Does Ti record the crystallization temperature of zircon?

The discovery of the Ti-in-zircon thermometer (Watson and Harrison, 2005) has wide ranging implications for investigating crystallisation temperatures of rocks from differing geologic settings. We have simultaneously measured 49Ti relative to silicon oxide (44 amu) on the ANU SHRIMP II multicollector, thereby both reducing analysis times to just a few minutes and normalising many potential fractionation effects. The isotope 49Ti is chosen to avoid potential interferences from atomic species as well as doubly charged Zr atoms. Results indicate SiO/49Ti ratios can be measured consistently in both natural zircons and synthetic glasses down to at least 1 ppm Ti. Analytical precision for NIST glass is better than 0.5% at 1 ppm, and better than 0.2% at 40 ppm Ti. External precision based on replicate SiO/49Ti ratios in a 6 ppm Ti natural zircon standard (SL13) is ca. 0.5% for a single analytical session (24 hrs). We have determined the Ti concentrations in natural zircons from many different thermal regimes, in both igneous and metamorphic rocks. While Ti temperatures for metamorphic zircons are consistent with independent estimates from other thermometers, derived temperatures for igneous zircons are often lower than expected and have unsuspected structure within individual grains. Using the ANU SHRIMP-RG at high resolution, we have measured the concentrations of Sc (a proxy for tri-valent trace element substitution) and Ti in standard zircon Temora 2. Sc and Ti concentrations are strongly correlated and correspond to cathodoluminescence zones. These domains demonstrably grew together under the same temperature regime. While the Ti contents of igneous zircons appear to be broadly controlled by temperature, processes which are responsible for the incorporation of other trace elements into the zircon lattice also operate for Ti.