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Polyphase low-grade metamorphism of the Ingleton Group, northern England, UK: a case study of metamorphic inversion in a mudrock succession

  • S. J. KEMP (a1) and R. J. MERRIMAN (a1)

A series of boreholes in Horton Quarry, northwest Yorkshire (Horton-in-Ribblesdale Inlier) penetrated mudstones and slates belonging to the Austwick Formation (Windermere Supergroup) overlying laminated mudstones of the Ingleton Group. Illite (IC) and chlorite (ChC) crystallinity measurements indicate a metamorphic inversion between the two groups of mudrocks. The Windermere Supergroup mudrocks are mostly in the high anchizone or epizone, whereas the Ingletonian samples are lower grade in terms of IC, and are mostly deep diagenetic zone or low anchizone. Hence younger strata at higher grades rest on older strata at lower grades, creating a metamorphic inversion. Ingletonian slates exposed at Pecca Falls on the River Twiss show epizonal and anchizonal IC values, and greywacke samples from Ingleton Quarry contain pumpellyite. This suggests that grade in the Ingletonian may increase to the NW from the Horton to Ingleton inliers. K-white mica b cell dimensions show further differences between the Ingleton Group and the Windermere Supergroup. The Ingletonian samples are characterized by low b cell values (8.989–9.035, mean 9.007 Å), whereas the Windermere Supergroup has higher values in the range 9.022–9.034, mean 9.027 Å. The Windermere Supergroup values are similar to those recorded from the Windermere Supergroup of the southern Lake District, and Lower Palaeozoic rocks from the Scottish Southern Uplands, and are consistent with metamorphism in a low heat flow, convergent geotectonic setting. The Ingletonian b cell values suggest metamorphism in a higher heat flow setting, most likely an extensional basin. The metamorphic inversion at Horton and differences in K-white mica b cell dimensions suggest that the Ingleton Group and Windermere Supergroup strata evolved in different geotectonic settings and record two separate metamorphic events. The discovery of the metamorphic inversion at Horton provides further evidence in favour of an Ordovician rather than Neoproterozoic depositional age for the controversial Ingleton Group.

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I. Abad , G. Gutiérrez-Alonso , F. Nieto , I. Gertner , A. Becker & A. Cabero 2003. The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz republic): comparison with more recent subduction complexes. Tectonophysics 365, 103–27.

P. Árkai 1991. Chlorite crystallinity: an empirical approach and correlation with illite crystallinity, coal rank and mineral facies as exemplified by Palaeozoic and Mesozoic rocks of northeast Hungary. Journal of Metamorphic Geology 9, 723–34.

S. W. Bailey 1987. X-ray diffraction identification of the polytypes of mica, serpentine, and chlorite. Clays and Clay Minerals 36, 193213.

N. G. Berridge 1982. Petrography of the Pre-Carboniferous rocks of the Beckermonds Scar borehole in the context of the magnetic anomaly at the site. Proceedings of the Yorkshire Geological Society 44, 8998.

R. E. Bevins & R. J. Merriman 1988. Co-existing prehnite–actinolite and prehnite–pumpellyite facies assemblages in the Tal y Fan Metabasite Intrusion, North Wales: Implications for Caledonian metamorphism. Journal of Metamorphic Geology 6, 1739.

S. H. Bottrell , P. B. Greenwood , B. W. D. Yardley , T. J. Shepherd & B. Spiro 1990. Metamorphic and post-metamorphic fluid flow in the low-grade rocks of the Harlech Dome, north Wales. Journal of Metamorphic Geology 8, 131–43.

M. Dalla Torre , K. J. T. Livi , D. R. Veblen & M. Frey 1996. White K-mica evolution from phengite to muscovite in shales and shale matrix melange. Contributions to Mineralogy and Petrology 123 (4), 390405.

G. Davies , A. Gledhill & C. Hawkesworth 1985. Upper crustal recycling in southern Britain: evidence from Nd and Sr isotopes. Earth and Planetary Science Letters 75, 112.

