iPlex Lunch spring-2017

Investigations of continental collisions often focus on thrust belts oriented perpendicular to the plate-convergence direction, excluding belts that surround the corners and flanks of a continental indenter despite being crucial to understanding the collisional process. Research of the Himalayan orogenic system, for example, has mostly focused on the east-trending thrust belt between the eastern and western syntaxes, leaving the north-trending Indo-Burma Ranges bounding the eastern margin of India inadequately examined. We present the first comprehensive geologic investigation of the Northern Indo-Burma Range (NIBR), the northernmost segment of the Indo-Burma Ranges and easternmost extension of the Himalayan orogenic system. By integrating field mapping with U-Pb geochronology, thermobarometry, and whole-rock geochemistry, we show that major Himalayan lithologic units and thrust faults extend across the eastern Himalayan syntaxis to the NIBR. The structural framework of the NIBR consists of a southwest-directed thrust belt cored by a hinterland-dipping duplex, similar to the rest of the Himalaya. However, the Northern Indo-Burma thrust belt is distinct based on (1) the absence of the South Tibetan detachment fault, (2) crustal shortening greater than 80 %, (3) a narrow orogen width of 7-33 km, (4) the exposure of an ophiolitic mélange complex as klippen, (5) and right-slip shear along the active range-bounding thrust fault. Furthermore, lithospheric deformation adjacent to the northeast corner of India is characterized by right-slip transpression partitioned between the thrust belt and orogen-bounding right-slip faults. Such a strain regime is interpreted to accommodate both contraction and clockwise rotation of Tibetan lithosphere around India, consistent with continuum deformation and rotation models rather than extrusion of internally-rigid blocks along strike-slip faults. We integrate our knowledge of the paleogeography of southern Asia and kinematics of indenter-induced continental deformation in a holistic model for the evolution of the entire Himalayan orogenic system.