Chemical-physical constraints of the 2015 eruptive activity of Mt. Etna: new insights from thermo-barometry and geochemistry of olivine-hosted melt inclusions

<p>The concomitant activation off all four summit craters of Mt. Etna during the December 2015 eruptive event allow us to investigate the chemical-physical crystallization conditions and magma dynamics in the shallower portion of the open-conduit feeding system. In this study, we discuss new petrological, geochemical and thermo-barometric data as well as the composition of major element and volatile content (H<sub>2</sub>O, CO<sub>2</sub>, F, Cl and S) of olivine-hosted melt inclusions from the explosive and effusive products emitted during the December 2015 eruptive event.</p><p>Results and rhyolite-MELTS thermodynamic modelling of mineral phase stability highlight the relatively shallow crystal equilibrium depth prior to the eruption ranging from 400-500 MPa for Central Crater and North East Crater, up to 200 MPa below the New South East Crater. The study of high-pressure and high-temperature homogenized olivine-hosted melt inclusions allowed us to identify the composition of the almost primary alkali-basalt magma (11.8 wt% MgO) containing up to 4.9 wt% and 8151 ppm of H<sub>2</sub>O and CO<sub>2 </sub>respectively. The results, together with those already reported for the previous paroxystic events of the 2011-2012 (Giacomoni et al., 2018), reinforce the model of a vertically extended feeding system and highlight that the activity at the New South East Crater was fed by a magma residing at significant shallower depth with respect to Central Craters and North East Crater, although all conduits are fed by a common deep (P = 530-440 MPa) basic magmatic refilling. Plagioclase stability model and dissolution and resorption textures confirm its dependence on H<sub>2</sub>O content, thus suggesting that further studies on the effect that flushing from fluids with different H<sub>2</sub>O/CO<sub>2</sub> ratio are needed in order to understand the eruption triggering mechanisms of paroxystic fountaining.</p><p> </p><p><strong>References</strong></p><p>Giacomoni P., Coltorti M., Mollo S., Ferlito C., Braiato M., Scarlato P. 2018. The 2011-2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system. JVGR 349, 370-391.</p>

Spatial Trends in Mineral Abundances across Tyrrhena Terra on Mars derived from Geomorphological and Mineralogical Mapping

<p>Tyrrhena Terra hosts an intriguing variety of aqueously altered materials accompanied by unaltered mafic rocks. Our study region extends from the southern rim of the Isidis impact basin, including the Libya Montes region, southward to the Hellas Basin rim (Fig. 1). The NW part is dominated by lava flows from Syrtis Major that grade southwards into the TT highlands, dissected by fluvial channels and overprinted by abundant impact craters. These landforms together with lobate and fan-shaped deposits within impact craters are evidence for a variable history of erosion and deposition. Ancient phyllosilicate-rich materials have been exposed and uplifted from the subsurface, as they often occur in crater ejecta and central crater uplifts.</p><p>Our previous studies used CRISM spectral data together with CTX, HiRISE, and HRSC images as well as their derived topography data to create geomorphological maps of the southern Isidis region and Tyrrhena Terra. These datasets were used to map and characterize the types and occurrences of phyllosilicates, chlorite, opal, zeolites, carbonates, olivines, and pyroxenes and to assess the relationships between selected aqueous outcrops and surface features.</p><p>In this work, we build on these results by seeking correlations between aqueous mineral detections with our geomorphological map to assess 1) whether or not there are relationships between specific units and mineral occurrences, and 2) if there are trends across the study region in terms of mineral occurrence and abundance.</p><p>The mineralogical map originates from a study that spans not only the inter-Isidis-Hellas region, but also extends northwards to Nili Fosse and westwards to Terra Sabea. The focus of that study was on the metamorphic- and hydrothermally-related alteration history using CRISM targeted and mapping data, including hundreds of calibrated MTRDR images. These mineral detections were available to us as a mapped shape file, enabling us to assess the minerals in context with the geomorphological map. We utilized ESRI’s ArcGIS system and conducted multiple statistical queries in terms of mineral occurrence/type versus map unit in order to reveal possible trends within and across the study region.</p><p>Fe/Mg-phyllosilicates are the dominant aqueous mineral type within the study region and are more abundant in the central region compared to the proximity of either the Isidis or Hellas impact basin. Chlorites increase in abundance with distance from both impact basins, which could be an indication of hydrothermal processes from geothermal flux. The large Hellas impact event appears to have produced more varied temperatures and water chemistries, resulting in increased mineral variability near its rim.</p>

