Hostname: page-component-78c5997874-fbnjt Total loading time: 0 Render date: 2024-11-08T02:47:48.081Z Has data issue: false hasContentIssue false
  • English
  • Français

Geodynamic significance of post-Variscan intrusive and extrusive potassic magmatism in SW England

Published online by Cambridge University Press:  03 November 2011

P. T. Leat ,
R. N. Thompson ,
M. A. Morrison ,
G. L. Hendry  and
S. C. Trayhorn
P. T. Leat
Affiliation:
Department of Geology, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BP, England.
R. N. Thompson
Affiliation:
Department of Geology, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BP, England.
M. A. Morrison
Affiliation:
Department of Geological Sciences, University of Birmingham, Birmingham B15 2TT, England.
G. L. Hendry
Affiliation:
Department of Geological Sciences, University of Birmingham, Birmingham B15 2TT, England.
S. C. Trayhorn
Affiliation:
Department of Geology, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BP, England.
Get access Rights & Permissions [Opens in a new window]

Abstract

Post-Variscan magmatism in SW England involved the synchronous emplacement of basaltic and potassic lavas, minette dykes and the Cornubian granite batholith at c. 290 Ma. The basaltic and potassic rocks have high contents of Ni and Cr, which suggest that both are not excessively fractionated. The basaltic lavas are moderately enriched in LREE and LIL elements relative to HREE, whereas the chemically-varied potassic lavas are more strongly enriched in LREE and LIL elements, with notable depletions in Nb, Ta and Ti relative to LREE. These features are consistent with the view that these rocks are subduction-related. Possibly the potassic rocks were derived from an ultimate source in lithosphere subducted or downthrust during the Variscan orogeny. The source of the basaltic rocks was probably in the asthenosphere. The minette dykes are chemically similar to the potassic lavas, suggesting that they are genetically related. Most dykes occur in a zone up to 25 km wide around the margin of the granite batholith, in a “shadow-zone” relationship. The granite batholith (c. 48,000 km3) is moderately enriched in Th and HFS elements, but is strongly enriched in Rb. Rb-Th relationships indicate an origin for the granite by fractionation from potassic magma in addition to melting of crust.

Keywords

assimilationbasaltCornubian batholithgraniteminettepetrogenesisrhyoliteRubidiumshoshoniteS-type graniteThorium
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 77 , Issue 4 , 1987 , pp. 349 - 360
Copyright
Copyright © Royal Society of Edinburgh 1987

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Appleton, J. D. 1972. Petrogenesis of potassium-rich lavas from the Roccamonfina volcano, Roman region, Italy. J PETROL 13, 425–56.Google Scholar
Bacon, C. R., Macdonald, R., Smith, R. L. and Baedecker, P. A. 1981. Pleistocene high-silica rhyolites of the Coso volcanic field, Inyo County, California. J GEOPHYS RES 86, 10223–41.Google Scholar
Baker, B. H. & McBirney, A. R. 1985. Liquid fractionation, Part III: geochemistry of zoned magmas and the compositional effects of liquid fractionation. J VOLCANOL GEOTHERM RES 24, 55–81.Google Scholar
