Evidence for a smaller magma chamber beneath the East Pacific Rise at 9°30′ N

The size and shape of magma chambers beneath mid-ocean ridges are fundamental features that control the availability of melt, composition of magmas and formation of oceanic crust. (3) The finite-difference migration algorithm assumes that the velocity is locally constant, and therefore is unable to...

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Bibliographic Details
Published in:Nature (London) 1990-04, Vol.344 (6267), p.650-653
Main Authors: Kent, G. M, Harding, A. J, Orcutt, J. A
Format: Article
Language:English
Subjects:
Algorithms
Chambers
Diffraction
Finite difference method
Hypotheses
Interfaces
Lava
Magma
Mid-ocean ridges
Migration
Ocean floor
Oceanic crust
Seismological data
Ships
Sleep
Thickness
Topography
Upper bounds
Velocity
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Summary:The size and shape of magma chambers beneath mid-ocean ridges are fundamental features that control the availability of melt, composition of magmas and formation of oceanic crust. (3) The finite-difference migration algorithm assumes that the velocity is locally constant, and therefore is unable to account for refraction effects at interfaces (for example, the water/sea-floor interface). Because of the inherent problems with migration, and the excellent velocity control in the upper crust, we believe that the widths calculated using synthetic diffractions are more reliable. The possibility of a lowerboundary gradient model existing precludes any strict upper bounds on the magma lens thickness; however, a thin lens of melt ( -10-50 m) is consistent with the available seismic data, and therefore, a potential model for the magma chamber. If the magma chamber is a thin layer of melt, it is more plausible to expect gaps in the image of the reflector resulting from interference effects as the thickness of the layer decreases to zero (or resulting from navigational error which no longer places the ship above the narrow body); however, if the magma chamber is very large, it becomes difficult to explain the discontinuous nature of the reflector since this would imply a closely spaced and segmented system of large magma chambers along the rise-crest.
ISSN:0028-0836
1476-4687
DOI:10.1038/344650a0