Late Precambrian structural evolution of Pigeon Point, Minnesota and relations to the Lake Superior syncline

1976 ◽  
Vol 13 (7) ◽  
pp. 877-888 ◽  
Author(s):  
M. G. Mudrey Jr.
Keyword(s):  
Lake Superior ◽  
Volcanic Rocks ◽  
Structural Evolution ◽  
Cook County ◽  
Tectonic Event ◽  
Late Precambrian ◽  
North Shore ◽  
Volcanic Group ◽  
The North ◽  
Tectonic Events

A sequence of semi-brittle deformational tectonic events in gently dipping middle Precambrian argillite and graywacke, and late Precambrian sandstone and volcanic rocks on the northwest coast of Lake Superior is interpreted from detailed geologic mapping in the Pigeon Point, Cook County, Minnesota area. The earliest tectonic event was broad, open folding in the middle Precambrian Rove Formation along N 35 °E axes and the development of two sets of joints (North and N 70° E). The second event was eastward trending, high-angle faulting in the Rove Formation and the disconformably overlying late Precambrian Puckwunge sandstone and North Shore Volcanic Group; the south sides moved upward relative to the north sides. These faults and associated joints were the loci of emplacement of 'early mafic' dikes of ilmenite-bearing diabase, which probably correlate with the 'Logan intrusions'. Subsequently, east-northeastward trending olivine diabase sills and dikes were emplaced in the Rove Formation and the North Shore Volcanic Group, and they cross-cut the early mafic dikes and sills. The third event occurred after cessation of igneous activity; two sets of regional joints (N 14 °W and N 53 °E) were formed, apparently as a result of fracturing accompanying initial subsidence of the so-called 'Lake Superior syncline' to the southeast. The fourth event was the development of a zone of cataclastic rock trending N 65 °E from the Pigeon Point area northeastward at least 60 km. To the north of this fracture zone, bedding in the Rove Formation dips 15–25 °SE. Copper and silver mineralization was subsequently emplaced within this fracture zone.The first three tectonic events appear to represent reactivation of structures of early Precambrian age, and appear to control the general outcrop pattern. The fourth event is an entirely Keweenawan feature, and marks the beginning of subsidence of the 'Lake Superior syncline'. It may correlate in time with the deposition of the Copper Harbor Conglomerate, and other late middle Keweenawan events.

Geochemistry of North Shore Hypabyssal dikes and sills in the Midcontinent Rift of Minnesota: an example — the 47th Avenue sill

2004 ◽  
Vol 41 (7) ◽  
pp. 829-842 ◽  
Author(s):  
Karl E Seifert ◽  
James F Olmsted
Keyword(s):  
Lake Superior ◽  
Geochemical Data ◽  
Rift System ◽  
Midcontinent Rift ◽  
North Shore ◽  
Volcanic Group ◽  
The North ◽  
Midcontinent Rift System ◽  
Basalt Composition

This study presents geochemical data for several of the numerous small to large dikes and sills, including the 47th Avenue sill, exposed along the shore of Lake Superior in and north of Duluth, Minnesota. These intrusions are late magmatic features of the Proterozoic Midcontinent Rift System and together form the North Shore Hypabyssal Group. The dikes are geochemically distinct from the sills, and, when the two are exposed together, the younger dike intrudes the older sill. Dikes are primitive with Mg# up to 68, have positive εNd values, and are oriented approximately north–south with steep westerly or near vertical dips. The older sills are more evolved, usually have εNd values near or below 0, and have the same gentle easterly dip as the thick sequence of North Shore Volcanic Group flows they intrude. Dike compositions correlate best with a mixture of widespread basalt compositions types 4 and 5, with primitive geochemistry and positive εNd values, whereas sill compositions are similar to widespread basalt composition type 4 typical of most North Shore Volcanic Group flows. The 47th Avenue sill in Duluth is an evolved single intrusion North Shore Hypabyssal Group diabase sill with trough banding, sharp lower and upper contacts, and a spectacular fractured and undulating roof zone containing blocks of the overlying ferroandesite flow.

Water in the Wilderness: The Group of Seven and the Coastal Identity of Lake Superior

2021 ◽  
pp. e20200049
Author(s):  
Isabelle Gapp
Keyword(s):  
Environmental History ◽  
Lake Superior ◽  
Indigenous Communities ◽  
Coastal Lake ◽  
Group Of Seven ◽  
North Shore ◽  
The North ◽  
The People ◽  
Coastal Landscapes ◽  
History Of

