Deep Crustal Structure of the Capricorn Orogen from Gravity and Seismic Data

Abstract

The integration of geophysical data including deep seismic reflection, receiver function and gravity data provides the ability to image the deep crustal structure of Capricorn Orogen. In this study, we aim to reconcile seismic models of crustal structure with gravity measurements. S-wave seismic velocities from receiver function models were converted to P-wave velocity and density. Geology interpreted from deep seismic reflection profiles was depth converted based on the velocity data. An initial density model was constructed based on the depth converted seismc interpretation and densities estimated from velocities. To match observed variations in Bouguer anomaly the initial densities were modified based primarily on the comparability the wavelength of Bouguer anomaly and calculated gravity response of the model. We found that the Bandee Seismic Province (BSP) has a high density compared to the density of the adjacent regions and the underlying lower crustal blocks. This province, a 'deep crustal seismic terrane' without surface expression, recognised from the seismic data. Sensitivity testing suggests the mantle, the lower crust and the upper crust are less likely sources of the coincident high gravity anomaly. This observation is supported by receiver function models that reveal a high S-wave seismic velocity in mid-crust. Importantly, the region of higher density in the middle crust, unlike the BSP, does not extend south of the Talga Fault. This suggests the Talga Fault is a more significant structure than suggested by previous interpretations and the area around its surface outcrop may be more prospective than previously thought.