The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses,...The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses, intruded by mafic dykes of gabbroic composition. Many highly strained rocks were previously misinterpreted as supracrustal sequences and represent mylonitized granitoids and sheared dykes. Our single zircon dating documents magmatic granitoid emplacement ages between 2.52 Ga and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses, possibly reflecting an older basement. A few granitic gneisses have emplacement ages between 2.35 and 2.1 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after -2.1 Ga. Intrusion of gabbroic dykes occurred at -1920 Ma, and all Hengshan rocks underwent granulite-facies metamorphism at 1.88-1.85 Ga, followed by retrogression, sheafing and uplift. We interpret the Hengshan and adjacent Fuping granitoid gneisses as the lower, plutonic, part of a late Archaean to early Palaeoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the nearby Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Major deformation and HP metamorphism occurred in the late Palaeoproterozoic during the Luliang orogeny when the Eastern and Western blocks of the North China Craton collided to form the Trans-North China orogen. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of HP metamorphism, and we suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Palaeoproterozoic （〈1.85 Ga）.展开更多
The Hengshan complex is located in the central part of SE China, which underwent rapid tectonic uplift in the Cretaceous just like many other complexes on the continent. （40）~Ar-（39）~Ar geochronological data from ...The Hengshan complex is located in the central part of SE China, which underwent rapid tectonic uplift in the Cretaceous just like many other complexes on the continent. （40）~Ar-（39）~Ar geochronological data from the Hengshan complex suggest that two episodes of crustal cooling/extension took place in this part of the continent during the Cretaceous time. The first stage of exhumation was active during ca. 136-125 Ma, with a cooling rate of 〉 10 ℃Ma. The second stage of exhumation happened at ca. 98-93 Ma, with a cooling rate of 〉 10 ℃/Ma. Considering the folding in the Lower Cretaceous sedimentary rocks and the regional unconformity underneath the Upper Cretaceous red beds, it is believed that the Cretaceous crustal extension in SE China was interrupted by a compressional event. The reversion to extension, shortly after this middle Cretaceous compression, led to the rapid cooling/exhumation of the Hengshan complex at ca. 98-93 Ma. The Cretaceous tectonic processes in the hinterland of SE China could be controlled by interactions between the continental margin and the Paleo-pacific plate.展开更多
Our field investigation indicates that the northern piedmont fault of the Hengshan Mountain has dislocated proluvial fan and terrace I of the gully mouth on the northern border of the Hengshan Mountain. Stratigraphic ...Our field investigation indicates that the northern piedmont fault of the Hengshan Mountain has dislocated proluvial fan and terrace I of the gully mouth on the northern border of the Hengshan Mountain. Stratigraphic age data indicates that the surface layer in the middle and rear part of the proluvial fan and on the terrace I of the gully mouth on the mountain border consists of sediments of about 5200～6800a B.P. The Hezhuang and Niucaoyu trenches excavated in the front of Hengshan Mountain revealed that 3 paleoseismic events have occurred along the northern piedmont fault of Hengshan Mountain since the early Holocene. The 3 paleoseismic events occurred in 2260±190～4370±150a BP, nearly 5628±150a BP, and 8083±250～8430±720a BP, respectively, and their recurrence interval is 2313a,2628a and 2471a on average. The coseismic vertical displacement produced by these events is 1 0～3 0m. The elapsed time of the latest movement along the fault has exceeded the recurrence interval of these paleoearthquakes. Thus, there exists the possibility of strong earthquake occurrence along the fault from now onward, so the fault is in need of observation.展开更多
