弧形走滑砂箱构造物理模型及其大地构造意义

Strike slip analogue experiment with a curved basement fault system and its tectonic implication

利用砂箱构造物理模型和"实验-实例"互证思想,探讨弧形剪切走滑变形构造特征及其意义。基于弧形吕德尔和弥散性走滑砂箱构造物理模型模拟实验,揭示弧形走滑构造变形导致砂箱浅表断层以R型和Y型走滑破裂为主,形成相互叠置的花状构造冲起带;但弧形带内侧和外侧具有明显不一致的几何学与运动学特征。弧形吕德尔剪切模型中弧形带内侧和外侧走滑断层与基底断层走向夹角范围分别为4°~23°、6°~23°,内外侧走滑断层端点与基底断层间距离分别为1~6mm、4~5mm;弧形弥散性剪切走滑变形过程中弧形带内侧、外侧走向角分别为4°~30°、11°~25°,断层间距分别为1.1~5.7mm、1.6~4.7mm,且弧形带内侧断层倾角主要为~45°,而弧形带外侧断裂倾角主要为65°和75°,总体上揭示出弧形剪切带内侧走滑上冲构造特征显著强于外侧。同时,砂箱浅表物质PIV监测揭示弧形基底断层带外侧冲起构造带的地质体走向上水平走滑速率逐渐减小、垂直运动速率逐渐增大,揭示了走滑断层构造属性逐渐转变的过程,即由走滑断裂逐渐转变为(走滑)上冲断裂,断层沿走向的倾角逐渐减小、断距增大,空间上呈现为螺旋状断面特征。四川盆地周缘弧形(走滑)构造变形带,即大凉山-小江弧形走滑构造带和大巴山城口弧形走滑上冲构造带,它们的形成过程及其构造特征与弧形(走滑)结构带密切相关。

Based on analogue experiments,two sets of scaled models are conducted to understand the characteristics of strike-slip with a curved basement-fault system and its tectonic implications.Two sets of models dominate with Riedel shear and distributed shear along a curved basement-fault,respectively.Both of them show predominant R-shear and Y-shear with increasing strike-slip,and form overlapped flower structures.However,the convex side shows distinct difference in deformation in contrast to the concave side.In the Riedel shear models,the angle between faults and the trace ofthe main curved fault at the surface is 4°~23° on the concave side and 6°~23° on the convex side.While distance of fault at surface to the main curved fault is 1~6 mm on the concave side,in contrast to 4~5 mm on the convex side.In the distributed shear models,the angle and distance of fault are 4°~30° and 1.1~5.7 mm on the concave side,11°~25°and 1.6~4.7 mm on the convex side,respectively.In particular,the fault dip is dominated with about 45° on the concave side,much smaller than dips of 65° and 75°on the convex side,an indication of a much strong deformation occurred on the concave side.Furthermore,there is a distinct decrease in strike-slip velocity,and increase in uplift velocity in the strike of the 2 models indicated by the PIV monitor system.It suggests a transfer of strike-slip to thrusting along the strike,combined with decreased fault dips and increased fault displacement,as a heliciform geometry of fault.Compared the Daliangshan-Xiaojiang with the Dabashan strike-slip fault systems,the models reveal that those systems are genetically related to strong strike-slip with curved faults.