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  • 1
    Electronic Resource
    Electronic Resource
    The transition from calc-alkaline to potassic orogenic magmatism in the Aeolian Islands, Southern Italy (1988)
    Springer
    Bulletin of volcanology 50 (1988), S. 386-398 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Aeolian volcanic arc displays a wide range of magmatic products. Mafic lavas range from hypersthene normative calc-alkaline basalts to silica-undersaturated potassic absarokites, although the former are spatially and temporally dominant, consistent with the subduction-zone tectonic setting. In addition, intermediate and acidic members of the various fractionation series may be recognised. Large variations in trace element and isotope ratios accompany the rapid calc-alkaline to potassic transition, and it is argued that these may be largely explained in terms of subduction-zone mantle enrichment involving components derived from both basaltic ocean crust and subducted sediments. In addition, it seems that the mantle wedge itself was substantially heterogeneous prior to the onset of subduction zone processes. Not only are these subduction components similar to those proposed in a number of island arcs, but they also resemble those recognised in the ultra-potassic lavas of the Roman province, supporting recent subduction-related petrogenetic models of the Roman magmatism. Although subducted sediment plays an important role in the generation of some potassic magmatism, it is not uniquely responsible for K2O-rich lavas, which are also produced without a large sediment contribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01050638
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence from Re–Os isotopes for plume–lithosphere mixing in Karoo flood basalt genesis (1992)
    [s.l.] : Nature Publishing Group
    Nature 359 (1992), S. 718-721 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Picrite basalts from the Karoo flood basalt province have been the subject of extensive geochemical study8"10, in part because they are considered to represent primitive magmas similar to parental liquids that evolve to form the abundant, tholeiitic basalts typical of this and other flood basalt ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/359718a0
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  • 3
    Electronic Resource
    Electronic Resource
    Elemental and isotopic variations in subduction related basalts: evidence for a three component model (1988)
    Springer
    Contributions to mineralogy and petrology 98 (1988), S. 72-80 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Subduction related basalts display wide ranges in large ion lithophile element ratios (e.g., Rb/Ba and Rb/ Sr) which are unlikely to result from mixing, but suggest a role for small degree partial melting of a relatively Rb-poor mantle wedge source. However, these variations do not correlate with other trace element criteria, such as the depletions of high field strength elements (HFSE) and light rare earth elements (LREE) relative to the LILE, which characterise subduction related magmatism. Integration of radiogenic isotope and trace element data demonstrates that the elemental enrichment cannot be simply related to two component mixtures inferred from isotopic variations. Thus a minimum of three components is required to describe the geochemistry of subduction zone basalts. Two are subduction related: high Sr/Nd material is derived from the dehydration of subducted basaltic ocean crust, and a low Sr/Nd component is thought to be from subducted terrigenous sediment. The third component is in the mantle wedge, it is usually similar to the source of MORB, particularly in its isotopic composition. However, in some cases, notably continental areas, more enriched mantle wedge material with relatively high 87Sr/86Sr, low 143Nd/144Nd and elevated incompatible trace element contents may be involved Mixing of these three components is capable of producing both the entire range of Sr, Nd and Pb isotope signatures observed in destructive margin basalts, and their distinctive trace element compositions. The isotope differences between Atlantic and Pacific island arc basalts are attributed to the isotope compositions of sediments in the two oceans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371911
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  • 4
    Electronic Resource
    Electronic Resource
    Nitroarylidene pyridine carboxylic acid hydrazides as new narrow range acid-base indicators (1978)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 293 (1978), S. 224-224 
    Details
    ISSN: 1618-2650
    Keywords: Verw. von Nitroaryliden-pyridincarbonsäurehydraziden als Indicatoren ; Säure/Base
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491054
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  • 5
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    The role of HIMU metasomatic components in the North African lithospheric mantle: petrological evidence from the Gharyan lherzolite xenoliths, NW Libya (2008)
    In:  Geological Society Special Publication 293: 253-277.
