Ilmenite-hematite Solid Solution Research Articles

Ferromagnetism and exchange bias in compressed ilmenite-hematite solid solution as a source of planetary magnetic anomalies.

We propose a compressed ilmenite-hematite solid solution as a new potential source of Earth’s magnetic anomalies. The 0.5FeTiO3·0.5Fe2O3 solid solution compressed by collision synthesis with super-high-energy ball milling showed a decrease in molar volume of approximately 1.8%. Consequently, the sample showed a saturation magnetization of 1.5 ampere square meter per kilogram (Am2/kg) at 300 kelvin, a Curie temperature of 990 kelvin, and a magnetic exchange bias below 100 kelvin, e.g., 1.7 × 105 ampere per meter at 60 kelvin. Ilmenite-hematite solid solutions are common mineral systems in most mafic igneous and metamorphic rocks, and the compressive force in the rocks is generated by the high pressure in the upper mantle or by shock events with high pressure such as the collision of these rocks with meteorites. Therefore, we consider that the compressed ilmenite-hematite solid solution is an additional candidate source of other planetary magnetic anomalies including those in the Moon and Earth.

Magnetite-rutile symplectite in ilmenite records magma hydration in layered intrusions

Abstract The textures and geochemical characteristics of the rocks in layered intrusions potentially provide insights into the physicochemical processes that have taken place in mafic magma chambers. Diverse exsolution textures of Fe-Ti oxides in layered intrusions may record the variation of subsolidus temperature and oxygen fugacity (fO2) of cooling magma chambers. Here we investigated ilmenitehematite solid solution (Ilmss) relationships evident in preserved intergrowths of magnetite-rutile and ilmenite-hematite in the gabbro of the Xinjie layered intrusion. The crystallographic orientation and 3D morphology of the two intergrowth types constrain the transformation mechanism of the exsolution textures from Ilmss. The results reveal that the interface of the ilmenite-hematite intergrowth is more energetically favorable than that of the magnetite-rutile symplectite when they are transformed from Ilmss on cooling. The QUILF equilibria suggests that the magnetite-rutile symplectite can be transformed from Ti-rich ilmenite with Ilm≥0.85 above 550 °C when the subsolidus T-fO2 trend is buffered by the biotite-ilmenite-feldspar-ulvöspinel (KUIlB) mineral assemblages crystallized from hydrated mafic magmas. The magnetite-rutile symplectite may be used as a unique texture indicator of magma hydration in the evolution history of terrestrial, martian, and lunar magmas.

Textural and Geochemical Evidence for Magnetite Production upon Antigorite Breakdown During Subduction

AbstractMagnetite stability in ultramafic systems undergoing subduction plays a major role in controlling redox states of the fluids liberated upon dehydration reactions, as well as of residual rocks. Despite their relevance for the evaluation of the redox conditions, the systematics and geochemistry of oxide minerals have remained poorly constrained in subducted ultramafic rocks. Here, we present a detailed petrological and geochemical study of magnetite in hydrous ultramafic rocks from Cerro del Almirez (Spain). Our results indicate that prograde to peak magnetite, ilmenite–hematite solid solution minerals, and sulfides coexist in both antigorite-serpentinite and chlorite-harzburgite at c. 670 °C and 1·6 GPa, displaying successive crystallization stages, each characterized by specific mineral compositions. In antigorite-serpentinite, magnetite inherited from seafloor hydration and recrystallized during subduction has moderate Cr (Cr2O3 < 10 wt%) and low Al and V concentrations. In chlorite-harzburgite, polygonal magnetite is in textural equilibrium with olivine, orthopyroxene, chlorite, pentlandite, and ilmenite–hematite solid solution minerals. The Cr2O3 contents of this magnetite are up to 19 wt%, higher than any magnetite data obtained for antigorite-serpentinite, along with higher Al and V, derived from antigorite breakdown, and lower Mn concentrations. This polygonal magnetite displays conspicuous core to rim zoning as recognized on elemental maps. Cr–V–Al–Fe3+ mass-balance calculations, assuming conservative behavior of total Fe3+ and Al, were employed to model magnetite compositions and modes in the partially dehydrated product chlorite-harzburgite starting from antigorite-serpentinite, as well as in the serpentinite protolith starting from the chlorite-harzburgite. The model results disagree with measured Cr and V compositions in magnetite from antigorite-serpentinites and chlorite-harzburgites. This indicates that these two rock types had different initial bulk compositions and thus cannot be directly compared. Our mass-balance analysis also reveals that new magnetite formation is required across the antigorite-breakdown reaction to account for the mass conservation of fluid-immobile elements such as Cr–V–Al–Fe3+. Complete recrystallization and formation of new magnetite in equilibrium with peak olivine (Mg# 89–91), chlorite (Mg# ∼95), orthopyroxene (Mg# 90–91), and pentlandite buffer the released fluid to redox conditions of ∼1 log unit above the quartz–fayalite–magnetite buffer. This is consistent with the observation that the Fe–Ti solid solution minerals (hemo-ilmenite and ilmeno-hematite) crystallized as homogeneous phases and exsolved upon exhumation and cooling. We conclude that antigorite-dehydration reaction fluids carry only a moderate redox budget and therefore may not be the only reason why the magmas are comparatively oxidized.