Barberi, F., Innocenti, F., Ferrara, G., Keller, J. & Villari, L. 1974. Evolution of the Eolian arc volcanism (southern Tyrrhenian Sea). EARTH PLANET SCI LETT 21, 269–76.CrossRefGoogle Scholar
Bott, M. H. P., Day, A. A. & Masson, Smith D. 1958. The geological interpretations of gravity and magnetic surveys in Devon and Cornwall. PHILOS TRANS R SOC LONDON A251, 161–91.Google Scholar
Bowden, P. 1985. The geochemistry and mineralization of alkaline ring complexes in Africa (a review). J AFR EARTH SCI 3, 17–39.Google Scholar
Brooks, M., Mechie, J. & Llewelyn, D. J. 1983. Geophysical investigations in the Variscides of southwest Britain. In Hancock, P. L. (ed.) The Variscan fold belt in the British Isles, 186–97. Bristol: Adam Hilger.Google Scholar
Charoy, B. 1986. The genesis of the Cornubian batholith (South-West England): the example of the Carnmenellis pluton. J PETROL 27, 571–604.CrossRefGoogle Scholar
Civetta, L., Innocenti, F., Manetti, P., Peccerillo, A. & Poli, G. 1981. Geochemical characteristics of potassic volcanics from Mts Ernici (Southern Latium, Italy). CONTRIB MINERAL PETROL 78, 37–47.CrossRefGoogle Scholar
Cosgrove, M. E. 1972. The geochemistry of potassium-rich Permian volcanic rocks of Devonshire, England. CONTRIB MINERAL PETROL 36, 155–70.CrossRefGoogle Scholar
Cosgrove, M. E. & Elliott, M. H. 1976. Supra-batholithic volcanism of the southwest England granites. PROC USSHER SOC 3, 391–401.Google Scholar
Cosgrove, M. E. & Hamilton, N. 1973. Geochemical and preliminary palaeomagnetic results of the Lemail lamprophyre, Wadebridge, Cornwall. PROC USSHER SOC 2, 482.Google Scholar
Cundari, A. 1980. Role of subduction in the genesis of leucite-bearing rocks: facts on fasion. CONTRIB MINERAL PETROL 73, 432–4.CrossRefGoogle Scholar
Darbyshire, D. P. F. & Shepherd, T. J. 1985. Chronology of granite magmatism and associated mineralization, SW England. J GEOL SOC LONDON 142, 1159–77.CrossRefGoogle Scholar
Doe, B. R., Leeman, W. P., Christiansen, R. L. & Hedge, C. E. 1982. Lead and strontium isotopes and related trace elements as genetic tracers in the upper Cenozoic rhyolite-basalt association of the Yellowstone plateau volcanic field. J GEOPHYS RES 87, 4785–806.CrossRefGoogle Scholar
Edgar, A. D. 1980. Role of subduction in the genesis of leucite-bearing rocks: discussion. CONTRIB MINERAL PETROL 73, 429–31.Google Scholar
Edmonds, E. A., McKeown, M. C. & Williams, M. 1975. British Regional Geology: South West England, 4th edn. London: HMSO.Google Scholar
Exley, C. S. & Stone, M. 1982. Petrogenesis. In Sutherland, D. S. (ed.) Igneous Rocks of the British Isles, 311–20. Chichester: Wiley.Google Scholar
Exley, C. S., Stone, M. & Lees, G. L. 1982. Petrology of the granites and minor intrusions. In Sutherland, D. S. (ed.) Igneous Rocks of the British Isles, 293–302. Chichester: Wiley.Google Scholar
Exley, C. S., Stone, M. & Floyd, P. A. 1983. Composition and petrogenesis of the Cornubian granite batholith and postorogenic volcanic rocks in southwestern England. In Hancock, P. L. (ed.) The Variscan fold belt in the British Isles, 153–77. Bristol: Adam Hilger.Google Scholar
