De. Boerner et al., THE GREAT FALLS TECTONIC ZONE - SUTURE OR INTRACONTINENTAL SHEAR ZONE, Canadian journal of earth sciences, 35(2), 1998, pp. 175-183
The Great Falls Tectonic Zone is generally considered to be the bounda
ry between the Archean Hearne and Wyoming provinces. Although complete
ly buried beneath the western Canadian sedimentary basin, the zone can
be studied indirectly through variations in Phanerozoic sedimentation
patterns, faulting, basement geochronology, and xenoliths, and with g
eophysical remote sensing methods. While tectonically active ca. 1.8 G
a and clearly truncating the potential field fabrics of Wyoming Provin
ce and Medicine Hat Block, the Great Falls Tectonic Zone lacks a colin
ear magmatic are, suggesting that the Hearne-Wyoming juxtaposition did
not involve subduction of oceanic lithosphere. Furthermore, electroma
gnetic studies fail to detect a response that can be interpreted as a
plate-edge foreland basin, typical of exposed Proterozoic suture zones
. The only conductivity anomaly associated with the zone is weak and a
ppears at depths exceeding 20 km, well below the top of the Proterozoi
c basement. Taken together, these observations suggest the Great Falls
Tectonic Zone may be better interpreted as a reactivated Archean(?) i
ntracontinental shear zone rather than a Proterozoic age suture betwee
n Archean provinces.