Abstract:

By the analysis of natural earthquakes, we obtained the depth, the style of activation, and the strength of the detachment layer in the middle crust. Based on above study and combined with the interpretation of the gravity and magnetic anomalies of the basement of the study region, we propose that there is a regional detachment layer formed in the middle crust in the North China Block, and its depth determines the transition between the shallow and deep deformation in the study region. The detachment layer is the floor boundary of the deformation during the extension of the North China Block. When units of upper crust of the region slip along the detachment layer, owing to different velocities and boundary conditions, the derived cutoff lines, transverse faults and minor related highs and depressions are formed； all these are the basal tectonic units consisting of the upper crust of the North China Block, and they controlled the distribution of the basins and ranges and tectonic landforms basically in the study region. The division scheme of the upper crust in the North China Block is brought forward: there are 9 firstscale units (ⅠⅨ) and 23 secondscale units. Among them, the firstscale units are: Ⅰ EWtrending faulted block of the regional depression in the northern Yinshan; Ⅱ faulted block of YanshanYinshan regional high; Ⅲ faulted block of regional Taihangshan high; Ⅳ faulted block of regional Dabieshan high; Ⅴ faulted sags and uplifts in the Bohai Bay basin; Ⅵ faulted sags and uplifts of southern North China basin; Ⅶ regional faulted uplifts in west Shangdong; Ⅷ regional faulted sags and uplifts in the Lower Yangtze; Ⅸ regional faulted sag of the Ordos.

Key words:

Key words: upper crust; extensional setting; detachment layer; tectonic unit; North China Block