Foreword: The Roles of Petrology and Experimental Petrology in Understanding Global Tectonics
Canberra
Frankfurt
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A VOLUME IN HONOUR OF THE WORK OF DAVID HEADLEY GREEN ON THE OCCASION OF HIS 18TH BIRTHDAY, 29 FEBRUARY 2008 |
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Born and educated in Tasmania, where S. Warren Carey was Professor of Geology, David Green began his undergraduate study of ultramafic and related rocks in 1956 with the field mapping and petrology of an ultramafic complex in northern Tasmania. His ‘literature’ thesis was an evaluation of the status of palaeomagnetism. The ‘Continental Drift Symposium’ was also held in Hobart in 1956 and showcased both S. W. Carey's detailed reconstructions of Gondwana and Laurasia and E. Irving's use of the palaeomagnetism of Jurassic dolerites as a tool for demonstrating continental drift. These formative experiences shaped David Green's career-long interest in ultramafic and mafic rocks and their place in global tectonics. Following graduation, two years of field mapping and petrological study of ultramafic complexes in north Queensland and Papua–New Guinea were followed by PhD research under C. E. Tilley at the University of Cambridge (UK) in 1959–1962. The results of his study of the Lizard peridotite, Cornwall, were published in two influential papers (Green, 1964a
, 1964b) describing the internal evidence for a solid-state, high-temperature decompression path within the lherzolite and the superimposition of a high-temperature, granulite-facies metamorphism on enclosing epidote–amphibolite metamorphic rocks. Recruited to the Australian National University by J. C. Jaeger to work with A. E. Ringwood, their first collaboration (Green & Ringwood, 1963) applied the observations from petrology to prediction of the petrological character of the upper mantle (the ‘pyrolite’ model). This was also the starting point for an experimental programme at high pressures and temperatures, focused on the characteristics of, and processes within, the Earth's upper mantle.
From 1962 to 1976, David Green and Ted Ringwood demonstrated one of the most creative and influential research collaborations in the earth sciences at the time. Two papers in Nature in 1964 (Green & Ringwood, 1964; Ringwood & Green, 1964) gave notice of three major papers (Ringwood & Green, 1966; Green & Ringwood, 1967a, 1967b), which demonstrated a new direction and methodology in experimental petrology. The ability of solid media piston-cylinder apparatus to reproduce the P,T conditions of the deep crust and uppermost mantle was combined with the newly developed electron probe microanalyser (EPMA) to methodically study mineral reactions, including partial melting, in complex natural rock compositions. A paper on the gabbro to eclogite reactions (Green & Ringwood, 1967a), demonstrated the role of bulk compositions and specific element ratios such as Mg-number in ferromagnesian minerals or Ca/(Ca + Na) in plagioclase, in controlling the appearance or disappearance of phases in P,T space. The application of the petrological study to global tectonics (Ringwood & Green, 1966) included the role of gabbro to eclogite reactions as a ‘tectonic engine’ and reflects both the debates of the time and the vigour of the co-authors’ collaboration in that the paper derived two contradictory concluding models using the ‘eclogite engine’—a ‘fixist’ continental margin growth model and a ‘subduction and continental drift’ model, reflecting the respective co-authors’ formative years.
With his experience and knowledge in field geology and petrology, David Green has been adept at selecting significant petrological observations or hypotheses and devising experimental strategies to investigate them. The diversity of deep crustal and upper mantle mineral equilibria to which he has contributed has been possible through collaborators, initially PhD students and, later, also visitors and post-doctoral fellows, both at ANU and the University of Tasmania. The gabbro to eclogite work led naturally to B. J. Hensen's and S. L. Harley's work on high-pressure and high-temperature granulites of pelitic, peraluminous compositions; to A. Råheim's and D. J. Ellis's work to calibrate the garnet/clinopyroxene Fe/Mg thermometer, and to details of the plagioclase lherzolite, spinel lherzolite, garnet lherzolite and pargasite lherzolite stability fields as functions of P,T and volatile contents (C, H, O). A recent paper (Niida & Green, 1999) exemplifies the detail attainable in multiphase assemblages using micro-imaging and micro-analysis techniques to reproduce in fine detail the mineralogy and petrology of the upper mantle.
