The Postspinel Phases in the Mg2SiO4-Fe2SiO4 System
Science (New York, N.Y.)
|January 10, 1975
Summary
High-pressure experiments show that olivine and spinel minerals disproportionate into magnesium-iron oxide and stishovite (a high-pressure form of silica) under extreme conditions. This reveals new mineral phase transformations under deep Earth pressures.
Area of Science:
- Geochemistry
- Mineral Physics
- High-Pressure Science
Background:
- Olivine and spinel are key rock-forming minerals in Earth's mantle.
- Understanding their behavior under extreme pressure and temperature is crucial for deep Earth geodynamics.
Purpose of the Study:
- To investigate the phase transformations of olivine and spinel at high pressures and temperatures.
- To determine the products of disproportionation reactions in these minerals.
Main Methods:
- Samples of olivine and spinel with varying compositions were subjected to pressures up to 250 kilobars using a diamond anvil cell.
- In situ heating up to ~1700°C was achieved using a continuous-wave YAG laser.
- Temperature was measured using optical pyrometry.
- X-ray diffraction was used to analyze sample compositions after quenching and unloading.
Main Results:
- X-ray diffraction patterns confirmed that olivine and spinel disproportionate under the applied conditions.
- The observed products were identified as (Mg, Fe)O and stishovite (SiO(s)).
Conclusions:
- Olivine and spinel undergo disproportionation into (Mg, Fe)O and stishovite at pressures exceeding 250 kilobars and temperatures around 1700°C.
- These findings provide insights into mineral stability and transformations within Earth's deep interior.
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