    Details
    Publication Date: 2008-01-25
    Description: The NeogeneQuaternary alkali-basalthawaiite lavas of the Gharyan volcanic field (NW Libya) contain mantle xenoliths. These mostly consist of protogranular spinel lherzolites with superimposed metasomatic textures represented by reaction patches where primary orthopyroxene (opx), clinopyroxene (cpx) and spinel (sp) are the main reacting phases. The secondary parageneses include clinopyroxene (cpx2), olivine (ol2) and feldspar (feld) as reaction rims around opx, spongy-textured clinopyroxene with recrystallized portions (cpx2{+/-}feldspar), and brown spinel destabilized in a higher Cr/(Cr+Al) black vermicular aggregate (sp2) generally associated with feldspar microlites. Cpx2 are typically depleted in Na2O and Al2O3 relative to cpx; feldspar includes both alkali-feldspar (Or 1751) and plagioclase (An 2364). Bulk rocks have flat heavy rare earth element (HREE) patterns (1.22.3 times chondrite) and are variably enriched in light REE (LREE; LaN/YbN up to 6.6). The constituent clinopyroxenes are characterized by flat HREE distributions (814.5 times chondrite) and variable LREE enrichment with LaN/YbN up to seven, which generally conform to the bulk-rock chemistry. Samples relatively unaffected by metasomatism have clinopyroxene SrNd isotopic composition (87Sr/86Sr down to 0.7023, 143Nd/144Nd up to 0.5139) that approaches the depleted mantle (DM), suggesting that the lithospheric mantle beneath the area underwent a long-term depletion probably by pre-Palaeozoic extraction of basic melts. The remaining samples approach 87Sr/86Sr c. 0.7030, 143Nd/144Nd c. 0.5130, with 206Pb/204Pb up to 19.66. These data imply that the causative agents of metasomatism were Na-alkali silicate melts with a clear HIMU affinity, in accordance with the isotopic signature of the host lavas (87Sr/86Sr=0.7032, 143Nd/144Nd=0.5130, 206Pb/204Pb=19.60). This prevalent HIMU geochemical signature is comparable with that recorded in Cenozoic alkaline basic lavas and associated mantle xenoliths from other occurrences of the northerncentral African lithosphere, suggesting a common regional sub-lithospheric component. The relatively low 3He/4He of the Gharyan xenoliths (5.36.5 Ra) indicates that this component originates within the upper mantle and is unrelated to the deep-seated mantle plume source of the EthiopianYemen plateau basalts. Therefore, the Cenozoic volcanic districts of the Saharan belt could be related to smaller-scale shallow mantle upwellings (also referred to as hot fingers') triggered by intraplate reactivation of regional tectonic lineaments within the Pan-African cratonic basement, as a foreland reaction of the AfricanEurope collisional system.
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  • 6
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    Man-made versus natural CO2 leakage: A 400 k.y. history of an analogue for engineered geological storage of CO2 (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-03-22
    Description: To evaluate sites for long-term geological storage of CO 2 and optimize techniques for monitoring the fate of injected CO 2 , it is crucial to investigate potential CO 2 migration pathways out of a reservoir and surface leakage magnitudes. For the first time, we calculate CO 2 leakage rates and volumes from ancient fault-related travertines and from an abandoned borehole. U-Th–dated travertine along two faults near Green River, Utah (western United States), shows that leakage has occurred in this area for over 400 k.y. and has switched location repeatedly over kilometer-scale distances. One individual travertine was active for at least 11 k.y. Modern leakage is predominantly through the active Crystal Geyser, which erupts from an abandoned exploration well. Using age data and travertine volume, we calculate magnitudes and rates of CO 2 emission. Fault-focused leakage volume is twice as great as diffuse leakage through unconfined aquifers. The leakage rate from a poorly completed borehole is 13 times greater than the long-term time-averaged fault-focused leakage. Although magnitudes and rates of any leakage from future storage sites will be highly dependent on local geology and pressure regime, our results highlight that leakage from abandoned wells is likely to be more significant than through faults.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    Gondwana break-up related magmatism in the Falkland Islands (2016)
    Geological Society of London
    Details
    Publication Date: 2016-01-07
    Description: Jurassic dykes ( c . 182 Ma) are widespread across the Falkland Islands and exhibit considerable geochemical variability. Orthopyroxene-bearing NW–SE-oriented quartz-tholeiite dykes underwent fractional crystallization at 〉1 GPa, and major element constraints suggest that they were derived by melting of a pyroxenite-rich source. They have Nd 182 in the range –6 to –11 and 87 Sr/ 86 Sr 182 〉0.710 and therefore require an old lithospheric component in their source. A suite of basaltic-andesites and andesites exhibit geochemical compositions transitional between Ferrar and Karoo magma types, and are similar to those seen in the KwaZulu-Natal region of southern Africa and the Theron Mountains of Antarctica. Olivine-phyric intrusions equilibrated at 〈0.5 GPa, and have isotopic compositions (Nd 182 1.6–3.6 and 87 Sr/ 86 Sr 182 0.7036–0.7058) that require limited interaction with old continental lithosphere. A suite of plagioclase-phyric intrusions with 87 Sr/ 86 Sr 182 c . 0.7035 and Nd 182 c . +4, and low Th/Ta and La/Ta ratios ( c . 1 and c . 15, respectively) also largely escaped interaction with the lithosphere. These isotopically depleted intrusions were probably emplaced synchronously with Gondwana fragmentation and the formation of new oceanic lithosphere. Estimates of mantle potential temperature from olivine equilibration temperatures do not provide unequivocal evidence for the presence of a plume thermal anomaly beneath the Falkland Islands at 182 Ma. Supplementary materials: Mineralogical data, XRF major and trace element data and Ar-Ar results for Falkland Islands intrusions are available at http://www.geolsoc.org.uk/sup18873 .
