Compositional vs. thermal buoyancy and the evolution of subducted lithosphere

James B. Gaherty, Bradford H. Hager

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


We formulate 2‐D Cartesian finite element models that explore the fate of compositionally defined lithosphere as it encounters a viscosity increase at the boundary between the upper and lower mantle. Subducted lithosphere is represented as a cold, stiff, layered composite of denser eclogite underlain by more buoyant harzburgite. Slabs impinging on a lower mantle 30 and 100 times more viscous than the upper mantle thicken and fold strongly as they penetrate the lower mantle. Approximately a factor of two thickening occurs via pure shear just above the discontinuity, with additional enhancement due to folding by over a factor of two. No separation of the individual slab components occurs at the discontinuity, and direct comparison with models in which compositional buoyancy is explicitly ignored indicates that slab evolution is largely controlled by the thermal buoyancy. These results are at odds with hypotheses about slab evolution in which the compositional buoyancy contributions lead to component separation and the formation of slab megaliths or a compositionally layered upper mantle.

Original languageEnglish (US)
Pages (from-to)141-144
Number of pages4
JournalGeophysical Research Letters
Issue number2
StatePublished - Jan 15 1994
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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