Another 1967 paper ‘The genesis of basaltic magmas’ (Green & Ringwood, 1967b) remains a major reference demonstrating the effect of pressure on the liquidus phase relations of primitive basalts, the continuity of high-pressure peridotite melting from low-degree nepheline-normative alkali olivine basalts to high-degree melts of olivine tholeiite to tholeiitic picrite, and the role of mantle heterogeneity and open-system magma chamber processes in determining incompatible trace element and related isotopic abundances. Arising from this paper, David Green continued a two-pronged experimental programme, examining the melting behaviour of lherzolite (selecting enriched Hawaiian pyrolite, fertile MORB pyrolite and depleted Tinaquillo lherzolite as three lherzolite compositions differing only in minor elements and trace elements) in parallel with high-pressure liquidus studies of primitive basalts selected on the basis of hosting mantle xenoliths and having high Mg-number, and possibly olivine phenocrysts of Fo89 to Fo93 composition. David Green's publication list (Supplementary Data at http://petrology.oxfordjournals.org/) details the investigations adding H2O, CO2, H2O + CO2, and C + H + O fluid under controlled (reduced) fO2 conditions. Major emphasis was on intra-plate magmatism, where the importance in the source region of small quantities of both H2O and CO2 as volatile components is unequivocal. The strength of the two-pronged experimental approach and the parallel studies of volcanic provinces and mantle samples is well illustrated by the study (Frey & Green, 1974) of spinel lherzolite xenoliths identifying component A (residue from basalt extraction) and later addition of component B (cryptic metasomatism by incompatible element-rich fluid/melt). This relationship remained enigmatic until study of peridotite + H2O + CO2 revealed a stability field for sodic, dolomitic carbonatite melt in equilibrium with pargasite lherzolite (Wallace & Green, 1988). The upper bound of the carbonatite field is a decarbonation reaction converting lherzolite wall-rock towards apatite-bearing wehrlite (Green & Wallace, 1988; Yaxley et al., 1991; Yaxley & Green, 1996) and releasing CO2 vapour. Study of intraplate volcanism demonstrated the importance of small-degree melting fluxed by H2O and CO2 (Brey & Green, 1975, 1976) and led to a very specific model of the Earth's lithosphere and asthenosphere, first outlined by Green (1971) and updated by Green et al. (1987) and Green & Falloon (1998, 2005). The geophysical aspects of this petrologically defined model were explored by Green & Liebermann (1976).
The Apollo lunar expeditions invited the application of experimental techniques to lunar mare basalts in particular. David Green's particular contributions in 1972–1975 were to the Apollo 12, 15 and 17 mare basalt suites, where he combined study of glasses and phenocryst compositions to identify parental magmas in different suites and then used experimental techniques to determine eruption temperatures and to constrain depths and temperatures of multiple phase saturation (and thus of probable magma segregation).
This approach of identifying the most primitive and higher temperature magmas developed for the lunar samples was then applied to terrestrial magmas, most notably to Archaean peridotitic komatiite magmas (Green, 1975, 1981; Green et al., 1975) and more recently to mid-ocean ridge and hotspot basalts (Green et al., 1979, 2001; Falloon & Green, 1988; Green & Falloon, 2005). In convergent margin settings, the identification of primitive back-arc basin magmas (Duncan & Green, 1987; Falloon et al., 1999), boninites (Dallwitz et al., 1966; Crawford et al., 1989; Falloon et al., 1989) and island arc ankaramites (Green et al., 2004) was integrated with studies of water-saturated melting of peridotite (Green, 1973, 1976) and evidence of involvement of both carbonatitic and rhyodacitic melts from within the mantle wedge (carbonatitic melts) and upper (eclogitic) part of the subducted slab (rhyodacitic to dacitic melts).
