Evolution of fluid-rock interaction in the Reykjanes geothermal system, Iceland: Evidence from Iceland Deep Drilling Project core RN-17B

Andrew P.G. Fowler, Robert A. Zierenberg, Peter Schiffman, Naomi Marks, Gumundur Ómar Frileifsson

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


We describe the lithology and present spatially resolved geochemical analyses of samples from the hydrothermally altered Iceland Deep Drilling Project (IDDP) drill core RN-17B. The 9.3m long RN-17B core was collected from the seawater-dominated Reykjanes geothermal system, located on the Reykjanes Peninsula, Iceland. The nature of fluids and the location of the Reykjanes geothermal system make it a useful analog for seafloor hydrothermal processes, although there are important differences. The recovery of drill core from the Reykjanes geothermal system, as opposed to drill cuttings, has provided the opportunity to investigate evolving geothermal conditions by utilizing in-situ geochemical techniques in the context of observed paragenetic and spatial relationships of alteration minerals. The RN-17B core was returned from a vertical depth of ~2560m and an in-situ temperature of ~345°C. The primary lithologies are basaltic in composition and include hyaloclastite breccia, fine-grained volcanic sandstone, lithic breccia, and crystalline basalt. Primary igneous phases have been entirely pseudomorphed by calcic plagioclase+magnesium hornblende+chlorite+titanite+albitized plagioclase+vein epidote and sulfides. Despite the extensive hydrothermal metasomatism, original textures including hyaloclastite glass shards, lithic clasts, chilled margins, and shell-fragment molds are superbly preserved. Multi-collector LA-ICP-MS strontium isotope ratio (87Sr/86Sr) measurements of vein epidote from the core are consistent with seawater as the dominant recharge fluid. Epidote-hosted fluid inclusion homogenization temperature and freezing point depression measurements suggest that the RN-17B core records cooling through the two-phase boundary for seawater over time to current in-situ measured temperatures. Electron microprobe analyses of hydrothermal hornblende and hydrothermal plagioclase confirm that while alteration is of amphibolite-grade, it is in disequilibrium and the extent of alteration is dependent upon protolith type and water/rock ratio. Alteration in the RN-17B core bares many similarities to that of Type II basalts observed in Mid-Atlantic Ridge samples.

Original languageEnglish (US)
Pages (from-to)47-63
Number of pages17
JournalJournal of Volcanology and Geothermal Research
StatePublished - Sep 1 2015
Externally publishedYes

Bibliographical note

Funding Information:
RN-17B was recovered at considerable expense, thanks in large part to funding from NSF's Continental Dynamics Program. The research described herein was supported by the National Science Foundation grant EAR 0507518 . Samples for this study were provided by IDDP. I would like to thank Qin-Zhu Yin and Josh Wimpeny for coordinating access to the LA-MC-ICP-MS facility at UC Davis. I would also like to thank HS Orka for their hospitality and for providing access to drill core samples at the Reykjanes geothermal field.

Publisher Copyright:
© 2015 Elsevier B.V.


  • Epidote
  • Geothermal
  • Hydrothermal alteration
  • Iceland
  • RN-17B Drill Core
  • Reykjanes


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