HR: 1340h
AN: T13A-0433    [Abstracts]
TI: Mantle Fabric at Multiple Scales Across an Archean-Proterozoic Boundary, Eastern Ontario, Canada
AU: Ferguson, I J
EM: ferguso@ms.umanitoba.ca
AF: University of Manitoba, Department of Geological Sciences University of Manitoba, Winnipeg, MB R3T 2N2 Canada
AU: * Frederiksen, A W
EM: frederik@cc.umanitoba.ca
AF: University of Manitoba, Department of Geological Sciences University of Manitoba, Winnipeg, MB R3T 2N2 Canada
AU: Eaton, D W
EM: deaton@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences University of Western Ontario, London, ON N6A 5B7 Canada
AU: Miong, S
EM: ummiongs@cc.umanitoba.ca
AF: University of Manitoba, Department of Geological Sciences University of Manitoba, Winnipeg, MB R3T 2N2 Canada
AU: Gowan, E
EM: evangowan@yahoo.ca
AF: University of Manitoba, Department of Geological Sciences University of Manitoba, Winnipeg, MB R3T 2N2 Canada
AB: In eastern Ontario, Canada, the Proterozoic Grenville orogen abuts against the Archean Superior province; the complex tectonic history of the region is reflected in the pattern of electrical and seismic anisotropy within the lithosphere, while asthenospheric anisotropy is expected to reflect current patterns of mantle flow. Magnetotelluric and teleseismic data from the POLARIS and FedNor experiments and the Lithoprobe Abitibi-Grenville transect are examined for SKS splitting and geoelectric strike, and receiver functions are generated at selected stations, in order to characterize both vertical and horizontal variations in anisotropy in the eastern Ontario upper mantle. The average shear-wave split direction coincides with the direction of plate motion. Split times splits are found to be strongest in the southern part of the Grenville, where asthenospheric flow is enhanced by the presence of a lithospheric divot; the Ottawa-Bonnechere graben corresponds to a region of altered split direction indicative of a lithospheric component of anisotropy. North of the Grenville Front, there is a reorientation of the split direction from ESE to ENE at approximately 48°N, which is not easily attributable to crustal tectonics, and may represent the northern limit of lithospheric deformation produced by the Grenville orogen. Electrical anisotropy is pervasive in the study area. The magnetotelluric pattern of strikes is more complex than the SKS pattern, though the Groom-Bailey geoelectric strikes correlate fairly well with SKS measurements at nearby stations; the obliquity between SKS and magnetotelluric results shows no consistent orientation. Receiver-function analysis at three selected stations is indicative of a subcrustal anisotropic layer with a consistent SSE fast direction, underlain at station GAC by a sequence of anisotropic layers with varying directions; this sequence is not observed at station SADO. Combining these results, we interpret the strength and direction of anisotropic fabric in the Grenville to vary strongly with depth; the upper part of the lithosphere contains thin anisotropic layers perhaps related to eclogitization and relict slabs, but is insufficient to explain the observed SKS splits. The lower lithosphere is likely to be more ductile and uniformly anisotropic, and may be the main control on mantle electrical anisotropy as well as a significant contributor to SKS splitting. The largest contributor to SKS splitting in this region is interpreted to be asthenospheric anisotropy related to absolute plate motion.
DE: 0699 General or miscellaneous
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 9350 North America
SC: Tectonophysics [T]
MN: Fall Meeting 2005