A record of shortening rates in the Himalayan thrust belt in Bhutan: integrating geochronology, thermochronology, deformation geometry, and kinematics
Crustal shortening within the Himalayan thrust belt has played a major role in accommodating convergence between the Indian and Asian plates. However, temporal records of Himalayan shortening have only been estimated at the shortest (GPS) and longest (total shortening from balanced cross-sections) timescales. Intriguing petrologic and geochronologic studies focused on 1st-order Himalayan structures indicate the possibility of Myr-scale temporal variability in the amount of India-Asia convergence accommodated in the Himalayan thrust belt. However, quantifying this variability, and interpreting these variations in the larger context of the full Himalayan-Tibetan orogenic system, requires documenting incremental shortening rates over the span of construction of the thrust belt.
In this presentation, the geometry and kinematics of the Himalayan thrust belt in the kingdom of Bhutan are integrated with peak temperature data, the timing of prograde metamorphism, and a suite of thermochronologic ages, in order quantify a detailed record of the burial, displacement, and exhumation history of the thrust belt, and to constrain a four-part record of Himalayan shortening rates from ca. 23 Ma and the present. The results highlight significant temporal variability in shortening rates, which are placed in the larger spatial framework of deformation in all major components of the Himalayan-Tibetan orogenic system. These results have important implications for the history and magnitude of strain partitioning in the eastern part of the orogen.
