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The upper mantle transition region: Eclogite?
Author(s) -
Anderson Don L.
Publication year - 1979
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl006i006p00433
Subject(s) - eclogite , geology , peridotite , transition zone , mantle (geology) , stishovite , geochemistry , mantle wedge , mantle convection , spinel , basalt , petrology , geophysics , subduction , quartz , tectonics , seismology , paleontology
The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post‐spinel assemblages. There are difficulties associated with attempts to explain the 220, 400 and 670 km discontinuities in terms of phase changes in a peridotitic mantle. Moreover, in a differentiated earth there should be large quantities of eclogite in the upper mantle. Eclogite is denser than Al 2 O 3 ‐poor mantle to depths of 670 km, but it stays in the garnet stability field to pressures in excess of those required to transform depleted mantle to denser phases such as ilmenite and perovskite. Eclogite, therefore, remains above 670 km. The seismic properties of the transition region are more consistent with eclogite than peridotite. Most of the mantle's inventory of incompatible trace elements may be in this layer, which is a potential source region for some basalt magmas. The radioactivity in this layer is the main source of mantle heat flow, 0.7 µcal/cm² sec, and drives upper mantle convection.