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  • 1
    Electronic Resource
    Electronic Resource
    The Aegir Rift: Crustal Structure of an Extinct Spreading Axis (1997)
    Springer
    Marine geophysical researches 19 (1997), S. 1-23 
    Details
    ISSN: 1573-0581
    Keywords: Extinct spreading axis ; oceanic crust ; seismic refraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two seismic refraction and gravity lines were obtained along and normal to the axis of the Aegir Rift, an extinct spreading centre in the Norway Basin. Velocity-depth solutions and crustal structure models are derived from ocean-bottom records using two-dimensional ray tracing and synthetic seismogram modelling techniques. Gravity data are used to generate models consistent with the lateral variations in thickness of the layers in the crustal models. The resulting models require considerable degree of lateral inhomogeneity along and perpendicular to the rift axis. Crust within the extinct spreading centre is found to be thinner and of low P-wave velocity when compared with the crust sampled off-axis. To explain reduced velocities of the lower crust we suggest that, due to the relationship between fracturing and seismic velocity, the decreasing spreading rate leading up to extinction let the mechanically strong layer thicken, so that faulting and fracturing extended to greater depths . Low velocities are also observed in the uppermost mantle underlying the extinct spreading ridge. This zone is attributed to hydrothermal alteration of upper mantle peridotites. Furthermore, after spreading ceased 32-26 my ago, ongoing passive hydrothermal circulation was accompanied by the precipitation of alteration products in open void spaces, thereby decreasing the porosity and increasing the velocity. Consequently the typical low velocities of layer 2 found at active mid-ocean ridges have been replaced by values typical of mature oceanic crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004288815129
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ocean bottom refraction seismograph (OBRS) (1978)
    Springer
    Marine geophysical researches 3 (1978), S. 357-379 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper describes a pop-up ocean bottom seismograph designed primarily for refraction surveys both on the continental shelf and in deep sea. Its development is the extension of our system based on seismic detectors located on the sea floor with radio transmission of seismic signals and used for seismic refraction studies on the continental shelf. The seismic detectors (vertical geophone or hydrophone and two orthogonally mounted horizontal geophones) are located outside of the pressure vessel on the main frame. Optionally, the seismic sensors may be decoupled from the main frame assembly. This decoupling is performed by a mobile arm positioning the separate three component sensor package on the sea floor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00347673
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Mud volcano field seaward of the Barbados Accretionary Complex: A submersible survey (1990)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 95 (B6). pp. 8931-8943.
    Details
    Publication Date: 2018-08-28
    Description: We describe a 0.55 km2 semicircular mud pie and three adjacent diapiric mounds explored using the submersible Nautile near 13°50′N, 12 km seaward of the Barbados accretionary complex deformation front. This diapiric field had been previously explored with an acoustically navigated deep‐towed side scan sonar, thus providing an accurate base map. The mud pie is situated at a depth of 4938 m. In addition to visual observations, water, rock, sediment, and biological sampling, we measured temperature gradients and made geochemical analyses of the samples. Fluid venting associated with chemosynthetic animal communities is widespread on all four structures but is maximal in the central third of the mud pie. The chemosynthetic life distribution on the mud pie displays a concentric zonation which we relate to an increase in venting activity toward the center, as evidenced by thermal gradients. Recent mud flows are present in the centralmost part of the mud pie. The simplest interpretation of the structure is that it is a mud lake covered by a mechanically resistant carbonate crust. We determine that approximately 106 m3 of fluid are advected upward through the crust of the mud lake every year. This large amount of fluid implies large‐scale lateral transport.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/JB095iB06p08931
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Reflection seismic profiles from the Central Ionian Sea (Mediterranean) and their geodynamic interpretation (1981)
    Bornträger
    Details
    Publication Date: 2022-07-26
    Description: Five reflection seismic profiles from the borderland between Messina Abyssal Plain and Malta Ridge (= Medina Rise), recorded during "Meteor" cruise no. 50 in 1978, are described. The subbottom/bottom structures are interpreted as a pattern of broad grabens and intercalated SW-NE striking narrow horsts. Within the grabens great thicknesses of Messinian evaporites as well as of Quaternary turbiditic sediments, depending on the respective differential sinking, were accumulated. Some of the horsts rise above the surrounding seafloor. Ontop of the horsts, being mainly composed of pre-Messinian series, only little or no evaporites at all were deposited. The cover of Quaternary sediments depends on the position of the horst with respect to the seafloor. The thickness of Pliocene sediments is constant within the whole studied area. The authors conclude from the observations that the pattern of horsts and grabens acted already during Messinian time producing the variable thickness of the evaporite layer. The relative movements between grabens and horsts as well as a general sinking of the whole area must have acted also in Pliocene and Quaternary time.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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