The upper mantle transition region - Eclogite
TLDR
The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post-spinel assemblages.Abstract:
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 Al2O3-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 microcalorie/sq cm-sec, and drives upper mantle convection.read more
Citations
More filters
Journal ArticleDOI
Mantle plumes from ancient oceanic crust
TL;DR: In this article, the authors propose a model for the origin of hot-spot volcanism, where oceanic crust is returned to the mantle during subduction and sinks into the deeper mantle and accumulates at some level of density compensation, possibly the core-mantle boundary.
Journal ArticleDOI
Postspinel transformations in the system Mg2SiO4‐Fe2SiO4 and some geophysical implications
Eiji Ito,Eiichi Takahashi +1 more
TL;DR: In this article, the phase boundaries between ilmenite-perovskite in MgSiO3 and between Mg2SiO4 spinel and MgO periclase were determined using a uniaxial split-sphere apparatus.
Book
Theory of the Earth
TL;DR: Theory of the Earth as mentioned in this paper is a theory of the origin, composition, evolution, and evolution of the entire Earth from the perspective of geology, petrology, mineralogy, geochemistry, geodesy, and seismology.
Journal ArticleDOI
Layered convection induced by phase transitions
TL;DR: In this paper, the authors performed two-dimensional numerical calculations of convection in a domain containing a divariant phase change and found that the critical value of the negative Clapeyron slope, which must be surpassed in order to induce layered convection, decreases in magnitude with increasing Rayleigh number Ra in the range 104 ≤ Ra ≤ 2×106.
References
More filters
Journal ArticleDOI
Composition of the Earth
TL;DR: In this article, the authors reported that the resulting densities in the lower mantle are in good agreement with shock-wave measurements on rocks having FeO contents in the range 10 ± 2% by weight.
Journal ArticleDOI
Chemical Characteristics of Oceanic Basalts and the Upper Mantle
TL;DR: In this article, it was shown that oceanic tholeiites are either complete melts of the upper mantle or are generated from a mix of this tholeite and a magnesium-rich peridotite or dunite in proportions up to perhaps 1:4.
Journal ArticleDOI
Convection in the earth's mantle: towards a numerical simulation
TL;DR: In this article, a review of the geophysical information and the fluid dynamics of convection in a Boussinesq fluid of infinite Prandtl number is presented and analyzed in terms of simple physical models.
Journal ArticleDOI
Chemical Characteristics and Origin of Oceanic Ridge Volcanic Rocks
TL;DR: Oceanic ridge volcanic rocks alkali metal, alkaline earth, rare earth, nickel and major element content, observing partial melting as mentioned in this paper. But this is not the case for all volcanic rocks.
Journal ArticleDOI
A pyroxene geotherm
TL;DR: In this article, phase equilibria determined in high-pressure studies of the systems Mg2Si2O6-CaMgSi 2O6 and MgSiO3-Mg3Al2Si3O12 can be used to estimate equilibration conditions of ultramafic rocks containing the assemblage enstatite + diopside + garnet.