Results 171 to 180 of about 17,328 (228)
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Ferropericlase—a lower mantle phase in the upper mantle
Lithos, 2004Experiments on compositions along the join MgO–NaA3+Si2O6 (A=Al, Cr, Fe3+) show that sodium can be incorporated into ferropericlase at upper mantle pressures in amounts commonly found in natural diamond inclusions. These results, combined with the observed mineral parageneses of several diamond inclusion suites, establish firmly that ferropericlase ...
Gerhard P Brey +2 more
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On the seismic discontinuities in the upper mantle
Physics of the Earth and Planetary Interiors, 1995Abstract Mode conversions and reflections at upper-mantle seismic discontinuities may be contained in earthquake seismograms as weak secondary phases that often become visible only after special signal processing techniques are applied to the data. To extract fully the information these secondary phases carry about the three-dimensional structure of ...
Bock, G. +7 more
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Metal saturation in the upper mantle
Nature, 2007The oxygen fugacity f(O2)of the Earth's mantle is one of the fundamental variables in mantle petrology. Through ferric-ferrous iron and carbon-hydrogen-oxygen equilibria, f(O2) influences the pressure-temperature positions of mantle solidi and compositions of small-degree mantle melts.
Rohrbach, A. +5 more
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The electrical conductivity of upper-mantle rocks: water content in the upper mantle
Physics and Chemistry of Minerals, 2007The electrical conductivity of upper-mantle rocks—dunite, pyroxenite, and lherzolite—was measured at ∼2–3 GPa and ∼1,273–1,573 K using impedance spectra within a frequency range of 0.1–106 Hz. The oxygen fugacity was controlled by a Mo–MoO2 solid buffer.
Duojun Wang +3 more
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Tectonophysics, 1965
Abstract All current tectonic hypotheses assign the cause of vertical crustal movements to processes within the earth. Some suppose an expansion and contraction of mantle material, probably caused by physical transitions (polymorphic, phase and electronic) and chemical reactions.
S.I. Subbotin +2 more
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Abstract All current tectonic hypotheses assign the cause of vertical crustal movements to processes within the earth. Some suppose an expansion and contraction of mantle material, probably caused by physical transitions (polymorphic, phase and electronic) and chemical reactions.
S.I. Subbotin +2 more
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Diamond Accumulation in the Upper Mantle
Nature, 1970THE present high gradient of density in the upper mantle provides neutral buoyancy zones in which certain minerals may have been accumulated in the past or to which they may still be migrating. The necessary condition for progressive accumulation in such a zone is that the mineral concerned has opportunities of rising or sinking relative to its ...
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Phase Changes in the Upper Mantle
Science, 1967The C-region of the upper mantle has two transition regions 75 to 90 kilometers thick. In western North America these start at depths of 365 kilometers and 620 kilometers and involve velocity increases of about 9 to 10 percent. The locations of these transition regions, their general shape, and their thicknesses are consistent with, first, the ...
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1967
Publisher Summary The term “mantle” signifies the region of the earth that extends from the Mohorovicic discontinuity (lower boundary of the crustal layers) down to the central core. The “upper mantle” delimits the outer part of the earth's mantle and can be regarded as a spheroidal shell lying from the Mohorovicic discontinuity to a depth of nearly ...
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Publisher Summary The term “mantle” signifies the region of the earth that extends from the Mohorovicic discontinuity (lower boundary of the crustal layers) down to the central core. The “upper mantle” delimits the outer part of the earth's mantle and can be regarded as a spheroidal shell lying from the Mohorovicic discontinuity to a depth of nearly ...
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On the rheology of the upper mantle
Reviews of Geophysics, 1973Mechanisms permitting the steady state deformation of crystalline solids are critically reviewed, and an approximate constitutive relationship is derived for fluid phase transport in a partial melt. (Fluid phase transport has a linear stress dependence and an inverse squared grain size dependence.) A set of rheologic material constants for olivine ...
R. L. Stocker, M. F. Ashby
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Contributions to Mineralogy and Petrology, 1969
Despite several lines of indirect evidence, there has hitherto been little unambiguous evidence of a volatile bearing phase in the upper mantle. Mica has been found as a primary phase in several specimens of peridotite and one specimen of garnet lherzolite from the Lashaine volcano, northern Tanzania.
Dawson, J. B., Powell, D. G.
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Despite several lines of indirect evidence, there has hitherto been little unambiguous evidence of a volatile bearing phase in the upper mantle. Mica has been found as a primary phase in several specimens of peridotite and one specimen of garnet lherzolite from the Lashaine volcano, northern Tanzania.
Dawson, J. B., Powell, D. G.
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