Variations in Deformation and Kinematics Along and Across the Himalayan Arc through Time: Insights from the Darjeeling-Sikkim-Tibet Transect

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The Himalayan mountain belt is the result of continent - continent collision between the Indian and Eurasian tectonic plates that started 50-55 million years ago and is continuing to the present day. A significant portion of the total ~650 km plate convergence went to forming shortening structures in the Himalayan ranges. Because of the arcuate form of the Himalayas shortening varies along its length. The amounts of shortening have previously only been documented in the western Himalayas (Kashmir, Kumaon, Nepal). This project is undertaking a pair of detailed transects along the Tista drainage (~89 degrees East longitude), to fill a gaping hole in our knowledge of terra incognita (viz. the eastern Himalaya). Traditional structural mapping techniques are being combined with geodetic (satellite global positioning system [GPS]) data and age dating of river terraces formed during mountain building and erosion.The research is determining: (1) the amount of shortening across the eastern Himalaya, (2) the variation of convergence along the Himalayan arc, and (3) whether the rates of convergence are the same for geologic time scales as compared to current [GPS] rates. This study, together with earlier work in southern Tibet under Project INDEPTH, is providing the first complete structural transect across the Himalayas from India to Tibet, and will form the basis for developing comprehensive models of mountain belt evolution in active belts. The study is also revealing whether or not zones in the mountain belt are building anomalous strain that could lead to great earthquakes in this region that has one of the highest seismic hazard risks along the Himalayan arc. The study is promoting collaboration of researchers from two countries, melding different field techniques, and helping in the training of future geologists.