Primary Discussion about Tectonic Deformation Characteristics in East Yarlungzangbo Suture and Subsurface Structure of Yarlhashampo Dome Revealed by Deep Seismic Reflection Profile

India plate-Asia plate collision is the largest scale and most classic continent to continent collision orogeny event in Cenozoic. Yarlungzangbo suture is not only surface collision boundary between India plate and Asia plate but also representing new-Tethys subduction and extinction process. People are looking forward to knowing the deep fine structure of India-Asia continental collision zone, crustal deformation characteristics and deep internal processes caused by collision. Meanwhile, Lhagoikangri dome belt which locate in the southern margin of Yarlungzangbo river and North Himalayas is one of the important extension structure in main collision belt, forming from Miocene. Yarlhashampo dome is one typical gneiss dome locating in east part of Lhagoikangri dome belt. This dome is one key-place to understand structural deformation condition of dome belt and knowing the north Himalaya crustal feature. Hence, for understanding tectonic characteristics in north Himalayas, deciphering the continent to continent collision and orogeny process in Himalaya-Tibet plateau, one deep seismic reflection profile acrossing Yarlungzangbo suture along 92°E has been conducted at Shannan Prefecture of east Tibet in 2017(line A).

Three type explosive sources in the field data acquisition process: 48kg shots in single shot hole at 30m depth with 250m intervals, 192kg shots in pairs of shot holes with 50m at interval of 1km and 2000kg shots in clusters of 15 shot holes at 50m depth at interval of 50km. Data were recorded by 720 receiver traces over a 60s two-way travel time window and field experimental setup provided a nominal 60-fold common mid-point (CMPs) stacked section. Processing used Kirchoff pre-stack time migration.

The finally processed deep seismic reflection profile outline fine subsurface structure of Yarlhashampo dome and the relationship between STD system and dome, and also, finding one concealed thrust fault beneath dome which has cut STD, may as one symbol of N-S direction compression event from 13Ma in plateau, on the other hand, furtherly both proving that Indian crust underthrusted into southern Lhasa terrain only to a limited degree, and clearly showing the duplexing process which is one of the reason causing uplift from the past 50 Ma as well as the nonuniform-tearing subduction process in east Himalayas.