Ilmenite Inclusions Research Articles

Uranium-Bearing Srilankite from High-Pressure Garnetites of the Southern Urals: First Data

This work presents the results of studying srilankite, a rare zirconium titanate (ZrTi2O6), associated with ilmenite, rutile, zircon, uraninite, and other minerals discovered in high-pressure garnetites of the lherzolite Mindyak massif (Southern Urals). Srilankite occurs as inclusions in ilmenite and rutile of up to several tens of microns in size. It was established for the first time that srilankite contains a significant UO2 admixture (up to 20%). The negative correlation between Zr and U is evidence of isomorphism in the srilankite–brannerite system. The association of srilankite with high-Zr rutile indicates that formation of these minerals occurred at T > 850°С.

Rare earth elements and Sm-Nd isotope redistribution in apatite and accessory minerals in retrogressed lower crust material (Bergen Arcs, Norway)

In the Bergen Arcs (Norway), Grenvillian granulite retrogressed under eclogite- and amphibolite-facies conditions during Caledonian subduction/collision offer a unique opportunity to investigate rare earth elements (REE) and Sm-Nd isotope redistribution in accessory minerals during fluid-assisted metamorphism. Our sampling targeted apatite-bearing REE-rich protoliths (mangerite and jotunite) that preserve distinct mineral assemblages, depending on the external fluid availability and metamorphic conditions. REE concentrations in apatite are the highest in the granulite. Two populations are present: magmatic apatite (Ap1) relics that occur as inclusions in ilmenite-hematite, and intergranular apatite (Ap2) formed under granulite-facies conditions. The presence of abundant needle-like monazite and sulphide inclusions in Ap2 indicate that granulite reactions were fluid assisted. A thin (typically <10μm) rim of REE-rich epidote (Ep1) commonly surrounds Ap2. In these accessory minerals, U and Th contents are too low, or grains are too small, for in situ U-Th-Pb dating. Sm-Nd isotope data of Ap2, monazite and Ep1 give an isochron age of 601±69Ma, which is interpreted to represent a partially reset Grenvillian age, affected by Caledonian fluid-assisted mineral growth. In amphibolitized samples, granulite Ap2 is replaced by apatite (Ap3) with lower REE contents and no monazite inclusions. The REE released by this replacement are redistributed in a corona of epidote group minerals (Ep2) surrounding Ap3. The in situ Sm-Nd isotope data for Ep2 and titanite, found in replacement of ilmenite-hematite, return an isochron age of 395±65Ma, recording the timing of amphibolite-facies mineral growth when fluids were introduced into the rock. In eclogitized samples, eclogitic apatite (Ap4) occurs as polycrystalline aggregates, suggesting for a complex replacement process during deformation. REE contents of Ap4 are low, as REE originally contained in the precursor apatite were redistributed mainly into zoisite. Apatite shielded as inclusions in ilmenite and garnet preserve the REE-rich signature of the initial magmatic (Ap1) and granulite (Ap2) apatite, indicating these grains did not undergo further re-equilibration during Caledonian metamorphism. The resistance of apatite to compositional re-equilibration in this case confirms the petrological potential of apatite inclusions shielded in chemically inert minerals to track early magmatic, or metamorphic, crystallisation stages.

Textures, trace element compositions, and U–Pb ages of titanite from the Mangling granitoid pluton, East Qinling Orogen: Implications for magma mixing and destruction of the North China Craton