At ANU from 1962 to 1976, University of Tasmania from 1976 to 1994 and returning to ANU from 1994 to the present, David Green was able to build research teams applying complementary approaches to diverse problems related to the petrology and geochemistry of natural rocks and, by the use of experimental techniques, to understand their petrogenesis in the context of global tectonics. He has been able to initiate new techniques in experiment design and the analysis of experimental changes, including applications in IR spectroscopy, quenched vapour analysis and electron microscopy. His investigations have led him to compositional rather than thermal buoyancy as the cause of ‘mantle plumes’; to mantle potential temperatures of 
1430°C in the modern Earth but considerably higher in the Archaean; to a specific model [quantified by Green & Liebermann (1976) and Green & Falloon (2005)] for the Earth's lithosphere and asthenosphere. These are debatable and mainstream research themes and current debates find expression in some of the papers submitted for this volume.
On February 29, 2008, David Green celebrated his 18th birthday in his 72nd year. A symposium in his honour was held at the Goldschmidt Conference in Melbourne in 2006 and a number of papers in this volume are by speakers at that symposium. Authors include former students, and all are colleagues who share his enthusiasm for study of rocks as they occur, for new surprises in both observation and experiment, and for the gathering of a body of high-quality experimental information. David Green's research, and that of his students and collaborators, has had and continues to have major impact on our understanding of global geodynamics, demonstrating that geodynamic models have to be based on knowledge of the materials and properties of real rocks—on petrology and petrophysics.
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Supplementary data for this Foreword are available at Journal of Petrology online.
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FOOTNOTES |
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March 2008
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REFERENCES |
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Brey G, Green DH. The role of CO2 in the genesis of olivine melilitite. Contributions to Mineralogy and Petrology (1975) 49:93–103.[CrossRef][Web of Science]
Brey G, Green DH. Solubility of CO2 in olivine melilitite at high pressure and role of CO2 in the Earth's upper mantle. Contributions to Mineralogy and Petrology (1976) 55:217–230.[CrossRef][Web of Science]
Crawford AJ, Falloon TJ, Green DH. Classification, petrogenesis and tectonic setting of boninites. In: Boninites and Related Rocks—Crawford AJ, ed. (1989) London: Unwin Hyman. 1–49.
Dallwitz WB, Green DH, Thompson JE. Clinoenstatite in a volcanic rock from the Cape Vogel area, Papua. Journal of Petrology (1966) 7:375–403.
Duncan RA, Green DH. The genesis of refractory melts in the formation of oceanic crust. Contributions to Mineralogy and Petrology (1987) 96:326–342.[CrossRef][Web of Science]
Falloon TJ, Green DH, Jaques AL, Hawkins JW. Refractory magmas in back-arc basin settings—Experimental constraints on the petrogenesis of a Lau Basin example. Journal of Petrology (1999) 40:255–277.[CrossRef][Web of Science]
Falloon AJ, Green DH, McCulloch MT. Petrogenesis of high-Mg and associated lavas from the north Tonga Trench. In: Boninites and Related Rocks—Crawford AJ, ed. (1989) London: Unwin Hyman. 357–395.
Frey F, Green DH. The mineralogy, geochemistry and origin of lherzolite inclusions in Victorian basanites. Geochimica et Cosmochimica Acta (1974) 38:1023–1059.[CrossRef][Web of Science]
Green DH. The metamorphic aureole of the peridotite at the Lizard, Cornwall. Journal of Geology (1964a) 72:543–563.[Web of Science]
Green DH. The petrogenesis of the high-temperature peridotite intrusion in the Lizard area, Cornwall. Journal of Petrology (1964b) 5:134–188.
Green DH. Compositions of basaltic magmas as indicators of conditions of origin: application to oceanic volcanism. Philosophical Transactions of the Royal Society of London, Series A (1971) 268:707–725.[CrossRef]
Green DH. Experimental melting studies on a model upper mantle composition at high pressure under water-saturated and water-undersaturated conditions. Earth and Planetary Science Letters (1973) 19:37–53.[CrossRef][Web of Science]
Green DH. Genesis of Archaean peridotitic magmas and constraints on Archaean geothermal gradients and tectonics. Geology (1975) 3:15–18.
