Revised potential field model of the Gilmore Fault Zone
Deepika Venkataramani 1 4 Robert J. Musgrave 2 David A. Boutelier 1 Alistair C. Hack 1 William J. Collins 31 School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.
2 Geological Survey of New South Wales, PO Box 344, Hunter Region Mail Centre, NSW 2310, Australia.
3 Department of Applied Geology, Curtin University, Bentley, WA 6102, Australia.
4 Corresponding author. Email: Deepika.venkataramani@uon.edu.au
Exploration Geophysics 49(4) 572-583 https://doi.org/10.1071/EG16148
Submitted: 29 November 2016 Accepted: 26 June 2017 Published: 4 September 2017
Abstract
The Gilmore Fault Zone (GFZ) marks a distinct geophysical contrast between metasediments of the Wagga Metamorphic Belt (high gravity and low magnetic intensity) and the Macquarie Arc and Silurian rift basins (low gravity and high magnetic intensity) in the Eastern Lachlan Orogen, Australia. This study uses a geologically constrained inversion of magnetic and gravity data to provide a revised model of the GFZ.
This model results in a significant improvement in fit to all previous models of the same profiles and involves repeated two-way exchange between geologists and geophysicists.
Two profiles corresponding to the seismic reflection lines 99AGSL1-L2 and 99AGSL3, and extending for more than 80 km, were simultaneously inverted by forward modelling of total magnetic intensity and gravity data. This was done through iterative modification of body geometry correlating to mapped geology. Profiles were further constrained by reflection seismics and physical property contrasts.
This model is used to clearly define the dip direction of the GFZ (west-dipping) and suggests a separate classification of the Barmedman Fault (east-dipping). The Barmedman Fault is a shallow fault flake, previously considered part of the GFZ, which has contributed to the confusion around the regional extent of the GFZ. This new work also has the potential to inform future tectonic interpretations of this area.
Key words: 3D modelling, faults, petrophysics, potential fields.
References
Bosch, M., Meza, R., Jiménez, R., and Hönig, A., 2006, Joint gravity and magnetic inversion in 3D using Monte Carlo methods: Geophysics, 71, G153–G156| Joint gravity and magnetic inversion in 3D using Monte Carlo methods:Crossref | GoogleScholarGoogle Scholar |
Chopping, R., and Kennett, B., 2015, Maximum depth of magnetisation of Australia, its uncertainty, and implications for Curie depth: GeoResJ, 7, 70–77
| Maximum depth of magnetisation of Australia, its uncertainty, and implications for Curie depth:Crossref | GoogleScholarGoogle Scholar |
Crawford, A., Glen, R., Cooke, D., and Percival, I., 2007, Geological evolution and metallogenesis of the Ordovician Macquarie Arc, Lachlan Orogen, New South Wales: Australian Journal of Earth Sciences, 54, 137–141
| Geological evolution and metallogenesis of the Ordovician Macquarie Arc, Lachlan Orogen, New South Wales:Crossref | GoogleScholarGoogle Scholar |
Direen, N., 1998, The palaeozoic Koonenberry Fold and Thrust Belt, Western NSW: a case study in applied gravity and magnetic modelling: Exploration Geophysics, 29, 330–339
| The palaeozoic Koonenberry Fold and Thrust Belt, Western NSW: a case study in applied gravity and magnetic modelling:Crossref | GoogleScholarGoogle Scholar |
Direen, N., Lyons, P., Korsch, R., and Glen, R., 2001, Integrated geophysical appraisal of crustal architecture in the eastern Lachlan Orogen: Exploration Geophysics, 32, 252–262
| Integrated geophysical appraisal of crustal architecture in the eastern Lachlan Orogen:Crossref | GoogleScholarGoogle Scholar |
Fisher, R. A., 1953, Dispersion on a sphere: Proceedings of the Royal Society of London. Series A, 217, 295–305
| Dispersion on a sphere:Crossref | GoogleScholarGoogle Scholar |
Glen, R., Korsch, R., Direen, N., Jones, L., Johnstone, D., Lawrie, K., Finlayson, D., and Shaw, R., 2002, Crustal structure of the Ordovician Macquarie Arc, Eastern Lachlan Orogen, based on seismic‐reflection profiling: Australian Journal of Earth Sciences, 49, 323–348
| Crustal structure of the Ordovician Macquarie Arc, Eastern Lachlan Orogen, based on seismic‐reflection profiling:Crossref | GoogleScholarGoogle Scholar |
Glen, R. A., Dawson, M. W., and Colquhoun, G. P., 2007, Eastern Lachlan Orogen Geoscience Database (on DVD-ROM) Version 2. Geological Survey of New South Wales, Department of Primary Industries, Maitland, NSW, Australia.
Koenigsberger, J., 1938, Natural residual magnetism of eruptive rocks: Journal of Geophysical Research, 43, 119–130
| Natural residual magnetism of eruptive rocks:Crossref | GoogleScholarGoogle Scholar |
Lane, R., FitzGerald, D., Guillen, A., Seikel, R., and McInerney, P., 2007, Lithologically constrained inversion of magnetic and gravity data sets: Preview, 129, 11–17
Musgrave, R. J., and Dick, S., 2017, A 3D model for the Koonenberry Belt from geologically constrained inversion of potential field data: Geological Survey of New South Wales, Quarterly Notes, 149, 1–13
Oldenburg, D., and Pratt, D., 2007, Geophysical inversion for mineral exploration : a decade of progress in theory and practice, in B. Milkereit, ed., Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration, 61–95.
Percival, I. G., and Glen, R. A., 2001, Correlation of successions within the Ordovician Macquarie Arc, central New South Wales: Geological Survey of New South Wales, 47–60.
Scheibner, E., 1985, Suspect terranes in the Tasman Fold Belt System, east Australia: Tectonostratigraphic Terranes of the Circum-Pacific Region, 1, 493–514
Scheibner, E., and Basden, H. (eds.) 1998, Geology of New South Wales — Synthesis. Volume 1, Structural Framework: Geological Survey of New South Wales, Memoir Geology 13(1).
Stuart-Smith, P. G., 1991, The Gilmore Fault Zone—the deformational history of a possible terrane boundary within the Lachlan Fold Belt New South Wales: BMR Journal of Australian Geology and Geophysics, 12, 35–49
Suppel, D. W., Warren, A. Y. E., Watkins, J. J., Chapman, J., Tenison Woods, K., and Barron, L., 1986, A reconnaissance study of the geology and gold deposits of the west Wyalong-Temora-Adelong District: New South Wales Geological Survey, Quarterly Notes, 64, 1–23
Venkataramani, D., 2017, Subsurface modelling of the Gilmore Fault Zone: implications for Lachlan Tectonic reconstructions: M.Ph. thesis, University of Newcastle, Newcastle, NSW, Australia.
Warren, A. Y. E., Gilligan, L. B., and Raphael, N. M., 1995, Geology of the Cootamundra 1 : 250 000 map sheet. viii + 160 pp. Geological Survey of New South Wales, Sydney.
Wormald, R. J., and Price, R. C., 1990, The gabbro-qtz monzodiorite-alkai granite association in southern New South Wales: implications for intrusive related gold mineralisation: Geological Society of Australia Abstracts, 25, 265
Wyatt, B. W., Yeates, A. N., and Tucker, D. H., 1980, A regional review of the geological sources of magnetic and gravity fields in the Lachlan Fold belt of NSW: BMR Journal of Australian Geology and Geophysics, 5, 289–300