Long memory of mantle lithosphere fabric — European LAB constrained from seismic anisotropy

Abstract

We present a uniform updated model of the European lithosphere–asthenosphere boundary (LAB) recalculated from data collected during our regional studies of seismic anisotropy and other tomographic experiments, and show results of mapping of large-scale domains of mantle lithosphere characterized by uniform fossil fabrics. Exploiting the long memory of the fabric of the deep continental lithosphere, we define the LAB as a boundary between a fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere. Analysis of static terms of teleseismic P-wave travel time deviations shows that the LAB topography is more distinct beneath the Phanerozoic part of Europe than beneath its Precambrian part and deepens down to ∼ 220 km beneath the two Alpine roots, the South Carpathians and eastward of the Trans-European Suture Zone. Separation of the relative P residuals into static and directional-dependent terms, shear-wave splitting analysis and joint inversion of anisotropic parameters, reveals that the mantle lithosphere consists of domains with consistent olivine fabrics, which can be modelled by peridotite aggregates with plunging foliation or lineation. Changes of the fossil fabric allow us to map the domain boundaries within the mantle lithosphere. We propose processes which could create the observed fossil fabric as a consequence of successive subduction and accretion of micro-continent fragments outboard of continental cratons and a gradual stabilization of the LAB by a mantle flow after a detachment of the lower parts of subducting slabs. We advocate the importance of combining different methods and data in Earth structure studies and applying 3D approaches considering both seismic anisotropy and the general orientation of symmetry axes to construct more realistic models of large-scale lithospheric structure.