Macquarie Arc and the Lachlan Orocline hypothesis: Magnetic analysis and development of geologically constrained forward model of lithospheric magnetisation.

Abstract

Potential field analysis, with focus on magnetic interpretation is ideally suited to geological problems where the targets are deep, totally undercover, or when there is little or no outcrop available for mapping or sampling. In these scenarios understanding the location, orientation and relationships between deep geological structures is the key to developing a clear picture of an areas tectonic history. In this project, we conduct a comprehensive magnetic analysis of the Lachlan Orocline and Macquarie Arc, both located in the Lachlan Orogen, eastern Australia to test the potential relative rotation of this block to the surrounding units. These results are compared with palaeomagnetic data from the region and a series of geologically constrained crustal-scale forward models of lithospheric magnetisation for the project area, with focus on the large-scale structural components of the Lachlan Orocline. The forward model method treats each geological unit present in both the Macquarie Arc itself and the surrounding areas as independent parameterised stratigraphic units. Using a Geographical Information System (GIS) approach, known geological, structural and physical properties are used to produce a series of vertically integrated value grids. These grids are then used as input to model the regional magnetisation in the global scale magnetic field forward model.