南海西南部珊瑚礁区活动断裂分析

利用SEABAT8111多波束系统在南海西南部珊瑚礁区海域进行地形地貌探测,同时还进行了单道和多道地球物理调查。探测表明该区珊瑚礁礁体的活动断裂主要有NE、NW、SN向3组。NE向断裂主要分布在岛礁区内,是晚燕山期南海第一次海底扩张时形成的断裂系,强烈活动于晚白垩世—始新世,晚第三纪以来继承性活动,以张剪性断裂为主,现今活动性中等至弱。NW向断裂主要分布在曾母盆地,以张剪性断裂为主,切割至基底,强烈活动于渐新世至上新世,构成了曾母盆地的主要张裂期,第四纪仍有活动,均为弱活动断裂。SN向断裂主要有南海西部的滨海断裂带,它是南海SN向扩张时期的转换断层,具张剪性,为中活动断裂,是南海西南部珊瑚礁区活动性较强的断裂,该断裂带历史上曾有火山活动和地震活动的记录。

Active faults in coral reef areas of southwestern South China Sea

Based on the data of seismic profile and multi-beam detection, the paper analyses the basic characteristics and distribution of active faults in coral reef areas of the southwestern South China Sea. The NW direction fault like Beikang-Tingjia fault is a horizontal moving fault. Two groups of active faults in NE and NW directions exist in the survey area. The NE active fault, formed during the first seaflJP 2]oor extension in late Yanshan period, had intensive activity in late Cretaceous and Eocene, and kept active in late Tertiary. It is mainly an expanding-shearing fault. Now it has medium and weak activity. The NW fault is an extending-shearing fault which cuts the basement. It had intensive activity from Oligocene to Pliocene, which was the main extending period of Zengmu Basin. It is still active in Quaternary but only a fault of weak activity. The S-N fault zone is a typical dextral strike-slip fault system. It is the western border of the South China Sea opening. The formation of the system is due to the collision of India with Tibet since Cretaceous, the extract of Indochina Peninsula and the spreading of the South China Sea in Cenozoic. The whole length of this system is about 600km, and it consists of the front extension imbricate fan in the southern segment, the pull-apart extension duplex in the middle segment and the trailing push-up contracted imbricate fan in the northern segment. The basins in the western South China Sea are controlled by the fault zone. The fault zone has medium activity and has records of volcano and earthquake activities in the history.