Hostname: page-component-7c8c6479df-nwzlb Total loading time: 0 Render date: 2024-03-28T22:40:15.869Z Has data issue: false hasContentIssue false

Lachlan Fold Belt granitoids: products of three-component mixing

Published online by Cambridge University Press:  03 November 2011

W. J. Collins
Affiliation:
W. J. Collins, Department of Geology, University of Newcastle, Newcastle, NSW, 2308, Australia.

Abstract:

The paradox of Lachlan Fold Belt (LFB) granitoids is that although contrasted chemical types (S- and I-types) imply melting of distinct crustal sources, the simple Nd–Sr–Pb–O isotopic arrays indicate a continuum, suggesting mixing of magmatic components. The paradox is resolved by the recognition that the previously inferred, isotopically primitive end-member is itself a crust-mantle mix, so that three general source components, mantle, lower crust and middle crust, comprise the granitoids. Based on Nd isotopic evidence, mantle-derived basaltic magmas melted and mixed with Neoproterozoic-Cambrian, arc-backarc-type material to produce primitive I-type, parental granitoid magmas in the lower–middle crust. Ordovician metasediment, locally underthrust to mid-crustal levels, was remobilised under the elevated geotherms and is most clearly recognised as diatexite in the Cooma complex, but it also exists as gneissic enclaves in S-type granites. The diatexite mixed with the hybrid I-type magmas to produce the parental S-type magmas. Unique parent magma compositions of individual granite suites reflect variations within any or all of the three major source components, or between the mixing proportions. For example, chemical tie-lines between Cooma diatexite and mafic I-type Jindabyne suite magma encompass almost all mafic S-type granites of the vast Bullenbalong supersuite, consistently in the proportion Jindabyne: Cooma, 30:70. The modelling shows that LFB S-type magmas are heavily contaminated I-type magmas, produced by large-scale mixing of hot I-type material with lower temperature diatexite in the middle crust. The model implies a genetic link between migmatite and pluton-scale, crustally derived (S-type) granites.

Given the chemical and isotopic contrasts of the crustally derived source components, and their typically unequal proportions in the magmas, it is not surprising that the LFB granitoids are so distinctive and have been categorised as S- and I-type. The sublinear chemical trends of the granitoid suites are considered to be secondary effects associated with crystal fractionation of unique parental magmas that were formed by three-component mixing. The model obviates the necessity for multiple underplating events and Proterozoic continental basement, in accordance with the observed tectonostratigraphy of the Lachlan Fold Belt.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 1996

