LISPB – IV. Crustal structure of Northern Britain

Summary. This paper presents those results from the 1974 Lithospheric Seismic Profile in Britain (LISPB) which relate to the compressional velocity structure of the crust and uppermost mantle beneath Northern Britain. A combination of interpretation techniques suitable for modelling laterally inhomogeneous media, including two‐dimensional ray‐tracing and time‐term analysis, has resulted in a detailed seismic cross‐section across the Caledonian orogenic belt. The main features of this section are a possible horizontal discontinuity in the Pre‐Caledonian’basement, a change in the relationship between the lower crust and the uppermost mantle from north to south and a considerable thickening of the crust beneath the Caledonian fold belt. These results place considerable constraints upon tectonic models for the evolution of the Caledonides in particular in their implication of differing crustal structures north and south of the Southern Uplands and their indication of the primary significance of the Southern Uplands Fault.