HR: 1340h
AN: T33A-1325    [Abstracts]
TI: Finite-difference modeling of upper-mantle heterogeneities imaged by Lithoprobe's controlled-source seismic experiments beneath the Precambrian platform of Western Canada
AU: * Gorman, A R
EM: andrew.gorman@otago.ac.nz
AF: University of Otago, Department of Geology, P.O. Box 56, Dunedin, 9015 New Zealand
AU: Nemeth, B
EM: binemeth@potashcorp.com
AF: PotashCorp, 500 - 122 1st Avenue South, Saskatoon, SK S7K 7G3 Canada
AU: Clowes, R M
EM: clowes@eos.ubc.ca
AF: University of British Columbia, Department of Earth and Ocean Sciences, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Hajnal, Z
EM: zoltan.hajnal@usask.ca
AF: University of Saskatchewan, Department of Geological Sciences, 114 Science Place, Saskatoon, SK S7N 5E2 Canada
AB: Observations of upper mantle reflectivity at numerous locations around the world have been linked to the presence of a heterogeneous distribution of rock types within a broad layer of the upper mantle. This phenomenon is observed in wide-angle reflection data from Lithoprobe's Alberta Basement Transect (the SAREX and Deep Probe Seismic Experiment of 1995) and Trans-Hudson Orogen Transect (the THoRE experiment of 1993). SAREX and Deep Probe image the Archean lithosphere of the Hearne and Wyoming Provinces, whereas THoRE images the Archean/Proterozoic lithosphere of the Trans-Hudson Orogen and surrounding areas. Finite-difference modeling schemes are applied to constrain the position and physical properties of the reflective layer. SAREX / Deep Probe modeling uses a 2D visco-elastic finite-difference routine; THoRE modeling uses a pseudospectral algorithm. In both cases, the upper mantle is parameterized in terms of two media. One medium is the background matrix; the other is statistically distributed within the first as a series of elliptical bodies. Such a scheme is suitable for modeling: (1) variations in lithology (e.g., a peridotite matrix with eclogite lenses) or (2) variations in rheology (e.g., lenses of increased strain within a less strained background.) Results indicate that the thickness of the heterogeneous upper-mantle layer in western Canada varies. Beneath the Trans-Hudson Orogen in Saskatchewan, the layer is best modeled to lie at depths between 80 and 160 km. Based on observations from perpendicular profiles, anisotropy of the heterogeneities is inferred. Beneath Alberta, 400 km to the west, upper-mantle heterogeneities are modeled to occur between depths of 90 and 140 km. In both cases, the heterogeneous bodies within the model have cross-sectional lengths of tens of km and vertical thicknesses on the order of 1 km.
DE: 7260 Theory and modeling
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8159 Rheology--crust and lithosphere
DE: 7218 Lithosphere and upper mantle
DE: 0902 Computational methods, seismic
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting