U-PB DETRITAL GEOCHRONOLOGY AND HF ISOTOPIC ANALYSES FROM MESOPROTEROZOIC KEWEENAWAN SUPERGROUP STRATA OF THE MIDCONTINENT RIFT, NORTHERN MICHIGAN

A hydrogeologic model of stratiform copper mineralization in the Midcontinent Rift System, Northern Michigan, USA

Geofluids ◽

10.1111/j.1468-8123.2004.00062.x ◽

2004 ◽

Vol 4 (1) ◽

pp. 1-22 ◽

Cited By ~ 14

Author(s):

J. B. Swenson ◽

M. Person ◽

J. P. Raffensperger ◽

W. F. Cannon ◽

L. G. Woodruff ◽

...

Keyword(s):

Rift System ◽

Midcontinent Rift ◽

Copper Mineralization ◽

Midcontinent Rift System ◽

Northern Michigan

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Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: implications for multiple mantle sources during rift development

Canadian Journal of Earth Sciences ◽

10.1139/e17-041 ◽

1997 ◽

Vol 34 (4) ◽

pp. 504-520 ◽

Cited By ~ 53

Author(s):

Suzanne W. Nicholson ◽

Klaus J. Schulz ◽

Steven B. Shirey ◽

John C. Green

Keyword(s):

Mantle Source ◽

Lake Superior ◽

Flood Basalt ◽

Great Depth ◽

Rift System ◽

Midcontinent Rift ◽

Western Lake ◽

Isotopic Analyses ◽

Mantle Sources ◽

Midcontinent Rift System

Magmatism that accompanied the 1.1 Ga Midcontinent rift system (MRS) is attributed to the upwelling and decompression melting of a mantle plume beneath North America. Five distinctive flood-basalt compositions are recognized in the rift-related basalt succession along the south shore of western Lake Superior, based on stratigraphically correlated major element, trace element, and Nd isotopic analyses. These distinctive compositions can be correlated with equivalent basalt types in comparable stratigraphic positions in other MRS localities around western Lake Superior. Four of these compositions are also recognized at Mamainse Point more than 200 km away in eastern Lake Superior. These regionally correlative basalt compositions provide the basis for determining the sequential contribution of various mantle sources to flood-basalt magmatism during rift development, extending a model originally developed for eastern Lake Superior. In this refined model, the earliest basalts were derived from small degrees of partial melting at great depth of an enriched, ocean-island-type plume mantle source (εNd(1100) value of about 0), followed by magmas representing melts from this plume source and interaction with another mantle source, most likely continental lithospheric mantle (εNd(1100) < 0). The relative contribution of this second mantle source diminished with time as larger degree partial melts of the plume became the dominant source for the voluminous younger basalts (εNd(1100) value of about 0). Towards the end of magmatism, mixtures of melts from the plume and a depleted asthenospheric mantle source became dominant (εNd(1100) = 0 to +3).

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PGE-Enrichment in Magnetite-Bearing Olivine Gabbro: New Observations from the Midcontinent Rift-Related Echo Lake Intrusion in Northern Michigan, USA

Minerals ◽

10.3390/min9010021 ◽

2018 ◽

Vol 9 (1) ◽

pp. 21 ◽

Cited By ~ 2

Author(s):

Alexander Koerber ◽

Joyashish Thakurta

Keyword(s):

Sulfide Minerals ◽

Group Element ◽

Olivine Gabbro ◽

Rock Unit ◽

Midcontinent Rift ◽

Upper Peninsula ◽

Titaniferous Magnetite ◽

Sulfide Melt ◽

Sudden Decrease ◽

Northern Michigan

The Echo Lake intrusion in the Upper Peninsula (UP) of Michigan, USA, was formed during the 1.1 Ga Midcontinent Rift event in North America. Troctolite is the predominant rock unit in the intrusion, with interlayered bands of peridotite, mafic pegmatitic rock, olivine gabbro, magnetite-bearing gabbro, and anorthosite. Exploratory drilling has revealed a platinum group element (PGE)-enriched zone within a 45 m thick magnetite-ilmenite-bearing olivine gabbro unit with grades up to 1.2 g/t Pt + Pd and 0.3 wt. % Cu. Fine, disseminated grains of sulfide minerals such as pyrrhotite and chalcopyrite occur in the mineralized interval. Formation of Cu-PGE-rich sulfide minerals might have been caused by sulfide melt saturation in a crystallizing magma, which was triggered by a sudden decrease in fO2 upon the crystallization and separation of titaniferous magnetite. This PGE-enriched zone is comparable to other well-known reef-like PGE deposits, such as the Sonju Lake deposit in northern Minnesota.

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