Volatile Content Implications of Increasing Explosivity of the Strombolian Eruptive Style along the Fracture Opening on the NE Villarrica Flank: Minor Eruptive Centers in the Los Nevados Group 2

Potential flank eruptions at the presently active Villarrica, Southern Andes Volcanic Zone (33.3–46 °S) require the drawing of a comprehensive scenario of eruptive style dynamics, which partially depends on the degassing process. The case we consider in this study is from the Los Nevados Subgroup 2 (LNG2) and constitutes post-glacial minor eruptive centers (MECs) of basaltic–andesitic and basaltic composition, associated with the northeastern Villarrica flank. Petrological studies of the melt inclusions volatile content in olivine determined the pre-eruptive conditions of the shallow magma feeding system (<249 Mpa saturation pressure, 927–1201 °C). The volatile saturation model on “pressure-dependent” volatile species, measured by Fourier Transform Infrared Microspectrometry (FTIR) (H2O of 0.4–3.0 wt.% and CO2 of 114–1586 ppm) and electron microprobe (EMP), revealed that fast cooling pyroclasts like vesicular scoria preserve a ~1.5 times larger amount of CO2, S, Cl, and volatile species contained in melt inclusions from primitive olivine (Fo76–86). Evidence from geological mapping and drone surveys demonstrated the eruption chronology and spatial changes in eruption style from all the local vents along a N45° corridor. The mechanism by which LNG2 is degassed plays a critical role in increasing the explosivity uphill on the Villarrica flank from volcanic vents in the NE sector (<9 km minimum saturation depth) to the SW sector (<8.1 km), where many crystalline ballistic bombs were expulsed, rather than vesicular and spatter scoria.

Thermal remote sensing reveals communication between volcanoes of the Klyuchevskoy Volcanic Group

Volcanoes are traditionally considered isolated with an activity that is mostly independent of the surrounding, with few eruptions only (< 2%) associated with a tectonic earthquake trigger. Evidence is now increasing that volcanoes forming clusters of eruptive centers may simultaneously erupt, show unrest, or even shut-down activity. Using infrared satellite data, we detail 20 years of eruptive activity (2000–2020) at Klyuchevskoy, Bezymianny, and Tolbachik, the three active volcanoes of the Klyuchevskoy Volcanic Group (KVG), Kamchatka. We show that the neighboring volcanoes exhibit multiple and reciprocal interactions on different timescales that unravel the magmatic system’s complexity below the KVG. Klyuchevskoy and Bezymianny volcanoes show correlated activity with time-predictable and quasiperiodic behaviors, respectively. This is consistent with magma accumulation and discharge dynamics at both volcanoes, typical of steady-state volcanism. However, Tolbachik volcano can interrupt this steady-state regime and modify the magma output rate of its neighbors for several years. We suggest that below the KVG the transfer of magma at crustal level is modulated by the presence of three distinct but hydraulically connected plumbing systems. Similar complex interactions may occur at other volcanic groups and must be considered to evaluate the hazard of grouped volcanoes.

The Rare Trachyandesitic Lavas at Mount Etna: A Case Study to Investigate Eruptive Process and Propose a New Interpretation for Magma Genesis

The growth of Mount Etna volcano reflects the superimposition of various eruptive centers, the most voluminous of which is the Ellittico, whose stratigraphic sequence is well exposed on the steep walls of Valle del Bove. The uppermost levels of the sequence have been sampled and investigated through a new set of geochemical data on mineral phases and bulk rock. Sampled rocks display a marked bimodality with aphyric banded trachyandesites, which are some of the most evolved and rare products of the entire Etnean succession (SiO2 58–60 wt.%), intercalated in plagioclase rich porphyritic mugearites (SiO2 49–50 wt.%, P.I. 35–40). In this paper, we provide a detailed textural, mineralogical, and chemical characterization of these products, providing a new interpretative model for their genesis and significance in the context of the Etnean system. Our approach discusses, in a critical way, the “classic” fractional crystallization model of magmas, not supported by field evidence, and proposes a novel hypothesis in which the aphyric-banded trachyandesites represent be the primary products of a gas-induced partial melting of hypabyssal sills and dykes. This hypothesis represents a step towards a comprehensive description of igneous systems that takes into account not exclusively the evolution of basaltic melts, but also the role of volatile contributions in governing volcanic behavior.

