Compressional-wave seismic velocity, bulk density, and their empirical relations for geophysical modeling of the Midcontinent Rift System in the Lake Superior region

First posted July 19, 2023 For additional information, contact: Center Director, Geophysics, and Geochemistry Science CenterU.S. Geological SurveyBox 25046, Mail Stop 973Denver, CO 80225 Compressional-wave seismic velocity (velocity) bulk density (density) data were compiled from published sources for rock suites earth materials that are significant geophysical modeling of the Mesoproterozoic Midcontinent Rift System in Lake Superior region. The include laboratory measurements outcrop drill core samples, refraction studies, a sonic log 1.5-kilometer-deep exploration well. Rock basalts Keweenawan Supergroup, Oronto Group sedimentary rocks (divided into arenaceous versus argillaceous units), several formations overlying have been correlated across area. Intrusive units diabase, gabbro, felsic igneous rocks. Other geologic important region Archean crystalline crust, Paleoproterozoic metasedimentary rocks, lower Holocene to Pleistocene surficial deposits.Empirical velocity-density relations each suite determined by comparing relations, such as Nafe-Drake curve, Gardner’s relation, best-fit equations developed different types studies. Graphical representations these provide way easily understand how differ between tectonic settings type. Overlaps ranges especially implications interpretation data. Important examples similar velocities but differing densities basalt Supergroup. Similar found diabase gabbro. In addition, expected type show high-velocity intervals (6.9–7.1 kilometers per second) interpreted previous seismic-reflection studies more likely indicate or suggesting interpretations may warrant consideration.