CADOMIAN TERRANES, WRENCH FAULTING AND THRUSTING IN THE CENTRAL-EUROPE VARISCIDES - GEOPHYSICAL AND GEOLOGICAL EVIDENCE

Sixty five per cent of the Paleozoic basement of western and central E urope is hidden by a sedimentary cover and/or sea. This work aims to r emove that blanket to detect new structures which could used to build a more comprehensive model of the Variscan orogeny. It is based on the interpretation of various forms of data: (a) published gravity maps c orrected for the effects of the crust-mantle boundary topography and l ight sedimentary basins; (b) aeromagnetic maps; (c) measurements of de nsities; and (d) induced and remanent magnetizations on rocks from Pal eozoic outcrops of the upper Rhenish area. From the northern Bohemian Massif to the eastern Paris Basin, the Saxothuringian is characterized by a 500 km long belt of gravity highs, the most important being the Kraichgau high. Most of the corresponding heavy bodies are buried unde r a post-early Visean cover. They are interpreted as relies of Late Pr oterozoic terranes overlain by an Early to Middle Paleozoic sequence, equivalent to the Bohemian terrane in the Bohemian Massif. The most pr obable continuation of these dense Bohemian terranes toward the west i s the Southern Channel-Northern Brittany Cadomian terrane. The gravity lows are correlated with Variscan granites and pre- and early Varisca n metagranites. Gravity and magnetic maps demonstrate large-scale disp lacement in Devonian-Early Carboniferous times along the parallel and equidistant, NW-SE striking, Vistula, Elbe, Bavarian, Bray and South A rmorican dextral wrench faults. In the Vosges-Schwarzwald and Central Massif the faults continue with the east-west striking Lalaye-Lubine-B aden-Baden and Marche faults and with south vergent thrusts. The Bavar ian faults shift the Kraichgau terrane by 150 km relative to the Bohem ian terrane, whereas the offset of the Northern Brittany Cadomian rela tive to the Northern Vosges-Kraichgau terranes is estimated at 400 km along the Pray fault. Sinistral wrench faults are the NE-SW striking S illon Houiller, Rheingraben, Rodl, Vitis and Diendorf faults. The sout hern Vosges-Schwarzwald Devonian-Dinantian basin is interpreted as a p ull-apart basin at the south-easterly extremity of the Bray fault. The Bohemian and Kraichgau body form allochthonous terranes which were th rust over the Saxothuringian crust. Thrusting to the north-west was ac companied by back-thrusting and led to the formation of pop-up structu res. Contemporaneous dextral and sinistral wrench faulting resulted in transpressive strain during collision. The zonal structure of the Var iscides in the sense of Kossmat (1927) is relevant only to the Rhenohe rcynian Foreland Belt. Kossmat (1927) already spoke of a Moldanubian R egion because it displays no real zonal structure. The Saxothuringian Zone was formed by terrane accretion. Their apparent zonal structure i s not a pre-collisional feature, but only the result of accretion and collision.