THE CONCEALED CALEDONIDE BASEMENT OF EASTERN ENGLAND AND THE SOUTHERNNORTH-SEA - A REVIEW

Field mapping, analysis of borehole core and studies of geophysical po tential field and seismic data can be used to demonstrate the existenc e of a number of distinct crustal blocks within Eastern Avalonia benea th eastern England and the southern North Sea. At the core of these bl ocks is the Midlands Microcraton which is flanked by Ordovician volcan ic are complexes exposed in Wales and the Lake District. A possible vo lcanic are complex of comparable age in eastern England is concealed b y late Palaeozoic and Mesozoic cover. These volcanic are complexes res ulted from subduction of oceanic lithosphere beneath Avalonia prior to collision with Baltica and Laurentia in late Ordovician and Silurian time, respectively. The nature of the crust north and east of the conc ealed Caledonides of Eastern England and south of the Iapetus Suture/T ornquist Sea Suture, which forms the basement to the southern North Se a, is unclear. Late Ordovician metamorphic ages from cores penetrating deformed metasedimentary rocks on the Mid-North Sea High suggest thes e rocks were involved in Avalonia-Baltica collision before final closu re of the Iapetus Ocean between Laurentia and Avalonia.