Lithospheric mantle cooling recorded by zoned diamonds: forward modelling the nitrogen aggregation thermometer

Continental growth, buoyancy and stability are key processes in the evolution of the Earth and are governed by temperature. To constrain the thermal history of continental lithosphere over Gyr timescales, we present a novel application of the nitrogen aggregation geothermometer to zoned diamonds. By simultaneously forward modelling nitrogen aggregation in the core and rim of single diamonds, cooling rates and initial temperatures are calculated. Our method is accessible, locally specific and scalable for global coverage. We demonstrate its application on samples from Diavik, Canada, finding most likely cooling rates of 42–62 K/Gyr, depending on the selection of zone ages from literature. Further uncertainty is primarily controlled by the quality of age determinations. Respective core and rim isochrons of 3.52 ± 0.17 and 1.86 ± 0.19 Ga produce asymmetric 95% confidence limits of around 30 and 80 K/Gyr when their uncertainties are jointly propagated with Monte Carlo analysis. Initial temperatures remain tightly constrained around 1200 °C. Extensive investigations show the method to be resilient to other sources of systematic and random error, and to potential effects of transient thermal events. Confidence in the model is further supported by its agreement with previous inclusion thermometry and tectonic evolution models of the studied area. It also reconciles previously discrepant results yielded by the simple application of the nitrogen aggregation thermometer and inclusion trapping temperatures, emphasising the inaccuracy of the former. Applying our model to other localities will allow a global picture of the thermal evolution of the lithospheric mantle to be built.