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Media type:
Electronic Thesis;
E-Book
Title:
Impact of bending-related faulting on the seismic properties of the incoming oceanic lithosphere offshore of Nicaragua
Contributor:
Ivandic, Monika
[Author]
Published:
OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel), 2008
Extent:
text
Language:
English
Origination:
Footnote:
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Description:
The subduction of H2O is inherently related to the hydrogeology of the oceanic lithosphere entering the trench. Water transported within the subducting oceanic plate affects a number of processes, such as intraslab earthquakes and arc magmatism. Bending related faulting in the subducting lithospheres may intensify hydrothermal flow through aged crust and provide pathways for seawater to reach lower crustal and upper mantle depths. A number of seismic wide-angle reflection and refraction experiments were conducted offshore of Nicaragua to investigate the impact of bending related normal faulting on the seismic properties of the oceanic lithosphere prior to subduction. Based on the reflectivity pattern of multi-channel seismic reflection (MCS) data collected offshore of Nicaragua it has been suggested that bending-related faulting facilitates hydration and serpentinization of the incoming oceanic plate. First seismic wide-angle and refraction data were collected along the profile p50 which extends from the region well seaward of the outer rise, not yet affected by subduction, into the trench northwest of the Nicoya Peninsula, where multibeam bathymetric data show prominent normal faults on the seaward trench slope. A tomographic joint inversion of the seismic refraction and wide-angle reflection data yields a decrease in P-wave velocities in the crust and uppermost mantle as the plate approaches the trench. Seaward of the outer rise velocities are typical for »24 Myr old oceanic lithosphere. In the near-trench region, however, crustal velocities are reduced by 0.2-0.5 km/s compared to normal mature oceanic crust. Seismic velocities of the uppermost mantle are 7.6-7.8 km/s and hence 5-7% lower than the typical velocity of mantle peridotite. These systematic changes in P-wave velocity indicate an evolutionary process in the subducting slab consistent with percolation of seawater through the faulted and fractured lithosphere and serpentinization of mantle peridotites. Two other profiles, located northwest of the ...