The Volsci Volcanic Field (central Italy): Anatomy of a tectonically controlled, carbonate-seated, volcanic activity

&lt;p&gt;The Quaternary Volsci Volcanic Field (VVF) represents one of the products of the west-directed subduction of the Adriatic slab that drove the development of the Apennine mountain belt in central Italy. Here, we present new results on the eruptive history and the diatreme processes of exemplar tectonically controlled carbonate-seated maar-diatreme volcanoes. The VVF is defined by phreatomagmatic surge deposits, rich in accidental carbonate lithics, and subordinate Strombolian scoria fall deposits and lava flows, locally sourced from some tens of monogenetic eruptive centers, mostly consisting of small volume (0.01-0.1 km3) tuff rings and scoria cones. In light of new 40Ar/39Ar geochronological data and compositional characterization of juvenile eruptive products, we refine the history of VVF activity and envisage the implications on the pre-eruptive magma system and the continental subduction processes involved. Leucite-bearing, high-K (HKS) magmas mostly fed the early phase of activity (&amp;#8764;761&amp;#8211;539 ka); primitive, plagioclase-bearing (KS) magmas appeared during the climactic phase (&amp;#8764;424&amp;#8211;349 ka), partially overlapping with HKS ones, and then prevailed during the late phase of activity (&amp;#8764;300&amp;#8211;231 ka). As the volcanic centers cluster along high-angle faults, we investigate the relationships between faulting and explosive magma-water interaction, as well as the distribution pattern of the eruptive centers. New field data allowed to retrieve the fold-and-thrust belt structure associated with the eruptive centers. Analysis of componentry, grain-size, degrees of whiteness and roundness of carbonate lithic inclusions, along with their micropaleontological features, has allowed to establish volcano tectonic correlations. In our interpretation, the clustering of eruptive centers is controlled by tectonic features. Specifically, a first order control is tentatively related to crustal laceration and deep magma injection along a ENE-trending Quaternary lateral tear in the slab and to Mesozoic rift-related normal faults. A second-order control is provided by orogenic structures (mainly thrust and extensional faults). In particular, magma-water explosive interaction occurred at multiple levels (&lt; 2.3 km depth), depending on the structural setting of the Albian-Cenomanian aquifer-bearing carbonates, which are intersected by high-angle faults. The progressive comminution, rounding and whitening of entrained carbonate lithics allow us to trace multistage diatreme processes. Finally, our findings bear implications on volcanic hazard assessment in the densely populated (&gt; 0.4 million people) areas of the Volsci Range and adjoining Pontina Plain and Middle Latin Valley.&lt;/p&gt;

Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile

&lt;p&gt;In the Atacama Desert, at the Precordillera of northern Chile, a series of Paleocene-Eocene caldera deposits and ring-faults are exceptionally well-preserved&lt;sup&gt;1&lt;/sup&gt;. Here we aim to build on previous mapping efforts to consider the location, timing and style of pre, syn and post caldera volcanism in the region. We focus on the partially nested caldera complexes of Lomas Bayas and El Durazno&lt;sup&gt;2,3&lt;/sup&gt; where deposits record several stages of caldera evolution (pre-collapse, collapse/intra-caldera and extra-caldera, resurgence and post-collapse eruptive deposits). The pre-caldera basement is a thick sequence of early Paleocene mafic lavas&lt;sup&gt;4, 5&lt;/sup&gt;. The caldera complex formed between around 63 and 54 Ma&lt;sup&gt;4, 5&lt;/sup&gt;. Both calderas constitute subcircular structures approximately 13 km in diameter and are cut by several NNW to NNE-trending felsic dikes which are spatially related to felsic domes interpreted as resulting from post caldera formation unrest&lt;sup&gt;1,&lt;/sup&gt;&lt;sup&gt;4&lt;/sup&gt;. These calderas have been interpreted as part of the Carrizalillo megacaldera complex&lt;sup&gt;2 &lt;/sup&gt;. We combine field observations, such as the attitude of dikes, as well as information on their dimension and composition, the size, location and composition of domes and lava flows, as well as the evidence of the regional stress field operating during the caldera evolution from measurements of fault kinematics. This data will be used as the input to finite element method models to investigate the effect of nested caldera geometry, ring-faults and crustal heterogeneities on the location of domes and eruptive centers generated during caldera unrest. The results will be potentially useful for constraining models of eruption forecasting during periods of unrest in calderas and ore deposition models which have been shown to be linked to caldera structure and magma emplacement.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1 &lt;/sup&gt;Rivera, O. and Falc&amp;#243;n, M. (2000). Calderas tipo colapso-resurgentes del Terciario inferior en la Pre-Cordillera de la Regi&amp;#243;n de Atacama: Emplazamiento de complejos volcano-plut&amp;#243;nicos en las cuencas volcano-tect&amp;#243;nicas extensionales Hornitos y Indio Muerto: IX Congreso Geol&amp;#243;gico Chileno, v. 2.&amp;#160;Soc. Geol. de Chile, Puerto Varas.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2 &lt;/sup&gt;Rivera, O., and Mpodozis, C. (1994). La megacaldera Carrizalillo y sus calderas anidadas: Volcanismo sinextensional Cret&amp;#225;cico Superior-Terciario inferior en la Precordillera de Copiap&amp;#243;, paper presented at VII Congreso Geol&amp;#243;gico Chileno. Acad. de Cienc. del Inst. Chilecol. de Geol. de Chile, Concepci&amp;#243;n.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3 &lt;/sup&gt;Rivera, O. (1992). El complejo volcano-plut&amp;#243;nico Paleoceno-Eoceno del Cerro Durazno Alto: las calderas El Durazno y Lomas Bayas, Regi&amp;#243;n de Atacama, Chile. Tesis Departamento de Geolog&amp;#237;a, Universidad de Chile, 242. (Unpublished).&lt;/p&gt;&lt;p&gt;&lt;sup&gt;4 &lt;/sup&gt;Ar&amp;#233;valo, C. (2005). Carta Los Loros, Regi&amp;#243;n de Atacama. Servicio Nacional de Geolog&amp;#237;a y Miner&amp;#237;a, Carta Geol&amp;#243;gica de Chile, 92, 1(100.000), 53 p.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;5 &lt;/sup&gt;Iriarte, S., Ar&amp;#233;valo, C., Mpodozis, C. (1999). Mapa Geol&amp;#243;gico de la Hoja La Guardia, Regi&amp;#243;n de Atacama. Servicio Nacional de Geolog&amp;#237;a y Miner&amp;#237;a. Mapas Geol&amp;#243;gicos, 13, 1(100.000).&lt;/p&gt;

Magmatic processes under Villarrica stratovolcano (Central Southern Volcanic Zone, Chile).

