Geology Reference
In-Depth Information
Glossary of Paleomagnetic and Rock
Magnetic Acronyms
AAR, anisotropy of anhysteretic remanence: The ani-
sotropy that occurs when an ARM or a partial ARM
is applied in a minimum of six different orientations
to a sample, usually along the three orthogonal
sample coordinate axes ( X , Y and Z ) and along the
three orthogonal directions between each of these
axes ( XY , YZ and XZ ). Some workers prefer to abbre-
viate this measurement as AARM for anisotropy of
anhysteretic remanent magnetization.
AIR, anisotropy of isothermal remanence: The anisot-
ropy that occurs when an IRM is applied in a
minimum of six different orientations to a sample
(i.e. X , Y , Z , XY , YZ and XZ ). Often used to activate
higher-coercivity minerals than those that can be
activated by an ARM.
AMS, anisotropy of magnetic susceptibility: The ani-
sotropy that results for an induced magnetization
that is caused by application of a magnetic fi eld in at
least six different orientations to a sample. The mag-
netic fi eld typically has the strength similar to the
Earth ' s magnetic fi eld, c. 50 μ T.
ARM, anhysteretic remanent magnetization: A labo-
ratory remanence that results from applying a small
DC magnetic fi eld (c. 50-100 μT) to a sample in the
presence of an alternating magnetic fi eld that is
decreased from some peak value to 0. In most labo-
ratories the peak fi eld is c. 100 mT. A partial ARM
can be applied by only switching on the DC fi eld over
a limited range of alternating fi eld during the
decrease from a peak alternating fi eld value.
B c : The coercivity of a sample that results from a
hysteresis loop measurement. It is the fi eld that is
required to reduce the magnetization of a sample to
0 while the fi eld is being applied.
B cr : The coercivity of remanence of a sample that
results from a hysteresis loop measurement. It is the
fi eld required to reduce the magnetization of a
sample to 0 after the fi eld has been turned off, i.e. the
sample is measured in 0 fi eld.
CRM, chemical remanent magnetization: The rema-
nent, or spontaneous, magnetization acquired when
a ferromagnetic mineral grows chemically, or crys-
tallizes, in the presence of a magnetic fi eld. When
new crystal grains grow through a certain volume,
typically submicron in size, the spontaneous mag-
netization becomes stable.
ChRM, characteristic remanent magnetization: The
stable magnetization that results from the complete
demagnetization of a sample at the higher demag-
netization fi elds or temperatures. If a sample has
multiple components of magnetization revealed
during demagnetization, the ChRM is the magneti-
zation removed at the highest demagnetization fi eld
or temperature.
DRM, detrital remanent magnetization (or, to some,
depositional remanent magnetization): The mag-
netization acquired by a sediment when its primary
depositional magnetic minerals are aligned with the
ambient magnetic fi eld at deposition.
EI, elongation - inclination: Used for an inclination
shallowing correction technique in which the elon-
gation (ellipticity) of the directional scatter resulting
from secular variation at a given latitude is matched
to the mean inclination that would occur in a GAD
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