for building team spirit in Japanese companies as a tool to enhance group cohesion and the training of employees. The essential characteristic of human behavior and organizational performance is given by the working group and the influence on group members, so members of the group leader should use in order to achieve a ...

  6. Cultural skepticism and 'group representation'

    OpenAIRE

    Phillips, Anne

    2011-01-01

    Arguments for group representation have commonly faced three objections: (1) that representing people via their membership of a group promotes sectionalism, parochialism, and the pursuit of vested interests; (2) that it raises impossible questions about which groups qualify for group representation; (3) that it falsely presumes the existence of a group with sufficiently shared interests, perspectives, values, or concerns for some of those group members fairly to represent the others. I have s...

  7. Group Leader Development: Effects of Personal Growth and Psychoeducational Groups

    Science.gov (United States)

    Ohrt, Jonathan H.; Robinson, E. H., III; Hagedorn, W. Bryce

    2013-01-01

    The purpose of this quasi-experimental study was to compare the effects of personal growth groups and psychoeducational groups on counselor education students' (n = 74) empathy and group leader self-efficacy. Additionally, we compared the degree to which participants in each group valued: (a) cohesion, (b) catharsis, and (c) insight. There were no…

  8. Group Development and Situational Leadership: A Model for Managing Groups.

    Science.gov (United States)

    Carew, Donald K.; And Others

    1986-01-01

    An integration of the concepts of situational leadership with what is known about group development and functioning of work groups is discussed as a tool in helping managers, trainers, and group members understand group development and determine the appropriate leader behaviors to use in various situations to build unified, cohesive, and…

  9. On Sufism, Sufi Group Study and Group Leadership.

    Science.gov (United States)

    Einhorn, Jay

    1979-01-01

    Sufism is an ancient tradition of experiential human development. Sufi human development specialists utilize the group setting as a major study format. Comparison with group counseling might broaden perspectives on the possibilities and pitfalls of group process, and pinpoint several important issues relevant to group leadership. (Author)

  10. Post-Disaster Social Justice Group Work and Group Supervision

    Science.gov (United States)

    Bemak, Fred; Chung, Rita Chi-Ying

    2011-01-01

    This article discusses post-disaster group counseling and group supervision using a social justice orientation for working with post-disaster survivors from underserved populations. The Disaster Cross-Cultural Counseling model is a culturally responsive group counseling model that infuses social justice into post-disaster group counseling and…

  11. Automorphism Groups of Finite p-Groups: Structure and Applications

    CERN Document Server

    Helleloid, Geir T

    2007-01-01

    This thesis has three goals related to the automorphism groups of finite $p$-groups. The primary goal is to provide a complete proof of a theorem showing that, in some asymptotic sense, the automorphism group of almost every finite $p$-group is itself a $p$-group. We originally proved this theorem in a paper with Martin; the presentation of the proof here contains omitted proof details and revised exposition. We also give a survey of the extant results on automorphism groups of finite $p$-groups, focusing on the order of the automorphism groups and on known examples. Finally, we explore a connection between automorphisms of finite $p$-groups and Markov chains. Specifically, we define a family of Markov chains on an elementary abelian $p$-group and bound the convergence rate of some of those chains.

  12. Group Milieu in systemic and psychodynamic group therapy

    DEFF Research Database (Denmark)

    Lau, Marianne Engelbrecht

    subscales: Cohesion (p< 0.05), Leader support (p=0.001), Expressiveness (p< 0.001), Task Orientation (p=0.01) and Order and Organization (p< 0.001). Conclusions: Substantial differences in the group milieu were seen. The systemic group turned out to be evaluated as the most structured therapy and also to be...... randomized study of systemic versus psychodynamic group therapy, that the short-term outcome for patients who received systemic group psychotherapy was significantly better than the outcome for patients who received psychodynamic group psychotherapy. The current study assessed the group milieu in both groups....... Methods: This randomized prospective study included 106 women: 52 assigned to psychodynamic group psychotherapy and 54 assigned to systemic group psychotherapy. The Group Environment Scale (GES) was filled in the mid phase of therapy and analysed in three dimensions and 10 subscales. Results: The systemic...

  13. The analytic renormalization group

    Science.gov (United States)

    Ferrari, Frank

    2016-08-01

    Finite temperature Euclidean two-point functions in quantum mechanics or quantum field theory are characterized by a discrete set of Fourier coefficients Gk, k ∈ Z, associated with the Matsubara frequencies νk = 2 πk / β. We show that analyticity implies that the coefficients Gk must satisfy an infinite number of model-independent linear equations that we write down explicitly. In particular, we construct "Analytic Renormalization Group" linear maps Aμ which, for any choice of cut-off μ, allow to express the low energy Fourier coefficients for |νk | < μ (with the possible exception of the zero mode G0), together with the real-time correlators and spectral functions, in terms of the high energy Fourier coefficients for |νk | ≥ μ. Operating a simple numerical algorithm, we show that the exact universal linear constraints on Gk can be used to systematically improve any random approximate data set obtained, for example, from Monte-Carlo simulations. Our results are illustrated on several explicit examples.

