Discrimination of TiO2 polymorphs in sedimentary and metamorphic rocks

Abstract

Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO 2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase, whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase trace element characteristics and re-equilibration of relict rutiles.Evaluation of trace element contents obtained by electron microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO 2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand. For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO 2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace elements proves to be a valuable tool besides Raman spectroscopy.

The Proto‐Zagros Foreland Basin in Lorestan, Western Iran: Insights From Multimineral Detrital Geothermochronometric and Trace Elemental Provenance Analysis

“…Zircon, apatite, and rutile are common accessory phases in siliciclastic systems and form in a wide range of petrogenetic environments and incorporate up to 1-5 wt.% of trace elements, making them highly versatile provenance tools (e.g., Bruand et al, 2017;Grimes et al, 2015;Triebold et al, 2011). The trace element geochemistry of these minerals primarily reflects magma composition, degree of melt fractionation, and …”

“…Metapelitic rutile has low Cr and high Nb, metabasic rutile contains low Cr and low Nb, rutile from metacumulates has high Cr, and low Nb Rutile formed in magmatic environments can be identified based on extremely elevated concentrations of V, Cr, Nb, Sn, Sb, and/or W (Zack, von Eynatten, & Kronz, 2004). For example, kimberlitic rutile may contain up to~21 wt.% Nb 2 O 5 and 7 wt.% Cr 2 O 3 , whereas hydrothermal rutile associated with mineral deposits can exhibit >1 wt.% of V, Nb, Sn, Sb, and/or W. Trace elements, such as Cr, V, Fe, and Nb, can be used to distinguish rutile from its polymorphs, anatase, and brookite (Triebold et al, 2011). Importantly, Zr-in-rutile content serves as a robust geothermometer (Watson et al, 2006;Zack, Moraes, & Kronz, 2004).…”

Recent developments in TiO2 as n- and p-type transparent semiconductors: synthesis, modification, properties, and energy-related applications

“…B 1g (unresolved doublet around 513-519 cm -1 ), E g (639/640 cm -1 ). According to space group theory, 36 Raman-active modes are predicted for Brookite TiO 2 (nine A 1g , nine B 1g , nine B 2g and nine B 3g ) [188][189][190], out of which 17 bands were experimentally observed by several groups and assigned as follows: A 1g ( [191][192][193][194][195]. Other Raman modes are masked by a high level of coincidence and weak band intensities.…”

The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

“…However, the precision and accuracy of Zr measurements in rutile and trace elements measured in zircon were evaluated by additional analyses performed on a rutile standard, containing 1 wt % of Zr 2 O 3 , available to one of the authors (GG) and on synthetic glasses and natural zircon standards, available at the Eugen F. Stumpfl laboratory. Rutile was also investigated by Raman spectroscopy, to distinguish it from its polymorphs, anatase and brookite, as suggested by [32]. Raman spectra were collected using a LABRAM (ISA Jobin Yvon, Albuquerque, NM, USA), instrument at the University of Leoben.…”