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  • 1
    Publication Date: 2015-01-22
    Description: This Special Publication provides a snapshot of our understanding of volcanic processes through the use of palaeomagnetic and rock magnetic techniques. Here, we provide a context for the book, placing individual chapters within the milieu of previous work, including some magnetic techniques that were not used in the particular studies described herein. Thermoremanent magnetization is a powerful tool to understand processes related to heating and cooling of rocks, including estimating the temperature of emplacement of pyroclastic deposits, which may allow us to better understand the rates of cooling during eruption and transport. Anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics, and allow the interpretation of flow dynamics in dykes, lava flows and pyroclastic deposits, as well as the location of the eruptive vents. Rock magnetic characteristics can help in the correlation of volcanic deposits but also provide means to date volcanic deposits and to better understand the processes of cooling of the deposits, as the magnetic minerals can change with temperature. In addition, volcanic rocks may be key recorders of past magnetic fields, allowing a better understanding of changes in field intensity and, perhaps, providing clues of how the magnetic field is formed.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 2
    Publication Date: 2014-09-04
    Description: The Miocene Cabo de Gata volcanic arc in SE Spain comprises a wide variety of volcanic facies and eruptive styles in subaqueous to subaerial environments. In the SW sector of the area, 5–100 m-thick, NNW–SSE-orientated dykes feed and intrude submarine hyaloclastite deposits. We analysed the anisotropy of magnetic susceptibility (AMS) of six dykes and five hyaloclastite sites from three volcanic units: the Cerro Cañadillas, Los Frailes, and El Barronal formations. The main magnetic minerals are primary low-Ti titanomagnetite and magnetite. The AMS ellipsoids in the dykes are generally oblate-triaxial in shape, with magnetic foliations subparallel to the dyke walls. Kinematic field evidence supports the inferred flow directions deduced from magnetic lineation and imbrication of magnetic foliation. The geometric relationships between dyke margins and AMS axes indicate that dykes at El Barronal were emplaced via prevalent subvertical upward magma flow. The inferred flow directions are reproduced well by analogue models of AMS simulating magma migration in dykes with a diapiric geometry. The other dykes were emplaced by lateral magma propagation. Conversely, hyaloclastite shows a large scatter of the AMS axes reflecting different degrees of fragmentation. We observe a gradual increase in scatter in the AMS from confined dykes to fragmented hyaloclastite.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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