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Decorah Complex geophysics
Geophysical anomalies over Decorah Complex, Iowa. From Drenth and others, 2015, doi:10.1139/cjes-2014-0178.

Why is USGS interested in the Northeast Iowa Intrusive Complex?

A fundamental, and enigmatic, feature of the Northeast Iowa Intrusive Complex is a series of large circular- or horseshoe-shaped magnetic anomalies. Our research group has identified two to three hypothesis of the water geologic source of the anomalies may be. One possible interpretation is that these features are part of a Keweenawan age (~1,100 Ma) mafic igneous complex. This has major implications for the regional geologic framework and mineral potential, since it would be the second largest known Midcontinent Region-related igneous complex. However, the true geologic source can only be known through new drilling, which would give us a chance to directly determine the nature and age of these rocks.

What research is USGS conducting?

We plan to drill a new borehole through Paleozoic cover to Proterozoic rocks in northeastern Iowa and recover core from the Proterozoic basement sufficient for petrologic and radiometric analyses. Our primary goal is to to test geophysical interpretations of the Proterozoic geology in the area. Our secondary goals are to obtain rarely-available data on the overlying Proterozic section, fluid characteristics, in-situ stress conditions, and thermal conditions at the Proterozoic-Paleozoic unconformity.

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