Pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window. On the other hand, survivor, fragmented clasts embedded in the quenched material are also very important, in that they provide information about the energy spent to create new fracture surfaces. In this paper, I study the temperature evolution of clasts subjected to the heat dissipated by a just‐formed, molten pseudotachylyte (PT) vein. In particular, I find the analytical solutions for the temperature evolution within the PT vein, the surrounding, undamaged host rock, and inside a clast. According to the proposed model, the numerical results show that the clasts tend to preferentially melt in the inner part of the PT vein (i.e., they are completely assimilated by the PT). In contrast, some clasts can survive far from the PT vein center. My solutions, although based upon a simplified model, can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the PT center. The distribution of these survivor clasts follows a power‐law relation in terms of their radius, and its features generally agree with field and laboratory observations.