33 research outputs found
S, Cl and F degassing as an indicator of volcanic dynamics: The 2001 eruption of Mount Etna
Arrival of extremely volatile-rich high-Mg magmas changes explosivity of Mount Etna
The volcanic hazard potential of Mount Etna volcano is currently nourished by long-lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world's largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (FS) basalts ejected violently 4 k.y. ago. The FS primitive magmas (13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H2O and 3300 ppm CO2), and bear a trace element signature of a garnet-bearing, metasomatized source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo91), clinopyroxene (Mg# 92.5), and Cr spinel deep in the plumbing system (>5 kbar), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the FS fallout, provides a good explanation for major compositional and eruptive features of Mount Etna
Petrology of some amphibole-bearing volcanics of the pre-ellittico period (102-80 ka) Mt. Etna
We present here petrological and
geochemical data on volcanics cropping out in
southern and northeastern walls of the Valle del
Bove (Mt. Etna), belonging to the Rocche, Serra
Giannicola Grande and Canalone della Montagnola
Units. These units constitute the remnants of several
volcanoes that were active in the time span 102-80
ka, i.e. before the growth of the Ellittico-Mongibello
strato-volcano. Their products, range in composition
from hawaiites to benmoreites. Amphibole
(kaersutite) is present as phenocryst in all the studied
rocks, and commonly shows breakdown coronas
of rhönite ± clinopyroxene and plagioclase formed
during magma ascent. Nevertheless, in mafic rocks,
amphibole occurs as an early liquidus phase enclosed
in a Ca-rich plagioclase (up to An87). We propose that
early cotectic crystallization of amphibole and Caplagioclase
may reflect H2O-rich melts. Variations in
major and trace elements among lavas erupted from
coeval centres, suggest that fractional crystallization
was the principal evolutionary process but at the same
time magmas feeding the various volcanoes belonging
to the Rocche Unit were more heterogeneous with
respect to the younger Units studied here
Metodologia di preparazione di cristalli di olivina contenuti in piroclastiti dell'Etna per l'analisi delle melt inclusions
Elemental and isotope covariation of noble gases in mineral phases from Etnean volcanics erupted during 2001–2005, and genetic relation with peripheral gas discharges
During 2001–2005, Mount Etna was characterized by intense eruptive activity involving the emission of
petrologically different products from several vents, which involved at least two types of magma with
different degrees of evolution. We investigated the ratios and abundances for noble-gas isotopes in fluid
inclusions trapped in olivines and pyroxenes in the erupted products. We confirm that olivine has the most
efficient crystalline structure for preserving the pristine composition of entrapped gases, while pyroxene can
suffer diffusive He loss. Both the minerals also experience noble gas air contamination after eruption. Helium
isotopes of the products genetically linked to the two different magmas fall in the isotopic range typical of
the Etnean volcanism. This result is compatible with the metasomatic process that the Etnean mantle is
undergoing by fluids from the Ionian slab during the last ten kyr, as previously inferred by isotope and trace
element geochemistry. Significant differences were also observed among olivines of the same parental
magma that erupted throughout 2001–2005, with 3He/4He ratios moving from about 7.0 Ra in 2001
volcanites, to 6.6 Ra in 2004–2005 products. Changes in He abundances and isotope ratios were attributed to
variations in protracted degassing of the same magma bodies from the 2001 to the 2004–2005 events, with
the latter lacking any contribution of undegassed magma. The decrease in 3He/4He is similar to that found
from measurements carried out every fifteen days during the same period in gases discharged at the
periphery of the volcano. To our knowledge this is the first time that such a comparison has been performed
so in detail, and provides strong evidence of the real-time feeding of peripheral emissions by magmatic
degassing
The role of cryptotephra in refining the chronology of Late Pleistocene human evolution and cultural change in North Africa
© 2014.Sites in North Africa hold key information for dating the presence of Homo sapiens and the distribution of Middle Stone Age (MSA), Middle Palaeolithic (MP) and Later Stone Age (LSA) cultural activity in the Late Pleistocene. Here we present new and review recently published tephrochronological evidence for five cave sites in North Africa with long MSA/MP and LSA cultural sequences. Four tephra horizons have been identified at the Haua Fteah (Cyrenaica, Libya). They include cryptotephra evidence for the Campanian Ignimbrite (CI) eruption dating to ~39 ka that allows correlation with other Palaeolithic sequences in the eastern Mediterranean and as far north as Russia. Cryptotephra have also been recorded from the Moroccan sites of Taforalt, Rhafas and Dar es-Soltane 1. At Taforalt the geochemical composition suggests a provenance in the Azores, while examples from Sodmein (Egypt) appear to derive from central Anatolia and another unknown source. In these latter examples chemical compositional data from relevant proximal volcanic centres is currently lacking so the identification of tephra in layers of known age and cultural association provides the first reliable age determinations for distal volcanic events and their geographical extent. The future potential for tephrochronological research in North Africa is also discussed
Constraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism
Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from Southern Italy (seven Eolian Islands, Mt. Vulture, Etna, Ustica, Pantelleria) range from 2.3 to 7.1 Ra. Importantly the phenocryst 3He/4He correlate well with whole rock Sr isotopic composition (0.70309-0.70711) reflecting the mixing of two sources. A significant contribution of He from crustal contamination is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr (and decrease in 143Nd/144Nd and 206Pb/204Pb) that is due to increasing metasomatic enrichment of the mantle wedge via subduction of the Ionian-Adriatic plate. Calculations based on the ingrowth of 4He in the wedge and on the 4He content of the subducting crust show that mechanisms of enrichment in radiogenic He are effective only if the wedge is strongly depleted in He relative to best estimates of the depleted mantle. This can be accommodated if the process of metasomatism by the subduction fluids depletes the mantle wedge. The 3He/4He of Pantelleria, Etna, Iblei, Ustica, Alicudi and Filicudi basalts (7.0 ± 0.6 Ra) define the mantle composition least affected by subduction-related metasomatism. Although these volcanoes are from a variety of tectonic regimes (subduction-related, intraplate, rifting) their similarities suggest a common origin of geochemical features. Their characteristics are consistent with a HIMU-type mantle that is either younger than the Cook-Austral island end-member, or has a lower 238U/204Pb
Comparing satellite and ground-based observations of paroxysmal degassing events at Etna volcano, Italy
Mount Etna, Italy, is one of the most active volcanoes in the world, and is also regarded as one of the strongest volcanic sources of sulfur dioxide (SO2) emissions to the atmosphere. Since October 2004, an automated ultraviolet (UV) spectrometer network (FLAME) has provided ground-based SO2 measurements with high temporal resolution, providing an opportunity to validate satellite SO2 measurements at Etna. The Ozone Monitoring Instrument (OMI) on the NASA Aura satellite, which makes global daily measurements of trace gases in the atmosphere, was used to compare SO2 amount released by the volcano during paroxysmal lava-fountaining events from 2004 to present. We present the first comparison between SO2 emission rates and SO2 burdens obtained by the OMI transect technique and OMI Normalized Cloud-Mass (NCM) technique and the ground-based FLAME Mini-DOAS measurements. In spite of a good data set from the FLAME network, finding coincident OMI and FLAME measurements proved challenging and only one paroxysmal event provided a good validation for OMI. Another goal of this work was to assess the efficacy of the FLAME network in capturing paroxysmal SO2 emissions from Etna, given that the FLAME network is only operational during daylight hours and some paroxysms occur at night. OMI measurements are advantageous since SO2 emissions from nighttime paroxysms can often be quantified on the following day, providing improved constraints on Etna’s SO2 budget
Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)
In this paper, fluid source(s) and processes controlling the chemical composition of volatile organic compounds (VOCs) in gas discharges from Mt. Etna and Vulcano Island(Sicily, Italy) were investigated. The main composition of the Etnean and Volcano gas emissions is produced by mixing, to various degrees, of magmatic and hydrothermal components. VOCs are dominated by alkanes, alkenes and aromatics, with minor, though significant, concentrations of O-, S- and Cl(F)-substituted compounds. The main mechanism for the production of alkanes is likely related to pyrolysis of organic-matterbearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alkene and aromatic compounds via catalytic reactions (dehydrogenation and dehydroaromatization, respectively). Nevertheless, an abiogenic origin for the light hydrocarbons cannot be ruled out. Oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions, typical of these volcanic-hydrothermal fluids, may explain the production of alcohols, esters, aldehydes, as well as O- and S-bearing heterocycles. By comparing the concentrations of hydrochlorofluorocarbons (HCFCs) in the fumarolic discharges with respect to those of background air, it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes. Finally, chlorofluorocarbon (CFC) abundances appear to be consistent with background air, although the strong air contamination that affects the Mt. Etna fumaroles may mask a possible geogenic contribution for these compounds. On the other hand, no CFCs were detected in the Vulcano gases, which are characterized by low air contribution. Nevertheless, a geogenic source for these compounds cannot be excluded on the basis of the present data
Slab disruption, mantle circulation, and the opening of the Tyrrhenian basins
Plate tectonic history, geological, geochemical (element and isotope ratios), and
seismological (P-wave tomography and SKS splitting) data are combined with laboratory
modeling to present a three-dimensional reconstruction of the subduction history
of the central Mediterranean subduction. We fi nd that the dynamic evolution
of the Calabrian slab is characterized by a strong episodicity revealed also by the
discrete opening of the Tyrrhenian Sea. The Calabrian slab has been progressively
disrupted by means of mechanical and thermal erosion leading to the formation of
large windows, both in the southern Tyrrhenian Sea and in the southern Apennines.
Windows at lateral slab edges have caused a dramatic reorganization of mantle convection,
permitting infl ow of subslab mantle material and causing a complicated pattern
of magmatism in the Tyrrhenian region, with coexisting K- and Na-alkaline igneous
rocks. Rapid, intermittent avalanches of large amounts of lithospheric material at
slab edges progressively reduced the lateral length of the Calabrian slab to a narrow
(200 km) slab plunging down into the mantle and enhancing the end of the subduction
process