Analysis on the trends of groundwater level changes in the allusive plain of Taihang Mountain piedmount region suggested that:①the dropping-down of groundwater level was mainly caused by water use in wheat growing se...Analysis on the trends of groundwater level changes in the allusive plain of Taihang Mountain piedmount region suggested that:①the dropping-down of groundwater level was mainly caused by water use in wheat growing season,which is the dry season of the year.②The amount of precipitation in wheat growing season,corn growing season and the whole year are strongly correlated with the dropping-down of groundwater level in the corresponding period. Statistic analysis indicated that when precipitation increased by 100mm in wheat growing season,corn growing season and the whole year,the dropping-down of groundwater level decreased by 0.365m,0.436m and 0.56m respectively. The difference in different levels of dropping-down during different periods was possibly resulted from the difference in recharge of groundwater in different seasons and the effectiveness of rainfall for the crops.③The analysis also implied that the accelerated dropping-down of groundwater level was mainly caused by decrease of groundwater recharge. Before 1985,the groundwater level usually raised over 0.8m in contrast with less than 0.4m after 1986.④Compared to 1970s′,the amount of water use in wheat growing season could be decreasing suggested by a gradual decrease in groundwater dropping-down during this period. On the other hand,water use in corn growing season could be increasing.⑤Based on the analysis of groundwater level changes,it was suggested that,in order to keep the sustainable use of groundwater in this region,150 mm of irrigation has to be saved each year in the future. Considering an annual 250mm of soil evaporation was not used for crop growth and some results from water-saving experiments,to achieve this target is possible.展开更多
Mesozoic contraction deformation in the Yanshan and Taihang mountains is characterized by basement-involved thrust tectonics,basement-cored buckling anticlines and ductile thrust and nappe tectonics.Most of these defo...Mesozoic contraction deformation in the Yanshan and Taihang mountains is characterized by basement-involved thrust tectonics,basement-cored buckling anticlines and ductile thrust and nappe tectonics.Most of these deformations are orientated west-east,west-northwest and northeast to north-northeast.The contraction deformations began in the Permian,continued through the Triassic and Jurassic and terminated in the Early Cretaceous,and constitute an important part of the destruction of the North China Craton.It is estimated,from balanced cross-section reconstructions,that the north-south shortening of the central part of the Yanshan belt before 135 Ma was around 38%.The initial crust thickness,pre-dating the major contraction deformation in late Paleozoic and early Mesozoic,was estimated to be around 35 km based on paleogeographic characteristics.Assuming that the inferred depth of ductile thrusting deformation,20-25 km,was the crust thickness involved in the contraction deformation,and also assuming that the N-S contraction deformation was accommodated by vertical crust thickening,the thickness of the crust after the contraction deformation was expected to be around 47-50 km.This was the approximate crust thickness required for the eclogitization of the lower crust for delamination.The gravity potential accumulated by the isostatic uplift of the thickened crust,together with the decrease in crustal strength caused by the coeval magmatisms associated with the contraction deformation,led to the subsequent extensional collapse of the middle and upper crust although the regional stress regime associated with the plate interactions remained constant.It is inferred that the Mesozoic contraction deformations in the Yanshan and Taihang mountains were not only a significant tectonic process contributing to the destruction of the craton in middle and upper crust but also stimulated delamination at a deep level and the extension of the shallow crust.In other words,both the suspected delamination of the lower crust and upper ma展开更多
文摘Analysis on the trends of groundwater level changes in the allusive plain of Taihang Mountain piedmount region suggested that:①the dropping-down of groundwater level was mainly caused by water use in wheat growing season,which is the dry season of the year.②The amount of precipitation in wheat growing season,corn growing season and the whole year are strongly correlated with the dropping-down of groundwater level in the corresponding period. Statistic analysis indicated that when precipitation increased by 100mm in wheat growing season,corn growing season and the whole year,the dropping-down of groundwater level decreased by 0.365m,0.436m and 0.56m respectively. The difference in different levels of dropping-down during different periods was possibly resulted from the difference in recharge of groundwater in different seasons and the effectiveness of rainfall for the crops.③The analysis also implied that the accelerated dropping-down of groundwater level was mainly caused by decrease of groundwater recharge. Before 1985,the groundwater level usually raised over 0.8m in contrast with less than 0.4m after 1986.④Compared to 1970s′,the amount of water use in wheat growing season could be decreasing suggested by a gradual decrease in groundwater dropping-down during this period. On the other hand,water use in corn growing season could be increasing.⑤Based on the analysis of groundwater level changes,it was suggested that,in order to keep the sustainable use of groundwater in this region,150 mm of irrigation has to be saved each year in the future. Considering an annual 250mm of soil evaporation was not used for crop growth and some results from water-saving experiments,to achieve this target is possible.
基金supported by the National Natural Science Foundation of China (Grants Nos. 90814002,40672150,40272086)
文摘Mesozoic contraction deformation in the Yanshan and Taihang mountains is characterized by basement-involved thrust tectonics,basement-cored buckling anticlines and ductile thrust and nappe tectonics.Most of these deformations are orientated west-east,west-northwest and northeast to north-northeast.The contraction deformations began in the Permian,continued through the Triassic and Jurassic and terminated in the Early Cretaceous,and constitute an important part of the destruction of the North China Craton.It is estimated,from balanced cross-section reconstructions,that the north-south shortening of the central part of the Yanshan belt before 135 Ma was around 38%.The initial crust thickness,pre-dating the major contraction deformation in late Paleozoic and early Mesozoic,was estimated to be around 35 km based on paleogeographic characteristics.Assuming that the inferred depth of ductile thrusting deformation,20-25 km,was the crust thickness involved in the contraction deformation,and also assuming that the N-S contraction deformation was accommodated by vertical crust thickening,the thickness of the crust after the contraction deformation was expected to be around 47-50 km.This was the approximate crust thickness required for the eclogitization of the lower crust for delamination.The gravity potential accumulated by the isostatic uplift of the thickened crust,together with the decrease in crustal strength caused by the coeval magmatisms associated with the contraction deformation,led to the subsequent extensional collapse of the middle and upper crust although the regional stress regime associated with the plate interactions remained constant.It is inferred that the Mesozoic contraction deformations in the Yanshan and Taihang mountains were not only a significant tectonic process contributing to the destruction of the craton in middle and upper crust but also stimulated delamination at a deep level and the extension of the shallow crust.In other words,both the suspected delamination of the lower crust and upper ma
