Geochemistry of Chromium in the Earth’s Mantle

This book provides an analysis of an actual problem of the evolution of deep matter under the conditions of the upper mantle, transition zone, and uppermost lower mantle. This issue has a fundamental importance in geochemistry, petrology, mineralogy, and crystalochemistry of the mantle, at different depths. The authors discuss new experimental research on the composition and conditions of the chromium-bearing minerals genesis and their associations in the Earth’s mantle. The experimental data are compared with the natural mineral assemblages, allowing a refinement of the structure and composition of the deep Geospheres of the Earth. The results of the physicochemical experiments in the "MgO–SiO2–Cr2O3" model and the multicomponent systems play a major role in understanding the phase diagrams of these systems, the structural patterns of chromium-bearing phases and the influence of Cr on P-T parameters in the Earth’s mantle.

PART I. Chromium and chromium-bearing phases in the Earth

Chapter 1.1. High-pressure Cr-bearing phases in the Earth’s mantle

1.1.1. (Mg,Fe)Cr2O4 polymorphs

1.1.2. Majoritic and knorringitic garnets

1.1.3. Clinopyroxenes

1.1.4. (Mg,Fe)2SiO4 polymorphs

1.1.5. (Mg,Fe)SiO3 polymorphs

1.1.6. Other Cr-bearing phases in the Earth’s mantle

Chapter 1.2. Cr-rich rocks and mechanisms of Cr concentration in the Earth’s mantle

PART II. Experimental study of Cr-bearing phases at high pressures

Chapter 2.1. Experimental and analytical techniques

2.1.1. Multi-anvil apparatus

2.1.2. Toroidal (“anvil-with-hole”) apparatus

2.1.3. Analytical procedure

Chapter 2.2. Review of the experimental data

2.2.1. Systems with high-pressure components of garnets

2.2.2. Influence of Cr and other minor elements on Mg2SiO4 polymorphs

Chapter 2.3. Experimental study of the model system SiO2-MgO-Cr2O3 at high P-T parameters

2.3.1. Mg4Si4O12-Mg3Cr2Si3O12 section at 10-24 GPa and 1600 C

Phase relations

Compositions of the phases

Topology and phase diagram of the Mg4Si4O12-Mg3Cr2Si3O12 psedo-section

2.3.2. Mg2SiO4-MgCr2O4 section at 10-24 GPa and 1600 C

Phase relations

Compositions of the phases

Topology and phase diagram of the Mg2SiO4-MgCr2O4 psedo-section