Hornblende＇s plastic and superplastic deformation mechanisms were studied on the basis of some new information obtained from amphibolite samples in the Hengshan Mountains （Hengshan, Shanxi, China）.For this purpose,...Hornblende＇s plastic and superplastic deformation mechanisms were studied on the basis of some new information obtained from amphibolite samples in the Hengshan Mountains （Hengshan, Shanxi, China）.For this purpose, the samples were measured and analyzed by optical microscope （OM）, electron probe microanalysis （EPMA）, transmission electron microscope （TEM） and electron backscattered diffraction （EBSD） respectively.Because localized strong strain is more than 1000%, it is presumed that structural superplastic deformation was developed during the ductile shearing process.It is calculated that deformation occurred at 650-679℃ and 0.770-0.914 GPa, based on the study of plagioclase-hornblende geothermometry and geobarometry.TEM images show that new hornblende grains developed few dislocations and hornblende crystals exhibit straight grain boundaries.EBSD of strongly deformed hornblendes reveals a fabric dominated by a {100} lattice preferred orientation （LPO）, indicative of new grain recrystallization along the lineation direction （X axis）.Thus superplastic deformation of hornblendes from the Hengshan Mountains was developed by mainly solid-state diffusive mass transfer and grain boundary sliding.展开更多
Hengshan granulite facies terrane consists of tonalite-trondhjemite-granodiorite(TTG)gneisses and minor high-pressure mafic granulite blocks.LA-ICP-MS zircon dating for two TTG gneiss samples indicates metamorphic age...Hengshan granulite facies terrane consists of tonalite-trondhjemite-granodiorite(TTG)gneisses and minor high-pressure mafic granulite blocks.LA-ICP-MS zircon dating for two TTG gneiss samples indicates metamorphic ages of 1916.7±9.9 Ma and1850–1930 Ma,and magmatic protolith age of ca.2.5 Ga,with similar HREE-rich patterns.Phase equilibria modelling in ZrO2-bearing system reveals that zircon abundance varies inversely with melt abundance in suprasolidus metamorphism,zircon growth occurs with melt crystallization during cooling,and thus,the newly grown zircon can only record the age of retrograde metamorphism.Consequently,we suggest that the Hengshan granulite facies terrane experienced slowly uplifting and cooling during 1.85–1.93 Ga in an extensional setting under middle-crust,while the collision orogeny corresponding to peak stage of high-pressure granulite may have happened much earlier.展开更多
基金funded by the German Science Foundation(DFG,grant Kr 590/62)the National Natural Science Foundation of China(grant Nos.49832030,49772143 and 49572140 to Li Jianghai)
文摘The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses, intruded by mafic dykes of gabbroic composition. Many highly strained rocks were previously misinterpreted as supracrustal sequences and represent mylonitized granitoids and sheared dykes. Our single zircon dating documents magmatic granitoid emplacement ages between 2.52 Ga and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses, possibly reflecting an older basement. A few granitic gneisses have emplacement ages between 2.35 and 2.1 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after -2.1 Ga. Intrusion of gabbroic dykes occurred at -1920 Ma, and all Hengshan rocks underwent granulite-facies metamorphism at 1.88-1.85 Ga, followed by retrogression, sheafing and uplift. We interpret the Hengshan and adjacent Fuping granitoid gneisses as the lower, plutonic, part of a late Archaean to early Palaeoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the nearby Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Major deformation and HP metamorphism occurred in the late Palaeoproterozoic during the Luliang orogeny when the Eastern and Western blocks of the North China Craton collided to form the Trans-North China orogen. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of HP metamorphism, and we suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Palaeoproterozoic （〈1.85 Ga）.
