The Roles of Climate and Tectonics in the Tectonomorphic Evolution of the Sagarmatha (Mt. Everest) Region, Eastern Nepal Himalaya

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 the Sagarmatha (Mt. Everest)-Rolwaling-Okhaldhunga region in eastern Nepal. We present new low-temperature thermochronological data and thermal history models focused on two transects along the Tama Kosi and Dudh Kosi Rivers up to the Sagarmatha/Mt. Everest 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 leverage thermochronometric constraints to create sample-specific inverse thermal history models, which show a northward-younging trend of Middle-Late Miocene rapid cooling independent of structural position. In contrast, the kinematic history of the thrust belt in this region shows a southward propagation of thrusting. Thus, tectonic processes alone do not account for the observed cooling and exhumation patterns. Instead, we propose that northward propagating incision and subsequent isostatic uplift, likely triggered by the late Miocene development of the Lesser Himalayan duplex ca. 8–5 Ma, have driven spatially variable exhumation. Preservation of Middle-Late Miocene dates in the northern High Himalaya and on the Numbur high-elevation low-relief surface in the Sagarmatha region indicate that the incisional wave has not extended to the northernmost eastern Nepal Himalaya.