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Media type:
E-Book;
Electronic Thesis
Title:
Bending-related faulting and mantle serpentinization at the Nicaraguan subduction zone
Contributor:
Lefeldt, Marten
[Author]
imprint:
OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel), 2008
Extent:
text
Language:
English
Origination:
Footnote:
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Description:
At a convergent margin large amounts of structurally bound water are carried into the Earth’s interior and - as the subducting plate descends and the temperature rises - are driven off to some extent into the mantle wedge, where they are thought to trigger intermediate-depth earthquakes in the Wadati-Benioff zone and melting under volcanic arcs. However, a largely uncertain fraction outlasts sub-arc fluid release and hence enters the deeper mantle, which leads to a connection between the oceans and the Earth’s deep water cycle. Thus, a detailed knowledge of the water budget of a subduction zone is not only important to understand arc volcanism, but as well to comprehend the chemical development of the Earth’s mantle. For this purpose, profound information about the amount of water that is subducted along with the oceanic plate is indispensable. The present thesis uses geophysical methods to determine the degree of hydration of the Cocos Plate offshore Nicaragua, which is subducted beneath the Caribbean Plate. In general it was assumed that structured water is transported into the slab in sediments and the upper crust only, though in recent years growing evidence suggested that lower crust and upper mantle might contain capacious amounts of fluids as well, since the bending of the incoming oceanic plate leads to a reactivation or creation of normal faults (bend-faults), which are visible in batrymetric data and have been inferred to cut deep enough into the plate to provide a pathway for seawater to penetrate into the lithosphere, changing ”dry” peridotites to ”wet” serpentinites, which contain up to 13% of water. Such a mechanism could transport much more fluids into the earth’s interior than any other considered possibility. However, the cutting depth of these bend-faults and hence the depth that seawater could penetrate into the mantle was not well-defined, for one reason since focal depth of earthquakes associated with the bend-faults were poorly known. Yet previous studies assumed cutting depths such that ...