Search results for "Geochemistry"

Isotope composition of rain water, well water and fumarole steam on the island of Vulcano, and their implications for volcanic surveillance

1992

Abstract Water samples from eight wells in the Vulcano Porto area and fumarole steam from the crater of Vulcano (Southern Italy) were collected at monthly intervals over a two-year period from February 1987 to January 1989. Samples of bulk precipitation were also collected in three points at Vulcano Porto and Vulcano Piano (island of Vulcano) and Castroreale (Tyrrhenian coast of Sicily), again at monthly intervals. The weighted mean isotopic composition of rain water on Vulcano is δ D =−32‰ , and δ D 18 O =−6.4‰ . Results for well waters tend to support the existence of at least two water bodies: one of purely meteoric water and the other of brackish thermal water. An intermediate water bod…

Plume composition and volatile flux of Nyamulagira volcano, Democratic Republic of Congo, during birth and evolution of the lava lake, 2014-2015

2017

Very little is known about the volatile element makeup of the gaseous emissions of Nyamulagira volcano. This paper tries to fill this gap by reporting the first gas composition measurements of Nyamulagira’s volcanic plume since the onset of its lava lake activity at the end of 2014. Two field surveys were carried out on 1 November 2014, and 13–15 October 2015. We applied a broad toolbox of volcanic gas composition measurement techniques in order to geochemically characterize Nyamulagira’s plume. Nyamulagira is a significant emitter of SO2, and our measurements confirm this, as we recorded SO2 emissions of up to ~ 14 kt/d during the studied period. In contrast to neighbouring Nyiragongo volc…

2018

Volcanoes are a significant halogen source to the atmosphere. After water, carbon dioxide and sulfur compounds, halogens are often the most abundant gases in volcanic plumes. In the past, less attention was given to the heavy halogens bromine and iodine. However, the discovery of bromine monoxide (BrO) in volcanic plumes led to new interest especially in volcanic bromine chemistry and its impact on atmospheric processes. The BrO detection came along with advances in volcanic remote sensing techniques, in particular, robust DOAS applications and the possibility of continuous measurements by automated instruments located at safe distances from the volcano. As one of the consequences, the volc…

Emission of bromine and iodine from Mount Etna volcano

2005

[1] Constraining fluxes of volcanic bromine and iodine to the atmosphere is important given the significant role these species play in ozone depletion. However, very few such measurements have been made hitherto, such that global volcanic fluxes are poorly constrained. Here we extend the data set of volcanic Br and I degassing by reporting the first measurements of bromine and iodine emissions from Mount Etna. These data were obtained using filter packs and contemporaneous ultraviolet spectroscopic SO2 flux measurements, resulting in time-averaged emission rates of 0.7 kt yr−1 and 0.01 kt yr−1 for Br and I, respectively, from April to October 2004, from which we estimate global Br and I flu…

BrO formation in volcanic plumes

2006

Volcanoes have only recently been recognized as a potentially major source of reactive bromine species to the atmosphere, following from the detection of bromine monoxide (BrO) in the plume emitted by Soufriere Hills Volcano, Montserrat. However, BrO is not expected to be emitted in significant quantity from magma, presenting a puzzle regarding its formation. We report here new field measurements of the tropospheric plume emitted by Mt. Etna, Italy, which provide the first direct evidence of fast oxidation of halogen species in a volcanic plume, and lead to an explanation of how BrO is generated from magmatic HBr emissions. We show that the timescale of BrO formation (a few minutes after em…

Structurally controlled drainage basin development in the south of Menorca (Western Mediterranean, Spain)

2005

Abstract The south of Menorca consists of a gently folded Upper Miocene carbonate platform over which a drainage system has developed. Three areas with different drainage characteristics have been delimited: the central area, the eastern area and the western area. The central area is characterised by deep streams with steep slopes, whereas the western and eastern areas have slightly incised streams with gentle slopes. The drainage development has been controlled by the inversion of a normal fault in Pliocene times, resulting in a wide anticline with a NNE–SSW orientation. The deep streams of the central area follow the faults associated with this anticline. The amount of incision achieved b…

Phase equilibria modelling of retrograde amphibole and clinozoisite in mafic eclogite from the Tso Morari massif, northwest India: constraining the P…

2014

Phase equilibria modelling of post-peak metamorphic mineral assemblages in (ultra)high-P mafic eclogite from the Tso Morari massif, Ladakh Himalaya, northwest India, has provided new insights into the potential behaviour and source of metamorphic fluid during exhumation, and constrained the P–T conditions of hydration. A series of P–M(H2O) pseudosections constructed in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (NCKFMASHTO) system show that a number of petrographically distinct hydration episodes occurred during exhumation from peak P–T conditions (~640 °C, 27–28 kbar), resulting in the formation of abundant compositionally zoned amphibole and minor clinozoisite poikiloblasts at the exp…

Cognate xenoliths in Mt. Etna lavas: witnesses of the high-velocity body beneath the volcano

2013

Various xenoliths have been found in lavas of the 1763 (“La Montagnola”), 2001, and 2002–03 eruptions at Mt. Etna whose petrographic evidence and mineral chemistry exclude a mantle origin and clearly point to a cognate nature. Consequently, cognate xenoliths might represent a proxy to infer the nature of the high-velocity body (HVB) imaged beneath the volcano by seismic tomography. Petrography allows us to group the cognate xenoliths as follows: i) gabbros with amphibole and amphibole-bearing mela-gabbros, ii) olivine-bearing leuco-gabbros, iii) leuco-gabbros with amphibole, and iv) Plg-rich leuco gabbros. Geobarometry estimates the crystallization pressure of the cognate xenoliths between …

Tectonics and seismicity of the Tindari Fault System, southern Italy: Crustal deformations at the transition between ongoing contractional and extens…

2006

[1] The Tindari Fault System (southern Tyrrhenian Sea, Italy) is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab. Onshore structural data, an offshore seismic reflection profile, and earthquake data are analyzed to constrain the present geometry of the Tindari Fault System and its tectonic evolution since Neogene, including the present seismicity. Results show that this zone of deformation consists of a broad NNW trending system of faults including sets of right-lateral, left-lateral, and extensional faults as well as early strike-slip faults rewor…

A ∼700 Ma Sm–Nd garnet–whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic histo…

2007

Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko–Dom Feliciano–Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ∼580–550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of t…