Oxygen isotope fractionation in double carbonates

Area of Science:

• Geochemistry
• Isotope Geochemistry
• Mineralogy

Background:

• Oxygen and carbon isotope fractionations are crucial for understanding geological processes.
• Double carbonates exhibit complex isotopic behaviors influenced by their structure.
• Previous studies have explored isotope partitioning in simple carbonates, but less is known about double carbonates.

Purpose of the Study:

• To calculate and experimentally determine oxygen and carbon isotope fractionations in double carbonates.
• To investigate the influence of crystal structure on oxygen isotope partitioning.
• To compare experimental results with theoretical predictions for various double carbonate systems.

Main Methods:

• Increment method for calculating oxygen isotope fractionations.
• Synthesis experiments at 60°C and 100°C to measure isotope fractionations.
• Comparison of experimental data with theoretical models for different carbonate structures.

Main Results:

• Double carbonates with calcite structure are enriched in oxygen-18 compared to aragonite and mixed structures.
• Consistent oxygen isotope fractionation factors were obtained for double carbonates against quartz, calcite, and water across a wide temperature range (0-1200°C).
• Experimental carbon isotope fractionation for PbMg[CO3]2 and BaMg[CO3]2 against CO2 aligns with cerussite-CO2 predictions, not magnesite-CO2.

Conclusions:

• Crystal structure significantly impacts oxygen isotope partitioning in double carbonates.
• Theoretical calculations and experimental data show good agreement, validating the models.
• The findings provide insights into the effects of crystal structure and kinetics on oxygen isotope partitioning in these minerals.