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Recent experiments have largely reshaped our knowledge of maar volcanism. A new evolutionary model promoting the role of explosion depth and vent migration during the formation of maars has provided an alternative approach to previous models. Despite a few attempts to test this model with real cases, there is still a need for field-based studies exploring the depositional characteristics of maars to better understand the factors affecting the model constraints. More investigations on less known felsic maars are required to elucidate the possible differences from their more common mafic counterparts. Here, we explore compositionally distinct monogenetic clusters within the Acıgöl caldera (NW of Central Anatolian Volcanic Province, CAVP), with four felsic maars (İnallı, Kalecitepe, Acıgöl, and Korudağ) and one mafic maar (İcik). Our field observations reveal a successive formation between rhyolitic maars and adjacent lava domes. The mugearitic İcik coalescent maar and the adjacent scoria cone are synchronously formed, which is disclosed by the intercalation of the maar and scoria cone deposits. The geochemistry of the maar juveniles suggests a parental basaltic magma source that has been possibly differentiated by varying degrees of fractional crystallization. Our findings identify the main factors in maar formation (i.e., optimum scaled depth-OSD, water-magma interaction, and basement lithology). We also determine some differences between the felsic and mafic maars in the region, such as higher juvenile content, less amount of sedimentary structure, and a clear transition from phreatomagmatic to magmatic explosions through the end of stratigraphy. All these reflect the complexity of maars, mainly formed by different depths of explosions that occurred in the shallowest few hundred meters rather than a systematic incremental decrease of the eruption locus. Further geophysical and geochronological studies will complete our proposed evolutionary model for the youngest monogenetic activity in the Acıgöl caldera that would also warrant volcanic hazard assessment due to the presence of low-velocity anomalies, shallow Curie depths, and prevalent geothermal activity.

The petrologic diversity of volcanic rocks reflects the dynamics of magma reservoirs and the temporal evolution of magma chemistry can provide valuable information for hazard assessment. While some stratovolcanoes monotonously produce intermediate magmas (55–68 wt% SiO2), dominantly erupted magma types (e.g., basaltic andesite, andesite or dacite) frequently differ even between neighboring volcanoes. If such differences arise due to thermal maturation processes over time or are predetermined by other properties of magmatic systems remains poorly understood. This study helps to elucidate the underlying factors modulating the chemistry of the magma preferentially erupted by Nevado de Toluca volcano in Central Mexico. We present a new dataset of bulk-rock and mineral chemistry spanning the entire 1.5 Million years of the volcanos’ eruptive history. The results reveal that Nevado de Toluca dacites and minor andesite originate in a stable configuration of pre-eruptive processes and plumbing system architecture by hybridization between an upper crustal silicic mush and deeper sourced basaltic andesite magmas. Yet, a subtle trend toward increasing silica content with time (2 wt% in 1.5 Ma) and episodicity in magma hybridization conditions are observed. We use thermal simulations of pulsed magma injection to probe the controlling variables on the temporal variation and compositional mode of magma geochemistry. The results show that the subtle temporal trend toward increasing bulk-rock SiO2 content is plausibly explained by slightly dropping recharge rates and continued upper crustal reservoir growth. Our modeling also shows that the dominant composition of eruptible magmas (“petrologic mode”) can shift as a function of magma flux, extrusive:intrusive ratio and temperature of the recharge magma. A comparison of SiO2 whole rock distributions for monotonous Mexican stratovolcanoes and their peripheral cones shows that their petrologic modes vary in concert, indicating that the recharge magma chemistry or temperature is a major control on the preferentially erupted magma composition for these volcanoes.

Linking tectonic setting to eruptive activity in volcanic arcs provides a framework to understand processes that control the production, accumulation and eruption of magma on Earth. We use the Holocene eruptive records of 162 volcanoes, which are selected based on an assessment of recording biases, to calculate the probability of recording large eruptions (between Magnitudes 4 and 7). We quantify regional variability in the sizes of volcanic eruptions and compare it with subduction parameters influencing the generation, transport and storage of magma. Given the tectonic setting of a subduction zone is multidimensional (e.g., age, speed, obliquity of the subducting plate) we use a graphical model to explore the strength of probabilistic relationships between tectonic and volcanic variables. The variable that exhibits the strongest probabilistic relationship with eruption size is convergence obliquity, with larger eruptions favored in settings where convergence is normal. Normal convergence favors the storage and accumulation of larger volumes of magma, whereas oblique convergence favors the transport and eruption of smaller volumes of magma. In low-obliquity arcs where magma storage is promoted, the subduction of older slabs results in higher mantle productivity, which thermally favors the accumulation of eruptible magma and larger eruptions on average. However, the highest mantle productivity also results in more frequent magma injection and pressurization of crustal reservoirs. Consequently, arcs with moderate slab ages and low obliquity produce the highest proportion of larger eruptions. In high-obliquity arcs mantle productivity does not dominantly control eruption sizes. Instead, thinner crust facilitates frequent transport of magma to the surface, resulting in smaller eruptions. For the largest eruptions on Earth (e.g., Magnitude 8), however, accumulation of eruptible magma will be dominantly controlled by thermomechanical modification of the crust and not the frequency of magma intrusion. Despite the importance of convergence obliquity, our results show that variability in the sizes of volcanic eruptions is controlled by complex relationships with other parameters including slab age and crustal thickness. By using a graphical model, we have been able to explore complex volcano-tectonic relationships. We suggest a similar approach could be extremely valuable for exploring other complex multidimensional datasets within the Earth Sciences.

The Holuhraun–Bárdarbunga (Iceland) eruption lasted approximately 6 months. Magma propagated laterally through a 40 km long dyke, while Bárdarbunga caldera was collapsing. This event was intensely monitored, providing an opportunity to investigate the relationships between eruption dynamics and erupted products. Whole rock and melt inclusion data do not show chemical variations of magma during the eruption. Nevertheless, zoning patterns in clinopyroxene suggest temporal variations of intensive parameters during crystallization. We investigated the chemical zoning of clinopyroxene using a data driven approach, on major and trace elements analyses from lava flow lobes emplaced during the eruption. We applied hierarchical clustering (HC) to identify compositional groups based on major and trace element chemistry. This analysis identifies five compositional groups, which can be associated with specific petrographic features. One cluster represents the chemistry of hourglass sectors, two constitute the oscillatory zoned mantle of the crystals, one cluster corresponds to a seldom present bright rim (in back scattered electron images) in the outer portions of the crystals, and a last one represents most of the outer rims. HC applied to trace elements also identifies five compositional clusters, which highlight progressively more evolved clinopyroxene compositions from the core to the rim of the crystals. Two of the clusters identified with trace elements corresponds to major element clusters. All together the data suggest that the chemical zoning in the inner portions of the clinopyroxene crystals was generated by crystallization in the magma reservoir and interaction between hot magma propagating through the dyke and unerupted magma cooling within the dyke. The fraction of zones produced by interaction with colder portion of the magma residing within the dyke dropped during the eruption, potentially signaling the thermal maturation of the dyke. Some of the analyses reveal that relatively close to the eruption time (i.e., the outer portions of the crystals) the dyke intercepted a lens of low temperature magma with a chemical composition that is distinguishable from the 2014 to 2015 Bárdarbunga eruption. Our approach can provide insights on the evolution of deep processes occurring during long-lasting eruptions by combining the analysis mineral chemistry of erupted products with multiparametric monitoring signals.