Occurrence of atoll garnets in the garnet amphibolites, Aktyuz HP metamorphic complex, Northern Tien-Shan, Kyrgyzstan

抄録

The occurrence of complete and atoll-shaped garnets in garnet amphibolites in the Aktyuz complex, northern Kyrgyz Tien-Shan has been described. Based on the mineral textures and chemical compositions of minerals, the possible mechanism of formation of atoll garnets has been discussed. It is suggested that the atoll garnets were formed by breakdown of pre-existing inclusion-rich, Ca- and Mn-rich garnet core (incipient of garnet resorption from the core) by infiltration of fluids along fractures during the prograde HP-HT metamorphism.