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

Abstract

New 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.

Transversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian Massif

“…Weak VTI anisotropy explaining the velocity drop in the lower crust is in agreement with the results of previous studies (e.g. Luo et al, 2013;Shapiro et al, 2004;and Qiao et al, 2018). The subtle v S decrease in the top of the LPC of the ANT model (see Figs.…”

“…However, the mantle velocities beneath the Moho remain lower than expected. Nevertheless, the lower velocities are in agreement with the ANT results of Ren et al (2013), the teleseismic body-wave tomography results of studies such as Amaru ( 2007), Plomerová et al (2016), and reference therein, and the full wave-form inversion results of Fichtner and Villasenor (2015). The shear velocities in the upper crust are in agreement with the v P CSS models considering the standard v P /v S ratio.…”

“…Nevertheless, no velocity decrease in the lower crust that we observe in the BM is mapped in their well-resolved regions. On the other hand, a low-velocity zone in the mid-lower crust, representing a mechanically weak zone channelling material transport, was observed in south-east Tibet (Qiao et al, 2018). Also, Luo et al (2013) suggest an anisotropy in the lower crust beneath the Dabie orogenic belt between two cratons in central China, based on their ANT study.…”

Transversely Isotropic Lower Crust of Variscan Central Europe imaged by Ambient Noise Tomography of the Bohemian Massif

“…Nevertheless, the lower velocities are in agreement with ANT of Ren et al(2013), or results of teleseismic body-wave tomography (e.g., Amaru, 2007;Plomerová et al, 2016 and reference there in), as well as with full wave-form inversion (Fichtner and Villasenor, 2015). The shear velocities in the upper crust are in agreement with the v P CSS models considering the standard v P /v S ratio.…”

Active Magmatic Underplating in Western Eger Rift, Central Europe

“…One of them is connected with the source of the magma in the lithospheric mantle. A possible origin of the magmatic material is discussed by Plomerová et al () based on a teleseismic tomography. They see low‐velocity perturbations in the P , S , and PKP wave models at ~80–170 km depths.…”