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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The volcanic rocks of the South Atlantic Ocean islands of Fernando de Noronha and Trindade comprise a diverse magmatic series ranging from nephelinites and basanites to phonolites and, on Fernando de Noronha, trachytes. All rock types are highly silica undersaturated with the exception of Fernando de Noronha trachytes_, and have high abundances of incompatible trace elements and strongly LREE (light rare earth element)-enriched REE patterns. Crystal fractionation of parental basanitic magmas produced evolved phonolites and trachytes which display severe trace-element fractionation, even among trace elements (Nb, Ta, Zr, Hf) which normally behave highly incompatibly during crystallisation of alkaline magmas. Moderately to highly evolved compositions develop strongly MREE (middle REE)-depleted REE patterns, and become increasingly depleted in elements such as Nb and, in particular, Ta. Ratios of Nb/Ta and Zr/Hf are highly fractionated in phonolites (60–65, 64–77 respectively in Fernando de Noronha phonolites) compared to ratios in basanites (14, 45 respectively). The compatibility of Nb, Ta, and the REE, and the strong fractionation of Nb/Ta and Zr/Hf ratios and the MREE, during crystallisation from basanite to phonolite are attributable to the crystallisation of small amounts (〈5%) of sphene. Trace-element behaviour is relatively insensitive to the major phenocryst phases, and is controlled by minor phases in highly undersaturated alkaline suites. Incompatible trace-element ratios (e.g. La/Nb, Th/Ta) in nephelinites and basanites from Fernando de Noronha and Trindade are generally comparable with those in basaltic and hawaiitic OIB (ocean island basalt) lavas from other South Atlantic islands, but are distinct from those of Gough and Tristan da Cunha OIB. The mantle source for the highly undersaturated volcanism on Fernando de Noronha and Trindade is similar in trace-element characteristics to the “typical” OIB source which produces alkaline lavas with significant relative enrichment in Nb and Ta compared to other trace elements (as expressed by low La/Nb, Ba/Nb and Th/Ta ratios). The highly undersaturated nature of the magmas and the slight fractionation of some incompatible-element ratios (elevated Ba/Nb, Ba/Rb, Ba/Th etc.) is consistent with a smaller degree of melting of a “typical” OIB source, but with residual phlogopite in the source to account for significant K depletion and LIL-element fractionation.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Archaean granulites from the type charnockite locality of Pallavaram, Madras City, Tamil Nadu, southern India consist of a bimodal suite of basic and silicic orthogneisses, associated with metasedimentary gneisses (khondalites). Charnockite is the dominant rock type. Basic granulites display a tholeiitic trend of strong iron enrichment accompanied by an increase in the concentration of the rare earth elements (REE), and the development of appreciable negative europium anomalies. These trends are considered to reflect low pressure fractional crystallisation of pyroxene-plagioclase assemblages under conditions of lowf O 2. Ultramafic granulites may represent the cumulus material of such a process. The silicic granulites (charnockites) are generally K2O rich and in marked contrast to the low K2O (tonalitic) silicic gneisses which dominate most granulite facies terrains. Their REE abundances, however, embrace the complete range of patterns observed in both K-rich and K-poor Archaean gneisses. The presence of a large number of pre-granulite facies potassic pegmatites in the area suggests metasomatism of an originally less potassic suite of rocks. Trace element considerations lead to a model whereby metasomatism and partial fusion of silicic gneisses in the terrain preceded the granulite facies metamorphic event. This sequence of events is best related to fluctuations in the composition of metamorphic fluids in the lower crust.
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  • 3
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    Unknown
    PANGAEA
    In:  Supplement to: Weaver, Barry L; Marsh, Nicholas G; Tarney, J (1983): Trace element geochemistry of basaltic rocks recovered at Site 516, Rio Grande Rise, Deep Sea Drilling Project Leg 72. In: Barker, PF; Carlson, RL; Johnson, DA; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 72, 451-456, https://doi.org/10.2973/dsdp.proc.72.114.1983
    Publication Date: 2019-04-16
    Description: The geochemistry of basalts recovered during Leg 72 is described with emphasis on trace elements. Only Hole 516F penetrated basement; the basalts recovered are plagioclase-phyric and olivine-phyric and pervasively altered. Chemically, the basalts from Hole 516F are rather uniform in composition. However, four distinct geochemical units can be recognized, although the chemistry of two of the units appears to be controlled by chemical mobility associated with alteration. The two less-altered units cannot be related by fractional crystallization processes. Hole 516F basalts have a trace element chemistry characteristic of T-type mid-ocean ridge basalt; rare-earth element patterns (as indicated by Ce/Y ratios) are mildly fractionated flight rare-earth element enriched), and a number of incompatible element ratios are close to chondritic.
    Type: Dataset
    Format: text/tab-separated-values, 612 data points
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  • 4
    Publication Date: 2004
    Keywords: CC 1/1 ; Coordinating Committee ; Himalayas
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Samarium–neodymium isotope data for tectonically interleaved fragments of lithospheric mantle and meta-komatiite from the North Atlantic craton provide the first direct record of mantle differentiation before 3r800 Myr ago. The results confirm the magnitude of light-rare-earth-element ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 310 (1984), S. 575-577 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Previous estimates of the major element composition of the continental crust derived by various means4"8 are given in Table 1. These estimates suggest that the continental crust has an intermediate chemical composition. More recent attempts at estimating the composition of the crust have centred ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 289 (1981), S. 47-49 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The intrusion of the Scourie dolerite dykes has been dated at 2,390 Myr (ref. 12). In the Assynt region, the dyke suite may have been intruded over a time span as great as 200 Myr (ref. 13), intrusion of the early dolerites being followed by intrusion of ultramafic dykes and later, rather minor, ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 286 (1980), S. 342-346 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Calculations suggest that if the widespread upper mantle depletion in lithophile elements, as represented by the negative correlation between Nd and Sr isotopes in basalts, has resulted from continental crustal extraction, then extraction of observed Archaean crustal compositions best explains the ...
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  • 9
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 109 data points
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  • 10
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 190 data points
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