![]() Within the caldera of the Campi Flegrei (southern Italy) are presented and discussed. In this paper the results of a geochemical survey carried out on submarine and subaereal gas discharges located In contrast to large-scale subduction of overthickened oceanic crust associated with slab melting, the subduction of a relatively small oceanic plateau may be responsible for the characteristics of the Iwojima magma, in which slab material itself does not play an important role in magma genesis but slab-derived volatiles make a significant contribution. As for its origin, we believe that the unusual tectonic setting around Iwojima may be responsible: (1) subduction of the Ogasawara Plateau, which brings a significant volume of thick crustal blocks into the mantle wedge beneath Iwojima (2) flattened subduction as a consequence of the buoyancy of the subducting Ogasawara Plateau and (3) propagation of the back-arc basin rift axes in the Mariana Trough. Enhanced outputs of slab-derived carbon and helium (3.5×109 and 4.0×103 mol/year) indicate a large input of slab component to the mantle wedge and/or effective devolatilization of slab materials. The elevated carbon/helium ratio of the slab-derived component also suggests decoupling during the subduction process probably resulting from the preferential loss of helium from the subducting slab beneath the forearc region. This difference is probably caused by different provenance in subducting materials carrying them to melt generation depth in the mantle wedge. This is in agreement with other petrological and geochemical features which imply a greater role of subducted materials, although the precise relative contributions of each source materials are somewhat different for several of the tracers. Based on a mixing calculation using helium–carbon isotope systematics, an extremely large contribution of slab-derived components (31% for 4He and more than 95% for 12C) is required to explain the unusual features of helium and carbon isotopes of Iwojima. These unusual features strongly suggest the involvement of slab-derived volatiles in the magma, although the possibility of a shallow origin for the low 3He/4He ratio still remains. The noble gas and carbon isotopic characteristics of Iwojima magma are quite distinct from other volcanoes in the Izu–Ogasawara–Mariana arc system: (1) a low 3He/4He ratio of 5.6RA (2) enrichment in heavy noble gases and (3) a heavy carbon isotope ratio (+1.5‰) almost equivalent to the highest value for marine carbonates. In order to elucidate the behavior of volatile elements during the subduction process in generating this unusual magma, noble gas and carbon isotope ratios of volcanic. Iwojima volcano, located on the southernmost part of the Izu–Ogasawara arc, is characterized by a magma chemistry, which differs from that of the other volcanoes in the arc, suggesting a larger contribution of subducted component. These results can be used to improve volcanic hazard assessment and monitoring through robust petrology-based conceptual frameworks for different eruption styles. I performed experiments to find that magma storage conditions for explosive and effusive eruptions were similar, and I demonstrate that ascent rates and viscosity vary with eruption style. I show that explosive eruptions are likely driven by fluid accumulation and degassing that began months before eruption. #Morro notsu series#I relate these variables to the time series of monitoring data for the same events. In this thesis, I address some unknowns to this topic by quantitatively determining the magmatic processes, storage conditions, timescales, and ascent rates of three eruptions at Kelud (1990, 2007, 2014). This is challenging for most volc anoes, including Kelud (Indonesia), that erupts effusively and explosively. Our capacity to anticipate volcanic eruptions depends on accurate interpretation of unrest signals coupled with understanding of the magmatic system and processes. ![]()
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