Bouguer gravity anomaly map of the northern Michigan-Lake Superior region

Joint Inversion of SPREE Receiver Functions and Surface Wave Dispersion Curves for 3‐D Crustal and Upper Mantle Structure Beneath the U.S. Midcontinent Rift

“…Seismic analyses identified 2 km of sediments sitting atop a >30‐km‐thick segment of volcanics (Vp 5.2–7.2 km/s) underlain by up to 20 km of underplated lower crust (Vp 7.0–7.3 km/s) down to a maximum sub‐axis depth of 55 km (Hamilton & Mereu, 1993; Shay & Tréhu, 1993). Combining the seismic analyses with gravity data (Klasner et al., 1979; Thomas & Teskey, 1994) and petrological analyses of exposed Keweenawan volcanics (Halls, 1969; Lippus, 1988), as well as the incorporation of geophysical interpretations of other MCR seismic lines (Chandler et al., 1989) provided the basis for models involving a large volume (up to 1.3 million km 3 ) of hot spot‐derived volcanic rift in‐fill as well as a dense (3.08 g/cm 3 ) layer of underplated lowermost crust (Hutchinson et al., 1990).…”

Lineaments and faults of Wisconsin, Minnesota, and the western part of the northern peninsula of Michigan

“…Where maps of the same area differed the most recent interpretation was depicted. Klasner and others (1979) was the primary source for faults beneath in Lake Superior.…”

“…Additional evidence for faults is provided by closely- Most of the faults in Precambrian rocks have-been inferred from geophysical data. These faults include the faults of northwestern Minnesota (Sims, 1970), most of the faults of north-central Wisconsin (Sims and others, 1978), and all underwater faults in Lake Superior (Klasner and others, 1979). Locations of many of the inferred faults are approximate.…”

“…The faults shown by Klasner and others (1979) are defined by steep gravity graidents and offsets of major gravity anomalies, but the interpreted locations of the faults could easily be in error by 5 to 10 km (3 to 6 mi.). Other interpretations of the geophysical data are possible as well.…”

A structural analysis of the Midcontinent Rift in Michigan and Minnesota

“…Further geophysical work conducted over the Lake Superior region during the 1960s and 1970s was in the form of gravity studies (Canada Department of Energy, 1974;Craddock et al, 1970;Ervin and Hammer, 1974;Weber and Goodacre, 1966;Wold and Berkson, 1977), magnetic studies (Hinze et al, 1966;White, 1966;Wold and Ostenso, 1966), heat flow (Steinhart et al, 1968), and seismic reflection studies (Wold, 1979;Wold and Ostenso, 1966;Zumberge and Gast, 1961), all of which confirmed the synclinal structure of the Lake Superior Basin and approximated thicknesses of the volcanic and sedimentary rocks. Land gravity and magnetic studies of the Keweenawan rocks in the area were published by Bacon (1966), Meshref and Hinze (1970), Oray et al (1973), and Klasner et al (1979). Paleomagnetic studies during the past 20 years (Dubois, 1962;Palmer, 1970;Books, 1972;Green and Books, 1972;Halls, 1974) determined the polarity of the basalts, while geochronological studies were undertaken by Silver and , 1963), Goldich (1968), and Van Schmus (1976 to obtain some of the ages for the Keweenawan Super Group.…”