GEOLOGICAL MAP (1:400,000) OF THE OKHALDHUNGA REGION, EASTERN NEPAL HIMALAYA

The Himalaya fold-thrust belt stretches ~2300 km along strike with orogen-wide thrust faults that characterize it as a at a collisional plate boundary. To investigate deformation in this classic fold-thrust belt, we integrate detailed geological mapping, detrital zircon U-Pb geochronology and igneous zircon U-Pb geochronology with balanced cross sections and kinematic restorations along two transects. We present a new geological map of the Sagarmatha-Okhaldhunga region of eastern Nepal (1:400,000), accompanied by two crustal-scale balanced cross-sections and kinematic restorations along the Dudh Kosi and Tama Kosi Rivers. Primarily, this region comprises a ~140 km long and ~50 km wide erosional oval-shaped window in Proterozoic-Cambrian Greater Himalayan rocks that exposes structurally lower Paleo-Mesoproterozoic Lesser Himalayan rocks and middle Paleozoic Gondwana Sequence rocks. The Lesser Himalayan Duplex is exposed in the frontal part of the Okhaldhunga window, above a major footwall ramp in the Main Himalayan Thrust. Neoproterozoic-Cambrian Greater Himalayan rocks in the hanging wall of the Main Central Thrust are exposed toward the south in the synformal Mahabharat Range and in the north in the Rolwaling-Sagarmatha (Mt. Everest) region. A new minimum shortening estimate of ~500 km for rocks structurally below the South Tibetan detachment indicates that heterogeneous post-collisional crustal shortening determines the current tectonic configuration of the Himalaya.