THE EARTH'S CRUST BENEATH LAKE SUPERIOR--AN INTERPRETATION OF CROSS-STRUCTURE SEISMIC REFRACTION PROFILES

• Main Author: LUETGERT, JAMES HOWARD
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1982
• Subjects: Geophysical engineering; Geophysics
• ISBN: 9798205151276

Crustal cross sections for several seismic refraction lines in Lake Superior provide structural models of the upper 10-15 km of crust. These models substantiate the view of western Lake Superior as an asymmetric synclinal trough whose axis trends along the south shore of the lake. Travel-time offsets are used to confirm the westward and eastward extension of the Isle Royale Fault and to demonstrate the existence of a 30-km-wide fault-bounded feature in the center of western Lake Superior. This feature is interpreted as a portion of the uplifted northern boundary of the rift basin. Profiles in eastern Lake Superior show the thick accumulation of Keweenawan volcanics coincident with the rift axis trending south toward the Michigan Basin from a point east of the Keweenaw peninsula. Faults bounding the central rift may be inferred, but not precisely described from the eastern data. Gravity models for the entire crust, which include structures deduced from seismic refraction data, clarify the positions of the high-density from seismic refraction data, clarify the positions of the high-density axial zone of the Midcontinent Rift System beneath Lake Superior. An apparent broadening of the rift in the eastern basin coincident with its change in direction supports the view of Lake Superior as the site of an ancient triple junction. Although travel-time offsets are identified on two of the seismic profiles that might support the existence of the hypothesized Thiel Fault transecting the eastern lake, the dissimilarity of the modeled features suggests that they are related only in being responses to the juncture of rift arms.