The energy spectra of reflected electrons from the substrates of targets have been calculated by the bipartition model of electron transport, the contributions of the inner shen ionization events produced by the refle...The energy spectra of reflected electrons from the substrates of targets have been calculated by the bipartition model of electron transport, the contributions of the inner shen ionization events produced by the reflected electrons from the substrates in the targets to the x-ray counting in a St(Li) detector have been estimated. It has been confirmed that, by such correction to the measured data, the experimental results of inner shell ionization cross sections by electron impact with fine precision may be obtained under the condition of thick substrate.展开更多
Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet) Plateau, the three dimensional (3-D) seismic velocity structures in Qinghai-Xizang Plateau were...Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet) Plateau, the three dimensional (3-D) seismic velocity structures in Qinghai-Xizang Plateau were obtained by using the regional body wave tomography and surface wave tomography. The results from these two tomography methods have similar characteristics for P- and S-wave velocity structures in crust and upper mantle. They show that there are remarkable low velocity zones in the upper crust of Lhasa block in the southern Qinghai-Xizang Plateau and the lower crust and upper mantle of Qiangtang block in the northern Qinghai-Xizang Plateau. These phenomena may be related to the different steps of collision process in southern and northern Qinghai-Xizang Plateau.展开更多
Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust,and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal...Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust,and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal materials and the crust-mantle interaction.This study presents a review of geochronology and geochemistry for postcollisional mafic igneous rocks from the Hong’an-Dabie-Sulu orogens and the southeastern edge of the North China Block.The available results indicate two types of the crust-mantle interaction in the continental subduction zone,which are represented by two types of mafic igneous rocks with distinct geochemical compositions.The first type of rocks exhibit arc-like trace element distribution patterns(i.e.enrichment of LILE,LREE and Pb,but depletion of HFSE)and enriched radiogenic Sr-Nd isotope compositions,whereas the second type of rocks show OIB-like trace element distribution patterns(i.e.enrichment of LILE and LREE,but no depletion of HFSE)and depleted radiogenic Sr-Nd isotope compositions.Both of them have variable zircon O isotope compositions,which are different from those of the normal mantle zircon,and contain residual crustal zircons.These geochemical features indicate that the two types of mafic igneous rocks were originated from the different natures of mantle sources.The mantle source for the second type of rocks would be generated by reaction of the overlying juvenile lithospheric mantle with felsic melts originated from previously subducted oceanic crust,whereas the mantle source for the first type of rocks would be generated by reaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts from subsequently subducted continental crust of the South China Block.Therefore,there exist two types of the crust-mantle interaction in the continental subduction zone,and the postcollisional mafic igneous rocks provide petrological and geochemical records of the slab-mantle interactions in continental collision orogens.展开更多
文摘The energy spectra of reflected electrons from the substrates of targets have been calculated by the bipartition model of electron transport, the contributions of the inner shen ionization events produced by the reflected electrons from the substrates in the targets to the x-ray counting in a St(Li) detector have been estimated. It has been confirmed that, by such correction to the measured data, the experimental results of inner shell ionization cross sections by electron impact with fine precision may be obtained under the condition of thick substrate.
文摘Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet) Plateau, the three dimensional (3-D) seismic velocity structures in Qinghai-Xizang Plateau were obtained by using the regional body wave tomography and surface wave tomography. The results from these two tomography methods have similar characteristics for P- and S-wave velocity structures in crust and upper mantle. They show that there are remarkable low velocity zones in the upper crust of Lhasa block in the southern Qinghai-Xizang Plateau and the lower crust and upper mantle of Qiangtang block in the northern Qinghai-Xizang Plateau. These phenomena may be related to the different steps of collision process in southern and northern Qinghai-Xizang Plateau.
基金supported by the Chinese Ministry of Science and Techno-logy(Grant No.2015CB856102)the National Natural Science Foundation of China(Grant Nos.41125012,41221062)
文摘Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust,and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal materials and the crust-mantle interaction.This study presents a review of geochronology and geochemistry for postcollisional mafic igneous rocks from the Hong’an-Dabie-Sulu orogens and the southeastern edge of the North China Block.The available results indicate two types of the crust-mantle interaction in the continental subduction zone,which are represented by two types of mafic igneous rocks with distinct geochemical compositions.The first type of rocks exhibit arc-like trace element distribution patterns(i.e.enrichment of LILE,LREE and Pb,but depletion of HFSE)and enriched radiogenic Sr-Nd isotope compositions,whereas the second type of rocks show OIB-like trace element distribution patterns(i.e.enrichment of LILE and LREE,but no depletion of HFSE)and depleted radiogenic Sr-Nd isotope compositions.Both of them have variable zircon O isotope compositions,which are different from those of the normal mantle zircon,and contain residual crustal zircons.These geochemical features indicate that the two types of mafic igneous rocks were originated from the different natures of mantle sources.The mantle source for the second type of rocks would be generated by reaction of the overlying juvenile lithospheric mantle with felsic melts originated from previously subducted oceanic crust,whereas the mantle source for the first type of rocks would be generated by reaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts from subsequently subducted continental crust of the South China Block.Therefore,there exist two types of the crust-mantle interaction in the continental subduction zone,and the postcollisional mafic igneous rocks provide petrological and geochemical records of the slab-mantle interactions in continental collision orogens.