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

9. References

Ague, J. J.&Brimhall, G. H. 1987. Granites of the batholiths of California: products of local assimilation and regional-scale crustal contamination. GEOLOGY 15, 63–6.2.0.CO;2>CrossRefGoogle Scholar
Aitchison, J.C .Ireland, T. R., Blake, M. C. Jr&Flood, P. G. 1992. 530 Ma zircon for ophiolite from the New England Orogen: oldest rocks known from eastern Australia. GEOLOGY 20, 125–8.2.3.CO;2>CrossRefGoogle Scholar
Beams, S. D. 1980. Magmatic evolution of the southeast Lachlan Fold Belt, Australia. Ph.D. Thesis. La Trobe University.Google Scholar
Beard, J. S. and Lofgren, G. E. 1991. Dehydration melting and watersaturated melting of basaltic and andesitic greenstones and amphibolites at 1, 3 and 6·9 kb. J PETROL 32, 365401.CrossRefGoogle Scholar
Brown, M. 1994. The generation, segregation, ascent and emplacement of granite magma: the migmatite-to-crustally-derived granite connection in thickened orogens. EARTH-SCI REV 36, 83130.CrossRefGoogle Scholar
Cas, R. A. F. 1983. A review of the palaeogeographic and tectonic development of the Palaeozoic Lachlan Fold Belt of southeastern Australia. SPEC PUBL GEOL SOC AUST 10.Google Scholar
Chappell, B. W. 1979. Granites as images of their source rocks. GEOL SOC AM ABSTR PROGRAMS 11, 400.Google Scholar
Chappell, B. W. 1984. Source rocks of S- and I-type granites in the Lachlan Fold Belt, southeastern Australia. PHIL TRANS R SOC LONDON A310, 693707.Google Scholar
Chappell, B. W. 1994. Lachlan and New England: fold belts of contrasting magmatic and tectonic development. J PROC R SOC NSW 127, 4759.Google Scholar
Chappell, B. W.&Stephens, W. E. 1988. Origin of infracrustal (I-type) granite magmas. TRANS R SOC EDINBURGH EARTH SCI 79, 7186.Google Scholar
Chappell, B. W.&White, A. J. R. 1974. Two contrasting granite types. PACIFIC GEOL 8, 173–4.Google Scholar
Chappell, B. W.&White, A. J. R. 1992. I- and S-type granites in the Lachlan Fold Belt. TRANS R SOC EDINBURGH EARTH SCI 83, 126.Google Scholar
Chappell, B. W., White, A. J. R.&Wyborn, D. 1987. The importance of residual source material (restite) in granite petrogenesis. J PETROL 28, 1111–38.CrossRefGoogle Scholar
Chappell, B. W., White, A. J. R.&Hine, R. 1988. Granite provinces and basement terranes in the Lachlan Fold Belt, southeastern Australia. AUST J EARTH SCI 35, 505–21.CrossRefGoogle Scholar
Chappell, B. W., White, A. J. R.&Williams, I. S. 1991. A transverse section through granites of the Lachlan Fold Belt. In Second Hutton Symposium Excursion Guide, Canberra. BMR GEOL GEOPHYS REC 1991 p. 122.Google Scholar
Chen, Y.&Williams, I. S. 1990. Zircon inheritance in mafic inclusions from Bega Batholith granites, southeastern Australia: an ion microprobe study. J GEOPHYS RES 95, 17787–96.Google Scholar
Chen, Y., Price, R. C.&White, A. J. R. 1989. Inclusions in three S-type granites from southeastern Australia. J PETROL 30, 1181–218.Google Scholar
Clemens, J. D.&Wall, V. J. 1981. Origin and crystallization of some peraluminous (S-type) granitic magmas. CAN MINERAL 19, 111–31.Google Scholar
Clemens, J. D.&Wall, V. J. 1984. Origin and evolution of a peraluminous silicic ignimbrite suite: the Violet Town volcanics. CONTRIB MINERAL PETROL 88, 354–71.CrossRefGoogle Scholar
Collins, W. J. 1994. Upper and middle crustal response to delamination: an example from the Lachlan Fold Belt, eastern Australia. GEOLOGY 22, 143–6.2.3.CO;2>CrossRefGoogle Scholar
Collins, W. J.&Vernon, R. H. 1992. Palaeozoic arc growth, deformation and migration across the Lachlan Fold Belt, southeastern Australia. TECTONOPHYSICS 214, 381400.CrossRefGoogle Scholar
