49-7 The role of climate and tectonics on the tectonomorphic evolution of the Sagarmatha (Everest) region, eastern Nepal Himalaya

Session: Exploring Feedbacks Between Tectonics and Climate on Lithospheric Evolution Using Multidisciplinary Approaches

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Understanding the relative control of tectonics and climate on erosion via surface processes is crucial for our understanding of the temporal longevity and establishment of high topography in orogenic systems. To understand the interplay of climate and tectonics in driving long-term erosion and landscape evolution in the Himalayan orogen, this study examines the tectono-thermal evolution of Sagarmatha (Everest)-Rolwaling-Okhaldhunga region in eastern Nepal. We present new low-temperature thermochronology and thermal history models focused on two transects along the Tama Kosi and Dudh Kosi Rivers running up to the Everest/Sagarmatha region in eastern Nepal. New zircon (U-Th)/He cooling dates for 10 samples and apatite fission track cooling dates for 16 samples were combined with published muscovite ⁴⁰Ar/³⁹Ar and zircon fission track data to investigate regional cooling patterns. We then leverage thermochronometric constraints with published kinematic models to create sample-specific forward and inverse thermal history models. Forward thermal models indicate discrepancies between kinematic reconstructions and observed thermochronometric datasets, while inverse models show a northward-younging trend of rapid cooling, independent of structural position. In tandem, these results suggest that tectonic processes alone cannot account for the observed exhumation patterns. Instead, we propose that northward propagating incision and subsequent isostatic uplift, likely linked to the late Miocene development of the Lesser Himalayan duplex coupled with a major river capture event in the Sun Kosi River ca. 8-5 Ma, has driven spatially variable exhumation. Preservation of Middle-Late Miocene ages at the highest elevations and on the Numbur high-elevation low-relief (HELR) surface in the Sagarmatha region indicate that the incisional wave has not extended to the northernmost parts of the eastern Nepal Himalaya.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9297

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