Lithospheric structure of the Pilbara Craton, Capricorn Orogen and northern Yilgarn Craton, Western Australia, from teleseismic receiver functions

Abstract

The upper lithospheric structure from the Pilbara Craton, across the Capricorn Orogen, to the northern Yilgarn Craton is determined from high-fidelity broadband seismic data. Three-component temporary stations were deployed in a line running southwards from Marble Bar, Western Australia, at approximately 118°E longitude. They were in position between July and October 2000. Receiver functions are calculated from the recorded teleseismic earthquakes stacked to improve the signal to noise ratio and, finally, the stacked waveforms used to model the seismic velocity profile under each recording station. Data from the permanent Global Seismic Network station, MBWA, at Marble Bar, which was installed in August 2001, are also used. The method provides a means of probing the deep structure of the Earth's crust and the nature of the seismic Moho at an intermediate scale between that of detailed active-source refraction techniques and the regional structure obtained from earthquake seismic tomography. The receiver functions and modelled seismic velocity structures along the north-south profile show the crust-mantle boundary under the Pilbara Craton to be shallow, at 30 km (±2 km), with a sharp Moho and high-velocity crust beneath the exposed Pilbara granite-greenstone terrane. The sharp Moho extends under the metasediments of the Hamersley Basin. Beneath the Capricorn Orogen the Moho is barely discernible, showing a small seismic velocity contrast and a broad zone of high-velocity gradient. The northern Yilgarn Craton, which extends beneath the basins exposed on the surface, is deeper, at 40 km (±2 km), and again shows a sharply defined Moho.