Although its linear trend from north-central to
southwest Iowa is evident, the intensities of the
aeromagnetic anomaly associated with the MRS in Iowa are
only slightly above background levels. Comparisons with
MRS rocks in the outcrop belt and magnetic modeling
suggest that the volcanic rocks on the Iowa Horst include
a thick sequence of early reversely-polarized lavas,
overlain by a thinner sequence of normally-polarized
basalts. The two sequences effectively cancel one
another, leaving a minimal net magnetic anomaly.
- Reds and yellows signify positive anomalies.
- Blues and purples identify negative anomalies.