Floyd, P. A. 1982a. Geological setting of Upper Palaeozoic magmatism. In Sutherland, D. S. (ed.) Igneous Rocks of the British Isles, 217–25. Chichester: Wiley.Google Scholar
Floyd, P. A. 1982b. The Hercynian trough: Devonian and Carboniferous volcanism in south-western Britain. In Sutherland, D. S. (ed.) Igneous Rocks of the British Isles, 227–42. Chichester: Wiley.Google Scholar
Floyd, P. A. & Winchester, J. A. 1978. Identification and discrimination of altered and metamorphosed volcanic rocks using immobile elements. CHEM GEOL 21, 291–306.Google Scholar
Foden, J. D. & Varne, R. 1980. The petrology and tectonic setting of Quaternary-Recent volcanic centres of Lombok and Sumbawa, Sunda arc. CHEM GEOL 30, 201–26.CrossRefGoogle Scholar
Gill, J. B. 1970. Geochemistry of Viti Levu, Fiji, and its evolution as an island arc. CONTRIB MINERAL PETROL 27, 179–203.CrossRefGoogle Scholar
Goode, A. J. J. 1973. The mode of intrusion of Cornish elvans. INST GEOL SCI REP 73/7.Google Scholar
Hall, A. 1982. The Pendennis peralkaline minette. MINERAL MAG 45, 257–66.CrossRefGoogle Scholar
Hampton, C. M. & Taylor, P. N. 1983. The age and nature of the basement of southern Britain: evidence from Sr and Pb isotopes in granites. J GEOL SOC LONDON 140, 499–509.CrossRefGoogle Scholar
Hancock, P. L. (ed.) 1983. The Variscan Fold Belt in the British Isles. Bristol: Adam Hilger.Google Scholar
Harland, W. B., Cox, A. V., Llewellyn, P. G., Pickton, C. A. G., Smith, A. G. & Walters, R. 1982. A Geological Time Scale. Cambridge: Cambridge University Press.Google Scholar
Harris, N. B. W. 1985. Alkaline complexes from the Arabian shield. J AFR EARTH SCI 3, 83–8.Google Scholar
Harris, N. B. W., Dayverman, H. J. & Almond, D. C. 1983. The trace element and isotope geochemistry of the Sabaloka igneous complex, Sudan. J GEOL SOC LONDON 140, 245–56.CrossRefGoogle Scholar
Hawkes, J. R. 1981. A tectonic ‘watershed’ of fundamental consequence in the post-Westphalian evolution of Cornubia. PROC USSHER SOC 5, 128–31.Google Scholar
Hawkesworth, C. J., Rogers, N. W., van Calsteren, P. W. C. & Menzies, M. A. 1984. Mantle enrichment processes. NATURE 311, 331–5.CrossRefGoogle Scholar
Henderson, P. & Williams, C. T. 1981. Application of intrinsic Ge detectors to the instrumental neutron activation analysis for rare earth elements in rocks and minerals. J RADIOANAL CHEM 67, 445–52.Google Scholar
Hildreth, W. 1981. Gradients in silicic magma chambers: implications for lithospheric magmatism. J GEOPHYS RES 86, 10153–92.CrossRefGoogle Scholar
Holder, M. T. & Leveridge, B. E. 1986. Correlation of the Rhenohercynian Variscides. J GEOL SOC LONDON 143, 141–7.Google Scholar
Houseman, G. A., McKenzie, D. P. & Molnar, P. 1981. Convective instability of a thickened boundary layer and its relevance for the thermal evolution of continental convergent belts. J GEOPHYS RES 86, 6115–32.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1985. Cooling and contamination of mafic and ultramafic magmas during ascent through continental crust. EARTH PLANET SCI LETT 74, 371–86.Google Scholar
Isaac, K. P., Turner, P. J. & Stewart, I. J. 1982. The evolution of the Hercynides of central SW England. J GEOL SOC LONDON 139, 521–31.CrossRefGoogle Scholar
