How is topography maintained in the western Himalayan and where is plate convergence accommodated?

• Applicant: Privatdozent Dr. Rasmus C. Thiede
• Subject Area: Geology ; Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429470703

Despite major advances in understanding how plate motion is accommodated at convergent plate boundaries, it is still controversially debated how topography of orogenic fronts is sustained and where exactly plate convergence is partitioned. This is reflected by frequently contradictory short- and long-term derived crustal shortening rates and their interpretation in the context of the seismotectonic segmentation of range fronts - a problem that may be intimately associated with temporal and spatial variations of deformation in orogenic wedges. Are such disparate levels of activity systematic or are they triggered by random processes? Answering this question is fundamental for understanding the mechanisms and loci of wedge deformation and its timing, which is ultimately necessary for hazard mitigation and risk reduction in tectonically active mountain ranges. To address this problem obtaining deformation rates and measuring the locus of faulting on intermediate timescales is a key task to assess the deformation mechanisms and earthquake patterns and to decipher earthquake recurrence patterns.The Himalaya constitutes a stack of thrust sheets, i.e. the orogenic wedge, scraped off India as it is subducted beneath Tibet. All primary fault systems within the wedge sole into the Main Himalayan Thrust (MHT), the main basal décollement. Competing hypotheses suggest that Himalayan topography is sustained and plate convergence is accommodated by deformation either solely along the basal décollement or through more broadly distributed deformation across multiple thrust faults. However, both hypotheses could be true as orogenic wedge activity may be characterized by these end-member scenarios over time, depending on the criticality of the orogenic wedge, which is fundamentally influenced by accretion and erosion in the advancing thrusts.Based on my previous work in the region I hypothesize that the tectonics of the Himalayan wedge may indeed follow a pattern between two end-member deformation styles. The temporal and spatial variations in climate and erosion have generated ubiquitous Late Pleistocene and Holocene fluvial terraces across the entire length of the Himalayan front. The excellent preservation of these geomorphic features in the western Himalaya (73°E to 80°E), thus makes this region a prime area to quantify the timing of terrace formation and transient sediment loading, terrace abandonment and deformation. Here I propose to quantify potential links and interactions between crustal shorting, late Pleistocene sedimentary loading, Late Pleistocene and Holocene fault displacement rates, and erosion. Our ultimate goal is to quantify the spatial and temporal characteristics of mountain-front deformation in the context of orogenic wedge dynamics.

• DFG Programme: Research Grants
• International Connection: India, USA
• Cooperation Partners: Professor Dr. Ramon Arrowsmith, Ph.D.; Professor Vikrant Jain, Ph.D.
• Co-Investigator: Professor Dr. Bodo Bookhagen, Ph.D.