Exhumation of the Ladakh batholith revealed through the combined analysis of bedrock and detrital zircon (U-Th)/He data

Recent studies of the Ladakh batholith, in the northwestern Indian Himalaya, have yielded various hypotheses for its exhumation history and relationship with the evolution of the southwestern margin of the Tibetan Plateau, which is today bounded by the Karakoram fault. Different hypotheses are supported by various datasets with differing spatial and temporal resolution. First, low-temperature thermochronologic and thermobarometric data provide constraints on long term exhumation (10^6 - 10^7 yr) and suggest that the Ladakh batholith experienced multiple tilting events since ~40 Ma (Kirstein, Tectonophysics, 2011). Second, cosmogenic nuclide concentrations (CNCs), which provide evidence for erosion rates averaged over millennial timescales (10^2-10^4 yr), suggest that erosion rates increase toward the Karakoram fault (Dortch et al., Geomorphology, 2011). A third dataset comprises detrital zircon (U-Th)/He data obtained from the mouth of the Basgo catchment, on the southern flank of the Ladakh batholith (Tripathy-Lang et al., JGR-ES, 2013). This exceptionally large detrital dataset provides information about both the bedrock age distribution and recent erosion rates that sample different parts of the catchment. Interpreting this dataset requires an understanding of the erosion history at multiple timescales. To these already existing datasets, we add new bedrock zircon (U-Th)/He data from an age-elevation transect collected from the base to range crest of the Basgo catchment, which we use to verify models of bedrock age distribution. Through the combined analysis of the datasets, the resolution of both the long term exhumation rate and the spatial distribution of modern erosion rates can be greatly improved, thus advancing our understanding of this part of the Tibetan margin. With this aim, we use thermo-kinematic models to predict bedrock ages that we compare to our new bedrock data. We test different modern erosion rate distributions to generate synthetic detrital thermochronometric and CNC data. Through the comparison of predicted and measured data (both detrital thermochronometric data and CNC data) we infer long term exhumation histories and also modern erosion rate distribution.