3-D geometry of the Moine thrust and its implications for 3-D strain distribution and thrust sheet kinematics

大多数逆冲断层痕迹本质上是弧形的，由一系列凸起和凹陷组成，这表明逆冲断层总体上是非平面的。逆冲面几何形状的这种三维复杂性可能是控制逆冲断层运动学的一个重要因素。考虑一下冰川冰流过不规则底板的类比。移动的主要阻力不是由于两种材料之间的摩擦(表面覆盖的压力融化水大大减少了摩擦)，而是由于冰在流经表面不规则处时的变形。ThrustSheet可能会以类似的方式运行。断裂岩比围岩弱得多，因此，这种岩石的持续变形可能不是大规模逆冲片侵位的因素。PI表明，推力面几何形状的三维不规则性在推力片运动学中起主要作用。如果是这样的话，人们应该预料到，沿给定逆冲断层走向观察到的应变模式将反映逆冲断层的几何形状。初步研究表明，c轴图形和残余颗粒形状沿断层走向变化，很可能是由于断层几何效应。最初的数据表明，在一个突出的突出点内，变形几乎是平面应变；但沿着突出点的边缘，有一个较强的扁平应变分量。然而，需要对该地区的毒株进行进一步检查，才能真正解决这种模式。通过测量残留石英颗粒形状和对石英c轴组构进行采样，确定了该地区的三维有限应变几何形状。此外，通过确定三维重结晶石英颗粒形状和三维石英生长几何形状来测量最终阶段增量应变也是有用的。只有通过检验增量应变史，PI才能全面了解逆冲断层的运动学特征，然而，现有的力学模型没有考虑非平面应变的存在，因此只能对现实的褶皱冲断带行为进行一阶预测。为了建立更真实的褶皱冲断带演化模型，我们必须开始考虑几何上复杂的逆冲断层的非平面应变单元。

Most thrust fault traces are arcuate in nature and are comprised of a series ofsalients and recesses suggesting that thrust faults are, in general, non-planar. Such three-dimensional complexities in the thrust surface geometry may be an important factorcontrolling the thrust fault kinematics. Consider the analogy of glacial ice flowing overan irregular substrate. The major resistance to movement is not due to the frictionbetween the two materials (which is greatly reduced by pressure-melt water that coats thesurface) but due to the distortion of the ice as it flows past surface irregularities. Thrustsheets may behave in a similar manner. Fault rocks are considerably weaker than thehost rock and, therefore, the continued deformation of such rocks may not be the factor inlarge-scale thrust sheet emplacement. The PI suggests that three-dimension irregularities inthrust surface geometry play a major role in thrust sheet kinematics. If this is the case,one should expect that the strain patterns observed along strike of a given thrust fault willreflect the thrust fault geometry. Preliminary studies have shown that both c-axespatterns and relict grain shapes vary along the strike of the fault most likely due to thefault geometry effects. Initial data suggest that deformation is nearly plane strainwithin a prominent salient; but along the margins of the salient there is a strongercomponent of flattening strains. However, further examination of the strains in thisregion are needed to truly resolve this pattern. Three-dimensional finite strain geometrieshave been determined in this region by measuring relict quartz grain shapes andexamining quartz c-axes fabrics. Moreover, it may also be useful to measure final stageincremental strains by determining three-dimensional recrystallized quartz grain shapesand three-dimensional quartz overgrowth geometries. It is only through examiningincremental strain histories that the PI can fully understand the kinematics of thrust faults.Nevertheless, current mechanical models do not take into account the existence ofnon-plane strains and therefore only predict realistic fold-thrust belt behavior to a first-order. In order to make more realistic models for the evolution of fold-and-thrust beltswe must start to incorporate the non-plane strain elements of geometrically complexthrust faults.