METAMORPHIC P-T-T PATHS RECORD THE LOWER CRUSTAL REWORKING OF THE MUZTAGHATA DOME, NORTHEASTERN PAMIR

Unlike the predominant upper amphibolite facies Cenozoic metamorphism in Central-South Pamir domes, the Muztaghata dome in the northeastern Pamir stands out due to its significantly higher metamorphic grade and much more variable timing of the high grade metamorphism according to different chronometers. In order to unravel the P-T-t history of Muztaghata dome, and better constrain the timing of peak metamorphism, we applied zircon U-Pb depth profiling geochronology combining with thermobarometry of a mafic granulite and its surrounding rocks (pelitic garnet gneiss and garnet amphibolite). The mafic granulite has petrographic features of retrograde eclogite, which involve white coronas of garnet porphyroblasts and oriented albite inclusions of clinopyroxene porphyroblasts. The Grt-Cpx thermobarometer yield 850±50 ᵒC/30±5 kbar eclogite facies metamorphism; the Grt-Cpx-GCPQ thermobarometers yield 750±50 ᵒC / 15±1 kbar high pressure granulite facies retrograde metamorphic condition; and the Grt-Hbl, Hbl-Pl, and zirconium in sphene thermometers with GHPQ and Hbl-Pl aluminum exchange barometers provide an upper amphibolite facies retrograde metamorphic condition of 700±50 ᵒC/ 10±2 kbar. The latter similar to the peak metamorphic conditions of 710 ᵒC/10 kbar of the surrounding pelitic garnet gneiss. Zircons from the mafic granulite and a garnet-biotite amphibolite record Early Miocene U-Pb ages of 15-24 Ma. The zircons in the mafic granulite shows typical features of retrograde growth such as strong MREE depletion and an inclined HREE pattern due to the coeval sphene growth and garnet decomposition, respectively. The eclogite to high pressure granulite facies metamorphism may have occurred during the Early Jurassic based on zircon U-Pb ages with flat HREE patterns from previous studies, but the timing of the prograde metamorphism with garnet growth is not fully constrained. The P-T-t paths of the mafic granulite and its surrounding rocks possibly represent a process of a Jurassic eclogite grade metamorphic event being nearly completely overprinted by a lower, upper amphibolite to granulite facies metamorphic event during the Cenozoic. Our zircon depth profiling documents final exhumation in the Early Miocene from granulite facies conditions during exhumation of the Central Pamir gneiss domes.