Lg. Fullerton et al., CONTRIBUTIONS OF CRETACEOUS QUIET ZONE NATURAL REMANENT MAGNETIZATIONTO MAGSAT ANOMALIES IN THE SOUTHWEST INDIAN-OCEAN, J GEO R-SOL, 99(B6), 1994, pp. 11923-11936
The Magsat magnetic anomalies over the Southwest Indian Ocean are mode
led using a combination of induced plus viscous remanent magnetization
(IM/VRM) and natural remanent magnetization (NRM). Two broad, roughly
parallel, SW to NE trending triple-peaked positive anomalies dominate
the region, one lying south of Africa and the other north of Antarcti
ca. Although these anomaly peaks generally correspond with the Agulhas
Plateau/Maud Rise, Mozambique Plateau/Astrid Ridge, and Madagascar Ri
dge/Conrad Rise conjugate pairs, the IM/VRM contribution from structur
al characteristics (i.e., crustal thickness) accounts for only about 2
0% of the anomaly amplitudes. A spatially variable but observationally
constrained NRM contribution in Cretaceous Quiet Zone (KQZ) crust is
required to account for the location, shape, and amplitude contrast of
these anomalies. Many crustal features in the Southwest Indian Ocean
near Antarctica have little geophysical data to constrain their struct
ure but do have tectonic conjugates near Africa for which much more ge
ophysical data are generally available. Using geophysical and geologic
al constraints from one member to model the magnetization structure of
its conjugate reproduces the observed Magsat reduced-to-pole anomalie
s over both structures very well. This suggests that no significant al
teration in their magnetization structure has occurred since the featu
res split. Models of these conjugate structures show that IM/VRM repro
duces the Magsat anomalies associated with non-KQZ crust but that both
IM/VRM and a dominant NRM component are required to explain the anoma
lies associated with KQZ crust.