Abstract
The aim of the present research is to provide the base line details of the NNW-SSE trending Raintoli fault (RF) which is running parallel to the North Almora Thrust (NAT) along the Saryu valley from Seraghat-Naichun to Seri in the central sector of the Uttarakhand Himalaya, India. The RF is characterized as dextral strike slip fault and behaves as a ductile shear zone within the zone of NAT. The dextral sense of shear movement of RF is delineated by the fabric of the shear zone rocks including microscopically observed indicators such as sigma and delta porphyroclasts, quartz c-axis, and the field structural data. Additionally, in the quaternary period the dextral strike slip fault is reactivated with oblique slip component as characterized by various geomorphic indicators, for example, triangular facets, abandoned river channels, unpaired fluvial terraces, and V-shaped valleys with recurrent seismicity. Further, the morphometric parameters including Valley Floor Width to Valley Height (Vf), asymmetry factor (AF), and gradient index (GI) further prove active nature of RF as suggested by low values of hypsometric integration, V-shaped valley, higher gradient index, and tilting of Saryu basin.
Highlights
The Himalaya has been divided into four lithotectonic subdivision from south to north, for example, Siwalik or SubHimalaya, Lesser Himalaya, Higher Himalaya, and Tethys Himalaya [1]
The Raintoli Fault (RF) is characterized by the right lateral strike-slip fault which runs parallel to the North Almora Thrust (NAT) for about 20 km along the Saryu valley from Seraght-Naichun-Raintoli to Seri section in the Central Kumaun Himalaya
The structural data suggest two phases of deformation, for example, D1 and D2, the former is related to the development of schistosity and affected by tight to isoclinal folds and the latter may have resulted due to the development of crenulation cleavage
Summary
The Himalaya has been divided into four lithotectonic subdivision from south to north, for example, Siwalik or SubHimalaya, Lesser Himalaya, Higher Himalaya, and Tethys Himalaya [1]. The intracrustal boundary thrusts, for example, Himalayan Frontal Thrust (HFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT), and Trans Himadri Fault (THF), have been separating the lithotectonic unit from south to north, respectively (Figure 1(a)). The Lesser (Central) Kumaun Himalaya, stretching from Nepal to Himachal Pradesh, is characterized by allochthons nappes (Thrust sheets), for example, Almora nappe, Ramgarh nappe, and Krol nappe, and tectonic windows within which the Precambrian-Cambrian autochthons are exposed [1, 2]. The Almora nappe is a consequence of tectonic transport of the rocks of Higher Himalayan Metamorphic Belt to the Lesser Himalaya over the Main Central Thrust (MCT) during Eocene–Oligocene [3, 4]. The northern and southern flanks of Almora nappe were described as the North Almora Thrust (NAT) and South Almora Thrust (SAT), respectively [2]. The thrust bounded synclinal nappes and the subsidiary thrusts/faults have been reactivated in the Journal of Geological Research
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