INTRODUCTION

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

Chapter 2.4. Experimental study of multicomponent systems with Cr-bearing phases at high P-T parameters

2.4.1. Influence of minor Al concentrations on crystallization of garnet in the majorite-knorringite system

2.4.2. Crystallization of knorringitic garnet in the pyrolite system

Chapter 2.5. Structural patterns of Cr-bearing phases

PART III. Implication of experimental results to geochemistry of Cr in the Earth's mantle

Chapter 3.1. Mineral hosts for Cr

Chapter 3.2. Influence of Cr on structural pattern of the major mantle phases