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Papers by Trevor Green

Chemical Geology, 1994

An electron microprobe was used to measure partition coefficients (D-values) for Ti, Sr, La, Sm, ... more An electron microprobe was used to measure partition coefficients (D-values) for Ti, Sr, La, Sm, Ho and Lu in amphiboles, clinopyroxenes and Sr-and REE-enriched basanitic melts, D-values were found to be negatively correlated with pressure at pressures from 0.5 to 3.0 GPa. This effect is greatest for Ti and smallest for Lu. Changes in D-values accompanying changes in temperature are less apparent than those caused by changes in pressure. Only Dcu for clinopyroxene shows a small but consistent increase as temperature increases from 1050 ° to 1200 ° C. D-values for amphibole are not noticeably affected by changes in fo2. In contrast, D-values for clinopyroxene become larger as fo2 increases. The correlations between D-values and pressure may be related to changes in site volumes and electrostatic potentials accompanying shifts in the relative concentrations of AI iv, AI vl and Na +.

Australian Journal of Earth Sciences, 1972

Page 1. CRYSTALLIZATION OF GARNET-BEARING RHYODACITE UNDER HIGH-PRESSURE HYDROUS CONDITIONS By TR... more Page 1. CRYSTALLIZATION OF GARNET-BEARING RHYODACITE UNDER HIGH-PRESSURE HYDROUS CONDITIONS By TREVOR H. GREEN & AE RINGWOOD (With 3 Tables and 6 Text-Figures) (Received 22 November, 1971: read by title at Perth, 13 March, 1972) ...

In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate system... more In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate systems, numerous studies providing new data have filled many of the gaps in knowledge of trace-element partitioning evident at that conference. The advent of new microbeam techniques for in situ trace-element analysis has provided great impetus for this work. For example, values for large ion lithophile element (LILE) and high field strength element (HFSE) partitioning between olivine, pyroxene, garnet, amphibole and titanate minerals and silicate liquids have been determined. When plotted on mantle normalizing geochemical diagrams, partition coefficients for the main mantle silicate minerals show steeply inclined patterns (over several orders of magnitude) from LILE to heavy rareearth elements (HREE). Amphibole, however, has a relatively flat pattern (though still favouring HREE over LILE by about an order of magnitude). Also, there is a notable flattening of the patterns for HREE in pyroxenes and garnet relative to olivine.

Can J Earth Sci, 1969

Page 1. High-pressure experimental studies on the origin of anorthosite TREVOR H. GREEN Hoflman L... more Page 1. High-pressure experimental studies on the origin of anorthosite TREVOR H. GREEN Hoflman Laboratory, Harvard University, 20 Oxford St., Cambridge, Mass. 02138, USA Received November 26, 1968 Accepted for publication February 28, 1969 ...

Int Geol Rev, 1995

... that form Page 4. 854 TREVOR H. GREEN FIG. 1. Experimentally ... at Sr. Interpreted PT condi ... more ... that form Page 4. 854 TREVOR H. GREEN FIG. 1. Experimentally ... at Sr. Interpreted PT condi tions of formation are from 800 to 1100° C at 0.8 to 2.5 GPa. The Eifel data (Witt-Eickschen and Harte, 1994) fall into two groups (Fig. 2). The ...

JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY, 1997

Transactions of the Royal Society of Edinburgh: Earth Sciences, 1992

Physics of the Earth and Planetary Interiors, 1970

Abstract Diorite and gabbroic anorthosite have been proposed as two possible overall compositions... more Abstract Diorite and gabbroic anorthosite have been proposed as two possible overall compositions constituting the lower crust. The mineral assemblages stable in these compositions under anhydrous conditions at temperatures of 900–1200 C and pressures ...

