71-3 Kinematic Evolution of the India-Burma-Eurasia Triple Junction at the Eastern Terminus of the Himalayas

Session: The Geodynamic Evolution of the Himalaya: From Mountain Building to Modern Seismicity and Climate Change (Posters)

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Abstract:

The evolution of the eastern Himalaya is controlled by several factors including indenter tectonics, the transition from collision to oblique subduction, and the convergence of the Burma terrane. The orogen terminates at the triple junction defined by the intersection of the Mishmi Thrust of the Himalayan wedge, the Naga Thrust of the Indo-Burman Range, and the Noa-Dihing fault (NDF), a reverse fault at the northern end of the Sagaing fault system that separates the Burma Terrane from the Eurasian plate. Few studies have attempted to address the impact of the Burma Terrane accretion on the kinematic evolution of the eastern Himalayas. This study presents outcrop and microstructural fabric analyses to characterize ductile strain near the NDF and assess the role of the Burma Terrane accretion in the tectonic evolution of the triple junction. We present new maps and cross-sections from two transects of the Eastern Himalayan wedge located 50 km and 25 km north of the triple junction, respectively. Preliminary results show kinematic variation in the structural data between the northern and southern transects, with the dominant foliation in both transects oriented parallel to the Himalayan wedge. In the northern transect (Lohit River), we observe northwest-trending, steeply inclined, isoclinal folds in the foliation of the Tidding and Mayodia Groups towards the hinterland, and more shallowly dipping, northwest-trending foliations in the Lalpani Group towards the foreland. Stretching lineations plunge down-dip, characteristic of a thrust wedge. In the southern transect (Kamlang river), we observe a more complex foliation pattern, where shallowly dipping foliations in the Lalpani Group are folded by west-vergent folds and rotated to steeper orientations towards the foreland. Stretching lineations trend obliquely on the foliation surfaces, possibly indicative of transpression. Additionally, we observe that the Miocene Sewak Group is present in the southern transect but absent in the northern transect where it was likely underthrust below the Himalayan wedge. Future quartz EBSD analysis and in situ UVLAMP ⁴⁰Ar/³⁹Ar dating are planned as part of this study to characterize spatial patterns in strain type and determine the timing of deformation along each transect. Our results will characterize the kinematics and timing of ductile strain where the Burma Terrane is converging with the triple junction at the easternmost terminus of the Himalaya. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8122

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