Field guide across the exhumed Himalayan mid-crust along the Tama Kosi and Rolwaling valleys of east-central Nepal

Kyle Larson, and Dawn Kellett

The upper Tama Kosi and Rolwaling valleys in east-central Nepal expose the exhumed midcrustal core of the Himalayan orogen. The region provides an easily accessible transect across, and good exposure of, rocks preserved within that core. Traveling northward from Dolakha in the south to the Tibet border in the north, the rocks record an inverted metamorphic field gradient ranging from chlorite-grade phyllite at lowest structural levels to sillimanite-grade migmatite and leucogranite at the uppermost structural levels. Rocks along this transect are pervasively deformed and preserve dominantly south-directed thrust shear sense indicators. Moreover, they are interrupted by a metamorphic, deformational, and geochronologic discontinuity. Investigation of such structures has helped to reveal the processes responsible for assembly of the Himalayan mid-crust and evolution of the present day kinematic framework. Moreover, integration of available field, microstructural, petrochronologic, and pressure-temperature data has provided insight into the relationship between processes accommodating foreland - hinterland convergence. This field guide describes a number of exposures along the Tama Kosi and Rolwaling valleys in which the deformation, metamorphism, and anatexis at various different structural positions can be observed and compared.

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