Lithos, 1990

. Experimental study of barium partitioning between phlogopite and silicate liquid at upper-mantl... more . Experimental study of barium partitioning between phlogopite and silicate liquid at upper-mantle pressure and temperature. Lithos, 24: 83-95. Barium partition coefficients for phlogopite crystallized from a natural lamproite at 10-30 kbar and 900-1150°C show a three-fold decrease in partition coefficient (D) with increasing pressure from 10 to 30 kbar (e.g., from 0.75 to 0.23), and 35-50% increase in D with increasing temperature from 1000 ° to 1100°C at 10 and 15 kbar (e.g., from 0.51 to 0.75). The variation with temperature is contrary to most recorded variations olD, and is attributed to a compositional control in the phlogopite. D correlates with substitution of titanium in the phlogopite. Thus as the titanium content increases with increasing temperature, the barium content, and hence D, increases. Application of partitioning data for barium in models for lamproite genesis suggests that phlogopite of metasomatic origin, and possibly some barium-rich accessory phases, are present in the source rocks for lamproite, and phlogopite plays a major role in the generation of lamproitic magma.

Journal of Petrology, 1997

alkaline melts, modelled on glasses found in many mantle xenoliths, The compositions of silicate ... more alkaline melts, modelled on glasses found in many mantle xenoliths, The compositions of silicate melts potentially in equishow that part of this compositional range is saturated with librium with the Earth's mantle have long been of interest harzburgite (or possibly lherzolite) under anhydrous conditions. to petrologists and geochemists. Much useful information Under C-O-H fluid-saturated conditions with X H2O =0·5, phloabout such melts has come from the study of melt gopite mica is present along with anhydrous phases similar to those inclusions in phenocrysts in volcanic rocks and in the found under dry conditions. Phlogopite is the sole liquidus phase minerals of ultramafic mantle xenoliths. In addition, when X H2O =1·0. At X H2O =0·5 and 3·0 GPa, garnet, kyanite many mantle xenoliths contain silicate glasses as a discrete and carbonate minerals appear as near-liquidus phases and the phase, rather than (or in addition to) inclusions (see shape of the liquidus surface is reminiscent of that of the carbonated Appendix A for references). In this paper, we will refer peridotite solidus. Saturation of these liquids with harzburgite, and to discrete-phase xenolith glasses simply as xenolith comparisons with calculated melt silica activities, suggests that these glasses and those found as inclusions in minerals as liquids would face no chemical or thermal obstacles to circulating inclusion glasses. Xenolith glasses have been reported amongst and coexisting with harzburgitic mantle. Also, there is from mantle xenoliths hosted by alkaline, mafic magmas textural evidence that these melts may be mobile. Accordingly, these both from intra-plate and from subduction-related teckinds of liquids could act as cryptic metasomatic agents. If mantle tonic settings. The glasses have a wide range of com-at~45-90 km depth is pre-enriched in low-melting-temperature positions and textural relations: they are found as components, and probably volatiles, via the ascent and percolation intergranular blebs, irregular patches, veins, and thin of alkaline, mafic liquids (along geotherms that cross inflections in films that appear to wet all grain faces. Most glasses the solidus of CO 2 -bearing peridotite), then subsequent low-degree account for, at most, only a few volume percent of their partial melts could yield the liquids that are ultimately trapped as host xenolith, and some much less than 1 vol. %. xenolith glasses.

Geology, 1976

Experimental generation of cordierite-or garnet-bearing granitic liquids from a pelitic compositi... more Experimental generation of cordierite-or garnet-bearing granitic liquids from a pelitic composition ABSTRACT High-pressure experimental melting studies on a pelitic composition with 2 and 5 percent by weight of added water demonstrate that cordierite, quartz, biotite, sillimanite, ...

Earth and Planetary Science Letters, 1999

We report new experimental results obtained under nominally anhydrous conditions at 1.0–1.5 GPa o... more We report new experimental results obtained under nominally anhydrous conditions at 1.0–1.5 GPa on a synthetic melt whose composition is typical of extreme-composition xenolith glasses. These results demonstrate that part of this extreme compositional range is in ...

Contributions to Mineralogy and Petrology, 1982

Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series ... more Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite, and (2) crystallizing similar natural rock compositions progressively until apatite appears, demonstrate a close dependence between apatite saturation and silica content of the magma, and determine P2Os levels at a given silica value and temperature at which that composition may be expected to crystallize apatite. The effect of pressure on apatite solubility is not great, and is most significant for silicic compositions.

