%0 Journal Article
%T Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hs邦ehshan range, Taiwan
%A S. Kidder
%A J.-P. Avouac
%A Y.-C. Chan
%J Solid Earth (SE) & Discussions (SED)
%D 2013
%I Copernicus Publications
%R 10.5194/se-4-1-2013
%X The accuracy, reliability and best practises of Ti-in-quartz thermobarometry (TitaniQ) in greenschist facies rocks have not been established. To address these issues, we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from the Hs邦ehshan range, Taiwan. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~100每200 米m) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1每10 ppm) relative to detrital porphyroclasts (Ti ~0.1每200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10每20 米m) has a further restricted Ti concentration peaking at 0.8每2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Unlike previously documented examples, Ti concentration in the quartzite is inversely correlated with blue cathodoluminescence. Deformation was associated with a minimum grain boundary diffusivity of Ti on the order of 10 22m2 s 1. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250每350 ∼C and 300每410 ∼C, respectively, with lithostatic pressure of 3每4 kbar (assuming a geothermal gradient of 25∼ km 1), and with hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure and these temperatures, the Thomas et al. (2010) calibration yields Ti concentrations within error of concentrations measured by SIMS. If fluid pressure is instead used, predicted temperatures are ~30每40 ∼C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 ∼C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted.
%U http://www.solid-earth.net/4/1/2013/se-4-1-2013.html