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  • 1
    Electronic Resource
    Electronic Resource
    Deformation patterns in a high-viscosity lava flow inferred from the crystal preferred orientation and imbrication structures: an example from Salina (Aeolian Islands, southern Tyrrhenian Sea, Italy) (1996)
    Springer
    Bulletin of volcanology 57 (1996), S. 555-562 
    Details
    ISSN: 1432-0819
    Keywords: Lava flow ; Crystal preferred orientation Deformation ; Simple shear ; Bingham/viscoplastic flows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Shape-preferred orientation and imbrication structures of crystals have been measured on samples representative of the base, centre and top of a highly viscous lava flow on Salina (Aeolian Islands, southern Tyrrhenian Sea). The data allow zones with different deformation patterns to be identified. In the base and top of the flow, deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals. The sense of shear is right-lateral at the base and left-lateral at the top of the flow. Shear strain can be estimated by the analysis of crystal preferred orientation. Deformation increases from the flow centre to the outer, more viscous boundary layers. Random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava. The textural features of the studied lava may be related to different mechanisms (i.e. lateral expansion). We conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non-deforming walls. The walls are represented by the solidified, broken upper and basal crust of the flow. The low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event. Crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near-solidus outer margins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00304439
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  • 2
    Electronic Resource
    Electronic Resource
    The evolution of the lithospheric mantle along the N. African Plate: geochemical and isotopic evidence from the tholeiitic and alkaline volcanic rocks of the Hyblean plateau, Italy (1998)
    Springer
    Contributions to mineralogy and petrology 131 (1998), S. 307-322 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The geochemical characteristics of primitive tholeiitic and alkaline volcanic rocks that erupted in the Plio-Pleistocene along fissures on the Hyblean plateau in Sicily (Italy) were used to constrain the mantle sources involved in the volcanic activity of this area of the Mediterranean. It is shown that some of the Hyblean plateau magmas with the most extreme isotopic compositions have combined radiogenic Nd, Sr and Pb, a feature that is distinct from the mixing end-members of the oceanic array. In addition, alkalinity in the basalts is found to be positively correlated with an increase in some HFSE ratios (e.g. Nb/Ta, Zr/Hf) and negatively correlated with ratios between HFSE and MREE (e.g. Ti/Eu), a characteristic that is attributed to a mantle source that has been modified by a carbonatitic metasomatic agent. This metasomatic enrichment had the effect of increasing the U/Pb of portions of the lower lithosphere, possibly by adding phases such as sodic pyroxene and apatite to the basalt-depleted lithosphere. It is suggested that rock types that formed by melting metasomatized portions of lithosphere-asthenosphere boundary affected by this recent enrichment in U/Pb fall along a trend with a shallow slope in a plot of 206Pb/204Pb versus 207Pb/204Pb, and have Nd isotopic compositions that are as radiogenic as present day MORB. The isotopic compositions and trace-element concentrations of the Hyblean plateau basalts are, therefore, mostly consistent with the interaction of a MORB-type mantle source with a young lithosphere that was probably formed in the Phanerozoic and metasomatized by CO2-rich fluids, possibly during the Jurassic. The absence of a geochemical component indicative of involvement of older Proterozoic lithosphere and continental crust in the evolution of these magmas distinguishes them from those erupted along the margins of the Tyrrhenian sea, and supports the suggestion that at least portions of the lithosphere underneath Sicily have oceanic affinity and may be genetically related to the adjacent Ionian abyssal plain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050395
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    Paper (German National Licenses)
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