Publication 99
Electromagnetic image of the Trans-Hudson orogen: THOT94 transect
Garcia, X. and A.G. Jones
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.
Source
Canadian Journal of Earth Sciences, 42, 479-493, 2005.
MTNet Home Page
Alan's Home Page
Alan G Jones / 21 April 2006 /
alan-at-cp.dias.ie