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 8
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    The Ediacaran-Cambrian transition in the Cantabrian Zone (northern Spain): sub-Cambrian weathering, K-metasomatism and provenance of detrital series (2016)
    Geological Society of London
    Details
    Publication Date: 2016-07-05
    Description: The Upper Ediacaran detrital succession in the Cantabrian Zone shows geochemical and mineralogical changes resulting from sub-Cambrian weathering during the Late Ediacaran worldwide sea-level fall. Relative to the unaltered rocks the altered ones show crosscutting rubefaction of varying thickness and remarkable increase in illite, K 2 O, Rb and Cs indicating K-metasomatism, and also depletion in MgO, CaO, Na 2 O, Be and Sr, but not in Zr, Nb, Y or Sc. The basal Cambrian siliciclastic rocks mostly consist of detritus derived from the Ediacaran materials, as demonstrated by the geochemical and Nd-isotope data ( Nd ( t ) ranges are –3.4 to –2.1 and –3.6 to –1.8, respectively). However, these geochemical features of the basal Cambrian change upwards to more evolved compositions with lower Nd ( t ) values (–4.9 to –5.8). This change coincides with the Ediacaran–Cambrian unconformity in the Central Iberian Zone, and the Ediacaran siliclastic rocks of this zone and their unaltered equivalents of the Cantabrian Zone share the same geochemical features. This geochemical homogeneity rules out a significant coeval juvenile contribution to the Upper Ediacaran series. Thus, the juvenile supply was from a geological setting different from that in which the Ediacaran series were finally deposited. Supplementary material: Details of sampling, sample location, analytical techniques, diffractograms, tables of analyses and figures are available at https://doi.org/10.6084/m9.figshare.c.2850016 .
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 9
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    Crustal Differentiation Processes at Krakatau Volcano, Indonesia (2012)
    Oxford University Press
    Details
    Publication Date: 2012-12-21
    Description: Anak Krakatau is a basaltic andesite cone that has grown following the famous caldera-forming 1883 eruption of Krakatau. It breached sea level in 1927 and since the 1950s has been growing at an average rate of ~8 cm a week. We present new major and trace element data combined with whole-rock 18 O, Sr and Nd isotope data for 1883, 1993 and 2002 Krakatau eruptive products and the surrounding crust. Bombs erupted from Anak Krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism, plastic deformation and partial melting. Contact-metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high-temperature metamorphism and incorporation at mid- to upper-crustal depth. Energy-constrained assimilation and fractional crystallization modelling of whole-rock data suggests that the Anak Krakatau magmas have a genetic relationship with the 1883 eruption products. The geochemical impact of crustal contaminants on whole-rock compositions is apparently small, and we conclude that low levels of assimilation of a quartzo-feldspathic sediment are recorded in Anak Krakatau magmas. Plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning, however, and are also isotopically variable with a total range in 87 Sr/ 86 Sr of 0·7043–0·7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry. This suggests that although shallow crustal assimilation appears to have had a limited effect on whole-rock chemistry, a complex late-stage differentiation history is recorded within the magma’s cargo of crystals and xenoliths.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 10
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    Stratigraphy of Cretaceous to Lower Pliocene sediments in the northern part of Cyprus based on comparative 87Sr/86Sr isotopic, nannofossil and planktonic foraminiferal dating (2013)
    Cambridge University Press
    Details
    Publication Date: 2013-05-04
    Description: New age data from Sr isotope analysis and both planktonic foraminifera and nannofossils are presented and discussed here for the Upper Eocene–Upper Miocene sedimentary rocks of the Degirmenlik (Kythrea) Group. New dating is also given of some Cretaceous and Pliocene sediments. In a revised stratigraphy the Degirmenlik (Kythrea) Group is divided into ten formations. Different Upper Miocene formations are developed to the north and south of a regionally important, E–W-trending syn-sedimentary fault. The samples were dated wherever possible by three independent methods, namely utilizing Sr isotopes, calcareous nannofossils and planktonic foraminifera. Some of the Sr isotopic dates are incompatible with the nannofossil and/or the planktonic foraminiferal dates. This is mainly due to reworking within gravity-deposited or current-affected sediments. When combined, the reliable age data allow an overall biostratigraphy and chronology to be erected. Several of the boundaries of previously defined formations are revised. Sr data that are incompatible with well-constrained biostratigraphical ages are commonly of Early Miocene age. This is attributed to a regional uplift event located to the east of Cyprus, specifically the collision of the Anatolian (Eurasian) and Arabian (African) plates during Early Miocene time. This study, therefore, demonstrates that analytically sound Sr isotopic ages can yield geologically misleading ages, particularly where extensive sediment reworking has occurred. Convincing ages are obtained when isotopic dating is combined with as many forms of biostratigraphical dating as possible, and this may also reveal previously unsuspected geological events (e.g. tectonic uplift or current activity).
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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