Contributions to Mineralogy and Petrology, 1972

Page 1. Contr. Mineral. and Petrol. 34, 150-166 (1972) 9 by Springer-Verlag 1972 Crystallization ... more Page 1. Contr. Mineral. and Petrol. 34, 150-166 (1972) 9 by Springer-Verlag 1972 Crystallization of Calc-Alkaline Andesite under Controlled High-Pressure Hydrous Conditions TI~EVOI~ H. GREEN School of Earth Sciences ...

Contributions to Mineralogy and Petrology, 1977

Melting experiments on a model pelitic composition yield low-spessartine garnet as an important r... more Melting experiments on a model pelitic composition yield low-spessartine garnet as an important residual phase at pressures above 7 kb. The K D values for distribution of iron and magnesium between coexisting garnet and liquid in the pelitic composition are mainly sensitive to temperature, but also have a small pressure dependence. At tempera-<4% MnO) to an Mn-richer rim (typically >4% MnO) and may reflect continued growth of the garnet in a low pressure regime, stabilized by Mn concentrated in the residual liquid fractions of the crystallizing magma.

Contributions to Mineralogy and Petrology, 1967

The sub-solidus fields of crystallization of a spectrum of synthetic aluminous basic compositions... more The sub-solidus fields of crystallization of a spectrum of synthetic aluminous basic compositions (high-alumina basalt, anorthite-enriched high-alumina basalt, kyanite eclogite, grosspydite and gabbroic anorthosite) have been investigated at pressures of up to 36 kb. At low pressures the assemblages are characterized by abundant plagioelase, clinopyroxene and possibly minor olivine and orthopyroxene. These correspond to natural gabbroie and pyroxene granulite assemblages. As pressure is increased garnet appears and increases gradually in amount at the expense of other ferromagnesian minerals and plagioelase, until finally at pressures of >23 kb at 1,100 ~ C, plagioclase disappears and high pressure clinopyroxene + garnet + kyanite =]= quartz assemblages equivalent to eclogite are obtained. In the eclogite stability field, with further rise in pressure, the ratio ga/cpx and the grossular content of the garnet increase. In the high-alumina basalt composition the transitional garnet granulite assemblage (clinopyroxene + plagioclase-~ garnet ~ quartz) is spread over a pressure interval of 11 kb at 1,100 ~ C. This is a greater interval than observed for other basalt compositions and is important in considering the hypothesis that the Mohorovicic Discontinuity is a phase change from basalt to eclogite. It indicates that the change in Vp would be spread over a significant depth range, and no sharp seismic velocity discontinuity could result. The first experimental synthesis of kyanite eclogite from both high-alumina basalt and kyanite eclogite compositions has been obtained, as well as synthesis of unusual grossular-clinopyroxene-kyanite assemblages (grosspydite) from grosspydite and gabbroic anorthosite compositions. The pressures needed to synthesize these assemblages are somewhat greater than the pressures needed to synthesize ecl0gite from basic compositions of lower alumina content at the same temperature. Experimental confirmation of the observation that there is a direct Gross Jd relation between Alm+ Py ratio of garnet and the ~-ratio of co-existing pyroxene in grosspydite and kyanite eelogite assemblages found in kimberlite pipes has also been obtained.

Contributions to Mineralogy and Petrology, 1989

... Jingfeng Guo and Trevor H. Green School of Earth Sciences, Macquarie University, Sydney, NSW ... more ... Jingfeng Guo and Trevor H. Green School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia Abstract. ... The lack of knowledge about the temperature and pressure of crystallization seriously limits their utiliza-tion (Shimizu 1974; Drake and Weill 1975). ...

