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Abstract
In order to investigate the tectonic evolution of the Arunta Block and the Ngalia and Amadeus Basins, a regional north‐south seismic reflection line 420 km long from the Northern Arunta Province to the southern part of the Amadeus Basin, and an east‐west refraction profile over 400 km within the Arunta Block, were recorded by the Bureau of Mineral Resources in 1985. The most significant basement features observed in the reflection data are prominent bands of northerly dipping reflections originating from beneath the Northern Arunta Province and the Ngalia Basin at times of between 4 and 10 s. In this region, reflected energy with frequencies as high as 100 Hz is present at two‐way times of 5–6 s, implying that the rocks have high Q to depths of at least 18 km. The character of the reflections changes markedly with varying frequency, which suggests that they arise by interference phenomena, probably associated with laterally varying lamellar structures. Deep crustal features on the reflection profiles from the Central Arunta Province are less clear, although the refraction data suggest an average crustal thickness of about 55 km. Below the Southern Arunta Province there is a zone of northerly dipping reflectors at depths between 21 and 30 km, which suggests deeply buried rocks of sedimentary origin. Beneath the southern part of the Amadeus Basin, prominent bands of reflections, similar in character to those observed beneath the Southern Arunta Province, occur at times between 6 and 10 s, but have an apparent dip to the south. The reflections from the sediments of the Ngalia and Amadeus Basins are generally weak, except for those below the Missionary Plain in the northern part of the Amadeus Basin where strong, excellent‐quality reflections were obtained. Data from an expanding spread recorded in this area give well‐constrained velocity estimates throughout the 10 km thick sedimentary sequence, thus enabling the local thickness of the basin to be accurately determined.