Constraining the thermal history of the North American Midcontinent Rift System using carbonate clumped isotopes and organic thermal maturity indices

2017 ◽  
Vol 294 ◽  
pp. 53-66 ◽  
Author(s):  
Timothy M. Gallagher ◽  
Nathan D. Sheldon ◽  
Jeffrey L. Mauk ◽  
Sierra V. Petersen ◽  
Nur Gueneli ◽  
...  
Keyword(s):  
North American ◽  
Thermal History ◽  
Rift System ◽  
Clumped Isotopes ◽  
Thermal Maturity ◽  
Midcontinent Rift ◽  
The North ◽  
Maturity Indices ◽  
Midcontinent Rift System ◽  
History Of

Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution

1997 ◽  
Vol 34 (4) ◽  
pp. 476-488 ◽  
Author(s):  
D. W. Davis ◽  
J. C. Green
Keyword(s):  
North American ◽  
Lake Superior ◽  
Flood Basalt ◽  
North American Plate ◽  
Rift System ◽  
Midcontinent Rift ◽  
Subsidence Rate ◽  
The North ◽  
Western Lake ◽  
Midcontinent Rift System

Volcanism in the Midcontinent rift system lasted between 1108 and 1086 Ma. Rates of flood-basalt eruption and subsidence in the western Lake Superior region appear to have been greatest at the beginning of recorded activity (estimated 5 km/Ma subsidence rate at 1108 Ma) and rapidly waned over a period of 1–3 Ma during a magnetically reversed period. The age of the paleomagnetic polarity reversal is now constrained to be between 1105 ± 2 and 1102 ± 2 Ma. A resurgence of intense volcanism began at 1100 ± 2 Ma in the North Shore Volcanic Group and lasted until 1097 ± 2 Ma. This group contains a ca. 7 Ma time gap between magnetically reversed and normal volcanic sequences. A similar disconformity appears to exist in the upper part of the Powder Mill Group. The average subsidence rate during this period was approximately 3.7 km/Ma. Latitude variations measured from paleomagnetism on dated sequences indicate that the North American plate was drifting at a minimum rate of 22 cm/year during the early history of the Midcontinent rift. An abrupt slowdown to approximately 8 cm/year occurred at ca. 1095 Ma. These data support a mantle-plume origin for Midcontinent rift volcanism, with the plume head attached to and drifting with the continental lithosphere. Resurgence of flood-basalt magmatism at 1100 Ma may have been caused by extension of the superheated lithosphere following continental collision within the Grenville Orogen to the east.

Geophysical investigations and crustal structure of the North American Midcontinent Rift system

1992 ◽  
Vol 213 (1-2) ◽  
pp. 17-32 ◽  
Author(s):  
William J. Hinze ◽  
David J. Allen ◽  
Adam J. Fox ◽  
Don Sunwood ◽  
Timothy Woelk ◽  
...  
Keyword(s):  
Crustal Structure ◽  
North American ◽  
Rift System ◽  
Midcontinent Rift ◽  
The North ◽  
Midcontinent Rift System ◽  
Geophysical Investigations

Geophysical investigations and crustal structure of the North American Midcontinent Rift system

1992 ◽  
pp. 17-32 ◽  
Author(s):  
William J. Hinze ◽  
David J. Allen ◽  
Adam J. Fox ◽  
Don Sunwood ◽  
Timothy Woelk ◽  
...  
Keyword(s):  
Crustal Structure ◽  
North American ◽  
Rift System ◽  
Midcontinent Rift ◽  
The North ◽  
Midcontinent Rift System ◽  
Geophysical Investigations

Seismic history of Minnesota and its geological significance

1981 ◽  
Vol 71 (1) ◽  
pp. 199-210 ◽  
Author(s):  
Harold M. Mooney ◽  
G. B. Morey
Keyword(s):  
Maximum Intensity ◽  
Rift System ◽  
Tectonic Zone ◽  
Midcontinent Rift ◽  
Western Margin ◽  
The North ◽  
Midcontinent Rift System ◽  
History Of ◽  
Tectonic Features ◽  
Felt Area

abstract Twelve earthquakes have been documented in Minnesota in the last 120 yr. The first nine were felt, whereas the last three (all in 1979) were detected instrumentally by a six-element seismic array which has recently been put into operation. Estimated magnitudes range from 0.1 (instrumental only) to 4.8, with four of magnitude 4.3 or greater. The highest intensity values were VI to VII. Depths where obtainable are estimated at 5 to 20 km. The best documented event occurred on 9 July 1975 near Morris, Minnesota, with a magnitude of 4.6, a maximum intensity of VI, and a felt area of 82,000 km2 covering parts of four states. The event was recorded to epicentral distances of at least 38°. The epicenters show a clear relationship to tectonic features of the state. Four epicenters lie along the newly defined Great Lakes Tectonic Zone, an east-northeast-trending belt extending across several states and into Canada. The zone separates 3,000 to 3,600 m.y. rocks of a gneissic terrane to the south from 2,700 m.y. rocks of a greenstone-granite terrane to the north. Four other events lie on known major northwest-trending faults in the greenstone-granite terrane. Two and possibly three events are associated with the western margin of the Midcontinent Rift System.

Re-Os isotopic compositions of Midcontinent rift system picrites: implications for plume – lithosphere interaction and enriched mantle sources

1997 ◽  
Vol 34 (4) ◽  
pp. 489-503 ◽  
Author(s):  
Steven B. Shirey
Keyword(s):  
Isotopic Composition ◽  
Rift System ◽  
Magmatic Activity ◽  
Midcontinent Rift ◽  
The North ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Midcontinent Rift System ◽  
Sedimentary Fill ◽  
Nearly Continuous

Picrites and tholeiites from the Mamainse Point Formation, a 5.3 km thick section of Keweenawan (1100 Ma) volcanic and sedimentary fill on the eastern flank of the central portion of the Midcontinent rift system, contain a nearly continuous record of rift magmatic activity. Picrites occur primarily in the lowermost two units of the formation. In this study, they are compared to rarely exposed, slightly older Keweenawan basalts from the North Shore Volcanic Group and the Powder Mill Group to constrain mantle source compositions during early phases of rift magmatic activity. The most primitive picrites analyzed have low Re content (0.069–0.18 ppb), high Os content (0.8–2.1 ppb), and low 187Re/188Os (0.28–1.18). A Re–Os isochron with an age of 1128 ± 54 Ma and an initial 187Os/188Os of 0.1267 ± 0.0013 (γOs = +5.7) was obtained from a 24-point isochron on all but two analyzed samples. The Re–Os data, regressed separately for the older basalts, and the groups 1 and 2 samples from the Mamainse Point Formation, have barely resolvable initial 187Os/188Os that decrease up-stratigraphy from initial γOs(1100) of +12.2 to +6.2 and +4.2, respectively, and couple with changes in initial Nd isotopic composition. These data can be explained by mixing of melts of an enriched mantle plume and unradiogenic continental lithospheric mantle. A radiogenic initial Os isotopic composition (γOs of +8 or higher) for the Keweenawan plume marks the first known appearance of demonstrably radiogenic plume-derived magmas on Earth. Plume-derived magmas with radiogenic Os signatures are more common later. The radiogenic Os signatures of Keweenawan plume magmas may mark the appearance of melts derived from mantle containing recycled slab components from late Archean subduction.

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.

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