龙门山北段构造变形特征与物理模拟

Tectonic deformation features and physical modeling of northern section of Longmen Mountains

龙门山构造带位于扬子板块与松潘—甘孜褶皱带的交接部位,具有NE分带、EW分段的变形特征。龙门山北段逆冲推覆带是以出露轿子顶杂岩和唐王寨向斜为典型特征;推覆-滑覆带变形强烈,地表主要为一系列NW往SE的叠瓦推覆体,地腹发育双重构造;而前陆坳陷变形较弱,地表主要为SE倾伏的单斜,地腹则发育断层相关褶皱。通过构造物理模拟认为:1)龙门山北段构造变形受力边界主应力与断裂走向间的锐夹角为70°,为羌塘地块与西秦岭造山带共同挤压所形成;2)构造变形样式上后缘为基底卷入式背冲型断层组合,前缘为前展型叠瓦式组合,断层向上延伸受下侏罗统滑脱层限制;3)构造具有3个阶段的变形过程,早期须家河组三段晚期的挤压作用产生叠瓦状断层,中期遂宁组沉积期和晚期白田坝组沉积期发生同沉积挤压变形。

Longmen Mountains tectonic belt is located in the intersection area of Yangtze plate and Songpan-Ganzi fold belt and shows the deformation features of NE zoning and EW blocking.The northern section of Longmen thrust belt is characterized by outcropping Jiaoziding complex rock and Tangwangzhai syncline.The structural deformation of nappe-slumped overthrust zones is very strong.Land surface is mainly a series of imbricate nappes thrusting from NW to SE,with the duplex developed in reservoir.The deformation of foreland depression is relatively weak and the surface is mainly the monoclines pitching in SE direction,with the folds related to faults developed in reservoir.According to structural physical modeling,it is considered that： a） the acute angle between the direction of main stress in structural deformation boundary and fault strike is 70° in the northern section of Longmen Mountains,created by the compaction Qiangtang block and the orogenic zone of West Qinling;b） the following edge is base-rolling back-thrusting fault complex with regard to the structural deformation patterns,with the imbricate fault complex in front edge.The upward fault extension is restricted by the slip formation of Lower Jurassic;c） the structural deformation can be divided into three stages： the imbricate faults caused by the compression at the early period of second-third section of Xujiahe Formation,the syndepositional compression deformation in the depositional stage of middle Suining Formation and in the depositional stage of late Baitianba Formation.