  14. Oklo working group meeting

    International Nuclear Information System (INIS)

    Natural analogue studies have been carried out for several years in the framework of the European Community's R and D programme on radioactive waste; and within its recent fourth five-year programme on 'Management and storage of radioactive waste (1990-94)' the Community is participating in the Oklo study, natural analogue for transfer processes in a geological repository. The Oklo project is coordinated by CEA-IPSN (F) and involves laboratories from several CEA directorates (IPSN, DTA and DCC) which collaborate with other institutions from France: CREGU, Nancy; CNRS, Strasbourg and ENSMD, Fontainebleau. Moreover, institutes from non-EC member States are also taking part in the Oklo study. The second joint CEC-CEA progress meeting of the Oklo Working Group was held in April 1992 in Brussels and gave the possibility of reviewing and discussing progress made since its first meeting in February 1991 at CEA in Fontenay-aux-Roses. About 40 participants from 15 laboratories and organizations coming from France, Canada, Gabon, Japan, Sweden and the USA underline the great interest in the ongoing research activities. The meeting focused on the different tasks within the CEC-CEA Oklo project concerning (i) field survey and sampling, (ii) characterization of the source term, (iii) studies of the petrographical and geochemical system, and (iv) studies of the hydrogeological system and hydrodynamic modelling. (author) 17 papers are presented

  15. Reflexive Analysis of Groups

    Science.gov (United States)

    Lefebvre, Vladimir A.

    This chapter develops further a model I previously introduced, of an agent facing a choice between the positive and the negative poles. Here I will consider agents whose individual behavior depends on a ‘society’ compounded by all of them. Four ideas underlie the theory. The first idea is to consider relationships between the subgroups of agents, not just pairs of agents; this idea allows us to represent a decomposable graph corresponding to an agent or a group of agents as a tree of subgraphs. The second idea is to establish a correspondence between decomposable graphs and polynomials, allowing us to replace a tree of subgraphs with a tree of polynomials representing a computational process. The third idea consists of the interpretation of the tree of polynomials as an agent who has images of the self, which can have images of the self, etc. Finally, the fourth idea is putting an equation into correspondence to the agent, allowing us to find out the agent’s state. The theory is illustrated here with several examples from modern geopolitics, including scenarios of current interest.

  16. The Liabilities Management Group

    International Nuclear Information System (INIS)

    The Liabilities Management Group (LMG) was initiated by DTI. It is a cooperative forum which was set up in 1995. The current participants are DTI, UKAEA, NLM (for BNFL), MOD and Magnox Electric. The LMG was initiated to produce closer cooperation between public sector liability management organizations, achieve more cost-effective management of UK nuclear liabilities and enhance development of the UK nuclear decommissioning and waste management strategy. The objectives are to compare practices between liabilities management organizations discuss the scope for collaboration identify priority areas for possible collaboration agree action plans for exploring and undertaking such collaboration.Four task forces have been formed to look at specific areas (R and D, safety, contracts, and project management) and each reports separately to the LMG. The LMG has achieved its original aim of bringing together those with public sector liability management responsibilities. All participants feel that the LMG has been useful and that it should continue. Looking to the future, there is a continuing need for the LMG to facilitate removal of barriers to the achievement of best value for money. The LMG might also consider addressing the 'business process' elements that a liability management organization must be good at in order to define best practice in these. (author)

  17. Fermilab Steering Group Report

    Energy Technology Data Exchange (ETDEWEB)

    Beier, Eugene; /Pennsylvania U.; Butler, Joel; /Fermilab; Dawson, Sally; /Brookhaven; Edwards, Helen; /Fermilab; Himel, Thomas; /SLAC; Holmes, Stephen; /Fermilab; Kim, Young-Kee; /Fermilab /Chicago U.; Lankford, Andrew; /UC, Irvine; McGinnis, David; /Fermilab; Nagaitsev, Sergei; /Fermilab; Raubenheimer, Tor; /SLAC /Fermilab

