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CORRECTION GSA TODAY | www.geosociety.org/gsatoday

“Crustal magnetism, tectonic inheritance, and continental rifting
in the southeastern United States,” by E.H. Parker Jr., GSA Today,
v. 24, no. 4/5, p. 4–9, doi: 10.1130/GSAT-G192A.1.

An error has been found in the modeling used to generate
magnetic anomalies in Figure 3 (in Parker, 2014, p. 6). During
construction of crustal models, the coordinates of the polygons
used to represent Gondwanan crust were entered incorrectly
(counterclockwise). This resulted in two errors: (1) it reversed the
polarities of the computed anomalies, which then necessitated a
reversal in magnetic polarity (assignment of a 180° declination)
for remanent magnetization, in order to match the overall pattern
of the observed anomalies; and (2) it generated an unintended
lateral variation in the contribution to the magnetic anomaly
from induced magnetization. The second error was small, because
of the small value for susceptibility (k = 0.01 SI) assigned to all
polygons, but the first resulted in a 180° error in the orientation of
the contrast in remanent magnetization between Gondwanan and
Laurentian crust.

The accompanying figure shows the corrected anomalies.
The changes in the overall shapes of the anomalies are relatively
minor, but the remanent magnetization is now shown as local-
ized and reversed in Laurentian rather than Gondwanan crust.
This is equivalent to reversed magnetization for both crustal
blocks, where (e.g., for profile A) the value of 0.47 A/m then
represents the contrast due to slightly stronger magnetization for
Laurentian crust. This is consistent with the original interpreta-
tion that magnetization was acquired during the Kiaman super-
chron (320–263 Ma) and Alleghanian collision, while the region
was near the equator.

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