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Enclaves and their bearing on the origin of the Cornubian batholith, southwest England

Published online by Cambridge University Press:  05 July 2018

James A. Stimac ,
Alan H. Clark ,
Yanshao Chen  and
Sammy Garcia
James A. Stimac
Affiliation:
Earth and Environmental Sciences, MS-D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Alan H. Clark
Affiliation:
Department of Geological Sciences, Queen’s University, Kingston, Ontario, Canada K7L 3N6
Yanshao Chen
Affiliation:
Department of Geological Sciences, Queen’s University, Kingston, Ontario, Canada K7L 3N6
Sammy Garcia
Affiliation:
INC-15, MS-G776, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Abstract

Enclaves of diverse origin are present in minor amounts in the coarse-grained biotite granites of the Cornubian batholith, southwest England. The most common enclave type is layered, rich in biotite, cordierite and aluminosilicates, and has textures and compositions that reveal variable degrees of melt extraction from metasedimentary source rocks. Rare sillimanite-bearing enclaves represent residual material, either from the region of magma generation or its ascent path, but most such enclaves were probably derived from the contact aureole closer to the present level of exposure. These non-igneous enclaves (NIE) and their disaggregation products are present in all major plutons, comprising from < 2 to 5 vol.% of the granites. Enclaves of igneous origin are also present in all major plutons except Carnmenellis, generally comprising < 1 vol.% of the granites. The most common type is intermediate in composition, with microgranular texture, and mineral compositions and textures consistent with an origin by magma mixing. Large crystals of K-feldspar, plagioclase and quartz, common in these microgranular enclaves (ME) but absent in NIE, represent phenocrysts derived from the silicic end-member during magma mixing events rather than products of metasomatism as suggested previously. Although the composition of the mafic end-member (basaltic or lamprophyric) involved in the mixing process is poorly constrained, the presence of ME in the granites, and the preponderance of mantle-derived mafic rocks in the coeval Exeter Volcanics, indicate that mafic magma injection into the crust was a factor in the generation of the batholith. Advection of sub-crustal heat provides an explanation for large-volume crustal melting in regions of relatively thin crust such as southwest England.

Keywords

enclavesmagma mixingS-type graniteCornubian batholith
Type
Geochemistry
Information
Mineralogical Magazine , Volume 59 , Issue 395 , June 1995 , pp. 273 - 296
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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Footnotes

*

Present address: Dept. of Physics, University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7

