| It is well known that a reliable determination of the geomagnetic paleointensity, the strength of the Earth's magnetic field in the geologic past, is a notoriously difficult task. Yet it constitutes an essential property of the field that is crucial for our understanding of the geodynamo. Many lavas that have acquired a thermoremanent magnetization (TRM) appear to be not suited for paleointensity determination with classic protocols, i.e. with 'Thellier-Thellier' methodology. This research proposal groundthruths a very recently proposed new paleointensity determination protocol, the multispecimen parallel differential partialTRM method (Dekkers and Böhnel, 2006, EPSL, 284, 508-517). With this method, all magnetic domain states can be processed so that many more lavas flows can be evaluated than would be possible with classical methodology which is restricted to very fine grains. While results so far are extremely encouraging, there are several unresolved issues that warrant a critical assessment for the new protocol to become a valid addition to existing paleointensity methods. This involves establishing a methodology to recognize incipient alteration that adversely affects paleointensity determination. To this end, a combination of mineral-magnetic methods and scanning and transmission electron microscopy will be utilized. Particular attention will be given to the analysis of acquisition curves of the anhysteretic remanent magnetization that has most diagnostic power in the small grain-size range of interest. Further, the domain state independence of the new method that is predicted by first-order theory, will be experimentally tested. Finally, its robustness with respect to various lava compositions and domain states will be investigated by analyzing historic and recent lavas from the Etna, Hawaii and the trans-Mexican volcanic belt that each represent a different geodynamic setting. We will evaluate our results with respect to the classic Thellier-Thellier method. |
