北京南口-孙河断裂与黄庄-高丽营断裂交会区沉积速率差异对断裂活动性的响应

THE DIFFERENCE OF DEPOSITION RATE IN THE BOREHOLES AT THE JUNCTION BETWEEN NANKOU-SUNHE FAULT AND HUANGZHUANG-GAOLIYING FAULT AND ITS RESPONSE TO FAULT ACTIVITY IN THE BEIJING AREA

通过对北京地区南口-孙河断裂与黄庄-高丽营断裂交会处钻孔剖面开展磁性地层学研究,结合沉积物岩石组合特征以及浅部测年数据进行分析,建立了钻孔剖面的第四纪地层格架,由于地层沉积速率对控盆断裂的活动具有较好的响应,对比钻孔沉积速率的变化特征能够对目标断裂的第四纪活动性进行探讨。研究表明,南口-孙河断裂与黄庄-高丽营断裂交会处所控制的断块在第四纪时期存在明显的差异性沉降。早更新世至全新世,南口-孙河断裂活动性表现为强弱交替的特点,黄庄-高丽营断裂则表现为逐渐减弱的特点。早更新世,黄庄-高丽营断裂活动强度大于南口-孙河断裂,之后南口-孙河断裂的活动强度大于黄庄-高丽营断裂的活动强度,直至全新世,2条断裂的活动性趋于一致。

Beijing plain area has been always characterized by the tectonic subsidence movement since the Pliocene. Influenced and affected by the extensional tectonic environment,tensional normal faulting occurred on the buried NE-trending faults in this area,forming the 'two uplifts and one sag'tectonic pattern. Since Quaternary,the Neocathaysian stress field caused the NW-directed tensional shear faulting,and two groups of active faults are developed. The NE-trending active faults include three major faults,namely,from west to east,the Huangzhuang-Gaoliying Fault,Shunyi Fault and Xiadian Fault. The NW-trending active faults include the Nankou-Sunke Fault,which strikes in the direction of NW320° ~ 330°,with a total length of about 50 km in the Beijing area. The northwestern segment of the fault dips SW,forming a NW-directed collapse zone,which controls the NW-directed Machikou Quaternary depression. The thickness of the Quaternary is more than 600 meters; the southeastern segment of the fault dips NE,with a small vertical throw between the two walls of the fault.Huangzhuang-Gaoliying Fault is a discontinuous buried active fault,a boundary line between the Beijing sag and Xishan tectonic uplift. In the Beijing area,it has a total length of 110 km,striking NE,dipping SE,with a dip angle of about 50 ~ 80 degrees. It is a normal fault,with the maximum fault throw of more than 1 000 m since the Tertiary. The fault was formed in the last phase of Yanshan movement and controls the Cretaceous,Paleogene,Neogene and Quaternary sediments.There are four holes drilled at the junction between Nankou-Sunhe Fault and HuangzhuangGaoliying Fault in Beijing area. The geographic coordinates of ZK17 is 40°5'51″N,116°25'40″E,the hole depth is 416. 6 meters. The geographic coordinates of ZK18 is 40°5'16″N,116°25'32″E,the hole depth is 247. 6 meters. The geographic coordinates of ZK19 is 40°5'32″N,116°26'51″E,the hole depth is 500. 9 meters. The geographic coordinates of ZK20 is 40°4'27″N,116°26'30″E,the hole depth is 308. 2 meters. The total number of paleomagnetism samples is 687,and 460 of them are selected for thermal demagnetization. Based on the magnetostratigraphic study and analysis on the characteristics of sedimentary rock assemblage and shallow dating data,Quaternary stratigraphic framework of drilling profiles is established. As the sedimentation rate of strata has a good response to the activity of the basin-controlling fault,we discussed the activity of target fault during the Quaternary by studying variations of deposition rate. The results show that the fault block in the junction between the Nankou-Sunhe Fault and the Huangzhuang-Gaoliying Fault is characteristic of obvious differential subsidence. The average deposition rate difference of fault-controlled stratum reflects the control of the neotectonic movement on the sediment distribution of different tectonic units.The activity of Nankou-Sunhe Fault shows the strong-weak alternating pattern from the early Pleistocene to Holocene. In the early Pleistocene the activity intensity of Huangzhuang-Gaoliying Fault is stronger than Nankou-Sunhe Fault. After the early Pleistocene the activity intensity of Nankou-Sunhe Fault is stronger than Huangzhuang-Gaoliying Fault. The activity of the two faults tends to consistent till the Holocene.