New data on the genesis and evolution of the primitive magmas of Mount Cameroon: contribution of melt inclusions

Mount Cameroon is a Plio-Quaternary volcanic massif, without a central crater, made up ofmore than 140 pyroclastic cones. It is one of the active volcanoes of the Cameroon Line. Mount Cameroon magmatic inclusions are found in microdroplets trapped in the early minerals (olivines) from the pyroclastic products. The analysis of these magmatic inclusions allowed us to find primitive liquids compared to lavas. Major elements study of the magmatic inclusions, trapped in the most magnesian olivines (Mg#84-86) of Mount Cameroon revealed "primitive" liquids of basanite and alkaline basalt type with variable composition compared to the much more uniform basalts of the magmatic series of Mount Cameroon. The study of these trapped liquids shows that: (i)- the original primitive lavas did not undergo the process of evolution by FC, but rather underwent fundamentally (or exclusively) the process of partial melting; (ii) the emitted lavas, evolved essentially by FC; (iii) the variations in the trace element contents of the primitive liquids directly reflect a variation in the rate of partial melting of a homogeneous mantelic source. The very high La/Yb ratios of the Mount Cameroon inclusions (> 20) characterize a garnet lherzolite source. Spectra of the magmatic inclusions show a negative anomaly or depletion in K, Rb and Ba as those of HIMU. The "primitive" liquids and lavas of Mount Cameroon represent a co-genetic sequence formed by varying degrees of partial melting of a source considered as homogeneous.

The remarkable volcanism of Shastina, a stratocone segment of Mount Shasta, California

Mount Shasta, a 400 km3 volcano in northern California (United States), is the most voluminous stratocone of the Cascade arc. Most Mount Shasta lavas vented at or near the present summit; relatively smaller volumes erupted from scattered vents on the volcano’s flanks. An apron of pyroclastic and debris flows surrounds it. Shastina, a large and distinct cone on the west side of Mount Shasta, represents a brief but exceptionally vigorous period of eruptive activity. Its volume of ∼13.5 km3 would make Shastina itself one of the larger Holocene Cascade stratovolcanoes. Its andesite-dacite lavas average 63 wt% SiO2 and have little compositional or petrographic variation; they erupted almost entirely from one central vent, although a single vent below Shastina’s north side erupted a flow of the same composition. Eruptions ended with explosive enlargement and breaching of the central crater and successive emplacement of four, more-silicic dacite domes within the crater and pyroclastic flows down its flank. Black Butte, a large volcanic dome and pyroclastic complex below the west flank of Shastina, is petrographically and chemically distinct but only slightly younger than Shastina itself, part of a nearly continuous Shastina–Black Butte eruptive episode. Shastina overlies the widespread pumice of Red Banks, erupted from the Mount Shasta summit area and 14C dated at ca. 10,900 yr B.P. (calibrated). Shastina and Black Butte pyroclastic deposits have calibrated 14C ages indistinguishable from one another at ca. 10,700 cal. yr B.P. A cognate granitic-textured inclusion in a late Shastina lava flow yields a 238U-230Th date on zircons within error of those ages. Our conclusion that the entire, voluminous Shastina–Black Butte episode lasted no more than a few hundred years is confirmed by almost identical remanent magnetic directions of all of the lavas and pyroclastic deposits. Although extremely similar, the remanent magnetic directions do reveal a short path of secular variation through the eruptive sequence. We conclude that the entire Shastina–Black Butte eruptive episode lasted no more than ∼200 yr. The magmas that produced the Shastina and Black Butte eruptions were separate individual bodies at different crustal levels. Each of these eruptive sequences probably represents magma approximating a liquid composition that experienced only minimal differentiation or crustal contamination and remained separated from the main central conduit for most eruptions of Mount Shasta. The probability of another rapidly developing, brief but voluminous eruptive episode at Mount Shasta is low but should not be ignored in evaluating future possible eruptive hazards.