基金supported by the basic outlay of scientific research work from the Ministry of Science and Technology(DZLXJK201302)the National Science and Technology Project(SinoProbe–08–01)the Chinese National Fund of Science grant(no.41202154)
文摘The Hengshan complex is located in the central part of SE China, which underwent rapid tectonic uplift in the Cretaceous just like many other complexes on the continent. （40）~Ar-（39）~Ar geochronological data from the Hengshan complex suggest that two episodes of crustal cooling/extension took place in this part of the continent during the Cretaceous time. The first stage of exhumation was active during ca. 136-125 Ma, with a cooling rate of 〉 10 ℃Ma. The second stage of exhumation happened at ca. 98-93 Ma, with a cooling rate of 〉 10 ℃/Ma. Considering the folding in the Lower Cretaceous sedimentary rocks and the regional unconformity underneath the Upper Cretaceous red beds, it is believed that the Cretaceous crustal extension in SE China was interrupted by a compressional event. The reversion to extension, shortly after this middle Cretaceous compression, led to the rapid cooling/exhumation of the Hengshan complex at ca. 98-93 Ma. The Cretaceous tectonic processes in the hinterland of SE China could be controlled by interactions between the continental margin and the Paleo-pacific plate.
文摘Our field investigation indicates that the northern piedmont fault of the Hengshan Mountain has dislocated proluvial fan and terrace I of the gully mouth on the northern border of the Hengshan Mountain. Stratigraphic age data indicates that the surface layer in the middle and rear part of the proluvial fan and on the terrace I of the gully mouth on the mountain border consists of sediments of about 5200～6800a B.P. The Hezhuang and Niucaoyu trenches excavated in the front of Hengshan Mountain revealed that 3 paleoseismic events have occurred along the northern piedmont fault of Hengshan Mountain since the early Holocene. The 3 paleoseismic events occurred in 2260±190～4370±150a BP, nearly 5628±150a BP, and 8083±250～8430±720a BP, respectively, and their recurrence interval is 2313a,2628a and 2471a on average. The coseismic vertical displacement produced by these events is 1 0～3 0m. The elapsed time of the latest movement along the fault has exceeded the recurrence interval of these paleoearthquakes. Thus, there exists the possibility of strong earthquake occurrence along the fault from now onward, so the fault is in need of observation.
基金supported by National Natural Science Foundation of China(Grant No.40772133)
文摘Hornblende＇s plastic and superplastic deformation mechanisms were studied on the basis of some new information obtained from amphibolite samples in the Hengshan Mountains （Hengshan, Shanxi, China）.For this purpose, the samples were measured and analyzed by optical microscope （OM）, electron probe microanalysis （EPMA）, transmission electron microscope （TEM） and electron backscattered diffraction （EBSD） respectively.Because localized strong strain is more than 1000%, it is presumed that structural superplastic deformation was developed during the ductile shearing process.It is calculated that deformation occurred at 650-679℃ and 0.770-0.914 GPa, based on the study of plagioclase-hornblende geothermometry and geobarometry.TEM images show that new hornblende grains developed few dislocations and hornblende crystals exhibit straight grain boundaries.EBSD of strongly deformed hornblendes reveals a fabric dominated by a {100} lattice preferred orientation （LPO）, indicative of new grain recrystallization along the lineation direction （X axis）.Thus superplastic deformation of hornblendes from the Hengshan Mountains was developed by mainly solid-state diffusive mass transfer and grain boundary sliding.
基金supported by the National Natural Science Foundation of China (41172055 and 41121062)the China Survey of Geology (1212011121062)
文摘Hengshan granulite facies terrane consists of tonalite-trondhjemite-granodiorite(TTG)gneisses and minor high-pressure mafic granulite blocks.LA-ICP-MS zircon dating for two TTG gneiss samples indicates metamorphic ages of 1916.7±9.9 Ma and1850–1930 Ma,and magmatic protolith age of ca.2.5 Ga,with similar HREE-rich patterns.Phase equilibria modelling in ZrO2-bearing system reveals that zircon abundance varies inversely with melt abundance in suprasolidus metamorphism,zircon growth occurs with melt crystallization during cooling,and thus,the newly grown zircon can only record the age of retrograde metamorphism.Consequently,we suggest that the Hengshan granulite facies terrane experienced slowly uplifting and cooling during 1.85–1.93 Ga in an extensional setting under middle-crust,while the collision orogeny corresponding to peak stage of high-pressure granulite may have happened much earlier.
