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  • 1
    Electronic Resource
    Electronic Resource
    Inception and demise of a Neoproterozoic ocean basin: evidence from the Ougda complex, western Hoggar (Algeria) (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 619-631 
    Details
    ISSN: 1437-3262
    Keywords: Pan-African ; tectonics ; geochemistry crustal extension ; island arc tholeIIte ; calc-alkali gabbro
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Neoproterozoic Ougda magmatic complex occurs within platformal carbonate rocks in the western part of the Pan-African fold belt of the Tuareg shield (NW Africa). It is composed of - 800 Ma old, relatively high P-T (i.e., Grt + Cpx-bearing: P 〉 5 kbar; T≈900'Q, tholeiitic mafic/ultramafic cumulates and related rocks intruded by intermediate to mafic calcalkali plutons (e.g., Cpx+Hbl-bearing gabbro) and dikes. Apparent contrasts in structural level of crystallization indicate that the calc-alkali rocks are significantly younger than the tholeiites, which temporally correlate with a period of regional extension in this part of Africa. Intrusion of the calc-alkali rocks may have occurred during the formation of an arc after the tholeiitic rocks had been (diapirically?) emplaced within the shelf carbonates, and prior to (〉 630 Ma) the Pan-African orogeny. Data reported herein indicate that the Ougda complex records the inception and demise of a Neoproterozoic ocean basin. Similar crustal sections have been described from collisional (e.g., Aleutian islands) and extensional (e.g., Ivreä-Verbano zone) settings, indicating that processes operating in both environments can generate nearly indistinguishable igneous suites; the prevalence of shallow-level calc-alkali rocks in both settings may mask the presence of more mafic, tholeiitic rocks at depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02440100
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  • 2
    Electronic Resource
    Electronic Resource
    Cretaceous alkaline lamprophyres from northeastern Czech Republic: geochemistry and petrogenesis (1998)
    Springer
    Geologische Rundschau 87 (1998), S. 67-77 
    Details
    ISSN: 0016-7835
    Keywords: Key words Lamprophyre ; Geochemistry ; Petrogenesis ; Cretaceous ; Czech Republic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The northeast part of the Czech Republic (Moravia) and the adjoining part of Poland host a 100-km-long and 15- to 25-km-wide belt containing numerous isolated bodies (mainly sills) of lamprophyre of Lower Cretaceous age. The lamprophyres range from mafic (melanocratic) to evolved, feldspar-rich (mesocratic) variants. Mineralogically, they are characterized by compositionally zoned kaersutite phenocrysts, biotite and high Al–Ti salitic to diopsidic clinopyroxene. The lamprophyres are typically alkaline as shown by high contents of P2O5, TiO2, alkalies and incompatible trace elements such as light REE, Zr, Nb, Y, Ba and Sr, and by high Ti/V (〉50) and chondrite-normalized (La/Yb)n (8–25) ratios. They resemble alkali basalts, basanites and nephelinites. Major element composition and trace element patterns and Nd–Sr isotopic values (εNd ca. +5.5 to +6.6 and εSr ca. –9.5 to –24.0) indicate that the lamprophyric magma was derived from a mantle source that was compositionally similar to the source of ocean island basalts with HIMU affinities and some continental extension-related alkali basaltic suites. The lamprophyres do not show any subduction imprint. They were generated in the garnet stability field by a variable degree of melting. Evolved lamprophyres were formed by clinopyroxene-dominated fractional crystallization of mafic lamprophyric magma. The lamprophyres are interpreted to have been emplaced along conduits formed during the formation of a basin/graben structure in the Early Cretaceous.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050190
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    Paper (German National Licenses)
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