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  • 1
    Online Resource
    Online Resource
    SO 145 - EXCO II: Austauschprozesse zwischen Kruste und Ozean am Ostpazifischen Rücken südlich der Garret Bruchzone (14[Grad]S) : Abschlussbericht zum BMBF-Projekt 03G0145A (2002)
    Bremen
    Details Availability
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: Online-Ressource (91 p., 10,1 Mb.) , ill., graphs
    Edition: [Elektronische Ressource]
    URL: https://edocs.tib.eu/files/e01fb04/37729392X.pdf
    URL: https://doi.org/10.2314/GBV:37729392X
    URL: https://edocs.tib.eu/files/e01fb04/37729392Xl.pdf
    DOI: 10.2314/GBV:37729392X
    Language: German
    Note: Contract BMBF 03G0145A. - Differences between the printed and electronic version of the document are possible , Also available as printed version , A multibeam-sonar, magnetic and geochemical flowline survey at 14[grad]14'S on the southern East Pacific Rise: insights into the fourth dimension of ridge crest segmentation / Ingo Grevemeyer... , Systemvoraussetzungen: Acrobat reader.
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  • 2
    Article
    Article
    Gashydrate als Energiepotentiale der Zukunft (2002)
    Bremen
    Associated volumes
    Details Availability
    In: Impulse aus der Forschung, Bremen : Univ., 1986, (2002), Seite 12-15, 0179-9495
    In: year:2002
    In: pages:12-15
    Type of Medium: Article
    Pages: Ill., graph. Darst.
    ISSN: 0179-9495
    Language: German
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  • 3
    Electronic Resource
    Electronic Resource
    Seismic velocities of the uppermost igneous crust versus age (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismic refraction velocity data from the acoustic basement (called layer 2A) have been compiled for different mid-ocean ridges. The data from post-1970 studies show a strong correlation between velocity and basement age. Importantly, velocities double in less than 10 Myr for all ridges, but for older crust, up to 160 Myr in age, velocities do not increase significantly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb07041.x
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Hotspot-ridge interaction in the Indian Ocean: constraints from Geosat/ERM altimetry (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Upper-mantle structure of Indian Ocean spreading ridges was investigated by track segments of Geosat/ERM altimeter measurements. To determine the upper-mantle structure of the Earth's gravity field, a low-degree and -order spherical harmonic representation of the geoid was removed. A test of several reference fields suggested that a degree 2–25 field with gradually rolled off coefficients (Sandwell & Renkin 1988) offers an adequate representation of the long-wavelength geoidal undulations.Filtered profiles of three individual ridge segments display a strong asymmetry in geoid versus age trends of conjugated rift flanks. The unusually low geoid slopes on one flank can perhaps best be explained as a dynamic or thermal phenomenon reflecting a flow connection between a neighbouring off-axis hotspot plume and the ridge axis, while the other flank simply cools as it spreads away from the axial zone. It seems reasonable to hypothesize that the Southwest Indian Ridge and the Southeast Indian Ridge act as sinks for plumes beneath Agulhas Plateau and Kerguelen Islands, respectively. The Carlsberg Ridge data suggest that the Réunion hotspot contaminated northwestern African lithosphere until 15 Ma. Moreover, symmetric flattening of geoid versus age trends of conjugated ridge flanks offers evidence that plume events affect geoid versus age trends
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04703.x
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  • 5
    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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  • 6
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    Component parts of the World Heat Flow Data Collection (2004)
    PANGAEA
    Details
    Publication Date: 2023-09-01
    Keywords: Area/locality; Heat flow; LATITUDE; LONGITUDE; Method comment; Number; Sample, optional label/labor no
    Type: Dataset
    Format: text/tab-separated-values, 70 data points
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  • 7
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    Component parts of the World Heat Flow Data Collection (1999)
    PANGAEA
    Details
    Publication Date: 2023-09-01
    Keywords: Area/locality; Conductivity, average; Heat flow; LATITUDE; LONGITUDE; Method comment; Number; Number of conductivity measurements; Number of temperature data; Sample, optional label/labor no; Temperature gradient
    Type: Dataset
    Format: text/tab-separated-values, 690 data points
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    DATA PANGAEA
  • 8
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    An implosive seismoacoustic source for seismic experiments on the ocean floor (1998)
    Springer
    In:  Marine Geophysical Researches, 20 (3). pp. 239-247.
