Origin of kink bands in the Golconda allochthon, Toiyabe Range, Nevada
The orientation of monoclinal and conjugate kink bands in three thrust sheets of the Golconda allochthon in the southern Toiyabe Range, Nevada, provides information about shortening directions during the late-stage emplacement of the allochthon. The kink bands are the youngest of the structures within the allochthon and postdate the stacking of internal thrust sheets. The reoriented attitudes of the kink bands along the Golconda thrust, the sole of the allochthon, indicate that the kinks formed before the latest movement along the thrust. Calculated shortening directions from kink bands are interpreted to represent synchronous orthogonal contractions that led to the formation of two discrete groups of monoclinal and local conjugate kink bands. One group apparently was caused by an east-west shortening subparallel to the direction of tectonic transport of the allochthon, and the other, by an approximately north-south shortening subparallel to the strike of the allochthon. The biaxial contraction may have been generated owing to the spoon-shaped configuration of the sole thrust of the allochthon. Kink bands probably were developed during ramping of the allochthon up the continental margin when cleavage rotated to gentler dips and erosional unroofing reduced the normal stress across the cleavage for slip to occur parallel to cleavage.