    2007-01-01

    The Fermilab Steering Group has developed a plan to keep U.S. accelerator-based particle physics on the pathway to discovery, both at the Terascale with the LHC and the ILC and in the domain of neutrinos and precision physics with a high-intensity accelerator. The plan puts discovering Terascale physics with the LHC and the ILC as Fermilab's highest priority. While supporting ILC development, the plan creates opportunities for exciting science at the intensity frontier. If the ILC remains near the Global Design Effort's technically driven timeline, Fermilab would continue neutrino science with the NOVA experiment, using the NuMI (Neutrinos at the Main Injector) proton plan, scheduled to begin operating in 2011. If ILC construction must wait somewhat longer, Fermilab's plan proposes SNuMI, an upgrade of NuMI to create a more powerful neutrino beam. If the ILC start is postponed significantly, a central feature of the proposed Fermilab plan calls for building an intense proton facility, Project X, consisting of a linear accelerator with the currently planned characteristics of the ILC combined with Fermilab's existing Recycler Ring and the Main Injector accelerator. The major component of Project X is the linac. Cryomodules, radio-frequency distribution, cryogenics and instrumentation for the linac are the same as or similar to those used in the ILC at a scale of about one percent of a full ILC linac. Project X's intense proton beams would open a path to discovery in neutrino science and in precision physics with charged leptons and quarks. World-leading experiments would allow physicists to address key questions of the Quantum Universe: How did the universe come to be? Are there undiscovered principles of nature: new symmetries, new physical laws? Do all the particles and forces become one? What happened to the antimatter? Building Project X's ILC-like linac would offer substantial support for ILC development by accelerating the

  18. Fermilab Steering Group Report

    Energy Technology Data Exchange (ETDEWEB)

    Steering Group, Fermilab; /Fermilab

    2007-12-01

    The Fermilab Steering Group has developed a plan to keep U.S. accelerator-based particle physics on the pathway to discovery, both at the Terascale with the LHC and the ILC and in the domain of neutrinos and precision physics with a high-intensity accelerator. The plan puts discovering Terascale physics with the LHC and the ILC as Fermilab's highest priority. While supporting ILC development, the plan creates opportunities for exciting science at the intensity frontier. If the ILC remains near the Global Design Effort's technically driven timeline, Fermilab would continue neutrino science with the NOvA experiment, using the NuMI (Neutrinos at the Main Injector) proton plan, scheduled to begin operating in 2011. If ILC construction must wait somewhat longer, Fermilab's plan proposes SNuMI, an upgrade of NuMI to create a more powerful neutrino beam. If the ILC start is postponed significantly, a central feature of the proposed Fermilab plan calls for building an intense proton facility, Project X, consisting of a linear accelerator with the currently planned characteristics of the ILC combined with Fermilab's existing Recycler Ring and the Main Injector accelerator. The major component of Project X is the linac. Cryomodules, radio-frequency distribution, cryogenics and instrumentation for the linac are the same as or similar to those used in the ILC at a scale of about one percent of a full ILC linac. Project X's intense proton beams would open a path to discovery in neutrino science and in precision physics with charged leptons and quarks. World-leading experiments would allow physicists to address key questions of the Quantum Universe: How did the universe come to be? Are there undiscovered principles of nature: new symmetries, new physical laws? Do all the particles and forces become one? What happened to the antimatter? Building Project X's ILC-like linac would offer substantial support for ILC development by accelerating the

  19. Instrumentation Working Group Summary

    Science.gov (United States)

    Zaller, Michelle; Miake-Lye, Richard

    1999-01-01

    The Instrumentation Working Group compiled a summary of measurement techniques applicable to gas turbine engine aerosol precursors and particulates. An assessment was made of the limits, accuracy, applicability, and technology readiness of the various techniques. Despite advances made in emissions characterization of aircraft engines, uncertainties still exist in the mechanisms by which aerosols and particulates are produced in the near-field engine exhaust. To adequately assess current understanding of the formation of sulfuric acid aerosols in the exhaust plumes of gas turbine engines, measurements are required to determine the degree and importance of sulfur oxidation in the turbine and at the engine exit. Ideally, concentrations of all sulfur species would be acquired, with emphasis on SO2 and SO3. Numerous options exist for extractive and non-extractive measurement of SO2 at the engine exit, most of which are well developed. SO2 measurements should be performed first to place an upper bound on the percentage of SO2 oxidation. If extractive and non-extractive techniques indicate that a large amount of the fuel sulfur is not detected as SO2, then efforts are needed to improve techniques for SO3 measurements. Additional work will be required to account for the fuel sulfur in the engine exhaust. Chemical Ionization Mass Spectrometry (CI-MS) measurements need to be pursued, although a careful assessment needs to be made of the sampling line impact on the extracted sample composition. Efforts should also be placed on implementing non-intrusive techniques and extending their capabilities by maximizing exhaust coverage for line-of-sight measurements, as well as development of 2-D techniques, where feasible. Recommendations were made to continue engine exit and combustor measurements of particulates. Particulate measurements should include particle size distribution, mass fraction, hydration properties, and volatile fraction. However, methods to ensure that unaltered

  20. 2010 Chemical Working Group Status

    Science.gov (United States)

    Reid, Concha M.

