A Potential Field Approach to Defining Major Lithospheric Structures along the Margin of the West Australian Craton

Abstract

SummaryPotential field and tomography data have been used to investigate major lithospheric structures associated with the margin of the West Australian craton. This study provides results on the location and geometry of major structural discontinuities at a lithospheric scale, using gravity and magnetic data. These results form part of a wider study that aims to understand the structural architecture of craton margins in terms of strain partitioning and accretionary processes. These data are used as inputs into automated edge detection, potential field inversions, and more traditional filtering techniques in order to understand the structural architecture across the craton margin.Automated edge detection was performed on the total magnetic intensity and Bouguer gravity data over the Fraser orogen Yilgarn craton transition. Four major orogen parallel features were identified. These features are interpreted as major faults and/or shear zones that extend to significant crustal depths. They are interpreted to be related to more ‘primary’ craton margin structures at depth. Moho inversions of the gravity data were performed across the craton margin. They aimed of identifying steps in the topography of the Moho caused by crustal penetrating shear zones. These initial models were unable to resolve the base of the crust, but did however provide information related to domains and boundaries within the deep crust. Surface wave tomography data was used to investigate possible structures within the sub-continental lithospheric mantle. A large linear gradient in Vs was imaged approximately parallel to the Fraser orogen at 75km depth when filtered for the total horizontal gradient. This gradient was overprinted by a major east-west trending features at 100km, a trend that is also apparent within seismic depth estimates of the Moho.