    Details
    Publication Date: 2018-02-08
    Description: Bottom shots have been used for a number of years in seismic studies on the ocean floor. Most experiments utilized explosives as the energy source, though researchers have recognized the usefulness of collapsing water voids to produce seismoacoustic signals. Implosive sources, however, suffered generally from a lack of control of source depth. We present a new experimental tool, called SEEBOSEIS, to carry out seismic experiments on the seafloor utilizing hollow glass spheres as controlled implosive sources. The source is a 10-inch BENTHOS float with penetrator. Inside the sphere we place a small explosive charge (two detonators) to destabilize the glass wall. The time of detonation is controlled by an external shooting device. Test measurements on the Ninetyeast Ridge, Indian Ocean, show that the implosive sources can be used in seismic refraction experiments to image the subbottom P- wave velocity structure in detail beyond that possible with traditional marine seismic techniques. Additionally, the implosions permit the efficient generation of dispersed Scholte waves, revealing upper crustal S-wave velocities. The frequency band of seismic energy ranges from less than 1 Hz for Scholte modes up to 1000 Hz for diving P-waves. Therefore, broadband recording units with sampling rates 〉2000 Hz are recommended to sample the entire wave field radiated by implosive sources.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1023/A:1004552406168
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  • 9
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    Crustal underplating and its implications for subsidence and state of isostasy along the Ninetyeast Ridge hotspot trail (2000)
    Wiley
    In:  Geophysical Journal International, 142 (2). pp. 643-649.
    Details
    Publication Date: 2018-01-31
    Description: Recent seismic field work has revealed high lower-crustal velocities under Ninetyeast Ridge, Indian Ocean, indicating the presence of crustal underplating (Grevemeyer et al. 2000). We used results from Ocean Drilling Program (ODP) drill cores and cross-spectral analysis of gravity and bathymetric data to study the impact of the underplating body on the subsidence history and the mode of isostatic compensation along Ninetyeast Ridge. Compared with the adjacent Indian basin, the subsidence of Ninetyeast Ridge is profoundly anomalous. Within the first few millions of years after crustal emplacement the ridge subsided rapidly. Thereafter, however, subsidence slowed down significantly. The most reliable model of isostasy suggests loading of a thin elastic plate on and beneath the seafloor. Isostatic compensation of subsurface loading occurs at a depth of about 25km, which is in reasonably good agreement with seismic constraints. Subsurface loading is inherently associated with buoyant forces acting on the lithosphere. The low subsidence may therefore be the superposition of cooling of the lithosphere and uplift due to buoyant material added at the base of the crust. A model including prolonged crustal growth in the form of subcrustal plutonism may account for all observations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1046/j.1365-246x.2000.00154.x
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  • 10
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    Crustal architecture and deep structure of the Ninetyeast Ridge hotspot trail from active-source ocean bottom seismology (2001)
    Wiley
    In:  Geophysical Journal International, 144 (2). pp. 414-431.
    Details
    Publication Date: 2018-01-31
    Description: A 550-km-long transect across the Ninetyeast Ridge, a major Indian ocean hotspot trail, provided seismic refraction and wide-angle reflection data recorded on 60 ocean bottom instruments. About 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track. Two approaches have been chosen: (i) a first-arrival tomographic inversion yielding crustal properties; and (ii) forward modelling of mantle phases revealing the structure at the crust–mantle boundary region and of the uppermost mantle. Away from the volcanic edifice, seismic recordings show the typical phases from oceanic crust, that is, two crustal refraction branches (Pg), a wide-angle reflection from the crust–mantle boundary (PmP) and a wave group turning within the upper mantle (Pn). Approaching the edifice, three additional phases have been detected. We interpret these arrivals as a wide-angle reflection from the base of material trapped under the pre-hotspot crust (Pm2P) and as a wide-angle reflection (PnP) and its associated refraction branch (PN) from a layered upper mantle. The resulting models indicate normal oceanic crust to the west and east of the edifice. Crustal thickness averages 6.5–7 km. Wide-angle reflections from both the pre-hotspot and the post-hotspot crust–mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere, and hotspot volcanism has underplated the pre-existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks (7.5–7.6 km s−1). In total, the crust is up to ≈ 24 km thick. The ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0.7. An important observation is that underplating continued to the east under the Wharton Basin. During the shield-building phase, however, Ninetyeast Ridge was located adjacent to the Broken Ridge and was subsequently pulled apart along a transform fault boundary. Therefore, underplating eastwards of the fracture zone separating the edifice from the Wharton Basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield-building stage. This fact, however, requires mantle flow along the fossil hotspot trail. The occurrence of PnP and PN arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1046/j.0956-540X.2000.01334.x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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