The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South...The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South China Block(SCB).In the Late Mesozoic,several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB,which was neglected in previous studies.These shear zones play an essential role in the tectonic evolution of the East Asia continents.This study focuses on the deformation and geochronology of two shear zones distributed along the SDZ,identified in the Shaliangzi and Maanqiao areas.The shear sense indicators and kinematic vorticity numbers(0.54–0.90)suggest these shear zones have sinistral shear and sub-simple shear deformation kinematics.The quartz’s dynamic recrystallization and c-axis fabric analysis in the Maanqiao shear zone(MSZ)revealed that the MSZ experienced deformation under green-schist facies conditions at∼400–500℃.The Shaliangzi shear zone deformed under amphibolite facies at∼500–700℃.The^(40)Ar/^(39)Ar(muscovite-biotite)dating of samples provided a plateau age of 121–123 Ma.Together with previously published data,our results concluded that QOB was dominated by compressional tectonics during the Late Early Cretaceous.Moreover,we suggested that the Siberian Block moved back to the south and Lhasa-Qiantang-Indochina Block to the north,which promoted intra-continental compressional tectonics.展开更多
A new ootype collected from the Upper Cretaceous Lijiacun Formation in the Shangdan Basin,Shaanxi Province is described in this paper. Based on general external shape, size, eggshell thickness and honeycomb-like eggsh...A new ootype collected from the Upper Cretaceous Lijiacun Formation in the Shangdan Basin,Shaanxi Province is described in this paper. Based on general external shape, size, eggshell thickness and honeycomb-like eggshell microstructure, eggs are referable to the oofamily Faveoloolithidae. Compared with other members of Faveoloolithidae, specimens described in this paper show special characteristics:adjacent pores are usually separated by two eggshell units between which often develop interspaces;columnar eggshell units are relatively closely arranged in radial view. According to these characteristics,we erect a new oogenus and a new oospecies: Duovallumoolithus shangdanensis oogen. et oosp. nov. The new discovery expands the diversity of Faveoloolithidae.展开更多
Studies on the metamorphism and deformation conditions of rocks in the suture zone are good ways to discuss the orogenic process and mechanism. The microstructure and ultramicrostructure features of minerals are true ...Studies on the metamorphism and deformation conditions of rocks in the suture zone are good ways to discuss the orogenic process and mechanism. The microstructure and ultramicrostructure features of minerals are true embodiment of formation environment of the orogenic belt. Based on the study of microstructure, ultramicrostructure deformation characteristic and compositional zonation of garnets in garnets-mica schists in the Tongbai mountain, east section of the Shangdan fault zone, the results show that the three types of garnets have suffered various states of plastic deformation. The dynamic recrystallization of garnets is due to the subgrain growth and boundary migration. The dislocations are mainly free dislocation and dislocation walls. The free dislocation density ρ = 6.14 × 108/cm2, and dislocation movement are mainly slips;slip planes are 1/2 {110} and {001}. Garnet microprobe analysis shows that it belongs to almandine, and reflects it has undergone epidote-amphibolite to amphibolite facies metamorphism. Compositional zonation of garnet shows that the rocks had experienced progressive metamorphism. First metamorphic environment was continuous temperature-pressure and in mid-term there were two non-synchronous transient cooling and decompression processes, and it finally underwent decompression and warming process of the thermal relaxation environment. The formation condition of garnet-mica schist is estimated: T = 562°C - 617°C, and P = 0.77 - 1.02 GPa. The differential stress is 0.511 GPa and strain rate is 4.97536 × 10-10 m/s. After systemic analysis, a conclusion is drawn that the plastic deformation mode, deformation mechanism and formation environment of garnets are closely related to the formation and development of the Shangdan fault zone. It truly reflects that the Shangdan fault zone, as the suture zone of Yangtze and north China plate, has been subjected to early medium-grade metamorphism. With the continuous compression after the collision, the left-lateral shearing happened and caused the formation of high density dislocations and subgrains of the garnets;finally the plastic deformation happened and the bulging recrystallization formed in the period of heat relaxation had a relative low stress.展开更多
对商丹盆地茶房村剖面210个样品进行了野外调查及粒度实验分析。结果表明:丹江一级阶地上的沉积物是55 000 a BP以来堆积的风成黄土;粒度特征主要以粉砂和粘粒为主,二者总和为86.65%,其中粗粉砂为优势组分,在剖面中含量达46.81%;粘粒含...对商丹盆地茶房村剖面210个样品进行了野外调查及粒度实验分析。结果表明:丹江一级阶地上的沉积物是55 000 a BP以来堆积的风成黄土;粒度特征主要以粉砂和粘粒为主,二者总和为86.65%,其中粗粉砂为优势组分,在剖面中含量达46.81%;粘粒含量为23.94%;古土壤层的粒度组成较黄土层偏细,显示了二者风化成壤作用的差异,即古土壤层风化程度强于黄土层;茶房村剖面粒度特征的变化反映了商丹盆地自55 000 a BP以来区域气候的变化特征:55 000~11 500 a BP时期气候寒冷干燥。全新世早期(11 500~8 500 a BP),气温有升高,降水增加。全新世中期(8 500~3 100 a BP),为大暖期,气候温暖湿润。全新世晚期(3 100 a BP至今),气温降低,降水减少。展开更多
基金the National Natural Science Foundation of China who provided necessary financial support for this study(Nos.41872218,41572179,and 41372204)the State Key Laboratory of Continental Dynamics,Northwest University,Xi’an for providing a special fund to accomplish this study.
