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

Geophysical Research Letters
By: , and 

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Abstract

We 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 mafic composition of the graben fill and constrain its total thickness to be at least 30km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55–60km) 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 100km 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.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data
Series title Geophysical Research Letters
DOI 10.1029/91GL00826
Volume 18
Issue 4
Year Published 1991
Language English
Publisher American Geophysical Union
Contributing office(s) Woods Hole Coastal and Marine Science Center, Coastal and Marine Geology Program
Description 4 p.
First page 625
Last page 628
Country Canada, United States
Other Geospatial Lake Superior
Online Only (Y/N) N
Additional Online Files (Y/N) N