Geology Reference
In-Depth Information
is calculated by dividing the ARM by the strength of
the DC fi eld used during application of the ARM.
TRM, thermal remanent magnetization or thermore-
mament magnetization: The magnetization acquired
by a ferromagnetic mineral grain during cooling of
the grain through its Curie temperature or its block-
ing temperature. Blocking temperature is a function
of magnetic grain size and is always less than the
Curie temperature. It is the temperature below
which the magnetization of the grain becomes stable
for geologically signifi cant lengths of time.
TVRM, thermoviscous remanent magnetization: A
viscous magnetization (see VRM below) acquired by
a ferromagnetic mineral grain at a given tempera-
ture for a given length of time, usually a temperature
elevated above typical conditions in the laboratory.
VGP, virtual geomagnetic pole: The position of the
north magnetic pole on the surface of the Earth
that would generate the paleomagnetic direction
observed for a rock sample, assuming that the
Earth ' s fi eld is caused by a dipole at the center of the
Earth. Since PSV has not been time averaged, VGPs
do not typically lie on the N geographic pole (spin
axis of the Earth) but cluster around the N geo-
graphic pole during times of normal polarity.
VRM, viscous remanent magnetization: The magneti-
zation acquired by a ferromagnetic mineral grain
during exposure to a magnetic fi eld, either in the
laboratory or the Earth's magnetic fi eld, over a given
length of time. VRM is acquired as a function of the
log of time in the laboratory. Its acquisition is greater
at higher temperatures.
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