Lawsonite-bearing eclogites are recog-nized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions i...Lawsonite-bearing eclogites are recog-nized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions in garnet, indicating ec-logite-facies metamorphism. Peak metamorphic con-ditions for equilibrium lawsonite-omphacite-phengite- garnet peak assemblages are estimated to be 2.1―2.4 GPa and 420―500℃, which is in the stability field of lawsonite eclogite-facies. A low geotherm of 6―8℃/km is referred, which is in consistent with a cold subduction. The occurrences of lawsonite-bearing eclogites in both NQL and NAT provide further evi-dence that the NAT HP/LT metamorphic belt is pos-sibly the northwestward extension of the NQL HP/LT metamorphic belt offset by the Altyn Tagh left-lateral slip fault. The NQL and NAT lawsonite-bearing ec-logites are formed by subduction of oceanic crust before collision of the Alashan and Qilian blocks in early Paleozoic.展开更多
文摘Lawsonite-bearing eclogites are recog-nized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions in garnet, indicating ec-logite-facies metamorphism. Peak metamorphic con-ditions for equilibrium lawsonite-omphacite-phengite- garnet peak assemblages are estimated to be 2.1―2.4 GPa and 420―500℃, which is in the stability field of lawsonite eclogite-facies. A low geotherm of 6―8℃/km is referred, which is in consistent with a cold subduction. The occurrences of lawsonite-bearing eclogites in both NQL and NAT provide further evi-dence that the NAT HP/LT metamorphic belt is pos-sibly the northwestward extension of the NQL HP/LT metamorphic belt offset by the Altyn Tagh left-lateral slip fault. The NQL and NAT lawsonite-bearing ec-logites are formed by subduction of oceanic crust before collision of the Alashan and Qilian blocks in early Paleozoic.
