Combining Seismic Data from Passive and Active Sources for understanding the terrane structure of the Eastern Goldfields, Western Australia

Abstract

A passive seismic survey to investigate variations in crustal structure across the Yilgarn craton has shown significant contrasts in seismic velocity models between neighbouring terranes/superterranes. The Eastern Goldfields showed a unique variability in crustal structure in agreement with a recent reinterpretation of terrane boundaries within the Yilgarn craton. We further investigated the Eastern Goldfields region using a 3-way approach which combined conventional passive seismic analysis with innovative seismic noise-correlation methods and constraints from active source data. Conventional passive seismic analysis enables the Receiver Function S-velocity structure, and hence composition, of the lower crust to be constrained. Noise -correlation analysis allows seismic velocity models in the 5-15 km depth range to be determined and provides medium resolution coverage across regions not previously explored using active seismic methods. Where active source data have been acquired, shallow structure and deeper seismic velocity determinations are added, providing an unprecedented combination of seismic constraints on the structure of this complex and economically important region. We find that, although some individual terrane boundaries within the new Eastern Goldfields reinterpretation are open to question, the concept of the multi-terrane amalgamation is substantially justified by the exceptional variability of the lower crustal structure. Upper crustal structure is often characterised by seismic discontinuities which may represent detachment surfaces or layered structure that varies between terranes over a sub-100 km length scale. The accretionary history of the superterrane and associated regional tectonic setting of numerous formations of economic significance would now appear to be beyond question.