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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Major element compositions of submarine basalts, quenched glasses, and contained phenocrysts are reported for samples from 25 dredge stations along the Mohns-Knipovich Ridge between the Jan Mayen fracture zone and 77°30′N. Most of the basalts collected on the Jan Mayen platform have a subaerial appearance, are nepheline normative, rich in incompatible elements, and have REE-patterns strongly enriched in light-REE. The other basalts (with one exception) are tholeiitic pillow basalts, many of which have fresh quenched glass rims. From the Jan Mayen platform northeastwards the phenocryst assemblage changes from olivine±plagioclase±clinopyroxene±magnetite to olivine +plagioclase±chrome-spinel. This change is accompanied by a progressive decrease in the content of incompatible elements, light-REE enrichments and elevation of the ridge that are similar to those observed south of the Azores and Iceland hotspots. Pillow basalts and glasses collected along the esternmost part of the Mohns Ridge (450 to 675 km east of Jan Mayen) have low K2O, TiO2, and P2O5 contents, light-REE depleted patterns relative to chondrites, and Mg/(Mg+Fe2+) ratios between 0.64 and 0.60. Pillow basalts and glasses from the Knipovich Ridge have similar (Mg/Mg+Fe2+) ratios, but along the entire ridge have slightly higher concentrations of incompatible elements and chondritic to slightly light-REE enriched patterns. The incompatible element enrichment increases slightly northward. Plagioclase phenocrysts show normal and reverse zoning on all parts of the ridge whereas olivines are unzoned or show only weak normal zoning. Olivine-liquid equilibrium temperatures are calculated to be in the range of 1,060–1,206° C with a mean around 1,180° C. Rocks and glasses collected on the Jan Mayen Platform are compositionally similar to Jan Mayen volcanic products, suggesting that off-ridge alkali volcanism on the Jan Mayen Platform is more widespread than so far suspected. There is also evidence to suggest that the alkali basalts from the Jan Mayen Platform are derived from deeper levels and by smaller degrees of partial melting of a mantle significantly more enriched in light-REE and other incompatible elements than are the tholeiitic basalts from the Eastern Mohns and Knipovich Ridge. The possibility of the presence of another hitherto unsuspected enriched mantle region north of 77° 30′ N is also briefly considered. It remains uncertain whether geochemical gradients revealed in this study reflect: (1) the dynamics of mixing during mantle advection and magma emplacement into the crust along the Mid-Atlantic Ridge (MAR) spreading axis, (e.g. such as in the mantle plume — large-ion-lithophile element depleted asthenosphere mixing model previously proposed); or (2) a horizontal gradation of the mantle beneath the MAR axis similar to that observed in the overlying crust; or (3) a vertical gradation of the mantle in incompatible elements with their contents increasing with depth and derivations of melts from progressively greater depth towards the Jan Mayen Platform.
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  • 2
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Forty lavas from the Azores Islands have been analyzed for 87Sr/86Sr ratios, major elements, first transition series metals, and LIL elements. The samples belong to the alkali basalt magma series but range from transitional hy-normative basalts from Terceira to basanitoids from Santa Maria. Differentiated lavas include both typical trachytes and comenditic trachytes and comendites. Major and trace element concentrations define smooth trends on variation diagrams, and these trends can be related to phases crystallizing in the rocks. Systematic interisland differences are also apparent in these variation diagrams. LIL element concentrations in island basalts are roughly twice as high as those in tholeiites from the adjacent Mid-Atlantic Ridge which transects the Azores Plateau. 87Sr/86Sr ratios in lavas from 6 of the 9 islands range from 0.70332 to 0.70354, a range similar to that found in tholeiites from the Mid-Atlantic Ridge transect of the Azores Plateau. This suggests that lavas from these islands and this portion of the Mid-Atlantic Ridge may be derived from a similar source. However, lavas from the islands of Faial and Pico have 87Sr/86Sr ratios up to 0.70394 and ratios in Sao Miguel lavas range up to 0.70525, suggesting basalts from these islands are derived from a chemically distinct source. Differences in the average LIL element concentrations of the least fractionated ridge tholeiites from the Azores Plateau and alkali basalts from the islands result from differences in extent of partial melting and residual mineralogy. The alkali basalts are derived by roughly half as much melting as are the tholeiites. Trace element concentrations in Azores peralkaline lavas preclude their derivation by partial melting of peridotitic mantle or basaltic crust; rather the data suggest they are produced by fractional crystallization of a basaltic parent.
