Effect of anatexis on mineral thermometers used in ultrahigh-temperature metamorphism

Ultrahigh-temperature (UHT) metamorphism is crucial for deciphering thermal and tectonic regimes of orogen and is frequently accompanied by anatexis. However, accurate estimation of UHT metamorphic temperatures remains challenging, particularly due to the ambiguous effects of anatexis on mineral thermometers. The Paleoproterozoic pelitic granulites in the Kongling terrane, which have experienced both UHT metamorphism and significant anatexis, provide an ideal window to investigate this issue. Through integrated petrological, geochronological, and geochemical analyses, we evaluate the impact of anatexis on four widely used thermometers: Zr-in-rutile, Ti-in-zircon, ternary feldspar, and Ti-in-garnet. Petrological evidence, including melt pseudomorph (quartz + plagioclase + biotite + rutile/ilmenite) and cuspate plagioclase grains, confirms anatexis. Monazite geochronology constrains the timing of anatectic melt cooling to ∼2.0 Ga. Our results demonstrate that Zr contents in rutile and Ti contents in zircon are significantly influenced by diffusion and re-equilibration, respectively, in anatectic melts/fluids. The two thermometers yielded temperatures ranges of 443–859 °C (Zr-in-rutile) and 600–700 °C (Ti-in-zircon, majority data). Ternary feldspar thermometer records both UHT conditions (930–990 °C) and retrograde cooling temperatures (580–770 °C), while Ti-in-garnet preserves robust UHT conditions (∼940 °C). This study offers new insights into the fidelity and limitations of the mineral thermometers for UHT studies, particularly regarding their susceptibility to anatectic processes, and highlights the necessity of integrating multiple methods to reconstruct UHT thermal histories.