The Uplift Mechanism of the Eastern Himalayan Syntaxis

The Eastern Himalayan Syntaxis (EHS) has undergone intense crustal shortening, giving rise to spectacular topography in the Tibetan Plateau. Several tectonic models have been proposed to explain its deformation, including crustal-scale folding, indenter corner dynamics, and tectonic aneurysm mechanisms. Understanding the crustal architecture and present-day state of the EHS is essential for deciphering its tectonic evolution. We deployed a 100-km-long magnetotelluric profile across the Eastern Himalayan Syntaxis and performed three-dimensional inversion of the acquired data, yielding a high-resolution 3D electrical model that finely constrains the crustal structure and material state. Based on this model, we analyzed the crustal material conditions, estimated partial melt fractions, and assessed crustal rheology. Integrating our results with complementary geophysical and petrological evidence, we found that crustal materials on the northwestern side of the EHS show extensive partial melting, indicative of channel flow or upward migration of hot material. In contrast, the southeastern side exhibits pronounced strike-slip characteristics. Thus, the rapid uplift of the EHS appears to result primarily from a combination of crustal partial melting within the syntaxis and intense erosion by the Yarlung Tsangpo Gorge.