Iron, magnesium, and titanium isotopic fractionations between garnet, ilmenite, fayalite, biotite, and tourmaline: Results from NRIXS, ab initio, and study of mineral separates from the Moosilauke metapelite

Interpreting isotopic signatures documented in natural rocks requires knowledge of equilibrium isotopic fractionation factors. Here, we determine equilibrium Fe isotope fractionation factors between several common rock-forming minerals using a comparative approach involving three independent methods: (i) isotopic analyses of natural minerals from a metapelite from Mt. Moosilauke, New Hampshire, for which equilibration temperature and pressure are well constrained to be near the aluminosilicate triple point (T ≃ 500 °C, P ≃ 4 kbar), (ii) Nuclear Resonant Inelastic X-ray Scattering (NRIXS) measurements of Fe force constants of minerals, and (iii) Density Functional Theory (DFT) ab initio calculations of Fe force constants of minerals.The minerals studied for Fe isotopes include, in increasing order of their β-factors: garnet < ilmenite ≈ fayalite < biotite < tourmaline < muscovite ≈ plagioclase. Some of this ordering is affected by the presence of Fe3+ in the minerals, which tends to form stiffer bonds and be associated with heavy Fe isotope enrichments relative to Fe2+. We are, however, able to assess the magnitude of the effect of the ratio Fe3+/ΣFe on equilibrium fractionation factors, notably on the ilmenite-hematite solid solution. Equilibrium Fe isotopic fractionation factors between garnet, ilmenite, biotite, tourmaline and fayalite are determined. We also report Mg and Ti isotopic compositions of selected Moosilauke minerals that allow us to better constrain the equilibrium fractionation factors for garnet-biotite-tourmaline (Mg isotopes) and biotite-ilmenite (Ti isotopes).We show how the newly determined equilibrium fractionation factors can be used to address diverse problems in Earth and planetary sciences, notably (i) Fe and Mg isotopic fractionation during anatexis, (ii) Fe isotopic fractionation in lunar ilmenite, and (iii) Ti isotopic fractionation during fluvial transport of minerals.

Transformation of TiO2 (nano)particles during sewage sludge incineration

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.

Towards Iron-Titanium Oxide Nanostructures from Ecuadorian Black Mineral Sands

Ecuadorian black mineral sands were used as starting material for the production of iron-titanium oxide nanostructures. For this purpose, two types of mineral processing were carried out, one incorporating a pre-treatment before conducting an alkaline hydrothermal synthesis (NaOH 10 M at 180 °C for 72 h), and the other prescinding this first step. Nanosheet-assembled flowers and nanoparticle agglomerates were obtained from the procedure including the pre-treatment. Conversely, nanobelts and plate-like particles were prepared by the single hydrothermal route. The nanoscale features of the product morphologies were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The ilmenite and hematite molar fractions, within the ilmenite-hematite solid solution, in the as-synthetized samples were estimated by Brown’s approach using the computed values of unit-cell volumes from Le Bail adjustments of X-ray powder diffraction (XRPD) patterns. The resulting materials were mainly composed of Fe-rich ilmenite-hematite solid solutions (hematite molar contents ≥0.6). Secondary phases, which possibly belong to lepidocrocite-like or corrugated titanate structures, were also identified. The current study demonstrated the feasibility of employing Ecuadorian mineral resources as low-cost precursors to synthesize high-added-value nanostructures with promising applications in several fields.

