The thermal structure of orogenies is subject to wide debate and remains largely uncertain, especially in the lower crust. Here we present a new seismic thermometer based on the eclogite-granulite transition to provide a new constraint on orogenic geotherms. We calibrate our thermometer using thermodynamic modeling of two endmember average lower crustal compositions. Acceptable ranges of water content, oxidation state, and bulk composition produce an uncertainty of ±50°C at a given pressure. Based on geophysical analysis, eclogite has been widely accepted as the cause of the ‘Moho doublet’, a pair of positive lower crustal wave speed increases in the Tibetan lower crust. Here, we compile and calculate receiver functions for available seismic stations to map the northern extent of the Moho doublet. We interpret the northern extent of the Moho doublet as the eclogite-granulite transition in the Tibetan lower crust. Our results predict the existence of cold lower crustal temperatures (<800±75°C at 65–70 km) 100–400 km further along dip than recent Himalayan orogenic thermal models.