Geomagnetic field variations and persistent non-dipole field contributions recorded by an approximately 130.000 year old lava sequence on Tristan da Cunha

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The morphology and intensity of the geomagnetic field have changed considerably during geological time. An accurate and detailed spatial and temporal record of geomagnetic variations is a prerequisite to a better understanding of geodynamo processes and of convection in the Earth`s outer core. Ancient magnetic field directions and intensities are accurately recorded by magnetic minerals in igneous rocks after cooling below their blocking temperature. Hotspot-related lava sequences on oceanic islands provide reliable paleomagnetic information, often with high temporal resolution. We propose a study of geomagnetic direction and intensity variations recorded in a thick sequence of lavas on Tristan da Cunha in the South Atlantic Ocean, combined with hig-precision radiometric dating. The oldest flow in the 60-flow sequence was emplaced approximately 130 thousand years ago, but its younger limit is not yet known. We chose this sequence because of its ideal age and location to test for the presence of persistent non-dioplar geomagnetic field contributions in the south Atlantic region. We hope to identify the approximately 110 to 120 thousand year old Blake Geomagnetic Excursion and to date it precisely using the 40 Ar/39 Ar method.