The Mangling granitoid pluton, located along the southern margin of the North China Craton, consists mainly of monzogranite with minor amounts of diorite. The monzogranite contains abundant mafic microgranular enclaves (MMEs) and is intruded by numerous mafic dikes, providing an opportunity to study magma mixing and its role in the formation of the granitioid pluton. In this paper, we present in situ analysis of U–Pb isotopes and trace element compositions of titanite from the MMEs and the host monzogranite using Laser Ablation–Inductively Coupled Plasma-Mass Spectrometry to document the role of magma mixing in the formation of the Mangling granitoid pluton. Titanite grains from the MMEs (type 1) are euhedral with patchy zoning, whereas the varieties from the closely associated host monzogranite are euhedral and consist of two types (type 2 and type 3). Type 2 titanite is more abundant and has oscillatory zoning without Fe–Ti oxide inclusions, whereas type 3 grains commonly have Fe–Ti oxide inclusions in the core that is rimmed by inclusion-free overgrowths with weak oscillatory zoning. Titanite from monzogranite without MMEs (type 4) is euhedal and has weak oscillatory zoning, with rare ilmenite inclusions in the core. Titanite from a mafic dike intruding the monzogranite (type 5) is anhedral and has sector zoning. Titanite grains from MMEs and the monzogranite (type 1, 2 and 3) have U–Pb ages that are indistinguishable (149±1Ma, 148±1Ma and 148±2Ma, respectively). These ages agree well with zircon U–Pb ages of 150±1Ma, 150±1Ma and 149±1Ma for the MMEs, host monzogranite, and mafic dike, respectively. The age consistency thus confirms coeval formation of the MMEs, the host monzogranite, and the mafic dikes, demonstrating a mafic magmatic, rather than extraneous or restitic origin for the MMEs.Titanite grains from the MMEs (type 1) and mafic dike (type 5) have much lower Al2O3, REE, Nb/Zr, Y/Zr, and Lu/Hf, but higher (Ce+Nd)/Y and La/Ce ratios compared to those from the monzogranite (type 2 and type 4). These compositional differences suggest that titanite grains from the MMEs and the host monzogranite crystallized from different magmas. Type 3 titanite contains abundant Fe–Ti oxide inclusions and is characterized by dissolution and reprecipitation textures; the composition of its core and rims are comparable to those of type 1 and type 4 titanites, respectively. The compositional variation between the core and rims of the type 3 titanite grains implies that they were re-equilibrated with high temperature mafic magma and then continued to crystallize within the granitic magmas with low fO2. The textural, geochronological, and geochemical data of titanite grains can be best explained in term of mixing of mafic and felsic magmas. We conclude that both the fine-grained MMEs and the host monzogranite are hybrid products of mafic and felsic end-member magmas. When combined with other geological and geochronological data in the North China Craton, our results suggest that the widespread late Jurassic to early Cretaceous granitoid intrusions were generated in an extensional setting related to craton destruction.

Large 12-Rayed Black Star Sapphire from Sri Lanka with Asterism Caused by Ilmenite Inclusions

Large 12-Rayed Black Star Sapphire from Sri Lanka with Asterism Caused by Ilmenite Inclusions

P–T–t–D paths of the North Himalayan metamorphic rocks: Implications for the Himalayan orogeny

Metamorphic P–T–t–D paths have been determined in the Yardoi gneiss dome of the eastern Himalaya that place new constraints on the genesis of the North Himalayan Gneiss Dome and tectonic evolution of the Himalayan orogen. Our study shows that the schists from the Yardoi dome underwent at least three stages of metamorphism and deformation. The first stage of prograde metamorphism is represented by the core of porphyroblastic garnet, showing distinct growth compositional zoning, and hosting mineral inclusions of biotite, muscovite, quartz and ilmenite; the curved inclusion trails define the first stage of deformation foliation (S1). The second stage of peak metamorphism is represented by the rim of porphyroblastic garnet and the aligned matrix minerals of biotite, muscovite, plagioclase, quartz, kyanite and staurolite, which define the main deformation foliation (S2). The third stage of retrograde metamorphism is characterized by occurrence of biotite, plagioclase, muscovite and sillimanite within the distributed shear bands, which define the late deformation foliation (S3). Phase equilibrium modeling reveals that Yardoi schists witnessed a peak metamorphism of upper amphibolite-facies under P–T conditions of 7–8kbar and 615–665°C, and records a clockwise P–T–t–D path with a prograde process of both temperature and pressure increase and subsequent retrogression of isothermal decompression. The zircon U–Pb dating indicates that the prograde process occurred during the Middle Eocene of 48–36Ma and the retrograde metamorphism probably lasted to ca. 16Ma. The present result shows that the formation of the Yardoi schists was related to the subduction and exhumation of Indian crust, the initial collision of Indian and Asian continents occurred at ca. 50Ma, the northeastern margin of the Indian continent was shallowly underthrusted beneath the Asian continent, and distinct tectonic discontinuity is present in the Greater Himalayan Sequence.