Chemical Geology, 1995

A mantle value of -I 7.5 for Nb/Ta appears well established; less well established are crustal va... more A mantle value of -I 7.5 for Nb/Ta appears well established; less well established are crustal values of -I I -12, although it appears that Nb/Ta for crustal-derived melts is less than mantle Nb/Ta, demonstrating fractionation of these two elements during crustal evolution, and suggesting that Nb/Ta variation may be indicative of a particular chemical process within the crust-mantle system. Experimental studies on silicate and carbonatitic liquids at high pressure indicate that, although silicate minerals such as garnet, amphibole and clinopyroxene do fractionate Nb and Ta, the partition coefficients (D's) for both elements are very low. Thus involvement of these minerals may explain relatively small changes in Nb/Ta, but appears inadequate to explain the crust-mantle variation. However, high-quality data for Nb, Ta may be used to provide information on mantle melting or metasomatic processes (e.g.. amphibole in the source region decreases Nb/Ta in derived melts. while carbonatitic metasomatism will increase Nb/Ta in affected mantle). Titanate minerals have high D's for Nb and Ta. and do fractionate these elements (e.g., DNb/DTa rutile/liquid of 0.5-0.8), and their involvement in crystal fractionation would increase Nb/Ta in derivative liquids. In contrast, DJD,, for rutile/fluid is -1.25. so that rocks affected by fluid equilibrated with residual rutile will show a decrease in Nb/ Ta. Some Archaean gneisses appear to have high Nb/Ta, and may be a complementary component to that part of the crust which has a relatively low Nb/Ta: such as crustal-derived magmas (e.g., A-and I-type granites and silicic volcanics). Within the crustal system pegmatites are known to have extremely high and variable Nb, Ta contents, often with low Nb/Ta. A fluid is generally considered to be involved in the generation of these rocks. Thus it is possible that fluid/melt partitioning may be the key to fractionating Nb and Ta, with preference for Ta in the fluid, and enrichment of Ta relative to Nb into the mid-upper crustal system, as the crust evolved, through upward movement of fluid. 0009-2541/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOOO9-2541(94)00145-6

Chemical Geology, 1994

In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate system... more In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate systems, numerous studies providing new data have filled many of the gaps in knowledge of trace-element partitioning evident at that conference. The advent of new microbeam techniques for in situ trace-element analysis has provided great impetus for this work. For example, values for large ion lithophile element (LILE) and high field strength element (HFSE) partitioning between olivine, pyroxene, garnet, amphibole and titanate minerals and silicate liquids have been determined. When plotted on mantle normalizing geochemical diagrams, partition coefficients for the main mantle silicate minerals show steeply inclined patterns (over several orders of magnitude) from LILE to heavy rareearth elements (HREE). Amphibole, however, has a relatively flat pattern (though still favouring HREE over LILE by about an order of magnitude). Also, there is a notable flattening of the patterns for HREE in pyroxenes and garnet relative to olivine.

Chemical Geology, 1994

An electron microprobe was used to measure partition coefficients (D-values) for Ti, Sr, La, Sm, ... more An electron microprobe was used to measure partition coefficients (D-values) for Ti, Sr, La, Sm, Ho and Lu in amphiboles, clinopyroxenes and Sr-and REE-enriched basanitic melts, D-values were found to be negatively correlated with pressure at pressures from 0.5 to 3.0 GPa. This effect is greatest for Ti and smallest for Lu. Changes in D-values accompanying changes in temperature are less apparent than those caused by changes in pressure. Only Dcu for clinopyroxene shows a small but consistent increase as temperature increases from 1050 ° to 1200 ° C. D-values for amphibole are not noticeably affected by changes in fo2. In contrast, D-values for clinopyroxene become larger as fo2 increases. The correlations between D-values and pressure may be related to changes in site volumes and electrostatic potentials accompanying shifts in the relative concentrations of AI iv, AI vl and Na +.

Australian Journal of Earth Sciences, 1972

Page 1. CRYSTALLIZATION OF GARNET-BEARING RHYODACITE UNDER HIGH-PRESSURE HYDROUS CONDITIONS By TR... more Page 1. CRYSTALLIZATION OF GARNET-BEARING RHYODACITE UNDER HIGH-PRESSURE HYDROUS CONDITIONS By TREVOR H. GREEN &amp;amp; AE RINGWOOD (With 3 Tables and 6 Text-Figures) (Received 22 November, 1971: read by title at Perth, 13 March, 1972) ...

In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate system... more In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate systems, numerous studies providing new data have filled many of the gaps in knowledge of trace-element partitioning evident at that conference. The advent of new microbeam techniques for in situ trace-element analysis has provided great impetus for this work. For example, values for large ion lithophile element (LILE) and high field strength element (HFSE) partitioning between olivine, pyroxene, garnet, amphibole and titanate minerals and silicate liquids have been determined. When plotted on mantle normalizing geochemical diagrams, partition coefficients for the main mantle silicate minerals show steeply inclined patterns (over several orders of magnitude) from LILE to heavy rareearth elements (HREE). Amphibole, however, has a relatively flat pattern (though still favouring HREE over LILE by about an order of magnitude). Also, there is a notable flattening of the patterns for HREE in pyroxenes and garnet relative to olivine.

