Electromagnetic image of the Trans-Hudson orogen — THO94 transect

Abstract

Abstract:The North American Central Plains (NACP) anomaly in enhanced electric conductivity and its relationship with the Paleoproterozoic Trans-Hudson orogen (THO) has been studied under the auspices of Lithoprobe for over a decade. The NACP anomaly was the first geophysical evidence of the existence of the THO beneath the Phanerozoic sediments of the Central Plains. This anomaly, detected geomagnetically in the late 1960s, has been the subject of a number magnetotelluric studies from the early 1980s. The PanCanadian and Geological Survey of Canada experiments in the 1980s and the Lithoprobe experiments in the 1990s together comprise four east-west and one north-south regional-scale profiles in Saskatchewan perpendicular to the strike of the orogen. In this paper, data from the northernmost line, coincident with seismic line S2B, are analysed and interpreted, and are shown to be key in determining the northern extension of the NACP anomaly. Dimensionality analysis confirms the rotation of deep crustal structures eastward to Hudson Bay, as earlier proposed on the basis of broad-scale geomagnetic studies. On this profile, as with the profile at the edge of the Paleozoic sediments, the NACP anomaly is imaged as lying within the La Ronge domain, in contact with the Rottenstone domain, and structurally above the Guncoat thrust, a late compressional feature. The location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds, by graphite, or by a combination of both. Our interpretation of the data is consistent with that from other profiles, and suggests that the NACP anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the THO beneath the Hearne craton. On the southern part of this profile, a resistive structure is identified as the Sask craton, suggesting that Proterozoic rocks are above Archean rocks in the THO. 493Résumé : L'anomalie des plaines du centre de l'Amérique du Nord en conductivité électrique amplifiée et sa relation avec l'orogène trans-hudsonien (Paléoprotérozoïque) ont été étudiées dans le cadre du projet Lithoprobe depuis plus d'une décennie. Cette anomalie a été la première évidence géophysique de l'existence de l'orogène trans-hudsonien sous les sédiments phanérozoïques des plaines centrales. Cette anomalie, détectée par des techniques géomagnétiques à la fin des années 1960, a été le sujet de nombreuses études magnétotelluriques (MT) à partir du début des années 1980. Les expériences de PanCanadian et de la Commission géologique du Canada dans les années 1980, ainsi que celles du projet Lithoprobe dans les années 1990, comprennent ensemble, à l'échelle régionale, en Saskatchewan, quatre profils est-ouest et un profil nord-sud qui sont perpendiculaires à la direction de l'orogène. Dans cet article, les données de la ligne la plus au nord, coïncidant avec la ligne sismique S2B, sont analysées et interprétées; elles s'avèrent ...

A tale of two orogens: Crustal processes in the Proterozoic Trans‐Hudson and Grenville Orogens, eastern Canada

“…Magnetotelluric studies [ Ferguson et al , ; Garcia and Jones , ; Jones et al , ] show a complex resistivity structure with good agreement with the interpretations from seismic reflection. Archean crustal material, including the Sask craton, is more resistive than the crust beneath Proterozoic domains.…”

Structural geology and tectonics of the paleoproterozoic rocks of the Mount Rushmore Quadangle, Black Hills, Souh Dakota

“…Possibly the least well understood geophysical feature associated with Laurentian assembly is the North American Central Plains electrical conductivity anomaly (NACP; Figure 38). Extensive studies have shown that the NACP extends from northern Canada into the Dakotas (e.g., Alabi et al, 1975;Camfield and Gough, 1975;Jones et al, 1993Jones et al, , 2005Garcia and Jones, 2005). Camfield and Gough (1977) suggested that the NACP marks the Proterozoic collisional zone from the southern Rockies to northern Canada.…”

“…Jones and Savage (1986) relocated the NACP boundary eastward, where it coincides with the eastern boundary of the later discovered Dakota block (Nelson, 1993;Jones et al,1993;Baird et al, 1996). The cause and tectonic significance of the NACP is still under investigation (e.g., Jones et al, 2005;Garcia and Jones, 2005;Ferguson et al, 2005;Evans et al, 2003Evans et al, , 2005. Most workers (e.g., Jones et al, 1997Jones et al, , 2005Garcia and Jones, 2005;Ferguson et al, 2005;Evans et al, 2003Evans et al, , 2005 associate the NACP with sulfide mineralization, not graphite mineralization (Camfield and Gough, 1977).…”

“…The cause and tectonic significance of the NACP is still under investigation (e.g., Jones et al, 2005;Garcia and Jones, 2005;Ferguson et al, 2005;Evans et al, 2003Evans et al, , 2005. Most workers (e.g., Jones et al, 1997Jones et al, , 2005Garcia and Jones, 2005;Ferguson et al, 2005;Evans et al, 2003Evans et al, , 2005 associate the NACP with sulfide mineralization, not graphite mineralization (Camfield and Gough, 1977). Geologically, the NACP has been interpreted to be related to "carbonated and metamorphosed slate rocks" deposited in foreland basins (Boerner et al, 1996) or sulfide deposits in fold-hinges of volcanic rocks (Jones et al, 1997.…”

“…Based largely on seismic reflection and refraction (e.g. Baird et al, 1995Baird et al, , 1996Lucas et al, 1993Lucas et al, , 1994Nelson et al, 1993;White et al, 1994;Latham et al, 1988), magnetotelluric (e.g., Jones et al, 1993Jones et al, , 1995Garcia and Jones, 2005), electromagnetic (e.g. Jones et al, 2005 and references therein; Toft et al, 1993), geomagnetic depth sounding (e.g., Jones et al, 2005;Camfield and Gough, 1977;Camfield et al, 1970), paleomagnetic (e.g., Stauffer, 1984) and gravity (e.g.…”