Cenozoic volcanism in the Bohemian Massif in the context of P‐ and S‐velocity high‐resolution teleseismic tomography of the upper mantle

Abstract

AbstractNew high‐resolution tomographic models of P‐ and S‐wave isotropic‐velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel‐time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30–50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity‐perturbations of the P‐ and S‐wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low‐velocity anomaly, which would validate the “baby‐plume” concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low‐velocity perturbations beneath the Eger Rift, observed in about 200km‐broad zone, agree with shear‐velocity models from full‐waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.