    2010-01-01

    The Steering Group for the Interagency Advanced Power Group (IAPG) held their business meeting on November 30-December 1st in McLean, Virginia. Status reports were presented from each of the IAPG's Working Groups. These charts contain a brief summary of the IAPG Chemical Working Group's activities during 2010 and its plans for 2011.

  1. A Typology for Finite Groups

    Science.gov (United States)

    Tou, Erik R

    2013-01-01

    This project classifies groups of small order using a group's center as the key feature. Groups of a given order "n" are typed based on the order of each group's center. Students are led through a sequence of exercises that combine proof-writing, independent research, and an analysis of specific classes of finite groups…

  2. About Hebei Jianxin Construction Group

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ Hebei Jianxin Construction (Group) Ltd. was incorporated in August 1984. As the holding company, Hebei Jianxin Construction (Group)Ltd. along with five companies under its holding, such as Baoding New Generation Real Estate Development Co., Ltd. and Baoding New Generation Property Management Co., Ltd., formed Hebei Jianxin Architectural Group (hereafter, the Group).

  3. Anomaly-safe discrete groups

    International Nuclear Information System (INIS)

    We show that there is a class of finite groups, the so-called perfect groups, which cannot exhibit anomalies. This implies that all non-Abelian finite simple groups are anomaly-free. On the other hand, non-perfect groups generically suffer from anomalies. We present two different ways that allow one to understand these statements

  4. Group B Streptococcus and Pregnancy

    Science.gov (United States)

    f AQ FREQUENTLY ASKED QUESTIONS FAQ105 PREGNANCY Group B Strep and Pregnancy • What is group B streptococcus (GBS)? • What does it mean to be ... a planned cesarean birth? •Glossary What is group B streptococcus (GBS)? Group B streptococcus is one of ...

  5. Holographic renormalization group

    International Nuclear Information System (INIS)

    The holographic renormalization group (RG) is reviewed in a self-contained manner. The holographic RG is based on the idea that the radial coordinate of a space-time with asymptotically AdS geometry can be identified with the RG flow parameter of boundary field theory. After briefly discussing basic aspects of the AdS/CFT correspondence, we explain how the concept of the holographic GR emerges from this correspondence. We formulate the holographic RG on the basis of the Hamilton-Jacobi equations for bulk systems of gravity and scalar fields, as introduced by de Boer, Verlinde and Verlinde. We then show that the equations can be solved with a derivative expansion by carefully extracting local counterterms from the generating functional of the boundary field theory. The calculational methods used to obtain the Weyl anomaly and scaling dimensions are presented and applied to the RG flow from the N = 4 SYM to an N = 1 superconformal fixed point discovered by Leigh and Straussler. We further discuss the relation between the holographic RG and the noncritical string theory and show that the structure of the holographic RG should persist beyond the supergravity approximation as a consequence of the renormalizability of the nonlinear σ-model action of noncritical strings. As a check, we investigate the holographic RG structure of higher-derivative systems. We show that such systems can also be analyzed based on the Hamilton-Jacobi equations and that the behavior of bulk fields are determined solely by their boundary values. We also point out that higher-derivative gravity systems give rise to new multicritical points in the parameter space of boundary field theories. (author)

  6. ASYNCHRONOUS ELECTRONIC DISCUSSION GROUP:

    Directory of Open Access Journals (Sweden)

    Tina Lim Swee KIM

    2007-01-01

    Full Text Available This paper examines the practice of online discussion in a course specially tailored for in-service teachers who are pursuing their basic degree qualification at a teacher training institute. Analyses of postings to the asynchronous electronic discussion group were made according to the type of postings as proposed by Poole (2000. Four focus areas were looked into, that is, content, technical, procedural, or non-academic. Analyses were done for each quarter of the 12 weeks of interaction. At the end of the learners’ participation in the EDG and before their end-of-course examination, the participants were then given a paper-based questionnaire asking their perceptions on the use of EDG as part of their coursework on the whole. Six aspects of EDG were examined, these are;Ø technical aspects, Ø motivation to use the EDG, Ø quality of interaction, Ø tutor’s response, Ø perceived learning, and Ø attitude towards EDG. Analyses on postings for the EDG showed that the bulk of the postings were made in the last quarter of the online discussions. Further, 97.8% of the postings were on content and the types of content posting registered were predominantly questions (41.19% and those that sought clarification/elaboration (37.48%. Findings from this study suggest that overall the participants were satisfied with the six aspects of EDG examined. The aspect that recorded the highest mean was ‘motivation to read tutor’s responses’ whilst the lowest mean (and the only one with negative perception was for ‘worthiness of time spent on online discussions’.

