Crustal refraction surveys across the Trans‐Hudson Orogen/Williston Basin of south central Canada

Abstract

Eight reversed seismic refraction profiles have been recorded across the Phanerozoic Williston sedimentary basin that overlies the margins of the Superior and Wyoming Arcbean cratons and the Proterozoic Trans-Hudson orogen. These clata have been modeled using two-dimensional ray-tracing techniques to match the times and amplitudes of primary and coherent secondary arrivals. Within the southern extension of the Superior craton margin (Thompson belt) a high-velocity (•6.4 km/s) lid overlies a narrow region of high electrical conductivity, and a zone of westerly dipping reflections is nearly coincident with a weak velocity discontinuity that seems to delineate the western edge (Thompson fault) of the craton margin. Complex zones of low-velocity material and the North American Central Plains electrical conductivity anomaly are concluded to lie within the southern extension of the Reindeer-South Indian Lakes terrain, a component of the Trans-Hudson orogen. A high-velocity (•> 7.0 km/s) lower crustal layer, which represents a zone of complexity separating "normal" crust from the upper mantle, extends throughout the region. The crust is relatively thick, with depths to Moho varying smoothly between 41 and 48 km. There is no evidence in the relatively low-resolution seismic refraction data for abrupt changes in the level of the Moho, but there may be a minor (3-4 km) thinning of the crust near the center of the Williston Basin. iments were the eastern edge of the Superior craton, the Trans-Hudson orogen [Hoffman, 1981], the North American Central Plains (NACP) electrical conductivity anomaly [Camfield and Gough, 1977], and the Williston Basin. During the three field campaigns, approximately 2250 km of reversed inline refraction data were collected along eight profiles arranged in the following geometry: (1) four N-S lines (A, C, D, and E), three of which were parallel to the major tectonic axes of the buried Precambrian shield, (2) three lines (E, F, and G) in a triangular configuration (included one of the N-S lines), and (3) two E-W lines (B and H) that cut across the axis of the Trans-Hudson orogen and that connected most of the other lines. Fan shooting into the three sides of the equilateral triangle E, F, and G was also performed. Preliminary analyses of parts of these data have been published by Green et al. [1980], Delandro and Moon [1982], Hajnal et al. [1984], and Kanasewich and Chiu [1985]. The interpretation of lines A and B by Green et al. [1980] was based on inversions of first arrival times assuming simple dipping models and synthetic seismogram analyses using the Fuchs and Muller [1971] reflectivity algorithm. Delandro and Moon's [1982] interpretation of the same lines incorporated slightly more complex structures using the Whittall and Clowes [1979] two-dimensional ray-tracing program and the WKBJ method for calculating one-dimensional synthetic seimograms [Chapman, 1978]. The interpretation of lines C, D, • Now at Texaco Canada Resources, and H (western shot) by Hajnal et al. [1984] was based on one-dim...

Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining velocity and density structure in the upper crust

“…The Williston Basin provides a useful test case for evaluating subsequent inversions including the H/V ratio because it is known to have a total sedimentary thickness of ∼3 km, with weakly consolidated sediments in the upper few hundred meters underlain by multiple sedimentary strata of Ordovician to Cretaceous ages [ Blackwell et al , 2006; Gerhard et al , 1982]. Active source refraction data are consistent with an average Vp of ∼3.5 km/s for the sedimentary layer [ Hajnal et al , 1984; Morel‐a‐l'Huissier et al , 1987], though high‐frequency wellbore data show that distinct sedimentary units exhibit large variations [e.g., Spikes , 2011]. Using a reasonable range of sedimentary Vp/Vs values (1.65–2 [ Mavko et al , 1998]) implies a Vs of 1.75–2.12 km/s for the upper 3 km, whereas Model 1 finds a much higher value of 3 km/s.…”

Chapter 15: Crustal structure of the continental interior

“…The Grenville province is labeled GR, and the Basin and Range province is labeled BR. on July 3, 2015 memoirs.gsapubs.org Downloaded from Steinhart and Meyer, 1961;Tuve, 1955 AP24 E. Tennessee Warren, 1968;Prodehl and others, 1984AP25 S. Appalachian Time Terms Long and Liow, 1986AP26 S. Appalachian Long and Liow, 1986AP27 N. Georgia Dorman, 1972AP28 Georgia-South Carolina Kean and Long, 1980 E. Basin and Range Berg and others, 1960 BR8 American Falls-Flaming Gorge Willden, 1965BR9 Bingham -N Martin, 1978BR10 Bingham -S Keller and others, 1975BR11 Bingham -NE Braile and others, 1974BR32 N. Utah Tatel and Tuve, 1955Steinhart and Meyer, 1961 Gasbuggy -SW Warren and Jackson, 1968CP3 Gasbuggy -S Toppozada and Sanford, 1976CP4 Gila Bend-Sunrise Warren, 1969Healy and Warren, 1969 CP5 Blue Mountain-Bylas Warren, 1969;Healy and Warren, 1969 CP6 Bilby -SE Archambeau and others, 1969 CP7 Arizona-New Mexico Tatel and Tuve, 1955;Steinhart and Meyer, 1961 Green and others, 1980;Delandro and Moon, 1982 Morel-a-L'Huissier and others, 1987 MC3 Superior-Churchill -EW Green and others, 1980;Delandro andMoon, 1982 Morel-a-L'Huissier andothers, 1987;Hajnal, 1986 MC4 W. Manitoba Hajnal andothers, 1984;Morel-a-L'Huissier andothers, 1987 MC5 N. Minnesota Tuve, 1953;Steinhart and Meyer, 1961;Tatel and oth...…”

Generation of continental rifts, basins, and swells by lithosphere instabilities

“…We now assess whether the flow can induce the geological structures that are observed at Earth's surface. This is also true for the Williston basin, below which no significant crustal thinning can be detected [Morel-à-l'Huissier et al, 1987;Nelson et al, 1993]. Indeed, one of the most remarkable features of intracontinental rifts, swells, and basins, as well as the Cameroon line, is the lack of significant crustal thinning.…”

“…There is only a very modest (%2 km) change of crustal thickness beneath the southern Oklahoma aulacogen and it is a thickness increase [Keller and Baldridge, 2006]. This is also true for the Williston basin, below which no significant crustal thinning can be detected [Morel-à-l'Huissier et al, 1987;Nelson et al, 1993]. Indeed, Nelson et al [1993] state that the geophysical evidence "militates against the idea that crustal stretching played a significant role in the formation of the basin."…”