Nanolite Crystallization in Volcanic Glasses: Insights From High-Temperature Raman Spectroscopy and Low-Temperature Rock-Magnetic Analysis

Abstract

High-temperature Raman spectroscopy offers a cost-effective alternative to extensive infrastructure and sensitive instrumentation for investigating nanolite crystallization in undercooled volcanic melts, a key area of interest in volcanology. This study examined nanolite formation in anhydrous andesite melts in situ at high temperatures, identifying distinct Raman peaks at 310 and 670 cm⁻¹ appearing above the glass transition temperature. The initial amorphous glass remained stable up to 655°C, beyond which Fe-Ti-oxide nanolites progressively formed at higher temperatures, as also confirmed by complementary XRD analysis. The evolution of the 310 cm⁻¹ peak depends only on the magnitude of nanolite crystallization, while the intensity of the 670 cm⁻¹ peak is temperature-dependent and challenging to observe above 500°C. Complementary low-temperature rock-magnetic analyses confirmed Fe-Ti-oxide nanocrystallization with nanolites around 20 nm in diameter. The study tested lasers of different wavelengths (from 355 to 514 nm) and found the green laser to be the most effective for collecting spectra at both room and high temperature. However, above 720°C, black body radiation significantly hinders Raman observation with the green laser when using a non-confocal setup and analyzing poorly transparent samples. If higher temperature measurements are desired, switching to a confocal setup and using lower wavelength lasers should be considered. This research offers a protocol for studying nanolite formation and melt dynamics at high temperatures, providing a foundation for future studies of volcanic processes.