Unveiling the Pressure–Temperature Stability of Kalsilite: Insights into Ultrapotassic Magmatism and Mantle Processes

Kalsilite (KAlSiO₄) is a key feldspathoid mineral diagnostic of ultrapotassic, silica-undersaturated magmas and metasomatized mantle sources. Despite its relevance as a potential reservoir of potassium and large lithophile elements in the Earth’s interior, the pressure–temperature stability fields of its polymorphs remain poorly constrained. This project aims to map the phase diagram of kalsilite through in situ synchrotron X-ray powder diffraction using the multianvil press at ESRF-ID06. We will track subsolidus phase relations, decomposition reactions, and melting boundaries, providing the first comprehensive assessment of its high-pressure and high-temperature behavior. The results will establish robust phase boundaries, clarify the mechanisms controlling kalsilite stability, and offer a comparative framework with related feldspathoids such as nepheline and leucite, shedding new light on the role of alkali-bearing phases in deep Earth processes.