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