Data on phase and chemical compositions of black sands from "El Ostional" beach situated in Mompiche, Ecuador.

Data revealing the phase and chemical compositions of natural black sands from “El Ostional” beach, located in the northern Ecuadorian Pacific coast have been presented. The samples were collected from six points over the shore area of approximately 500 × 40 m2. The data on crystalline phases (iron titanium oxide, orthoclase feldspar and zircon) were determined by X-ray powder diffraction (XRPD), while semi-quantitative chemical analyses of major (Fe and Ti) and trace elements were obtained by X-ray fluorescence spectroscopy (XRF). The phase composition was verified by scanning electron microscopy (SEM), using backscattered electron (BSE) mode and energy dispersive spectroscopy (EDS). These comprehensive data are a contribution to valorize ilmenite-hematite solid solutions from natural resources towards the identification of novel technological applications.

Effect of thermal treatment on the structural, electrical, and dielectric properties of volcanic scoria

The effects of thermal treatment on the structural, electrical, and dielectric properties of scoria collected from Harrat Rahat in Saudi Arabia have been investigated. The raw scoria was thermally treated at two different temperatures (800 and 1000 °C). The crystalline phase, morphology, and chemical group functions of natural and treated scoria samples were studied using XRD, SEM, FTIR/Raman spectroscopies, respectively. The XRD results showed no apparent differences between the raw sample and treated at the temperature of 800 °C. While it showed a decrease in the intensities of the XRD pattern and Raman spectra of the scoria treated at the temperature of 1000 °C, this could be attributed to the formation of a hematite–ilmenite solid solution. The tested raw scoria showed excellent thermal stability up to the temperature of 800 °C. At higher temperatures, however, its mineral and chemical compositions can be slightly affected. Electrical and dielectric properties were explored in detail at different temperatures and frequencies. The results did not show any considerable changes between raw and treated scoria samples. Likewise, conductivities and dielectric constants revealed stable values up to 700 K. This type of scoria, therefore, can be a promising material for use as high-voltage power insulators.

Mineralogical Characteristics and Isothermal Oxidation Kinetics of Ironsand Pellets

An in-depth understanding of mineralogical characteristics and the oxidation behaviors of ironsand is of great significance to make the best of ironsand and develop Ti-containing pellets. This paper quantitatively characterized the mineralogical characteristics of the ironsand from East Java in Indonesia through X-ray diffraction (XRD-Rietveld) and scanning electron microscope (SEM-EDS). The results indicated that the mineral composition of the ironsand was magnetite (22.7%), titanomagnetite (40.9%), enstatite (17.1%), hematite–ilmenite solid solution (14.5%), and magnesium iron aluminum silicon oxide (5.8%). The microstructure characterization of pellets after oxidation showed that the porosity of the pellets decreased from 20.7% to 11.7% with temperatures ranging from 1073 to 1473 K. Moreover, the activation energies of ironsand pellets were calculated by using model-function method. The calculated data of different mechanism functions indicated that the chemical reaction mechanism for the early stage of the oxidation fit A2 (random nucleation and nuclei growth) well, the chemical reaction mechanism for the post-oxidation at 1073–1273 K fit F1 (chemical reaction) well, and the chemical reaction mechanism for the post-oxidation at 1373 and 1473 K fit D4 (diffusion) well. The reaction mechanism and the limited link was finally discussed based on the kinetic analysis and the mineralogical characteristics.

