Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-23T19:44:57.639Z Has data issue: false hasContentIssue false
  • English
  • Français

Metamorphic rocks of an intermediate facies series juxtaposed at the Start boundary, southwest England

Published online by Cambridge University Press:  01 May 2009

D. Robinson
D. Robinson
Affiliation:
Department of Geology Queen's BuildingUniversity WalkBristol BS8 1TR, England
Get access Rights & Permissions [Opens in a new window]

Summary

X-ray diffraction analysis of metamorphic rocks from the Start peninsula shows that the dominant mineral assemblage in the Start schists is quartz-muscovite-chlorite ± paragonite ± albite. The assemblage in the Devonian phyllites to the north of the Start boundary is quartz-muscovite-chlorite and the crystallinity of the white mica there is indicative of greenschist fades. The b0 parameter of white micas indicates that the metamorphism was of an intermediate facies series (Barrovian type), but of a lower pressure variety to the north of the Start boundary juxtaposed against a higher pressure variety to the south. No evidence exists of the high pressure metamorphism needed to support tectonic models in which the Start boundary is identified as a suture representing a Variscan subduction margin.

Type
Articles
Information
Geological Magazine , Volume 118 , Issue 3 , May 1981 , pp. 297 - 301
Copyright
Copyright © Cambridge University Press 1981

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

Bromley, A. V. 1979. Ophiolitic origin of the Lizard complex. Camborne Sch. Mines Mag. 79, 25–38.Google Scholar
Dewey, J. F. & Burke, K. C. A. 1973. Tibetan, Variscan, and Precambrian basement reactivation: Products of continental collision. J. Geol. 81, 683–92.CrossRefGoogle Scholar
Dodson, M. H. & Rex, D. C. 1971. Potassium-argon ages of slates and phyllites from southwest England. Q. Jl geol. Soc. Lond. 126, 465–99.CrossRefGoogle Scholar
Fettes, D. J., Graham, C. M., Sassi, F. P. & Scolari, A. 1976. The basal spacing of potassic white micas and facies series variation across the Caledonides. Scott. J. Geol. 12, 227–36.CrossRefGoogle Scholar
Frey, M. 1970. The step from diagenesis to metamorphism in pelitic rocks during Alpine orogenesis. Sedimentology 15, 261–79.CrossRefGoogle Scholar
Guidotti, C. V. & Sassi, F. P. 1976. Muscovite as a petrogenetic indicator mineral in pelitic schists. Neues Jb. Miner. Abh. 127, 97–142.Google Scholar
Hendriks, E. M. L. 1939. The Start–Dodman–Lizard boundary zone in relation to the Alpine structure of Cornwall. Geol. Mag. 76, 385–401.CrossRefGoogle Scholar
Hobson, D. M. 1977. Polyphase folds from the Start complex. Proc. Ussher Soc. 4, 102–10.Google Scholar
Matthews, S. C. 1977. The Variscan foldbelt in southwest England. Neues Jb. Geol. Paläont. Abh. 154, 94–127.Google Scholar
Phillips, F. C. 1964. Metamorphic rocks of the sea floor between Start point and Dodman point, S.W. England. J. mar. biol. Ass. U.K. 44, 665–73.CrossRefGoogle Scholar
Sadler, P. M. 1974. An appraisal of the ‘Lizard-Dodman-Start Thrust’ concept. Proc. Ussher Soc. 3, 71–81.Google Scholar
Sassi, F. P. & Scolari, A. 1974. The b 0 value of the potassic white micas as a barometric indicator in low-grade metamorphism of pelitic schists. Contr. Mineral. Petrol. 45, 143–52.CrossRefGoogle Scholar
Strong, D. F., Stevens, R. K., Malpas, J. & Badham, J. P. N. 1975. A new tale for the Lizard (Abstract). Proc. Ussher Soc. 3, 252.Google Scholar
Tilley, C. E. 1923. The petrology of the metamorphosed rocks of the Start area (South Devon). Q. Jl geol. Soc. Lond. 79, 172–204.CrossRefGoogle Scholar