  7. Graph-Constrained Group Testing

    OpenAIRE

    M. Cheraghchi; A. Karbasi; S. Mohajer; Saligrama, V.

    2012-01-01

    Non-adaptive group testing involves grouping arbitrary subsets of $n$ items into different pools. Each pool is then tested and defective items are identified. A fundamental question involves minimizing the number of pools required to identify at most $d$ defective items. Motivated by applications in network tomography, sensor networks and infection propagation, a variation of group testing problems on graphs is formulated. Unlike conventional group testing problems, each group here must confo...

  8. Embeddings into Thompson's group V and coCF groups

    OpenAIRE

    Bleak, Collin; Matucci, Francesco; Neunhöffer, Max

    2016-01-01

    Lehnert and Schweitzer show in [21] that R. Thompson's group V is a co-context-free (coCF ) group, thus implying that all of its finitely generated subgroups are also coCF groups. Also, Lehnert shows in his thesis that V embeds inside the coCF group QAut(T2;c), which is a group of particular bijections on the vertices of an infinite binary 2-edge-colored tree, and he conjectures that QAut(T2;c) is a universal coCF group. We show that QAut(T2;c) embeds into V , and thus obtain a new form for L...

  9. Groups possessing extensive hierarchical decompositions

    CERN Document Server

    Januszkiewicz, T; Leary, I J

    2009-01-01

    Kropholler's class of groups is the smallest class of groups which contains all finite groups and is closed under the following operator: whenever $G$ admits a finite-dimensional contractible $G$-CW-complex in which all stabilizer groups are in the class, then $G$ is itself in the class. Kropholler's class admits a hierarchical structure, i.e., a natural filtration indexed by the ordinals. For example, stage 0 of the hierarchy is the class of all finite groups, and stage 1 contains all groups of finite virtual cohomological dimension. We show that for each countable ordinal $\\alpha$, there is a countable group that is in Kropholler's class which does not appear until the $\\alpha+1$st stage of the hierarchy. Previously this was known only for $\\alpha= 0$, 1 and 2. The groups that we construct contain torsion. We also review the construction of a torsion-free group that lies in the third stage of the hierarchy.

  10. Secure Group Communications for Large Dynamic Multicast Group

    Institute of Scientific and Technical Information of China (English)

    Liu Jing; Zhou Mingtian

    2003-01-01

    As the major problem in multicast security, the group key management has been the focus of research But few results are satisfactory. In this paper, the problems of group key management and access control for large dynamic multicast group have been researched and a solution based on SubGroup Secure Controllers (SGSCs) is presented, which solves many problems in IOLUS system and WGL scheme.

  11. Infinitesimal group schemes as iterative differential Galois groups

    OpenAIRE

    Maurischat, Andreas

    2009-01-01

    This article is concerned with Galois theory for iterative differential fields (ID-fields) in positive characteristic. More precisely, we consider purely inseparable Picard-Vessiot extensions, because these are the ones having an infinitesimal group scheme as iterative differential Galois group. In this article we prove a necessary and sufficient condition to decide whether an infinitesimal group scheme occurs as Galois group scheme of a Picard-Vessiot extension over a given ID-field or not. ...

  12. Ornstein-Uhlenbeck semi-groups on stratified groups

    CERN Document Server

    Lust-Piquard, Francoise

    2009-01-01

    We consider, in the setting of stratified groups G, two analogues of the Ornstein-Uhlenbeck semi-group, namely Markovian diffusion semi-groups acting on $L^q(pd g)$, whose invariant density $p$ is a heat kernel at time 1 on G.

  13. Structuring the Group Experience: A Format for Designing Psychoeducational Groups.

    Science.gov (United States)

    Furr, Susan R.

    2000-01-01

    Presents six-step model for moving from a general statement of purpose to a psychoeducational group design that includes didactic content, experiential activities, and processing. By following this model the group facilitator will be able to develop a psychoeducational group that provides a logical sequence of learning activities fostering…

  14. An Exploration of Group and Member Development in Experiential Groups

    Science.gov (United States)

    Ohrt, Jonathan H.; Prochenko, Yulia; Stulmaker, Hayley; Huffman, David; Fernando, Delini; Swan, Karrie

    2014-01-01

    In this phenomenological study, we explored 52 group members' development in experiential groups. Specifically, participants completed 10 weekly journal reflections about their experiences as members and also reflected on the group's overall development. Four overall themes--exploration, transition, working, closure--as well as multiple…

  15. PI-groups and PI-representations of groups

    OpenAIRE

    Aladova, E.; Plotkin, B.

    2009-01-01

    It is well known that many famous Burnside-type problems have positive solutions for PI-groups and PI-algebras. In the present article we also consider various Burnside-type problems for PI-groups and PI-representations of groups.

