Hostname: page-component-78c5997874-fbnjt Total loading time: 0 Render date: 2024-11-19T09:23:31.707Z Has data issue: false hasContentIssue false
  • English
  • Français

Local processes involved in the generation of migmatites within mafic granulites

Published online by Cambridge University Press:  03 November 2011

Rhoda E. Tait  and
Simon L. Harley
Rhoda E. Tait
Affiliation:
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, U.K.
Simon L. Harley
Affiliation:
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Processes involved in the formation and evolution of melts within the lower crustal mafic granulites are considered with reference to mafic migmatites from late Proterozoic (1200-1000 Ma) granulites of the Rauer Group, East Antarctica. Metaluminous dioritic and noritic leucocratic veins on scales of 1 cm to 1 m show agmatitic, stromatic and schlieren structures. These possible melts are compositionally distinct from charnockitic and enderbitic orthogneisses, which show intrusive contacts with the migmatites in areas of low strain.

Important field relationships include the following:

(a) Leucocratic veins contain plagioclase and rare quartz, coarse subhedral to euhedral orthopyroxene, ilmenite and apatite. Finer (2 cm) veins and layers are richer in mafic phases than larger (2-10 cm) veins.

(b) Selvedges or melanosomes are developed between the larger melt areas and enclosing mafic gneisses. These melanosomes consist of garnet, orthopyroxene, plagioclase and biotite and are apatite-rich.

(c) Pyroxene granulite palaeosomes typically display bleached zones (1-2 cm) adjacent to selvedges and veins, in which the modal proportion of clinopyroxene diminishes in favour of orthopyroxene.

Geochemical and petrological studies demonstrate that localised or near-localised partial melting of the mafic granulites occurred during decompression from 8-9 kb to 7 kbar at a minimum temperature of 800-850°C. Geochemical mass balance calculations using measured vein, selvedge and palaeosome compositions indicate that near-closed system melting behaviour is likely for a large number of major and trace elements, but LILE behaviour is affected by the introduction of biotite probably associated with late stage fluids. Minor- and rare-earth element modelling predicts similar percentages of melting to those observed in the field, but yields reasonable results only when garnet is included as a minor residual phase. HREE concentrations in melanosomes do not show expected enrichments, probably as a result of later subsolidus changes including the breakdown of garnet during decompression.

This study demonstrates that migmatites may form through the near-localised partial melting of basic lithologies within the granulite facies. The exact role of fluids in this case cannot be determined but melting is interpreted to be vapour-undersaturated. This process may be important in the production of volumetrically significant amounts of dioritic to tonalitic calc-alkaline magmas.

Keywords

Antarcticacalc-alkaline magmasmass balancenear-localised partial meltingsubsolidus changes
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 79 , Issue 2-3: The Origin of Granites , 1988 , pp. 209 - 222
Copyright
Copyright © Royal Society of Edinburgh 1988