Epitaxial nucleation of garnet on biotite in the polymetamorphic metapelites surrounding the Vedrette di Ries intrusion (Italian Eastern Alps)

Garnet in a metapelite from the aureole of the Vedrette di Ries tonalite, Eastern Alps, is found in two distinctive microstructural settings relative to a large single crystal of biotite: it forms a narrow polycrystalline layer in a reaction zone between plagioclase and biotite, and nearby it occurs in clusters of crystals interspersed with the biotite. In the reaction zone, morphological and microchemical evidence document multiple nucleation events along the interface between biotite and plagioclase, with ilmenite inclusions marking the original plagioclase–biotite boundary. Electron backscatter diffraction analysis shows that for all garnet in both microstructural settings, (110) grt || (001) bt with [100] grt || [100] bt . This single, recurring orientation for all garnet crystals adjacent to the biotite grain implies that nucleation was dominantly epitaxial during crystallization of the garnet. The occurrence is remarkable for the clear genetic relationships revealed by the microstructures and for its preservation of the mica substrate on which the garnet nucleated, which allows unambiguous determination of not only the coincident lattice planes but also the coincident lattice directions involved in the epitaxy.

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

Abstract We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though strongly thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and in contact with the peridotites, and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence, garnet decreases whereas biotite increases in modal proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈ 5 to 200 μm, with a mean size of ≈ 30–40 μm. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈ 850 °C and 12–14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈ 800–850 °C and 5–6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Late‐stage orogenic loading revealed by contact metamorphism in the northern Appalachians, New York

AbstractPelitic schists from contact aureoles surrounding mafic–ultramafic plutons in Westchester County, NY record a high‐P (~0.8 GPa) high‐T (~790 °C) contact overprint on a Taconic regional metamorphic assemblage (~0.5 GPa). The contact metamorphic assemblage of a pelitic sample in the innermost aureole of the Croton Falls pluton, a small (&lt;10 km2) gabbroic body, consists of quartz–plagioclase–biotite–garnet–sillimanite–ilmenite–graphite–Zn‐rich Al‐spinel. Both K‐feldspar and muscovite are absent, and abundant biotite, plagioclase, sillimanite, quartz and ilmenite inclusions are found within subhedral garnet crystals. Unusually low bulk‐rock Na and K contents imply depletion of alkalic components and silica through anatexis and melt extraction during contact heating relative to typical metapelites outside the aureole. Thermobarometry on nearby samples lacking a contact overprint yields 620–640 °C and 0.5–0.6 GPa. In the aureole sample, WDS X‐ray chemical maps show distinct Ca‐enriched rims on both garnet and matrix plagioclase. Furthermore, biotite inclusions within garnet have significantly higher Mg concentration than matrix biotite. Thermobarometry using GASP and garnet–biotite Mg–Fe exchange equilibria on inclusions and adjacent garnet host interior to the high‐Ca rim zone yield ~0.5 ± 0.1 GPa and ~620 ± 50 °C. Pairs in the modified garnet rim zone yield ~0.9 ± 0.1 GPa and ~790 ± 50 °C. Thermocalc average P–T calculations yield similar results for core (~0.5 ± ~0.1 GPa, ~640 ± ~80 °C) and rim (~0.9 ± ~0.1 GPa, ~800 ± ~90 °C) equilibria. The core assemblages are interpreted to record the P–T conditions of peak metamorphism during the Taconic regional event whereas the rim compositions and matrix assemblages are interpreted to record the P–T conditions during the contact event. The high pressures deduced for this later event are interpreted to reflect loading due to the emplacement of Taconic allochthons in the northern Appalachians during the waning stages of regional metamorphism (after c. 465 Ma) and before contact metamorphism (c. 435 Ma). In the absence of contact metamorphism‐induced recrystallization, it is likely that this regional‐scale loading would remain cryptic or unrecorded.

Oxide, sulphide and carbonate minerals in a mantle polymict breccia: Metasomatism by proto-kimberlite magmas, and relationship to the kimberlite megacrystic suite