  16. Quantization on nilpotent Lie groups

    CERN Document Server

    Fischer, Veronique

    2016-01-01

    This book presents a consistent development of the Kohn-Nirenberg type global quantization theory in the setting of graded nilpotent Lie groups in terms of their representations. It contains a detailed exposition of related background topics on homogeneous Lie groups, nilpotent Lie groups, and the analysis of Rockland operators on graded Lie groups together with their associated Sobolev spaces. For the specific example of the Heisenberg group the theory is illustrated in detail. In addition, the book features a brief account of the corresponding quantization theory in the setting of compact Lie groups. The monograph is the winner of the 2014 Ferran Sunyer i Balaguer Prize.

  17. Saving Face and Group Identity

    DEFF Research Database (Denmark)

    Eriksson, Tor; Mao, Lei; Villeval, Marie-Claire

    2015-01-01

    Are people willing to sacrifice resources to save one's and others' face? In a laboratory experiment, we study whether individuals forego resources to avoid the public exposure of the least performer in their group. We show that a majority of individuals are willing to pay to preserve not only...... their self- but also other group members' image. This behavior is frequent even in the absence of group identity. When group identity is more salient, individuals help regardless of whether the least performer is an in-group or an out-group. This suggests that saving others' face is a strong social norm....

  18. Group analysis of differential equations

    CERN Document Server

    Ovsiannikov, L V

    1982-01-01

    Group Analysis of Differential Equations provides a systematic exposition of the theory of Lie groups and Lie algebras and its application to creating algorithms for solving the problems of the group analysis of differential equations.This text is organized into eight chapters. Chapters I to III describe the one-parameter group with its tangential field of vectors. The nonstandard treatment of the Banach Lie groups is reviewed in Chapter IV, including a discussion of the complete theory of Lie group transformations. Chapters V and VI cover the construction of partial solution classes for the g

  19. Topologies induced by group actions

    OpenAIRE

    Dobrowolski, Jan

    2014-01-01

    We introduce some canonical topologies induced by actions of topological groups on groups and rings. For $H$ being a group [or a ring] and $G$ a topological group acting on $H$ as automorphisms, we describe the finest group [ring] topology on $H$ under which the action of $G$ on $H$ is continuous. We also study the introduced topologies in the context of Polish structures. In particular, we prove that there may be no Hausdorff topology on a group $H$ under which a given action of a Polish gro...

  20. Paleoproterozoic source contributions to the São Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

    Directory of Open Access Journals (Sweden)

    Larry Michael Heaman

    2012-12-01

    Full Text Available The So Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 8.5 Ma and 2247 13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of So Roque Group. Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 29 Ma found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield TDM ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower ENd(t values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation.

  1. Paleoproterozoic source contributions to the Sao Roque Group sedimentation: LA-MC-ICPMS U-Pb dating and Sm-Nd systematics of clasts from metaconglomerates of the Boturuna Formation

    Energy Technology Data Exchange (ETDEWEB)

    Henrique-Pinto, Renato; Janasi, Valdecir de Assis; Tassinari, Colombo Celso Gaeta [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Simonetti, Antonio [University of Notre Dame, South Bend (United States). Dept. of Civil Engineering and Geological Sciences; Heaman, Larry Michael, E-mail: renatohp@usp.br, E-mail: vajanasi@usp.br, E-mail: ccgtassi@usp.br, E-mail: antonio.simonetti.3@nd.edu, E-mail: larry.heaman@ualberta.ca [University of Alberta, Edmonton (Canada). Dept. of Earth and Atmospheric Sciences

    2012-12-15

    The Sao Roque Group is characterized by volcano-sedimentary sequences, in which deposition probably started in the late Paleoproterozoic. U-Pb dating by LA-MC-ICPMS of zircons extracted from predominantly equigranular monzogranites clasts from Morro Doce and Morro do Polvilho regions, yield paleoproterozoic ages of 2199 {+-}8.5 Ma and 2247 {+-}13 Ma, respectively. These represent the ages for the main source of granite for the metaconglomerates from the Boturuna Formation (basal unit of Sao Roque Group). Its polycyclic history is reinforced by the presence of inherited Archean zircons (2694 {+-}29 Ma) found within the clasts. Moreover, these clasts have also been affected by the Neoproterozoic overprinting event as indicated by their lower intercept Concordia ages. Sm-Nd isotope data for the main clast varieties from the Morro Doce metaconglomerates yield T{sub DM} ages of 2.6 to 2.7 Ga, demonstrating that these granites are the recycling products of an Archean crustal component. The metaconglomerate arkosean framework yields slightly lower {epsilon}{sub Nd(t)} values than those for the clasts, indicating that a younger and/or more primitive source also contributed to the Boturuna Formation. (author)

  2. Group Lasso with Overlaps: the Latent Group Lasso approach

    CERN Document Server

    Obozinski, Guillaume; Vert, Jean-Philippe

    2011-01-01

    We study a norm for structured sparsity which leads to sparse linear predictors whose supports are unions of prede ned overlapping groups of variables. We call the obtained formulation latent group Lasso, since it is based on applying the usual group Lasso penalty on a set of latent variables. A detailed analysis of the norm and its properties is presented and we characterize conditions under which the set of groups associated with latent variables are correctly identi ed. We motivate and discuss the delicate choice of weights associated to each group, and illustrate this approach on simulated data and on the problem of breast cancer prognosis from gene expression data.

