Crustal structure of Northeast India as evidenced by receiver function imaging: tectonic and geodynamic implications

Crustal structure beneath the major tectonic domains comprising northeast India is investigated using receiver function analyses of teleseismic earthquakes recorded at 19 new broadband seismic stations, combined with Moho depth and Poisson’s ratio information from 14 previous studies. Velocity structure inverted from receiver functions are combined with results from H–k stacking and validated using forward modeling of gravity data. The Shillong Plateau in the western Brahmaputra River Valley, later representing the Himalayan foredeep, is inferred to have a thin (33–35 km) felsic crust. A dome-shaped, 5-km-thick high-velocity layer in the upper crust likely accounts for positive Bouguer anomaly over the plateau. The Upper Assam basin in the eastern Brahmaputra River Valley is marked by pronounced gravity low, high Poisson’s ratio, and a pair of low- and high-velocity layers in the crust. This narrow segment demarcates the crust of oceanic affinity extending from the Indo-Burmese Wedge. Further to the south of Dauki fault, under the ~ 10-km-thick wedge, a two-layered crust comprising 5–15-km-thick delta sediments overlying a ~ 20-km-thick basement of oceanic affinity extends from Bay of Bengal to the Churachandrapur-Mao Fault, where the deep basement subducts upon collision with the Burmese micro-plate. East of the collision boundary, the overriding Burmese micro-plate having a thin crust of ~ 30 km, including ~ 15-km-thick low-velocity sediments, is imaged beneath Central Myanmar Basin. The findings shed new light on the tectonic reactivation of the different domains of northeast India upon collision with the Himalaya to the north and Burmese micro-plate to the east.

Graphical Abstract