甘肃石包城盆地新生代沉积特征及与阿尔金断裂的关系研究

Cenozoic tectonics and sedimentation of Shibaocheng Basin,Gansu Province and its relationship with Altyn Tagh fault

阿尔金断裂是由阿尔金主干断层及其它次级断裂组成的巨型走滑断裂系,其分布规律符合左行走滑挤压模式。石包城盆地位于阿尔金断裂带内,为祁连山所围限,面积大约为3 000 km^2。通过对盆地上新统地层、砾岩砾石成份、古流向等沉积特征的综合研究分析表明:盆地南部边缘位于土大坂以南,主要由砾岩和含砾砂岩组成,其中灰岩占砾石成份80%以上;盆地东部边缘在石包城乡地区,砾岩砾石成份以花岗岩、片岩和片麻岩等变质岩居多,夹杂少量硅质岩;盆地的沉降中心位于双泉井子附近,靠近阿尔金断裂一侧;石包城盆地古水流方向为北西和北北西方向,说明该地区地势自南东至北西方向逐渐降低,盆地南东方向应为隆起区;石包城盆地双泉井子以西物源区应为盆地南缘的大雪山等一系列山体,而东北部物源应来自石包城乡附近的山体。石包城盆地是阿尔金断裂带中主干断层与分枝断层联合作用形成的走滑分枝盆地,从上新世以来,盆地至今扩张量约为30～40 km。按相同的位移速率,本文估算了阿尔金主干断层石包城段自渐新世以来的走滑量,大约为218 km。

The Altyn Tagh fault,a major strike-slip fault system in NW China,is consists of the main fault and the subsidiary faults with a distribution pattern corresponds to a simple shear model. Shibaocheng Basin is located in the south of the eastern section of Ahyn Tagh fault, confined by Qilian Mountains, covered an area of approximately 3 000 km^2. The sedimentary characteristics, such as the Pliocene stratigraphic features, conglomerate gravel compositions and paleocurrent,has been studied. The southern fringe of the Shibaocheng Basin,located at south of Tudaban, is composed mainly by the conglomerate and pebbly sandstone, which limestone gravel components accounted for more than 80%. The eastern edge of Shibaocheng Basin, situated near Shibaocheng Town,is consist of sandstone and siltstone with some conglomerate, which gravel compositions mostly are granite, schist, gneiss and other metamorphic rocks. The sedimentary center of the basin is located in the vicinity of Shuangquanjingzi, close to the side of the Altyn Tagh fault. The paleocurrent direction of Pliocene formation was from SE to NW and N-W-N. The terrain of Shibaocheng Basin was gradual lowering from South East to North West during Pliocene. The source area of the western Shibaocheng Basin was the Daxue Mountains and some other mountain,which is located in the southern to the Shibaocheng Basin. The source area of the eastern Shibaocheng Basin was the uplift mountains near the Shibaocheng town. Shibaocheng Basin is a strike-slip branch basin formed by interaction of the Altyn main fault and its branch faults. The Basin began to extend in Pliocene and its extensional width is now about 30 -40 km. The extending rate of the Shibaocheng Basin is about 0.66 cm/a. Based on the same rate, the displacement of the Altyn main fault is approximately estimated 218 km from Oligocene in Subei-Shibaocheng segment.