Emma Louise Chambers , Javier Fullea, Duygu Kiyan, Sergei Lebedev, Christopher J. Bean, Pat Meere, Stephen Daly, Nicola Willmot Noller, Robert Raine, Sarah Blake, Brian M. O'Reilly

High-quality maps of subsurface temperature and the geothermal gradient are essential when assessing the geothermal potential of a region. However, determining geothermal potential is a challenge when direct measurements of in-situ temperature and thermal property information are sparse. In addition, indirect geophysical methods are sensitive to a range of parameters, not solely temperature. We determine the geothermal gradient across Ireland by inverting seismic, in addition to other geophysical and petrophysical input datasets, directly for temperature. The multi-parameter output models of the joint, geophysical-petrological, thermochemical inversion fit the input data and reveal the thermal structure within the crust and mantle, including the upper-crustal geothermal gradient (20 to 40 °C/km). Variations in the lithospheric thickness influence the temperature gradient, with thinner lithosphere resulting in elevated geotherms. In some locations, the observed geotherms are elevated further due to high radiogenic heat production in granitic rocks. In Northern Ireland a thin lithosphere coupled with a weakly conductive basalt layer overlying warm crust, results in elevated temperatures which call for further geothermal exploration. These are the first temperature maps for Ireland that include uncertainty estimates, providing ranges for the subsurface temperature values, and demonstrate that the maps are in good agreement with available direct borehole temperature measurements, which are observed to fall within the model uncertainty. Our new methodology provides workflows for determining the 3D geothermal potential in areas with limited direct temperature measurements. The final temperature model provides useful constraints for geothermal exploration and utilisation on the island of Ireland.