The concealed Caledonide basement of Eastern England and the southern North Sea — A review

Abstract

The Precambrian and early Palaeozoic ('Caledonian') metamorphic basement of E England and the southern North Sea comprises a number of distinct structural elements. The Midlands Microcraton was a persistent structural element throughout the early Palaeozoic. It lay in the back-arc region of subduction-related magmatic arc systems in Ordovician time, and was probably emergent. In Silurian time, it formed a fault-bounded platform distinct from deep water basins in Wales, N England and E Anglia. Acadian deformation and metamorphism was rather weak. The Concealed Caledonides of E England have a NW-SE structural grain and were more intensely deformed and metamorphosed by the Acadian orogenic phase. Deep seismic reflection surveys in the offshore part of this belt indicate the presence of inclined zones of reflectivity in the mid-crust, interpreted as thrusts. The age of these structures is uncertain.

Timing of magmatism, foreland basin development, metamorphism and inversion in the Anglo-Brabant fold belt

“…Accelerated subsidence in the Silurian and ?lowermost Devonian in the Anglia Basin and in the Brabant Massif, indicates a foreland basin development. The Acadian deformation of the Anglo-Brabant fold belt expresses the final collision with another part of Avalonia, the supposed North Sea plate (Pharaoh, England & Lee, 1995), which in turn would have collided with Baltica. This model implies the possible existence of two subduction zones, related to the Avalonia-Baltica collision, one along the Anglo-Brabant fold belt and the other along the North German-Polish Caledonides with its prolongation under the North Sea.…”

“…The magmatism was generated in response to subduction of oceanic lithosphere from the Tornquist Sea beneath the Avalonia Microplate (Pharaoh, Brewer & Webb, 1993;Pharaoh, England & Lee, 1995). The thickness of extrusive and hypabyssal rocks in the Brabant Massif is considerably less than the 6000 m of ?Llandeilo-Caradoc volcanic rocks related to the subduction of Avalonia under Laurentia, but comparable to that of the Ashgill volcanic rocks of the Lake District (Cooper et al 1993).…”

The deep crustal magnetic structure of Britain

“…Cornwell & Walker (1989) suggested a Precambrian basement source. ESH East Shetland High Donato & Tully (1982) suggested an association with a granite pluton but Holloway et al (1991) (Pharaoh et al , 1995; early Palaeozoic magnetic metasediments (Lee et al, 1993); Precambrian basement (Wills 1978); Devonian metamorphism (Allsop 1987) FVP Forties Volcanic Province Jurassic volcanic province (Ritchie et al 1988;Smith & Ritchie 1993). …”

Palaeozoic amalgamation of Central Europe: an introduction and synthesis of new results from recent geological and geophysical investigations

“…Cawood et al 1994), and the onset of Windermere Supergroup sedimentation in the English Lake District (Cooper et al 1993). The basement to the southern North Sea (the Southern North Sea-Luneberg Terrane (SNSLT) of Pharaoh et al (1995) was probably an extension of Avalonia, possibly separated from Avalonia proper by a small, perhaps marginal, oceanic basin. If so, the ABDB was an intra-Avalonian mobile belt, perhaps developed in the Acadian orogenic phase, when Avalonia was moulding itself on to the margins of Baltica and Laurentia.…”