Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphi...Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth took place at rates of approximately 9.5-10.5 km/Ma and exhumation from depths 〉160 km to the base of the crust at -30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin lithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.展开更多
Objective Shandong Province is divided into two parts by the Tan -Lu fault zone： the western part （Luxi） and the eastern part （Jiaodong）. Large-scale volcanic activity occurred during the Late Mesozoic in Shando...Objective Shandong Province is divided into two parts by the Tan -Lu fault zone： the western part （Luxi） and the eastern part （Jiaodong）. Large-scale volcanic activity occurred during the Late Mesozoic in Shandong Province, eastern China （Fig. lb）, and was controlled by the Tan-Lu fault zone and its secondary faults. Mesozoic volcanic rocks in Shandong Province mainly occur within the Cretaceous Qingshan group, overlying the Laiyang group and underlying the Wangsi group. The Qingshan group has been divided into four volcanic cycles, i.e., the Houkuang, Bamudi, Shiqianzhuang and Fanggezhuang formations from the oldest to the youngest. Although geochronology data indicate the volcanic activity occurred during the Early Cretaceous, the starting time and duration of volcanic activity are still equivocal. Two zircon U-Pb ages of volcanic rocks from strata at the lower base of the volcanic sequence along the Tan-Lu fault zone were reported in this paper, which provide new evidence for the discussion of the geological age.展开更多
The Taiping-Huangshan composite intrusion is a unique complex with characteristics changing from calc-alkaline (Taiping intrusion) to alkaline (Huangshan intrusion). Huangshan intrusion samples show a spectacular tetr...The Taiping-Huangshan composite intrusion is a unique complex with characteristics changing from calc-alkaline (Taiping intrusion) to alkaline (Huangshan intrusion). Huangshan intrusion samples show a spectacular tetrad effect in their REE distribution patterns as well as non-CHARAC (charge-and radius-controlled) trace element behavior, indicating a highly evolved late-stage magma component. This composite intrusion provides a rare opportunity to investigate the variance of tectonic setting and lithospheric thinning of the southeastern Yangtze Craton in late Mesozoic era. Zircon SHRIMP U-Pb analyses yield an emplacement age of 140.6±1.2 Ma for the Taiping intrusion, and ages of 127.7±1.3, 125.7±1.4, 125.1±1.5, and 125.2±5.5 Ma for four samples from the Huangshan intrusion respectively. The ages for four different phases of the Huangshan intrusion agree within their small analytical errors, indicating that the emplacement was in a short time. The Taiping and Huangshan intrusions are intimately associated, but there is about 15 Ma interval between their intrusion, and the magma characters change from calc-alkaline to alkaline without transition. This probably corresponds to lithospheric thinning of the southeastern Yangtze Craton. This event possibly happened from about 141 Ma (the emplacement age of the Taiping intrusion), to 128 Ma (start of emplacement of the Huangshan intrusion). The thinning mechanism is dominantly delamination.展开更多
基金the National 973 Project of Chinese Ministry of Science and Technology （Grant No. 2003CB716502） the Natural Science Foundation of China （Grant No. 40399143） +1 种基金 the German Science Foundation （DFG grant No. GE 1152/2-2 , WE2850/3- 1）.
文摘Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth took place at rates of approximately 9.5-10.5 km/Ma and exhumation from depths 〉160 km to the base of the crust at -30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin lithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.
基金financially supported by the Chinese Ministry of Science and Technology (grant No.2014DFR21270)the China Geological Survey (grants No.12120114085401 and 121201102000150021)
文摘Objective Shandong Province is divided into two parts by the Tan -Lu fault zone： the western part （Luxi） and the eastern part （Jiaodong）. Large-scale volcanic activity occurred during the Late Mesozoic in Shandong Province, eastern China （Fig. lb）, and was controlled by the Tan-Lu fault zone and its secondary faults. Mesozoic volcanic rocks in Shandong Province mainly occur within the Cretaceous Qingshan group, overlying the Laiyang group and underlying the Wangsi group. The Qingshan group has been divided into four volcanic cycles, i.e., the Houkuang, Bamudi, Shiqianzhuang and Fanggezhuang formations from the oldest to the youngest. Although geochronology data indicate the volcanic activity occurred during the Early Cretaceous, the starting time and duration of volcanic activity are still equivocal. Two zircon U-Pb ages of volcanic rocks from strata at the lower base of the volcanic sequence along the Tan-Lu fault zone were reported in this paper, which provide new evidence for the discussion of the geological age.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40772048, 40503006 and 40472035)China Geological Survey (Grant No. 1212010711814)
文摘The Taiping-Huangshan composite intrusion is a unique complex with characteristics changing from calc-alkaline (Taiping intrusion) to alkaline (Huangshan intrusion). Huangshan intrusion samples show a spectacular tetrad effect in their REE distribution patterns as well as non-CHARAC (charge-and radius-controlled) trace element behavior, indicating a highly evolved late-stage magma component. This composite intrusion provides a rare opportunity to investigate the variance of tectonic setting and lithospheric thinning of the southeastern Yangtze Craton in late Mesozoic era. Zircon SHRIMP U-Pb analyses yield an emplacement age of 140.6±1.2 Ma for the Taiping intrusion, and ages of 127.7±1.3, 125.7±1.4, 125.1±1.5, and 125.2±5.5 Ma for four samples from the Huangshan intrusion respectively. The ages for four different phases of the Huangshan intrusion agree within their small analytical errors, indicating that the emplacement was in a short time. The Taiping and Huangshan intrusions are intimately associated, but there is about 15 Ma interval between their intrusion, and the magma characters change from calc-alkaline to alkaline without transition. This probably corresponds to lithospheric thinning of the southeastern Yangtze Craton. This event possibly happened from about 141 Ma (the emplacement age of the Taiping intrusion), to 128 Ma (start of emplacement of the Huangshan intrusion). The thinning mechanism is dominantly delamination.
