Fig. 4: Cooling rate modeling and closure temperature estimation.

a TL signal (signal saturation level, n/N) growth with temperature under different cooling rates for the bedrock sample LUM4774. With a cooling rate of 11.3 °C Ma⁻¹, the modeled signal saturation level equals to the measured one. The (n/N)_ss means the signal at the thermal equilibrium state under a certain temperature, i.e., the sample stays at that temperature for infinitely long time. b TL signal growth with temperature under different cooling rates for the bedrock sample LUM4775. c Detrapping/trapping rate ratio vs Temperature (Depth) for the two bedrock samples. Depth below surface is calculated based on a geothermal gradient of 25 °C km⁻¹. d Modeling the effective closure temperature (T_C) under different cooling rates (2–10 °C Ma⁻¹ with an interval of 1 °C Ma⁻¹, and 10–200 °C Ma⁻¹ with an interval of 5 °C Ma⁻¹) and dose rates (0.1–2.0 Gy ka⁻¹ with an interval of 0.1 Gy ka⁻¹). For the T_C modeling, the E is fixed at 1.80 eV, the s at 10¹⁴s⁻¹, the D₀ at 5000 Gy, and the surface temperature at 10 °C.