Jahn, B., Sun, S.–S. & Nesbitt, R. W. 1979. REE distribution and petrogenesis of the Spanish Peaks igneous complex, Colorado. CONTRIB MINERAL PETROL 70, 281–98.CrossRefGoogle Scholar
Jaques, A. L., Lewis, J. D., Smith, C. B., Gregory, G. P., Ferguson, J., Chappell, B. W. & McCulloch, M. T. 1984. The diamond-bearing ultrapotassic (lamproitic) rocks of the west Kimberley Region, Western Australia. In Kornprobst, J. (ed.) Kimberlites, 1. Kimberlites and Related Rocks, 225–54. Amsterdam: Elsevier.Google Scholar
Jefferies, N. L. 1985. The distribution of the rare earth elements within the Carnmenellis pluton, Cornwall. MINERAL MAG 49, 495–504.Google Scholar
Jolly, W. T., 1971. Potassium-rich igneous rocks from Puerto Rico. BULL GEOL SOC AM 82, 399–408.Google Scholar
Knill, D. C. 1969. The Permian igneous rocks of Devon. BULL GEOL SURV G B 29, 115–38.Google Scholar
Knill, D. C. 1982. Permian volcanism in south-western England. In Sutherland, D. S. (ed.) Igneous Rocks of the British Isles, 329–32. Chichester: Wiley.Google Scholar
Kuehner, S. M., Edgar, A. D. & Arima, M. 1981. Petrogenesis of the ultrapotassic rocks from the Leucite Hills, Wyoming. AM MINERAL 66, 663–77.Google Scholar
Leat, P. T., Macdonald, R. & Smith, R. L. 1984. Geochemical evolution of the Menengai volcano, Kenya. J GEOPHYS RES 89, 8571–92.Google Scholar
Leeder, M. R. 1982. Upper Palaeozoic basins of the British Isles—Caledonian inheritance versus Hercynian plate margin processes. J GEOL SOC LONDON 139, 479–91.Google Scholar
Le Fort, P. 1981. Manaslu leucogranite: a collision signature of the Himalaya. A model for its genesis and emplacement. J GEOPHYS RES 86, 10545–68.CrossRefGoogle Scholar
Macdonald, R., Thorpe, R. S., Gaskarth, J. W. & Grindrod, A. R. 1985. Multi-component origin of Caledonian lamprophyres of northern England. MINERAL MAG 49, 485–94.CrossRefGoogle Scholar
Mahood, G. A. 1981. Chemical evolution of a pleistocene rhyolitic centre: Sierra La Primavera, Jalisco, Mexico. CONTRIB MINERAL PETROL 77, 129–49.CrossRefGoogle Scholar
Mahood, G. A. 1984. Pyroclastic rocks and calderas associated with strongly peralkaline magmatism. J GEOPHYS RES 89, 5840–52.Google Scholar
Mahood, G. A. & Hildreth, W. 1983. Large partition coefficients for trace elements in high-silica rhyolites. GEOCHIM COSMOCHIM ACTA 47, 11–30.CrossRefGoogle Scholar
Manning, D. A. C. 1986. Contrasting styles of Sn-W mineralization in peninsular Thailand and SW England. MINERAL DEPOSITA 21, 44–52.Google Scholar
McCulloch, M. T., Jaques, A. L., Nelson, D. R. & Lewis, J. D. 1983. Nd and Sr isotopes in kimberlites and lamproites from Western Australia: an enriched mangle origin. NATURE 302, 400–3.CrossRefGoogle Scholar
Miller, J. A., Shibata, K. & Munro, M. 1962. The potassium-argon age of the lava of Killerton Park, near Exeter. GEOPHYS J 6, 394–6.CrossRefGoogle Scholar
Mitchell, R. H. & Bell, K. 1976. Rare earth element geochemistry of potassic lavas from the Biranga and Toro-Ankole regions of Uganda, Africa. CONTRIB MINERAL PETROL 58, 293–303.CrossRefGoogle Scholar
Molnar, P. & Gray, D. 1979. Subduction of continental lithosphere: some constraints and uncertainties. GEOLOGY 7, 58–62.Google Scholar
Morrison, G. W. 1980. Characteristics and tectonic setting of the shoshonite rock association. LITHOS 13, 97–108.Google Scholar
