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Published June 1999 | public
Journal Article

CO_2, ^(13)C/^(12)C and H_2O variability in natural basaltic glasses: a study comparing stepped heating and ftir spectroscopic techniques

Abstract

A comparison of two independent techniques was used to assess the homogeneity of CO_2 and H_2O concentrations in a number of natural basaltic glasses. Variations in carbon concentration and isotopic ratio were determined by comparison of stepped heating data obtained in two different laboratories. Dissolved volatile concentrations were also obtained by stepped heating and Fourier Transform Infrared (FTIR) spectroscopy. Replicate stepped heating analyses of a mid-ocean ridge basaltic glass show that the concentration and ^(13)C/^(12)C of bulk magmatic and dissolved CO_2 vary by less than ±10% and ±0.5‰, respectively. A similar degree of correlation is observed for replicate stepped heating analyses of Mariana Trough glasses conducted in two different laboratories. Dissolved CO_2 concentrations determined by stepped heating also correlate well with concentrations measured by FTIR spectroscopy. The correspondence of results obtained in these experiments provide an upper limit to the degree of natural variation in concentrations 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 heating and FTIR also show excellent agreement.

Additional Information

© 1999 Elsevier. (Received June 10, 1998; accepted in revised form March 16, 1999) We thank John Pace for construction of the La Jolla stepped heating system, and Professor Mark Thiemens and Joel Savarino (UCSD Chemistry) for access to, and assistance with, cross calibration of our manometric measurement system. Professor Kurt Marti and Dr. Thomas Graf (UCSD Chemistry) gave advice on the construction of a high temperature resistance furnace. Professor Martin Wahlen and Dr. Bruce Deck (SIO) are thanked for allowing us to use their quadrupole and gas source mass spectrometers. Samples were provided by Professors Peter Stoffers (Kiel), as part of an on-going study of Mariana Trough basalts, and Harmon Craig (SIO). This contribution benefited from thoughtful reviews by Drs. Jackie Dixon and Françoise Pineau. Work in La Jolla was supported by SIO "startup" funds to DRH. The stable isotope laboratory at RHUL is part-funded by the University of London as an Intercollegiate Analytical Facility.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023