Magnetic modelling of the Umvimeela and East Dykes: evidence for regional tilting of the Zimbabwe Craton adjacent to the Limpopo Belt

An environmental analysis of the Umvimeela and East Dykes of Zimbabwe.Models of the Umvimeela and East dykes of Zimbabwe have been deduced from aeromagnetic data. Assuming a constant magnetic susceptibility and direction of remanent magnetization the models show the two dykes are essentially vertical with a mean dip of 84 towards the Great Dyke for the Umvimeela dyke and 89° away from the Great Dyke for the East dyke (excluding results from south of latitude 20.5 S). There is a large variation in the width of the dykes. A mean width of 204 m for the Umvimeela dyke and 106 m for the East dyke were obtained. The large errors may represent true variations in width or result from variations in the susceptibility. Both dykes have shallower dips south of latitude 20.5 S. The Umvimeela dyke has a mean dip of 70 and the East dyke of 80°. This, together with palaeomagnetic data from the Umvimeela dyke, suggests a tilting of the Zimbabwe craton adjacent to the Limpopo Belt over a zone about 100 km in width. The axis of rotation is roughly parallel to the northern margin of the Limpopo Belt

Subsurface geometry of the Revell Batholith by constrained geophysical modelling, NW Ontario, Canada

The Revell batholith is located within the Western Wabigoon terrane of the Superior Province, Northwestern Ontario, Canada, and is a potential site for a deep geological repository (DGR). This batholith is considered to have favourable geoscientific characteristics for hosting a DGR, including a sufficient volume of relatively homogenous rock. The subsurface geometry of the batholith plays an important role in determining its volume, as well as assessing regional-scale hydraulics, rock mechanics, and glacial stress disturbances on the bedrock, which are other important features and processes that can impact the batholith over the timeframes of concern for long-term storage of used nuclear fuel. Subsurface geometry is complicated to unravel, and surface mapping alone is inadequate to obtain the information at depth. However, gravity, magnetic, or seismic data can be used to enhance understanding by approximating the geometry.This study aims to refine the subsurface geometry and distribution of the Revell batholith from a constrained forward and inverse geophysical model, incorporating high-resolution geophysical data together with a compilation of historic and recent geological field data. The Revell batholith was previously cited as a flat-based pluton with a depth of 1.6 km, where our findings suggest the batholith is deeper than previously thought, with an uneven contact geometry at its base that extends slightly deeper than 3.5 km. Model uncertainties were assessed by varying probabilistic constraints on volume overlap/commonality and shape within GeoModeller™. Results indicate that overall batholith-greenstone contact is generally unchanged when the geological constraints are varied, providing a high degree of confidence that the Revell batholith has a sufficient volume of relatively homogeneous bedrock