Collins, W. J.&Vernon, R. H. 1994. A rift-drift-delamination model of crustal growth: Phanerozoic tectonic development of eastern Australia. TECTONOPHYSICS 235, 249–75.CrossRefGoogle Scholar
Compston, W.&Chappell, B. W. 1979. Sr-isotope evolution of granitoid source rocks. In McElhinny, M. W. (ed.) The earth, its origin, structure and evolution. 377426. London: Academic Press.Google Scholar
Conrad, W. K., Nicholls, I. A.&Wall, V. J. 1988. Water-saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb: evidence for the origin of silicic magmas in the Taupo Volcanic Zone, New Zealand, and other occurrences. J PETROL 29, 765803.CrossRefGoogle Scholar
Crawford, A. J. and Berry, R. F. 1992. Tectonic implications of Late Proterozoic-Early Palaeozoic igneous rock associations in western Tasmania. TECTONOPHYSICS 214, 3756.CrossRefGoogle Scholar
Crawford, A. J., Cameron, W. E.&Keays, R. R. 1984. The association boninite, low T andesite, tholeiite in the Heathcote Greenstone Gelt, Victoria. AUST J EARTH SCI 31, 161–75.CrossRefGoogle Scholar
Elburg, M. A. and Nicholls, I. A. 1995. Origin of microgranitoid enclaves in the S-type Wilson's Promontory Batholith, Victoria: evidence for magma mingling. AUST J EARTH SCI 42, 423–35.CrossRefGoogle Scholar
Ellis, D. J.&Obata, M. 1992. Migmatite and melt segregation at Cooma, New South Wales. TRANS R SOC EDINBURGH EARTH SCI 83, 95106.Google Scholar
Fergusson, C. L.&Coney, P. J. 1992. Convergence and intraplate deformation in the Lachlan fold Belt of southeastern Australia. TECTONOPHYSICS 214, 417–39.CrossRefGoogle Scholar
Finlayson, D. M., Collins, C. D. N.&Denham, D. 1980. Crustal structure under the Lachlan Fold Belt, eastern Australia. PHYS EARTH PLANET INTER 21, 321–42.CrossRefGoogle Scholar
Glen, R. A. 1992. Thrust, extensional and strike-slip tectonics in an evolving Palaeozoic orogen—a structural synthesis of the Lachlan Orogen of southeastern Australia. TECTONOPHYSICS 214, 341–80.CrossRefGoogle Scholar
Gray, C. M. 1984. An isotopic mixing model for the origin of granitic rocks in southeastern Australia. EARTH PLANET SCI LETT 70, 4760.CrossRefGoogle Scholar
Gray, C. M. 1990. A strontium isotopic traverse across the granitic rocks of southeastern Australia: petrogenetic and tectonic implications. AUST J EARTH SCI 37, 331–49.CrossRefGoogle Scholar
Gray, C. M. 1995. Discussion of ‘Lachlan and New England: fold belts of contrasting magmatic and tectonic development’. J PROC R SOC NSW 128, 2932.Google Scholar
Griffin, T. J., White, A. J. R.&Chappell, B. W. 1978. The Moruya Batholith and geochemical contrasts between the Moruya and Jindabyne suites. J GEOL SOC AUST 25, 235–47.CrossRefGoogle Scholar
Hildreth, W.&Moorbath, S. 1988. Crustal contributions to arc magmatism in the Andes of central Chile. CONTRIB MINERAL PETROL 98, 455–89.CrossRefGoogle Scholar
Hine, R. H., Williams, I. S., Chappell, B. W.&White, A. J. R. 1978. Geochemical contrasts between I- and S-type granitoids of the Kosciusko Batholith. J GEOL SOC AUST 25, 215–34.CrossRefGoogle Scholar
Johnson, S.&Vernon, R. H. 1995. Stepping stones and pitfalls in the determination of an anticlockwise P–T–t–deformation path: the low-P, high-T Cooma Complex, Australia. J METAMORPH GEOL 13, 165–83.Google Scholar
Landenberger, B.&Collins, W. J.Derivation of A-type granites from a dehydrated charnockitic lower crust: evidence from the Chaelundi complex, eastern Australia. J PETROL 37, 145–70.CrossRefGoogle Scholar
McCulloch, M. T.&Chappell, B. W. 1982. Nd isotopic characteristics of S- and I-type granites. EARTH PLANET SCI LETT 58, 5164.CrossRefGoogle Scholar
McCulloch, M. T.&Woodhead, J. D. 1993. Lead isotopic evidence for deep crustal-scale fluid transport during granite petrogenesis. GEOCHIM COSMOCHIM ACTA 57, 659–74.CrossRefGoogle Scholar
