Joint inversion of local, regional and teleseismic data for crustal thickness in the Eurasia-Africa plate boundary region

Abstract

SUMMARY A new map for the Moho discontinuity (EAM02) in the Eurasia‐Africa plate boundary region is presented. Reliable results have also been obtained for the southern and eastern Mediterranean Basin, the northern African coasts and the eastern Atlantic Ocean, regions only occasionally considered in studies on the Mediterranean region. The Moho topography model is derived from two independent sets of constraints. Information contained in the fundamental and highermode Rayleigh waves obtained from waveform modelling is used to constrain the Moho depth between estimates of crustal thickness taken from published reflection and refraction surveys, gravity studies and receiver function analysis. Strong lateral variations in the Moho topography have been observed in the Mediterranean Sea, confirming the complex evolution of this plate boundary region. In the west, the Moho discontinuity has been found at 15‐20 km depth, suggesting extended and, at least in some locations, oceanic crust, while in the east the crust is on average 25‐30 km thick. There it is interpreted either as Mesozoic oceanic or thinned Precambrian continental crust covered by thick sedimentary deposits. Standard continental crust (30‐35 km) is observed along the eastern part of the northern African coast, while to the west a rapid change from a relatively deep Moho (down to 42 km) below the Atlas Mountain Range to the thin crust of the southwestern Mediterranean Sea has been found. The crust beneath the eastern North Atlantic Ocean can be up to 5 km thicker compared with standard oceanic crust (6 km). The crust has been interpreted to be heterogeneous as a consequence of irregular magma supply at the Mid-Atlantic ridge. In addition, serpentinization of the subMoho mantle could contribute to the imaging of apparently anomalous thick oceanic crust. In Europe, the presence of crustal roots (>45 km) beneath the major mountain belts has been confirmed, while thin crust (<25 km) has been found beneath extensional basins. Comparing the obtained Moho topography and Moho depth computed assuming isostatic compensation at 60 km depth shows that most of the Mediterranean and eastern Atlantic region appears to be in isostatic equilibrium. The large positive residuals observed for the eastern Mediterranean are likely to be due to overestimating crustal thickness, owing to the thick sediment deposits present.