No Plumes Along Mid-Ocean Ridges Page 3
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NoRidgePlumes.html
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Figure 2. Pressure-temperature diagram showing solidus curves for carbonated lherzolite and volatile-
free lherzolite, after Figure 1 of Presnall & Gudfinnsson (2005); based on the data of Hirschmann
(2000), Dalton & Presnall (1998), Gudfinnsson & Presnall (2005) and Falloon & Green (1989). (From
Presnall & Gudfinnsson, 2007).
Clague (2007) found that effusive and strombolian (explosive) eruptive features at oceanic ridges
always occur together. In the model of Presnall & Gudfinnsson (2007), oceanic ridges are born when
stresses cause fracturing through the entire thickness of the oceanic lithosphere and momentarily
expose the partly melted seismic low-velocity zone to zero pressure. This causes explosive escape of
CO
, which carries melt with it to the surface, and a mature spreading ridge gradually develops. The
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energy for melting is decompression of rising mantle from the low-velocity zone. The flashing of CO
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to vapor merely controls the P-T conditions for escape of the magma. Ridges die when stresses shift,
close the fracture, and open a new fracture at a different locality where a new ridge develops. No
interaction with the deep mantle is involved. This model accounts for the absence of thermal
disturbances at the 410- km discontinuity beneath the entire length of the East Pacific Rise
(Melbourne & Helmberger, 2002) beneath which the presumed Easter plume is supposd to lie.
References
Clague, D. A., 2007, Simultaneous effusive and strombolian eruptions along mid-ocean
ridges, Geophys. Res. Abstracts, 9, abstract 02096.
Dalton, J. A. & Presnall, D. C., 1998, Carbonatitic melts along the solidus of model lherzolite in
the system CaO-MgO-Al
O
-SiO
-CO
from 3 to 7 GPa. Contrib. Min. Petrol., 131, 123-135,
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doi: 10.1007/S004100050383.
Eggler, D. H., 1976, Does CO2 cause partial melting in the low-velocity layer in the mantle?,
Geology, 4, 67-72.
Falloon, T. & Green, D. H., 1989, The solidus of carbonated, fertile peridottite, Earth Planet.
Sci. Lett., 94, 364-370, doi:10.1016/0012-821 x (89)90153-2.
Gudfinnsson, G. H. & Presnall, D. C., 2005, Continuous gradations among primary
carbonatitic, kimberlitic, melilititic, bsaltic, picritic, and komatiitic melts in equilibrium with
garnet lherzolite at 3-8 GPa, J. Petrol., doi:10.1039/petrology/egi029.
Hirschmann, M. M., 2000, Mantle solidus: Experimental constraints and the effects of
peridotite compositions, Geochem., Geophys., Geosys., 1, doi:10.1029/2000GC000070.
Klein, E. M., & Langmuir, C. H., 1987, Global correlations of ocean ridge basalt chemistry with
axial depth and crustal thickness, J. Geophys. Res., 92, 8089-8115.
Klein, E. M., & Langmuir, C.H., 1989, Local versus global variations in ocean ridge basalt
compositions: A reply, J. Geophys. Res., 94, 4241-4252.
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