Hostname: page-component-78c5997874-dh8gc Total loading time: 0 Render date: 2024-11-19T15:46:58.333Z Has data issue: false hasContentIssue false
  • English
  • Français

Significance of illite crystallinity and bo values of K-white mica in lowgrade metamorphic rocks, North Hill End Synclinorium, New South Wales, Australia

Published online by Cambridge University Press:  05 July 2018

R. Offler  and
E. Prendergast
R. Offler
Affiliation:
Department of Geology, University of Newcastle, NSW, Australia, 2308
E. Prendergast
Affiliation:
Department of Geology, University of Newcastle, NSW, Australia, 2308
Get access Rights & Permissions [Opens in a new window]

Abstract

A study of low-grade metamorphism in late Silurian to early Carboniferous rocks in the North Hill End Synclinorium and adjacent anticlinoria has been made by the determination of illite crystallinity and bo values of K-white mica in eighty slates and phyllites. Illite crystallinity values vary from 0.40 Δ°2θ on the Molong Anticlinorium to 0.12 Δ°2θ within the axis of the synclinorium, suggesting anchizonal to epizonal metamorphic conditions. This is in agreement with previous observations on Ca-Al-hydrosilicate assemblages which indicated a change from prehnite-pumpellyite facies in the anticlinoria adjacent to the synclinorium to middle greenschist facies in the axis. Local variations in crystallinity are attributed to variation in ak+ in fluids migrating along cleavage zones.

The mean bo value obtained from the pelites is 9.017 Å (σn = 0.008; n = 80) which is in close agreement with that obtained from part of the adjacent Capertee Anticlinorium ( = 9.019 Å; σn = 0.007; n = 52). However, ‘t’ tests indicate that two bo populations are present in the synclinorium ( = 9.019 and 9.022 Å), with the lower values concentrated in the southern portion of this structure. The two populations are considered to be the result of slightly different metamorphic conditions prevailing during the deformation of the rocks in the synclinorium. A higher geothermal gradient affecting rocks giving the lower bo values is attributed to the presence of granitoids at shallower depths than elsewhere in the synclinorium.

Keywords

illitemicametamorphic rocksNorth Hill End SynclinoriumNew South WalesAustralia
Type
Research Article
Information
Mineralogical Magazine , Volume 49 , Issue 352 , June 1985 , pp. 357 - 364
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1985

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

Åberg, G., Aguirre, L., Levi, B., and Nystrom, J. O. (1984) In Marginal Basin Geology: Volcanic and associated sedimentary and tectonic processes in modern and ancient marginal basins (Kokelaar, B. P. and Howells, M. F., eds.). Geol. Soc. Spec. Publ. 16, 185-93.CrossRefGoogle Scholar
Bureau of Mineral Resources. Bouguer Anomalies, Bathurst Sheet, 1:500000,I55/B2-8-0.Google Scholar
Bureau of Mineral Resources. Bouguer Anomalies, Dubbo Sheet, 1:500 000, I55/B2-4.Google Scholar
Cas, R. (1983) Geol. Soc. Aust. Inc. Spec. Publ. No. 10.Google Scholar
Etheridge, M. A., Wall, V. J., and Vernon, R. H. (1983) J. Metamorphic Geol. 1, 205-26.CrossRefGoogle Scholar
Frey, M., Teichmüller, M., Teichmüller, R., Mullis, J., Kunzi, B., Breitschmid, A., Gruner, U., and Schwizer, B. (1980) Eclogae geol. Helv. 73, 173-203.Google Scholar
Guidotti, C. V., and Sassi, F. P. (1976) Neues Jahrb. Mineral. Abh. 127, 97-142.Google Scholar
Kisch, H. J. (1980) Eclogae geol. Helv. 73, 753-77.Google Scholar
Kisch, H. J. (1983) In Developments in Sedimentology 25B (Larsen, G. and Chilingar, G. V., eds.). Elsevier, 289–493.Google Scholar
Kubler, B. (1966) In Colloque sur les Étages Tectoniques. A la Baconnière, 105-22, Neuchâtel. Google Scholar
Lackenbruch, A. H., and Sass, J. H. (1977) Geol. Soc. Am. Mem. 152, 209-50.Google Scholar
Offter, R., and Pemberton, J. (1983) Sixth Geol. Soc. Austr. Convention, Canberra, Abst. 62.Google Scholar
Padan, A., Kisch, H. J., and Shagam, R. (1982) Contrib. Mineral. Petrol. 79, 85-95.CrossRefGoogle Scholar
Plyusina, L. P., and Ivanov, I. P. (1979) Int. Geol. Rev. 20, 791-801.CrossRefGoogle Scholar
Prendergast, E. (1981) B.Sc. (Hons.) thesis, Macquarie University.Google Scholar
Primmer, T. J. (1983) Proc. Ussher Soc. 5, 421-7.Google Scholar
Robinson, D. (1981) Geol. Mag. 3, 297-301.CrossRefGoogle Scholar
Sassi, F. P., and Scolari, A. (1974) Contrib. Mineral. Petrol. 45, 143-52.CrossRefGoogle Scholar
Schiffman, P., and Liou, J. G. (1980) J. Petrol. 21, 441-74.CrossRefGoogle Scholar
Smith, R. E. (1969) J. Petrol. 10, 144-63.CrossRefGoogle Scholar
Stephens, M. B., Glasson, M. J., and Keays, R. R. (1979) Am. J. Sci. 279, 12960.CrossRefGoogle Scholar
Turner, F. J. (1981) Metamorphic Petrology, McGraw-Hill, 524 pp.Google Scholar
Velde, B. (1967) Contrib. Mineral. Petrol. 14, 250-8.CrossRefGoogle Scholar
Vernon, R. H., and Flood, R. H. (1979) Tectonophysics, 58, 127-37.CrossRefGoogle Scholar
Weber, K. (1972) Neues Jahrb. Mineral. Monatsh. 267-76.Google Scholar
White, S. M., and Johnston, D. C. (1981) J. Struct. Geol. 3, 279-90.CrossRefGoogle Scholar