FTIR and Raman spectroscopy characterization of fluorine-bearing titanian clinohumite in antigorite serpentinite and chlorite harzburgite

Kenneth T Koga,José A Padrón-Navarta,María T Gómez-Pugnaire,Vicente López Sánchez-Vizcaíno,Carlos J Garrido

doi:10.1186/1880-5981-66-60

Abstract

Titanian clinohumite is an accessory phase found in peridotites, and it can be a key repository of volatile and other trace elements in sub-arc mantle. To characterize spectroscopic variations due to volatile elements in the phase, we have investigated the infrared spectroscopic characteristics of a suite of naturally occurring Ti clinohumite minerals with varying F and Ti concentrations. Samples were ultramafic rocks from Cerro del Almirez, Spain and Cima di Gagnone, Switzerland. The infrared spectra corresponding to OH vibrations showed systematic variation in regard to the abundance of F in Ti clinohumite. In particular, the intensity ratios of infrared absorption spectra at 3,565 and 3,390 cm-1 correlated linearly with the abundance of F independently of the crystal orientation. Raman spectra did not corroborate the Fourier transform infrared (FTIR) results. This intensity ratio provides an alternative analytical criterion for the characterization of Ti clinohumite.

Highlights

Titanian clinohumite is an accessory phase found in peridotites, and it can be a key repository of volatile and other trace elements in sub-arc mantle
Analytical methods Electron microprobe analysis Major elemental compositions of Titanian clinohumite (TiChu) were measured on the same spots from which Fourier transform infrared (FTIR) spectra were collected; this was done using a SX-100 CAMECA electron microprobe (EMP) at the Laboratoire Magmas et Volcans (Clermont-Ferrand, France) with a 15-kV accelerating voltage, a 30-nA sample current, and a counting time ranging from 10 to 30 s using thallium acid phthalate (TAP), and pentaerythritol (PET) refraction crystals
The analytical spots for FTIR, Raman, and the electron microprobe were all at the same coordinates and identified by the sample textures

Summary

Introduction

Titanian clinohumite is an accessory phase found in peridotites, and it can be a key repository of volatile and other trace elements in sub-arc mantle. To characterize spectroscopic variations due to volatile elements in the phase, we have investigated the infrared spectroscopic characteristics of a suite of naturally occurring Ti clinohumite minerals with varying F and Ti concentrations. The infrared spectra corresponding to OH vibrations showed systematic variation in regard to the abundance of F in Ti clinohumite. The intensity ratios of infrared absorption spectra at 3,565 and 3,390 cm−1 correlated linearly with the abundance of F independently of the crystal orientation. Raman spectra did not corroborate the Fourier transform infrared (FTIR) results. This intensity ratio provides an alternative analytical criterion for the characterization of Ti clinohumite

Methods

Results

Conclusion