Imaging a mafic underplate in 3D: an example from the east Albany–Fraser Orogen and Yilgarn Craton margin

Summary

In this study a mafic underplate along the margin of the Proterozoic east Albany–Fraser Orogen and Archean Yilgarn Craton is imaged using 3D gravity forward modelling. The 3D model was constructed in GeoModeller and tested by 3D gravity forward modelling, an approach selected due to the distinct, regional-scale gravity anomalies observed along the margin. Important constraints on the model include an interpreted bedrock geology map, Moho depth points from a passive seismic survey and three deep crustal reflection seismic lines. The Moho model shows a zone of thickened crust extending, parallel to the Albany-Fraser Orogen, along the length of the orogen. 3D gravity forward modelling demonstrates that dense material is required in this zone of thickened crust and also demonstrates that this dense material is most likely in the lower crust, coincident with a large non-reflective zone imaged in reflection seismic data. This zone is interpreted to represent a mafic underplate that formed in the lower crust of the Yilgarn Craton during the Proterozoic. Some of the possible tectonic settings for the emplacement of this voluminous mafic underplate include Paleo-Mesoproterozoic extension that occurred along the margin or during the Mesoproterozoic Albany–Fraser Orogeny.

• 3D modelling
• gravity
• mafic underplate