Interplay between faulting and base level in the development of Himalayan frontal fold topography

Abstract

[1] Fold topography preserves a potentially accessible record of the structure and evolution of an underlying thrust fault system, provided we understand the factors that shape that topography. Here we examine the morphology and fault geometry of two active folds at the northwest Himalayan front. The Chandigarh and Mohand anticlines show the following patterns: (1) most (∼60%–70%) growth in catchment size and relief (across multiple scales) is accomplished within ∼5 km of the fault tips, (2) range-scale relief is divided unevenly between the fold flanks because of base level contrasts, (3) mean gradients of the uplifting catchments correspond to different flank-averaged rock uplift rates, (4) high hillslope-scale relief coincides with areas of fast rock uplift and stronger lithologies, and (5) existing relief represents only ∼15% of the total rock eroded since faulting began, implying significant erosion. The first-order fold topography is developed quickly and asymmetrically as a result of fault-generated rock uplift (which sets the space available for the fold and the distribution of rock uplift rates) with some modulation by base level (which affects the erosional response of the landscape to the uplift). A linear rate of growth in catchment relief with range half-width correlates with catchment-averaged rock uplift rate, suggesting that this metric may be used to infer variations in fault dip at depth. In these frontal fold settings, high slip rates, weak uplifting rocks, and rapid erosion may combine to quickly limit the topographic growth of emerging folds and disconnect their morphology from the displacement field.