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On the possibility of recovering paleo-diurnal magnetic variations in transitional lava flows: I. Constraints from thermoremanence modelling for an experimental protocol

Winklhofer, Michael, Karl Fabian, Roman Leonhardt, and Christian Verard (2008), On the possibility of recovering paleo-diurnal magnetic variations in transitional lava flows: I. Constraints from thermoremanence modelling for an experimental protocol, Phys. Earth Planet. Inter., doi:10.1016/j.pepi.2008.07.019.

Abstract
One of the tenets in paleomagnetism is that perturbations of the ground magnetic
field due to magnetospheric or ionospheric current systems are too small to
leave a detectable paleomagnetic signature in lava flows. As suggested by recent
work in paleomagnetosphere modeling, however, external field perturbations may
be significantly enhanced during periods of transitional field behaviour, particularly
when the dipole-field axis is strongly tilted towards the equator, which then leads to
an extremely dynamic magnetosphere on the diurnal time scale even for quiet solar
wind conditions.We here demonstrate that thin (rapidly cooled) lava flows (∼ 50 cm
thick) with high magnetic blocking temperatures (within ∼ 50 − 100°C below the
Curie temperature) indeed have the potential to record such diurnal perturbations.
Further, an experimental protocol is suggested to paleomagnetically extract these
perturbations. Our proof-of-concept is based on numerical modelling of thermoremanence
(TRM) acquisition and simulation of thermal demagnetization surfaces
for discrete temperature steps in function of vertical position in the flow. The TRM
direction recovered at a given thermal demagnetization step varies with vertical
position in the flow and reflects the wave form of the external field variation. Characteristically,
the vertical position of a captured signal changes systematically with
unblocking temperature, which reflects the oblique orientation of cooling isochrons,
along which the signals are blocked. The signals have their largest amplitudes at
the maximum unblocking temperatures, but decay away at lower temperatures. It
is by these systmatic trends that external field perturbations, if trapped, can be
paleomagnetically identified and distinguished from a secondary overprint. The experimental
procedure requires a sample spacing of 1 cm (with 1 cm drill cores) and small
thermal demagnetization steps (15°C) at elevated temperatures.
Further information
BibTeX
@article{id1321,
  author = {Michael Winklhofer and Karl Fabian and Roman Leonhardt and Christian Verard},
  journal = {Phys. Earth Planet. Inter.},
  month = {jul},
  title = {{On the possibility of recovering paleo-diurnal magnetic variations in transitional lava flows: I. Constraints from thermoremanence modelling for an experimental protocol}},
  year = {2008},
  url = {http://dx.doi.org/10.1016/j.pepi.2008.07.019},
  doi = {10.1016/j.pepi.2008.07.019},
}
EndNote
%0 Journal Article
%A Winklhofer, Michael
%A Fabian, Karl
%A Leonhardt, Roman
%A Verard, Christian
%D 2008
%J Phys. Earth Planet. Inter.
%T On the possibility of recovering paleo-diurnal magnetic variations in transitional lava flows: I. Constraints from thermoremanence modelling for an experimental protocol
%U http://dx.doi.org/10.1016/j.pepi.2008.07.019
%8 jul
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Printed 06. Dec 2019 12:02