Mantle‐earthquake geothermometry of rejuvenated Proterozoic lithosphere, western Saudi Arabia

Harrat Lunayyir is a Quaternary volcanic field above a 2009 dyke intrusion located in the Arabian Shield ~100 km east of the Red Sea rift. We use 3D common conversion point stacking of P-wave receiver functions to show that the Moho is at 38 ± 2 km depth, close to the 40-km crustal thickness measured in the center of the Arabian craton, whereas the lithosphere-asthenosphere boundary is at 60 ± 5 km depth (Figure 1), far shallower than the 150 km seen further east in the Arabian shield. We re-located 64 highfrequency earthquakes with mL ≤ 2.5 at depths of 42–48 km, clearly beneath the Moho, ~30 km eastsoutheast of the 2009 dyke-intrusion beneath Harrat Lunayyir (Figure 1). These brittle-failure earthquakes, that must have nucleated at temperatures T ≤ 900°C, show that the lithosphere is not in thermal equilibrium with the underlying asthenosphere that has a petrologically calibrated potential temperature of ~1350°C at 60 km depth (Blanchette et al., 2018).