Long-term Research Program initiated by Professor Bob Nesbitt between 1963 – 1970 in the Department of Geology & Mineralogy, The University of Adelaide
R.W. Nesbitt, Emeritus Professor, University of Southampton, UK (Nov 2017)
The Giles Complex is an iconic geological province straddling the junction of South Australia, Western Australia and Northern Territory. It was explored by Reg Sprigg and his colleagues in the 1950s as part of a mining company (Southwestern Mining) evaluation of its mineral potential and the SA sector was later mapped by the South Australian Geological Survey in the late 1950s. These early geological studies were essentially exploratory, setting out the distribution of the major rock types, but they provided little detail of the geological evolution and origin of these ancient rocks. In 1963, the area, being a remote and scientifically challenging geological province, provided an exciting challenge to a small University of Adelaide group. An important consideration at the time was the fact that as a University-based group we were not inhibited by State boundaries which allowed us to examine the whole igneous province on both sides of the WA-SA border. Several years of field studies, petrological, mineralogical and geochemical research were undertaken by me and my colleagues and post-graduate students in the Department of Geology & Mineralogy. The results were summarized in post-graduate research theses, reported at National and International conferences, and published widely in scientific journals (list attached). The theses and rock samples collected over the many field seasons, together with the respective thin and polished sections for petrographic study, are archived in the Mawson Collection in the Mawson Building.
This comprehensive suite of studies was largely completed in the early 1970s with later follow-up isotopic studies by Chris Gray when based at the ANU and later at La Trobe. The area was re-surveyed by the Australian Geological Survey Organisation (AGSO, Commonwealth Government) in 1987 and 1990 (AGSO Bulletin 239, 1996) which built on the work of Adelaide University.
Later work by the Geological Survey of Western Australia (http://www.dmp.wa.gov.au/Geological-Survey/West-Musgrave-Province-21418.aspx) was restricted to the Western Australian sector of the Complex. In South Australia, further studies have been significantly restricted because access is controlled by the local indigenous population.
Simplified geological map showing the location and distribution of the Giles Complex Intrusions (after Nesbitt et al, 1970)
Scientific significance & outcomes
The major outcomes of the work carried out by the Adelaide University group can be summarized as follows:
- The intrusive rocks of the Giles Complex were emplaced as a series of individual mafic-dominated sheets of varying dimensions, some as large as 25km in length and 4km thickness. The present outcrop area occurs over an area of about 2,500 sq.km.
- The intrusions were emplaced at varying depths in the crust with those in the east of the Complex being at deep crustal depths progressing to shallow depths in the west. The mapping and subsequent laboratory studies demonstrated that the Giles Complex rocks present an east to west vertical section of continental crust with the volcanics (at Tollu in Western Australia) representing the final extrusive sequence. Petrographic studies by Goode and Moore demonstrated that the layered intrusions in South Australia were emplaced at pressures equivalent to 30 to 40 km depth. Such pressures indicate that the intrusions were emplaced near the base of the continental crust with subsequent geological events bringing them to their present surface position.
- The Adelaide group, working with isotope geochemists at the Australian National University (Compston & Nesbitt 1967) were the first to determine the age of the Giles Complex rocks as 1060 Ma. This age has been subsequently verified by The Geological Survey of Western Australia using the latest zircon dating techniques (1040 to 1090 Ma) and AGSO in Canberra (1080 Ma)
- The intrusions were emplaced into already deformed high-grade gneisses and granulites representing at least one previous major tectonic event and, after emplacement, were subsequently deformed into varying orientations with some (e.g. Mt Davies) being overturned.
- Studies by Moore (1973) and Goode (1978) confirm that shortly after consolidation, magma chambers in the east suffered high temperature-high pressure strain in localised areas. These zones (sometimes more than 100 metres across) point to major deformation events deep in the crust which were responsible for the disruption of the original intrusions. Such zones are marked by spectacular gneissic deformation structures where most of the original minerals have been totally recrystallized leaving residual highly deformed crystals or augen within a fine-grained groundmass.
- Field studies demonstrate that during cooling, the magma-crystal mix behaved like aqueous sediments producing characteristic structures such as cross-bedding, slumping, load structures and ripple marks. This phenomenon was modelled by Goode in a series of important papers (1967a, b, c). Using this model allowed us to determine the original orientation of the magma bodies prior to the deformation event. Laboratory studies on fractionation trends in mineral groups also confirmed this interpretation (e.g. Kleeman & Nesbitt 1967).
- In several areas, the contacts of the intrusions, particularly in the east, are well exposed. Given that the intrusions crystallised from high temperature magmas (> 1100°C) one would expect a strong cooling reaction where the magma reacted to the host country rock. The fact that this reaction is surprisingly muted indicates that the temperature difference was small and this in turn indicates the host rocks were at high pressure at emplacement. Field and petrographic studies at the margins of Mt Davies has revealed the presence of incipient melting producing granophyre veins and inclusions. On-going research using laser ICPMS isotopic techniques is aimed at understanding the degree of involvement of the host granulite rocks.
