Abstract
We present a new approach to determine in situ CO 2 and H 2 O concentrations in apatite via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Absolute carbon and hydrogen measurements by nuclear reaction analysis (NRA) and elastic recoil detection (ERD) are used to calibrate ATR-FTIR spectra of CO 2 and H 2 O in apatite. We show that CO 2 and H 2 O contents in apatite can be determined via linear equations ( r 2 > 0.99) using the integrated area of CO 2 and H 2 O IR absorption bands. The main benefits of this new approach are that ATR-FTIR analyses are non-destructive and can be conducted on polished sample material surfaces with a spatial resolution of ~ 35 μm. Furthermore, the wavenumber of the phosphate IR absorption band can be used to determine the crystallographic orientation of apatite, which allows for accurate quantification of CO 2 and H 2 O in randomly orientated apatite grains. The limit of quantification of H 2 O in apatite is ~ 400 ppm and ~ 100 ppm for CO 2 . Via two examples, one from a carbonatite and one from a metasedimentary rock, we show that this new technique opens up new possibilities for determining volatile concentrations and behavior in a wide range of hydrothermal, igneous, and metamorphic systems.