Tecionophysrcs. 177 (1990) 15-3-l Elsevter Science Publishers B.V., Amsterdam - Pnnted m The Netherlands 15 Superimposed Variscan, Caledonian and Proterozoic features inferred from deep seismic profiles recorded between southern Ireland, southwestern Britain and western France C. BOIS ‘, J.-P. LEFORT 2, B. LE GALL 3, J.-C. SIBUET 4, 0. GARIEL ‘. B. PINET ’ and M. CAZES 5 ’ Institut Franqanls du P&role, B.P. 311, 92506 Rued-Malmazson. Ct!dex (France) ’ UnrversrtP de Rennes, Instrtut de GPologte, Campus de BeaulIeu. avenue Gkhral Leclerc. 35042 Rennes. CPde.x (France) ’ UmversrtP de Bretagne Occrdentale, DPpartement des Scrences de la Terre, 6 avenue L.e Gorgeu . 29293 Brest, Ct!de.r (France) ’ IFREMER, Centre de Brest, B. P. 70, 292 73 Plouzane (France) ’ SNEA (P), Tour Elf, La D;Jense, 92078 Parts. CCdex 45 (France) (Accepted June 15. 1989) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ Abstract Bars, C., Lefort, J.-P., Le Gall. B., Sibuet, J.-C., Ganel, 0.. Pinet, B. and Gazes. M., 1990. Superimposed Vanscan, Caledonian and Proterozoic features mferred from deep seismic profiles recorded between southern Ireland, southwestern Britain and western France. In: Ph. Matte (Editor), Terranes m the Variscan Belt of Europe and Circum-Atlantic Paleozoic Orogens. Tectonophysics, 177: 15-37. From southern Ireland to the northern Bay of Biscay, subduction was active from the Proterozoic to the late Palaeozoic. They led to the Cadomian, Caledonian and Variscan collisions. Features charactenzing these three orogenies have been crossed by the WINCH, SWAT, WAM and Bay of Biscay deep seismic profiles recorded by the BIRPS and ECORS groups. In the Celtic Sea, the Vanscan front is characterized by a S-dipping ramp rismg directly from the middle crust with much less northward flattening than shown by the front in the northern France and West Germany profiles. South of the Variscan front, other S-dipping reflections occur above a possible deep detachment. The Lizard ophiolitic suture marks S-dipping events traversing the entire crust and the present Moho in the English Channel. Several sets of prominent N-dipping reflections occurring in the Celtic Sea and south Irish Sea are interpreted as Caledoman features running parallel to the Caledonian Iapetus suture and the pattern of folds and faults recogmzed m Wales and southeastern Ireland. Proterozoic S-dippmg subduction is recorded by geological data m northern Wales and the English Channel. Related crustal structures correspond to deep seismic events cutting across the lower crust and the Moho and show the same apparent dip as the Vatiscan features. Parallelism between dips and/or strikes of structural features with different ages suggests a tectonic heritage. The crust thus appears to be characterized by N and S-dipping features which cut across large parts of it and may be assigned to Vanscan, Caledonian or Candomtan thrusts or shear zones. The lower part of the crust shows a band of high-amplitude subhonzontal reflections and a flat Moho reflection, which seem to have overprinted the above-mentioned dipping features in a later period. The lack of evidence of any shallow detachment in the Caledonian and Variscan belts together with the presence of dippmg crustal thrust-like features suggest that the region may have reached the very latest collisional stage. the end of both of these orogenies. Introduction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA In 1983, the British BIRPS group recorded 1600 km of deep seismic profiles in the Celtic Sea and the English Channel with the financial and technical cooperation of the French ECORS Pro- ject (Fig. 1). This survey, called SWAT (South W estern Approaches Traverse), consisted of a 0040-1951/90/$03.50 0 1990 - Elsevier Science Publishers B.V.