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

大多数逆冲断层的迹线呈弧形，由一系列的凸起和凹陷组成，表明逆冲断层一般是非平面的。这种逆冲面几何结构的三维复杂性可能是控制逆冲断层运动学的重要因素。考虑冰川冰在不规则基底上流动的类比。运动的主要阻力不是由于两种材料之间的摩擦（由于覆盖表面的压力融化水大大减少了摩擦），而是由于冰流过不规则表面时的扭曲。推力板的行为可能与此类似。断层岩比主岩弱得多，因此，这种岩石的持续变形可能不是大规模逆冲板侵位的因素。PI表明，推力面几何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，我们就可以预料到沿某一逆冲断层走向所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轴模式和残余颗粒形状沿断层走向变化，很可能是由于断层几何形状的影响。初始数据表明，变形在一个突出的凸起内接近平面应变；但在突出部分的边缘，有一种更强的扁平化压力成分。然而，需要进一步检查该地区的菌株才能真正解决这一模式。通过测量残余石英颗粒形状和检测石英c轴结构，确定了该地区的三维有限应变几何形状。此外，通过确定三维再结晶石英晶粒形状和三维石英过度生长几何形状，也可以用于测量最后阶段的增量应变。只有通过检查增量应变历史，PI才能充分了解逆冲断层的运动学。然而，目前的力学模型没有考虑到非平面应变的存在，因此只能在一阶上预测真实的褶皱-冲断带行为。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复杂逆冲断层的非平面应变元素。

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.