HR: 1340h
AN: T33C-1483    [Abstracts]
TI: The Age and Tectonic Significance of the Paleoproterozoic Great Falls Tectonic Zone, Southwestern Laurentia
AU: * Mueller, P A
EM: mueller@geology.ufl.edu
AF: Department of Geological Sciences, Box 112120 Univ. of Florida, Gainesville, FL 32611, United States
AU: Foster, D A
EM: dfoster@geology.ufl.edu
AF: Department of Geological Sciences, Box 112120 Univ. of Florida, Gainesville, FL 32611, United States
AU: Mogk, D W
EM: mogk@montana.edu
AF: Department of Earth Sciences, Montana State Univ., Bozeman, MT 59717, United States
AU: Wooden, J L
EM: jwooden@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AB: The Great Falls tectonic zone (GFTZ) separates the Archean Wyoming province from the Hearne/Medicine Hat craton. Its northeastern limit is a high angle intersection with the Trans-Hudson orogen and marks the site of the Williston basin. Its southwestern extent probably reaches the Neoproterozoic margin of Laurentia. Though long recognized as a fundamental boundary in the accretionary history of Laurentia, its overall structure and developmental history are not well constrained. Limited exposures. Sm-Nd systematics and U-Pb ages zircons from metasedimentary rocks in the Little Belt Mountains (MT) and xenoliths provide strong evidence for consumption of juvenile oceanic crust and development of a continental magmatic arc at ~1.86 Ga on Paleoproterozoic to Archean crust of the Medicine Hat/Hearne blocks, rather than Wyoming crust. U-Pb ages (magmatic and xenocrystic zircons) and cooling ages (40Ar/39Ar) of exposed crust, drill cores, and xenoliths suggest that the eastern GFTZ beneath the Williston Basin has a similar history to crust formed in the central GFTZ and Trans-Hudson zones. The western GFTZ has a more complex crustal structure and metamorphic history involving Paleoproterozoic tectonic accretion and reworking of Archean crust (~1.77 Ga) as well as magmatic additions both younger (to ~1.65 Ga) and older (to ~2.45 Ga) than this event. This complexity strongly suggests the western GFTZ does not reflect a single collision following arc formation, but more likely indicates that the western GFTZ records collisions between multiple terranes, which may or may not include the Medicine Hat/Hearne block. The spatial coincidence of this complex collisional zone and the formation of the Belt basin provides an analog to the formation of the Williston basin of the eastern GFTZ. Tectonically, the formation of these major basins along the GFTZ suggests it originally developed with a strong transcurrent component that predisposed the GFTZ crust to basin development.
DE: 1040 Radiogenic isotope geochemistry
DE: 8103 Continental cratons
DE: 9350 North America
DE: 9619 Precambrian
SC: Tectonophysics [T]
MN: 2007 Fall Meeting