Figure 1. Spatial variations in rock uplift rate across a growing fold as calculated from deformed river terraces. A. Geometry of the Main Frontal Thrust (MFT) in central Nepal as reconstructed from surface dips in its hangingwall. The uplift rates (shown below) indicate a slip rate of 20 mm/yr along the fault. The offset stratigraphy indicates a minimum of 10 km of slip on the fault. Yet, the relief in the hangingwall is just a few hundred meters. Hence, uplift and erosion must be nearly balanced. Most of the uplifted strata are Neogene foreland basin strata. B. Surveyed Holocene terraces along the Bagmati River, Nepal, in the hangingwall of the MFT. Radiocarbon dates in the deposits overlying each terrace place limits on the age of each. Note the undulating upper terrace surfaces. C. Relative rock-uplift rates derived from the height of each terrace above the modern river. The spatial coincidence of rates for each terrace results from their kinematic tie to subtle changes in dip of the MFT. The remarkable persistence of uplift rates through time argues for steady Holocene slip on the MFT. C. Modified after Lavé and Avouac (2000).
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Oct28 09
