Slab remnants beneath the Myanmar terrane evidencing double subduction of the Neo-Tethyan Ocean.

Closure of the Neo-Tethyan Ocean is one of the most significant tectonic events of the Cenozoic, forming the longest continental collision belt on Earth and influencing global climate and biodiversity. However, whether late Mesozoic subduction of the Neo-Tethyan Ocean occurred along one single or a double subduction system remains controversial. Here, upper mantle imaging from seismic tomography and waveform modeling in the Myanmar region reveals two prominent, parallel, slab-like structures with high seismic velocities that trend to the north-south and dip to the east. The western high-velocity zone has been observed previously and represents the modern subducting slab. The eastern zone has not been previously reported and exhibits high-velocity anomalies of 1.0 to 2.5% to a depth of ~300 km. This zone likely represents a remnant of another Neo-Tethyan oceanic slab that subducted ~40 million years ago. Double subduction of the Neo-Tethyan Ocean during the late Mesozoic to early Cenozoic requires reevaluation of previous tectonic models.

Direct structural evidence of Indian continental subduction beneath Myanmar.

Indian continental subduction can explain Cenozoic crustal deformation, magmatic activity and uplift of the Tibetan Plateau following the India-Asia collision. In the western Himalayan syntaxis and central Himalaya, subduction or underthrusting of the Indian Plate beneath the Eurasian Plate is well known from seismological studies. However, because information on the deep structure of the eastern Himalayan syntaxis is lacking, the nature of the Indian subduction slab beneath Myanmar and the related tectonic regime remain unclear. Here, we use receiver function common conversion point imaging from a densely spaced seismic array to detect direct structural evidence of present-day Indian continental subduction beneath Asia. The entire subducting Indian crust has an average crustal thickness of ~30 km, dips at an angle of ~19°, and extends to a depth of 100 km under central Myanmar. These results reveal a unique continental subduction regime as a result of Indian-Eurasian continental collision and lateral extrusion.