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SUMMARY:Principles of triple oxygen isotope geochemistry - Daniel Herwartz
  (University of Cologne)
DTSTART:20160126T160000Z
DTEND:20160126T170000Z
UID:TALK62007@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Small but measurable variations in triple oxygen isotopic comp
 ositions result from purely mass dependent kinetic or equilibrium fraction
 ation. In this talk I will outline how the underlying processes (kinetic v
 s. equilibrium vs. mixing) can be identified and how this additional infor
 mation is used to solve geochemical problems. Presently\, the main applica
 tions are related to the global water cycle were the 17Oexcess parameter i
 s used just like the well-known d-excess parameter (both measures for the 
 deviation from a given reference line). However\, 17Oexcess can also be ap
 plied to silicates or carbonates. For instance\, the δ18O of metamorphic 
 gneisses from northwestern Russia is exceptionally low (-27‰). Strong wa
 ter-rock interaction with meltwaters from snowball earth glaciers 2.4 Ga a
 go is hypothesized as cause. The triple oxygen isotope data support this h
 ypothesis and imply that pristine meltwaters had δ18O of -40‰ or less. 
 The principles outlined here for oxygen can be applied to all isotope syst
 ems with at least three stable isotopes.
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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