Crustal Structure of the East Himalayan Syntaxis and the Relation to its Rapid Uplift and Exhumation

The unique East Himalayan Syntaxis (EHS) is featured with a sharp U-turn of all geological boundaries, geomorphic features and river systems at the east end of the Himalayan orogeny. The EHS is believed to be the region with strongest Cenozoic uplift and exhumation in Tibetan Plateau. Among the EHS, the most significant geomorphology feature is the over 7000m Gyara Peri (GP) and Namcha Barwa (NB) peaks, which rise abruptly from the <3000m surrounding Yarlung-Tsangpo canyon. The core Namcha Barwa area remains a high uplift rate since late Pliocene and forms a series of high-angle fault systems centered on EHS. To understand the mechanisms behind the rapid uplift of the study region, magnetotelluric array dataset were used to image the 3D electrical structure beneath the EHS. The inversion model reveals crustal high conductivity anomalies around the NB region. The rapid uplift of the region may lead to decompression melts of the thickened crust, which is correlated with local leucogranites outcrops commonly discovered in the region. The melts may provide the heat sources for the hydrothermal systems around Namcha Barwa. On the other hand, the crustal structure directly beneath NB is imaged as highly resistive NNE directed anomaly. This feature is consistent with previous regional magnetotelluric model and the high-velocity structure discovered by Rayleigh wave velocity results. The resistive "wedge" may reflect the northward intrusion of deep materials into the crust of the Lhasa block, which further induces the uplift of regional structure and the upwelling of hot materials at its north end. With the gradual intrusion of the wedge, the uplift may gradually expands to the northeast, forming the long and narrow surface compound anticline responses.