  3. Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales: Implications for the subduction-accretion process of a latest Proterozoic trench-forearc

    Science.gov (United States)

    Asanuma, Hisashi; Okada, Yoshihiro; Fujisaki, Wataru; Suzuki, Kazue; Sato, Tomohiko; Sawaki, Yusuke; Sakata, Shuhei; Yamamoto, Shinji; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

    2015-11-01

    The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench mélange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The mélange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U-Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608-601 Ma, and 2 at 564-539 Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey-Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650-600 Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.

  4. Provenance analysis of the Guaritas Group (RS conglomeratic sandstones: implications for the paleoclimate and paleogeography of the Eocambrian Central Camaquã sub-basin

    Directory of Open Access Journals (Sweden)

    Antonio Romalino Santos Fragoso-Cesar

    2013-06-01

    Full Text Available The Camaquã Supergroup, located in the central-south region of Rio Grande do Sul, Brazil, constitutes a rift-type post-orogenicsedimentary basin, whose deposition occurred in a continental environment between the Ediacaran and the Eocambrian.The upper succession of the Camaquã Supergroup is represented by the Guaritas Group, a unit formed by fluvial, eolian andalluvial fan deposits that keeps important records of the sedimentation right after the end of the neoproterozoic orogenesis thatgave rise to the Gondwana supercontinent. The objective of the present work was to apply sedimentary provenance analysis inconglomeratic arenites and conglomerates of the Guaritas Group, in order to explore the climatic and tectonic evolution historyof this unit. Based on the pebble compositional data, two main source areas were recognized for the deposits of this unit,a more distal one located to the north, related with a trunk river system parallel to the basin main axis, and a more proximalone located to the east, related to transversal fluvial systems and alluvial fans at the border of the basin. The comparison of theprovenance data with previous studies on facies and paleocurrents suggests that, during the entire evolution of the east borderof the basin, there was a same transversal fluvial system, whose catchment area suffered significative reductions due to thereactivation of the east border fault during the deposition of the Varzinha and Pedra Pintada Formations. The Serra do ApertadoFormation, the upper unit of Guaritas Group, shows a high correlation between the variation of quartzose and non quartzosepebbles composition, and it was attributed to a variation between more humid and more arid climatic conditions.

  5. Two-transitive Lie groups

    OpenAIRE

    Kramer, Linus

    2001-01-01

    Using a characterization of parabolics in reductive Lie groups due to Furstenberg, elementary properties of buildings, and some algebraic topology, we give a new proof of Tits' classification of 2-transitive Lie groups.

  6. Opechowski's theorem and commutator groups

    International Nuclear Information System (INIS)

    It is shown that the conditions of application of Opechowski's theorem for double groups of subgroups of O(3) are directly associated to the structure of their commutator groups. Some characteristics of the structure of classes are also discussed. (Author)

  7. Cognitive Development and Group Stages.

    Science.gov (United States)

    Saidla, Debie D.

    1990-01-01

    Attempts to integrate Perry's (1970) scheme of the cognitive development of college students with a model of group development adapted by Waldo (1985) based on Tuckman's (1965) formulation of developmental group stages. (Author)

  8. Group process among novice students.

    Science.gov (United States)

    Blumkin, M K

    1996-03-01

    This paper explores the experiences of a group of registered nurses returning to graduate school. The organizing framework used is an integration of Tuckman and Jensen's group process theory and Benner's novice to expert model. PMID:8716180

  9. Alternating Quotients of Fuchsian Groups

    OpenAIRE

    Everitt, Brent

    1999-01-01

    It is shown that any finitely generated non-elementary Fuchsian group has among its homomorphic images all but finitely many of the alternating groups. This settles in the affirmative a conjecture of Graham Higman.

  10. On -supersolvability of finite groups

    Indian Academy of Sciences (India)

    Izabela Agata Malinowska

    2015-05-01

    A number of authors have studied the structure of a group under the assumption that some subgroups of are well located in . We will obtain some new criteria of -supersolvability and -nilpotency of groups.

  11. Criminal groups and criminal subculture

    OpenAIRE

    Romanova N.M.

