Implications of a geoscientific traverse over the Darling Fault Zone, Western Australia

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Abstract
Deep seismic reflection data were collected, with a two‐way recording time of 12 s, along a 75 km long traverse that covered 50 km within the Archaean Yilgarn Craton and 25 km within the adjacent Phanerozoic Perth Basin in Western Australia. Magnetic data were recorded at 100 m intervals along the same traverse line and the area within the Yilgarn Craton was mapped at a scale of 1:10 000 along a 2 km wide corridor. The preferred interpretation of the seismic reflection data suggests that the crust beneath the western Yilgarn Craton may be divided vertically into three structural zones: (i) 0 to 7–9 km: a zone of thin‐skinned compressional tectonism expressed as a series of thrusts which link to a detachment surface at about 7–9 km depth; (ii) 7–9 to 25 km: a zone that contains several minor detachments (or shear zones) and seismic events that appear to characterize a large intrusive igneous body; and (iii) 25–40 km: continuous seismic events that dip eastward at about 25°. Reflection events between 11 and 12 s in the east of the profile may represent the top of the Moho reflection package. The seismic reflection data provide a good fault plane image of the Phanerozoic Darling Fault. This fault is distinct from the Archaean‐Proterozoic proto‐Darling Fault, which is interpreted to be coincident with a wide, non‐reflecting zone extending westward beneath the Perth Basin. Magnetic anomalies within the upper crustal zone define shallow igneous bodies with strong magnetic remanence. The remanence directions support the intrusion of such bodies prior to 1054 Ma, and rotation of these bodies by about 90° from their original azimuth of formation. Magnetic bodies within the intermediate crustal zone at depths of around 18–20 km are believed to represent a large layered mafic intrusion. The deep seismic reflection data, combined with the magnetic studies, indicate a complex history of both thin‐skinned and whole‐crust tectonism since the Late Archaean. Data recorded from the uppermost structural zone have also been correlated with surface geological mapping and indicate that the junctions between the Chittering and Jimperding Metamorphic Belts and between the Jimperding Belt and the Wheat Belt region to the east are marked by major shear zones. This supports the concept that the western portion of the Yilgarn Craton evolved by accretion of a number of separate terranes, probably between 2640 and 2575 Ma.