Magnetite-rutile symplectite derived from ilmenite-hematite solid solution in the Xinjie Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion (SW China)

A unique symplectitic intergrowth of magnetite + rutile is hosted by ilmenite in the gabbro of the Xinjie Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion. The crystallization of rutile in the symplectite is probably formed by oxidation of ilmenite-hematite solid solution (Ilm-Hem ss ). Segregation of Fe 3+ in the Ilm-Hem ss at the rutile-host interfaces triggered the crystallization of magnetite along the margin of the growing rutile, and shaped the vermicular morphology of the rutile. The crystallization of magnetite can also locally release Ti 4+ to enhance the progressive growth and subsequent nucleation of rutile in the symplectite. The growth of the symplectite ceased when the temperature decreased to that of the miscibility gap of Ilm-Hem ss and Fe 3+ began to exsolve to form hematite lamellae in the ilmenite.

Magnetic mean-field modelling of solid solutions: theoretical foundations and application to the hematite–ilmenite system

A spatially averaged mean-field model for fully or partially ordered members of the ilmenite–hematite solid solution series is rigorously derived from the Heisenberg Hamiltonian by first assuming no temporal correlation of atomic spins, and then by spatially averaging over spins at equivalent atomic positions. The model is based on the geometry of exchange interactions between nearest and next-nearest neighbours and predicts magnetization curves in homogenous solid solutions with variable degree of order. While the general framework presented can also be applied to atomic scale models, and to other solid solution series, here the symmetries of the ilmenite–hematite lattice are exploited to show that four different sublattice magnetizations and six independent combinations of exchange constants determine the temperature variation of the magnetization curves. Comparing measured Curie temperatures TC and Ms(T) curves to model predictions results in accurate constraints for these combinations. It is also possible to calculate predictions for high-field magnetization slopes χHF, which not only improve accurate experimental determination of the Curie temperature but also provide a new magnetic method to estimate the order parameter for ilmenite–hematite solid solution samples.

Microstructural properties of (112¯0)-oriented hematite–ilmenite solid solution films

Ilmenite–hematite solid solution (Fe2–xTixO3) is one of the candidates for high-temperature magnetic semiconductors. Well-crystallized and epitaxially formed Fe2–xTixO3 films on α-Al2O3 (112¯0) single-crystalline substrates were tried to fabricate by using reactive sputtering technique. The detailed structural properties of (112¯0)-oriented epitaxial Fe1.4Ti0.6O3 films were analyzed by using transmission electron microscope (TEM). The films showed large magnetization and typical semiconductive conduction at room temperature. However their anisotropic properties were rather small than expected, though the films had good crystallinity with preferred orientation. The TEM observations clearly revealed that the (112¯0)-oriented Fe1.4Ti0.6O3 films on α-Al2O3(112¯0) were partly composed of the (0001)-oriented grains. Formation of the (0001)-oriented grains could reduce the anisotropic properties of the (112¯0)-oriented films.

Textural and geochemical studies of detrital Fe–Ti oxides and test of their validity in provenance determination, a case study from Central Iran

This paper aims to test the reliability of texture and composition of detrital Fe–Ti oxides in provenance determination, via a case study on the most important siliciclastic unit of Central Iran (Upper Red Formation). Significant exposures of the formation in its basin margins and abundance of detrital Fe–Ti oxides in its component facies nominate it for this study. Samples from representative sections of the formation are studied by SEM, equipped with X-ray analyzer, for textural and compositional properties of the Fe–Ti oxides. In terms of texture, ∼75% of the studied grains are found heterogeneous with ilmenite exsolution/intergrowth in the titanomagnetite host (∼60%), magnetite–hematite exsolution/intergrowth (∼12%) and magnetite–pseudobrookite (∼2%) and magnetite–hematite–rutile (∼1%) intergrowths. Remaining grains (∼25%) are homogenous with titanomagnetite (∼19%), ilmenite (∼5%) and rutile and chromite (∼1%) composition. Four major types of texture (trellis, sandwich, composite and no distinct pattern) are discriminated in the heterogeneous grains, which characteristics and proportion provide significant information on their provenance. In terms of composition, majority of studied grains fall into magnetite–ulvöspinel and ilmenite–hematite solid solution series in the TiO2–FeO–Fe2O3 system. The FeO, MnO, MgO, ZnO, TiO2, Fe2O3, Al2O3 and Cr2O3 contents of the grains are used for their provenance determination.On the basis of results from textural and geochemical properties of the studied grains, intermediate (andesitic to dacitic) to basic volcanic rocks (dissected arc) are determined as parent rocks of the studied grains. These findings are combined with paleocurrent patterns of the hosting facies to locate the transportation pathways of the grains and their source area. Texture and composition of Fe–Ti minerals from nominated parent rocks are studied in similar methods. Comparison of texture and composition of the detrital Fe–Ti oxides with those in their nominated parent rocks clearly confirm the reliability of these parameters in provenance determination. Slight post-depositional alteration of the grains is understood from this comparison.

