Structural geometry, kinematics and paleostress of the Main Boundary Thrust: New constraints from the Hazara-Kashmir syntaxis, Northwest Himalayas, Pakistan

Abstract

• The two separate faulting phases are preserved along the shear zone of the Main Boundary Thrust. • These fault zone fabrics help in relative time reconstruction of tectonic events based on displaced relationships, cross-cutting, and overprinting. • The stress regime changes along the Main Boundary Thrust (MBT) compressional in the east and transpressional in the west. • The variation in fold axis trendings, axial planes, and inclined to steep plunges of folds results from deformation and cross folding. The Himalayan fold and thrust belt in Kashmir is investigated for structural geometry, kinematics, and Paleostress analysis of Main Boundary Thrust along the eastern limb of the Hazara Kashmir syntaxis, Northwest Himalayas , Pakistan. The Precambrian to Cenozoic cover stratigraphic unit of the Indian plate is imbricated and faulted along the Main Boundary Thrust (MBT). The Main Boundary Thrust separates the Late Proterozoic Dogra Formation and Permo-Triassic Panjal Group of rocks from the Murree Formation molasses of Early Miocene . The faults and folds along Main Boundary Thrust are developed due to the Tertiary Himalayan collision. The regional strike of the area is northwest-southeast, and dip changes from northeast to southwest. The brittle lineations found at the surface of faulted rocks are deformed and displaced. Slickensides are mainly calcite and quartz coated. The coated surfaces of slickenside with the calcite fiber crystal growth or quartz reveal earlier origin prior to the slickenside surfaces, uncoated or fresh polished. These older slickensides show older thrust movement along the Main Boundary Thrust Fault , and uncoated fresh slickensides horizontal to sub-horizontal in trend shows strike-slip movement. The features like offset streams (Neelum River), displaced drainages (Panjkot nalla), triangular facets, displaced ridges, uplifted terraces, nick points, and seismicity associated with Main Boundary Thrust show that fault is an active fault. In the footwall of the Main Boundary Thrust, the Z-type drag folds developed as a result of extreme deformation at various localities. These Z-type folds along fault indicate pure thrust movement subordinate strike-slip sense of shear. The paleostress analysis and shear indicators yield the detailed kinematics history of the Main Boundary Thrust. Due to stress in this region, the movement's characteristics, together with outcrop structures, indicate clearly that brittle deformation exists along the Main Boundary Thrust. The present analysis of kinematics indicators fault-related slickensides, conjugate fractures, folding, dragging, faulting, shearing, and paleo stress analysis shows that pure thrust with subordinate strike-slip movements present in the eastern limb of Hazara Kashmir Syntaxis along the Main Boundary Thrust.