References

Al-Turki, K. (1972) A Petragraphic and Chemical Study of the Carnmenellis Granite and Associated Rocks. Unpubl. Ph.D. thesis, University of Exeter.Google Scholar
Ayrton, S. N. (1991) Appinites, lamprophyres and mafic magmatic enclaves: three related products of interaction between acid and mafic magmas. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 465-78.Google Scholar
Bacon, C. R. (1986) Magmatic inclusions in silicic and intermediate volcanic rocks. J. Geophys. Res., 91, 6091–112.CrossRefGoogle Scholar
Barbarin, B. (1991) Enclaves of the Mesozoic calc-alkaline granitoids of the Sierra Nevada batholith, California. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 135-54.Google Scholar
Barbarin, B. and Didier, J. (1992) Genesis and evolution of mafic microgranular enclaves through various types of interaction between coexisting felsic and mafic magmas. Trans. Royal Soc. Edinburgh, 83, 145–53.CrossRefGoogle Scholar
Barbey, P. (1991) Restites in migmatites and auto-chthonous granites: Their main features and their genesis. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 479-92.Google Scholar
Brammall, A. and Harwood, H. F. (1932) The Dartmoor granites: their genetic relationships. Q. J. Geol. Soc. London, 88, 171–237.CrossRefGoogle Scholar
Bromley, A. (1989) Field Guide to the Cornubian Orefield. In 6th International Symposium on Water-Rock Interaction (Malvern, UK), Camborne School of Mines, 111 pp.Google Scholar
Bussy, F. (1990) The rapakivi texture of feldspars in a plutonic mixing environment: a dissolution-recrys-tallization process. Geol. J., 25, 319–24.CrossRefGoogle Scholar
Chappell, B. W. and White, A. J. R. (1992) I-and S-type granites in the Lachlan Fold Belt. Trans. Royal Soc. Edinburgh, 83, 1–26.CrossRefGoogle Scholar
Chappell, B. W., White, A. J. R. and Wyborn, D. (1987) The importance of residual source material (restite) in granite petrogenesis. J. Petrol, 28, 1111–38.CrossRefGoogle 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
Chen, Y., Clark, A. H., Farrar, E., Wasteneys, H. A. H. P., Hodgson, M. J. and Bromley, A. V. (1993) Diachronous and independent histories of plutonism and mineralisation in the Cornubian Batholith, SW England. J. Geol. Soc. London, 150, 1183–91.CrossRefGoogle Scholar
Chesley, J. T., Halliday, A. N., Snee, L. W., Mezger, K., Shepherd, T. J. and Scrivener, R. C. (1993) Thermochronology of the Cornubian batholith in southwest England: implications for pluton emplacement and protracted hydrothermal miner-alization. Geochim. Cosmochim. Ada, 57, 1817–35.CrossRefGoogle Scholar
Clark, A. H., Chen, Y., Farrar, E., Wasteneys, H. A. H. P., Stimac, J. A., Hodgson, M. J., Willis-Richards, J. and Bromley, A. V. (1993) The Cornubian Sn-Cu (-As, W) metallogenetic province: product of a 30 m.y. history of discrete and concomitant anatectic, intrusive and hydrothermal events. Proc. Ussher Soc, 8, 112–6.Google Scholar
Criss, J. (1980) ‘Fundamental parameters’ calculations on a laboratory microcomputer. In. Advances in X-Ray Analysis, 23, 93–7.CrossRefGoogle Scholar
Dangerfield, J. and Hawkes, J. R. (1981) The Variscan granites of SW England: additional information. Proc. Ussher Soc, 5, 116–20.Google Scholar
Darbyshire, D. P. F. and Shepherd, T. J. (1985) Chronology of granite magmatism and associated mineralization, SW England. J. Geol. Soc. London, 142, 1159–77.CrossRefGoogle Scholar
De La Beche, H. T. (1839) Report on the Geology of Cornwall, Devon, and West Somerset: Mem. Geol. Surv., London: Longman, Orme, Brown, Green, and Longmans.Google Scholar
Didier, J. (1973) Granites and their Enclaves: The Bearing of Enclaves on the Origin of Granites. Developments in Petrology, 3, Amsterdam: Elsevier, 393 pp.Google Scholar
Didier, J. and Barbarin, B., eds. (1991a) Enclaves and Granite Petrology, Developments in Petrology, 13, Amsterdam, Elsevier, 625 pp.Google Scholar
Didier, J. and Barbarin, B. (19916) The different types of enclaves in granites — nomenclature. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 19-23.Google Scholar
