阿尔金断裂带中侏罗世走滑活动及其断裂规模的探讨--来自软沉积物变形的证据  

Middle Jurassic strike slip movement and fault scale of the Altyn Tagh fault system: Evidence from the soft sediment deformation

作　　者：龚正[1] 李海兵[1] 孙知明[2] 刘栋梁[1] 潘家伟[1] 韩亮[1] 吴蝉[1] 

机构地区：[1]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《岩石学报》2013年第6期2233-2250,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41221061、41202143、41202156);中国地质调查局地质大调查项目(121201121267);行业基金项目(201011034)联合资助

摘　　要：阿尔金断裂带是青藏高原北部边界,它不仅切割了高原北部的不同构造单元,控制了高原北部的几何学特征及基本的构造格架,而且还是调节青藏高原变形和高原物质向东挤出的重要断裂之一,对它的形成时代、活动历史以及断裂带的生长过程和演化的研究是认识青藏高原形成过程和动力学问题的关键之一。本文以阿尔金断裂带中段肃北县城南部出露的中侏罗纪陆相湖沼地层为研究对象,在野外中侏罗世剖面中,共发现26层软沉积物变形层。软沉积物变形的方式主要是不同类型的砂土液化,包括负载、球-枕状构造、卷曲变形、液化角砾、液化底劈和砂火山构造;软沉积变形大多发生在细砂岩和泥质粉砂岩层中,细砂岩层易液化、变形剧烈;粒度统计显示发生液化的沙粒粒径在0.05～0.5mm之间,主要为0.2～0.3mm,这些砂土液化的软沉积物变形特征与历史地震和模拟实验获取的易液化扰动区间高度一致,因此,中侏罗世地层中发育的软沉积物变形是由于地震震动而形成。根据震级与液化最大震中距的关系,推测发生的最小震级在MS6～6.5之间,根据软沉积变形的类别与震级之间的关系推断最大可能发生的震级为7.5级。根据软沉积变形层出现的频率和组合关系,我们认为肃北剖面反应的是一个地震幕,发生的地震事件至少在4次以上,表明在中侏罗世(古)阿尔金断裂带发生了强烈的走滑运动,并且至少断裂带已延展到肃北一带,结合索尔库里地区晚三叠纪左旋走滑活动形成的糜棱岩以及玉门地区白垩纪的火山活动和软沉积物变形的事实,指示着阿尔金断裂带至少经历了晚三叠纪、中侏罗纪、晚白垩纪及新近纪的强烈走滑活动,并且其断裂带由索尔库里地区向东西两端逐渐扩展生长,由早期百千米到上千千米、一千多千米至约两千千米长的现今规模。Marking the northern margin of the Tibet Plateau,the Altyn Tagh fault system not only truncates various geological units, controlling both the geometric characters and tectonic framework in northern Tibet,but also comprises the main passage where the landmass easternward extrude. It is crucial to study the fault system’s forming,active ages and fault trace evolvement to probe the dynamic mechanism of the Tibet Plateau. Here,we take advantage of the soft sediment deformation revealed in Middle Jurassic lacustrine strata in southern Subei to explore such questions. There are generally 26 deformation layers found which can be further subdivided into 4 categories in the field： load and pillow structure,liquefied diapir and crater,liquefied breccia and convoluted structure. The grain size statistic shows the grains mainly range from 0.2～0.3mm （ 60% ） ,highly comparable with the modern earthquake ejected and experimental grains size,thuswe consider them as earthquake induced liquefaction. Based on the empirical statistical relation between the earthquake magnitude and the maximum liquefactiondistance,we presume the minimum magnitude is 6～6. 5,whereas,in view of the specific deformation structure with different magnitude,we suggest the maximum magnitude may exceed 7. 5. The 26 deformation layers represent an earthquake episode in Middle Jurassic,with at least4 earthquakes. The Altyn Tagh fault system was highly active in Middle Jurassic and the fault trace had already reached Subei area at least. Given the Triassic active agededuced from the mylonite in Xorkol and the volcano activities in Cretaceous and Jurassic,soft sediment deformation in Yumen area in Cretaceous,the Altyn Tagh fault may have experienced at least three active ages： the Late Triassic,the Middle Jurassic and the Cenozoic,with the fault length expand from several hundred kilometers to more than 1000 kilometers and to 2000 kilometers.

关 键 词：阿尔金断裂带 软沉积物变形 古地震 中侏罗世 肃北 

分 类 号：P542.3[天文地球—构造地质学]