Magma contains information on its source and on the processes the magma experienced en route to the surface. This information is, however, locked in the chemical and isotopic composition of minerals and groundmass. Petrologists can help understand volcanic phenomena and geochemical processes. The recent basaltic eruptions on Iceland and in the Canary Islands have now given us the opportunity to study the evolution of individual rift eruptions in extreme detail. Time-resolved sampling of erupted products allows detection of mineralogical and chemical changes on a daily to weekly timescale and gives us the opportunity to correlate this information with seismic data and changes in eruptive style. This allows us to identify rapid changes in magma composition and interpret these changes in respect to magma sources, magma storage, and magma transport.

The recent eruptions at Fagradalsfjall have shown rapid compositional changes in major and trace elements during the eruption, which has been interpreted as reflecting different mantle components that are sampled during a single eruption. Stable isotopes such as oxygen remain virtually unchanged, however, through the 2021 to 2022 events. The 2021 Tajogaite eruption on La Palma also showed rapid changes in lava composition during the first weeks of the eruption. This together with the seismic record indicates that the eruption was initially fed from a crustal reservoir, but later from a deeper upper mantle reservoir. In contrast to Fagradalsfjall, initial magmas show variable oxygen isotope compositions. The implication of these commonalities and differences are discussed in full in this presentation.

The Ohře/Eger Graben (OEG) marks one of the important spots of the Mesozoic to Cenozoic rift-related volcanic activity in central Europe, and extends over a length of more than 250 km. Here, the volcanic edifices comprise monogenetic maar-diatremes, scoria cones, and lava domes as well as large polygenetic stratovolcanoes. Their composition ranges between melilitite, nephelinite, basanite, and phonolite. It is precisely the northern flank of the OEG, where the timing of eruption has been sporadically dated with outdated methods.

Recent 40Ar/39Ar age analysis has provided new insights, revealing a chronological sequence spanning from 77 to 10 Ma and reshaping our understanding of eruption dynamics in the northern OEG rift structure. The oldest volcanics are melilite-bearing rocks with ages of around 77 to 65 Ma. With eruption ages at 10 Ma, the nephelinitic Landsberg and Buchhübel, as well as the basanitic Ascherhübel of the western Elbe Zone are the youngest volcanoes from the northern rift flank. Volcanoes of the Erzgebirge and Lusatia erupted between 37 and 29 Ma and 35 to 26 Ma, respectively. The age determination of the Vogtland yields younger ages at 30 to 23 Ma.

Melilite-bearing igneous rocks are known to be derived from the partial melting of dolomitic garnet-bearing lherzolite under CO₂-rich conditions at pressures between 27 and 40 kbar. However, there are still unresolved questions regarding their magma evolution. The Vogtland volcanic field is part of the Central European Cenozoic Igneous Province and hosts various olivine melilitite and melilite-bearing olivine-nephelinite diatremes, such as those at Bösenbrunn and Burkhardtsgrün.

The olivine melilitite and melilite-bearing rocks of these two locations are characterized by variable olivine content, often with skeletal or "hopper" morphology. They also contain clinopyroxene, melilite with a typical "pag" structure, magnetite, Cr-spinel, rare nepheline, apatite, zircon, and perovskite. Within some melilitites, the presence of reversely zoned melilite in clinopyroxene-bearing melilitites is probably the consequence of the co-precipitation of melilite with clinopyroxene. As clinopyroxene crystallization initiates, the Al/Mg ratio of the residual melt rises, causing a gradual depletion of åkermanite content from core to rim within the crystallizing melilites. Variations in major and trace elements, along with zoning patterns in coexisting minerals, may be influenced by their affiliation with either Ca-rich or -poor magma series. Trace-element fractionation during differentiation of these parental magmas suggests the existence of two mantle-derived magmas: (i) a melilite-bearing series formed at higher pressures (ca. 35 kbar), which was originally enriched in CO₂, Sr, Nb, and REE (La, Ce, etc) and differentiated at shallower depths, while (ii) a Ca-poor magma began fractionating only at around 17 kbar during magma ascent.

Magneto-mineralogical properties of volcanic rocks can be used to study their emplacement conditions and thus the eruptive behaviour of volcanoes. Two ICDP cores were drilled into the effusive and explosive units of the Bažina Maar, located in the Czech Republic. The drilled volcanic units are up to 160 m thick in total, and consist of lapilli tuff and effusive (sub-)volcanic rocks which are overlain by unconsolidated, highly weathered lapilli and scoria deposits. The units are locally overprinted by apatite-bearing sequences, possibly of hydrothermal origin. We used a KLY-5A Kappabridge to measure the out-of-phase (op) in addition to the traditionally measured in-phase (ip) temperature-dependent magnetic susceptibility and determined Curie-Temperatures (T_c), field depend magnetic susceptibility as well as the anisotropy of magnetic susceptibility (AMS). The most common sources for an op component in igneous rocks are vicous relaxation of superparamagnetic/single domain (titano-)magnetite grains and weak field hysteresis of ferrimagnetic phases like titanomagnetite and pyrrhotite. Ip and op T_cs between 170 – 300°C suggest a Ti-rich titanomagnetite as the main ferrimagnetic phase. Higher T_cs within the explosive products between 450 – 580°C suggest maghemitisation of the juvenile titanomagnetite. The ip AMS component for the effusive volcanic rocks reveals a moderate to steeply inclined magnetic foliation, suggesting an upwards flow as emplacement mechanism. For the lapilli units, the op AMS response is oblique to the ip AMS signal, revealing a magnetic subfabric. Our study demonstrates that the systematic study of ip and op susceptibility can add key information to unravel complex volcanological processes.

The Haukadalur thermal area in southwestern Iceland comprises numerous individual thermal springs, geysers, and hot pots arranged roughly in a north-south orientation. Situated on the eastern slope of a hill, this field is delimited by fissures associated with the Western Volcanic Zone. This study is based on high-resolution unmanned aerial vehicle (UAV) equipped with optical and radiometric infrared cameras to identify over 350 distinct thermal spots across various zones, and puts these in a larger context from geophysical experiments undertaken in the region. Close examination revealed that geysers and hot areas are clusters, but are generally aligning with the presumed tectonic trend in the region. Repeat thermal surveys realized in the past 10 years show systematic and chaotic changes in activity of the geysers. This presentation delves into the structural correlation between the deeper and shallower segments of these geysers, influence of the external effects and water table, and is shedding light on the mechanisms underlying geyser and hot pot activity, with broader implications applicable to thermal fields worldwide.