An Overview of the Main Central Thrust and a Regional Shear Zone across the Kaligandaki River, Nepal

Abstract

Investigations for a proposed hydropower project on Nepal’s Kali Gandaki River focused on the Main Central Thrust (MCT) and a prominent regional shear zone. Field traverses revealed lithological transitions from slates and Quartz-Mica Schist to Quartz-Biotite Gneiss, defining the MCT more precisely than prior regional interpretations. A persistent crushed leucocratic quartzo-feldspathic gneiss zone, aligned with off-white landslide scars and NW–SE river bends, appears to exert greater influence on engineering geology than the MCT. While the tightly bound MCT is unlikely to compromise major structures, the shear zone poses geotechnical risks, particularly for pressure and drop shafts, warranting targeted investigations.