Magmatic Evolution of the Cenozoic Strzelin Volcanic Field (SW Poland) – preliminary results from Raman spectroscopy of CO2 inclusions in mafic phenocrysts

This study employs Raman spectroscopy to measure the density of CO₂ inclusions trapped in olivines and pyroxenes from Cenozoic volcanic rocks of the Strzelin Volcanic Field, a part of the Central European Volcanic Province (CEVP). In this region, monogenetic volcanic fields are the most common manifestation of intraplate alkaline basaltic volcanism, which is usually linked to lithospheric extension, melting of upwelling asthenosphere, and interaction between lithospheric and asthenospheric melts. Rocks from the SW Poland show characteristics of mantle sources that are among the least enriched. Nephelinites, basalts and trachybasalts in the Strzelin Field scoria cones and lava flows show evidence of variable differentiation during magma rise towards the surface, but important details, such as storage and crystallization depths of magma, remained poorly constrained.

The study of the density of CO₂ inclusions is crucial for determining the ascent history of magma, the depths and conditions of crystallization and the structure of magmatic systems. The Raman spectrum of CO₂ consists of two characteristic peaks at ca. 1285 and 1388 cm⁻¹ (Fermi Diad). The distance between these peaks is directly proportional to the density of the inclusion which increases with entrapment pressure and thus, it is possible to calculate the pressure at which the inclusion was sealed. Combined with the temperature of inclusion formation, this method provides a reliable and rapid geothermobarometer, offering insight into the dynamics of magmatic processes.

Preliminary results of our study of 45 inclusions in 8 olivine phenocrysts in nephelinite suggest that magma crystallization occurred at depths of ca. 23-24.5 km. These values correspond to lower to middle crustal levels in this area and thus to relatively deep parts of the magmatic systems. Further studies of nephelinites, as well as basalts and trachybasalts (which represent more evolved compositions that resulted in more explosive eruptions), should reveal more details about the magmatic systems, their structure and evolution, and their influence on the eruptive processes in this region.