M. H. Dodson & D. Robinson 2006. A mid-Ordovician Rb–Sr isochron age from the Ingleton Group, North Yorkshire: metamorphism or diagenesis? Proceedings of the Yorkshire Geological Society 56, 81–5.

G. H. Grathoff & D. M. Moore 1996. Illite polytype quantification using Wildfire calculated X-ray diffraction patterns. Clays and Clay Minerals 44, 835–42.

J. Hower , E. V. Eslinger , M. E. Hower & E. A. Perry 1976. Mechanism of burial metamorphism of argillaceous sediments: Mineralogical and chemical evidence. Geological Society of America Bulletin 87, 725–37.

H. J. Kisch 1991. Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings and interlaboratory standards. Journal of Metamorphic Geology 9, 665–70.

B. C. Kneller , L. M. King & A. M. Bell 1993. Foreland basin development and tectonics on the northwest margin of eastern Avalonia. Geological Magazine 130, 691–7.

B. C. Kneller , R. W. Scott , N. J. Soper , E. W. Johnson & P. M. Allen 1994. Lithostratigraphy of the Windermere Supergroup in northern England. Geological Journal 29, 219–40.

G. P. Leedal & G. P. Walker 1950. A restudy of the Ingletonian Series of Yorkshire. Geological Magazine 87, 5766.

R. J. Merriman 2002. Contrasting clay mineral assemblages in British Lower Palaeozoic slate belts: the influence of geotectonic setting. Clay Minerals 37, 207–19.

R. J. Merriman & B. Roberts 1985. A survey of white mica crystallinity and polytypes in mudrocks of Snowdonia and Llŷn, N. Wales. Mineralogical Magazine 49, 305–19.

R. J. Merriman , D. C. Rex , N. J. Soper & D. R. Peacor 1995. The age of Acadian cleavage in northern England, UK: K–Ar and TEM analysis of a Silurian metabentonite. Proceedings of the Yorkshire Geological Society 50, 255–65.

S. R. Noble , R. D. Tucker & T. C. Pharaoh 1993. Lower Palaeozoic and Precambrian igneous rocks from eastern England and their bearing on Ordovician closure of the Tornquist Sea: constraints from U–Pb and Nd isotopes. Geological Magazine 130, 835–46.

R. Offler , S. McKnight & V. Morand 1998. Tectonothermal history of the western Lachlan Fold Belt, Australia: insights from white micas. Journal of Metamorphic Geology 16, 531–40.

R. K. O'Nions , E. R. Oxburgh , C. J. Hawkesworth & R. M. Macintyre 1973. New isotopic and stratigraphical evidence on the age of the Ingletonian. Journal of the Geological Society, London 129, 445–52.

R. K. O'Nions , P. J. Hamilton & P. J. Hooker 1983. A Nd isotope investigation of sediments related to crustal development in the British Isles. Earth and Planetary Science Letters 63, 229–40.

A. Padan , H. J. Kisch & R. Shagam 1982. Use of the lattice parameter b0 of dioctahedral illite/muscovite, for the characterisation of P/T gradients of incipient metamorphism. Contributions to Mineralogy and Petrology 79, 8595.

N. J. Soper & F. W. Dunning 2005. Structure and sequence of the Ingleton Group, basement to central Pennines of northern England. Proceedings of the Yorkshire Geological Society 55, 241–61.

J. Środoń 1999. Nature of mixed-layer clays and mechanisms of their formation and alteration. Annual Reviews of Earth and Planetary Science 27, 1953.

P. Stone & R. J. Merriman 2004. Basin thermal history favours an accretionary origin for the Southern Uplands terrane, Scottish Caledonides. Journal of the Geological Society, London 161, 829–36.

L. Warr & A. H. N. Rice 1994. Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology 12, 141–52.

I. A. Williamson 2005. Field Meeting in Lower Kingsdale and Chapel-le-Dale, Ingleton, northwest Yorkshire: Lancashire Group, 9 August 2003. Proceedings of the Geologists' Association 116, 143–7.

A. A. Wilson & J. D. Cornwell 1982. The Institute of Geological Sciences borehole at Beckermonds Scar, North Yorkshire. Proceedings of the Yorkshire Geological Society 44, 5988.

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