The occurrence of thrust-sense tectonometamorphic discontinuities within the exhumed Himalayan metamorphic core can be explained as part of the Main Central thrust system. This imbricate thrust structure, which significantly thickened the orogenic midcrustal core, comprises a series of thrust-sense faults that all merge into a single detachment. The existence of these various structures, and their potential for complex overprinting along the main detachment, may help explain the contention surrounding the definition, mapping, and interpretation of the Main Central thrust. The unique evolution of specific segments of the Main Central thrust system along the orogen is interpreted to be a reflection of the inherent basement structure and ramp position, and structural level of exposure of the mid-crust. This helps explain the variation in the timing and structural position of tectonometamorphic discontinuities along the length of the mountain belt. The occurrence of thrust-sense tectonometamorphic discontinuities within the exhumed 15 RECONCILING HIMALAYAN MIDCRUSTAL DISCONTINUITIES: THEHimalayan metamorphic core can be explained as part of the Main Central thrust system. 16This imbricate thrust structure, which significantly thickened the orogenic midcrustal 17 core, comprises a series of thrust-sense faults that all merge into a single detachment. The 18 existence of these various structures, and their potential for complex overprinting along 19 the main detachment, may help explain the contention surrounding the definition, 20 mapping, and interpretation of the Main Central thrust. The unique evolution of specific 21 segments of the Main Central thrust system along the orogen is interpreted to be a 22 reflection of the inherent basement structure and ramp position, and structural level of 23 exposure of the mid-crust. This helps explain the variation in the timing and structural 24 position of tectonometamorphic discontinuities along the length of the mountain belt. 25 26

Graphical abstract

The Upper Mustang region of west-central Nepal contains exposures of metamorphosed Tethyan Sedimentary Sequence rocks that have been interpreted to reflect either contact metamorphism related to the nearby Mugu pluton or regional metamorphism associated with the North Himalayan domes. New monazite geochronology results show that the Mugu leucogranite crystallized at c. 21.3 Ma, while the dominant monazite age peaks from the surrounding garnet ± staurolite ± sillimanite schists range between c. 21.7 and 19.4 Ma, generally decreasing in age away from the pluton. Metamorphic temperature estimates based on Ti-in-biotite and garnet–biotite thermometry are highest in the specimens closest to the pluton (648 ± 24°C and 615 ± 25°C, respectively) and lowest in those furthest away (578 ± 24°C and 563 ± 25°C, respectively), while pressure estimates are all within uncertainty of one another, averaging 5.0 ± 0.5 kbar. These results are interpreted to be consistent with contact metamorphism of the rocks in proximity to the Mugu pluton, which was emplaced at c. 18 ± 2 km depth after local movement across the South Tibetan detachment system had ceased. While this new dataset helps to characterize the metamorphic rocks of the Tethyan Sedimentary Sequence and provides new constraints on the thickness of the upper crust, it also emphasizes the importance of careful integration of metamorphic conditions and inferred processes that may affect interpretation of currently proposed Himalayan models.