The use of detrital mineral thermochronology to explore relationships among climate, erosion, and tectonics in the Nepal Himalaya

摘要

Numerical and analytical models of orogenic growth suggest that erosion can focus deformation in active convergent orogens, leading to a debate over the relative influence of climatic and tectonic forcing on erosion. In this thesis, geologic and observations, thermochronology, and thermo-kinematic numerical modeling are combined to quantify variations in long-term erosion in the Nepal Himalaya. Detrital mineral thermochronology is explored as a tool for quantifying tectonic and geomorphic process rates at a variety of spatial and temporal scales. The assumptions upon which catchment-wide erosion rate estimates based on detrital data depend are evaluated using statistical comparisons of 40Ar/39Ar ages from Nepal and catchment area-elevation distributions. Bedrock 40Ar/39Ar data indicate that erosion rate estimates from detrital thermochronology yield the same rate as the traditional approach of analyzing bedrock cooling ages over a range of elevations. Both bedrock and detrital 40Ar/39Ar data suggest a major acceleration of erosion rates at the Himalayan range front, and apatite fission-track data are used to pinpoint the timing of this acceleration to between 2.5 and 0.9 million years ago.