The Cenozoic metamorphism and tectonic evolution of the lower crust of Shakhdara dome,Pamir Mountains
Li Yipeng1, Ding Lin1, Liu Deliang1, Oimahmadov Ilhomjon2, Mustafo Gadoev2, Negmat Rajabov2, Li Shun1
1. The Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101;
2. The Institute of Geology, Earthquake Engineering and Seismology, AS Republic of Tajikistan, Dushanbe, Tajikistan
Pamir metamorphic crust is dominated by eight metamorphic domes exposed across Pamir from east to west,among which Shakhdara dome is the biggest one.Peak T-P condition of Shakhdara garnet-sillimanite gneiss is T～810 ℃/P～10kbar represented by its peak assemblage Grt+Ky+Bi+Rt+Pl+Qz,while the peak T-P condition undergone in Shakhdara's garnet-clinopyroxene granulite is T～824 ℃/P～16.3kbar calculated from the peak assemblage Grt+Cpx+Rt+Pl+Qz.As to garnet-amphibolites in Shakhdara,which had experienced relatively severe retrograde,T～683 ℃～873 ℃/P～8.6～11.7kbar is revealed as the metamorphism condition of its residual peak assemblage Grt+Pl+Hbl+ilm+Qz.Peak metamorphic age 19～35 Ma of the mafic granulites dated by U-Pb method on zircons may reflect the thickening and heating process of Pamir lower crust from Late Eocene to Early Miocene.The metamorphism of Pamir domes could be compared with that of High Himalaya crystalline complex and we suggest that Cenozoic Pamir intra-continental-subduction alone the formerly formed suture zone after India-Asia Collision could be the trigger of Cenozoic thickening and metamorphism of lower crust in Pamir.