Short title: Numerical modelling of the formation of HT-UHT terranes Significance statement Even though long-lived high to ultra-high temperature (HT-UHT) terranes which formed mostly during the Proterozoic have been widely studied, their mode of formation is still controversial. We address the intertwined timing of partial melting and granulite formation during the genesis of HT-UHT terranes in a manner that cannot be derived from the natural rocks archive. This paper is innovative in the sense that it illustrates this problem in a dynamic manner. We illustrate through 2D thermo-mechanical modelling of an orogenic cycle that i) the formation of HT-UHT terranes can be explained by an elevated crustal radiogenic heat production and ii) the timing and duration of partial melting and the formation of granulites (syn-convergence and/or syn-collapse). The numerical modelling code used is the well-tested open-source code Underworld (https://www.underworldcode.org) making the results and outcomes reproductible and transparent for the scientific community.