The next stage of research is to understand how these intrusions fit into the evolution of continental Australia. The presence of such large quantities of magma in the continental crust is indicative of a major mantle melting event and may provide a model for the Large Igneous Provinces (LIPS) which mark major tectonic events in several continents (e.g. the Deccan and Siberian Traps).
Publications & theses from the Giles Complex team 1964 – 2007
Collerson, K.D., Oliver, R.L. & Rutland R.W.R. (1972). An example of structural and metamorphic relationships in the Musgrave Orogenic Belt, central Australia. J. geol. Soc. Aust. 18, 379-394.
Compston, W. & Nesbitt, R.W. (1967). Isotopic age of the Tollu Volcanics, W.A. J. geol. Soc. Aust. 14, 235-238.
Facer, R.A. (1967). A preliminary study of the magnetic properties of rocks from the Giles Complex, central Australia. Australian J. Science 30, 237-238.
Facer, R.A. (1970). Magnetic properties of the Giles Complex, central Australia. Search 1, 76-77.
Facer R.A. (1971). Magnetic properties of rocks from the Giles Complex, central Australia. Royal Society of NSW Journal and Proceedings 104, 45-61.
Facer, R.A. (1971). Intrusion and magnetization of the Giles Complex, central Australia. Geophysical Journal of the Royal Astronomical Society 22(5), 517-520.
Goode, A.D.T. & Krieg G.W. (1967). The geology of the Ewarara Intrusion, Giles Complex, central Australia. J. geol. Soc. Aust. 14, 185-194.
Goode, A.D.T. & Nesbitt, R.W. (1969). Granulites and basic intrusions of part of the Eastern Tomkinson Ranges, central Australia. Spec. Pub. Geol. Soc. Aust. 2, 279-281.
Goode, A.D.T & Moore A.C. (1975). High pressure crystallisation of the Ewarara, Kalka and Gosse Pile intrusions, Giles Complex, central Australia. Contr. Mineral. Petrol. 51, 77-97.
Goode A.D.T. (1975). A transgressive picrite suite from the western Musgrave Block, central Australia. J. geol. Soc. Aust. 22, 187-194.
Goode, A.D.T. (1976a). Small scale primary igneous cumulus igneous layering in the Kalka layered intrusion, Giles complex, central Australia. J. Petrol. 17, 379-397.
Goode, A.D.T. (1976b). Sedimentary structures and magma current velocities in the Kalka layered intrusion, central Australia. J. Petrol. 17, 546-558.
Goode A.D.T. (1976c). Vertical igneous layering in the Ewarara layered intrusion, central Australia. Geol. Mag, 114, 365-374.
Goode, A.D.T. (1977). Flotation and remelting of plagioclase in the Kalka intrusion, central Australia: petrological implications for anorthosite genesis. Earth & Planetary Science Letters 34 (3), 375-380.
Goode, A.D.T. (1978). High temperature, high strain rate deformation in the lower crustal Kalka intrusion, Central Australia. Contr.Mineral. Petrol. 66, 137-148.
Gray, C.M (1977). The geochemistry of central Australian granulites in relation to the chemical and isotopic effects of granulite facies metamorphism. Contr. Mineral. Petrol. 65, 79-89.
Gray, C M. (1978). Geochronology of granulite-facies gneisses in the Western Musgrave Block, Central Australia. J. Geol. Soc. Aust. 25, 403-414.
Gray, C.M. (1987). Strontium isotopic constraints on the origin of Proterozoic anorthosites. Precambrian Research 37, 173-189.
Gray C.M. & Compston W. (1978). A rubidium-strontium chronology of the metamorphism and prehistory of central Australian granulites. Geochim. Cosmochim. Acta 42, 1735-1747.
Gray, C. M. & Goode, A.D.T. (1981). Strontium isotopic resolution of magma dynamics in a layered intrusion. Nature 294, 155-158.
Gray, C.M. & Goode, A.D.T. (1989). The Kalka layered intrusion, Central Australia: a strontium isotopic history of contamination and magma dynamics. Contr. Mineral. Petrol. 103, 35-43.
Gray, C.M., Cliff, R.A. & Goode, A.D.T. (1981). Neodymium-strontium isotopic evidence for extreme contamination in a layered basic intrusion. Earth Planet. Sci. Letts 56, 189-198
Kleeman, J.D. & Nesbitt, R.W. (1967). X-ray measurements on some plagioclases from the Mt. Davies Intrusion, South Australia. J. geol. Soc. Aust. 14, 39-42.
Moore, A.C. & Goode, A.D.T (2007). Petrography and origin of granulite‐facies rocks in the Western Musgrave Block, Central Australia. J. geol. Soc. Aust. 25, 341-358.
Moore, A.C. (1968). Rutile exsolution in orthopyroxene. Contr. Mineral. Petrol. 17, 233-236.