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

Ashworth, J. R. 1976. Petrogenesis of Migmatites in the Huntly-Portsoy area, north-east Scotland. MINERAL MAG 40, 315, 661–682.Google Scholar
Black, L. P. & McCulloch, M. T. 1987. Evidence for isotopic equilibration of Sm-Nd whole-rock systems in early-Archean crust of Enderby Land, Antarctica. EARTH PLANET SCI LETT 82, 15–24.CrossRefGoogle Scholar
Collerson, K. D. & Fryer, B. J. 1978. The role of fluids in the formation and subsequent development of early continental crust. CONTRIB MINERAL PETROL 67, 151–167.Google Scholar
Collerson, K. D. & Sheraton, J. W. 1986. Bedrock geology and crustal evolution of the Vestfold Hills. In Antarctic Oasis, 21–62. Canberra: Academic Press Australia.Google Scholar
De, Paolo D. J., Manton, W. I., Grew, E. S., & Halpern, M. 1982. Sm–Nd, Rb–Sr and U–Th-Pb systematics of granulite facies rocks from Fyfe Hills, Enderby Land, Antarctica. NATURE 298, 614–618.Google Scholar
Devey, C. W. 1986. Stratigraphy and geochemistry of the Decan Trap lavas, Western India. D.Phil. Thesis, University of OxfordGoogle Scholar
Dougan, T. W. 1979. Compositional and modal relationships and melting reactions in some migmatitic metapelites from New Hampshire and Maine. AM J SCI 279, 897–935.Google Scholar
Ewart, A. 1982. Petrogenesis of the Tertiary anorogenic volcanic series of southern Queensland, Australia, in the light of trace element geochemistry and O, Sr and Pb isotopes. J PETROL 24, 98–130.Google Scholar
Fukimaki, H.Tatsumoto, M. & Aoki, K. I. 1984. Partition coefficients of Hf, Sr and REE between phenocrysts and groundmasses. Proc. Fourteenth Lunar and Planet. Sci. Conf., Part 2. J GEOPHYS RES 89, Supplement, B662–B672.Google Scholar
Green, T. H. 1982. Anatexis of mafic crust and high pressure crystallisation of andesite. In Thorpe, R. S. (ed.) Orogenic Andesites and Related Rocks, 465–87. London: Wiley.Google Scholar
Harley, S. L. 1987. Precambrian Geological Relationships in high-grade gneisses of the Rauer Islands, East Antarctica. AUST J EARTH SCI 34, 175–207.CrossRefGoogle Scholar
Harley, S. L. (in press). Metamorphic evolution of granulites from the Rauer Islands, East Antarctica: decompression following Proterozoic collision. Proc. 5th Antarctic Earth Sciences Symposium, Cambridge, England.Google Scholar
Helz, R. T. 1976. Phase relations of basalts in their melting ranges at PH2O = 5kb. Part II Melt compositions. J PETROL 17, 138–93.CrossRefGoogle Scholar
Holloway, J. R. & Burnham, C. W. 1972. Melting relations of basalt with equilibrium water pressure less than total pressure. J PETROL 14, 1–29.CrossRefGoogle Scholar
Irving, A. J. & Frey, F. A. (1978) Distribution of trace elements between garnet megacrysts and host volcanic liquids of kimberlitic to rhyolitic composition. GEOCHIM COSMOCHIM ACTA 42, 771–787.CrossRefGoogle Scholar
Johannes, W. & Gupta, L. N. 1982. Origin and Evolution of a Migmatite. CONTRIB MINERAL PETROL 79, 114–123.CrossRefGoogle Scholar
McCulloch, M. T. & Black, L. P. 1984. Sm-Nd isotopic systematics of Enderby land granulites and evidence for the redistribution of Sm and Nd during metamorphism. EARTH PLANET SCI LETT 71, 46–58.Google Scholar
Menhert, K. R. & Busch, W. 1982. The initial stage of migmatite formation. NEUES JAHRB MINERAL ABH 145, 211–38.Google Scholar
Misch, P. 1968. Plagioclase compositions and non-anatectic origin of migmatite gneisses in Northern Cascade Mountains of Washington State. CONTRIB MINERAL PETROL 70, 299–318.Google Scholar
Olsen, S. N. 1977. Origin of the Baltimore Gneiss migmatites at Piney Creek, Maryland. BULL GEOL SOC AM 88, 1089–1101.2.0.CO;2>CrossRefGoogle Scholar
Olsen, S. N. 1982. Open and closed-system migmatites in the Front Range, Colorado. AM J SCI 282, 1596–1622.Google Scholar
