Wayne Taylor - Academia.edu (original) (raw)
Papers by Wayne Taylor
Journal of Geochemical Exploration, Apr 1, 2009
Journal of Geochemical Exploration, 2009
Contributions to Mineralogy and Petrology, Mar 16, 2023
Precambrian Research, 2020
Subductionrelated petrogenesis of Late Archean calc-alkaline lamprophyres in the Yilgarn Craton (... more Subductionrelated petrogenesis of Late Archean calc-alkaline lamprophyres in the Yilgarn Craton (Western Australia),
Contributions to Mineralogy and Petrology, 1986
The effects of H20 , CO2, CH4 and HF on partial melting of a model phlogopite harzburgite mantle ... more The effects of H20 , CO2, CH4 and HF on partial melting of a model phlogopite harzburgite mantle are considered with regard to the production of ultrapotassic magmas. Fluorine has a polymerising effect in HzO-poor conditions, but in the presence of abundant H20 where HF rather than F is dominant, the overall effect is depolymerisation. Methane also dissolves by forming (OH)-groups, and so has a depolymerising effect. Group I ultrapotassic rocks (lamproites) probably originate from primary magmas with SiO2 contents ranging from around 40 wt% to at least 52 wt%. This range can be explained by differing depths of origin from a similar source with a similar reduced H20-CH4-HF volatile mixture. The formation of silicarich initial melts from a model phlogopite harzburgite is assisted by the presence of CH 4 and HF. Dissociation of less than 0.1 wt% H20, driven by H2 loss, is sufficient to cause oxidation during emplacement to observed oxidation states. Silica-poor ultrapotassic rocks could be produced at higher pressures in a reduced environment, or in an oxidised environment with high CO2/(CO2 + H20) ratios. Group II (African Rift) potassic rocks may originate in H20-poor conditions in which fluorine will maintain a large phlogopite phase field, so that initial melts will be magnesian and silica-undersaturated.
Journal of Petrology, 2001
Hydrogen solubility and hydroxyl substitution mechanism in olivine INTRODUCTION at upper-mantle c... more Hydrogen solubility and hydroxyl substitution mechanism in olivine INTRODUCTION at upper-mantle conditions are not only a function of pressure, Since the recognition about 30 years ago that nominally temperature, water fugacity and hydrogen fugacity, but are also anhydrous minerals (NAM) can incorporate hydrogen influenced by silica activity. Olivine synthesized in equilibrium in lattice defects (Beran, 1970; Wilkins & Sabine, 1973; with magnesiowüstite displays hydroxyl stretching bands in the Beran & Putnis, 1983; Aines & Rossman, 1984), conwavenumber range from 3640 to 3430 cm-1. In contrast, olivine siderable experimental and analytical effort has been in equilibrium with orthopyroxene shows absorption bands in a expended on estimating the OHstorage capacity of narrower wavenumber range from 3380 to 3285 cm-1. The two mantle minerals and determining the key factors confundamentally different spectra are assigned to hydroxyl in tetrahedral trolling OHsubstitution (e.g.
Minerals, 2020
The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age... more The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age located in the Ngalia Basin of central Australia. The deposit is similar to the continental, fluvial Saltwash-type of sandstone-hosted U-V deposits which are well known from the Colorado Plateau, USA. Most mineralization at Bigrlyi occurs as thin, multiple-stacked, stratiform lenses at the base of fluvial channels near the contact between a grey sandstone succession and a hematitic, purple–red sandstone succession. A larger halo of lower grade vanadium mineralization extends beyond the main U-V-mineralized zone. The host is an immature, feldspathic sandstone, grading into arkose and lithic-rich variants. Lithic ‘rip-up’ clasts of clay-rich sediments are common in the basal parts of fluvial channels, and are frequently the focus of, and have acted as sites for, U-V mineralization. Coffinite and uraninite are the main uranium minerals, with the former dominant. Vanadium is mainly hosted b...
