Analysis of hydrogen and fluorine in pyroxenes:

Part II. Clinopyroxene

Jed L. Mosenfeldsr, George R. Rossman
Division of Geological and Planetary Sciences,
California Institute of Technology, M/C 170-25,
Pasadena, California 91125-2500, U.S.A.

ABSTRACT

We measured hydrogen in 13 natural clinopyroxenes using Fourier transform infrared (FTIR) spectroscopy. ¹⁶O¹H/³⁰Si and ¹⁹F/³⁰Si were also measured in the samples using secondary ion mass spectrometry (SIMS) and the H data were compared between the two techniques. Four of the clinopyroxenes are used as standards for SIMS calibration in multiple laboratories, and three have been measured previously using hydrogen manometry and/or elastic recoil detection analysis. Compared to clinopyroxenes in previous surveys comparing FTIR and SIMS, the 13 samples cover a broader range in chemistry and band positions in the O-H vibrational region. They also all lack detectable amphibole lamellae, which are otherwise commonly present in this mineral group. In contrast to orthopyroxene, the SIMS and FTIR data for clinopyroxene show significantly better correlations (r² = 0.96-0.98) when the frequency dependent IR calibration of Libowitzky and Rossman (1997) is applied, as opposed to the Bell et al. calibration (r² = 0.92-93). We derive a frequency-dependent molar absorption coefficient with parameters different from those of Libowitzky and Rossman's calibration, which was established using data on stoichiometric hydrous phases and gives poor agreement with the manometrically determined value for PMR-53. Comparison of data for PMR-53 to our SIMS calibrations for orthopyroxene and olivine suggests that the matrix effect among these phases is less than 20% relative. Fluorine concentrations vary depending on geological context, with the highest concentrations (up to 214 ppm) found in diopsides from crustal metamorphic environments. These diopsides also show a strong correlation between F and tetrahedral Al. Mantle samples follow similar geographic trends as in olivines and orthopyroxenes, with higher F in xenocrysts from Kilbourne Hole (46 ppm) and South African kimberlites (up to 29 ppm) compared to the Colorado Plateau (8 ppm).
These concentrations are much lower than those measured in recent experimental studies. Nevertheless, our data support suggestions that the F budget of the mantle can be entirely accommodated by incorporation in nominally anhydrous/fluorine-free minerals.

Raw Data: clinopyroxene samples:

IR Spectra (Microsoft Excel files with alpha, beta and gamma spectra):

All FTIR spectra in one file

CIT 17210
BP cpx A
FRB 118
HRV 147
JLM 77
KBH 2
LCA 236
PMR 53
RDS 62047
ROM 271 DI-10
ROM 271 DI-21
95adk 1A

Appendices: SIMS analyses and calibration data (Microsoft Excel files):

Appendix 2 cpx SIMS analysis