Palaeomagnetic variations across transitional lava flows: geomagnetic-field impulses or recording artifacts?

• Applicant: Professor Dr. Michael Winklhofer
• Subject Area: Geophysics
• Term: from 2004 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5429628

Rapid field variations observed at Steens Mountain are interpreted controversially: Either they are artifacts due to rock magnetic inhomogeneity or they reflect geomagnetic field changes. The latter possibility would have important implications for geodynamo theory if the variation is of internal origin, or for the transitional ionosphere and magnetosphere if the change is due to enhanced external field activity. Several studies on the Steens Mountain sequence failed to resolve this question. Therefore, to find evidence for or against highly dynamic transitional fields, we propose to investigate transitional lava flows from other locations with well documented directional and intensity records. In our preparatory work, we have developed a sampling strategy and measurement technique to discover rapid variations recorded in cooling lava flows. This new approach will allow us to assess if variations are of geomagnetic origin and to identify periodic field variations indicative of external sources. In the proposed project, we plan to apply this method to flows from the R3-N3 reversal on Iceland, where strong equatorial dipoles were observed, and to an already sampled profile across flow C-TP62 from the El Paso reversal on Gran Canaria, which yielded extremely low palaeointensity values (1.2 µT). Our measurements will provide high resolution rock- and palaeomagnetic profiles across these flows which will serve to develop optimum palaeointensity measurement strategies and to test reliability criteria used for palaeomagnetic sampling of lava flows whose NRM might have been affected by later reheating. We also have the unique chance to discover daily variations due to external field sources or unusually high rates of geomagnetic field variation, which then can be verified by our intrinsic consistency check.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1097: Geomagnetic Variations: Spatio-Temporal Structure, Processes, and Effects on System Earth
• Participating Person: Professor Dr. Karl Fabian