Double layering of a thermochemical plume in the upper
mantle beneath Hawaii
Authors: Maxim
D. Ballmer1*, Garrett Ito1, Cecily J. Wolfe2,3, and Sean C. Solomon3,4
1Department of
Geology and Geophysics, School of Ocean and Earth Sciences and Technology,
University of Hawaii at Manoa, Honolulu, HI 96822,
USA
2Hawaii
Institute of Geophysics and Planetology, School of Ocean and Earth Sciences and
Technology, University of Hawaii at Manoa, Honolulu,
HI 96822, USA
3Department
of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC
20015, USA
4Lamont-Doherty
Earth Observatory, Columbia University, Palisades, NY 10964, USA
*Correspondence to: ballmer@hawaii.edu
Abstract
According to classical plume theory, purely
thermal upwellings rise through the mantle, pond in a
thin layer beneath the lithosphere, and generate hotspot volcanism. Neglected
by this theory, however, are the dynamical effects of compositional
heterogeneity carried by mantle plumes even though this heterogeneity has been
commonly identified in sources of hotspot magmas. Numerical models predict that
a hot, compositionally heterogeneous mantle plume containing a denser eclogite component tends to pool at ~300–410 km depth
before rising to feed a shallower sublithospheric
layer. This double-layered structure of a thermochemical plume is more
consistent with seismic tomographic images at Hawaii than the classical plume
model. The thermochemical structure as well as time dependence of plume
material rising out of the deeper into the shallower layer can further account
for long-term fluctuations in volcanic activity and asymmetry in bathymetry,
seismic structure, and magma chemistry across the hotspot track, as are
observed.
(click image for movie)
pancake deep eclogitic pool