河西走廊中东段基底岩相构造分析和大地构造单元划分

Analysis of basement lithofacies structure and the division of tectonic units in the middle east section of the Hexi corridor

河西走廊中东段地处青藏高原东北缘,是我国地震多发区和重要的铜镍、铀、多金属和油气等矿产地.通过对该区2013年度获取1∶5万高精度航磁资料进行数据处理和反演,推断了深断裂10条、大断裂33条,分析了基底起伏和岩相构造情况,重新对大地构造单元进行了划分.结果表明:不同构造单元之间航磁特征和基底岩相构造均存在明显差异.阿拉善地块(二级)呈弧形磁异常,基底岩相以沉积—变质和变质建造为主,断裂具弧形特征;北祁连弧盆系(二级)以负磁异常为背景,基底以火山建造和浅变质复理石建造为主,断裂可分为北西西向、北东向、北西向和近东西向四组.上述2个二级单元可细分为5个三级单元、16个四级单元和4个五级单元.这一研究结果为进一步研究青藏高原的隆升机制、研究区地震预测及矿产资源的找矿潜力评价提供了重要依据.

Located in the northeast margin of the Qinghai Tibet Plateau,the Middle East section of the Hexi corridor is not only an earthquake prone area,but also an important mineral sources area of copper nickel,uranium,metal,oil and gas in China. However,because of being covered by the thick Quaternary strata, the basement lithofacies and structures of this area have not been researched systematically. Based on the aeromagnetic data processing and inversion of the latest high precision of 1 ∶50000 acquired in 2013,the author analyzes the proposition,and newly divides its tectonic units. The results show that the basement lithofacies and structures,as well as the aeromagnetic data,are obviously disparate among the different tectonic units.The Alxa block（ second-order） is characterized by an arc magnetic anomaly,and totally displays a gently change with the positive and negative magnetic field,which infers that its basement structures has a prominent south arc characteristic, and the lithofacies are dominated by sedimentary-metamorphic formation and metamorphic formation,with volcanic formation partially. the Alxa block is made form three third-order tectonic units： Chaoshui basin,Longshou Square basement complex belt and Bayan Hot basin. The third one is identified newly this time for its obvious basement depth. Chaoshui basin shows a hopeful prospect of oil-gas exploration,and is divided into five fourth-order and four fifth-order tectonic units. Among the fourth-order tectonic units,Shibanjin uplift is located in the southeast and may be a part of the south Bayan-uul uplift belt.With the fault structures divided into NWW,NE,NW and EW,North Qilian arc basin system（ second-order） shows a negative magnetic anomaly as the background. It can be divided into two third-order tectonic units（ Hexi corridor structure belt and North Qilian back-arc basin） based on the different basements. The former has a deeper basement and its lithofacies is dominated by shallow metamorphic flysch formation,whereas the latter’basement even can be found in the surface and is dominated by volcanic formation. The above two units can be further divided into eleven fourth-order tectonic units.Summarily,this research will provide important basis for the further study of the uplift mechanism of the Qinghai Tibet Plateau,earthquake prediction and prospecting potential evaluation of this area.