International Kimberlite Conference: Extended Abstracts, 1995
International Kimberlite Conference: Extended Abstracts, 1995
International Kimberlite Conference Extended Abstracts: 1995
International Kimberlite Conference: Extended Abstracts, 1995
Journal of Earth System Science, 1990
Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structura... more Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (< 15 A) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200-800 cm-1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from 'cage-like' motions of cations in their oxygen coordination polyhedra. In aluminosilicates these bands can provide information on the structural environment oral that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 em-1 is indicative of network-substituted AIO4 polyhedra in glasses with AI/(AI+Si)>0.25 and a band at 520-620 cm-1 is shown to be associated with AIO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of AI, Si tetrahedral site ordering. An important conclusion is that differences in AI, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity.
Geochimica et Cosmochimica Acta, 1994
A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimbe... more A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimberlite complex of the West African Craton have been investigated to determine their geochemical affinity relative to Group I (nonmicaceous) and Group II (micaceous) kimberlites of southern Africa. Comparison is made with altered kimberlites from Liberia, other West African and global kimberlites. Based on major element oxides, the Koidu kimberlites, though mica-bearing, show closest compositional similarity with the Group IA kimberlites of southern Africa. Based on major and trace elements, the Koidu kimberlites show an unusual geochemical signature. This signature is similar to that of the distinctive, micaceous Aries kimberlite of northwest Australia, and includes high Nb/U (most samples >46), Ce/ Sr(>0.4),Ta/Hf(>2),andNb/Zr(>l)ratiosandlowP~O5/Ce*1O4(<27),Ba/Rb(<32),andU/Th (~0.2) ratios compared with Group I kimberlites. Koidu kimberlites can be readily discriminated from Group II kimberlites by their higher Ti/K (>0.4) and Nb/La (> 1) ratios and lower Ba/Nb (<lo) and Pb/Ce (<OX%) ratios. The compositions of Liberian kimberlites are leached of mobile incompatible elements, but least a&&d samples show affinity to Group I. Guinea kimberlites appear to be of two types: one having affinity with Group IA and the other, micaceous variety, having affinity with the Aries kimberlite. Kimberlites with an Aries pochemical signature appear to exist on some other cratons, e.g., the Kundelungu kimberlites (Zaire) and two mica-bearing Group I kimberlites (S. Africa). The Koidu kimberlites exhibit compositionally-dependent isotopic heterogeneity though initial CNd and (asp values are broadly asthenospheric (i.e., near bulk earth) similar to Group I and Aries. A compositional spectrum appears to exist between nonmicaceous Group I kimberlites through mica-bearing Koidu kimberlites to extreme endmem~~ of the Aries type. This spectrum can be modelled as partial melts of heterogeneous peridotite sources which incorporate a potassic, high-Nb source component. The component may represent a fluoro-K-richterite-bearing peridotite residue derived by melt extraction from subduction-zone metasomatized peridot&es. Such materials may have been trapped, together with former oceanic lithosphere, in the Transition Zone of the mantle. In response to lower mantle upwelling, diapiric uprise accompanying reduced volatile degassing of the kimberlite source may occur. Because of differences in oxidation potential across the 400 km di~ntinuity, reactions in the as&ending diapir will lead to redox melting and ultimately segregation of the kimberlite melt at the base of the thermal boundary layer (P-13 GPa) separating the subcratonic lithosphere from the convective mantle.
