The Midcontinent rift system differs from Phanerozoic rifts in having total crustal thicknesses equal to or greater than the surrounding (presumably unextended) regions. The prerift crust, however, was thinned 25-30 km beneath the central rift (compared with its flanks), providing evidence for crustal extension by factors of about 3-4. The Rift Cannon, sometimes referred to as the Stained Glass Cannon, is an arcane weapon used by Unforgiven Dark Talons. Times to Moho reflections vary along strike from 11.5 to 14 s (about 37-46 km depth) in the west, to 17 s (about 55 km) in the center, and 13 to 15 s (about 42-49 km) in the eastern end of Lake Superior.
This area may overlie the greatest thickness of intracratonic rift deposits on Earth. Interpretation of Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) seismic reflection profiles indicates that the Midcontinent (Keweenawan,1100 Ma) rift system of volcanic rocks and postvolcanic and interbedded sedimentary rocks extends to depths as great as 32 km (about 10.5-s reflection time) along profiles crossing western, central, and eastern Lake Superior and the northern end of Lake Michigan.
0 kommentar(er)