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  • 3
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Rare earth abundances were determined by neutron activation in twenty Hawaiian lavas and one diabase of known chemical and mineralogical compositions. These results demonstrate a systematic relationship between the absolute or relative rare earth abundances and the petrochemistry of these rocks. Three distinct lava groups are recognized. These correspond to: (1) tholeiites, (2) alkali series, (3) nepheline-melilite basalts. Based on rare earths: a) The hawaiites and mugearite of the alkali series represent residual melts derived from alkali olivine basalts, most likely by fractional crystallization; the trachyte, however, seems to have a more complicated history. b) Fractional crystallization models linking nephelinites or alkali olivine basalts to tholeiites are possible. However, production of these three lava groups, independently, by various degrees of partial melting of the mantle is equally likely and cannot be distinguished from these fractional crystallization models. c) Daly limestone syntexis hypothesis to produce the nephelinites is unlikely.
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  • 4
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Dredge hauls of fresh submarine basalt collected from the axis of the Reykjanes Ridge (Mid-Atlantic Ridge) south of Iceland were taken aboard R/ V TRIDENT in 1967 and 1971. The samples show systematic changes as the water depth of collection (and eruption) decreases: radially elongate vesicles and concentric zones of vesicles appear at about 700 m depth and are conspicuous to shallow water; the smoothed volume percent of vesicles increases from 5% at 1000 m, 10% at 700 m, to 16% at 500 m, and the scatter in degree of vesicularity increases in shallower water; specific gravity decreases from 2.7±0.1 at 1000 m to 2.3±0.3 at 100 m. Bulk sulfur content for the outer 2 cm averages 843 ppm up to a depth of 200 m, then drops off rapidly in shallower water owing to degassing. Sulfur content below 200 m is independent of depth (or geographic position), and the melt is apparently saturated with sulfur, but the excess cannot escape the lava unless another vehicle carries it out. Only shallower than 200 m, where intense vesiculation of other gases occurs can excess sulfur be lost from the lava erupting on the sea floor. H2O+110° averages about 0.35 percent and H2O+150° about 0.25 percent, and both apparently decrease in water shallower than 200 m as a result of degassing. H2O+ (below 200 m) decreases with distance from Iceland or increasing depth, presumably as a result of either adsorption of water on the surface of shallower, more vesicular rocks; or more likely due to the presence of the Iceland hot mantle plume supplying undifferentiated primordial material, relative to lavas of the Reykjanes Ridge supplied from the low velocity layer already depleted in volatiles and large lithophile elements. The H2O+110°/S ratio of lava erupting below 200 m water depth ranges from 3 to 5 which is comparable to reliable gas analyses from oceanic basaltic volcanoes.
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  • 5
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    Unknown
    PANGAEA
    In:  Supplement to: Thompson, Geoffrey; Humphris, Susan E; Schilling, Jean-Guy (1983): Petrology and geochemistry of basaltic rocks from Rio Grande Rise, South Atlantic: Deep Sea Drilling Project Leg 72, Hole 516F. In: Barker, PF; Carlson, RL; Johnson, DA; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 72, 457-466, https://doi.org/10.2973/dsdp.proc.72.115.1983
    Publication Date: 2019-04-16
    Description: Basalts from Hole 516F, DSDP Leg 72 on the Rio Grande Rise are tholeiitic in character but differ from normal mid-ocean ridge basalts in the South Atlantic in higher concentrations of incompatible elements such as Ti, K, V, Sr, Ba, Zr, Nb, and light rare-earth elements and in lower concentrations of Mg, Cr, and Ni. They contrast with previously reported basalts from the Rio Grande Rise, which were highly alkalic in character. The Rio Grande Rise basalts from Hole 516F (age 84.5 Ma) are generally similar to basalts from the eastern end of the Walvis Ridge (80-100 Ma). It is suggested that they either originated, like the Walvis Ridge, from a mantle hot spot that is different from the present-day hot spot (Tristan da Cunha) and that has changed composition with time, or from a spreading center that was shallow and chemically influenced by the adjacent hot spot, similar to the present-day Mid-Atlantic Ridge near the Azores and Tristan da Cunha.
    Type: Dataset
    Format: text/tab-separated-values, 511 data points
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  • 6
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Schilling, Jean-Guy (1970): CICAR Marine geological sample inventory for R/V Trident Cruise 079 (TR-079). University of Rhode Island, unpublished, 3 pp, http://www.ngdc.noaa.gov/mgg/geology/data/1701/17015004/17015004.pdf
    Publication Date: 2018-09-27
    Description: The dredges described in this report were taken during the TR-079 Expedition in March 1970 by the University of Rhode Island from the R/V Trident. A total of 12 grabs were recovered and are available at the University of Rhode Island for sampling and study.
    Type: Dataset
    Format: text/tab-separated-values, 21 data points
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  • 7
    Publication Date: 2019-01-28
    Type: Dataset
    Format: text/tab-separated-values, 15 data points
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  • 8
    Publication Date: 2019-01-28
    Type: Dataset
    Format: text/tab-separated-values, 65 data points
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  • 9
    Publication Date: 2019-01-28
    Type: Dataset
    Format: text/tab-separated-values, 37 data points
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  • 10
    Publication Date: 2019-01-28
    Type: Dataset
    Format: text/tab-separated-values, 186 data points
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