Post-eruptive mobility of lithium in volcanic rocks

Area of Science:

• Geochemistry
• Volcanology
• Isotope geochemistry

Background:

• Volcanic rocks must preserve their composition from magmatic conditions through eruption and cooling for accurate petrogenetic studies.
• Post-eruptive processes can alter the chemical composition of volcanic rocks, complicating their interpretation.

Purpose of the Study:

• To investigate the impact of post-eruptive processes on the lithium (Li) inventory and isotopic composition of volcanic rocks.
• To understand the mobility and alteration of Li in welded ignimbrites from the Yellowstone-Snake River Plain magmatic province.

Main Methods:

• Analysis of phenocrysts and groundmass in microcrystalline and glassy ignimbrites.
• Comparison of Li concentrations and other trace elements between different cooling domains.
• Li isotopic measurements to track Li sources and alteration.

Main Results:

• Phenocrysts in slowly cooled ignimbrite interiors show significantly higher Li content than those in rapidly quenched glassy counterparts.
• Lithium (Li) remains mobile post-eruption, diffusing into phenocrysts as groundmass crystallization concentrates Li in residual melts.
• Li isotopic data indicate that cooling diffusion and surface degassing substantially modify volcanic rock Li inventories and isotopic signatures.

Conclusions:

• Post-eruptive processes, including diffusion during cooling and degassing, significantly affect the Li inventory and isotopic composition of volcanic rocks.
• The interpretation of Li in petrogenetic studies requires accounting for these post-eruptive modifications.
• Understanding Li mobility is crucial for reliable geochemical interpretations of volcanic materials.