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K–Ar age determinations on the fine fractions of clay mineral ‘Crystallinity Index Standards’ from the Palaeozoic mudrocks of southwest England

Published online by Cambridge University Press:  05 April 2019

Anna C. Schomberg ,
Klaus Wemmer ,
Laurence N. Warr  and
Georg H. Grathoff
Anna C. Schomberg*
Affiliation:
Geoscience Centre, University of Göttingen, 37077 Göttingen, Germany
Klaus Wemmer
Affiliation:
Geoscience Centre, University of Göttingen, 37077 Göttingen, Germany
Laurence N. Warr
Affiliation:
Institute of Geography and Geology, University of Greifswald, 17487 Greifswald, Germany
Georg H. Grathoff
Affiliation:
Institute of Geography and Geology, University of Greifswald, 17487 Greifswald, Germany
*
*E-mail: anna.schomberg@posteo.de
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Abstract

Clay mineral ‘Crystallinity Index Standards’ (CIS) composed of Palaeozoic mudrocks from southwest England were investigated systematically in five sub-fractions per sample for the first time. X-ray diffraction was used to determine mineral assemblages, calibrated 001 illite full-width-at-half-maximum (FWHM) values and illite polytype compositions, in addition to K–Ar isotopic analyses of all fine fractions. The FWHM results of the <2 µm fraction are consistent with previous studies and reflect the range of diagenetic to epizonal grades covered by the sample set SW1 to SW7 (~0.61–0.26°2θ). Diagenetic and lower anchizone samples also show significant broadening of 001 illite reflections in the finer fractions and contain mixtures of authigenic 1M + 1Md illite and detrital 2M1 white mica polytypes suitable for illite age analysis. The estimated end-member ages of the Bude (SW1-1992) and younger Crackington (SW3-2000) mudstones yield detrital ages of Late Cambrian to Middle Ordovician (493–457 Ma) and a broad range of 1M + 1Md illite ages between Middle Permian and Early Jurassic (271–190 Ma). The detrital age of the stratigraphically older Crackington Formation mudrock (SW2-1992) is Late Devonian (384–364 Ma) with 1M + 1Md illite ages between Late Triassic and Early Jurassic (219–176 Ma). The origin of Mesozoic 1M + 1Md illite ages may represent neocrystallized illite associated with Mesozoic hydrothermal events or similar events that thermally reset older authigenic illite with partial loss of radiogenic argon and no renewed crystal growth. In contrast, upper anchizonal and epizonal Devonian slates (SW3-2012, SW4-1992, SW6-1992 and SW7-2012) contain only the 2M1 polytype, with K–Ar ages younger than the stratigraphic age. The three finest fractions of SW4-1992 yield consistent Late Carboniferous ages (331–304 ± 7 Ma) that are considered to date the neocrystallized 2M1 mica. Most fractions of epizonal slate (SW6-1992, SW7-2012) yield Early Permian ages (293.6–273 Ma) corresponding to published cooling ages of the Tintagel High-Strain Zone and the intrusion of the Bodmin granite (291.4 ± 0.8 Ma). These first K–Ar age constraints for the fine fractions of the CIS should provide useful reference values for testing analytical procedures of illite age analysis.

Keywords

illite polytypesdiagenesismetamorphismanchizoneisotopesX-ray diffraction
Type
Article
Information
Clay Minerals , Volume 54 , Issue 1 , March 2019 , pp. 15 - 26
Copyright
Copyright © Mineralogical Society of Great Britain and Ireland 2019 

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Footnotes

This paper was originally presented during the session: ‘GG01 – Clays in faults and fractures + MI-03 Clay mineral reaction progress in very low-grade temperature petrologic studies’ of the International Clay Conference 2017.

