The concealed Caledonides of eastern England: preliminary results of a multidisciplinary study

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Abstract
SUMMARY: New petrological, geochemical and isotopic age data have been obtained from concealed Precambrian and Lower Palaeozoic rocks in eastern England. The geochemical data suggest that concealed felsic volcanic rocks are petrogenetically unrelated to the Charnian igneous suites, while new isotopic data suggest that the former are probably of late Ordovician age. The concealed volcanic rocks probably occur as a stratigraphic unit (or units) within a Lower Palaeozoic sedimentary sequence, as in Wales and Belgium. These data, together with structural and geophysical evidence and results from mica crystallinity studies of pelitic rocks, suggest that much of eastern England is underlain by a concealed NW-SE trending Caledonide deformation belt. Pelitic rocks show a low-grade metamorphic zonation, with grade increasing from diagenetic conditions on the Midlands Microcraton, through anchizonal to epizonal (greenschist facies) conditions in the internal zone of the belt beneath the Wash. The structure and stratigraphy of this Caledonide belt are poorly known at present, but are likely to be as complex as those of the Welsh Caledonides, of which the concealed Caledonides of eastern England appear to form a mirror image. The key to the stratigraphy of this belt is probably to be found in the Brabant and Ardennes Massifs of Belgium. The Caledonide Midlands Microcraton is now seen as a restricted wedge-shaped area, underlain throughout by Precambrian crust, and forming a rigid indenter within the Caledonide Orogen of Britain.