Nelson, D. R., McCulloch, M. T. & Sun, S.-S. 1986. The Origins of ultrapotassic rocks as inferred from Sr, Nd and Pb isotopes. GEOCHIM COSMOCHIM ACTA 50, 231–45.CrossRefGoogle Scholar
Nixon, P. H., Thirlwall, M. F., Buckley, F. & Davies, C. J. 1984. Spanish and western Australian lamproites: aspects of whole rock chemistry. In Kornprobst, J. (ed.) Kimberlites, 1: Kimberlites and Related Rocks, 285–96. Amsterdam: Elsevier.Google Scholar
Noble, D. C., Vogel, T. A.Peterson, P. S., Landis, G. P., Grant, N. K., Jezek, P. A. & McKee, E. H. 1984. Rare-elementenriched, S-type ash-flow tuffs containing phenocrysts of muscovite, andalustie, and sillimanite, southeastern Peru. GEOLOGY 12, 35–9.2.0.CO;2>CrossRefGoogle Scholar
Patriat, P. & Achache, J. 1984. India-Eurasia collision chronology has implications for crustal shortening and driving mechanisms of plates. NATURE 311, 615–21.Google Scholar
Pearce, J. A. 1982. Trace element characteristics of lavas from destructive plate boundaries. In Thorpe, R. S. (ed.) Andesites: Orogenic Andesites and Related Rocks, 525–48. Chichester: Wiley.Google Scholar
Pearce, J. A., Harris, N. B. W. & Tindle, A. G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J PETROL 25, 956–83.Google Scholar
Peccerillo, A. 1985. Roman comagmatic province (central Italy): evidence for subduction-related magma genesis. GEOLOGY 13, 103–6.2.0.CO;2>CrossRefGoogle Scholar
Peccerillo, A., Poli, G. & Tolomeo, L. 1984. Genesis, evolution and tectonic significance of K-rich volcanics from the Alban Hills (Roman comagmatic region) as inferred from trace element geochemistry. CONTRIB MINERAL PETROL 86, 230–40.Google Scholar
Pitcher, W. S. 1979. The nature, ascent and emplacement of granitic magmas. J GEOL SOC LONDON 136, 627–62.Google Scholar
Plant, J. A., O'Brien, C., Tarney, J. & Hurdley, J. 1985. Geochemical criteria for the recognition of high heat production granites. In High Heat Production (HHP) Granites, Hydrothermal Circulation and Ore Genesis, 263–85. London: Institute of Mining and Metallurgy.Google Scholar
Reid, C., Barrow, G. & Dewey, H. 1910. The geology of the country around Padstow and Camelford. MEM GEOL SURV G B (1 inch sheets 335 and 336).Google Scholar
Richardson, S. W. & Oxburgh, E. H. 1978. Heat flow, radiogenic heat production and crustal temperatures in England and Wales. J GEOL SOC LONDON 135, 323–38.Google Scholar
Rock, N. M. S. 1984. Nature and origin of calc-alkaline lamprophyres: minettes, vogesites, kersantites and spessarites. TRANS R SOC EDINBURGH: EARTH SCI 74, 193–227.Google Scholar
Rock, N. M. S., Gaskarth, J. W. & Rundle, C. C. 1986. Late Caledonian dyke swarms in southern Scotland: a regional zone of primitive K-rich lamprophyres and associated vents. J GEOL 93, 505–22.Google Scholar
Rogers, N. W., Hawkesworth, C. J., Parker, R. J. & Marsh, J. S. 1985. The geochemistry of potassic lavas from Vulsini, central Italy and implications for mantle enrichment processes beneath the Roman region. CONTRIB MINERAL PETROL 90, 244–57.Google Scholar
Rowell, W. F. & Edgar, A. D. 1983. Cenzoic potassium-rich mafic volcanism in the western U.S.A.: its relationship to deep subduction. J GEOL 91, 338–41.Google Scholar
