Hostname: page-component-78c5997874-4rdpn Total loading time: 0 Render date: 2024-11-11T09:44:21.876Z Has data issue: false hasContentIssue false
  • English
  • Français

Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age

Published online by Cambridge University Press:  05 July 2018

K. A. Rodgers ,
P. D. Kinny ,
V. R. McGregor ,
G. R. Clark  and
G. S. Henderson
K. A. Rodgers
Affiliation:
Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand
P. D. Kinny
Affiliation:
Department of Applied Physics, Curtin University of Technology, GPO Box UI987 Perth, Western Australia 6001
V. R. McGregor
Affiliation:
Atammik, DK-3912 Maniitsoq, Greenland. Denmark
G. R. Clark
Affiliation:
Department of Chemistry, University of Auckland, Private Bag 92019, Auckland, New Zealand
G. S. Henderson
Affiliation:
Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada
Get access Rights & Permissions [Opens in a new window]

Abstract

Golden iridescent, <1–100 mm crystals of alternating lamellae of anthophyllite and gedrite constitute the bulk of orthoamphibolite pods within quartz-cordierite gneisses of the Akulleq terrane at Simiuttat, SW Greenland. X-ray powder diffraction powder gave a = 18.526(7),b = 17.979(15), c = 5.285(23) Å; a single crystal has a = 18.546(7), b = 17.950(16), c = 5.280(1) Å, space group Pnma with some reflections being notably broader than others. Spot EMPA yielded composite analyses: AlIV = 0.89–1.3, Mg/(Mg+Fe2+) = 0.57–0.61, Na/AlIV = 0.22–0.26. AFM imaging of {210} cleavage surfaces, showed a uniform corrugated morphology parallel to [001]; wavelength was 190–350 nm, mean 250 nm, amplitude 3 nm. A plan view resembles TEM images of (010)-parallel exsolution textures of orthoamphiboles. A second set of corrugations may crosscut the [001]-parallel ridges at 20–25°, akin to reported lamellar intergrowths developed parallel to both (010) and (120). Unequivocal evidence linking topography with lamellae is absent. In contrast to the conventional multi-layer reflector model, the ridged surface provides an additional origin for iridescence, acting as a diffraction grating. Included zircons, 50–10 μm, have Hf/Zr = 0.008–0.012, Hf+FeIIc. 0.16. 207Pb/206Pb ages are from 2690 to 2770 Ma, averaging 2732±10 Ma. Coexisting, included Th-, La-, Ce-, Pr-, Nd-, Gd-, Y-monazites have 207Pb/206Pb ages from 2680 to 2720 Ma, averaging 2707±12 Ma. The included crystals grew during a late Archaean metamorphism that produced overgrowths on zircons within gneisses to the north, but with Simiuttat grains showing a more complex history. The lamellae may have developed at the same time, or during a reheating c. 2550 Ma, or in a subsequent Proterozoic metamorphism.

Keywords

anthophyllitegedritecell parameterscompositioniridescencelamellaeagenuummite
Type
Mineralogy
Information
Mineralogical Magazine , Volume 60 , Issue 403 , December 1996 , pp. 937 - 947
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1996

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

Appel, P.W.U. and Jensen, A. (1987) Gems and Gemology 36–42.CrossRefGoogle Scholar
Armstrong, J.T. (1988) In: Microbeam analysis-1988 pp.239-46, ed. Newbury, D.E.. San Francisco Press, San Francisco.Google Scholar
Baadsgaard, H., Lambert, R. St. J.and Krupicka, J. (1976) Geochim. Cosmochim. Acta., 40, 513–27.CrossRefGoogle Scholar
Beech, E.M. and Chadwick, B. (1980) Precamb. Res., 11, 329–55.CrossRefGoogle Scholar
Bøggild, O.B. (1905) Meddelelser om Gr0nland, 32, 1–625.Google Scholar
Bøggild, O.B. (1924) Det Kongelige Danske Videnskabernes Selshab Mathematiskfysiske Meddelelser, 6(3), 1–79.Google Scholar
Christie, O.H.J. and Olsen, A. (1974) Bull. Soc. Franc. Mineral. Cristallogr., 97, 386–92.Google Scholar
Droop, G.T.R. (1987) Mineral. Mag., 51, 431–5.CrossRefGoogle Scholar
Dymek, R.F. and Smith, M.S. (1990) Contrib. Mineral. Petrol., 105, 715–30.CrossRefGoogle Scholar
Friend, C.R.L., Nutman, A.P., Baadsgaard, H., Kinny, P.D. and McGregor, V.R. Timing of late Archaean terrane assembly, crustal thickening and granite emplacement in the Nuuk region, southern West Greenland. Earth Planet. Sci. Lett (in press).Google Scholar
Ghose, S. (1981) Reviews in Mineralogy, 9A, 325–72.Google Scholar
Gittos, M.F., Lorimer, G.W. and Champness, P.H. (1976) In Electron Microscopy in Mineralogy(Wenk, H., ed.) Springer Verlag, New York, pp. 238–47.CrossRefGoogle Scholar
Leake, B.E. (1978) Amer. Mineral., 63, 1023–52.Google Scholar
Maas, R., Kinny, P.D., Williams, I.S., Froude, D.O. and Compston, W. (1992) Geochim. Cosmochim. Acta, 56, 1281–300.CrossRefGoogle Scholar
McGregor, V.R. (1993) Geological map of Greenland 1:100,000, Qorqut 64 V.l Syd, descriptive text., 40 pp. Copenhagen, Geological Surevy, Greenland.Google Scholar
McGregor, V.R., Nutman, A.P. and Friend, C.R.L. (1986) LPI Technical Report, 86-04, 113–69.Google Scholar
McGregor, V.R., Friend, C.R., and Nutman, A.P. (1991) Bull. Geol. Soc, Denmark, 39, 179–97.Google Scholar
Milton, D.J. and Ito, J. (1961) Amer. Mineral., 46, 734–40.Google Scholar
Nutman, A.P., Friend, C.R.L., Baadsgaard, H. and McGregor, V.R. (1989) Tectonics, 8, 573–89.CrossRefGoogle Scholar
Pankhurst, R.J., Moorbath, S., Rex., D.C. and Turner, G. (1973) Earth Planet. Sci. Lett., 20, 157–70.CrossRefGoogle Scholar
Parker, A. (1995) Proc. Roy. Soc. Land., 262, 349–55.Google Scholar
Robinson, P., Ross, M. and Jaffe, H.W. (1971) Amer. Mineral., 56, 1005–41.Google Scholar
Robinson, P., Spear, F.S., Schummacher, J.C., Laird, J., Klein, C., Evans, B.W. and Doolan, B.L. (1982) Reviews in Mineralogy, 9B, 1–228.Google Scholar
Seki, Y. and Yamasaki, M. (1957) Amer. Mineral., 42, 506–20.Google Scholar
Smelik, E.A. and Veblen, D.R. (1993) Amer. Mineral., 78, 511–32.Google Scholar
Smith, J.V. and Brown, W.L. (1988) Feldspar Minerals. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Smith, M.S., Dymek, R.F. and Chadwick, B. (1992) Precambrian Res., 57, 49–90.CrossRefGoogle Scholar
Treloar, P.J. and Putnis, A. (1982) Mineral. Mag., 45, 55–62.CrossRefGoogle Scholar
Williams, I.S. and Claesson, S. (1987) Contrib. Mineral. Petrol., 97, 205–17.CrossRefGoogle Scholar