Geochimica et Cosmochimica Acta, 1994
A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimbe... more A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimberlite complex of the West African Craton have been investigated to determine their geochemical affinity relative to Group I (nonmicaceous) and Group II (micaceous) kimberlites of southern Africa. Comparison is made with altered kimberlites from Liberia, other West African and global kimberlites. Based on major element oxides, the Koidu kimberlites, though mica-bearing, show closest compositional similarity with the Group IA kimberlites of southern Africa. Based on major and trace elements, the Koidu kimberlites show an unusual geochemical signature. This signature is similar to that of the distinctive, micaceous Aries kimberlite of northwest Australia, and includes high Nb/U (most samples >46), Ce/ Sr(>0.4),Ta/Hf(>2),andNb/Zr(>l)ratiosandlowP~O5/Ce*1O4(<27),Ba/Rb(<32),andU/Th (~0.2) ratios compared with Group I kimberlites. Koidu kimberlites can be readily discriminated from Group II kimberlites by their higher Ti/K (>0.4) and Nb/La (> 1) ratios and lower Ba/Nb (<lo) and Pb/Ce (<OX%) ratios. The compositions of Liberian kimberlites are leached of mobile incompatible elements, but least a&&d samples show affinity to Group I. Guinea kimberlites appear to be of two types: one having affinity with Group IA and the other, micaceous variety, having affinity with the Aries kimberlite. Kimberlites with an Aries pochemical signature appear to exist on some other cratons, e.g., the Kundelungu kimberlites (Zaire) and two mica-bearing Group I kimberlites (S. Africa). The Koidu kimberlites exhibit compositionally-dependent isotopic heterogeneity though initial CNd and (asp values are broadly asthenospheric (i.e., near bulk earth) similar to Group I and Aries. A compositional spectrum appears to exist between nonmicaceous Group I kimberlites through mica-bearing Koidu kimberlites to extreme endmem~~ of the Aries type. This spectrum can be modelled as partial melts of heterogeneous peridotite sources which incorporate a potassic, high-Nb source component. The component may represent a fluoro-K-richterite-bearing peridotite residue derived by melt extraction from subduction-zone metasomatized peridot&es. Such materials may have been trapped, together with former oceanic lithosphere, in the Transition Zone of the mantle. In response to lower mantle upwelling, diapiric uprise accompanying reduced volatile degassing of the kimberlite source may occur. Because of differences in oxidation potential across the 400 km di~ntinuity, reactions in the as&ending diapir will lead to redox melting and ultimately segregation of the kimberlite melt at the base of the thermal boundary layer (P-13 GPa) separating the subcratonic lithosphere from the convective mantle.
International Kimberlite Conference Extended Abstracts: 1995
International Kimberlite Conference: Extended Abstracts, 1995
European Journal of Mineralogy, 1990
American Mineralogist, 1996
The availability of a synthetic multilayer crystal and accurately calibrated oxide and silicate s... more The availability of a synthetic multilayer crystal and accurately calibrated oxide and silicate standards make it possible to use the electron microprobe for precise a analysis of spinel. A requirement of the a measurement routine described is the use of repetitive statistical analyses of the a standards and subsequent corrections and recalibration. A representative set of a analyses for each spinel population studied is essential to obtain reliable data, and the danger of using single datum is emphasized. Magnesiochromite spinel grains, having broad compositional similarities but different petrogenetic and cooling histories, were analyzed for a and their stoichiometry was assessed. Diamond-indicator spinel from the Aries kimberlite and Argyle lamproite is stoichiometric. Spinel inclusions in olivine phenocrysts from Ti-poor tholeiite from the Hunter Fraction Zone and Ca-rich boninite from the Tonga Trench show a range of nonstoichiometry. High FeH / FeH values calculated assuming stoichiometry for such spinel are invalid. Spinel samples from metamorphosed volcanics from the Peak Hill-Glengarry Basin and the Heazlewood River Ultramafic Complex are also nonstoichiometric, having significant Fe8304-Cr8304 components. Our results demonstrate that nonstoichiometry is a common feature of Crrich spinel. This has important implications for the use of FeH and FeH concentrations to estimate the oxidation state or temperature of formation.