文摘The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South China Block(SCB).In the Late Mesozoic,several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB,which was neglected in previous studies.These shear zones play an essential role in the tectonic evolution of the East Asia continents.This study focuses on the deformation and geochronology of two shear zones distributed along the SDZ,identified in the Shaliangzi and Maanqiao areas.The shear sense indicators and kinematic vorticity numbers(0.54–0.90)suggest these shear zones have sinistral shear and sub-simple shear deformation kinematics.The quartz’s dynamic recrystallization and c-axis fabric analysis in the Maanqiao shear zone(MSZ)revealed that the MSZ experienced deformation under green-schist facies conditions at∼400–500℃.The Shaliangzi shear zone deformed under amphibolite facies at∼500–700℃.The^(40)Ar/^(39)Ar(muscovite-biotite)dating of samples provided a plateau age of 121–123 Ma.Together with previously published data,our results concluded that QOB was dominated by compressional tectonics during the Late Early Cretaceous.Moreover,we suggested that the Siberian Block moved back to the south and Lhasa-Qiantang-Indochina Block to the north,which promoted intra-continental compressional tectonics.
基金supported by the national natural science foundation (41672012, 41688103)
文摘A new ootype collected from the Upper Cretaceous Lijiacun Formation in the Shangdan Basin,Shaanxi Province is described in this paper. Based on general external shape, size, eggshell thickness and honeycomb-like eggshell microstructure, eggs are referable to the oofamily Faveoloolithidae. Compared with other members of Faveoloolithidae, specimens described in this paper show special characteristics:adjacent pores are usually separated by two eggshell units between which often develop interspaces;columnar eggshell units are relatively closely arranged in radial view. According to these characteristics,we erect a new oogenus and a new oospecies: Duovallumoolithus shangdanensis oogen. et oosp. nov. The new discovery expands the diversity of Faveoloolithidae.
文摘Studies on the metamorphism and deformation conditions of rocks in the suture zone are good ways to discuss the orogenic process and mechanism. The microstructure and ultramicrostructure features of minerals are true embodiment of formation environment of the orogenic belt. Based on the study of microstructure, ultramicrostructure deformation characteristic and compositional zonation of garnets in garnets-mica schists in the Tongbai mountain, east section of the Shangdan fault zone, the results show that the three types of garnets have suffered various states of plastic deformation. The dynamic recrystallization of garnets is due to the subgrain growth and boundary migration. The dislocations are mainly free dislocation and dislocation walls. The free dislocation density ρ = 6.14 × 108/cm2, and dislocation movement are mainly slips;slip planes are 1/2 {110} and {001}. Garnet microprobe analysis shows that it belongs to almandine, and reflects it has undergone epidote-amphibolite to amphibolite facies metamorphism. Compositional zonation of garnet shows that the rocks had experienced progressive metamorphism. First metamorphic environment was continuous temperature-pressure and in mid-term there were two non-synchronous transient cooling and decompression processes, and it finally underwent decompression and warming process of the thermal relaxation environment. The formation condition of garnet-mica schist is estimated: T = 562°C - 617°C, and P = 0.77 - 1.02 GPa. The differential stress is 0.511 GPa and strain rate is 4.97536 × 10-10 m/s. After systemic analysis, a conclusion is drawn that the plastic deformation mode, deformation mechanism and formation environment of garnets are closely related to the formation and development of the Shangdan fault zone. It truly reflects that the Shangdan fault zone, as the suture zone of Yangtze and north China plate, has been subjected to early medium-grade metamorphism. With the continuous compression after the collision, the left-lateral shearing happened and caused the formation of high density dislocations and subgrains of the garnets;finally the plastic deformation happened and the bulging recrystallization formed in the period of heat relaxation had a relative low stress.
文摘对商丹盆地茶房村剖面210个样品进行了野外调查及粒度实验分析。结果表明:丹江一级阶地上的沉积物是55 000 a BP以来堆积的风成黄土;粒度特征主要以粉砂和粘粒为主,二者总和为86.65%,其中粗粉砂为优势组分,在剖面中含量达46.81%;粘粒含量为23.94%;古土壤层的粒度组成较黄土层偏细,显示了二者风化成壤作用的差异,即古土壤层风化程度强于黄土层;茶房村剖面粒度特征的变化反映了商丹盆地自55 000 a BP以来区域气候的变化特征:55 000~11 500 a BP时期气候寒冷干燥。全新世早期(11 500~8 500 a BP),气温有升高,降水增加。全新世中期(8 500~3 100 a BP),为大暖期,气候温暖湿润。全新世晚期(3 100 a BP至今),气温降低,降水减少。