Guest Associate Editor: J.S. Kemp

References

Andrews, J.R., Day, J. & Marschall, J.E.A. (1996) A thermal anomaly associated with the Rusey Fault and its implications for fluid movements. Proceedings of the Ussher Society, 9, 68–71.Google Scholar
Brindley, G.W. & Brown, G. (1980) X-ray diffraction procedures for clay mineral identification. Pp. 305–356 in: Crystal Structures of Clay Minerals and Their X-Ray Identification (Brindley, G.W. & Brown, G., editors). Mineralogical Society, London, UK.Google Scholar
Clark, A.H., Chen, Y., Farrar, E., Northcote, B., Wastenays, H.A.H.P., Hodgson, M.J. & Bromley, A. (1994) Refinement of the time/space relationships of intrusion and hydrothermal activity in the Cornubian Batholith (abstract). Proceedings of the Ussher Society, 8, 345.Google Scholar
Clauer, N., O'Neil, J.R. & Furlan, S. (1995) Clay minerals as records of temperature conditions and duration of thermal anomalies in the Paris Basin, France. Clay Minerals, 30, 1–13.Google Scholar
Chen, Y., Clark, A., Farrar, E., Wasteneys, H., Hodgson, M. & Bromley, A. (1993) Diachronous and independent histories of plutonism and mineralization in the Cornubian Batholith, southwest England. Journal of the Geological Society, 150, 1183–1191.Google Scholar
Cornford, C., Yarnell, L. & Murchison, D.G. (1987) Initial vitrinite reflectance results from the Carboniferous of north Devon and north Cornwall. Proceedings of the Ussher Society, 6, 453–460.Google Scholar
Cox, S.F. & Munroe, S.M. (2016) Breccia formation by particle fluidization in fault zones: implications for transitory, rupture-controlled fluid flow regimes in hydrothermal systems. America Journal of Science, 316, 241–278.Google Scholar
Dallmeyer, R.D. & Takasu, A. (1992). 40Ar/39Ar ages of detrital muscovite and whole-rock slate/phyllite, Narragansett Basin, RI-MA, USA: implications for rejuvenation during very low-grade metamorphism. Contributions to Mineralogy and Petrology, 4, 515–527.Google Scholar
Dodson, M.H. & Rex, D.C. (1971) Potassium–argon ages of slates and phyllites from south-west England. Quarterly Journal of the Geological Society, 126, 465–498.Google Scholar
Eberl, D.D. (2003) User Guide to RockJock-A Program for Determining Quantitative Mineralogy from X-Ray Diffraction Data. US Geological Survey, Reston, VA, USA.Google Scholar
Fuhrmann, U., Lippolt, H.J. & Hess, J.C. (1987) Examination of some proposed K–Ar standards: 40Ar/39Ar analyses and conventional K–Ar data. Chemical Geology, 66, 41–51.Google Scholar
Freshney, E.C., McKeown, M.C. & William, M. (1972) Geology of the Coast between Tintagel and Bude. Memoirs of the Geological Survey of Great Britain. HM Stationery Office, Richmond, UK.Google Scholar
Friedrich, D. (1991) Eine neue Methode zur Bestimmung der Illit Kristallinität mit Hilfe digitaler Meßwerterfassung. Unpublished diploma thesis, University of Göttingen, Göttingen, Germany.Google Scholar
Grathoff, G.H. & Moore, D. (1996) Illite polytype quantification using WILDFIRE© calculated X-ray diffraction patterns. Clays and Clay Minerals, 44, 835–842.Google Scholar
Haines, S. & van der Pluijm, B.A. (2008) Clay quantification and Ar–Ar dating of synthetic and natural gouge: application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico. Journal of Structural Geology, 30, 525–538.Google Scholar
Halliday, A.N. & Mitchell, J.G. (1976) Structural, K–Ar and 40Ar–39Ar age studies of adularia K-feldspars from the Lizard Complex, England. Earth and Planetary Science Letters, 29, 227–237.Google Scholar
