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Geophysics seminar: Monika Korte (GFZ German Research Centre for Geosciences) "Geomagnetic Excursions Through the Past 100 kyr"

11/26/2019 - 12:00pm
Revelle Conference Room (IGPP 4301)
Event Description: 

Talk abstract:

Recently developed spherical harmonic paleomagnetic field models GGF100k and LSMOD.2
offer a new global view on several geomagnetic excursions throughout the past 100 kyr.
Excursions are brief episodes where the magnetic field directions deviate strongly from
normal dipole orientation, and are accompanied by lows in field intensity. Globally best
documented is the Laschamp excursion (~41 ka BP), found in volcanic rocks and sediments
from all over Earth. Other excursions, such as the Post-Blake (~95 ka), Norwegian-Greenland
Sea (~60 ka), Mono Lake / Auckland (~33 ka) and Hilina Pali (~17 ka) excursions have been
found only regionally or in a smaller number of records, and their ages in general appear
more widely dispersed. The global field models suggest that all these excursions are caused
by weakening of the axial dipole field contribution, with little change in the level of non-axial-
dipole secular variation. Excursions seem to manifest globally when power in the axial dipole
drops significantly below that in non-dipole terms, while regional excursions seem to
correspond to less drastic decreases in the axial dipole strength. Directional excursion
signatures ascribed to the Mono Lake and Hilina Pali excursions observed in different parts of
the world might be series of temporally offset regional excursions during prolonged times of
low axial dipole field. Consequently, care should be taken when considering geomagnetic
excursions as stratigraphic markers for dating purposes. Virtual geomagnetic pole paths for
all these excursions indicate some longitudinal preference, falling in particular in the Pacific
region. The models can be used to explore for indications of systematic mantle control on the
geodynamo. However, all interpretations have to consider certain limitations of the models
due to distribution, reliability and chronologies of the available data.

For more information on this event, contact: 
Steve Constable
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