Abstract
Archaen gneisses of the Vestfold Hills of East Antarctica are transected by several compositionally discrete suites of tholeiitic dykes. A representative of one of those suites, which has been dated in the present study, shows that not only Rb−Sr whole-rock isochrons, but also U−Pb zircon techniques (if not properly applied) can produce erroneous crystallisation ages. Two zircon populations were recovered from the mafic dyke itself, one of which is 2,483±9 Ma in age and clearly of xenocrystic origin. The other yields an age of 1,025±56 Ma, which is not ascribed to the magmatic crystallisation of the dyke, but rather to the time that it underwent metamorphic/metasomatic alteration as a response to high-grade tectonism in the adjacent mobile belt. It is presumed that the zircon in question formed by the breakdown of another mineral or minerals (possibly magmatic baddeleyite), due either to ingress of a siliceous fluid, or more probably by the release of silica from the breakdown of pyroxene to amphibole. A cogenetic 1–2 cm wide felsic vein, of late magmatic/early hydrothermal origin, also contains two zircon populations. Again, most of the grains therein, which are interpreted as of xenocrystic origin, grew at 2,483±9 Ma. However, a few euhedral zircons with very high U and Th contents grew at 1,248±4 Ma, which is taken to be the formation age of both the felsic vein and the enclosing mafic dyke.
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References
Arndt NT, Jenner GA (1986) Crustally contaminated komatiites and basalts from Kambalda, Western Australia. Chem Geol 56: 229–255
Arriens PA (1975) The Precambrian geochronology of Antaretica (abstract). In: Proterozoic geology. Geol Soc Aust, Adelaide, pp 97–98
Black LP, Gale NH, Moorbath S, Pankhurst RJ, McGregor VR (1971) Isotopic dating of very early Precambrian amphibolite facies gneisses from the Godthaab district, west Greenland. Earth Planet Sci Lett 12: 245–259
Black LP, Sheraton JW, James PR (1986) Late Archaean granites of the Napier Complex, Enderby Land, Antarctica: a comparison of Rb−Sr, Sm−Nd and U−Pb isotopic systematics in a complex terrain. Precambrian Res 32: 343–368
Black LP, Kinny PD, Sheraton JW, Delor CP (1991) Rapid production and evolution of Late Archaean felsic crust in the Vestfold Block of East Antarctica. Precambrian Res 50: 283–310
Claoue-Long JC, Compston W, Cowden A (1988) The age of the Kambalda greenstones resolved by ion-microprobe: implications for Archaean dating methods. Earth Planet Sci Lett 89: 239–259
Collerson KD, Sheraton JW (1986) Age and geochemical characteristics of a mafic dyke swarm in the Archaean Vestfold Block, Antarctica: inferences about Proterozoic dyke emplacement in Gondwana. J Petrol 27: 853–886
Collerson KD, Reid E, Millar D, McCulloch MT (1983a) Lithological and Sm−Nd isotopic relationships in the Vestfold Block: implications for Archaean and Proterozoic crustal evolution in the East Antarctic. In: Oliver RL, James PR, Jago JB (eds) Antarctic earth science. Australian Academy of Science, Canberra, pp 77–84
Collerson KD, Sheraton JW, Arriens PA (1983b) Granulite facies metamorphic conditions during the Archaean evolution and Late Proterozoic reworking of the Vestfold block, East Antarctica. In: Lithosphere dynamics and evolution of continental crust (abstract). Geol Soc Aust, Canberra, pp 53–54
Compston W, Williams IS, Meyer C (1984) U−Pb geochronology of zircons from lunar breccia 73217 using a sensitive high-resolution ion-microprobe. Proc 14th Lunar Sci Conf, J Geophys Res 89: B525–534
Cumming GL, Richards JR (1975) Ore lead isotope ratios in a continuously changing Earth. Earth Planet Sci Lett 28: 155–171
Davidson A, van Breemen O (1988) Baddeleyite-zircon relationships in coronitic metagabbro, Grenville Province, Ontario: implications for geochronology. Contrib Mineral Petrol 100: 291–299
