Date of Graduation

Spring 2023


Master of Natural and Applied Science in Geography, Geology, and Planning


Geography, Geology, and Planning

Committee Chair

Gary Michelfelder


Geochemical microanalysis of apatite crystals was conducted to model the composition and thermodynamic conditions of melts involved in explosive eruptions at Láscar volcano (NE Chile). Apatite crystals were extracted from representative samples of Láscar’s eruptive stages II (Soncor ignimbrite), III (Tumbres scoria deposit), and IV (1993 CE pumice). I used electron microprobe analysis, laser ablation - inductively coupled plasma mass spectrometry, and secondary ionization mass spectrometry to generate quantitative compositional maps and gather data of major, trace, and volatile element contents in crystals. Major and trace-element behavior in Láscar apatites reflects general whole-rock compositional trends of Láscar and other Andean volcanic centers. Additionally, trace element signatures of Láscar apatite mirror those of wholerock and glass data of their respective samples, making it an accurate compositional proxy for their parental melt. My crystal- and sample-scale textural observations reveal that Láscar apatite records a late stage of magmatic evolution where the compositional behavior of melts is primarily controlled by magma mixing and subsequent volatile saturation and exsolution. Thermodynamic effects of volatile exsolution drive temperature and compositional changes that allow for apatite syn-eruptive crystallization. Observations suggest that microphenocrystic apatite can record the composition and physical conditions of melts in the weeks to months before paroxysmic events at Láscar, making them an accurate proxy for the composition of melts in the weeks to months previous to past eruptions.


Láscar, apatite, microanalysis, volatile saturation, explosive eruptions, syneruptive crystallization

Subject Categories

Geochemistry | Geology | Volcanology


© Cesar Andres Bucheli Olaya

Available for download on Saturday, May 09, 2026

Open Access