Hartley, A.J. & Warr, L.N. (1990) Upper Carboniferous foreland basin evolution in SW Britain. Proceedings of the Ussher Society, 7, 212–216.Google Scholar
Heinrichs, H. & Herrmann, A.G. (1990) Praktikum der Analytischen Geochemie. Springer, Berlin, Germany.Google Scholar
Hunziker, J.C. (1986) The evolution of illite to muscovite: an example of the behavior of isotopes in low-grade metamorphic terrains. Chemical Geology, 57, 31–40.Google Scholar
Kelley, S.P. (2002) K–Ar and Ar–Ar dating. Reviews in Mineralogy and Geochemistry, 47, 785–818.Google Scholar
Kelm, U. & Robinson, D. (1989) Variscan regional metamorphism in north Devon and west Somerset. Proceedings of the Ussher Society, 7, 146–151.Google Scholar
Kowalska, S., Halas, S., Wójtowicz, A., Wemmer, K. & Mikolajewski, Z. (2017) Methodological aspects of K–Ar dating in application to sedimentary basins thermal history reconstruction. Abstract presented at the 16th International Clay Conference, Granada, Spain.Google Scholar
Kübler, B. (1966) La Cristallinité de l'Illite et les Zones Tout à Fait Supérieures du Métamorphisme. Baconnière, Neuchâtel, Switzerland.Google Scholar
McDougall, I. & Harrison, T.M. (1999) Geochronology and Thermochronology by the 40Ar/39Ar Method. Oxford University Press, Oxford, UK.Google Scholar
Merriman, R.J. & Peacor, D.R. (1999) Very low-grade metapelites: mineralogy, microfabrics and measuring reaction progress. Pp. 10–60 in: Low-Grade Metamorphism (Frey, M. & Robinson, R., editors). Blackwell Science, Oxford, UK.Google Scholar
Merriman, R.J. & Frey, M. (1996) Patterns of very low-grade metamorphism in metapelite rocks. Pp. 61–107 in: Low-Grade Metamorphism (Frey, M. & Robinson, R., editors). Blackwell Science, Oxford, UK.Google Scholar
Moore, D.M. & Reynolds, R.C. (1997) X-Ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford University Press, Oxford, UK.Google Scholar
Pamplin, C. (1990) A model for the tectono-thermal evolution of North Cornwall. Proceedings of the Ussher Society, 7, 208–211.Google Scholar
Pevear, D.R. (1999) Illite and hydrocarbon exploration. Proceedings of the National Academy of Science of the United States of America, 96, 3440–3446.Google Scholar
Primmer, T. (1985a) A transition from diagenesis to greenschist facies within a major Variscan fold/thrust complex in south-west England. Mineralogical Magazine, 49, 365–374.Google Scholar
Primmer, T. (1985b) Discussion on the possible contribution of metamorphic water to the mineralizing fluid of south-west England: preliminary stable isotope evidence. Proceedings of the Ussher Society, 6, 224–228.Google Scholar
Reuter, A. & Dallmeyer, R.D. (1987) Significance of 40Ar/39Ar age spectra of whole-rock and constituent grain-size fractions of anchizonal slates. Chemical Geology: Isotope Geoscience section, 66, 73–88.Google Scholar
Reuter, A. & Dallmeyer, R.D. (1989) K–Ar and 40Ar/39Ar dating of cleavage formed during very low-grade metamorphism: a review. Geological Society, London, Special Publications, 43, 161–171.Google Scholar
Sams, M.S. & Thomas-Betts, A. (1988) Models of convective fluid flow and mineralization in south-west England. Journal of the Geological Society, London, 145, 809–817.Google Scholar
Schuhmacher, E. (1975) Herstellung von 99.9997% 38Ar für die 40K/40Ar Geochronologie. Geochronologia Chimia, 24, 441–442.Google Scholar
Schomberg, A. (2017) K–Ar Age Determination on Clay Fine Fractions of CIS Samples (Crystallinity Index Standards). Unpublished MSc thesis, Georg-August-University Göttingen, Göttingen, Germany.Google Scholar
