Abstract
Proposed Proterozoic sutures in the Canadian Shield show paired positive and negative gravity anomalies. Previous interpretations ascribe the negative anomaly to an increase in crustal thickness of the older province towards the suture and the positive to increased density and thickness of the younger province. Here, the asymmetrical negative anomaly is interpreted to be the result of flexure of the older lithosphere as it is thrust under the younger, more buoyant plate. The absence of any visual correlation between topography and observed gravity over suture zones suggests the presence of subsurface loads, which are thought to be the primary sources for the related positive gravity anomalies. Two-dimensional modelling of suture anomalies has resulted in the following estimates for elastic plate thicknesses in the Canadian Shield: 60 km for the Slave plate and 75, 120, 125 km for the Cape Smith, Labrador and Grenville areas of the Superior province. Flexural rigidities at sutures increase with the age of the lithosphere when loaded, supporting previous results obtained in oceans and mountain ranges.
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