The stratigraphy and tectonics of the Manx Slate Series, Isle of Man

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Abstract
The geosynclinal sequence of the Manx Slate Series has been subdivided into eleven distinct formations with a thickness of about 25 000 ft. This thick sedimentary pile was deposited in the Caledonian geosyncline and is most probably all of Cambrian age. The stratigraphical positions of two thick sheets of slump-breccia have been established. The tectonics of the Manx Slate Series are more complex than previously envisaged. The island forms part of the polyphase Caledonian orogenic belt. Three phases of tectonic movement ( F 1 , F 2 , F 3 ) each formed large-scale folds and a suite of minor structures. Later structures deform those that originated earlier. The fundamental structure that affects the whole island is the acute Caledonoid Isle of Man syncline of F 1 age. During the second movement-phase ( F 2 ) this pre-existing fold was flexed into a major synform and two complementary antiforms. These more open flexures have Caledonoid hinges and their axial planes dip gently north-westwards. During the last phase of folding ( F 3 ), the complexity of the pile was further increased by several large, open cross-flexures round axial planes dipping steeply east-north-east. The final event in the Caledonian deformation was a brittle fracturing of the complex block by a sinistral system of large and small transcurrent faults with a north-westerly strike. Most of the small normal faults that also intersect the Manx Slates are probably post-Carboniferous in age.

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