Abstract

We report 8 Ma zircon rim ages from a kyanite-bearing leucocratic pod within the lower metamorphic core of the Himalayan orogen in western Nepal. Zircon cores yield ca. 1.84 Ga ages, interpreted to be inherited igneous cores, consistent with the sample’s structural position and a Paleoproterozoic source. The pod is boudinaged and hosted in a pervasively top-to-the-south sheared pelitic schist; the 8 Ma zircon rim ages therefore provide a maximum age constraint on recent shear deformation. This late Miocene shearing is inferred to be associated with renewed thrusting in the hinterland of the western Nepal Himalaya, coeval with thrusting and erosion of Lesser Himalayan sequence rocks in the foreland. Hinterland ductile deformation at ≤8 Ma was followed by cooling below 350 °C at 6 Ma. This rapid transition from ductile thrusting to exhumation highlights the need for high-resolution geochronology to resolve deformation episodes in orogenic systems.

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