CO2, C-13/C-12 and H2O variability in natural basaltic glasses: A study comparing stepped heating and FTIR spectroscopic techniques

A comparison of two independent techniques was used to assess the homogenei ty of CO2 and H2O concentrations in a number of natural basaltic glasses. V ariations in carbon concentration and isotopic ratio were determined by com parison of stepped heating data obtained in two different laboratories. Dis solved volatile concentrations were also obtained by stepped heating and Fo urier Transform Infrared (FTIR) spectroscopy. Replicate stepped heating ana lyses of a mid-ocean ridge basaltic glass show that the concentration and C -13/C-12 of bulk magmatic and dissolved CO2 vary by less than +/-10% and +/ -0.5 parts per thousand, respectively. A similar degree of correlation is o bserved for replicate stepped heating analyses of Mariana Trough glasses co nducted in two different laboratories. Dissolved CO2 concentrations determi ned by stepped heating also correlate well with concentrations measured by FTIR spectroscopy. The correspondence of results obtained in these experime nts provide an upper limit to the degree of natural variation in concentrat ions and isotopic ratios of these volatiles in basaltic glasses and suggest that intrinsic, magmatic carbon has a relatively homogeneous distribution in these glasses. Water concentrations determined through extraction by hea ting and FTIR also show excellent agreement. Copyright (C) 1999 Elsevier Sc ience Ltd.