The nature of the basement to the Cooper Basin region, South Australia

Abstract

Analyses of aeromagnetic and gravity data in the Cooper Basin area of South Australia, reveals varied basement lithologies and structure. Most of the observed magnetic responses arise from sources beneath the Cooper Basin sequence. A prominent northeast-trending structural basement grain is evident. Emplacement of a large igneous mass into the upper crust is interpreted beneath the Patchawarra Trough. Interpreted faulting along the southeastern edge of the igneous body resulted in up to 3.5 km of block uplift, coincident with the Gidgealpa and Merrimelia Ridges. A broad and prominent gravity low in the Nappamerri Trough region is attributed to Late Carboniferous Big Lake Suite granodiorite masses, which have intruded Warburton Basin strata. Intense gravity lows within the broader gravity low are attributed to granodiorite cupolas, which became non-tectonic palaeo-topographic highs during Cooper Basin deposition. Another broad gravity low in the Tenappera Trough region is due to a belt of Early Devonian granitoids that have intruded Proterozoic basement. A number of small magnetic anomalies, in the south of the survey, are interpreted as sourced from skarns above and adjacent to the granitoid intrusions. The only magnetic units above Proterozoic basement in the region are the basalts in the Warburton Basin sequence, which coincide with small magnetic anomalies. Depth to magnetic source modelling correlates well with the known depths of the basalts.