The reconstruction of thermal histories of rocks (thermochronometry) is a fundamental tool both in Earth science and in geological exploration. However, few methods are currently capable of resolving the lowtemperature thermal evolution of the upper 2km of the Earth's crust. Here we introduce a new thermochronometer based on the infrared stimulated luminescence (IRSL) from feldspar, and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions. Specifically, we present a new detailed Na-feldspar IRSL thermochronology from a well-documented thermallystable crustal environment at the German Continental Deep Drilling Program (KTB). There, the natural luminescence of Na-feldspar extracted from twelve borehole samples (0.1-2.3km depth, corresponding to 10-70 °C) can be either (i) predicted within uncertainties from the current g eothermal gradient, or (ii) inverted into a geothermal palaeogradient of 29 ±2 °Ckm−1, integrating natural thermal conditions over the last 65ka. The demonstrated ability to invert a depth-luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing recent ambient temperatures of the shallow crust (<0.3Ma, 40-70 °C range), or for studying equally recent and rapid transient cooling in active orogens (<0.3Ma, >200 °CMa−1range). Although Nafeldspar IRSL is prone to field saturation in colder or slower environments, the method's primary relevance appears to be for borehole and tunnel studies, where it may offer remarkably recent (<0.3Ma) information on the thermal structure and history of hydrothermal fields, nuclear waste repositories and hydrocarbon reservoirs.
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