Triple oxygen isotope exchange between chondrule melt and water vapor: An experimental study

We have conducted time and fO(2)-dependent oxygen isotope exchange experiments between chondrule analogue melts and H2O in the phase. The aim of our study is to address the question whether the oxygen isotope composition of chondrules is the result of exchange with the ambient nebular gas or has been inherited from the precursor material. The silicate melt-H2O vapor exchange experiments were carried out in a vertical gas-mixing furnace using the metal loop technique at 1500 degrees C. The duration ranged from 5 to 1440 min and fO(2) was set between IW - 3.8 and IW - 1.3 using the H2O/H-2 buffer. Our experiments show that 50% exchange between H2O gas and silicate melt occurs in similar to 4 h at fO(2) = IW -3.8 and in similar to 1 h at fO(2) = IW - 1.3. At solar nebula conditions, significant exchange occurs only if chondrule-melting times were several hours. (C) 2015 Elsevier Ltd. All rights reserved.