Albany–Fraser Experiment (ALFREX)

A 70-station passive seismic array was deployed in the east Albany–Fraser Orogen from November 2013 to January 2016. Data was analysed for receiver functions and ambient noise studies to yield maps of crustal thickness and bulk crustal density, profiles of Moho geometry and upper crustal surface-wave velocity maps.

The Albany–Fraser Orogen in Western Australia is a predominantly extensional orogen with a prolonged Paleo- to Mesoproterozoic history including at least one accretionary event (see GSWA Report 133 Tectonic links between Proterozoic sedimentary cycles, basin formation and magmatism in the Albany–Fraser Orogen, Western Australia). No major tectonothermal activity has occurred in the Albany–Fraser Orogen since the Mesoproterozoic. Thus, the lack of overprinting events provides direct clues to the Orogen formation, and contributes to the broad understanding of craton margin processes.

The passive seismic work is a product of the Australian Research Council Linkage Project LP130100413, a collaboration between the Australian National University , and the Geological Survey of Western Australia (GSWA). The objective of the project was to investigate the crustal and uppermost mantle structure of the Orogen by using passive seismic methods.

Results showed a belt of significantly thickened crust (10–15 km thicker than its surroundings) forming a V-shaped Moho trough that widens northwards. The deepest point of the Moho is located beneath the metamorphic rocks of the Fraser Zone which has clear signatures in the Vp/Vs ratio maps and the surface-wave velocity maps. These results are most likely indicative of a process of horizontal wedge indentation during a compressive period.

Full details of the experiment and results can be found in GSWA Report 177 Crustal and uppermost mantle structure of the east Albany–Fraser Orogen from passive seismic data.

3D view showing the Moho trough from the southwest and interpreted seismic profiles 12GA-AF1, AF2 and AF3. The Moho surface is produced from Moho picks on the profiles and receiver functions, located at the actual pierce point of the incoming wave

The objective of ALFREX is to delineate the 3D structure of the east Albany–Fraser Orogen and the lithospheric structure below it. This is achieved by using an array of more than 60 passive seismic stations deployed from 2013 to 2016 across the boundary of the Yilgarn Craton and the Albany–Fraser Orogen.

ALFREX is a collaborative project with the Seismology & Mathematical Geophysics research group at the Australian National University’s Research School of Earth Sciences. It is funded by the Australian Research Council (LP130100413 ‘Craton modification and growth: the east Albany–Fraser Orogen in 3D’).

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