TRACKING THE P–T PATH OF PRECAMBRIAN ECLOGITE USING PSEUDOSECTION, Ti-IN-QUARTZ AND Zr-IN-RUTILE THERMOBAROMETRY

International audienceSveconorwegian eclogite occur as a nappe within the high-grade metamorphic region in southernSweden, which constitutes a window into the deepest part of this Precambrian mountain belt. Distinctmicrostructural domains (i.e., garnet core, garnet rim, and matrix) in a Fe-Ti-rich eclogite variety containabundant quartz, rutile and zircon.A pseudosection approach was first applied and compared to results from a combination of Zr-in-rutileand Ti-in-quartz. The pressure input used for both thermometers was first deduced for each microstructuraldomain from the pseudosection. For the garnet core, Zr-in-rutile yields temperatures of 700-715°C and Ti-inquartz~ 635°C at 7 kbar. For the garnet rim, temperatures of 760-790°C (Zr-in-rutile) and 740-890°C (Ti-inquartz)at 12-18 kbar were calculated. Matrix rutile recorded temperatures of ~ 810°C, while quartz recordedtemperatures up to ~ 890°C. Additionally, direct combination of Ti content in quartz and Zr content in rutileisopleths (i.e., independent from the pseudosection) yield a prograde path in nearly perfect agreement withthe one deduced from the pseudosection.The pseudosection shows that rutile was produced by continuous breakdown of ilmenite during the earlystages of prograde metamorphism, a reaction that ran to completion at ~ 730°C. Most rutile grains in garnetrim and matrix are interpreted to subsequently form by recrystallization of smaller matrix grains. However,they generally do not record the peak-P temperatures and instead range mostly between 775 and 815°C,interpreted as a result of more efficient recrystallization during a dehydration reaction (progressivereplacement of hornblende by clinopyroxene).This study illustrates that both Zr-in-rutile and Ti-in-quartz thermometry cannot only robustly constrain aprograde evolution, but when combined with a pseudosection model can also yield information onrecrystallization processes. In fact, the combination of these three methods provides an unrivalled tool forpetrologic interpretation.The variation in Ti concentration in quartz is small regardless of crystal size. This P–T path reach veryhigh temperatures (up to 875°C) with a high dP/dT ratio, both during prograde and retrograde histories. Thesteep P–T path, together with preservation of garnet growth zoning, symplectitic textures and the lack ofsignificant Ti diffusion in quartz is consistent with a short residence time at high-temperature, implyingunusual fast burial and exhumation of the eclogite-bearing nappe