    2013-01-01

    The paper provides a classification of criminal groups, structured by the following parameters: a) operation mode (secret/open), b) law-enforcement and administrative support (presence/absence). We describe four types of criminal groups: a) legitimized criminal organization, b) secret criminal organization engaged in illegal business, c) secret general crime group, and d) general crime group operating openly. The four types differ in the content of criminal subculture. Modern criminal subcult...

  12. Costs of Control in Groups

    OpenAIRE

    Riener, Gerhard; Wiederhold, Simon

    2011-01-01

    This paper explores the role of social groups in explaining the reaction to control.We propose a simple model with a principal using control devices and a controlledagent, which incorporates the existence of social groups. Testing experimentally theconjectures derived from the model and related literature, we find that agents in socialgroups (i) perform more than other (no-group) agents; (ii) expect less control thanno-group agents; (iii) decrease their performance substantially when actual c...

  13. Homogeneity in the free group

    CERN Document Server

    Perin, Chloé

    2010-01-01

    We show that any non abelian free group $\\F$ is strongly $\\aleph_0$-homogeneous, i.e. that finite tuples of elements which satisfy the same first-order properties are in the same orbit under $\\Aut(\\F)$. We give a characterization of elements in finitely generated groups which have the same first-order properties as a primitive element of the free group. We deduce as a consequence that most hyperbolic surface groups are not $\\aleph_0$-homogeneous.

  14. Modelling group dynamic animal movement

    OpenAIRE

    Langrock, Roland; Hopcraft, Grant; Blackwell, Paul; Goodall, Victoria; King, Ruth; Niu, Mu; Patterson, Toby; Pedersen, Martin; Skarin, Anna; Schick, Robert Schilling

    2013-01-01

    1). Group dynamics are a fundamental aspect of many species' movements. The need to adequately model individuals' interactions with other group members has been recognized, particularly in order to differentiate the role of social forces in individual movement from environmental factors. However, to date, practical statistical methods, which can include group dynamics in animal movement models, have been lacking. 2). We consider a flexible modelling framework that distinguishes a group-level ...

  15. R-groups and parameters

    OpenAIRE

    Ban, Dubravka; Goldberg, David

    2011-01-01

    For classical groups we show the isomorphism of the Knapp-Stein $R$-group, which describes the structure of parabolically induced representations, and the Arthur $R$-group of the parameter associated to the inducing representation by the local Langlands conjecture. We do this in the case of inducing from discrete series representations. In the case of unitary groups we show this isomorphism under a mild assumption on the parameter, which we show holds in at least half the cases.

  16. Group Norms and Consumer Behaviour

    OpenAIRE

    Pillai, Rajasekharan; Rajan, Jainey S.; Variyamveettil, Sunitha; Mathew, Dhanu E.; Nath, Subodh S.

    2011-01-01

    The impact of group norms on forming consumer behaviour is an important attribute of man’s social life. The market segmentation principles acknowledge the presence of this phenomenon. People belong to different age group, professional status, income levels, educational status etc. are seemed to display some specific consumer behaviour that can be attributed to a particular group. The present study attempts to find the influence of certain selected group norms on consumption pattern.

  17. Group Theory: It's a SNAP.

    Science.gov (United States)

    Huetinck, Linda

    1996-01-01

    Introduces concepts of modern algebraic group theory in the form of a game. Peg boards and rubber bands represent nonnumerical group elements and are manipulated under the operation of reorienting a regular polygon. Symmetry groups are used to explore set properties, as well as commutative and noncommutative operations. (CMS)

  18. Internal communication in corporate groups

    OpenAIRE

    Grzesik, Katarzyna

    2015-01-01

    This chapter is dedicated to internal communication in corporate groups. It discusses internal communication systems operating in the explored corporate groups and their significance for effective human resources management in those organisations. The chapter presents both the theoretical analysis based on the results of literature studies, and empirical research carried out in the explored groups. Narodowe Centrum Nauki Katarzyna Grzesik

  19. The Variety of Group Learning

    Institute of Scientific and Technical Information of China (English)

    HaoYanyan; YuZhihao

    2004-01-01

    With the rapid enrollment expansion in the recent years,the author feels it urgent to reform the traditional group work,and therefore to form a new and more effective pattern of group learning. The new of group word is based on the principles of cooperation and that of the task with the more flexible marking system.

  20. Defense Mechanisms in Group Counseling.

    Science.gov (United States)

    Clark, Arthur J.

    1992-01-01

    Presents considerations and strategies for conceptualizing, recognizing, and modifying defense mechanisms through the group counseling process. Provides awareness of defense mechanisms in planning for and implementation of group counseling, describes interaction patterns for identifying defenses among group participants, and clarifies modification…