Potential-field interpretation of the Kars Belt, western NSW

Abstract

The Cambrian Ponto Group of the Koonenberry Belt is a suite of fore-arc rocks of the Mt Wright Arc, and includes basalts that are associated with copper mineralisation. Magnetic derivative maps allow the Ponto Group to be followed southwest under shallow cover, where they define the magnetic texture of the Kars Zone that flanks the southeastern margin of the Curnamona Craton. Shallow-sourced positive magnetic anomalies in the Kars one are superimposed on a longer-wavelength magnetic low; this contrasts with their equivalents along the Koonenberry Belt, which sit on broad magnetic highs. Gravity images of the Koonenberry Belt suggest that shallow dense sources associated with the Ponto Group overlie deeper mass excesses, while equivalent shallow and deep mass excesses appear to be uncoupled in the Kars Zone. Joint magnetic and gravity modelling of a profile across the Kars Zone suggests that high susceptibility, dense bodies representing the Ponto Group have been displaced to the northwest, over-riding in their path deep magnetic sources below the Menindee Trough. Similar deep magnetic sources below the Bancannia Trough have been interpreted as very large intrusive features forming the base of the Mt Wright Arc. Together, the potential field imagery and modelling suggests very large scale, low-angle thrusting of the Mt Wright fore-arc over a rigid basement of the Mt Wright Arc.