Origin and history of hydrothermal fluids of the Reykjanes and Krafla geothermal fields, Iceland - A stable isotope study

A. E. Sveinbjornsdottir*, M. L. Coleman, B. W.D. Yardley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)

Abstract

The Reykjanes and Krafla geothermal fields are both examples of active high temperature systems and show similar assemblages of alteration minerals, but the fluid at Reykjanes is dominantly sea water whereas that at Krafla is meteoric. Oxygen isotope analyses of surface rock and of drill chip samples from different depths are presented, together with results for the Krafla fluid, which is close to local precipitation (δ18O = -11.9‰, δD= -86.8‰). Calcite in both systems is apparently in equilibrium with the present deep fluid at the present field temperature, except for the upper 250 m at Reykjanes where the fluid may be more meteoric than at depth. Feldspar gives similar results. Quartz separates at Reykjanes are anomalously lighter than coexisting feldspar and give exceptionally high quartz-fluid temperatures. It is suggested that quartz originally grew when the fluid was more nearly meteoric (? glacial period) and has not re-equilibrated. Bulk-rock 18O depletion supports this interpretation of the history of the Reykjanes system. Quartz in the Krafla system is mostly in equilibrium at the present field conditions but anomalies occur near the boundary between the upper and lower parts of the system, suggesting that this is not entirely stable. A high fluid:rock ratio (10-100 minimum) is indicated for the Krafla field.

Original languageEnglish
Pages (from-to)99-109
Number of pages11
JournalContributions to Mineralogy and Petrology
Volume94
Issue number1
DOIs
Publication statusPublished - Sept 1986

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