Using titanium-in-quartz geothermometry and geospeedometry to recover temperatures in the aureole of the Ballachulish Igneous Complex, NW Scotland

Abstract

Titanium--in--Quartz geothermometry, originally pioneered by Wark and Watson [2006] then later modified by Kawasaki and Osanai [2008] and Thomas et al. [2010] promises accurate quartz crystallisation temperature determinations from straightforward measurements of Ti within the quartz lattice. These geothermometers are tested by applying them to a suite of contact metamorphosed quartzites from around the Ballachulish Igneous Complex in West Scotland. Results show that the original Ti--in--Quartz geothermometer gives results broadly in agreement with thermal modelling and pre--existing geothermometry data from Ballachulish and the latter geothermometers give temperatures which are consistently too low. However, despite a broad agreement between published temperature values and those derived from the original thermometer of Wark and Watson [2006], there is a lack of correlation between distance from the igneous contact and determined temperature, as well as unacceptably large errors in some cases. Furthermore, a rigorous test of the methodology employed in this and other studies suggests that the system is more complex than assumed, and a greater understanding of the substitution of other elements in quartz (such as aluminium) is necessary. In addition, various issues have been raised by other workers regarding the validity of Ti--in--Quartz as a geothermometry tool at all, inasmuch as the original equations were constructed with a disregard for a range of complicating factors. This study adds further weight to a growing mass of critiques of this technique of geothermometry and suggests a much greater understanding of the processes is necessary before Ti--in--Quartz can be convincingly upheld as a viable tool.

Comparison of thermal modeling, microstructural analysis, and Ti‐in‐quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

“…Previous studies have shown that the Thomas et al . [] calibration underestimates the quartz recrystallization temperature in the case of contact metamorphism [ Morgan et al ., ] and overestimates Ti solubility in granite and rhyolite crystallizing from a melt by a factor of two to five [ Huang and Audétat , ]. However, Ashley et al .…”

Scanning electron microscope cathodoluminescence imaging of subgrain boundaries, twins and planar deformation features in quartz

“…Götze (2009) mentions that the concentration of defects and dislocations in (sub)grain boundaries in quartz results in a high CL intensity, while others associate differences in SEM-CL with differences in quartz impurity and/or point defect content in the quartz grain (e.g. Morgan et al 2014).…”

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

“…The two different calibrations by Thomas et al (2010) and Huang & Aude¤ tat (2012) yield temperatures that can differ by more than 2008C at pressures of 0·2 GPa. Studies supporting both calibrations exist (Leeman et al, 2012;Wilson et al, 2012;Ashley et al, 2013;Aude¤ tat, 2013;Morgan et al, 2013;Kularatne & Aude¤ tat, 2014), suggesting that the two calibrations might be appropriate in different geological settings or that their success might be dependent on aTiO 2 (Leeman et al, 2012; Thomas & Watson, 2012;Wilson et al, 2012;Morgan et al, 2013;Kularatne & Aude¤ tat, 2014). It should be noted that an alternative TitaniQ calibration by Kawasaki & Osanai (2008), as well as the calibration by Wark & Watson (2006), does not include a pressure dependence and will not be included in the following discussion.…”

“…Our samples do not contain rutile, so we can be sure that aTiO 2 51, but they do contain Fe^Ti oxides, which should fix aTiO 2 at some intermediate value during subsolidus quartz crystallization (Qtz2) (e.g. Ghiorso & Gualda, 2013), assuming that equilibrium can be achieved (see Huang & Audetat, 2012;Morgan et al, 2013). For melt-present crystallization, several studies demonstrate that in silicic volcanic systems, aTiO 2 typically varies by 50·5 between compositionally similar samples from the same location (Leeman et al, 2012;Aude¤ tat, 2013;Ghiorso & Gualda, 2013;Kularatne & Aude¤ tat, 2014).…”