March 2008 MONTHLY MEETING

DATE: Wednesday 19th March 2008

VENUE: Rugby Club, Level 3, Rugby Place (near Pitt & Alfred St) Sydney

TIME: 5.30pm for 6:00pm

Technical Meeting

Potential field inversion and 3D modelling of complex geology on the regional scale - the Koonenberry Belt, NSW

Dr Robert Musgrave (NSW Dept of Primary Industries)

Abstract: Inversion of potential field data over the regional scale in structurally complex terrains is a challenging task, the more so when geological controls are patchy and the geologists involved hold competing, widely varying tectonic models. While inversion methods based around Bayesian statistical approaches are attractive and have produced some striking successes, they require a substantial degree of a priori geological constraint. Conventional inversion through iterative forward modelling allows complex, but poorly constrained, models to be developed and tested, and allows feedback of geophysical information into the conceptual framework of the geologists involved. The process can be long and tortuous, but the synergy between the geological and geophysical members of the modelling team greatly enhances the utility of the output.

Mapping of the Koonenberry Belt, which extends for more than 350 km in the northwest of NSW, has involved construction of a series of cross-sections arranged serially along the belt. When linked via surfaces defined by wavelet edge analysis (“worms”), these form the basis of a 3D geological model of the entire terrane. Initial geological controls on these sections was limited and hotly disputed between the geologists; the final sections, and 3D model, owe much of their definition to inversion of the magnetic and gravity data, and have led to a substantial revision of the tectonic understanding of the region.

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