Using satellite images taken on different dates,GIS analysis of aerial photos,bathymetric maps and other field survey data,tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted.The r...Using satellite images taken on different dates,GIS analysis of aerial photos,bathymetric maps and other field survey data,tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted.The results show that there have been three types of movement or migration of tidal trough in this area:(1) Periodic and restricted,this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the low reaches,so they have been obviously impacted by human activity and have longer swing periods;(2) Periodic and actively,this kind of trough,which swung with a fast rate and moved periodically on sand ridges,were mainly controlled by the swings of the host tidal troughs and hydrodynamic forces upon tidal sand ridge and influenced slightly by human constructions;(3) Steadily and slowly,they are the main tidal troughs with large scale and a steady orientation in this area and have slow lateral movement.The differences in migration mode of tidal trough shift result in different rates of migration and impact upon tidal sand ridges.Lateral accumulation on current tidal trough and deposition on abandoned tidal troughs are the two types of sedimentation of the tidal sand ridges formation.The whole radial sand ridge was generally prone to division and retreat although sand ridges fluctuated by the analysis of changes in talwegs of tidal troughs and shorelines of sand ridges.展开更多
本文利用电子探针分析了苏北地区三类榴辉岩中金红石的Nb、Cr和Zr含量,在Zack et al．(2002)的金红石Nb- Cr图解中,三类榴辉岩的原岩均为镁铁质岩,但它们具有不同的地球化学特征,即(1)小焦G类金红石榴辉岩中金红石的Nb含量最低,平均值为...本文利用电子探针分析了苏北地区三类榴辉岩中金红石的Nb、Cr和Zr含量,在Zack et al．(2002)的金红石Nb- Cr图解中,三类榴辉岩的原岩均为镁铁质岩,但它们具有不同的地球化学特征,即(1)小焦G类金红石榴辉岩中金红石的Nb含量最低,平均值为68ppm,而其它两类榴辉岩中金红石的Nb含量较高,平均值介于192～255ppm;(2)蓝晶石榴辉岩具有极高Cr含量,均值6106ppm,而许沟P类榴辉岩中金红石的Cr含量也较高,均值1233ppm,金红石榴辉岩中金红石Cr含量最低,均值为183ppm。利用Zaek et al．(2004)提出的金红石地质温度计,计算得出许沟P类榴辉岩的金红石形成温度介于600—751℃,平均温度689℃;演马厂M类榴辉岩的金红石温度介于507-641℃,平均温度557℃;小焦G类金红石榴辉岩金红石的形成温度介于541-673℃,平均温度613℃;新扬昌G类蓝晶石榴辉岩的金红石形成温度介于541-655℃,平均温度603℃。一种可能的解释是,榴辉岩在拆返过程中退变质作用明显,流体活动强烈,导致金红石中Zr扩散丢失,金红石中Zr含量不同程度地受到角闪岩相退变质过程中再平衡作用的影响,致使计算的温度偏低。展开更多
基金Supported by the National Basic Research Program of China (973 Program) (Nos 40176021,40676037 and 40706027)
文摘Using satellite images taken on different dates,GIS analysis of aerial photos,bathymetric maps and other field survey data,tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted.The results show that there have been three types of movement or migration of tidal trough in this area:(1) Periodic and restricted,this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the low reaches,so they have been obviously impacted by human activity and have longer swing periods;(2) Periodic and actively,this kind of trough,which swung with a fast rate and moved periodically on sand ridges,were mainly controlled by the swings of the host tidal troughs and hydrodynamic forces upon tidal sand ridge and influenced slightly by human constructions;(3) Steadily and slowly,they are the main tidal troughs with large scale and a steady orientation in this area and have slow lateral movement.The differences in migration mode of tidal trough shift result in different rates of migration and impact upon tidal sand ridges.Lateral accumulation on current tidal trough and deposition on abandoned tidal troughs are the two types of sedimentation of the tidal sand ridges formation.The whole radial sand ridge was generally prone to division and retreat although sand ridges fluctuated by the analysis of changes in talwegs of tidal troughs and shorelines of sand ridges.
文摘本文利用电子探针分析了苏北地区三类榴辉岩中金红石的Nb、Cr和Zr含量,在Zack et al．(2002)的金红石Nb- Cr图解中,三类榴辉岩的原岩均为镁铁质岩,但它们具有不同的地球化学特征,即(1)小焦G类金红石榴辉岩中金红石的Nb含量最低,平均值为68ppm,而其它两类榴辉岩中金红石的Nb含量较高,平均值介于192～255ppm;(2)蓝晶石榴辉岩具有极高Cr含量,均值6106ppm,而许沟P类榴辉岩中金红石的Cr含量也较高,均值1233ppm,金红石榴辉岩中金红石Cr含量最低,均值为183ppm。利用Zaek et al．(2004)提出的金红石地质温度计,计算得出许沟P类榴辉岩的金红石形成温度介于600—751℃,平均温度689℃;演马厂M类榴辉岩的金红石温度介于507-641℃,平均温度557℃;小焦G类金红石榴辉岩金红石的形成温度介于541-673℃,平均温度613℃;新扬昌G类蓝晶石榴辉岩的金红石形成温度介于541-655℃,平均温度603℃。一种可能的解释是,榴辉岩在拆返过程中退变质作用明显,流体活动强烈,导致金红石中Zr扩散丢失,金红石中Zr含量不同程度地受到角闪岩相退变质过程中再平衡作用的影响,致使计算的温度偏低。