The 2019 Stromboli eruption: the space-borne and ground-based InSAR contribution

<p>On 3 July 2019, Stromboli experienced a paroxysmal explosion without long-term precursors, as instead occurred before the last two effusive eruptions. In the following months, lava outpoured from a vent localized in the SW crater area, and sporadically from the NE one. On 28 August 2019, a new paroxysmal explosion occurred, followed by strong volcanic activity, culminating with a lava flow emitted from the SW-Central crater area. Subsequently, the eruptive activity decreased, although frequent instability phenomena linked to the growth of new cones on the edge of the crater terrace occurred. This contribution summarizes the measurements obtained through space-borne and ground-based InSAR sensors. The ground-based data allowed to detect pressurization of the summit area, as the instability of the newly emplaced material. The satellite data instead helped to identify the slope dynamics. The integration of the complementary systems strengthens the monitoring of both the eruptive activity and the instability phenomena.</p><p>This work is supported by the 2019-2021 Università di Firenze and Italian Civil Protection Department agreement, and by the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement.</p>

Keratoacanthoma of the Nasal Septum Secondary to Ranibizumab Use

Keratoacanthoma (KA) is a benign epithelial tumor that typically presents as a firm, cone-shaped, flesh-colored nodule with a central horn-filled crater. KA is considered to be a low-grade variant of squamous cell carcinoma (SCC). We report a rare case of a 72-year-old male who presented with a KA involving the nasal septum, possibly related to ranibizumab use. A flesh-colored lesion on the right anterior nasal septum lesion was visualized on examination. Histologic examination revealed a well-circumscribed, dome-shaped central crater filled with keratin, well-differentiated squamous epithelium with ground-glass cytoplasm with pushing margins, and intraepithelial microabscesses establishing the diagnosis of KA. KA of the nasal septum has only been reported once in the literature. This case is unusual because it normally presents on sun-exposed areas. Additionally, this patient was taking ranibizumab, a vascular endothelial growth factor (VEGF) inhibitor for macular degeneration. Despite ranibizumab not being directly linked to precancerous and cancerous skin lesions, agents in this medication class have been. Although it is difficult to prove associations in this isolated case, the role of ranibizumab causing cutaneous lesions should be further investigated.

Fluid geochemistry and seismic activityin the period 1998-2002 at Turrialba Volcano (Costa Rica)

Turrialba Volcano, located in Central-Southern Costa Rica, has been characterized, since the last period of eruptive activity in 1884-1886, by a weak and discontinuous fumarolic activity in the western area of its summit. During the 1998-2002 period, fumaroles discharging from central and West craters were collected for chemical analyses of major and trace gas compounds, 13C/12C in CO2 and 18O/16O and D/H (in one fumarolic condensate), isotopic ratios. Geophysical measurements (seismic activity and ground deformation), monitored in the same period, were compared to geochemical data to define the status of the volcanic system. Chemical and isotopic characteristics of fumaroles of Turrialba Volcano seem to be related to interaction processes between a magmatic source and a shallower hydrothermal aquifer. Since February 1997, seismicity at Turrialba Volcano gradually increased, while since August 2001 new fumaroles start to discharge from a new fracture system located in the area between central and West craters. Since September 2001, strong compositional changes of gas discharges have been recorded at central crater. These occurrences are possibly due to variations in the permeability of the conduit system feeding the fumaroles. Heat pulse episodes from a magmatic source have possibly caused the increase of vapour pressure at depth and, consequently, favoured the uprising of the magmatic fluids toward the surface. The observed evolution of chemical and physical parameters suggests that to forecast a possible renewal of the volcanic activity in the near future a full program of both geochemical and geophysical surveillance must be provided at Turrialba Volcano.