Lake Superior Basin Segment of the Midcontinent Rift System

10.1029/ft344 ◽  
1989 ◽  
Keyword(s):  
Lake Superior ◽  
Rift System ◽  
Midcontinent Rift ◽  
Midcontinent Rift System

Possible extension of the Midcontinent Rift in west Texas and eastern New Mexico

1994 ◽  
Vol 31 (4) ◽  
pp. 709-720 ◽  
Author(s):  
Donald C. Adams ◽  
G. Randy Keller
Keyword(s):  
New Mexico ◽  
Lake Superior ◽  
Igneous Rocks ◽  
Rift System ◽  
Central Basin ◽  
Midcontinent Rift ◽  
Sacramento Mountains ◽  
Midcontinent Rift System ◽  
Southern Oklahoma ◽  
Igneous Activity

The Midcontinent Rift System forms one of the most prominent gravity features in North America. The recognized geophysical anomaly extends in an arc from southern Oklahoma to Lake Superior and then into southern Michigan. The Midcontinent Rift System was active between 1185–1010 Ma, as indicated in the Lake Superior region by age determinations on intrusive igneous rocks. We suggest that the period of formation of the Midcontinent Rift was also a time of extensive igneous activity in Texas and New Mexico. This activity is represented by intrusions beneath the Central basin platform (Texas and New Mexico), intrusions which crop out at the Pajarito Mountain in the Sacramento Mountains (New Mexico), a basaltic debris flow in the Franklin Mountains (Texas), basalt flows at Van Horn (Texas), and the Crosbyton geophysical anomaly (east of Lubbock, Texas). These bodies and other bodies located by geophysical anomalies and wells drilled into mafic Precambrian rocks may be related to the Midcontinent Rift System. Alternatively this magmatism could be related to Grenville age tectonics in Texas. The mafic igneous rocks in this area form a 530 km diameter Middle Proterozoic igneous province, which formed between 1070 and 1220 Ma. Comparison of the Midcontinent Rift System and its extensions proposed here with the Mesozoic and Cenozoic African rift systems indicates that these features are of comparable scale and complexity.

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.

The Mesoproterozoic Midcontinent Rift System, Lake Superior Region, USA

2001 ◽  
Vol 141-142 ◽  
pp. 421-442 ◽  
Author(s):  
R.W Ojakangas ◽  
G.B Morey ◽  
J.C Green
Keyword(s):  
Lake Superior ◽  
Rift System ◽  
Midcontinent Rift ◽  
Midcontinent Rift System

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

1997 ◽  
Vol 34 (4) ◽  
pp. 504-520 ◽  
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).

Interpretation of seismic reflection and gravity profile data in western Lake Superior

1994 ◽  
Vol 31 (4) ◽  
pp. 652-660 ◽  
Author(s):  
John L. Sexton ◽  
Harvey Henson Jr.
Keyword(s):  
Fault Zone ◽  
Seismic Data ◽  
Seismic Reflection ◽  
Lake Superior ◽  
Rift System ◽  
Isle Royale ◽  
Midcontinent Rift ◽  
Detachment Faults ◽  
Western Lake ◽  
Midcontinent Rift System

The interpretation of 1047 km of seismic reflection data collected in western Lake Superior is presented along with reflection traveltime contour maps and gravity models to understand the overall geometry of the Midcontinent Rift System beneath the lake. The Douglas, Isle Royale, and Keweenaw fault zones, clearly imaged on the seismic profiles, are interpreted to be large offset detachment faults associated with initial rifting. These faults have been reactivated as reverse faults with 3–5 km of throw. The Douglas Fault Zone is not directly connected with the Isle Royale Fault Zone. The seismic data has imaged two large basins filled with more than 22 km of middle Keweenawan pre-Portage Lake and Portage Lake volcanic rocks and up to 8 km of upper Keweenawan Oronto and Bayfield sedimentary rocks. These basins persisted throughout Keweenawan time and are separated by a ridge of Archean rocks and a narrow trough bounded by the Keweenaw Fault Zone to the south. Another fault zone, herein named the Ojibwa fault zone, previously interpreted as the northeastern extension of the Douglas Fault Zone, has been reinterpreted as a reverse fault that closely follows the ridge of Archean rocks. Previous researchers have stated that neighboring segments of the rift display alternating polarity of basins associated with large detachment faults. Accommodation zones have been previously interpreted to exist between rift segments; however, the seismic data do not image a clearly identifiable accommodation zone separating the two basins in western Lake Superior. Thus, the seismic profile may lie directly above the pivot of a scissors-type accommodation fault zone, there is no vertical offset associated with the zone, or the zone does not exist. Seismic data interpretations indicate that application of a simple alternating polarity basin – accommodation zone model is an oversimplification of the complex geological structures associated with the Midcontinent Rift System.

Crustal structure of the Midcontinent rift system in eastern Lake Superior from controlled-amplitude analysis of GLIMPCE deep reflection seismic data

1992 ◽  
Vol 29 (4) ◽  
pp. 636-649 ◽  
Author(s):  
C. Samson ◽  
G. F. West
Keyword(s):  
Crustal Structure ◽  
Lake Superior ◽  
Bottom Topography ◽  
Seismic Survey ◽  
Rift System ◽  
Central Basin ◽  
Midcontinent Rift ◽  
Reflection Seismic ◽  
Midcontinent Rift System ◽  
Lake Bottom

The reprocessing of line F of the GLIMPCE deep marine reflection seismic survey according to controlled-amplitude principles provides new insights on the crustal structure of the Midcontinent rift system in eastern Lake Superior. The insertion of refraction static corrections in the processing sequence was crucial to recover the lateral continuity and amplitude strength of reflectors under rough lake-bottom topography. Coherent noise consisting mainly of waves scattered by irregularities on die lake bottom and first-order water reverberations was best attenuated by use of multiple passes of velocity filtering in different seismic domains rather than by trace editing. Overall, the variations in reflection style and strength on our final stacked and trace envelope sections allow for the identification of broad geological domains. Lava flows and postrift sediments can be traced uninterrupted across most of the rift basin, which is bounded to the north by a complex region of secondary sagging, felsic volcanism, and (or) intrusives, and to the south by the Keweenaw fault. The crust–mantle transition zone is characterized by both a smooth amplitude anomaly and by discontinuous packages of diffractions and reflections. It is overlain by an anomalous transparent lower crustal domain beneath the central basin. These observations suggest that, during rifting, magma rose from a layer of underplated material located at the base of the crust to the surface through numerous small feeders. They do not, however, fully exclude die possibility of complete crustal separation.

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