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Published October 14, 2014 | Supplemental Material + Published
Journal Article Open

Mantle updrafts and mechanisms of oceanic volcanism


Convection in an isolated planet is characterized by narrow downwellings and broad updrafts—consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.

Additional Information

© 2014 National Academy of Sciences. Freely available online through the PNAS open access option. Edited by W. G. Ernst, Stanford University, Stanford, CA, and approved August 12, 2014 (received for review June 2, 2014). Published online before print September 8, 2014. The paper was critically reviewed and improved by Warren Hamilton, Don Turcotte, Gillian Foulger, and several anonymous reviewers. Author contributions: D.L.A. contributed to discussion of geophysics; J.H.N. contributed to discussion of geochemistry; and D.L.A. and J.H.N. prepared the figures and wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission

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Published - E4298.full.pdf

Supplemental Material - pnas.201410229SI.pdf


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