中卫断裂带断层类型划分及其构造意义

Classification of Faults in the Zhongwei Fault Zone and Its Tectonic Implication

青藏高原东北缘的中卫断裂带在晚更新世以来的左旋走滑运动中,先存的挤压逆掩、逆冲断裂带发生了分化。某些断层或断层段继续活动;另一些先存断层在晚更新世以来不再活动;此外,还发育了一些新断层。因此,我们把中卫断裂带划分出三种断层类型,即新生断层、继承性断层和遗弃断层。新生断层就是在某次构造运动中新发育的断层。就中卫断裂带来说,是指晚更新世以来新发育的断层,这类断层是中卫断裂带左旋走滑运动的产物,在早期的挤压逆断运动中这些断层并不存在。通过对新生断层的调查研究可以获得以下资料:①反演晚更新世以来的构造应力场;②确定晚期构造运动的起始时代;③估算断层的断错幅度和速率。继承性断层是指在早期的挤压逆掩(冲)活动中已经存在的断层或断层段,在晚期的左旋走滑运动中继续活动。继承性断层的最大优点是包含了较多的信息量:①继承性断层记录了多期构造运动的信息;②继承性断层是中卫断裂带多期活动的见证;③继承性断层是研究构造演化过程的重要依据。遗弃断层即某些断层或断层段在早期构造运动中是主体断裂带的一部分,其活动习性与主体断裂带基本一致。当早期的构造运动终止之后,这些断层或断层段在后继的构造运动中不再活动而称之。遗弃断层的作用就在于它保留了早期构造运动的大部或全部信息,这些信息基本上没有受到后期构造运动的干扰破坏。因而通过对遗弃断层的研究可以获得早期构造运动的主要信息。①确定早期构造运动终止的年代;②反演早期构造应力场方向;③研究断层的滑动方式,即粘滑和蠕滑。

The left-lateral strike-slip movement of the Zhongwei fault zone since late Pleistocene caused the differentiation of preexisting overthrust faults in the zone. Some early-formed faults or fault segments continued to be active, while the others were inactive. In addition, some new faults were developed since then. The faults in the Zhongwei fault zone, therefore, can be classified into three categories, the newlygenerated, the inherited and the rejected faults. The newly-generated fault refers to those that developed newly by a certain tectonic movement. With regard to the Zhongwei fault zone, it refers to the one which developed since late Pleistocene. Such a fault is the result of the left lateral strike-slip movement of the Zhongwei fault zone, and did not exist during the early compressive overthrusting movement. The investigation on these newly generated faults may provide the following information. （1） The tectonic stress field since late Pleistocene; （2） the starting time of the late tectonic movement, and （3） the displacement amount and slip rate of the fault. The inherited fault refers to the fault or fault segment that existed before the late left-lateral strike-slip movement of the fault zone and was still active after the movement. The prominent advantage of the inherited fault is that the fault contains a lot of tectonic information. （1）the inherited faults recorded the information of multiple tectonic movements; （2）they are the witness to the multiple tectonic movements along the Zhongwei fault zone; and （3） they are the important basis for the study of the tectonic evolution history. The rejected fault refers to the fault or fault segment that was the part of the main fault zone and behaved in the same way as the main fault zone during the early tectonic movement. After the early tectonic movement, the fault or fault segment has become inactive during the subsequent tectonic movement, indicating that it was rejected. The fault may reserve most or all of the information about the early tectonic movement, which is basically not disturbed or destroyed by the late tectonic movement. The investigation of rejected faults, therefore, may provide the following essential information about the early tectonic movement. （1） the ceasing time of the early tectonic movement; （2） the feature of the early tectonic stress field; and （3） the mode of faulting, i.e. stick-slip or creep-slip.