The metamorphic evolution of Salma-type eclogite in Russia: Constraints from zircon/titanite dating and phase equilibria modeling

Combined geochronology with phase equilibria modeling, the P-T-t evolution of metamorphic rocks can be deciphered. Four different representative samples, including retrogressed eclogite, garnetite, paragneiss and tonalite-trondhjemite-granodiorite (TTG) gneiss have been selected for detailed petrography and U/Pb dating from the Belomorian Eclogite Province in Russia. Zircon cores yield Archean ages for the protoliths of these samples. Zircon rims of the TTG gneiss have recorded Neoarchean anataxis at ca 2.73 Ga, whereas 1.91-1.92 Ga zircon rims of the garnetite and the paragneiss have dated high-pressure granulite facies metamorphism. Titanite in the retrogressed eclogite has recorded amphibolite facies retrogression at ca 1.86 Ga. Phase equilibria modelings for retrogressed eclogite, garnetite, and paragneiss define P-T conditions of 17-18 kbar/below 790 degrees C for the peak eclogite facies metamorphism, 11-12 kbar/870-900 degrees C for the high-pressure granulite facies metamorphism, and 8-10 kbar/650-710 degrees C for titanite's stability which corresponds to the amphibolite facies metamorphism. A clockwise P-T path is inferred for the Salma-type eclogite, which is characterized by thermal relaxation from the peak eclogite facies to the high-pressure granulite facies, and nearly isobaric cooling from the high-pressure granulite facies to the amphibolite facies.