Other
Scientific paper
Nov 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..51..171c&link_type=abstract
Earth and Planetary Science Letters, Volume 51, Issue 1, p. 171-180.
Other
15
Scientific paper
Plateau-like features in ocean basins exhibit crustal structures which differ markedly from the relatively simple, three-layer model which applies to most of the oceanic crust. While some plateaus are known or thought to be fragments of continental crust (e.g. Rockall Bank, Lord Howe Rise), others appear to be of oceanic origin (e.g. Shatsky Rise, Broken Ridge), and their seismic structures, though variable, are significantly different. Continental fragments are similar in structure to continental shield areas: Depth to Moho is typically about 30 km, and the lower crust consists of a 6.8-7.0 km/s layer, 14-18 km thick, overlain by a 5.8-6.4 km/s layer of variable thickness, while velocity structures are variable at upper crustal levels. By contrast, the Moho apparently occurs at shallower levels beneath oceanic plateaus, which are characterized by the presence of a 7.3-7.6 km/s layer, 6-15 km thick at the base of the crust. This basal layer is commonly overlain by units having velocities typical of oceanic layers 2 and 3. Refractors having velocities which correspond to layer 3 tend to occur at deeper levels in continental fragments than they do beneath oceanic plateaus.
That high-velocity basal layers have been detected at the base of normal oceanic crust and in some ophiolites suggests that oceanic plateaus are truly marine in origin. Upper and middle crustal levels probably consist of basaltic and gabbroic rocks, respectively. The nature of the basal layer is difficult to assess. Olivine gabbro, mafic garnet granulite, and epidote amphibolite all exhibit velocities in the appropriate ranges, as does a mixture of mafic and ultramafic lithologies. Partially serpentinized peridotite cannot be ruled out on the basis of shear and compressional wave velocities alone.
Carlson Lynn Redding
Christensen Nikolas I.
Moore R. P.
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