40Ar–39Ar isotope constraints on the age of deformation in Charnwood Forest, UK

• Published in: Geological magazine 2008-09, Vol.145 (5), p.702-713
• Main Authors: CARNEY, J. N., ALEXANDRE, P., PRINGLE, M. S., PHARAOH, T. C., MERRIMAN, R. J., KEMP, S. J.
• Format: Article
• Language: English
• Subjects: absolute age; Acadian; Acadian Phase; Ar/Ar; argon; Caledonian; Caledonian Orogeny; Caledonides; Cambrian; Charnwood Forest; cratons; crystallization; dates; deformation; Devonian; England; Europe; fabric; geochemistry; Geochronology; Great Britain; isotopes; Lake District; Leicestershire England; Lower Devonian; metamorphic rocks; metamorphism; metapelite; metasedimentary rocks; Midlands; mineral composition; Neoproterozoic; Paleozoic; petrography; Precambrian; Proterozoic; schists; Structural geology; Swithland Formation; tectonics; textures; United Kingdom; upper Precambrian; Wales; Welsh Basin; Western Europe; X-ray diffraction data
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756808004950

40Ar–39Ar dating by a combination of spot analysis and step-heating has been carried out on mica fabrics from slaty cleavage and a shear zone in the Neoproterozoic to Cambrian rocks of Charnwood Forest, Leicestershire. The results indicate that crust adjacent to the eastern margin of the Midlands Microcraton was affected by localized epizonal metamorphism and penetrative deformation between 425 and 416 Ma (Silurian to earliest Devonian), somewhat earlier than the Acadian Phase of the Caledonian orogeny recorded elsewhere in southern Britain. The Charnwood cleavage geometry suggests that the deformation arose within a dextral transpressional regime along the eastern margin of the Midlands Microcraton. This tectonism may have overlapped with pre-Acadian sinistral transtensional movements documented for the Welsh Basin and Lake District areas, to the west and north of the Midlands Microcraton.