Wise, Tom1,2., Curtis, Stacey1,2,3 Robertoson, Kate1,2,4
1Geological Survey of South Australia, Adelaide. 2. Mineral Exploration Cooperative Research Centre. 3. University of South Australia. 4. University of Adelaide
Late Cambrian volcanic arc segments are recognised in the Stavely and Konnenberry belts, whilst the presence or absence of a similar segment in the South Australian section of the Delamerian Orogen has been debated. Regional scale geophysical imagery has been re-interpreted to suggest that the Mount Wright Volcanics, part of the calc-alkaline volcanic arc in the Koonenberry Belt, likely extends into South Australia beneath the central Murray Basin. This continuation into South Australia may link to fore-arc style magmatism near Keith (Foden et al., 2020), rendering a temporal-spatial link between the Stavely and Koonenberry belts unlikely due to the parallel nature of the potential arc segment near Keith with the Stavely Belt.
A potential volcanic arc/subduction system positioned along the eastern margin of South Australia has direct implications for the porphyry-epithermal potential of the Delamerian basement to the Murray Basin, but also prompts a re-evaluation of the regional effects of the Delamerian Orogeny. Province-wide magnetotelluric models provide information about the nature of the middle crust down to the lithospheric mantle, and reveal highly resistive zones associated with rift axes of the middle Cambrian Kanmantoo Group, whilst further east, where potential arc crust may reside, the crust and lithospheric mantle is less resistive.
If volcanic arc rocks in South Australia represent the earliest subduction products along the east Gondwana margin (Foden et al., 2020) prior to roll-back and subsequent subduction in the Stavely zone, post-tectonic intrusives in a belt from the Padthaway Ridge to Anabama can be re-examined in the context of regional extensional episodes. Foden et al., (2020) attribute post-tectonic magmatic suites to delamination and asthenospheric upwelling. However, the geometry of the post-tectonic belt may imply that a crustal tear was developed earlier during rollback-induced extension, and exploited favourable original Kanmantoo rift structures. Potential field interpretation/modelling tests this hypothesis, whilst drilling as part of the MinEx CRC National Drilling Initiative will provide greater constraint for the proposed geologic framework of the region.
Tom Wise is a Senior Geologist at the Geological Survey of South Australia, and is the Technical Lead for the Delamerian project of the MinEx CRC National Drilling Initiative.