Accretional curvature of lithosphere at magmatic spreading centers and the flexural support of axial highs

Publication Type  Journal Article
Year of Publication  2001
Authors  Buck, W. R.
Journal Title  Journal of Geophysical Research-Solid Earth
Volume  106
Issue  B3
Pages  3953-3960
Journal Date  Mar 10
ISBN Number  0148-0227
Accession Number  ISI:000167379500001
Key Words  east pacific rise; midocean ridges; oceanic-crust; statistical physics; seismic structure; fault patterns; model; beneath; segmentation; growth

Fluid magma should tend to rise up to the level of local isostatic equilibrium at an axis of plate spreading. The magma and underlying partial melt accretes to the side of the separating plates and gets denser as it cools and freezes. This load bends down the lithosphere and additional accretion forms a plate with concave upward curvature. The topography resulting from a curved plate passively moving off axis can be described analytically for accretion on the vertical side of uniform lithosphere when its flexural response is that of a thin elastic plate. Model predictions are consistent with the shape of the axial highs at fast spreading centers (typically similar to 400m high and similar to 20 km wide) as well as related gravity anomalies. This model requires at least several kilometers of lithospheric thickening within a few kilometers of the ridge axis. Seismic data appear consistent with this lithospheric structure. The magnitude and lateral distribution of faulting on the flanks of axial highs is crudely consistent with formation during plate unbending as lithosphere moves away from the axis. According to this model abandoned fast spreading centers should retain an elastically supported axial high, while for previous models abandoned highs should collapse.


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