Moore, A.C. (1969). Corona textures in granulites from the Tomkinson Ranges, central Australia. Spec. Publ. Geol. Soc. Aust. 2, 361-366.
Moore, A.C. (1970). Descriptive terminology for the textures of rocks in granulite facies terrains. Lithos 3, 123-127.
Moore, A.C. (1971a). Corundum-ilmenite and corundum-spinel associations in granulite facies rocks from central Australia. J. geol. Soc. Aust. 17, 227-230.
Moore, A.C. (1971b). Some aspects of the geology of the Gosse Pile Ultramafic intrusion. J. geol. Soc. Aust. 18, 69-80.
Moore, A.C. (1971c). Mineralogy of the Gosse Pile ultramafic intrusion, central Australia. Plagioclase. J. geol. Soc. Aust. 18, 115-126.
Moore, A.C. (1971d). Mineralogy of the Gosse Pile ultramafic intrusion, central Australia. Pyroxenes. J. geol. Soc. Aust. 18, 243-258.
Moore, A.C. (1973). Studies of igneous and tectonic textures and layering in the rocks of the Gosse Pile intrusion, central Australia. J. Petrol. 14, 49-80.
Nesbitt, R.W. & Kleeman, A.W. (1964). Layered intrusions of the Giles Complex. Nature 203, 391-393.
Nesbitt, R.W. & Talbot, J.L. (1966). The layered ultrabasic and basic rocks of the Giles Complex, central Australia. Contr. Mineral. Petrol. 13, 1-11.
Nesbitt, R.W. (1966). The Giles Complex, an example of a deeply eroded volcanic zone. Bull. Volcanogique 29, 271-282.
Nesbitt, R.W., Goode, A.D.T., Moore, A.C. & Hopwood, T.P. (1970). The Giles Complex, central Australia; a stratified sequence of mafic and ultramafic intrusions. Geol. Soc. S. Africa Spec. Publ. 1, 547-564.
Oliver, R.L., Collerson, K.D. & Nesbitt, R.W. (1969). Precambrian geology of the Musgrave Block. Excursion Guide No 13, ANZAS 1969, 37-40.
Bell, T.H. (1973). Mylonite development in the Woodroffe Thrust, central Australia. Unpubl. PhD thesis University of Adelaide.
Collerson K.D. (1972). High grade metamorphic and structural relationships near Amata, Musgrave Ranges, central Australia. Unpubl. PhD thesis University of Adelaide.
Facer, R.K. (1969). Magnetic properties of the Giles Complex, central Australia. Unpubl. PhD thesis University of Sydney.
Goode A.D.T. (1970). The petrology and structure of the Kalka and Ewarara layered basic intrusions, Giles Complex, central Australia. Unpubl. PhD thesis University of Adelaide.
Gray, C.M. (1971). Strontium isotopic studies in granulites. Unpubl. PhD thesis Australian National University.
Moore A.C. (1970). The geology of the Gosse Pile ultramafic intrusions and the surrounding granulites, Tomkinson Ranges, Central Australia. Unpubl. PhD thesis University of Adelaide.
Barnes, L. (1968). The petrography and geochemistry of some high grade metamorphic rocks from the Mt Davies-Giles region, central Australia. Unpubl. Honours thesis University of Adelaide.
Blight D.F. (1969). The geology, petrology and geochemistry of an area south of Tollu, W.A. Unpubl. Honours thesis University of Adelaide.
Bowden, P.R. (1969). Geology of the Tollu area Western Australia. Unpubl. Honours thesis University of Adelaide.
Coin, C.D.A. (1970). A study of the granulite facies terrain near Amata. Unpubl. Honours thesis University of Adelaide.
Goode, A.D.T. & Kreig, G.W. (1965). The geology of the Ewarara intrusion, Giles Complex, central Australia. Unpubl. Honours thesis, University of Adelaide.
Gray, C.M. (1967). The geology, petrology and geochemistry of the Teizi meta-anorthosite. Unpubl. Honours thesis University of Adelaide.
Kleeman J.D. (1964). Studies on the X-ray diffraction, analysis and geochemistry of plagioclase from the Mt Davies igneous intrusion. Unpubl. Honours thesis University of Adelaide.
Miller, C. (1966). A geochemical study of clinopyroxenes from the igneous intrusion South Davies, N.W. South Australia. Unpubl. Honours thesis University of Adelaide.
Smith, P.C. (1970). The geology of the Hinckley Ranges, W.A. Unpubl. Honours thesis University of Adelaide.
Steele, R.J. (1966). Gravimetric investigation of the Mt Davies and Gosse Pile intrusions of the Giles Complex. Unpubl. Honours thesis University of Adelaide.
Yong, S.K. (1964). The distribution of trace elements Ni, Cu, Sr, Cr, and Mn in the Mt Davies basic intrusion of South Australia. Unpubl. Honours thesis University of Adelaide.