Olsen, S. N. 1984. Mass-balance and mass-transfer in migmatites from the Colorado Front Range. CONTRIB MINERAL PETROL 85, 30–44.CrossRefGoogle Scholar
Pearce, J. A. 1983. Role of the sub-continental lithosphere in magma genesis at active continental margins. In Hawkesworth, C. J. & Norry, M. J. (eds) Continental Basalts and Mantle Xenoliths, 230–49. Nantwich: Shiva.Google Scholar
Raeside, R. P. & Ghent, E. D. 1986. The migmatisation of Hadrynian sedimentary rocks, Mica Creek, British Columbia. CAN MINERAL 24, 547–56.Google Scholar
Rudnick, R. L., McLennan, S. M. & Taylor, S. R. 1985 Large ion lithophile elements in rocks from high-pressure granulite facies terrains. GEOCHIM COSMOCHIM ACTA 49, 1645–1655.Google Scholar
Rudnick, R. L. & Taylor, S. R. 1986. Geochemical constraints on the origin of Archaean tonalitic-trondhjemitic rocks and implications for lower crustal composition. In Dawson, J. B., Carswell, D. A., Hall, J. & Wedepohl, K. H. (eds) The Nature of the Lower Continental Crust. 179–91. SPEC PUBL GEOL SOC LONDON 24. Oxford: Blackwell.Google Scholar
Sawyer, E. W. 1987 The role of partial melting and fractional crystallisation in determining discordant migmatite compositions. J PETROL 28, 445–73.1.CrossRefGoogle Scholar
Sheraton, J. W., Black, L. P. & McCulloch, M. T. 1984. Regional geochemical and isotopic characteristics of high-grade metamorphics of the Prydz Bay area: the extent of Proterozoic reworking of Archaean continental crust in East Antarctica. PRECAMB RES 26, 169–98.CrossRefGoogle Scholar
Sheraton, J. W. & Collerson, K. D. 1984. Geochemical evolution of Archean granulite-facies gneisses in the Vestfold Block and comparisons with other Archean gneiss complexes in the East Antarctic Shield. CONTRIB MINERAL PETROL 87, 51–64.CrossRefGoogle Scholar
Vernon, R. H. 1976. Metamorphic Processes. London: George Allen & Unwin.Google Scholar
Watson, E. B. & Harrison, T. M. 1983. Zircon saturation revisited: temperature and composition effects in variety of crustal magma types. EARTH PLANET SCI LETT 64, 295–304.CrossRefGoogle Scholar
Weaver, B. L. & Tarney, J. 1983. Elemental depletion in Archaean granulite-facies rocks. In Atherton, M. P. & Gribble, C. D. (eds) Migmatites, Melting and Metamorphism, 250–63. Nantwich: Shiva.Google Scholar
Weber, C., Barbey, P., Cuney, M. & Martin, H. 1985. Trace element behaviour during migmatisation. Evidence for a complex melt-residuum-fluid interaction in the St Malo migmative zone (France). CONTRIB MINERAL PETROL 90, 52–62.Google Scholar
Wendlandt, R. F. & Harrison, W. J. 1979. Rare Earth Partitioning between immiscible carbonate and silicate liquids and CO2 vapour: Results and implications for the formation of light rare earth-enriched rocks. CONTRIB MINERAL PETROL 69, 409–419.Google Scholar
White, A. J. R. & Chappell, B. W. 1977. Ultrametamorphism and granitoid genesis. TECTONOPHYSICS 43, 7–22.CrossRefGoogle Scholar
Windrum, D. P., McCulloch, M. T., Chappell, B. W. & Cameron, W. E. 1984. Nd and Sr isotopes and REE in central Australian Sapphirine granulites: a case study in REE mobility. EARTH PLANET SCI LETT 70, 27–39.Google Scholar
Wright, T. L. & Doherty, P. C. 1970. A linear programming and least squares computer method for solving petrological mixing problems. BULL GEOL SOC AM 81, 1995–2008.CrossRefGoogle Scholar
Wyllie, P. J. 1983. Experimental studies on biotite- and muscovite-granites and some crustal magmatic sources, pp. 12–26. In Atherton, M. P. & Gribble, C. D. (eds) Migmatites, melting and metamorphism, 12–26. Nantwich: Shiva.Google Scholar
Yardley, B. W. D. 1978. Genesis of the Skagit Gneiss migmatites, Washington, and the distinction between possible mechanisms of migmatization. BULL GEOL SOC AM 89, 941–51.2.0.CO;2>CrossRefGoogle Scholar