Crustal structure south of the Iapetus suture beneath northern England

Abstract

The crustal structure just south of the Iapetus suture¹ along a line extending from the mid-North Sea high across northern England to the Solway Basin has been investigated as part of the Caledonian Suture Seismic Experiment of 1982. This unique sea-to-land wide-angle explosion seismology project has produced data of unprecedented quantity and quality. The main innovation was the use of both closely spaced shots (mainly at sea) and closely spaced stations (mainly on land), yielding a data set which can eventually be arranged in a variety of new ways for phase correlation and modelling, such as constant offset and common mid-point. The line was extended by Irish and German groups across Ireland to the Shannon Estuary, having a total length of over 600 km, but here we present only preliminary results for northern England and adjacent marine regions. The results for this region differ radically from those of the earlier LISPB experiment² in that we have recognized a well-defined 6.15 km s⁻¹ basement interpreted as pre-Caledonian metamorphic basement beneath most of the line at relatively shallow depth, and there is a well-defined mid-crustal refractor starting at approximately 16 km depth beneath the North Sea and northern England which is not recognized beneath the Irish Sea.