Description: On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12 years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~9 km. Textural and compositional data fromphenocrysts fromthe erupted products have been inte- grated with geochemical and isotopic information frombulk rocks to elucidate the magmatic processes respon- sible for the reawakening of volcanic activity. Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites.Mineral-melt equilibria suggest an origin for the distinct phenocryst populations by mixing between a high-T (~1130–1150 °C), basaltic magma with fO2 (NNO buffer) typical of the lower crust inarc systems and a low-T (~1060–1080 °C), basaltic andesiticmagma with fO2 (NNO+1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg ex- change between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low-P (~150–250MPa) and low-T (~1000–1050 °C).Mixing between twochemically distinctmagmas is also ev- idenced by the occurrence of reverse zoned plagioclase phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcicmantles. Conversely, plagioclase rims exhibit disequilibriumcompositions addressed to de- compression kinetics (~10−3 MPa/s) driven by rapidmagma ascent to the surface (~0.03 m/s). Major and trace element modelling excludes fractional crystallization as the primarymechanismcontrolling the bulk rock variability,whereas geochemical data align along amixing trend between two end-members represen- tative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes ofmetaso- matic fluids and/ormelts produced by the subducted slab. The roleplayed by slab-fluid inputs of carbonate origin and slab-melts fromthe hemipelagic sediments seems to beminimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influ- enced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crust

Description: Published

Description: 110-122

Description: 3V. Proprietà dei magmi e dei prodotti vulcanici

Description: 4V. Dinamica dei processi pre-eruttivi

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: JCR Journal

Description: The 40 ka caldera-forming eruption of Campi Flegrei (Italy) is the largest known erup- tion in Europe during the last 200 k.y., but little is known about other large eruptions at the volcano prior to a more recent caldera-forming event at 15 ka. At 29 ka a widespread volcanic ash layer, termed the Y-3 tephra, covered 〉150,000 km2 of the Mediterranean. The glass compositions of the layer are consistent with Campi Flegrei being the source, but no prominent proximal equivalent in the appropriate chrono-stratigraphic position had been previously identified. Here we report new glass chemistry data and 40Ar/39Ar ages (29.3 ± 0.7 ka [2σ]) that reveal the near-source Y-3 eruption deposit in a sequence at Ponti Rossi and a nearby borehole (S-19) in Naples. The dispersal and thickness of the deposits associ- ated with this eruption, herein named the Masseria del Monte Tuff, were simulated using a tephra sedimentation model. The model indicates that ~16 km3 dense rock equivalent of the magma erupted was deposited as fall. This volume and the areal distribution suggest that the Masseria del Monte Tuff resulted from a magnitude (M) 6.6 eruption (corresponding to volcanic explosivity index [VEI] 6), similar to the 15 ka caldera-forming Neapolitan Yellow Tuff (M 6.8) eruption at Campi Flegrei. However, the lack of coarse, thick, traceable, near- vent deposit suggests peculiar eruption dynamics. Our reconstruction and modeling of the eruption show the fundamental role that distal tephrostratigraphy can play in constraining the scale and tempo of past activity, especially at highly productive volcanoes.

Description: Published

Description: 595-599

Description: 1V. Storia eruttiva

Description: JCR Journal