Schleicher, A.J., Warr, L.N., Kober, B., Laverret, E. & Clauer, N. (2006) Episodic mineralization of hydrothermal illite in the Soultz-sous-Foréts granite (Upper Rhine Graben, France). Contributions to Mineralogy and Petrology, 152, 349–364.Google Scholar
Sherlock, S., Zalasiewicz, J., Kelly, S.P. & Evans, J. (2008) Excess argon (40ArE) uptake during slate formation: a 40Ar/39Ar UV laserprobe study of muscovite strain-fringes from the Palaeozoic Welsh Basin, UK. Chemical Geology, 257(3–4), 203–217.Google Scholar
Steiger, R.H. & Jäger, E. (1977) Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters, 36, 359–362.Google Scholar
Szczerba, M. & Środoń, J. (2009) Extraction of diagenetic and detrital ages and of the 40K detrital/40Kdiagenetic ratio from K–Ar dates of clay fractions. Clays and Clay Minerals, 57, 93–103.Google Scholar
van der Pluijm, B.A., Hall, C.M., Vrolijk, P.J., Pevear, D.R. & Covey, M.C. (2001) The dating of shallow faults in the Earth's crust. Nature, 412, 172–175.Google Scholar
Warr, L.N. (1989) The structural evolution of the Davidstow Anticline, and its relationship to the Southern Culm Overfold, North Cornwall. Proceedings of the Ussher Society, 7, 136–140.Google Scholar
Warr, L.N. (2009) The Variscan orogeny: the welding of Pangaea. Pp. 271–294 in: Geological History of Britain and Ireland (Woodcock, N.H. & Strachan, R.A., editors). John Wiley and Sons, Chichester, UK.Google Scholar
Warr, L.N. (2018) A new collection of clay mineral ‘Crystallinity’ Index Standards and revised guidelines for the calibration of Kübler and Árkai indices. Clay Minerals, 53, 339–350.Google Scholar
Warr, L.N. & Mählmann, R.F. (2015) Recommendations for Kübler Index standardization. Clay Minerals, 50, 283–286.Google Scholar
Warr, L.N., Primmer, T. & Robinson, D. (1991) Variscan very low-grade metamorphism in southwest England: a diastathermal and thrust-related origin. Journal of Metamorphic Geology, 9, 751–764.Google Scholar
Warr, L.N. & Nieto, F. (1998) Crystallite thickness and defect density of phyllosilicates in low-temperature metamorphic pelites: a TEM and XRD study of clay mineral crystallinity-index standards. The Canadian Mineralogist, 36, 1453–1474.Google Scholar
Warr, L.N. & Rice, A. (1994) Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology, 12, 141–152.Google Scholar
Wemmer, K. (1991) K/Ar-Altersdatierungsmöglichkeiten für retrograde deformationsprozesse im spröden und duktilen Bereich–Beispiele aus der KTB-Vorbohrung (Oberpfalz) und dem Bereich der Insubrischen Linie (N-Italien). PhD thesis, Göttinger Arbeiten Geologie und Paläontologie 51, Göttingen, Germany.Google Scholar
Whitney, D.L. & Evans, B.W. (2010) Abbreviations for names of rock-forming minerals. American Mineralogist, 95, 185–187.Google Scholar
Willis-Richards, J. & Jackson, N.J. (1989) Evolution of the Cornubian ore field, southwest England; part 1, batholith modeling and ore distribution. Economic Geology, 84, 1078–1100.Google Scholar
Woodcock, N.H., Soper, N.J. & Strachan, R.A. (2007) A Rheic cause for the Acadian deformation in Europe. Journal of the Geological Society, 164, 1023–1036.Google Scholar
Ylagan, R.F., Kim, C.S., Pevear, D.R. & Vrolijk, P. (2002) Illite polytype quantification for accurate age determination. American Mineralogist, 87, 1536–1545.Google Scholar
Zwingmann, H., Clauer, N. & Gaupp, R. (1998) Timing of fluid flow in a sandstone reservoir of the North-German Rotliegen (Permian) by K–Ar dating of related hydrothermal illite. Pp. 91–106 in: Dating and Duration of Fluid Flow Events (Parnell, J., editor). Geological Society of London Special Publication, London, UK.Google Scholar