Preliminary kinematic data from a salient-recess pair along the Moine thrust, northwest Scotland
Matthew Strine, Gautam Mitra, 2004. "Preliminary kinematic data from a salient-recess pair along the Moine thrust, northwest Scotland", Orogenic curvature: Integrating paleomagnetic and structural analyses, Aviva J. Sussman, Arlo B. Weil
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In map pattern, fault traces in fold-thrust belts (FTBs) are typically curvilinear, often composed of a series of salients and recesses, and in three-dimensions, faults have non-planar geometries. The three-dimensional nature of fault surfaces has important implications for the overall kinematics of FTBs. We report quartz c-axis textures, grain-shape data, field measurements, and microstructural data from rock adjacent to the fault in a salient-recess pair along the Moine thrust. Within the salient, relict grains demonstrate low to moderate strains and weak to undeveloped quartz c-axis textures. On a Flinn diagram, grain shape data cluster around the k = 0.75 line. Within the recess, the footwall samples >35 m normal distance (nd) from the fault trace have quartz c-axis textures that indicate a general flattening strain. Grain shape data from these deformed relict grains yield lower k-values and higher strains than those seen within the adjoining salient. Samples closer to the thrust (within 8 m nd), also within the recess, are completely recrystallized and exhibit asymmetric c-axis patterns (some with vorticity parallel maxima) and Regime 3 type microstructures. The long axes of these recrystallized quartz grains are gently plunging and oriented sub-perpendicular to the regional transport direction. Within the hanging wall, quartz overgrowths form radially about opaque grains within the foliation plane, further supporting the inference of general flattening strains within the recess. The lateral variation seen between the salient and the recess reflects the variable kinematics within non-planar thrust systems and therefore thrust fault kinematics in general.