&lt;p&gt;Magmatic arcs are usually considered to be major sites of new continental crust formation. However, the detailed differentiation processes that produce the characteristic calc-alkaline trends are still controversial. More particularly, the depth of differentiation in the arc crustal column and possible changes during the lifespan of a volcano are current subject of discussion.&lt;/p&gt;&lt;p&gt;The Central Southern Volcanic Zone (CSVZ) in Chile is characterized by a thin crust (~ 35 km; Hickey-Vargas et al., 2016) and by the presence of a major dextral transpressional crustal scaled structure (Liqui&amp;#241;e-Ofqui Fault Zone), two features that favor a rapid ascent of magmas from the mantle wedge to the surface. Recent petrological data acquired on volcanoes of the CSZV further indicate that most of the differentiation takes place at about 0.2 GPa, a depth corresponding to a major intracrustal discontinuity. However, for Villarrica stratovolcano (VR; 39.3&amp;#176;S, 71.6&amp;#176;W), estimates suggest two depths of differentiation, respectively at 0.8 and 0.2 GPa (Morgado et al. 2015, 2017).&lt;/p&gt;&lt;p&gt;VR is one of the most active volcanoes in the Andean Cordilleras. Since the mid 80&amp;#8217;s, it has been constantly degasing through an open conduit filled by a summit lava lake. Several Holocene, monogenetic small eruptive centers (SECs) surround VR which forms together with Quetrupill&amp;#225;n and Lanin stratovolcanoes a NW-SE oriented chain. It gives thus a perfect opportunity to study how the mentioned features influence the differentiation processes, their corresponding depth and the observed differentiation trends. VR is mainly composed of basaltic andesites and basaltic lavas and pyroclasts with less andesitic lavas and minor dacitic &amp;#8211; rhyodacitic domes, while rocks from Quetrupill&amp;#225;n and Lanin are compositionally more evolved (e.g. Hickey-Vargas et al., 1989).&lt;/p&gt;&lt;p&gt;Here we present mineral compositions (plagioclase, olivine, clinopyroxene) and whole-rock (lavas, pyroclasts) geochemical data for different units of VR as well as for some nearby SECs (Los Nevados, Chaillup&amp;#233;n, San Jorge). The WR data combined with published analyses define a single differentiation trend extending from ~50 &amp;#8211; 71 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;, with a compositional &amp;#8220;Daly&amp;#8221; gap between 58 &amp;#8211; 62 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;. Moreover, a few VR samples have high Mg# up to 62 (SiO&lt;sub&gt;2&lt;/sub&gt; 50.3-52.6, MgO 7.98 wt.%) and a tholeiitic affinity (e.g. AFM, K&lt;sub&gt;2&lt;/sub&gt;O/Yb vs. Ta/Yb). The most mafic, tholeiitic basalts found in the area where produced by the proximate San Jorge SEC (Mg# 69, SiO&lt;sub&gt;2&lt;/sub&gt; 50.6, MgO 9.5 wt.%) and interpreted by McGee et al. (2019) as reflecting a deep, melt-exhausted region of the mantle wedge. Major- and trace elements data together with supportive mass balance modelling and thermodynamic simulations with rhyolite-MELTS imply fractional crystallization as a major differentiation process.&lt;/p&gt;

Geochemistry of noble gas and CO2 in fluid inclusions from lithospheric mantle beneath Eifel and Siebengebirge (Germany)

&lt;p&gt;The study of fluid inclusions (FI) composition (He, Ne, Ar, CO&lt;sub&gt;2&lt;/sub&gt;) integrated with the petrography and mineral chemistry of mantle xenoliths representative of the Sub Continental Lithospheric Mantle (SCLM) is a unique opportunity for constraining its geochemical features and evaluating the processes and the evolution that modified its original composition. An additional benefit of this type of studies is the possibility of better constraining the composition of fluids rising through the crust and used for volcanic or seismic monitoring. &amp;#160;&lt;/p&gt;&lt;p&gt;In this respect, the volcanic areas of Eifel and Siebengebirge in Germany represent a great opportunity to test this scientific approach for three main reasons. First, these volcanic centers developed in the core of the Central European Volcanic Province where it is debated whether the continental rift was triggered by a plume (Ritter, 2007 and references therein). Second, Eifel and Siebengebirge formed in Quaternary (0.5-0.01 Ma) and Tertiary (30-6 Ma), respectively, thus spanning a wide range of age. Third, Eifel is characterized by the presence of CO&lt;sub&gt;2&lt;/sub&gt;-dominated gas emissions and weak earthquakes that testify that local magmatic activity is nowadays dormant, but not ended (e.g., Br&amp;#228;uer et al., 2013). It is thus important to better constrain the noble gas signature expected in surface gases in case of magmatic unrest.&lt;/p&gt;&lt;p&gt;This work focuses on the petrological and geochemical study of mantle xenoliths sampled in the West Eifel and Siebengebirge volcanic areas (Germany) and aims at enlarging the knowledge of the local SCLM. Gautheron et al. (2005) carried out the first characterization of noble gases in FI of crystals analyzed by crushing technique (as in our study) but limited to olivines and to West Eifel eruptive centers. Here, we integrate that study by analyzing olivines, orthopyroxenes and clinopyroxenes from a new suite of samples and by including two eruptive centers from Siebengebirge volcanic field (Siebengebirge and Eulenberg quarries).&lt;/p&gt;&lt;p&gt;Xenoliths from the Siebengebirge localities are characterized by the highest Mg# for olivine, clinopyroxene and Cr# for spinel, together with the lowest Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; contents for both pyroxenes, suggesting &amp;#160;that the mantle beneath Siebengebirge experienced high degree of melt extraction (up to 30%) while metasomatic/refertilization events were more efficient in the mantle beneath West Eifel.&lt;/p&gt;&lt;p&gt;In terms of CO&lt;sub&gt;2&lt;/sub&gt; and noble gas concentration, clinopyroxene and most of the orthopyroxene show the highest gas content, while olivine are gas-poor. The &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He varies between 5.5 and 6.9 Ra. These values are comparable to previous measurements in West Eifel, mostly within the range proposed for European SCLM (6.3&amp;#177;0.4 Ra), and slightly below that of MORB (Mid-Ocean Ridge Basalts; 8&amp;#177;1Ra). The Ne and Ar isotope ratios fall along a binary mixing trend between air and MORB-like mantle. He/Ar* in FI and Mg# and Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; content in minerals confirm that the mantle beneath Siebengebirge experienced the highest degree of melting, while the metasomatic/refertilization events largely affected the Eifel area.&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Br&amp;#228;uer, K., et al. 2013. Chem. Geol. 356, 193&amp;#8211;208.&lt;/p&gt;&lt;p&gt;Gautheron, C., et al. 2005. Chem. Geol. 217, 97&amp;#8211;112.&lt;/p&gt;&lt;p&gt;Ritter, J.R.R., 2007. In: Ritter, J.R.R., Christensen, U.R. (Eds.), Mantle Plumes: A Multidisciplinary Approach. Springer-Verlag, Berlin Heidelberg, pp. 379&amp;#8211;404.&lt;/p&gt;

