Crustal thickness in Southern Ontario from constrained linearized gravity inversion
Abstract
We use crustal thickness estimates for POLARIS Southern Ontario stations as constraints in a linearized inversion of gridded Bouguer gravity data for topography of the crust-mantle boundary. Estimates of crustal thickness from receiver function analysis varies from 37 to 43 km; the thinnest crust is found in a SW-NE trending belt between Georgian Bay and Lake Ontario. Our gravity inversion assumes a constant density contrast between crust and mantle, and parameterizes the topography of the crust-mantle boundary as discrete rectangular blocks sitting at a reference depth. By assuming that the mass of one block is concentrated at its base, we obtain a linear relationship between the height of the block and the vertical component of gravity measured at the surface. For realistic Moho topography our forward model compares well with more accurate non-linear approaches that either distribute the mass across each discrete block or use a Fourier expansion in the wavenumber domain to parameterize the surface. To the resulting system of linear equations we add additional constraint equations provided by the teleseismically derived thicknesses at the appropriate grid locations. Our preliminary results show long-wavelength undulations in Moho topography. Residual gravity maps display mainly short wavelength features that are presumed to be caused by shallow anomalies. A comparison of the results with tectonic boundaries mapped at the surface show a thick crust underlying the Central Metasedimentary Belt, and thinner crust just SE of the Grenville Front.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.S33A..04B
- Keywords:
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- 1219 Local gravity anomalies and crustal structure;
- 7205 Continental crust (1242);
- 8122 Dynamics;
- gravity and tectonics