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  • Articles  (34)
  • 1985-1989  (34)
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  • Articles  (34)
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  • 1
    Electronic Resource
    Electronic Resource
    Anatomy of the magma reservoir (1989)
    [s.l.] : Nature Publishing Group
    Nature 339 (1989), S. 178-179 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] FULLY two-thirds of the Earth's crust is created by spreading at the mid-ocean ridge, a feature likened by the late Bruce Heezen to "a wound that never heals". Most of the molten rock that solidifies into oceanic crust resides within a shallow magma chamber beneath the axis of the ridge before ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/339178a0
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  • 2
    Electronic Resource
    Electronic Resource
    A new view of the mid-ocean ridge from the behaviour of ridge-axis discontinuities (1988)
    [s.l.] : Nature Publishing Group
    Nature 335 (1988), S. 217-225 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] High-resolution images covering large areas of the seafloor reveal numerous discontinuities along the mid-ocean ridge. These discontinuities occur at a range of scales (10–1,000 km) and define a fundamental segmentation of seafloor spreading centres. Some are transient; others persist for ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/335217a0
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  • 3
    Electronic Resource
    Electronic Resource
    Cracks in the Pacific plate and mantle convection (1988)
    [s.l.] : Nature Publishing Group
    Nature 331 (1988), S. 395-395 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR—Winterer and Sandwell1 interpret 'cross-grain' ridges on the Pacific plate which are oblique to both spreading-centre parallel topography and fracture zones as large-scale tensional cracks up to 200 km long and spaced —35 km apart. The cracks occur along topographic highs which ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/331395a0
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  • 4
    Electronic Resource
    Electronic Resource
    Propagating rifts exposed (1989)
    [s.l.] : Nature Publishing Group
    Nature 342 (1989), S. 740-741 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] MID-OCEAN ridges, where plates of oceanic lithosphere separate, are not invariant features. Major changes in spreading direction require the ridges to reorganize themselves. Spreading centres can 'jump' from one location to another. How do these changes occur? And what causes the large-scale ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/342740a0
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of faulting and abyssal hill formation on the flanks of the East Pacific Rise (21°N) using ALVIN (1985)
    Springer
    Marine geophysical researches 7 (1985), S. 515-535 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A wealth of geologic information has been collected during studies of the Matuyama/Brunhes magnetic reversal boundary on the East Pacific Rise at 21°N. Five ALVIN and two CYANA dives, and a series of deep-tow traverses show that abyssal hills in this region of the Pacific are created near the spreading axis by inward dipping normal faulting and by back-tilting of these fault blocks. Outward dipping faults occur but are of less importance in the creation of relief. Tectonic disruption of the crust, particularly through tilting, is less pronounced than in the Atlantic. Small volcanoes approximately 50 m high and 400 m wide are common on the abyssal hills. A significant number of the volcanoes may have split apart at the spreading axis attesting to the narrowness of the crustal accretion zone on the East Pacific Rise. Active faulting is restricted to less than 10 to 12 km off-axis, although minor recent faulting may have been detected 23 km off-axis. Crustal sections exposed by faulting reveal that massive lava flows and sheet flows are common in the upper portion of oceanic layer two, but are less abundant than pillow lavas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368953
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  • 6
    Electronic Resource
    Electronic Resource
    Near bottom magnetic profile across the Red Sea (1985)
    Springer
    Marine geophysical researches 7 (1985), S. 401-418 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Results are presented from a high precision geophysical profile made at an altitude of about 100 m above the sea floor with the Deep Two instrument package, crossing the Red Sea at 17°30′N. The emphasis is on the analysis and interpretation of the magnetic field, including an inversion which removes the distortions due to bathymetry and the orientation with respect to the earth's main field vector. The spreading rates are determined precisely and found to be highly asymmetric: only 5 mm yr-1 to the east and up to 10 mm yr-1 to the west. We conclude that the axis of spreading is located on a volcanic ridge, rather than on the axial graben, based on the presence of a zone of high magnetization. The magnetization high (40 Am-1) is about twice as great as found on the Mid-Atlantic Ridge with the same instrument and analysis. The quality of the recording of the magnetic anomalies in the oceanic crust is much greater than expected for such a low spreading rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316777
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  • 7
    Electronic Resource
    Electronic Resource
    Ocean bottom seismometer detection of earthquakes on the Gorda Rise near 41.5° north (1985)
    Springer
