Lithospheric temperature response to asthenosphere updoming and the upper mantle-crustal magmatic underplating in the Western Ohře (Eger) Rift area, Czechia

Abstract

The Western Ohře (Eger) Rift is characterized by frequent earthquake swarms, elevated CO₂ emissions, and Pleistocene volcanism. Understanding the lithospheric temperature is an essential for integrating these phenomena within a broader geodynamic context. In order to contribute to these research goals, we modelled thermal evolution of the region using an axisymmetric geothermal model and numerically solved the transient heat conduction equation. The simulation begins at 35 Ma, when the asthenosphere uplifted from 100 km to 75 km depth within a 90-km diameter-wide region. This updoming was followed by two episodes of basaltic underplating at depths of 30–33 km during 15–10 Ma and 5–1 Ma. We modelled the underplating as a sequence of ∼100 m thick intrusions, 30 km in diameter, emplaced at 1 Myr intervals. Each intrusion released latent heat of crystallization between the liquidus (1,387 °C) and solidus (720 °C) temperatures. The modelled lithospheric temperatures indicate that the 300 °C isotherm, often marking the brittle-ductile transition, is located at ∼11 km depth, consistent with the lower extent of the local swarm seismicity range (6.5–11 km). The base of the magmatic underplating remains just above the solidus, suggesting the presence of partially molten material. The residual melt may contribute to the ongoing CO₂ emissions observed in the area.