Publication 120
Geoelectric structure of the northeastern Williston Basin and underlying Precambrian lithosphere.
Gowan, E.J., I.J. Ferguson, A.G. Jones and J.A. Craven
Abstract
Magnetotelluric measurements were made in southern Manitoba, Canada as part of the
POLARIS project, in order to image the northeastern part of the Williston basin and
underlying Precambrian lithosphere. Data collected at 21 sites along a 400 km east-west
profile at 49.5° N and a 300 km north-south profile at 100° W were analyzed using robust
spectral analysis, tensor decomposition, and two-dimensional inversion. The resulting
resistivity models allow subdivision of the Williston basin into three layers: an upper layer of
1 to 5 ohm·m corresponding to Mesozoic and upper Paleozoic rocks, a 20 to 50 O·m layer
corresponding to lower Paleozoic carbonate rocks, and a 2 to 3 O·m layer corresponding to the
Ordovician Winnipeg Formation. Deeper penetrating MT responses, interpreted with other
MT data, reveal a region in the westernmost Superior craton with a southwest-northeast
geoelectric fabric that is oblique to subprovince boundaries. The observations can be
explained by Proterozoic deformation extending several hundred kilometres east of the
Superior boundary zone or by a separate Archean terrane adjacent to the boundary. The
TOBE (Thompson belt) conductor in the south of the study area has previously been
interpreted as part of the Superior boundary zone. However, MT results show that the
conductor does not extend continuously along the margin of the zone and they define
conductors on the margin of the Sask craton. The results suggest the TOBE conductor is
associated with the Sask craton margin. MT results indicate significant along-strike variation
of the Superior boundary zone in southern Manitoba.
Source
Canadian Journal of Earth Sciences, 46, 441-464, 2009.
MTNet Home Page
Alan's Home Page
Alan G Jones / 04 June 2009 /
alan-at-cp.dias.ie