Can J Earth Sci, 1969

Page 1. High-pressure experimental studies on the origin of anorthosite TREVOR H. GREEN Hoflman L... more Page 1. High-pressure experimental studies on the origin of anorthosite TREVOR H. GREEN Hoflman Laboratory, Harvard University, 20 Oxford St., Cambridge, Mass. 02138, USA Received November 26, 1968 Accepted for publication February 28, 1969 ...

Int Geol Rev, 1995

... that form Page 4. 854 TREVOR H. GREEN FIG. 1. Experimentally ... at Sr. Interpreted PT condi ... more ... that form Page 4. 854 TREVOR H. GREEN FIG. 1. Experimentally ... at Sr. Interpreted PT condi tions of formation are from 800 to 1100° C at 0.8 to 2.5 GPa. The Eifel data (Witt-Eickschen and Harte, 1994) fall into two groups (Fig. 2). The ...

JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY, 1997

Transactions of the Royal Society of Edinburgh: Earth Sciences, 1992

Physics of the Earth and Planetary Interiors, 1970

Abstract Diorite and gabbroic anorthosite have been proposed as two possible overall compositions... more Abstract Diorite and gabbroic anorthosite have been proposed as two possible overall compositions constituting the lower crust. The mineral assemblages stable in these compositions under anhydrous conditions at temperatures of 900–1200 C and pressures ...

Lithos, 1990

. Experimental study of barium partitioning between phlogopite and silicate liquid at upper-mantl... more . Experimental study of barium partitioning between phlogopite and silicate liquid at upper-mantle pressure and temperature. Lithos, 24: 83-95. Barium partition coefficients for phlogopite crystallized from a natural lamproite at 10-30 kbar and 900-1150°C show a three-fold decrease in partition coefficient (D) with increasing pressure from 10 to 30 kbar (e.g., from 0.75 to 0.23), and 35-50% increase in D with increasing temperature from 1000 ° to 1100°C at 10 and 15 kbar (e.g., from 0.51 to 0.75). The variation with temperature is contrary to most recorded variations olD, and is attributed to a compositional control in the phlogopite. D correlates with substitution of titanium in the phlogopite. Thus as the titanium content increases with increasing temperature, the barium content, and hence D, increases. Application of partitioning data for barium in models for lamproite genesis suggests that phlogopite of metasomatic origin, and possibly some barium-rich accessory phases, are present in the source rocks for lamproite, and phlogopite plays a major role in the generation of lamproitic magma.

Journal of Petrology, 1997

alkaline melts, modelled on glasses found in many mantle xenoliths, The compositions of silicate ... more alkaline melts, modelled on glasses found in many mantle xenoliths, The compositions of silicate melts potentially in equishow that part of this compositional range is saturated with librium with the Earth's mantle have long been of interest harzburgite (or possibly lherzolite) under anhydrous conditions. to petrologists and geochemists. Much useful information Under C-O-H fluid-saturated conditions with X H2O =0·5, phloabout such melts has come from the study of melt gopite mica is present along with anhydrous phases similar to those inclusions in phenocrysts in volcanic rocks and in the found under dry conditions. Phlogopite is the sole liquidus phase minerals of ultramafic mantle xenoliths. In addition, when X H2O =1·0. At X H2O =0·5 and 3·0 GPa, garnet, kyanite many mantle xenoliths contain silicate glasses as a discrete and carbonate minerals appear as near-liquidus phases and the phase, rather than (or in addition to) inclusions (see shape of the liquidus surface is reminiscent of that of the carbonated Appendix A for references). In this paper, we will refer peridotite solidus. Saturation of these liquids with harzburgite, and to discrete-phase xenolith glasses simply as xenolith comparisons with calculated melt silica activities, suggests that these glasses and those found as inclusions in minerals as liquids would face no chemical or thermal obstacles to circulating inclusion glasses. Xenolith glasses have been reported amongst and coexisting with harzburgitic mantle. Also, there is from mantle xenoliths hosted by alkaline, mafic magmas textural evidence that these melts may be mobile. Accordingly, these both from intra-plate and from subduction-related teckinds of liquids could act as cryptic metasomatic agents. If mantle tonic settings. The glasses have a wide range of com-at~45-90 km depth is pre-enriched in low-melting-temperature positions and textural relations: they are found as components, and probably volatiles, via the ascent and percolation intergranular blebs, irregular patches, veins, and thin of alkaline, mafic liquids (along geotherms that cross inflections in films that appear to wet all grain faces. Most glasses the solidus of CO 2 -bearing peridotite), then subsequent low-degree account for, at most, only a few volume percent of their partial melts could yield the liquids that are ultimately trapped as host xenolith, and some much less than 1 vol. %. xenolith glasses.