Munksgaard, N. C. 1988. Source of the Cooma Granodiorite, New South Wales—a possible role of fluid-rock interactions: AUST J EARTH SCI 35, 263378.CrossRefGoogle Scholar
Nelson, D. R., Crawford, A. J.&McCulloch, M. T. 1984. Nd–Sr isotopic and geochemical systematics in Cambrian boninites and tholeiites from Victoria, Australia. CONTRIB MINERAL PETROL 88, 164–72.CrossRefGoogle Scholar
Phillips, G. N., Wall, V. J.&Clemens, J. D. 1980. Petrology of the Strathbogie Batholith: a cordierite-bearing granite. CAN MINERAL 19, 4763.Google Scholar
Roberts, M. P.&Clemens, J. D. 1993. Origin of high-potassium, calcalkaline, I-type granitoids. GEOLOGY 21, 825–8.2.3.CO;2>CrossRefGoogle Scholar
Rollinson, H. R. 1993. Using geochemical data: evaluation, presentation, interpretation. Harlow: Longman Scientific and Technical.Google Scholar
Turner, S. P., Foden, J. D., Sandiford, M.&Bruce, D. 1993. Sm-Nd isotopic evidence for the provenance of sediments from the Adelaide Fold Belt and southeastern Australia with implications for episodic crustal additions. GEOCHIM COSMOCHIM ACTA 57, 1837–56.CrossRefGoogle Scholar
Vernon, R. H. 1983. Restite, xenoliths and microgranitoid enclaves in granites. J PROC R SOC NSW 116, 77103.Google Scholar
Vernon, R. H. 1990. Crystallization and hybridism in microgranitoid enclave magmas: microstructural evidence. J GEOPHYS RES 95, 17 849–59.Google Scholar
Vernon, R. H., Etheridge, M. E.&Wall, V. J. 1988. Shape and microstructure of microgranitoid enclaves: indicators of magma mingling and flow. LITHOS 22, 111.CrossRefGoogle Scholar
Wall, V. J., Clemens, J. D.&Clarke, D. B. 1987. Models for granitoid evolution and source compositions. J GEOL 95, 731–49.CrossRefGoogle Scholar
White, A. J. R.&Chappell, B. W. 1977. Ultrametamorphism and granitoid genesis. TECTONOPHYSICS 43, 722.CrossRefGoogle Scholar
White, A. J. R.&Chappell, B. W. 1988. Some supracrustal (S-type) granites of the Lachlan Fold Belt. TRANS R SOC EDINBURGH EARTH SCI 79, 169–82.Google Scholar
White, A. J. R.&Chappell, B. W. 1989. Geology of the Numbla 1:000 000 sheet (8624). Sydney: New South Wales Geological Survey.Google Scholar
White, A. J. R., Chappell, B. W.&Cleary, J. R. 1974. Geologic setting and emplacement of some Australian Paleozoic batholiths and implications for intrusion mechanisms. PACIFIC GEOL 8, 159–71.Google Scholar
White, A. J. R., Williams, I. S.&Chappell, B. W. 1976. The Jindabyne Thrust and its tectonic, physiographic and petrogenetic significance. J GEOL SOC AUST 23, 105–12.CrossRefGoogle Scholar
White, A. J. R., Williams, I. S.&Chappell, B. W. 1977. Geology of the Berridale 1:000 000 sheet (8625). Sydney: New South Wales Geological Survey.Google Scholar
Williams, I. S, Chappell, B. W., Chen, Y.&Crook, K. A. W. 1992. Inherited and detrital zircons—vital clues to the granite protoliths and early igneous history of southeastern Australia. TRANS R SOC EDINBURGH EARTH SCI 83, 503.Google Scholar
Wyborn, D., Chappell, B. W.&Johnston, R. W. 1981. Three S-type volcanic suites from the Lachlan Fold Belt, southeast Australia. J GEOPHYS RES 86, 10335–48.CrossRefGoogle Scholar
Wyborn, D., Turner, B. S.&Chappell, B. W. 1987. The Boggy Plains Supersuite: a distinctive belt of I-type igneous rocks of potential economic significance in the Lachlan Fold Belt. AUST J EARTH SCI 34, 2143.CrossRefGoogle Scholar
Wyborn, L. A. I.&Chappell, B. W. 1983. Geochemistry of the Ordovician and Silurian greywackes of the Snowy Mountains, southeastern Australia: an example of chemical evolution of sediments with time. CHEM GEOL 39, 8192.CrossRefGoogle Scholar