Eberz, G. W. and Nicholls, I. A. (1990) Chemical modification of enclave magma by post-emplace-ment crystal fractionation, diffusion, and metasomatism. Contrib. Mineral. Petrol, 104, 47–55.CrossRefGoogle Scholar
Exley, C. S. and Stone, M. (1964) The Granitic Rocks of South-west England. In Present Views of Some Aspects of the Geology of Cornwall and Devon (Hosking, K. F. G. and Shrimpton, G. J., eds.), Royal Geological Society of Cornwall, 131-84.Google Scholar
Exley, C. S. and Stone, M. (1982) Hercynian intrusive rocks. In Igneous Rocks of the British Isles (Sutherland, D. S. ed.), J. Wiley and Sons, 287-320.Google Scholar
Floyd, P. A. (1971) Temperature distribution in the Land's End granite aureole, Cornwall. Proc. Ussher Soc, 2, 335–51.Google Scholar
Ghosh, P. K. (1928) Petrology of the Bodmin Moor granite, Cornwall. Mineral. Mag., 21, 285–309.Google Scholar
Ghosh, P. K. (1934) The Carnmenellis granite: its petrology, metamorphism and tectonics. Q. J. Geol. Soc London, 90, 240–76.CrossRefGoogle Scholar
Grant, J. A. and Frost, B. R. (1990) Contact metamorphism and partial melting of pelitic rocks in the aureole of the Laramie anorthosite complex, Morton Pass, Wyoming. Amer. J. Set, 290, 425–72.Google Scholar
Hall, A. (1974) Granite porphyries in Cornwall. Proc. Ussher Soc, 3, 145–9.Google Scholar
Harris, N. (1981) The application of spinel-bearing metapelites to P/T determinations: an example from South India. Contrib. Mineral. Petrol, 76, 229–33.CrossRefGoogle Scholar
Hibbard, M. J. (1981) The magma mixing origin of mantled feldspars. Contrib. Mineral. Petrol, 76, 158–70.CrossRefGoogle Scholar
Hildreth, W. (1981) Gradients in silcic magma chambers: implications for lithospheric magmatism. J. Geophys. Res., 86, 10153–92.CrossRefGoogle Scholar
Huppert, H. H. and Sparks, S. J. (1988) The generation of granitic magmas by intrusion of basalt into continental crust. J. Petrol, 29, 599–624.CrossRefGoogle Scholar
Jefferies, N. L. (1985) The origin of sillimanite-bearing pelitic xenoliths within the Carnmenellis pluton, Cornwall. Proc. Ussher Soc, 6, 229–36.Google Scholar
Knill, D. C. (1969) The Permian igneous rocks of Devon. British Geol. Surv. Bull. 29, 115-38.Google Scholar
Knill, D. C. (1982) Permian volcanism in south-weslwin England. In Igneous Rocks of the British Isles (Sutherland, D. S., ed.). J. Wiley and Sons, 329-32.Google Scholar
Leat, P. T., Thompson, R. N., Morrison, M. A., Hendry, G. L. and Trayhorn, S. C. (1987) Geodynamic significance of post-Variscan intrusive and extrusive potassic magmatism in SW England. Trans. R. Soc. Edinburgh: Earth Set, 77, 349–60.CrossRefGoogle Scholar
Lister, C. J. (1984) Xenolith assimilation in the granites of south-west England. Proc Ussher Soc, 6, 46–53.Google Scholar
Miller, J. A., Shibata, K. and Munro, M. (1962) The potassium-argon age of the lava of Killerton Park, near Exeter. Geophys. J., 6, 394–6.CrossRefGoogle Scholar
Mitropoulos, P. (1982) REE patterns of the metasedi-mentary rocks of the Land's End granite aureole (southwest England). Chem. Geol, 35, 265–80.CrossRefGoogle Scholar
Montel, J. M., Didier, J. and Pichavant, M. (1991) Origin of surmicaceous enclaves in intrusive granites. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 509-28.Google Scholar
Nakamura, N. (1974) Determination of REE, Ba, Mg, Na and K in carbonaceous and ordinary chondrites. Geochim. Cosmochim. Ada 38, 757–75.CrossRefGoogle Scholar
Orsini, J. B., Cocirta, C and Zorpi, M. J. (1991) Genesis of mafic microgranular enclaves through differentiation of basic magmas, mingling anr! chemical exchanges with their host granitoid magmas. In Enclaves and Granite Petrology (Didier, J. and Barbarin, B., eds.). Developments in Petrology, 13, Amsterdam: Elsevier, 445-64.Google Scholar
Osman, C. W. (1928) The granites of the Scilly Isles and their relation to the Dartmoor granites. Q. J. Geol. Soc. London, 84, 258–92.CrossRefGoogle Scholar
