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Diamond formation due to a pH drop during fluid-rock interactions
Dimitri A Sverjensky1, Fang Huang1
1Department of Earth and Planetary Sciences, Johns Hopkins University, Charles and 34th Streets, Baltimore, Maryland 21218, USA.
Nature Communications
|November 4, 2015
Summary
Diamond formation can occur without changes in oxidation state. New research shows that decreasing pH during water-rock interactions can trigger diamond precipitation in deep Earth fluids.
Area of Science:
- Geochemistry
- Mineralogy
- Petrology
Background:
- Traditional diamond formation theories focus on redox reactions from methane or carbon dioxide.
- Previous models overlooked the role of ions and pH changes in deep Earth fluids.
- The impact of water-rock interactions on diamond genesis remains largely unexplored.
Purpose of the Study:
- To investigate the potential for diamond formation driven by pH changes during water-rock interactions.
- To develop a quantitative theory for diamond genesis linked to fluid migration and rock reactions.
- To explore diamond formation mechanisms independent of oxidation-reduction reactions.
Main Methods:
- Utilized a theoretical model of deep Earth fluids incorporating aqueous ions.
- Simulated irreversible reactions between deep fluids and eclogite at high pressure and temperature (900°C, 5.0 GPa).
- Analyzed the impact of pH and oxygen fugacity on mineral precipitation, including diamond.
Main Results:
- Demonstrated that a significant drop in pH can induce diamond formation.
- Identified the formation of diamond and secondary minerals due to fluid-rock interactions.
- Showed that diamond can precipitate under nearly constant oxygen fugacity conditions.
- Established a new quantitative theory linking diamond formation to water-rock reactions.
Conclusions:
- Diamond formation in the deep Earth can be driven by pH decreases during water-rock interactions.
- This process does not require changes in oxidation state, challenging previous assumptions.
- The findings provide a new perspective on the genesis of diamonds within the Earth's mantle.
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