Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data

Journal Article · Mon Apr 01 04:00:00 EST 1991 · Geophysical Research Letters (American Geophysical Union); (United States)

DOI:https://doi.org/10.1029/91GL00826· OSTI ID:5598153

Trehu, A; Shay, J ^[1]; Morel-a-l'Huissier, P; Milkereit, B ^[2]; Meyer, R; Jefferson, T; Shih, X R ^[3]; Karl, J ^[4]; Mereu, R; Epili, D ^[5]; Sexton, J; Wendling, S ^[6]; Hajnal, Z; Chan, W K ^[7]; Hutchison, D ^[8]

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1. Oregon State Univ., Corvallis (United States)
2. Geological Survey of Canada, Ottawa, Ontario (Canada)
3. Univ. of Wisconsin, Madison (United States)
4. Univ. of Saskatchewan, Saskatoon (Canada)
5. Univ. of Wisconsin, Oshkosh (United States)
6. Univ. of Western Ontario, London (Canada)
7. Southern Illinois Univ., Carbondale (United States)
8. Geological Survey, Woods Hole, MA (United States)

The authors present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly magic composition of the graben fill and constrain its total thickness to be at least 30 km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55-60 km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100 km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

• OSTI ID: 5598153
• Journal Information: Geophysical Research Letters (American Geophysical Union); (United States), Journal Name: Geophysical Research Letters (American Geophysical Union); (United States) Vol. 18:4; ISSN 0094-8276; ISSN GPRLA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
CONTINENTAL CRUST
DIMENSIONS
EARTH CRUST
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
GRAVITY SURVEYS
GREAT LAKES
LAKE SUPERIOR
LAKES
MAPS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
REFLECTIVITY
RIFT ZONES
SEISMIC SURVEYS
SURFACE PROPERTIES
SURFACE WATERS
SURVEYS
TECTONICS
THICKNESS
WAVE PROPAGATION