摘要
The North China rift zone,including the North China Plain rift zone and the middle Shanxi graben-rift zone,is a continental rift;geomorphologically,its most common and important characteristics are the multiple accordant summit levels (ASLs) in the denudational area.In this study three methods based on geomorphic analysis,that is,(1) unified topographic profiles,(2) cyclic knickpoints along longitudinal river profiles,and (3) depth contours of river downcutting,are used to identify the ASLs and analyze their tectonic deformation.The formation time of the ASLs is determined by geological and geomorphological evidence,the correlation with the sedimentary facies in the Plain rift zone,and K-Ar ages of basalts on the ASLs,indicating the rates of tectonic uplift.The North China rift zone has five ASLs,of which the highest and oldest ASL I is the remnant of a fossil peneplain formed before rifting and the other four lower and younger ones are pediplain-typed formed contemporaneously with rifting.Study of
The North China rift zone,including the North China Plain rift zone and the middle Shanxi graben-rift zone,is a continental rift;geomorphologically,its most common and important characteristics are the multiple accordant summit levels (ASLs) in the denudational area.In this study three methods based on geomorphic analysis,that is,(1) unified topographic profiles,(2) cyclic knickpoints along longitudinal river profiles,and (3) depth contours of river downcutting,are used to identify the ASLs and analyze their tectonic deformation.The formation time of the ASLs is determined by geological and geomorphological evidence,the correlation with the sedimentary facies in the Plain rift zone,and K-Ar ages of basalts on the ASLs,indicating the rates of tectonic uplift.The North China rift zone has five ASLs,of which the highest and oldest ASL I is the remnant of a fossil peneplain formed before rifting and the other four lower and younger ones are pediplain-typed formed contemporaneously with rifting.Study of ASLs in the denudational areas can provide geomorphical evidence about the evolutional history of the continental rift zone.