Saunders, A. D. & Tarney, J. 1984. Geochemical characteristics of basaltic volcanism within back-arc basins. In Kokelaar, B. P. & Howells, M. F. (eds) Marginal basin geology: volcanic and associated sedimentary and tectonic processes in modern and ancient marginal basins, 59–76. GEOL SOC LONDON SPEC PUBL 16.Google Scholar
Scott, Smith B. M. & Skinner, E. M. W. 1984. A new look at Prairie Creek, Arkansas. In Kornprobst, J. (ed.) Kimberlites, 1: Kimberlites and Related Rocks, 255–84. Amsterdam: Elsevier.Google Scholar
Shackleton, R. M., Ries, A. C. & Coward, M. P. 1982. An interpretation of the Variscan structures in SW England. J GEOL SOC LONDON 139, 533–41.Google Scholar
Sheraton, J. W. & Cundari, A. 1980. Leucites from Gaussberg, Antarctica. CONTRIB MINERAL PETROL 71, 417–27.Google Scholar
Smith, H. G. 1929. Some features of Cornish lamprophyres. PROC GEOL ASSOC. 40, 260–8.CrossRefGoogle Scholar
Smith, I. E. M. & Johnson, R. W. 1981. Contrasting rhyolite suites in the late Cenozoic of Papua New Guinea. J GEOPHYS RES 86, 10257–72.Google Scholar
Smith, R. L. 1979. Ash flow magmatism. SPEC PAP GEOL SOC AM 180, 5–27.Google Scholar
Smith, R. L. & Macdonald, R. 1979. Rhyolitic volcanism and its relationship to granitic plutonism. GEOL SOC AM ABSTR PROGRAM 11, 520.Google Scholar
Stone, M. & Austin, W. G. C. 1961. The metasomatic origin of the potash feldspar megacrysts in the granites of southwest England. J GEOL 69, 464–72.Google Scholar
Stone, M. & Exley, C. S. 1986. High heat production granites of southwest England and their associated mineralization: a review. TRANS INST MIN METALL 95B, 25–36.Google Scholar
Storey, M. 1981. Trachytic pyroclastics from Agua de Pau volcano, Sao Miguel, Azores: evolution of a magma body over 4,000 years. CONTRIB MINERAL PETROL 78, 423–32.Google Scholar
Strong, D. F. & Hanmer, S. K. 1981. The leucogranites of southern Brittany: origin by faulting, frictional heating, fluid flux and fractional melting. CAN MINERAL 19, 163–76.Google Scholar
Sun, S.-S. & Nesbitt, R. W. 1977. Chemical heterogeneity of the Archaean mantle, composition of the Earth and mantle evolution. EARTH PLANET SCI LETT 35, 429–48.Google Scholar
Sun, S.-S., Nesbitt, R. W. & Sharaskin, A. Y. 1979. Geochemical characteristics of mid-ocean ridge basalts. EARTH PLANET SCI LETT 44, 119–38.CrossRefGoogle Scholar
Taylor, S. R. & McLennan, S. M. 1985. The Continental Crust: its Composition and Evolution. Oxford: Blackwell.Google Scholar
Thompson, R. N. 1982. Magmatism of the British Tertiary volcanic province. SCOTT J GEOL 18, 49–107.Google Scholar
Thompson, R. N. 1985. Asthenospheric source of Ugandan ultrapotassic magma? J GEOL 93, 603–8.CrossRefGoogle Scholar
Thompson, R. N. & Fowler, M. B. 1986. Subduction-related shoshonite magmatism: a study of Siluro-Ordovician syenites from the Scottish Caledonides. CONTRIB MINERAL PETROL 94, 507–22.Google Scholar
Thompson, R. N., Morrison, M. A., Dickin, A. P. & Hendry, G. L. 1983. Continental flood basalts… arachnids rule OK? In Hawkesworth, C. J. & Norry, M. J. (eds) Continental basalts and mantle xenoliths. 158–185. Nantwich: Shiva.Google Scholar
