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    Lower crustal variability and the crust/mantle transition at the Atlantis Massif oceanic core complex

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    Article (1.231Mb)
    Figure S1: Details of the OBS refraction experiment at Atlantis Massif. (225.4Kb)
    Figure S2: Refracted arrivals recorded by ORB1 and OBH26 downward continued to the seafloor. (230.2Kb)
    Figure S3: Example of tests for Line 8 models with sharp Moho. (178.6Kb)
    Figure S4: Tomographic models for Lines 9a and 9b. (149.8Kb)
    Figure S5: Effect of starting model on tomographic result. (139.6Kb)
    Additional file information (4.061Kb)
    Table S1: Locations of relocated instruments along Line 8. (14.66Kb)
    Table S2: Locations of relocated instruments along Lines 9a and 9b. (10.31Kb)
    Date
    2010-12-18
    Author
    Blackman, Donna K.  Concept link
    Collins, John A.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4322
    As published
    https://doi.org/10.1029/2010GL045165
    DOI
    10.1029/2010GL045165
    Keyword
     Atlantis Massif; Marine refraction; Oceanic crust; Mid-Atlantic Ridge 
    Abstract
    Seismic refraction data provide new constraints on the structure of the lower oceanic crust and its variability across the Atlantis Massif oceanic core complex, ∼30°N on the Mid-Atlantic Ridge. A 40 km-long spreading-parallel profile constrains P-wave velocities to depths of up to ∼7 km beneath the seafloor. Two shorter spreading-perpendicular lines provide coverage to ∼2 km depth. The anomalous character of the massif's central dome crust is clear compared to the neighboring rift valley and similar-age crust on the opposite ridge flank. The domal core of the massif, unroofed via detachment faulting, has velocities >7.0 km/s at depths below ∼2.5 km sub-seafloor, increasing to 7.5–7.8 km/s over the depth range 4.8–6.8 km. Within the core complex, the Moho does not appear to be sharp as no PmP arrivals are observed. Within the axial valley, velocities do not reach mantle-transition zone values in the uppermost 6 km. We infer that crust there is of normal thickness but that a thinner than average mafic section is present in the central massif. Near IODP Hole U1309D, located on the central dome, there is a low velocity gradient interval at 1–3 km depth with velocities of 6.6–6.8 km/s, that coincides with a 3–5 km wide region where shallower velocities are highest. Given the predominantly gabbroic section recovered from the 1.4 km deep drillhole, this seismic structure suggests that the mafic body extends a few km both laterally and vertically.
    Description
    Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 37 (2010): L2430, doi:10.1029/2010GL045165.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Geophysical Research Letters 37 (2010): L2430
     

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