Harding RR, McLeod I (1967) Age of dolerite dykes in the Vestfold Hills, Antaretica. Nature 215: 149–150
Harley SL (1988) Proterozoic granulites from the Rauer Group, East Antarctica I: decompressional pressure-temperature paths deduced from mafic and felsic gneisses. J Petrol 29: 1059–1095
Harrison TM, Watson EB (1983) Kinetics of zircon dissolution and zirconium diffusion in granitic melts of variable water content. Contrib Mineral Petrol 84: 66–72
Harrison TM, Aleinikoff JN, Compston W (1987) Observations and controls on the occurrence of inherited zircon in Concord-type granitoids, New Hampshire. Geochim Cosmochim Acta 52: 2549–2558
Hergt JM (1987) The origin and evolution of the Tasmanian dolerites PhD thesis, Australian National University (unpubl)
Hofmann Jv, Kaiser G, Klemm W (1980) K−Ar alter Prakambrischer basite der Ostantarktis (Prince Charles Mountains, Oase Vestfold). Z Geol Wiss Berlin 8: 1561–1564
James PR, Black LP (1981) A review of the structural evolution and geochronology of the Archaean Napier Complex of Enderby land, Australian Antarctic Territory. In: Glover JE, Groves DI (eds) Archaean geology; Second International Symposium, Perth, 1980. Spec Pub Geol Soc Aust 7, pp 71–83
Kinny PD (1987) An ion microprobe study of uranium-lead and hafnium isotopes in natural zircon. PhD thesis, Australian National University (unpubl)
Kinny PD, Black LP (1990) Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands. In: Gondwana: terranes and resources (abstract). Geol Soc Aust, Hobart, pp 151–152
Krogh TE, Corfu F, Davis DW, Dunning DR, Heaman LM, Kamo SL, Machado N, Greenough JD, Nakamura E (1987) Precise U−Pb isotopic ages of diabase dykes and mafic to ultramafic rocks using trace amounts of baddeleyite and zircon. In: Halls HC, Fahrig WF (eds) Mafic dyke swarms. Geol Assoc Can Spec Pap 34, pp 147–152
Kuehner SM (1986) Mafic dykes of the East Antarctic Shield: experimental, geochemical and petrological studies focusing on the Proterozoic evolution of the crust and mantle. PhD thesis, University of Tasmania (unpubl)
Kuehner SM (1987) Mafic dykes of the East Antarctic Shield: a note on the Vestfold Hills and Mawson Coast occurrences. In: Halls HC, Fahrig WF (eds) Mafic dyke swarms. Geol Assoc Can Spec Pap 34, pp 429–430
LeCheminant AN, Heaman LM (1989) Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening. Earth Planet Sci Lett 96: 38–48
McGregor VR (1968) Field evidence of very old Precambrian rocks in the Godthaab area, West Greenland. Rapp Gronland Geol Unders 15: 31–35
Passchier CW, Bekendam RF, Hoek JD, Dirks PGHM, de Boorder H (1991) Proterozoic geological evolution of the northern Vestfold Hills, Antarctica. Geol Mag 128:307–318
Sheraton JW, Black LP (1981) Geochemistry and geochronology of Proterozoic tholeiite dykes of East Antarctica: evidence for mantle metasomatism. Contrib Mineral Petrol 78: 305–317
Sheraton JW, Collerson KD (1983) Arehaean and Proterozoic geological relationships in the Vestfold Hills-Prydz Bay area, Antarctica. BMR J Aust Geol Geophys 8: 119–128
Sheraton JW, Black LP, McCulloch MT (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. Precambrian Res 26: 169–198
Tingey RJ (1982) The geologic evolution of the Prince Charles Mountains—an Antarctic Archaean cratonic block. In: Craddock C (ed) Antarctic geoscience. Univ Wisconsin Press, Madison, pp 455–464
Williams IS, Compston W, Black LP, Ireland TR, Foster JJ (1984) Unsupported radiogenic Pb in zircon: a cause of anomalously high Pb−Pb, U−Pb and Th−Pb ages. Contrib Mineral Petrol 88: 322–327
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Black, L.P., Kinny, P.D. & Sheraton, J.W. The difficulties of dating mafic dykes: an Antarctic example. Contr. Mineral. and Petrol. 109, 183–194 (1991). https://doi.org/10.1007/BF00306478
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DOI: https://doi.org/10.1007/BF00306478