Lithos, 1992
Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 + 6Ma, intrude lower greenschi... more Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 + 6Ma, intrude lower greenschist facies rocks of the Early Proterozoic Pine Creek Inlier, of northern Australia. They are spatially, tempo. rally and probably genetically associated with a post-tectonic composite granite-syenite pluton (Mr. Bundey pluton). The dykes have unusually high contents of large-ion-lithophile (LILE) and LREE elements (e.g. Ba up to 10,000 ppm, Ce up to 550 ppm, K20 up to 7.5 wt. %) thal resemble the concentrations found in the West Kimberley olivine and leucite lamproites. However, mineralogically the Mt. Bundey lamprophyres resemble shoshonitic lamprophyres and lack any minerals diagnostic oflamproites; leucite or leucite-pseudomorphs are absent. Mineral compositions are also unlike those in lamproites: micas contain higher A1203 than lamproitic mica; amphiboles are secondary actinolites after diopside; and oxides consist of zincian-chromian magnetite and groundmass magnetite. Heavy mineral concentrates contain mantle-de~ved xenocrysts of magnesiochromite, pyrope, Cr-diopside and rutile indicating a depth of sampling > 70 ~a'J. ,'I~e Mr. Bundey lamproD~-':res are r,~r'.-treralk ~|ine to borderline ~
Geochimica et Cosmochimica Acta, 1996
Diamonds containing nitrogen impurities in the form of singly substituted C centres (type Ib diam... more Diamonds containing nitrogen impurities in the form of singly substituted C centres (type Ib diamond) are rare in nature because Ib nitrogen atoms aggregate to form A centres (type IaA diamond) during the long-term (~0.5 to 3 Gyr) upper mantle residence period experienced by most diamonds. Preservation of N-rich diamond with a type Ib component requires a young age of crystallization, or unusually cool conditions of mantle storage, or both. Quantitative constraints on the origin of Ib diamonds are possible if the kinetics of nitrogen aggregation are accurately known. However, previous experimental studies have produced significantly different values for the activation energy of Ib-. IaA conversion (Ea) which is at least partly due to sector dependence of the aggregation rate in the starting materials. We report a series of high-pressure (P), temperature (T) experiments on synthetic and natural type Ib diamond in which we have used infrared (IR) microspectrometry techniques to unravel the sector dependency. The results show that cube sectors have an Ea of 6.0-0.2 eV, which is significantly greater than the Ea of 4.4 +__ 0.3 eV determined for the octahedral sectors. Both values are in excellent agreement with a recent theoretical study in which the sector dependency is ascribed to different mechanisms of nitrogen migration. The higher Ea is most relevant to natural Ib diamond which are invariably of cube or cuboid habit. Application to the Kokchetav microdiamonds of metamorphic origin indicate that their aggregation state is consistent with peak temperatures of 950°C and a burial to exhumation history of 17 Myr. Application to yellow cubes and "coat" from Yakutia having ~20% Ib component, indicate this diamond generation grew-<7 Myr before kimberlite eruption for mantle T >-950°C but did not grow directly from the transporting kimberlite magma.
Journal of Geochemical Exploration, Apr 1, 2009
Journal of Geochemical Exploration, 2009
Contributions to Mineralogy and Petrology, Mar 16, 2023
Precambrian Research, 2020
Subductionrelated petrogenesis of Late Archean calc-alkaline lamprophyres in the Yilgarn Craton (... more Subductionrelated petrogenesis of Late Archean calc-alkaline lamprophyres in the Yilgarn Craton (Western Australia),
Contributions to Mineralogy and Petrology, 1986
The effects of H20 , CO2, CH4 and HF on partial melting of a model phlogopite harzburgite mantle ... more The effects of H20 , CO2, CH4 and HF on partial melting of a model phlogopite harzburgite mantle are considered with regard to the production of ultrapotassic magmas. Fluorine has a polymerising effect in HzO-poor conditions, but in the presence of abundant H20 where HF rather than F is dominant, the overall effect is depolymerisation. Methane also dissolves by forming (OH)-groups, and so has a depolymerising effect. Group I ultrapotassic rocks (lamproites) probably originate from primary magmas with SiO2 contents ranging from around 40 wt% to at least 52 wt%. This range can be explained by differing depths of origin from a similar source with a similar reduced H20-CH4-HF volatile mixture. The formation of silicarich initial melts from a model phlogopite harzburgite is assisted by the presence of CH 4 and HF. Dissociation of less than 0.1 wt% H20, driven by H2 loss, is sufficient to cause oxidation during emplacement to observed oxidation states. Silica-poor ultrapotassic rocks could be produced at higher pressures in a reduced environment, or in an oxidised environment with high CO2/(CO2 + H20) ratios. Group II (African Rift) potassic rocks may originate in H20-poor conditions in which fluorine will maintain a large phlogopite phase field, so that initial melts will be magnesian and silica-undersaturated.
