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SUMMARY:Applications of U isotope fractionation in nature
DTSTART:20140408T161500
DTEND:20140408T171500
DTSTAMP:20260916T064125Z
UID:eacc39ec37ef0cc5ea83060441e4441e64a009392bd14807226c5473
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr Stefan Weyer\, Mineralogy Institute\, Leibniz University\, 
 Hannover DE\nAbstract:\nRecent studies revealed that the two long-lived is
 otopes of uranium (238U and 235U) fractionation during physiochemical reac
 tions\, similarly as classical stable isotope systems (e.g. C\, O\, S) or 
 other metal isotopes (e.g. Cr\, Fe or Cu). For very heavy elements\, such 
 as U\, a nuclear volume-dependent mechanism\, so-called nuclear field shif
 t\, is the driving mechanism for the observed isotope fractionation in nat
 ure\, rather than mass dependent isotope fractionation. We developed a tec
 hnique of high precision U isotope analyses with a double spike on multi c
 ollector ICP-MS. With this technique\, we could resolve significant 238U/2
 35U isotope variations on Earth (≈ 1.4‰) and in meteorites (> 3‰). I
 n my talk\, I will show several examples and potential applications. On Ea
 rth\, the most significant process that generates U isotope fractionation 
 appears to be redox reactions\, in particular during U reduction. Such red
 ox-induced U isotope signatures may be used to characterize redox conditio
 ns in ancient periods of Earth’s history. However\, yet the driving mech
 anism of U isotope fractionation during U reduction is unknown. In ongoing
  studies we investigate the effect of abiotic and biotically induced U red
 uction on U isotope signatures and which other factors need to be consider
 ed for a proper interpretation of geological reservoirs.Short biography:\n
 Stefan Weyer is an experienced isotope geochemist with a focus on non-trad
 itional stable isotope systematics (i.e. Fe\, Li\, Cu\, Zn\, Mo and U). He
  developed new methods for high precision Fe and U isotope analyses and ch
 aracterized major reservoirs on Earth (Weyer and Schwieters 2003\; Weyer e
 t al.\, 2008). He applied U isotope signatures as paleoredox tracer (Monto
 ya Pino et al.\, 2010) and he investigated U isotope fractionation during 
 adsorption (Brennecka et al.\, 2011)\, weathering and transport and in ano
 xic water columns\, as well as U isotope variations in meteorites (Brennec
 ka et al.\, 2010).
LOCATION:GR A3 32 http://plan.epfl.ch/?room=GR%20A3%2032
STATUS:CONFIRMED
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