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Trace elements in the gas emissions from the Erta Ale volcano, Afar, Ethiopia

Abstract : High-temperature (1084 °C) fumarolic emissions from a spatter cone at the Erta Ale north pit crater granted a rare opportunity to collect Giggenbach bottles, condensates, and sublimates from the fumarolic gases of a rift/plume volcano in the immediate proximity of degassing lava. These results represent the highest-temperature gases sampled directly for trace elements and the first high-T fumarolic samples for a rift/plume volcano. Sixty-seven metals and metalloids were measured quantitatively by ICP-AES and ICP-MS in liquid gas condensates and solid sublimates. The total amount of trace elements in the gas (without Si) exceeded 170 ppm. The ten most abundant elements transported in nonsilicate modes were Na (61 ppm), Fe (41 ppm), K (32 ppm), Br (12.4 ppm), Cd (3.0 ppm), Se (2.3 ppm), Cu (2.0 ppm), Zn (2.0 ppm), Te (1.7 ppm), and As (1.2 ppm). The gases contained 27 ppb Re, 1.5 ppb Au, 0.5 ppb Pt, and 0.27 ppb Os. Rh- and Pd-containing phases were observed in solid sublimates. The only metal not detected by all analytical methods was ruthenium. Chalcophile elements (Cd, Cu, Zn, Se, Te, As) were transported primarily in the gaseous form. Alkali metals were emitted, at least partially, as liquid micron-size sulfate droplets, whereas alkali earths, aluminum, and REE had a high affinity to silicate aerosol in the form of basaltic microspheres. The silicate aerosol content was evaluated at 59 ppm on average but varied within a 7.5-fold range during sampling. Because of the extremely high temperature, refractory elements Ca, Ba, Ta, U, and LREE showed evidence of transport in the form of gaseous species. The SO2 flux in January 2011 was evaluated at 91 ± 24 t/d for the entire volcano, including ~ 31 t/d from the north crater and ~ 60 t/d from the lava lake. The daily output of trace elements from both Erta Ale craters (without Si) was estimated at 53 kg/d, including 20 kg of Na, 13.5 kg of Fe, 10.5 kg of K, 4.5 kg of chalcophile elements, 9 g of Re, 0.5 g of Au, and 0.17 g of Pt. The trace element pattern of Erta Ale fumarolic gases do not possess any distinct geochemical specialization and resemble TE patterns from fumarolic emissions of studied arc and plume volcanoes.
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Michael Zelenski, Tobias Fischer, J. Maarten de Moor, Bernard Marty, Laurent Zimmermann, et al.. Trace elements in the gas emissions from the Erta Ale volcano, Afar, Ethiopia. Chemical Geology, Elsevier, 2013, 357, pp.95 - 116. ⟨10.1016/j.chemgeo.2013.08.022⟩. ⟨hal-01764548⟩



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