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The Earth's Lower MantleUltramafic Lower-Mantle Mineral Association

The Earth's Lower Mantle: Ultramafic Lower-Mantle Mineral Association [The juvenile ultramafic lower mantle is composed of the mineral association: bridgmaniteBridgmanite + ferropericlase + CaSi-perovskiteCaSi-perovskite + free silica. Bridgmanite, with mg = 0.84–0.96 forms two compositional groups: low-Al and high-Al. High-Al bridgmaniteBridgmanite is richer in Fe and infers the characteristic of deeper layers in the lower mantle. The crystal structure of bridgmanite is orthorhombic through the entire lower mantle down to the D″ layer. The chemical composition of ferropericlaseFerropericlase is different from the predicted one with the magnesium index mg varying from 0.36 to 0.90. Low-Fe ferropericlase has a cubic rocksalt structure, which is stable throughout the entire lower mantle. Iron contents in both ferropericlase and bridgmanite and ferropericlase increase with pressure indicating the increase of Fe concentration in the lower mantle with depth. CaSi-perovskite is remarkably clean in its chemical composition with only minor admixtures of Ti, Al and Fe, but is enriched in trace elements. CaSi-perovskiteCaSi-perovskite within the lower mantle has a cubic structure which at low temperatures (in subsolidus conditions) may transfer into a tetragonal or orthorhombic structure. The presence of free silica in the lower mantle was identified in geological samples from all areas. In the upper part of the lower mantle it is represented by stishoviteStishovite; at a depth of 1600–1800 km stishovite transforms into the CaCl2-structured polymorph; and at the CMB, into a α-PbO2 phase seifertite. In addition to the major minerals, a variety of other mineral phases occurs in the lower mantle: Mg–Cr–Fe, Ca–Cr and other orthorhombic oxidesOrthorhombic oxides, jeffbeniteJeffbenite, ilmeniteIlmenite, native NiNative Ni and Fe, moissaniteMoissanite and some others.] http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png

The Earth's Lower MantleUltramafic Lower-Mantle Mineral Association

Part of the Springer Geology Book Series
Kaminsky, Felix V.
The Earth's Lower Mantle — May 23, 2017
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Publisher
Springer International Publishing
Copyright
© Springer International Publishing AG 2017
ISBN
978-3-319-55683-3
Pages
47 –160
DOI
10.1007/978-3-319-55684-0_4
Publisher site
See Chapter on Publisher Site

Abstract

[The juvenile ultramafic lower mantle is composed of the mineral association: bridgmaniteBridgmanite + ferropericlase + CaSi-perovskiteCaSi-perovskite + free silica. Bridgmanite, with mg = 0.84–0.96 forms two compositional groups: low-Al and high-Al. High-Al bridgmaniteBridgmanite is richer in Fe and infers the characteristic of deeper layers in the lower mantle. The crystal structure of bridgmanite is orthorhombic through the entire lower mantle down to the D″ layer. The chemical composition of ferropericlaseFerropericlase is different from the predicted one with the magnesium index mg varying from 0.36 to 0.90. Low-Fe ferropericlase has a cubic rocksalt structure, which is stable throughout the entire lower mantle. Iron contents in both ferropericlase and bridgmanite and ferropericlase increase with pressure indicating the increase of Fe concentration in the lower mantle with depth. CaSi-perovskite is remarkably clean in its chemical composition with only minor admixtures of Ti, Al and Fe, but is enriched in trace elements. CaSi-perovskiteCaSi-perovskite within the lower mantle has a cubic structure which at low temperatures (in subsolidus conditions) may transfer into a tetragonal or orthorhombic structure. The presence of free silica in the lower mantle was identified in geological samples from all areas. In the upper part of the lower mantle it is represented by stishoviteStishovite; at a depth of 1600–1800 km stishovite transforms into the CaCl2-structured polymorph; and at the CMB, into a α-PbO2 phase seifertite. In addition to the major minerals, a variety of other mineral phases occurs in the lower mantle: Mg–Cr–Fe, Ca–Cr and other orthorhombic oxidesOrthorhombic oxides, jeffbeniteJeffbenite, ilmeniteIlmenite, native NiNative Ni and Fe, moissaniteMoissanite and some others.]

Published: May 23, 2017

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