    Marine geophysical researches 7 (1985), S. 439-453 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The spatial and temporal distribution of microearthquake activity associated with the southern section of the Gorda Rise was monitored during a three week period using an array of four ocean bottom seismometers (OBS's) located at 41.5° N, 127.5° W on the rise axis. Sixty-two events were detected, of which roughly half occurred during a seismic swarm following an event of magnitude 4.9 that was well-recorded on land. A total of eighteen earthquakes could be located, seventeen of which originated from the valley floor, walls, and crestal mountains while the remaining event was located to the east of the rise in the Gorda plate. Well-constrained focal depths for four earthquakes ranged from roughly 4 to 12 km. Depths in excess of 10 km for two of the events provide strong evidence for the absence of a shallow steady-state magma chamber beneath the slow-spreading portion of the Gorda rise. Most of the events are believed to be the result of uplift of the crustal blocks comprising the valley walls. Four events located at an offset of the rise near 41.5° N may be related to strike-slip movement on a developing transform fault. Two of the events that occurred during the survey were large enough to be detected and located by land-based instruments. Comparison of these locations with the OBS locations indicates that well-recorded events having magnitudes of at least 4.5 are routinely mislocated 40–50 km to the east of their actual locations in this area while lower magnitude, poorly recorded earthquakes may have significantly larger location errors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368949
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  • 8
    Electronic Resource
    Electronic Resource
    A geological transect across the crest of the East Pacific Rise at 21°N latitude made from the deep submersible ALVIN (1985)
    Springer
    Marine geophysical researches 7 (1985), S. 467-488 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper is a report of geological observations made using the submersible ALVIN on the crest of the East Pacific Rise near 21°N. The profile is 6 km long and crosses a 5–10 km wide plateau which rises 100 m±above the rise flanks. At the axis are exposed fresh glassy pillow lavas with no sediment accumulation in a region termed the neovolcanic zone. This zone is about one kilometer wide and includes elongate ridges of pillow lavas and seventeen hydrothermal vent fields in the study area. Outside the neovolcanic zone the seafloor is extensively fissured in another zone which is up to two kilometers wide. The neovolcanic zone and the fissured zone are included within a rift valley or graben about 3 to 5 km wide and 50 m±deep. This rift valley is asymmetrically located on the west side of the axial plateau; the neovolcanic zone in the study area is asymmetrically located on the east side of the rift graben. Fissured crust is not common outside the rift graben or in the neovolcanic zone; similarly, large throw faults such as those which form the edges of the graben are not found outside of it. These observations can be interpreted according to a volcanic-tectonic cycle in which volcanic eruptions and hydrothermal circulation are followed by a tectonic phase which includes fissuring and vertical movements. When a new cycle starts it may involve a lateral shift of the spreading axis. Lavas along the dive profile are suggested to be no older than a few thousand years based on sediment accumulation. In contrast, seafloor spreading rates here predict crust up to 105 yr old. This observation suggests that lavas from the neovolcanic zone can spread laterally about a kilometer or more and overlap on older crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368951
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  • 9
    Electronic Resource
    Electronic Resource
    Tectonics of the Nereus Deep, Red Sea: A deep-tow investigation of a site of initial rifting (1986)
    Springer
    Marine geophysical researches 8 (1986), S. 131-148 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Nereus Deep (23°N) lies in the central portion of the Red Sea, in a region which marks a transition between the nearly continuous axial rift valley of the southern Red Sea and the northern Red Sea, where a well defined axial rift is absent. The deep-tow survey and associated heat flow measurements reported here show that the Nereus Deep is a short segment of axial rift, and it is the northernmost deep where petrology, heat flow, magnetics, and morphology all indicate classic seafloor spreading. Heat flow measured in the Nereus Deep is characterized by non-linear gradients and closely-spaced variability indicative of active hydrothermal circulation associated with seafloor spreading. The two axial highs which we have mapped in Nereus differ markedly in that the southernmost appears younger or at least has had a more recent phase of volcanism. The two axial highs are offset left laterally approximately 2 km. This small offset or bend in the axial course has been labelled the Nereus ‘shear zone’, and, despite its small extent, it mimics many of the major features of small offset, slow-slipping transform faults. This shear zone may result from shear stresses associated with misalignments in succeeding volcanic episodes. The Nereus Deep appears to represent one of the earliest phases of seafloor spreading. The Red Sea seems to be opening towards the north, and the Nereus Deep is near the tip of propagation, but it is clear from this study that rift propagation in a site of initial rifting differs greatly from that observed along a well developed, fast spreading center like the East Pacific Rise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338225
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  • 10
    Electronic Resource
    Electronic Resource
    Fine scale study of a small overlapping spreading center system at 12°54′ N on the East Pacific Rise (1988)
    Springer
    Marine geophysical researches 9 (1988), S. 115-130 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Overlapping spreading centers (OSCs) are a type of ridge axis discontinuity found along intermediate and fast spreading centers. The ridges at these locations overlap and curve towards each other. and are separated by an elongate overlap basin. A high resolution Deep-Tow survey was conducted over the 12°54′ N OSC (offset ≈1.6 km) on the East Pacific Rise in order to study the structure of a small OSC on a fine scale. A detailed tectonic study and Deep-Tow 3-D magnetic inversion were performed on the data. Towards the tips of both limbs, the apparent age of lava flows increases, the density of exposed faults and fissures increases, and the axial graben loses definition and disappears. No active hydrothermal vents were detected in the area. These observations suggest that the magmatic budget steadily decreases along axis approaching and OSC, even where the offset is small. In contrast with OSCs which have a large offset (〉5 km), the 3-D magnetic inversion solution for this OSC produced no evidence for highly magnetized areas near the tip of either spreading center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369244
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