The lithospheric trace of the Iapetus Suture in SW Ireland from teleseismic data

Abstract

The Caledonian Iapetus Suture is a tectonic boundary resulting from the amalgamation in a three-plate configuration of Laurentia and Baltica with Avalonia. In SW Ireland, seismic stations on a wide-angle seismic profile crossing the postulated path of the Iapetus Suture have recorded a set of teleseismic events. The P-wave residual times for an earthquake in the Aleutians (end-on to the line) and a nuclear test in China (nearly orthogonal to the line) show large variations, of about 0.5 s, along this relatively short profile. Heterogeneities in the crustal structure along this profile can account for very little of the variation in residual times and most of it must originate in heterogeneities below the crust. From an analysis of the residual time curves of the two teleseismic events, the probable trace of the Iapetus Suture at depth has been found in the upper mantle, between 30 and 110 km. The suture is defined by a velocity contrast of about 3% and it is located just south of the Shannon River Estuary. The interface dips steeply to the south, indicating that the closure of the Iapetus Ocean may have involved a southward subducted slab. The model obtained in SW Ireland is comparable with a teleseismic tomography model across the Urals. This could indicate a close evolution of these two orogenies since the Palaeozoic.