Oxygen isotope ratios of the Icelandic crust
Oxygen isotope ratios of hydrothermally altered basalts from depth of up to approx.3 km are reported from three localities in Iceland: International Research Drilling Project (IRDP) core at Reydarfjordur, eastern Iceland (Tertiary age); drill cuttings from Reykjavik (Plio-Pleistocene age); and Halocene drill cuttings from the active Krafla central volcano. Whole rock samples from these three localities have delta/sup 18/O values averaging +3.9 +- 1.3, +2.4 +- 1.1, and -7.7 +- 2.4%, respectively. The observed values in the deeper samples from Krafla are as low as the values for any rocks previously reported. There seems to be a slight negative gradient in delta/sup 18/O with depth at the former two localities and a more pronounced one at Krafla. Oxygen isotope fractionations between epidote and quartz and those between calcite and fluid suggests that the basalts were altered at temperatures of 300/sup 0/--400/sup 0/C. Low deltaD and delta/sup 18/O of epidote and low delta/sup 34/S of anhydrite indicate that the altering fluids in all three areas originated as meteoric waters and have undergone varied 'oxygen shifts'. Differences in the /sup 18/O shift of the fluids are attributed to differences in hydrothermal systems; low water/rock ratios (< or =0.1) are found in the IRDP core and the Reykjavik hole, but high water/rock ratios (>5) at Krafla. The convective hydrothermal activity, which is probably driven by silicic magma beneath the central volcanoes, has caused strong subsolidus depletion of /sup 18/O in the rocks. The primary-magnetic delta/sup 18/O value of the rocks in the Tertiary IRDP core was about +3.9%, which is lower than that obtained for fresh basalt from other places. Such exceptionally low delta/sup 18/O magmas are common in Iceland and may occur as the result of oxygen isotope exchange with or assimilation of altered rocks that form a thick sequence beneath the island due to isostatic subsidence.
- Research Organization:
- Department of Geology, University of Alberta, Edmonton, Alberta, Canada T6G 2E3
- OSTI ID:
- 6038561
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:B8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
15 GEOTHERMAL ENERGY
ICELAND
ISOTOPE RATIO
OCEANIC CRUST
BASALT
DRILL CORES
FRACTIONATION
GEOTHERMAL FIELDS
HYDROTHERMAL ALTERATION
OXYGEN 18
DEVELOPING COUNTRIES
EARTH CRUST
EUROPE
EVEN-EVEN NUCLEI
IGNEOUS ROCKS
ISLANDS
ISOTOPES
LIGHT NUCLEI
NUCLEI
OXYGEN ISOTOPES
ROCKS
SEPARATION PROCESSES
STABLE ISOTOPES
VOLCANIC ROCKS
WESTERN EUROPE
580100* - Geology & Hydrology- (-1989)
150202 - Geology & Hydrology of Geothermal Systems- Non-USA- (-1989)