Journal of Petrology, 2001
Hydrogen solubility and hydroxyl substitution mechanism in olivine INTRODUCTION at upper-mantle c... more Hydrogen solubility and hydroxyl substitution mechanism in olivine INTRODUCTION at upper-mantle conditions are not only a function of pressure, Since the recognition about 30 years ago that nominally temperature, water fugacity and hydrogen fugacity, but are also anhydrous minerals (NAM) can incorporate hydrogen influenced by silica activity. Olivine synthesized in equilibrium in lattice defects (Beran, 1970; Wilkins & Sabine, 1973; with magnesiowüstite displays hydroxyl stretching bands in the Beran & Putnis, 1983; Aines & Rossman, 1984), conwavenumber range from 3640 to 3430 cm-1. In contrast, olivine siderable experimental and analytical effort has been in equilibrium with orthopyroxene shows absorption bands in a expended on estimating the OHstorage capacity of narrower wavenumber range from 3380 to 3285 cm-1. The two mantle minerals and determining the key factors confundamentally different spectra are assigned to hydroxyl in tetrahedral trolling OHsubstitution (e.g.
Minerals, 2020
The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age... more The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age located in the Ngalia Basin of central Australia. The deposit is similar to the continental, fluvial Saltwash-type of sandstone-hosted U-V deposits which are well known from the Colorado Plateau, USA. Most mineralization at Bigrlyi occurs as thin, multiple-stacked, stratiform lenses at the base of fluvial channels near the contact between a grey sandstone succession and a hematitic, purple–red sandstone succession. A larger halo of lower grade vanadium mineralization extends beyond the main U-V-mineralized zone. The host is an immature, feldspathic sandstone, grading into arkose and lithic-rich variants. Lithic ‘rip-up’ clasts of clay-rich sediments are common in the basal parts of fluvial channels, and are frequently the focus of, and have acted as sites for, U-V mineralization. Coffinite and uraninite are the main uranium minerals, with the former dominant. Vanadium is mainly hosted b...
International Kimberlite Conference: Extended Abstracts, 1995
International Kimberlite Conference: Extended Abstracts, 1995
International Kimberlite Conference Extended Abstracts: 1995
International Kimberlite Conference: Extended Abstracts, 1995
Journal of Earth System Science, 1990
Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structura... more Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (< 15 A) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200-800 cm-1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from 'cage-like' motions of cations in their oxygen coordination polyhedra. In aluminosilicates these bands can provide information on the structural environment oral that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 em-1 is indicative of network-substituted AIO4 polyhedra in glasses with AI/(AI+Si)>0.25 and a band at 520-620 cm-1 is shown to be associated with AIO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of AI, Si tetrahedral site ordering. An important conclusion is that differences in AI, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity.
Geochimica et Cosmochimica Acta, 1994
A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimbe... more A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimberlite complex of the West African Craton have been investigated to determine their geochemical affinity relative to Group I (nonmicaceous) and Group II (micaceous) kimberlites of southern Africa. Comparison is made with altered kimberlites from Liberia, other West African and global kimberlites. Based on major element oxides, the Koidu kimberlites, though mica-bearing, show closest compositional similarity with the Group IA kimberlites of southern Africa. Based on major and trace elements, the Koidu kimberlites show an unusual geochemical signature. This signature is similar to that of the distinctive, micaceous Aries kimberlite of northwest Australia, and includes high Nb/U (most samples >46), Ce/ Sr(>0.4),Ta/Hf(>2),andNb/Zr(>l)ratiosandlowP~O5/Ce*1O4(<27),Ba/Rb(<32),andU/Th (~0.2) ratios compared with Group I kimberlites. Koidu kimberlites can be readily discriminated from Group II kimberlites by their higher Ti/K (>0.4) and Nb/La (> 1) ratios and lower Ba/Nb (<lo) and Pb/Ce (<OX%) ratios. The compositions of Liberian kimberlites are leached of mobile incompatible elements, but least a&&d samples show affinity to Group I. Guinea kimberlites appear to be of two types: one having affinity with Group IA and the other, micaceous variety, having affinity with the Aries kimberlite. Kimberlites with an Aries pochemical signature appear to exist on some other cratons, e.g., the Kundelungu kimberlites (Zaire) and two mica-bearing Group I kimberlites (S. Africa). The Koidu kimberlites exhibit compositionally-dependent isotopic heterogeneity though initial CNd and (asp values are broadly asthenospheric (i.e., near bulk earth) similar to Group I and Aries. A compositional spectrum appears to exist between nonmicaceous Group I kimberlites through mica-bearing Koidu kimberlites to extreme endmem~~ of the Aries type. This spectrum can be modelled as partial melts of heterogeneous peridotite sources which incorporate a potassic, high-Nb source component. The component may represent a fluoro-K-richterite-bearing peridotite residue derived by melt extraction from subduction-zone metasomatized peridot&es. Such materials may have been trapped, together with former oceanic lithosphere, in the Transition Zone of the mantle. In response to lower mantle upwelling, diapiric uprise accompanying reduced volatile degassing of the kimberlite source may occur. Because of differences in oxidation potential across the 400 km di~ntinuity, reactions in the as&ending diapir will lead to redox melting and ultimately segregation of the kimberlite melt at the base of the thermal boundary layer (P-13 GPa) separating the subcratonic lithosphere from the convective mantle.