Thompson, R. N., Morrison, M. A., Hendry, G. L. & Parry, S. J. 1984. An assessment of the relative roles of crust and mantle in magma genesis: an elemental approach. PHILOS TRANS R SOC LONDON A310, 549–90.Google Scholar
Thorpe, R. S. 1987. Permian K-rich volcanic rocks of Devon: petrogenesis, tectonic setting and geological significance. TRANS R SOC EDINBURGH: EARTH SCI 77, 361–66.Google Scholar
Thorpe, R. S., Cosgrove, M. E. & van Calsteren, P. W. C. 1986. Rare-earth element, Sr- and Nd-isotope evidence for petrogenesis of Permian basaltic and K-rich volcanic rocks from southwest England. MINERAL MAG 50, 481–90.Google Scholar
Tidmarsh, W. G. 1932. The Permian lavas of Devon. Q J GEOL SOC LONDON 88, 712–75.CrossRefGoogle Scholar
Turi, B. & Taylor, H. P. 1976. Oxygen isotope studies of potassic volcanic rocks of the Roman Province, central Italy. CONTRIB MINERAL PETROL 55, 1–31.Google Scholar
Ussher, W. A. E. 1902. The geology of the country around Exeter. MEM GEOL SURV G B (1 inch sheet 325).Google Scholar
Varne, R. 1985. Ancient subcontinental mantle: a source for K-rich orogenic volcanics. GEOLOGY 13, 405–8.Google Scholar
Venturelli, G., Capedri, S., Di Battistine, G., Crawford, A.Kogarko, L. N. & Celestini, S. 1984. The ultrapotassic rocks of southeastern Spain. LITHOS 17, 37–54.CrossRefGoogle Scholar
Vernon, R. H. 1986. K-feldspar megacrysts in granites—phenocrysts not porphyroblasts. EARTH SCI REV 23, 1–63.CrossRefGoogle Scholar
Vidal, P. L., Cocherie, A. & Le Fort, P. 1982. Geochemical investigations of the origin of the Manaslu leucogranite (Himalaya, Nepal). GEOCHIM COSMOCHIM ACTA 46, 2279–92.Google Scholar
Vollmer, R. & Norry, M. J. 1983. Possible origin of K-rich volcanic rocks from Virunga, East Africa, by metasomatism of continental crustal material: Pb, Nd and Sr isotopic evidence. EARTH PLANET SCI LETT 64, 374–86.Google Scholar
Vollmer, R., Ogden, P., Schilling, J.-G., Kingsley, R. H. & Waggoner, D. G. 1984. Nd and Sr isotopes in ultrapotassic volcanic rocks from the Leucite Hills, Wyoming. CONTRIB MINERAL PETROL 87, 359–68.Google Scholar
Watkins, P. J. & Thompson, M. 1983. Determination of beryllium and zirconium in 45 geochemical reference samples by inductively coupled plasma emission spectrometry. GEOSTANDARDS NEWSLETTER 7, 273–7.Google Scholar
Watson, E. B. 1979. Zircon saturation in felsic liquids: experimental results and implications to trace element geochemistry. CONTRIB MINERAL PETROL 70, 407–19.Google Scholar
Watson, J. V., Fowler, M. B., Plant, J. A. & Simpson, P. R. 1984. Variscan-Caledonian comparisons: late orogenic granites. PROC USSHER SOC 6, 2–12.Google Scholar
Weaver, B. L. & Tarney, J. 1980. Continental crust composition and nature of the lower crust: constraints from mantle Nd-Sr isotope composition. NATURE 286, 342–6.Google Scholar
Webb, P. C., Tindle, A. G., Barritt, S. D., Brown, G. C. & Miller, J. F. 1985. Radiothermal granites of the United Kingdom: comparisons of fractionation patterns and variations of heat production for selected granites. In High Heat Production (HHP) Granites, Hydrothermal Circulation and Ore Genesis, 409–24. London: Institute of Mining and Metallurgy.Google Scholar
Wolff, J. A. & Storey, M. 1984. Zoning in highly alkaline magma bodies. GEOL MAG 121, 563–75.Google Scholar