Lead isotopes behavior in the fumarolic environment of the Piton de la Fournaise volcano (Reunion Island)

International audienceThe recent activity of the Piton de la Fournaise volcano offers a rare opportunity to address the issue of Pb isotope behavior in volcanic fumaroles, as the composition of the degassing source is accurately and precisely known. Gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca. 100 degrees C include Na-K sulfate (aphthitalite), Ca-Cu sulfate (e.g., gypsum), Na sulfate (thenardite), Ca-Mg-Al-Fe fluoride (e.g., ralstonite) and native sulfur. The high-temperature deposits show trace element patterns typical of volcanic gas (with Pb concentration up to 836 ppm) while the low-temperature deposits are depleted in most volatile elements (Pb <1 ppm) with the exception of Pd and Tl (in fluorides) and Se (in native sulfur). Only for low-temperature fluoride samples do Pb isotope compositions plot significantly outside the field of lavas. The isotopic shift is ascribed to leaching ubiquitous unradiogenic phases (e.g., sulfides) by acidic gas condensates. The similarity in Pb isotope signature between lavas and sublimate samples more representative of the gas phase (sulfates) indicates that the net fractionation of Pb isotopes resulting from volatilization and condensation processes is smaller than the precision of Pb isotope measurements (better than 60 ppm/a.m.u.). The absence of net fractionation could result from negligible isotope fractionation during Pb volatilization followed by extensive condensation of gaseous Pb, with possibly significant isotopic fractionation at this stage. Although this scenario has to be refined by more direct measurement of the gas phase, and its general applicability tested, it suggests that a small fraction (<10\%) of initially volatilized Pb ultimately escapes to the atmosphere, while the remaining dominant fraction is trapped in sublimates. As sublimates are rapidly dissolved and entrained by runoff, the fumarolic environment appears as a factory efficiently transferring isotopically unfractionated Pb from magmas towards the hydrological system and seawater. Resolving very small isotopic differences between magmas and their gaseous products remains an analytical challenge. High-precision Pb isotope measurements rest not only on instrumental performance but also on high-yield chemistry, as Pb isotopes drastically fractionate (800 ppm/a.m.u.) upon elution on anionic resin. For 50\% Pb recovery, the estimated isotopic bias is plus or minus 60-80 ppm/a.m.u., depending on which of the early (isotopically light) or late (isotopically heavy) Pb fraction is lost. (c) 2012 Elsevier Ltd. All rights reserved

Nuclear field shift effect in the isotope exchange reaction of cadmium using a crown ether

Cadmium isotopes were fractionated by the liquid–liquid extraction technique with a crown ether, dicyclohexano-18-crown-6. The isotopic ratios of mCd/111Cd (m: 110, 112, 113, 114, and 116) were measured precisely by the multi-collector inductively coupled plasma spectrometry (MC-ICP-MS). When the isotope enrichment factors were calculated, the odd atomic mass isotopes (111Cd and 113Cd) showed excesses of enrichment comparing to the even atomic mass isotopes (110Cd, 112Cd, 114Cd and 116Cd). This odd–even staggering property originates from the nuclear field shift effect. The contribution of the nuclear field shift effect to the observed isotope enrichment factor was estimated to be 5 to 30%

Instrumental isotope fractionation in multiple-collector icp-ms

This work addresses the issue of how isotope mass biases in modern Multiple-Collector Inductively Coupled Plasma Mass Spectrometers (MC-ICP-MS) changes with increasing efficiency of ion transfer through the instrument, which is known as transmission (tau). For any element, when all the ions introduced into the source are accounted for at the collector, the instrumental mass bias must vanish. With the latest cone designs, such as Thermo Finnigan jet cones, transmissions in excess of 2 percent are now obtained for heavy elements and coincide with smaller values of instrumental isotope fractionation factors. Transmission of ions across the entire mass range has been measured on a Thermo Neptune Plus equipped with standard and jet cones. It was found that transmission tau of elements above mass 40 increases linearly with the atomic weight. Comparing this relationship with the well-established linear dependence of ion energy with atomic mass indicates that high transmission is intimately related to the thermodynamic reversibility of the gas flow in the interface. Instrumental isotope fractionation obeys an exponential law with beta as a coefficient. Instrumental isotopic fractionation is due to the transverse spread of the beam inherited from Ar thermal movements at the high temperatures of the plasma. It was found that, for tau 0.002, the exponential law coefficient beta approximate to -0.24 +/- 0.02 ln tau in contrast to beta approximate to 2 at lower transmission. The exponential mass fractionation coefficient can be approximated by the following law: beta = beta(0) (1 - tau(gamma))

The Piton de la Fournaise Volcano (Reunion Island, Indian Ocean): temporal evolution from high resolution Pb isotopes.

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The Piton de la Fournaise Volcano (Reunion Island, Indian Ocean): temporal evolution from high resolution Pb isotopes.

International audienc

Mass-independent isotopic fractionation of tin in chemical exchange reaction using a crown ether

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The Piton de la Fournaise Volcano (Reunion Island, Indian Ocean): temporal evolution from high resolution Pb isotopes.

International audienc