Geology, 1976

Experimental generation of cordierite-or garnet-bearing granitic liquids from a pelitic compositi... more Experimental generation of cordierite-or garnet-bearing granitic liquids from a pelitic composition ABSTRACT High-pressure experimental melting studies on a pelitic composition with 2 and 5 percent by weight of added water demonstrate that cordierite, quartz, biotite, sillimanite, ...

Earth and Planetary Science Letters, 1999

We report new experimental results obtained under nominally anhydrous conditions at 1.0–1.5 GPa o... more We report new experimental results obtained under nominally anhydrous conditions at 1.0–1.5 GPa on a synthetic melt whose composition is typical of extreme-composition xenolith glasses. These results demonstrate that part of this extreme compositional range is in ...

Contributions to Mineralogy and Petrology, 1982

Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series ... more Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite, and (2) crystallizing similar natural rock compositions progressively until apatite appears, demonstrate a close dependence between apatite saturation and silica content of the magma, and determine P2Os levels at a given silica value and temperature at which that composition may be expected to crystallize apatite. The effect of pressure on apatite solubility is not great, and is most significant for silicic compositions.

Contributions to Mineralogy and Petrology, 1972

Page 1. Contr. Mineral. and Petrol. 34, 150-166 (1972) 9 by Springer-Verlag 1972 Crystallization ... more Page 1. Contr. Mineral. and Petrol. 34, 150-166 (1972) 9 by Springer-Verlag 1972 Crystallization of Calc-Alkaline Andesite under Controlled High-Pressure Hydrous Conditions TI~EVOI~ H. GREEN School of Earth Sciences ...

Contributions to Mineralogy and Petrology, 1977

Melting experiments on a model pelitic composition yield low-spessartine garnet as an important r... more Melting experiments on a model pelitic composition yield low-spessartine garnet as an important residual phase at pressures above 7 kb. The K D values for distribution of iron and magnesium between coexisting garnet and liquid in the pelitic composition are mainly sensitive to temperature, but also have a small pressure dependence. At tempera-<4% MnO) to an Mn-richer rim (typically >4% MnO) and may reflect continued growth of the garnet in a low pressure regime, stabilized by Mn concentrated in the residual liquid fractions of the crystallizing magma.

Contributions to Mineralogy and Petrology, 1967

The sub-solidus fields of crystallization of a spectrum of synthetic aluminous basic compositions... more The sub-solidus fields of crystallization of a spectrum of synthetic aluminous basic compositions (high-alumina basalt, anorthite-enriched high-alumina basalt, kyanite eclogite, grosspydite and gabbroic anorthosite) have been investigated at pressures of up to 36 kb. At low pressures the assemblages are characterized by abundant plagioelase, clinopyroxene and possibly minor olivine and orthopyroxene. These correspond to natural gabbroie and pyroxene granulite assemblages. As pressure is increased garnet appears and increases gradually in amount at the expense of other ferromagnesian minerals and plagioelase, until finally at pressures of >23 kb at 1,100 ~ C, plagioclase disappears and high pressure clinopyroxene + garnet + kyanite =]= quartz assemblages equivalent to eclogite are obtained. In the eclogite stability field, with further rise in pressure, the ratio ga/cpx and the grossular content of the garnet increase. In the high-alumina basalt composition the transitional garnet granulite assemblage (clinopyroxene + plagioclase-~ garnet ~ quartz) is spread over a pressure interval of 11 kb at 1,100 ~ C. This is a greater interval than observed for other basalt compositions and is important in considering the hypothesis that the Mohorovicic Discontinuity is a phase change from basalt to eclogite. It indicates that the change in Vp would be spread over a significant depth range, and no sharp seismic velocity discontinuity could result. The first experimental synthesis of kyanite eclogite from both high-alumina basalt and kyanite eclogite compositions has been obtained, as well as synthesis of unusual grossular-clinopyroxene-kyanite assemblages (grosspydite) from grosspydite and gabbroic anorthosite compositions. The pressures needed to synthesize these assemblages are somewhat greater than the pressures needed to synthesize ecl0gite from basic compositions of lower alumina content at the same temperature. Experimental confirmation of the observation that there is a direct Gross Jd relation between Alm+ Py ratio of garnet and the ~-ratio of co-existing pyroxene in grosspydite and kyanite eelogite assemblages found in kimberlite pipes has also been obtained.