Geochimica et Cosmochimica Acta, 1994
A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimbe... more A suite of largely unaltered, aphanitic, mica-bearing hypabyssal kimberlites from the Koidu kimberlite complex of the West African Craton have been investigated to determine their geochemical affinity relative to Group I (nonmicaceous) and Group II (micaceous) kimberlites of southern Africa. Comparison is made with altered kimberlites from Liberia, other West African and global kimberlites. Based on major element oxides, the Koidu kimberlites, though mica-bearing, show closest compositional similarity with the Group IA kimberlites of southern Africa. Based on major and trace elements, the Koidu kimberlites show an unusual geochemical signature. This signature is similar to that of the distinctive, micaceous Aries kimberlite of northwest Australia, and includes high Nb/U (most samples >46), Ce/ Sr(>0.4),Ta/Hf(>2),andNb/Zr(>l)ratiosandlowP~O5/Ce*1O4(<27),Ba/Rb(<32),andU/Th (~0.2) ratios compared with Group I kimberlites. Koidu kimberlites can be readily discriminated from Group II kimberlites by their higher Ti/K (>0.4) and Nb/La (> 1) ratios and lower Ba/Nb (<lo) and Pb/Ce (<OX%) ratios. The compositions of Liberian kimberlites are leached of mobile incompatible elements, but least a&&d samples show affinity to Group I. Guinea kimberlites appear to be of two types: one having affinity with Group IA and the other, micaceous variety, having affinity with the Aries kimberlite. Kimberlites with an Aries pochemical signature appear to exist on some other cratons, e.g., the Kundelungu kimberlites (Zaire) and two mica-bearing Group I kimberlites (S. Africa). The Koidu kimberlites exhibit compositionally-dependent isotopic heterogeneity though initial CNd and (asp values are broadly asthenospheric (i.e., near bulk earth) similar to Group I and Aries. A compositional spectrum appears to exist between nonmicaceous Group I kimberlites through mica-bearing Koidu kimberlites to extreme endmem~~ of the Aries type. This spectrum can be modelled as partial melts of heterogeneous peridotite sources which incorporate a potassic, high-Nb source component. The component may represent a fluoro-K-richterite-bearing peridotite residue derived by melt extraction from subduction-zone metasomatized peridot&es. Such materials may have been trapped, together with former oceanic lithosphere, in the Transition Zone of the mantle. In response to lower mantle upwelling, diapiric uprise accompanying reduced volatile degassing of the kimberlite source may occur. Because of differences in oxidation potential across the 400 km di~ntinuity, reactions in the as&ending diapir will lead to redox melting and ultimately segregation of the kimberlite melt at the base of the thermal boundary layer (P-13 GPa) separating the subcratonic lithosphere from the convective mantle.
