Ti-in-zircon thermometry and crystallization modeling support hot Grenville granite hypothesis (vol 42, pg 267, 2014)

Quantitative modeling of crystallization histories using the program rhyolite-MELTS indicates that zircon crystallization in 1.0 to 1.2 Ga Grenville granitoids with Zr concentrations of 300-1200 ppm begins at 930-1000 degrees C, and always after onset of crystallization of most other phases (pyroxenes, feldspars, quartz, apatite, ilmenite). Zircon saturation temperatures, calculated from whole-rock compositions and Zr concentrations for modeled samples, range from 835 to 997 degrees C. Zircon in the two samples with the highest Zr (1201 and 829 ppm) analyzed by sensitive high-resolution ion microprobe (SHRIMP) yielded Ti contents of 10-77 ppm, corresponding to Ti-in-zircon temperatures as high as 1035 degrees C and 915 degrees C, respectively. These are among the highest Ti-in-zircon temperatures recorded in magmatic rocks. The modeling and SHRIMP data support the hypothesis that high-Zr Grenville granites are hot granites, and support tectonic models that invoke high-temperature (>900 degrees C) crustal conditions for generation of Grenville magmas.