Journal article
Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex
Precambrian research, Vol.347, p.105845
09/2020
DOI: 10.1016/j.precamres.2020.105845
Abstract
•Large amplitude aeromagnetic and gravity anomalies reflect a largely mafic-ultramafic intrusive complex concealed under Paleozoic cover, the northeast Iowa intrusive complex (NEIIC).•A new apatite U-Pb date of ~1170 Ma indicates the age of a nearby dike swarm.•Cross-cutting relations imaged in geophysical data indicate that the intrusive complex cuts the dike swarm, meaning the maximum age of the NEIIC is ~1170 Ma.•The NEIIC is a major intrusive component of the Midcontinent Rift System, and was likely emplaced during early stages of rifting.•The Belle Plaine fault zone and Fayette structural zone are possible lithospheric-scale structural discontinuities that facilitated NEIIC emplacement.
Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8–1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ~1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ~1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ~40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.
Details
- Title: Subtitle
- Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex
- Creators
- Benjamin J. Drenth - United States Geological SurveyA. Kate Souders - United States Geological SurveyKlaus J. Schulz - United States Geological SurveyJoshua M. Feinberg - University of MinnesotaRaymond R. Anderson - University of IowaVal.W. Chandler - United States Geological SurveyWilliam F. Cannon - United States Geological SurveyRyan J. Clark - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Precambrian research, Vol.347, p.105845
- Publisher
- Elsevier B.V
- DOI
- 10.1016/j.precamres.2020.105845
- ISSN
- 0301-9268
- eISSN
- 1872-7433
- Language
- English
- Date published
- 09/2020
- Academic Unit
- Iowa Geological Survey; IIHR--Hydroscience and Engineering; Earth and Environmental Sciences
- Record Identifier
- 9984702729202771
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