40Ar/39Ar thermochronology from the northwestern Dabie Shan: Constraints on the evolution of Qinling-Dabie orogenic belt, east-central China

Nine phengite and muscovite samples in eclogites, mylonitic shear zones, and metamorphic gneisses from four of the seven structural units have been dated by the 40Ar/39Ar step-heating method. Phengites from deformed eclogites in the HSB yield complex age spectra that we interpret as most likely indicating closure with respect to Ar loss between 350 and 430 Ma. The rock samples collected from the eclogite-bearing gneiss display a significant static recrystallization of quartz, which suggests temperatures in excess of ca 350-400 degrees C. The ages of 350-430 Ma from samples 9669B and 9669C are, therefore, interpreted as retrograde metamorphic ages for the eclogites. The 40Ar/39Ar data from the northwestern Dabie Shan suggest four distinctive cooling events. On the basis of the local structural framework and regional tectonic relationships, we suggest that the 410-350 Ma cooling event was related to either subduction of an oceanic plate beneath the Sino-Korean plate or collision between the Sino-Korean plate and a microcontinental block in the middle Paleozoic. The three younger episodes of cooling between the late Permian and the late Triassic may all have been related to the collision between the Sino-Korean and Yangtze Flares. Specifically, the 263-249 Ma event could have been a result of thrusting-induced denudation, whereas the 236-214 Ma cooling event is likely related to strike-slip faulting. The younger ages of 195-187 Ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the Sino-Korean and Yangtze plates. (C) 2000 Elsevier Science B.V. All rights reserved. Nine phengite and muscovite samples in eclogites, mylonitic shear zones, and metamorphic gneisses from four of the seven structural units have been dated by the 40Ar/39Ar step-heating method. Phengites from deformed eclogites in the HSB yield complex age spectra that we interpret as most likely indicating closure with respect to Ar loss between 350 and 430 Ma. The rock samples collected from the eclogite-bearing gneiss display a significant static recrystallization of quartz, which suggests temperatures in excess of ca 350-400 degrees C. The ages of 350-430 Ma from samples 9669B and 9669C are, therefore, interpreted as retrograde metamorphic ages for the eclogites. The 40Ar/39Ar data from the northwestern Dabie Shan suggest four distinctive cooling events. On the basis of the local structural framework and regional tectonic relationships, we suggest that the 410-350 Ma cooling event was related to either subduction of an oceanic plate beneath the Sino-Korean plate or collision between the Sino-Korean plate and a microcontinental block in the middle Paleozoic. The three younger episodes of cooling between the late Permian and the late Triassic may all have been related to the collision between the Sino-Korean and Yangtze Flares. Specifically, the 263-249 Ma event could have been a result of thrusting-induced denudation, whereas the 236-214 Ma cooling event is likely related to strike-slip faulting. The younger ages of 195-187 Ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the Sino-Korean and Yangtze plates. (C) 2000 Elsevier Science B.V. All rights reserved. Nine phengite and muscovite samples in eclogites, mylonitic shear zones, and metamorphic gneisses from four of the seven structural units have been dated by the 40Ar/39Ar step-heating method. Phengites from deformed eclogites in the HSB yield complex age spectra that we interpret as most likely indicating closure with respect to Ar loss between 350 and 430 Ma. The rock samples collected from the eclogite-bearing gneiss display a significant static recrystallization of quartz, which suggests temperatures in excess of ca 350-400 degrees C. The ages of 350-430 Ma from samples 9669B and 9669C are, therefore, interpreted as retrograde metamorphic ages for the eclogites. The 40Ar/39Ar data from the northwestern Dabie Shan suggest four distinctive cooling events. On the basis of the local structural framework and regional tectonic relationships, we suggest that the 410-350 Ma cooling event was related to either subduction of an oceanic plate beneath the Sino-Korean plate or collision between the Sino-Korean plate and a microcontinental block in the middle Paleozoic. The three younger episodes of cooling between the late Permian and the late Triassic may all have been related to the collision between the Sino-Korean and Yangtze Flares. Specifically, the 263-249 Ma event could have been a result of thrusting-induced denudation, whereas the 236-214 Ma cooling event is likely related to strike-slip faulting. The younger ages of 195-187 Ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the Sino-Korean and Yangtze plates. (C) 2000 Elsevier Science B.V. All rights reserved. Nine phengite and muscovite samples in eclogites, mylonitic shear zones, and metamorphic gneisses from four of the seven structural units have been dated by the 40Ar/39Ar step-heating method. Phengites from deformed eclogites in the HSB yield complex age spectra that we interpret as most likely indicating closure with respect to Ar loss between 350 and 430 Ma. The rock samples collected from the eclogite-bearing gneiss display a significant static recrystallization of quartz, which suggests temperatures in excess of ca 350-400 degrees C. The ages of 350-430 Ma from samples 9669B and 9669C are, therefore, interpreted as retrograde metamorphic ages for the eclogites. The 40Ar/39Ar data from the northwestern Dabie Shan suggest four distinctive cooling events. On the basis of the local structural framework and regional tectonic relationships, we suggest that the 410-350 Ma cooling event was related to either subduction of an oceanic plate beneath the Sino-Korean plate or collision between the Sino-Korean plate and a microcontinental block in the middle Paleozoic. The three younger episodes of cooling between the late Permian and the late Triassic may all have been related to the collision between the Sino-Korean and Yangtze Flares. Specifically, the 263-249 Ma event could have been a result of thrusting-induced denudation, whereas the 236-214 Ma cooling event is likely related to strike-slip faulting. The younger ages of 195-187 Ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the Sino-Korean and Yangtze plates. (C) 2000 Elsevier Science B.V. All rights reserved. Nine phengite and muscovite samples in eclogites, mylonitic shear zones, and metamorphic gneisses from four of the seven structural units have been dated by the 40Ar/39Ar step-heating method. Phengites from deformed eclogites in the HSB yield complex age spectra that we interpret as most likely indicating closure with respect to Ar loss between 350 and 430 Ma. The rock samples collected from the eclogite-bearing gneiss display a significant static recrystallization of quartz, which suggests temperatures in excess of ca 350-400 degrees C. The ages of 350-430 Ma from samples 9669B and 9669C are, therefore, interpreted as retrograde metamorphic ages for the eclogites. The 40Ar/39Ar data from the northwestern Dabie Shan suggest four distinctive cooling events. On the basis of the local structural framework and regional tectonic relationships, we suggest that the 410-350 Ma cooling event was related to either subduction of an oceanic plate beneath the Sino-Korean plate or collision between the Sino-Korean plate and a microcontinental block in the middle Paleozoic. The three younger episodes of cooling between the late Permian and the late Triassic may all have been related to the collision between the Sino-Korean and Yangtze Flares. Specifically, the 263-249 Ma event could have been a result of thrusting-induced denudation, whereas the 236-214 Ma cooling event is likely related to strike-slip faulting. The younger ages of 195-187 Ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the Sino-Korean and Yangtze plates. (C) 2000 Elsevier Science B.V. All rights reserved.