Pattison, D. R. M. (1992) Stability of andalusite and sillimanite and the Al2Si05 triple point: constraints from the Ballachulish Aureole, Scotland. J. Geol, 100, 423–46.CrossRefGoogle Scholar
Pattison, D. R. M. and Harte, B. (1989) A petrogenetic grid for pelities in the Ballachulish aureole and other Scottish thermal aureoles. J. Geol. Soc. London, 142, 7–28.CrossRefGoogle Scholar
Reid, C, Barrow, G., Sherlock, R., L., MacAlister, D. A., Dewey, H. and Bromehead, C. N. (1912) The Geology of Dartmoor. Memoir of the Geological Survey of England and Wales, Sheet 338, 102 pp.Google Scholar
Robson, J. (1964) The Cornish ‘Greenstones'. In Present Views of Some Aspects of the Geology of Cornwall and Devon (Hosking, K. F. G. and Shrimpton, G. J., eds.), Royal Geological Society of Cornwall, 115-30.Google Scholar
Stimac, J. A. and Pearce, T. H. (1992) Textural evidence of mafic-felsic magma interaction in dacitic lavas, Clear Lake, California. Amer. Mineral., 77, 795–809.Google Scholar
Stimac, J. A., Pearce, T. H., Donnelly-Nolan, J. M. and Hearn, B. C. (1990) Origin and implications of undercooled andesitic inclusions in rhyolites, Clear Lake, California. J. Geophys. Res., 95, 17729–46.CrossRefGoogle Scholar
Stimac, J. A. and Wark, D. A. (1992) Plagioclase mantles on sanidine in silicic lavas, Clear Lake, California: Implications for the origin of rapakivi texture. Geol. Soc. Amer. Bull, 104, 728–44.2.3.CO;2>CrossRefGoogle Scholar
Stone, M. (1990) The significance of almandine garnets in the Lundy and Dartmoor granites. Mineral. Mag., 52, 651–8.CrossRefGoogle Scholar
Stone, M. (1992) The Tregonning granite: petrogenesis of Li-mica granites in the Comubian batholith. Mineral. Mag., 56, 141–55.CrossRefGoogle Scholar
Stone, M. and Austin, W. G. C. (1961) The metasomatic origin of the potash feldspar megacrysts in the granites of southwest England. J. Geol., 69, 464–72.CrossRefGoogle Scholar
Stone, M. and Exley, C. S. (1986) High heat production granites of Southwest England and their associated mineralization: a review. In High Heat Production (HHP) Granites, Hydrothermal Circulation and Ore Genesis, Inst. Min. Metall., London, 571-93.Google Scholar
Stone, M. and Exley, C. S. (1989) Geochemistry of the Isles of Scilly pluton. Proc. Ussher Soc, 7, 152–7.Google Scholar
Thorpe, R. S. (1987) Permian K-rich volcanic rocks of Devon: petrogenesis, tectonic setting and geological significance. Trans. Roy. Soc. Edinburgh: Earth Sci., 77, 361–6.CrossRefGoogle Scholar
Thorpe, R. S., Cosgrove, M. E. and 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 south-west England. Mineral. Mag., 50, 481–90.CrossRefGoogle Scholar
Tidmarsh, W. G. (1932) The Permian lavas of Devon. Q. J. Geol. Soc. London, 88, 712–75.CrossRefGoogle Scholar
Ussher, W. A. E. (1902) The geology of the country around Exeter (sheet 325). Mem. Geol. Surv. U.K. (London: HMSO).Google Scholar
van der Laan, S. R. and Wyllie, P. J. (1993) Experimental interaction of granitic and basaltic magmas and implications for mafic enclaves. J. Petrol. 34, 491–517.CrossRefGoogle Scholar
Vernon, R. H. (1983) Restite, xenoliths, and micro-granitoid enclaves in granites. J. Proc. Royal Soc. New South Wales, 116, 77–103.Google Scholar
Vernon, R. H. (1990) Crystallization and hybridism in microgranitoid enclave magmas: microstructural evidence. J. Geophys. Res., 95, 17849–17859.CrossRefGoogle Scholar
Ward, C. D., McArthur, J. M. and Walsh, J. N. (1992) Rare earth element behaviour during evolution and alteration of the Dartmoor granite, SW England. J. Petrol, 33, 785–815.CrossRefGoogle Scholar
Willis-Richards, J. and Jackson, N. J. (1989) Evolution of the Comubian ore field, southwest England: Part I. Batholith modeling and ore distribution. Econ. Geol., 84, 1078–100.CrossRefGoogle Scholar
Zorpi, M. J., Coulon, C. and Orsini, J. B. (1991) Hybrization between felsic and mafic magmas in calc-alkaline granitoids — a case study in northern Sardinia, Italy. Chem. Geol, 92, 45–86.CrossRefGoogle Scholar