Epitaxial growth of the high temperature ferromagnetic semiconductor Fe1.5Ti0.5O3 on silicon-compatible substrate

The ilmenite-hematite (IH) solid solution Fe1.5Ti0.5O3 thin films with rhombohedral symmetry were epitaxially grown on silicon-compatible cubic SrTiO3(001) substrates. Ordered (R-3 symmetry) and disordered (R-3c symmetry) cation arrangement along the film c axis was obtained for different oxygen pressure during the IH growth. Drastic changes in magnetic properties of the films were observed as a function of the cation order. The IH thin films with R-3 symmetry have relatively high conductivity and saturation magnetization at 300 K (6 Ω−1 cm−1 and 0.4 μB/Fe respectively), and Curie temperature of 415 K, making IH a promising material for room-temperature spintronics applications.

Solid state reduction of Panzhihua titanomagnetite concentrates with pulverized coal

Titanomagnetite concentrates and pre-oxidized titanomagnetite concentrates were reduced isothermally at 1000–1200 °C by pulverized coal. XRD, SEM and EDS were used to characterize the samples. The influence of reduction conditions on the metallization degree of the samples, such as reduction temperature, C/Fe molar ratio, pre-oxidation and additives were studied. It was found that the pre-oxidation and additives played a considerable role in the metallization degree of titanomagnetite concentrates. During the pre-oxidation of titanomagnetite concentrates in air, the magnetite was oxidized to hematite and ilmenite was oxidized to hematite–ilmenite solid solution, hematite and TiO 2. The pre-oxidation destroyed the crystal lattice of raw titanomagnetite concentrates and formed pores in the particles, which accelerated the reduction process. The effect of different additives on the metallization degree of pre-oxidized titanomagnetite concentrates was also discussed. The results show that when 1.5 wt.% Na 2CO 3 is used as an additive, the metallization degree of pre-oxidized titanomagnetite concentrates reaches 96.4%, after heating for 1 h at 1200 °C. The final reduced sample was composed of metallic iron, pseudobrookite solid solution and TiO 2.

Mechanism of the lattice relaxation in thin epitaxial films of iron oxides: Generalization from the case of ilmenite–hematite solid solution

The overshoot of the in-plane lattice parameter above its expected value was previously observed for iron oxides on different substrates for initial stages of the film growth. The reasons for the overshoot provided in the previously published experimental studies have not satisfactorily explained the effect. In the present article the overshoot is explained in terms of the surface atom displacements at low thicknesses due to the strong lattice relaxation via dislocation formation. The ilmenite–hematite solid solution is used as an example for the experimental and theoretical descriptions of the overshoot. The theoretical model, based on the dislocation density, can be directly applied to describe the lattice relaxation as a function of the film thickness for other iron-based oxide films with a strong film/substrate lattice mismatch.

透過型電子顕微鏡によるナノスケール鉱物の磁気的性質

Magnetic minerals are distributed widely in the natural environment and are also present in a wide range of biological organisms, including humans. Magnetite-ulvöspinel and hematite-ilmenite solid solutions are the most common magnetic minerals in the Earth's crust. Their ability to record the past geomagnetic field depends on the crystal structure, chemical composition and geometric features of the consistent minerals. Magnetite and greigite crystals are also used as magnetic sensors in some microbes and animals, although their function is often still poorly understood. Recently, off-axis electron holography and Lorentz microscopy in the transmission electron microscope (TEM) have proven to be powerful techniques for studying geological and biological specimens, allowing both magnetic properties and crystallographic and chemical information to be imaged from the same region of a specimen. In this article, a selection of recent results that were obtained using these advanced TEM techniques is presented.

