Tectonic setting and neotectonic features along the easter syntaxial bend (Lohit and Dibang), Arunachal Himalaya

Five distinct thrust bound tectonostratigraphic units have been recognised along the Lohit and Dibang valleys of eastern Arunachal Pradesh.  In ascending tectonic order of superposition they are (i) Sewak Group, (ii) Lalpani Group, (iii) Mayodiya Group, (iv) Tidding Formation and (v) Lohit Plutonic Complex.  The Sewak and Lalpani groups represent lower and upper thrust sheets of Mishmi Crystallines of Lesser Himalaya whereas the Mayodiya Group (Basement rocks) belongs to Central Crystallines of Higher Himalaya.  The Tidding Formation and Lohit Plutonic Complex represent the Trans Himalaya.

In the south, the low-grade metasediments of the Sewak Group tectonically rests over the Brahmaputra Alluvium along the Sewak/Mishmi Thrust.  The Sewak Group is overthrust by Lalpani Group, which consists of medium-grade metasendiments.  High grade metamorphics of the Central Crystallines (Mayodiya Group) overlay the Lalpani Group along the Main Central Thrust (MCT).  The ophiolitic melange of Tidding Formation overlies the Mayodiya Group along the Tidding Thrust/Suture.  The Lohit Plutonic Complex is of batholithic dimension and has been thrust over the rocks of the Tidding Formation along the Lohit Thrust.

A large number of neotectonically active faults/thrusts, transverse and oblique to the Himalayan tectonic trend have been recognised in the region which not only displace the various tectonic boundaries but have also caused damage to recently constructed river bridge at Rohing in Dibang valley and subsidence of road at Lalpani in Lohit valley and at Hunli in Dibang valley.  Movements on faults and thrusts are also evident from abrupt rise of mounain front, occurrence of fresh unfarrowed huge landslides, triangular facets, abrupt narrowing down of wide meandering rivers, uplifted fluvial terraces and existence of big paleolake deposits at Anini in Dibang valley.