Green DH. Experimental testing of ‘equilibrium’ partial melting of peridotite under water-saturated, high pressure conditions. Canadian Mineralogist (1976) 14:255–268.
Green DH. Petrogenesis of Archaean ultramafic magmas and implications for Archaean tectonics. In: Precambrian Plate Tectonics—Kroner A, ed. (1981) Amsterdam: Elsevier. 469–489.
Green DH, Falloon TJ. Pyrolite: A Ringwood concept and its current expression. In: The Earth's Mantle: Composition, Structure and Evolution—Jackson I, ed. (1998) Cambridge: Cambridge University Press. 311–380.
Green DH, Falloon TJ. Primary magmas at mid-ocean ridges, ‘hotspots’, and other intraplate settings: constraints on mantle potential temperature. In: Plates, Plumes and Paradigms. Geological Society of America, Special Papers —Foulger G, Natland J, Presnall D, Anderson D, eds. (2005) 388:217–247.[CrossRef]
Green DH, Liebermann RC. Phase equilibria and elastic properties of a pyrolite model for the oceanic upper mantle. Tectonophysics (1976) 32:61–92.[CrossRef][Web of Science]
Green DH, Ringwood AE. Mineral assemblages in a model mantle composition. Journal of Geophysical Research (1963) 68:937–945.
Green DH, Ringwood AE. Fractionation of basalt magmas at high pressures. Nature (1964) 201:1276–1279.[CrossRef]
Green DH, Ringwood AE. An experimental investigation of the gabbro to eclogite transformation and its petrological applications. Geochimica et Cosmochimica Acta (1967a) 31:767–833.[Web of Science]
Green DH, Ringwood AE. The genesis of basaltic magmas. Contributions to Mineralogy and Petrology (1967b) 15:103–190.[CrossRef]
Green DH, Wallace ME. Mantle metasomatism by ephemeral carbonatite melts. Nature (1988) 336:459–462.[CrossRef]
Green DH, Falloon TJ, Taylor W. Mantle-derived magmas—roles of variable source peridotite and variable C–H–O fluid compositions. In. In: Magmatic Processes and Physicochemical Principles. Geochemical Society Special Publication—Mysen BO, ed. (1987) 1:139–154.
Green DH, Falloon TJ, Eggins SM, Yaxley GM. Primary magmas and mantle temperatures. European Journal of Mineralogy (2001) 13:437–451.
Green DH, Hibberson WO, Jaques AL. Petrogenesis of mid-ocean ridge basalts. In: The Earth: Its Origin, Structure and Evolution—McElhinney MW, ed. (1979) London: Academic Press. 265–290.
Green DH, Schmidt MW, Hibberson WO. Island-arc ankaramites: primitive melts from fluxed refractory lherzolitic mantle. Journal of Petrology (2004) 45(2):391–403.
Niida K, Green DH. Stability and chemical composition of pargasitic amphibole in MORB pyrolite under upper mantle conditions. Contributions to Mineralogy and Petrology (1999) 135:18–40.[CrossRef][Web of Science]
Ringwood AE, Green DH. Experimental investigations bearing on the nature of the Mohorovicic Discontinuity. Nature (1964) 201:566–567.[CrossRef]
Ringwood AE, Green DH. An experimental investigation of the gabbro–eclogite transformation and some geophysical implications. Tectonophysics (1966) 3:383–427.[CrossRef][Web of Science]
Wallace ME, Green DH. An experimental determination of primary carbonatite magma composition. Nature (1988) 335:343–346.[CrossRef]
Yaxley GM, Green DH. Experimental reconstruction of sodic dolomitic carbonatite melts from metasomatised lithosphere. Contributions to Mineralogy and Petrology (1996) 124:359–369.[CrossRef][Web of Science]
Yaxley GM, Crawford AJ, Green DH. Evidence for carbonatite metasomatism in spinel peridotite xenoliths from W. Victoria, Australia. Earth and Planetary Science Letters (1991) 107:305–317.[CrossRef][Web of Science]
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