Two subduction-related heterogeneities beneath the Eastern Alps and the Bohemian Massif imaged by high-resolution P-wave tomography

Abstract

Abstract. We present high-resolution tomographic images of the upper mantle beneath the E. Alps and the adjacent Bohemian Massif (BM) in the North based on data from the AlpArray-EASI and AlpArray Seismic Networks. The tomography locates the Alpine high-velocity perturbations between the Periadriatic Lineament and the Northern Alpine Front. The northward-dipping lithosphere keel is imaged down to ~200–250 km depth, without signs of delamination, and we associate it with the Adriatic plate subduction. Detached high-velocity heterogeneity, sub-parallel to and distinct from the E. Alps heterogeneity is imaged at ~100–200 km depths beneath the southern part of the BM. We associate this heterogeneity with the western end of a SW-NE striking heterogeneity beneath the south-eastern part of the BM, imaged in models of larger extent. The strike, parallel with the Moldanubian/Brunovistulian mantle-lithosphere boundary in the BM and with the westernmost part of the Carpathian front, lead us to consider potential scenarios relating the heterogeneity to (1) a remnant of the delaminated European plate, (2) a piece of continental-and-oceanic lithosphere mixture related to the building of the BM, particularly to the closure of the old Rheic ocean during the MD/BV collision or (3) a lithospheric fragment going through to the NW between the E. Alps and W. Carpathians fronts in a preceding subduction phase. The study is dedicated to our outstanding and respected colleague Vladislav Babuška, who coined innovative views on the European lithosphere and died on March 30, 2021.