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  • 1
    In: Journal of geophysical research. B, Solid earth, Hoboken, NJ : Wiley, 1978, 114(2009), 2169-9356
    In: volume:114
    In: year:2009
    In: extent:20
    Description / Table of Contents: Two end-member styles of crustal accretion are observed at two adjacent spreading segments at the Mid-Atlantic Ridge at 5°S: focused accretion to the segment center with rapid crustal thinning toward the transform in the northern segment and crustal thickening toward the transform at an oceanic core complex in the southern segment. Our results were obtained by tomographic inversion of wide-angle seismic reflection and refraction data collected along three intersecting profiles. The segment north of the 5°S fracture zone is characterized by a well-developed median valley with a pronounced seafloor bulge in the segment center. A discrete portion of anomalously low velocities (-0.4 to -0.5 km/s relative to average off-axis structure) at depths of ~2.5 km beneath this bulge is possibly related to the presence of elevated temperatures and perhaps small portions of partial melt. This suggests that this segment is currently in a magmatically active period, which is confirmed by the observation of fresh lava flows and ongoing high-temperature hydrothermal activity at the seafloor. Close to the current spreading axis, the crust thins rapidly from 8.5 km beneath the segment center to less than 3 km beneath the transform fault which indicates that melt supply here is strongly focused to the segment center. The reduction in crustal thickness is almost exclusively accommodated by the thinning of velocity portions indicative of seismic layer 3. The transform fault is characterized by more uniform velocity gradients throughout the entire crustal section and very low upper mantle velocities of 7.2-7.3 km/s indicating that serpentinization could be as much as 25% at 3.5 km depth. In contrast, ~4.1 Ma old crust of the northern segment shows only minor thinning from the segment center toward the segment end. Here, the transform is characterized by a normal seismic layer 2/3 transition suggesting robust melt supply to the segment end at those times. In the adjacent southern segment, the crust thickens from ~2.5 km beneath the flank of an oceanic core complex to ~5.0 km at the segment boundary. The observed changes in crustal thickness show a significant temporal and lateral variability in melt supply and suggest a more complex crustal emplacement process than predicted by models of focused melt supply to the segment centers.
    Type of Medium: Online Resource
    Pages: 20 , graph. Darst
    ISSN: 2169-9356
    Language: English
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  • 2
    In: Geophysical journal international, Oxford : Oxford Univ. Press, 1958, 178(2009), 2, Seite 1112-1131, 1365-246X
    In: volume:178
    In: year:2009
    In: number:2
    In: pages:1112-1131
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1365-246X
    Language: English
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  • 3
    Keywords: Hochschulschrift ; Mittelatlantischer Rücken ; Ozeanische Erdkruste
    Description / Table of Contents: The structure of the oceanic crust at the Mid-Atlantic Ridge at 5ʿ South is investigated using wide-angle seismic data. Here, two morphologically contrasting spreading segments are separated by a 70 km offset transform fault. Applying a first-arrival tomography and a joint refraction and reflection tomography the obtained models show strong lateral heterogeneity in both velocities and Moho depths. In the segment north of the 5ʿS fracture zone (FZ) the along-axis crustal thickness thins from 9 km at the segment center to 5-6 km at the segment ends. In contrast to the magmatically robust northern segment, spreading south of the 5ʿS FZ rather seems to be tectonically controlled. Here, an inside corner high has been split by a change in location of active seafloor spreading. Most parts of this segment are underlain by anomalously thin crust with the thinnest portions associated with the flanks of the inside corner high and a fossil second order ridge-axis discontinuity. The crust formed at the inside corner reveals throughoutly higher velocities than corresponding outside corner crust, which is consistent with models of asymmetric crustal accretion along a detachment fault.
    Type of Medium: Online Resource
    Pages: Online-Ressource (217 S.)
    DDC: 550
    Language: English
    Note: Kiel, Univ., Diss, 2006
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  • 4
    Keywords: Hochschulschrift ; Mittelatlantischer Rücken ; Ozeanische Erdkruste
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource ( 217Seiten = 36MB) , Ill., graph. Darst., Kt.
    Language: English
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