Remanent magnetization of maghemitized basalts from Krafla drill cores, NE-Iceland

• Published in: Studia Geophysica et Geodaetica
• Main Authors: Oliva-Urcia, Belén, Kontny, Agnes
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2012
• Subjects: Low temperature oxidation; NRM; Krafla; Iceland
• Online Access: http://hdl.handle.net/10261/100613; https://doi.org/10.1007/s11200-011-9013-9

[EN] We investigated the natural remanent magnetization (Jr) of hydrothermally altered basalts from two drill cores KH1 (200 m) and KH3 (400 m) situated at the rim of the Krafla caldera in NE Iceland, where a geothermal field (>150°C) is still active. Low temperature oxidation along with mineral reactions in the chlorite zone (<350°C) is the prevailing cause for the maghemitization and a strong decrease of Jr to occur in our study. Despite a significant decrease of Jr with respect to fresh basalts in surface outcrops of the same area, the stepwise demagnetization analyses of Jr show the presence of a stable magnetic component with the expected inclination of 77° in Iceland. Because the alteration temperature (<350°C) is above the Curie temperatures of most of the original titanomagnetite (40°−350°C), we suggest that a normal direction of remanence is chemically acquired during the low temperature alteration. We observed only one reliable negative inclination at 293.2 m in the KH3 core, which we rather interpret to be acquired during a geomagnetic excursion with reverse polarity than caused by a self-reversal mechanism. The funding to carry out this project comes from DFG grant number KO 1514/3. We are grateful to Leo Kristjánsson for his collaboration. We also thank Omar Friedleifson, Asgrimur Gudmundsson, Anett Blischke and Bjarni Gautason from Iceland Geosurvey, for their support on getting access to the drill core samples. Carsten Vahle is acknowledged for the demagnetization analyses. Two anonymous reviewers and Claire Carvallo together with the editor Eduard Petrovský are acknowledged for their useful remarks, which improved the first version of the manuscript significantly. Peer reviewed