Heavy mineral distributions of Maastrichtian deposits from the Haţeg basin, South Carpathians: Tectonic and palaeogeographic implications

This study represents the first extensive investigation of source-areas of the Maastrichtian continental deposits of the Haţeg basin using heavy mineral associations. The heavy mineral associations consist of garnet, hematite, magnetite, ilmenite, rutile, staurolite, kyanite, epidote, apatite, titanite, tourmaline and zircon. The general pattern indicates different source areas with contrasting metamorphic grades for the northern and southern parts of the basin. The sediments of the northern and central sectors of the basin show a high proportion of garnet, staurolite and kyanite and a low proportion of epidote, suggesting an amphibolite-facies metamorphic source, which is compatible with the lithology of the Getic upper plate on which the basin formed. The samples with abundant amphibolite-facies heavy mineral components have high proportions of magnetic Fe–Ti-oxides with complex exsolution/intergrowth features. These oxides belong chiefly to the hematite–ilmenite solid-solution series and indicate a high-grade metamorphic and/or igneous source area. In the south, the heavy mineral spectra change to epidote-rich, evidence of exhumation and erosion of the greenschist metamorphic rocks of the Danubian lower plate during updoming and core-complex formation. The study shows that for the northern and central parts of the basin, the Getic plate is the main source for the sediments. During the Maastrichtian time, due to increasing relief in the hinterland and exhumation of the lower plate, the Danubian unit fed the basin, as recorded in the sediments situated along Sibişel and Râul Bărbat valley.

Effect of strain on the stability and electronic properties of ferrimagnetic Fe2−xTixO3 heterostructures from correlated band theory

Based on density functional theory calculations including an on-site Hubbard U term, we investigate the effect of substrate-induced strain on the properties of ferrimagnetic hematite-ilmenite solid solutions and heterostructures. While the charge compensation mechanism through formation of a mixed Fe2+, Fe3+-contact layer is unaffected, strain can be used to tune the electronic properties of the system, e.g., by changing the position of impurity levels in the band gap. Straining Fe2O3–FeTiO3 films at the lateral lattice parameters of Al2O3(0001), commonly used as a substrate, is found to be energetically unfavorable as compared to films on Fe2O3(0001) or FeTiO3(0001)-substrates.

Metamorphic garnet pyroxenite from the 540–600 m main borehole of the Chinese Continental Scientific Drilling (CCSD) project

Compared to other mafic and ultramafic rocks from the CCSD main borehole as well as from the outcrops, rocks from the 540–600 m section is extraordinary in terms of its geophysical as well as geochemical properties. It consists of > 70% hematite–ilmenite garnet pyroxenite (HI-GPX) and < 30% intercalated rutile garnet pyroxenite (R-GPX). Whole-rock geochemical data show that HI-GPXs have: (1) relatively high V with an average of 606 ppm, but lower Nb and Ta; (2) highest TFeO, Fe 2O 3/FeO ratio, and highly variable but strong positive Eu anomalies with Eu/Eu⁎ up to 2.9; (3) anomalously high V/Sc ratios ranging from 8.39 to 43.23, average 15.03; and (4) high amounts of hematite–ilmenite solid solutions with a very fine intergrowth structure down to nanometer scale. V/Sc ratios in the CCSD garnet pyroxenites are correlated negatively with MgO, but positively with Fe 2O 3/FeO ratios. Both suites of pyroxenites have similar rare earth elements and high field strength elements geochemistry. These features demonstrate that these pyroxenites were formed from metamorphism of high-Fe and/or -Ti gabbroic cumulates. This can account not only for low high field strength elements (HFSE) and rare earth elements (REE) but also low Nb/Ta and Zr/Hf ratios in these rocks. Seemingly negative correlation between Nb/Ta and Zr/Hf in the CCSD metabasites, not significantly affected by UHP metamorphism, is also consistent with the silicate differentiation trend in a basaltic magma chamber.