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    Seismic evidence for large-scale compositional heterogeneity of oceanic core complexes

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    Article (4.289Mb)
    Additional file information (2.556Kb)
    Animation S1: Three-dimensional view of Atlantis OCC. (5.761Mb)
    Animation S2: Three-dimensional view of Kane OCC. (4.413Mb)
    Date
    2008-08-06
    Author
    Canales, J. Pablo  Concept link
    Tucholke, Brian E.  Concept link
    Xu, Min  Concept link
    Collins, John A.  Concept link
    DuBois, David L.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/3277
    As published
    https://doi.org/10.1029/2008GC002009
    DOI
    10.1029/2008GC002009
    Keyword
     Oceanic core complex; Detachment fault; Mid-Atlantic Ridge; Seismic structure; Gabbro; Serpentinized peridotite 
    Abstract
    Long-lived detachment faults at mid-ocean ridges exhume deep-seated rocks to form oceanic core complexes (OCCs). Using large-offset (6 km) multichannel seismic data, we have derived two-dimensional seismic tomography models for three of the best developed OCCs on the Mid-Atlantic Ridge. Our results show that large lateral variations in P wave velocity occur within the upper ~0.5–1.7 km of the lithosphere. We observe good correlations between velocity structure and lithology as documented by in situ geological samples and seafloor morphology, and we use these correlations to show that gabbros are heterogeneously distributed as large (tens to >100 km2) bodies within serpentinized peridotites. Neither the gabbros nor the serpentinites show any systematic distribution with respect to along-isochron position within the enclosing spreading segment, indicating that melt extraction from the mantle is not necessarily focused at segment centers, as has been commonly inferred. In the spreading direction, gabbros are consistently present toward the terminations of the detachment faults. This suggests enhanced magmatism during the late stage of OCC formation due either to natural variability in the magmatic cycle or to decompression melting during footwall exhumation. Heat introduced into the rift valley by flow and crystallization of this melt could weaken the axial lithosphere and result in formation of new faults, and it therefore may explain eventual abandonment of detachments that form OCCs. Detailed seismic studies of the kind described here, when constrained by seafloor morphology and geological samples, can distinguish between major lithological units such as volcanics, gabbros, and serpentinized peridotites at lateral scales of a few kilometers. Thus such studies have tremendous potential to elucidate the internal structure of the shallow lithosphere and to help us understand the tectonic and magmatic processes by which they were emplaced.
    Description
    Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q08002, doi:10.1029/2008GC002009.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Geochemistry Geophysics Geosystems 9 (2008): Q08002
     

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