DOCUMENTING VARIATION IN EXHUMATION PATTERNS WITHIN CENTRAL AND FAR WESTERN NEPAL’S GREATER HIMALAYA WITH DETRITAL APATITE FISSION TRACK ANALYSES: A PRELIMINARY STUDY

Detrital apatite fission track (AFT) analyses have been obtained from 9 samples collected from 7 drainages in Central and Far Western Nepal during 2016 and 2017. One of the main difficulties of using this technique in Nepal is the relative youthfulness of the range, and therefore, the initial goal of this study was to evaluate the viability of detrital AFT thermochronology in the Greater Himalaya. This was accomplished with a comparison of the distribution of single crystal AFT ages from 82 in-situ bedrock samples from the Marsyandi drainage (Blythe et al., 2007) with the distribution of detrital ages from a single detrital sample collected from the Marsyandi river just to the south of the Main Central Thrust (MCT). Although the spatial variations in exhumation within drainage basins cannot be documented with this technique, the detrital AFT ages provided a reasonable approximation of the temporal pattern of bedrock ages within the drainage basin. Based on these initial results, we have begun obtaining detrital AFT analyses on single samples from additional drainages where large data bases of bedrock AFT ages do not exist and would be difficult and costly to obtain. Six of the nine detrital samples were collected in the southern footwall of the MCT. For each detrital sample, we plan to obtain >100 single grain ages, and will identify separate populations of ages within the datasets using BinomFit (Brandon, 2002). Our preliminary data suggest that variations in the timing of exhumation along the MCT can be explored with detrital AFT analyses, allowing identification of regions that would benefit from a more detailed in-situ bedrock sampling strategy.