What lies beneath? Reconstructing the primitive magmas fueling voluminous silicic volcanism using olivine-hosted melt inclusions

Understanding the origins of the mantle melts that drive voluminous silicic volcanism is challenging because primitive magmas are generally trapped at depth. The central Taupō Volcanic Zone (TVZ; New Zealand) hosts an extraordinarily productive region of rhyolitic caldera volcanism. Accompanying and interspersed with the rhyolitic products, there are traces of basalt to andesite preserved as enclaves or pyroclasts in caldera eruption products and occurring as small monogenetic eruptive centers between calderas. These mafic materials contain MgO-rich olivines (Fo79–86) that host melt inclusions capturing the most primitive basaltic melts fueling the central TVZ. Olivine-hosted melt inclusion compositions associated with the caldera volcanoes (intracaldera samples) contrast with those from the nearby, mafic intercaldera monogenetic centers. Intracaldera melt inclusions from the modern caldera volcanoes of Taupō and Okataina have lower abundances of incompatible elements, reflecting distinct mantle melts. There is a direct link showing that caldera-related silicic volcanism is fueled by basaltic magmas that have resulted from higher degrees of partial melting of a more depleted mantle source, along with distinct subduction signatures. The locations and vigor of Taupō and Okataina are fundamentally related to the degree of melting and flux of basalt from the mantle, and intercaldera mafic eruptive products are thus not representative of the feeder magmas for the caldera volcanoes. Inherited olivines and their melt inclusions provide a unique “window” into the mantle dynamics that drive the active TVZ silicic magmatic systems and may present a useful approach at other volcanoes that show evidence for mafic recharge.

Stratigraphy and correlations in Deccan Volcanic Province, India: Quo vadis?

The Deccan Volcanic Province (DVP) is significant for its eruption close to Cretaceous–Paleogene (K-Pg) boundary. Chemostratigraphy established in its western parts is the foundation of postulated long distance correlations across the province and consequential models of its eruptive history. A critical review of diagnostic parameters used to characterize stratigraphic units shows them to be probabilistic rather than deterministic and therefore, they are ambiguous. We compile the previously overlooked mapping into district-wise altitude-controlled logs across the province. A reappraisal of the chronological and paleomagnetic data for the DVP shows that volcanism was not concurrent across the province and questions the validity of previous correlations. This analysis also shows that at least three separate eruptive phases occurred in disparate parts of the province, spread over ∼7 million years, of which only one preceded the K-Pg boundary. We resurrect an eruptive model involving multiple eruptive centers and endorse a zonal stratigraphy for the DVP. This approach provides a better context for correlations than the prevailing stratigraphy that clubs the entire province into a single entity.