Hostname: page-component-78c5997874-8bhkd Total loading time: 0 Render date: 2024-11-07T21:07:21.776Z Has data issue: false hasContentIssue false
  • English
  • Français

The volcanogenetic significance of garnet-bearing minor intrusions within the Borrowdale Volcanic Group Eskdale area, Cumbria

Published online by Cambridge University Press:  01 May 2009

B. Beddoe-Stephens  and
I. Mason
B. Beddoe-Stephens
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, U.K.
I. Mason
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

A number of garnetiferous minor intrusions have been mapped within the Borrowdale Volcanic Group. They underlie garnetiferous extrusive volcanic rocks which occur toward the top of a sequence of ignimbrite and lava – the Airy's Bridge Formation – which is the product of a major caldera-forming eruptive episode. Garnet and whole-rock geochemistry indicate that most of the intrusions are indistinguishable from garnetiferous dacite forming the final eruptive unit of the Airy's Bridge Formation: a co-magmatic link is therefore postulated. One of the intrusions, which intrudes the Airy's Bridge Formation, is distinct and may be related to the later Eskdale pluton.

It is suggested that following the emplacement of ignimbrites forming the basal half of the Airy's Bridge Formation, caldera collapse partially sealed a fissure-conduit system and degassed, garnet-bearing magma was intruded as dykes and sills and locally extruded as a post-explosive lava dome. It is also postulated that garnet crystallized in a high-level magma chamber (P < 3 kb) and that reverse chemical zoning was due to growth while sinking through compositionally stratified magma.

Type
Research Article
Information
Geological Magazine , Volume 128 , Issue 5 , September 1991 , pp. 505 - 516
Copyright
Copyright © Cambridge University Press 1991

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.)

Footnotes

‡

72 Gittin Street, Oswestry, Shropshire SY11 IDS, U.K.

References

Barley, M. E. 1987. Origin and evolution of mid-Cretaceous, garnet-bearing, intermediate and silicic volcanics from Canterbury, New Zealand. Journal of Volcanological and Geothermal Research 32, 247–67.CrossRefGoogle Scholar
Beddoe-Stephens, B., Aspden, J. A. & Shepherd, T. J. 1983. Glass inclusions and melt compositions from the Toba Tuffs, Northern Sumatra. Contributions to Mineralogy and Petrology 83, 278–87.CrossRefGoogle Scholar
Blake, S. 1981. Eruptions from zones magma chambers. Journal of the Geological Society of London 138, 281–7.CrossRefGoogle Scholar
Blake, S. 1984. Volatile oversaturation during the evolution of silicic magma chambers as an eruption trigger. Journal of Geophysical Research 89 (B10), 8237–44.CrossRefGoogle Scholar
Branney, M. J. & Soper, N. J. 1988. Ordovician volcano-tectonics in the English Lake District. Journal of the Geological Society of London 145, 367–76.CrossRefGoogle Scholar
Branney, M. J., Kokelaar, B. P. & McConnell, B. J. 1991. The Bad Step Tuff: A lava-like ignimbrite in a calc-alkaline piecemeal caldera, English Lake District. In High-temperature Silicic Eruptions (eds Wolff, J. A. and Henry, C. D.), pp. 000–00. IAVCEI, Proceedings in Volcanology. No. 4, Springer-Verlag (in press).Google Scholar
Caunt, S. 1984. Geochemical aspects of the Threlkeld Microgranite, Cumbria. Transactions of the Leeds Geological Association 10, 89–100.Google Scholar
Clemens, J. D. & Wall, J. 1981. Crystallisation and origin of some peraluminous (S-type) granitic magmas. Canadian Mineralogist 19, 111–32.Google Scholar
Clemens, J. D. & Wall, V. J. 1984. Origin and evolution of a peraluminous silicic ignimbrite suite: The Violet Town Volcanics. Contributions to Mineralogy and Petrology 88, 354–71.CrossRefGoogle Scholar
Ekren, E. B. & Byers, F. M. Jr. 1976. Ash-flow fissure vent in west-central Nevada. Geology 4, 247–51.2.0.CO;2>CrossRefGoogle Scholar
Fitton, J. G. 1972. The genetic significance of almandine-pyrope phenocrysts in the calc-alkaline Borrowdale Volcanic Group, northern England. Contributions to Mineralogy and Petrology 36, 231–48.CrossRefGoogle Scholar
Fitton, J. G., Thirwall, M. F. & Hughes, D. J. 1982. Volcanism in the Caledonian orogenic belt of Britain. In Andesites (ed. Thorpe, R. S.), pp. 611–36. Wiley.Google Scholar
Gilbert, J. S. & Rogers, N. W. 1989. The significance of garnet in the Permo-Carboniferous volcanic rocks of the Pyrenees. Journal of the Geological Society of London 146, 477–90.CrossRefGoogle Scholar
Green, T. H. 1977. Garnets in silicic liquids and its possible use as a P-T indicator. Contributions to Mineralogy and Petrology 65, 59–67.CrossRefGoogle Scholar
Hodges, K. V. & Spear, F. S. 1982. Geothermometry, geobarometry and the Al2SiO5 triple point at Mt. Moosilauke, New Hampshire. American Mineralogist 67, 1118–34.Google Scholar
Lipman, P. W. 1984. The roots of ash-flow calderas in west central North America: Windows into the tops of granitic batholiths. Journal of Geophysical Research 89 (B10), 8801–41.CrossRefGoogle Scholar
Millward, D. 1980. Three ignimbrites from the Borrowdale Volcanic Group. Proceedings of the Yorkshire Geological Society 42, 595–616.CrossRefGoogle Scholar
O'Brien, C., Plant, J. A., Simpson, P. R. & Tarney, J. 1985. The geochemistry, metasomatism and petrogenesis of the granites of the English Lake District. Journal of the Geological Society of London 142, 477–90.Google Scholar
Oliver, R. L. 1956. The origin of garnets in the Borrowdale Volcanic series and associated rocks, English Lake District. Geological Magazine 93, 121–39.CrossRefGoogle Scholar
Oliver, R. L. 1961. The Borrowdale volcanics and associated rocks of the Scafell area, English Lake District. Quarterly Journal of the Geological Society of London 117, 377–417.CrossRefGoogle Scholar
Reedman, A. J., Park, K. H., Merriman, R. J. & Kim, S. E. 1987. Welded tuff infilling a volcanic vent at Weolseong, Republic of Korea. Bulletin of Volcanology 49, 541–6.CrossRefGoogle Scholar
Rutherford, N. F. & Heming, R. F. 1978. The volatile content of Quaternary ignimbritic magmas from the North Island, New Zealand. Contributions to Mineralogy and Petrology 65, 401–11.CrossRefGoogle Scholar
Smith, R. L. 1979. Ash-flow magmatism. In Ash-flow Tuffs (eds Chapin, C. E. and Elston, W. E.), pp. 5–28. Geological Society of America Special Paper 180.CrossRefGoogle Scholar
Wolff, J. A. 1986. Welded tuff dykes, conduit closure and lava dome growth at the end of explosive eruption. Journal of Volcanology and Geothermal Research 28, 379–84.CrossRefGoogle Scholar