Abstract:
The Greater Himalayan klippen are erosionally isolated, thrust bounded rocks, overlying Lesser Himalayan rocks in the Himalayan thrust belt. Structural and thermochronological data gathered in the klippen illuminate how Greater Himalayan rocks were emplaced and deformed between ~30-10 Ma. The Almora-Dadeldhura klippe in northwest India and far western Nepal is composed of rocks with Greater and Tethyan Himalayan affinities. Researchers use interpretations of rock affinity, number of shear zones, metamorphic gradient, thermochronology and microstructural data to support the critical taper, channel flow, or wedge insertion models for the development of the Himalayan thrust belt. Channel flow is not supported if the timing of the Main Central Thrust (MCT) and South Tibet Detachment System (STDS) are interpreted to be different. Wedge insertion is not supported if the STDS in the hinterland and klippe are the same fault but do not slip at the same time. The critical taper model is the most difficult to refute because the model can accommodate slip in almost any part of a thrust belt as the thrust belt responds to maintain critical taper. The already published and original data, that support or refute each of the models are presented. A kinematic model is developed combining the existing thermochronology and structural data. In this model, the Almora-Dadeldhura klippe was emplaced over Lesser Himalayan rocks between 28-18 Ma if the klippe was formed by an intra-Greater Himalayan thrust or between 18-13 Ma if the fault that forms the klippe is the Main Central thrust. The building of the Lesser Himalayan duplex folded the overlying klippe rock to dip southward between at ~10-4 Ma. The northern part of the klippe was folded to dip south, beginning between 7-5 Ma due to the emplacement of the Main Boundary thrust and the Subhimalayan thrust system. This fits a model of forward propagating thrust system and conforms with the predictions of the critical taper model.