International Kimberlite Conference Extended Abstracts: 1995
International Kimberlite Conference: Extended Abstracts, 1995
European Journal of Mineralogy, 1990
American Mineralogist, 1996
The availability of a synthetic multilayer crystal and accurately calibrated oxide and silicate s... more The availability of a synthetic multilayer crystal and accurately calibrated oxide and silicate standards make it possible to use the electron microprobe for precise a analysis of spinel. A requirement of the a measurement routine described is the use of repetitive statistical analyses of the a standards and subsequent corrections and recalibration. A representative set of a analyses for each spinel population studied is essential to obtain reliable data, and the danger of using single datum is emphasized. Magnesiochromite spinel grains, having broad compositional similarities but different petrogenetic and cooling histories, were analyzed for a and their stoichiometry was assessed. Diamond-indicator spinel from the Aries kimberlite and Argyle lamproite is stoichiometric. Spinel inclusions in olivine phenocrysts from Ti-poor tholeiite from the Hunter Fraction Zone and Ca-rich boninite from the Tonga Trench show a range of nonstoichiometry. High FeH / FeH values calculated assuming stoichiometry for such spinel are invalid. Spinel samples from metamorphosed volcanics from the Peak Hill-Glengarry Basin and the Heazlewood River Ultramafic Complex are also nonstoichiometric, having significant Fe8304-Cr8304 components. Our results demonstrate that nonstoichiometry is a common feature of Crrich spinel. This has important implications for the use of FeH and FeH concentrations to estimate the oxidation state or temperature of formation.
Lithos, 1992
Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 + 6Ma, intrude lower greenschi... more Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 + 6Ma, intrude lower greenschist facies rocks of the Early Proterozoic Pine Creek Inlier, of northern Australia. They are spatially, tempo. rally and probably genetically associated with a post-tectonic composite granite-syenite pluton (Mr. Bundey pluton). The dykes have unusually high contents of large-ion-lithophile (LILE) and LREE elements (e.g. Ba up to 10,000 ppm, Ce up to 550 ppm, K20 up to 7.5 wt. %) thal resemble the concentrations found in the West Kimberley olivine and leucite lamproites. However, mineralogically the Mt. Bundey lamprophyres resemble shoshonitic lamprophyres and lack any minerals diagnostic oflamproites; leucite or leucite-pseudomorphs are absent. Mineral compositions are also unlike those in lamproites: micas contain higher A1203 than lamproitic mica; amphiboles are secondary actinolites after diopside; and oxides consist of zincian-chromian magnetite and groundmass magnetite. Heavy mineral concentrates contain mantle-de~ved xenocrysts of magnesiochromite, pyrope, Cr-diopside and rutile indicating a depth of sampling > 70 ~a'J. ,'I~e Mr. Bundey lamproD~-':res are r,~r'.-treralk ~|ine to borderline ~
Geochimica et Cosmochimica Acta, 1996
Diamonds containing nitrogen impurities in the form of singly substituted C centres (type Ib diam... more Diamonds containing nitrogen impurities in the form of singly substituted C centres (type Ib diamond) are rare in nature because Ib nitrogen atoms aggregate to form A centres (type IaA diamond) during the long-term (~0.5 to 3 Gyr) upper mantle residence period experienced by most diamonds. Preservation of N-rich diamond with a type Ib component requires a young age of crystallization, or unusually cool conditions of mantle storage, or both. Quantitative constraints on the origin of Ib diamonds are possible if the kinetics of nitrogen aggregation are accurately known. However, previous experimental studies have produced significantly different values for the activation energy of Ib-. IaA conversion (Ea) which is at least partly due to sector dependence of the aggregation rate in the starting materials. We report a series of high-pressure (P), temperature (T) experiments on synthetic and natural type Ib diamond in which we have used infrared (IR) microspectrometry techniques to unravel the sector dependency. The results show that cube sectors have an Ea of 6.0-0.2 eV, which is significantly greater than the Ea of 4.4 +__ 0.3 eV determined for the octahedral sectors. Both values are in excellent agreement with a recent theoretical study in which the sector dependency is ascribed to different mechanisms of nitrogen migration. The higher Ea is most relevant to natural Ib diamond which are invariably of cube or cuboid habit. Application to the Kokchetav microdiamonds of metamorphic origin indicate that their aggregation state is consistent with peak temperatures of 950°C and a burial to exhumation history of 17 Myr. Application to yellow cubes and "coat" from Yakutia having ~20% Ib component, indicate this diamond generation grew-<7 Myr before kimberlite eruption for mantle T >-950°C but did not grow directly from the transporting kimberlite magma.