ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
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 (δ 18 O = −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 18 O 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00371231
