Active bidirectional tectonic-tilting in a part of the Almora Klippe, Kumaun Lesser Himalaya, India: Insights from statistical analyses of geomorphic indices

Abstract

The NW-SE trending, synformal Almora Klippe in central Kumaun Lesser Himalaya is actively uplifting along the basal thrust, which is known as North Almora Thrust (NAT) and South Almora Thrust (SAT) along the northern and southern flanks, respectively. Geomorphic indices of ‘Basin Asymmetry Factor (AF)’ and ‘Transverse Topography Factor (T)’ of 77 drainage basins of third-order streams developed on this tectonic block have been computed to decipher active tilt-block tectonics of a part of this vast klippe. Statistical analyses of the basins' geomorphic indices revealed differential, gentle to steep, bidirectional tilting of the Almora Klippe vis-à-vis lent insight into correct perspective which these must be used for such studies. The tectonic block of Almora Klippe is partitioned into two minor tectonic blocks along the hinge of the synform. Differential movements along the basal thrust of the klippe have caused westward down-tilting of the northern fold flank (‘AF’ having χ2 value of 7.556 for 4 azimuth classes at 90% confidence level, and ‘T’ having vector mean (θ¯v) of 260° and vector magnitude (r) of 0.25 at p-value of 0.1154), and eastward down-tilting of the southern fold flank (‘AF’ having χ2 value of 13.73 for 4 azimuth classes at 90% confidence level, and ‘T’ having vector mean (θ¯v) of 56° and vector magnitude (r) of 0.26 at p-value of 0.0585). The westward down-tilting of the northern fold flank is due to its faster uplift in the east, along the NAT. Similarly, the eastward down-tilting of the southern fold flank is due to its faster uplift in the west, along the SAT.