Tectonic inheritance, orogenesis, and seismicity

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Mountain belts are constructed at the convergence and ultimately at the collision site of tectonic plates. The Himalaya is one of the youngest and certainly the largest mountain belt system on the planet today. Understanding this superbly exposed mountain belt is critical for the interpretation of many older and more poorly exposed systems in the rock record. It is an iconic template for tectonic thought for all of geologic time.******This program will study the interplay between pre-existing crustal faults (termed here inherited basement faults), mountain building processes, and earthquakes. To fully understand mountain-building processes, including earthquakes in and away from the active mountain front, it is imperative to clearly constrain the geometry of the colliding plates prior to mountain building. The Himalayan system is chosen in this proposal because of its unrivaled preservation and recent evolution, which consequently limits tectonic overprinting and enables the distinction between Himalayan and pre-Himalayan deformation. It is anticipated that this program will provide key links to understand basement faults in the evolution of older mountain belts, such as the Grenville, the Appalachians, and the Canadian Cordillera. Such deep-seated structures are interpreted to control earthquake ruptures, influence lateral sedimentary thickness variations and fold-thrust belt geometry, and to localize ore resources and control hydrocarbon migration through foreland sedimentary basins. In the case of the Himalayan system, such hidden geohazard controls can have tremendous repercussions for one of the most densely populated regions on Earth.******I postulate that major northeast-trending lithospheric-scale faults within the Indian plate continue beneath the Himalayan mountains and contribute to a multitude of changes expressed along the length of the mountain belt. I further hypothesize that these deep-seated structures have repeatedly reactivated. The reactivation history of the inherited faults may be recorded in along-strike changes in the pressure-temperature evolution of the metamorphic core of the Himalaya, as lateral ramps and/or along-strike sediment thickness variations in the foreland foldthrust belt, and in the present-day partitioning of Indian intraplate and Himalayan seismicity.******These potential interactions will be explored through several HQP-led themes that involve: investigation of intraplate active tectonics related to basement fault reactivation away from the Himalayan front; reconstruction of the foreland fold-thrust belt using seismic data; field and lab investigations to assess along-strike variation in strain, metamorphic peak conditions, and exhumation of the Himalayan metamorphic core; numerical stress modelling linking present-day seismicity, stress trajectories, and basement faults; and dynamically-scaled centrifuge analogue modelling of deformation. **