This paper challenges the wilderness ideology with which the Group of Seven’s coastal landscapes of the north shore of Lake Superior are often associated. Focusing my analysis around key works by Lawren Harris, A.Y. Jackson, J.E.H. MacDonald, and Franklin Carmichael, I offer an alternative perspective on commonly-adopted national and wilderness narratives, and instead consider these works in line with an emergent ecocritical consciousness. While a conversation about wilderness in relation to the Group of Seven often ignores the colonial history and Indigenous communities that previously inhabited coastal Lake Superior, this paper identifies these within a discussion of the environmental history of the region. That the environment of the north shore of Lake Superior was a primordial space waiting to be discovered and conquered only seeks to ratify the landscape as a colonial space. Instead, by engaging with the ecological complexities and environmental aesthetics of Lake Superior and its surrounding shoreline, I challenge this colonial and ideological construct of the wilderness, accounting for the prevailing fur trade, fishing, and lumber industries that dominated during the nineteenth and early twentieth centuries. A discussion of environmental history and landscape painting further allows for a consideration of both the exploitation and preservation of nature over the course of the twentieth century, and looks beyond the theosophical and mystical in relation to the Group’s Lake Superior works. As such, the timeliness of an ecocritical perspective on the Group of Seven’s landscapes represents an opportunity to consider how we might recontextualize these paintings in a time of unprecedented anthropogenic climate change, while recognizing the people and history to whom this land traditionally belongs.

scholarly journals Climate change and angling behavior on the North shore of Lake Superior (USA)

2020 ◽  
Vol 231 ◽  
pp. 105717
Author(s):  
Adam Hestetune ◽  
Paul M. Jakus ◽  
Christopher Monz ◽  
Jordan W. Smith
Keyword(s):  
Climate Change ◽  
Lake Superior ◽  
North Shore ◽  
The North

scholarly journals An Operational Evaluation of 3 Methoprene Larvicide Formulations for Use Against Mosquitoes in Catch Basins

2018 ◽  
Vol 12 ◽  
pp. 117863021876053 ◽  
Author(s):  
Justin E Harbison ◽  
Amy B Runde ◽  
Marlon Henry ◽  
Bridget Hulsebosch ◽  
Alka Meresh ◽  
...  
Keyword(s):  
Cook County ◽  
The Other ◽  
Storm Water ◽  
Effective Control ◽  
Control Effectiveness ◽  
North Shore ◽  
The North ◽  
Control Failure ◽  
Degree Of Control ◽  
Catch Basins

Effectiveness in controlling mosquitoes in storm water catch basins in the North Shore Mosquito Abatement District (northeastern Cook County, Illinois) was determined for 3 formulations of methoprene-based larvicides (Altosid XR 150-day Briquets, Altosid 30-day Pellets, Altosid 30-day Granules) in 2017 using a pass/fail evaluation criterion, in which emergence of a single adult from pupae collected from the basin constituted a control failure. Over the course of the 16-week study, basins receiving the 150-day briquets were treated once and basins receiving the pellet and granular formulations were treated every 4 weeks, with the first treatment occurring during the last week of May. Untreated basins were also observed for comparison with the treated basins. Over the course of the study, adult mosquitoes emerged from pupae collected in 94.2% of the untreated basins that contained pupae. All of the formulations evaluated in the study demonstrated some degree of control compared with the untreated basins, with pupae successfully emerging as adults in 64.6%, 55.5%, and 21.8% of samples from 150-day briquet, 30-day tablet, and 30-day pellet–treated basins that contained pupae, respectively. Pellets reapplied every 28 days provided significantly more effective control than the other formulations. The simple pass/fail criterion for evaluating control effectiveness proved to be a useful procedure for comparing effectiveness to untreated basins and among treatments.

Rb–Sr geochronology of the Coldwell Complex, northwestern Ontario, Canada

1982 ◽  
Vol 19 (9) ◽  
pp. 1796-1801 ◽  
Author(s):  
R. Garth Platt ◽  
Roger H. Mitchell
Keyword(s):  
Upper Mantle ◽  
Lake Superior ◽  
Parental Magma ◽  
Initial Ratio ◽  
North Shore ◽  
The North ◽  
Northwestern Ontario ◽  
Alkaline Intrusion ◽  
Intrusive Rocks ◽  
Igneous Activity

The Coldwell Complex of Northwestern Ontario is North America's largest structurally and petrologically complex alkaline intrusion. Situated on the north shore of Lake Superior, it consists of at least three intrusive centres and is cross-cut by a diverse suite of coeval–cogenetic dikes. The main intrusive rocks range from gabbros to ferroaugite syenites, nepheline syenites, and quartz syenites. The dikes are predominantly lamprophyric. A seventeen point whole rock Rb–Sr isochron (MSWD 2.22) gives an age of 1044.5 ± 6.2 Ma (2σ) and an initial ratio of 0.70354 ± 0.00016 (2σ). The age is late Neohelikian and is younger than the bulk of igneous activity (Keweenawan activity) prevalent in the Lake Superior Basin during the Neohelikian. The low initial ratio indicates an upper mantle origin for the parental magma of the complex.

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