BALANCED STRUCTURAL CROSSSECTION ACROSS HIMALAYAN FOOTHILLS (KALKA-DHARAMPUR)

Abstract

Fold thrust belts are one of the most interesting conundrums faced by structural geologists today. These are sedimentary basins deformed due to contractional forces. These forces scrap the sediments from base of the basin and lift them off the basin margin. The term was initially defined for deformed belts found at the fringes of orogenic belts but now days; it is known that these can be found in a variety of tectonic settings. This report attempts to develop a subsurface picture of such a classic thin -skiirned tectonic belt in the NW Himalayas. The chosen line of section is in Himalayan foothills, passing approximately through the cities of Kalka- Dharampur. It has been chosen in such a way that it is at high angle to major fault and axial traces so that there is no loss or gain of material in or out of the section. The area, as mentioned, lies in the Himalayan foothills and contains the lesser Himalayan rocks and sub-Himalayan rocks exposed. Foreland is located in the Indo-gangetic plain and the rocks become more and more deformed as one moves towards the hinterland. The structures are controlled by the major faults of the area and usually, faults are complemented by folds trending the orogeny, indicating an implicit relationship between two. In addition, a number of regional faults become important in this transect, besides the MBT and MCT. These faults gradually start rotating and interfering with each other as we move hinterland wards due to low ramp spacing, and added complexion due to out of sequence thrusts. The modelling has tried to decipher this present structure through a sequence of fault - bend folds and fault propagation folds. These assumptions lead to the development of an imbricate system in the SHZ tertiary rocks, which ride piggy- back on the MFT structure. A number of out-of sequence thrusts make the structure further complex by breaching the older structures in a break-back style. The kinematics and geometry of the section has been constrained with the help of surface strike and dip data and outcrop sequence and is in conformity with the structures observed on field.