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Contributions to Mineralogy and Petrology

, Volume 95, Issue 3, pp 343–349 | Cite as

Stable isotope relations in an open magma system, Laacher See, Eifel (FRG)

  • G. Wörner
  • R. S. Harmon
  • J. Hoefs
Article

Abstract

18O/16O and D/H ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic Laacher See tephra sequence (11000 y.b.p., East Eifel volcanic field, FRG) to study open-system behaviour of the associated magma system. Mineral and glass δ18O values appear to be largely undisturbed by low-temperature, secondary alteration, record isotopic equilibrium and confirm previous conclusions, based on radiogenic isotope evidence, of early, small-scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber. One sanidine-glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption. A sealing carapace of chilled magma, which itself was strongly contaminated, prevented large-scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system. D/H measurements of various glass types (glass inclusions, dense and pumiceous glass) and amphiboles gave conflicting results suggesting a combination of degassing, volatile exchange with country rocks and hydration. Stable isotope ratios for primitive parental magmas (δ18O=+5.5 to 7.0‰) and mantle megacrysts (δ18O=+ 5.5 to +6.0‰, δD=−21 to −38‰, for amphiboles and phlogopite, resp.) suggest a rather variable fluid composition for the sub-Eifel mantle.

Keywords

Tephra Meteoric Water Parental Magma Magma System Volcanic Field 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • G. Wörner
    • 1
  • R. S. Harmon
    • 2
    • 3
  • J. Hoefs
    • 3
  1. 1.Institut f. MineralogieRuhr UniversitätBochumFederal Republic of Germany
  2. 2.Department of Geological SciencesSouthern Methodist UniversityDallasUSA
  3. 3.Geochemisches InstitutUniversität GöttingenGöttingenFederal Republic of Germany

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