Contributions to Mineralogy and Petrology, 1989

... Jingfeng Guo and Trevor H. Green School of Earth Sciences, Macquarie University, Sydney, NSW ... more ... Jingfeng Guo and Trevor H. Green School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia Abstract. ... The lack of knowledge about the temperature and pressure of crystallization seriously limits their utiliza-tion (Shimizu 1974; Drake and Weill 1975). ...

Chemical Geology, 1995

A mantle value of -I 7.5 for Nb/Ta appears well established; less well established are crustal va... more A mantle value of -I 7.5 for Nb/Ta appears well established; less well established are crustal values of -I I -12, although it appears that Nb/Ta for crustal-derived melts is less than mantle Nb/Ta, demonstrating fractionation of these two elements during crustal evolution, and suggesting that Nb/Ta variation may be indicative of a particular chemical process within the crust-mantle system. Experimental studies on silicate and carbonatitic liquids at high pressure indicate that, although silicate minerals such as garnet, amphibole and clinopyroxene do fractionate Nb and Ta, the partition coefficients (D's) for both elements are very low. Thus involvement of these minerals may explain relatively small changes in Nb/Ta, but appears inadequate to explain the crust-mantle variation. However, high-quality data for Nb, Ta may be used to provide information on mantle melting or metasomatic processes (e.g.. amphibole in the source region decreases Nb/Ta in derived melts. while carbonatitic metasomatism will increase Nb/Ta in affected mantle). Titanate minerals have high D's for Nb and Ta. and do fractionate these elements (e.g., DNb/DTa rutile/liquid of 0.5-0.8), and their involvement in crystal fractionation would increase Nb/Ta in derivative liquids. In contrast, DJD,, for rutile/fluid is -1.25. so that rocks affected by fluid equilibrated with residual rutile will show a decrease in Nb/ Ta. Some Archaean gneisses appear to have high Nb/Ta, and may be a complementary component to that part of the crust which has a relatively low Nb/Ta: such as crustal-derived magmas (e.g., A-and I-type granites and silicic volcanics). Within the crustal system pegmatites are known to have extremely high and variable Nb, Ta contents, often with low Nb/Ta. A fluid is generally considered to be involved in the generation of these rocks. Thus it is possible that fluid/melt partitioning may be the key to fractionating Nb and Ta, with preference for Ta in the fluid, and enrichment of Ta relative to Nb into the mid-upper crustal system, as the crust evolved, through upward movement of fluid. 0009-2541/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOOO9-2541(94)00145-6

Chemical Geology, 1994

In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate system... more In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate systems, numerous studies providing new data have filled many of the gaps in knowledge of trace-element partitioning evident at that conference. The advent of new microbeam techniques for in situ trace-element analysis has provided great impetus for this work. For example, values for large ion lithophile element (LILE) and high field strength element (HFSE) partitioning between olivine, pyroxene, garnet, amphibole and titanate minerals and silicate liquids have been determined. When plotted on mantle normalizing geochemical diagrams, partition coefficients for the main mantle silicate minerals show steeply inclined patterns (over several orders of magnitude) from LILE to heavy rareearth elements (HREE). Amphibole, however, has a relatively flat pattern (though still favouring HREE over LILE by about an order of magnitude). Also, there is a notable flattening of the patterns for HREE in pyroxenes and garnet relative to olivine.