Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex

Benjamin J. Drenth; A. Kate Souders; Klaus J. Schulz; Joshua M. Feinberg; Raymond R. Anderson; Val W. Chandler; William F. Cannon; Ryan J. Clark

doi:10.1016/j.precamres.2020.105845

Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex

Benjamin J. Drenth, A. Kate Souders, Klaus J. Schulz, Joshua M. Feinberg, Raymond R. Anderson, Val W. Chandler, William F. Cannon, Ryan J. Clark

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

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.

Original language	English (US)
Article number	105845
Journal	Precambrian Research
Volume	347
DOIs	https://doi.org/10.1016/j.precamres.2020.105845
State	Published - Sep 2020

Bibliographical note

Funding Information:
This work was supported by the Mineral Resources Program of the U.S. Geological Survey . Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding Information:
This work was supported by the Mineral Resources Program of the U.S. Geological Survey. Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Publisher Copyright:
© 2020

Keywords

Apatite geochronology
Gravity anomaly data
Magnetic anomaly data
Midcontinent Rift system
Northeast Iowa intrusive complex

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@article{6535cb88e53b48f8aef21d0e05af4761,

title = "Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex",

abstract = "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.",

keywords = "Apatite geochronology, Gravity anomaly data, Magnetic anomaly data, Midcontinent Rift system, Northeast Iowa intrusive complex",

author = "Drenth, {Benjamin J.} and Souders, {A. Kate} and Schulz, {Klaus J.} and Feinberg, {Joshua M.} and Anderson, {Raymond R.} and Chandler, {Val W.} and Cannon, {William F.} and Clark, {Ryan J.}",

note = "Funding Information: This work was supported by the Mineral Resources Program of the U.S. Geological Survey . Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Funding Information: This work was supported by the Mineral Resources Program of the U.S. Geological Survey. Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Publisher Copyright: {\textcopyright} 2020",

year = "2020",

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doi = "10.1016/j.precamres.2020.105845",

language = "English (US)",

volume = "347",

journal = "Precambrian Research",

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AU - Drenth, Benjamin J.

AU - Souders, A. Kate

AU - Schulz, Klaus J.

AU - Feinberg, Joshua M.

AU - Anderson, Raymond R.

AU - Chandler, Val W.

AU - Cannon, William F.

AU - Clark, Ryan J.

N1 - Funding Information: This work was supported by the Mineral Resources Program of the U.S. Geological Survey . Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Funding Information: This work was supported by the Mineral Resources Program of the U.S. Geological Survey. Thomas Strong and Chris Holm-Denoma helped with mineral separation and imaging. We thank Dan Winester, Monica Youngman, and Jeff Kanney of the National Geodetic Survey for providing access to their absolute gravity base station information in Iowa, and for graciously establishing new high-quality base stations in the study area. Connie Dicken assisted with compilation of geologic data for Fig. 1. Thanks to Paul Sylvester for access to the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. We thank Laurel Woodruff and two anonymous reviewers for helpful comments. Finally, we thank editors Elson Oliveira and Wilson Teixeira for their thoughtful and efficient handling of this paper. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Publisher Copyright: © 2020

PY - 2020/9

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N2 - 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.

AB - 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.

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KW - Gravity anomaly data

KW - Magnetic anomaly data

KW - Midcontinent Rift system

KW - Northeast Iowa intrusive complex

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Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex

Abstract

Bibliographical note

Keywords

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