Refining the thermal structure of the European lithosphere by inversion of subsurface temperature data

Abstract

Abstract We present an updated thermal model of the European lithosphere based on a new stochastic modeling work flow. We developed this work flow to estimate subsurface temperatures from site- to regional-scale, up to the depth of the lithosphere-asthenosphere boundary (LAB). Our model is composed of four layers, consisting of sediments, upper crust, lower crust and lithospheric mantle. We asigned thermal properties, including radiogenic heat production and temperature- and pressure-dependent bulk thermal conductivity on the base of broad-scale lithological variation within the European crust. We corrected thermal properties with a 1D steady-state temperature approximation, assuming only vertical heat flow. Using these corrected thermal properties, we calculated the 3D thermal field with a conjugate-gradient method, assuming fixed temperatures at the surface and at the base of the lithosphere. To obtain more robust results for our thermal model, we applied data assimilation, aiming at consistency between temperature and heat flow observations and tectonic model predictions. We used an Ensemble Smoother Multiple with Data Assimilation (ES-MDA) method to update prior estimates of thermal properties and the thermal field with temperature data. We calibrated our European thermal model with available regional thermal models due to the present lack of a unified dataset with public borehole temperature measurements. A large dichotomy is observed in the model along the Trans-European Suture Zone (TESZ). Northeast of the TESZ, geothermal gradients up to 10 km depth are mainly below 20 °C km−1. Southwest of the TESZ, gradients range from 20 °C km−1 near the Adriatic coast to more than 50 °C km−1 in volcanically and tectonically active regions. We show that the large scale thermal structure is locally and regionally perturbed by non-conductive heat transfer and affected by transient effects.