THE FEATURES OF THE ZIJINGGUANFRACTURE IN THE NORTHERN SECTION OF THE TAIHANG MOUNTAINS AND THE INFERENCE OF THE PROCESS OF ITS FORMATION AND EVOLUTION

The Zijingguan fracture was discovered and named by the Hebei Regional Geological Survey Brigade in the course of the 1:200000-scale regional geological survey in the northern section of the Taihang Mountains in 1959. In recent, years it has been found that the linear image of this fracture extends farther, constituting another important longitudinal fracture zone in the eastern part of China. An on-the-spot investigation of the northern section of the Taihang Mountains shows that the fracture zone consists of three parallel fractures of NNE-SSW trend: （1） the Zijingguan fracture at the eastern side, which extends northwards and is stopped by the pre-existing NEE-trending Yanhecheng fracure; （2） the Beilizhuang fracture at the western side, which extends northwards and disappears past the Lesser Wutai Mountains; and （3） the Wulonggou fracture in the middle, which stretches farthest. The three fractures combine to form the "Zijingguan fracture zone". Of these fractures, the Zijingguan fracture has a vertical throw of more than a thousand meters. It initiated at the end of the Jurassic; at that time its western block （footwall） was tilted by a big margin, thus resulting in a tectonic pattern of "tilted fault block" in the western part of the fracture. It was completed at the end of the Cretaceous; at that time it was mainly subject to horizontal torsion, therefore it is characterized by the nature of marked inheritance. Throughout geological history, the fracture has long been in the pivotal position of crustal uplift and subsidence since the late precambrian, so they have played an important controlling role, thus giving rise to utterly different geological structral backgrounds at opposite sides of the fracture.