Polymict breccias entrained by kimberlites are mantle xenoliths comprising coarse-grained mantle minerals (porphyroclasts) and rock clasts, cemented together by ilmenite, rutile, phlogopite, olivine and minor sulphides. These unusual xenoliths are generally considered to result from ascending primitive/precursor kimberlite magmas that crystallised in the magma conduit at lithospheric mantle depths. To enhance our understanding of these processes, we investigated the oxide, sulphide and carbonate minerals of a new polymict breccia (DU-1) from the Bultfontein Dumps (Kimberley, South Africa).Xenolith DU-1 contains heterogeneous domains of ilmenite-rich breccia surrounded by spinel harzburgite wall rock. The breccia domains also host resorbed Cr-diopside porphyroclasts and occasional Fe–Ni–Co sulphides segregations. Ilmenite occurs as large (up to 5cm), chemically zoned lenses, associated with minor rutile. The ilmenite has Hf isotope values (initial εHf=2.1–3.0) in the range of South African Group I kimberlites and associated megacrysts. The ilmenite lenses host primary multiphase carbonate-rich, olivine-dominated, phlogopite-dominated and sulphide mineral inclusions. Carbonate-rich inclusions host abundant magnesite and dolomite, with subordinate kalsilite, phlogopite, alkali-carbonates, phosphates and chlorides.The occurrence of carbonate-rich inclusions suggests entrapment of a Ca–Mg-rich alkali-carbonate melt during ilmenite growth. However, geochemical modelling indicates that this melt was not parental to the ilmenite. Instead, it is suggested that the ilmenite (and other cementing phases) crystalised from ilmenite and the other cementing phases crystallised from a S-bearing Ti–Fe–K-rich ultramafic silicate melt, derived from an ascending proto-kimberlite melt, which was modified subsequently by wall rock assimilation and/or magma mixing, porphyroclast dissolution and crystal fractionation. The alkali-carbonate melt could be the residual liquid after these processes occurred. Alternatively, the ultramafic silicate and alkali-carbonate melts were produced by liquid immiscibility from a silicate-carbonate proto-kimberlite melt. The occurrence of ilmenite inclusions in sulphide segregations, and sulphide inclusions in ilmenite lenses is indicative of late-stage silicate-sulphide liquid immiscibility.The major and trace element concentrations, Hf isotope composition and mineral inclusion content of ilmenite are consistent with a genetic relationship between polymict breccia formation and the kimberlite megacryst suite. We propose that polymict breccias and megacrysts were produced at different depths by common silicate-carbonate magmas during the early stages of kimberlite magmatism.

Petrogenesis of mineral micro-inclusions in an uncommon carbonado

A unique Brazilian sample of a carbonado, displaying unusually large amount of diamond clasts merged within a fine-grained diamond matrix, has been studied by Secondary Ion Mass Spectrometry (SIMS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) on Focused Ion Beam (FIB)-extracted foils. We found for the first time in the diamond clasts (stage-1) micrometer to nanometer-sized inclusions of augite, ilmenite and phlogopite (all Fe-rich). Inclusions of metallic phases (Fe, Ti, Cr, Al and alloys of Fe-Cr, Al-Cr, Al-Fe Cr) described in worldwide carbonado occur in the studied sample exclusively within the fine-grained matrix (stage-2). The carbon isotopic composition of the diamond clasts and the fine-grained matrix falls within the range −27 ‰ to −32 ‰, like worldwide carbonado. The iron-rich silicate-oxide assemblage isolated inside clasts points to an initial growth of that diamond from mafic-rock minerals under oxidizing conditions ( f O 2 > IW). On the other hand metallic phases within the fine-grained matrix indicate an oxygen fugacity drop of at least 15 log units. This change in redox conditions is coeval with a deformation event under shearing stress at upper-mantle depth. During this metamorphic event, stage-1 diamonds were broken giving rise to the stage-2 fine-grained matrix, and syngenetic oxide inclusions were reduced to their metallic elements. This unique sample sheds new light on early 1970s hypotheses that interpreted carbonado as a high-pressure product from prograde metamorphism of crustal mafic rocks.

Rutile compositions in the Kalgoorlie Goldfields and their implications for exploration

The compositions of 188 grains of rutile from 12 samples from the Kalgoorlie Goldfields, in the Yilgarn Craton of Western Australia, show that grains associated with the Mt Charlotte stockwork-style mineralisation have generally low minor-element contents (except for Fe, which may reflect, in part, ilmenite inclusions). However, rutile in the Fimiston (Golden Mile) lode-style mineralisation is (Fe + W)-rich, and in the high-grade Green Leader mineralisation rutile is (V + W)-rich. The incorporation of W6 + into the rutile structure in these styles of mineralisation is balanced by the presence of Fe3 + and V3 + , although in rutile in the Green Leader mineralisation, V is present in both + 3 and higher oxidation states. Detailed examination of W-rich rutiles from the Fimiston lode indicates that they have a complex internal microstructure, with variations in lattice orientation within single rutile crystals, probably caused by the strain associated with incorporation of large amounts of foreign ions into the rutile structure. The composition and complex microstructure of rutile can potentially discriminate between Au anomalies of higher and lower significance in the region (lode- vs stockwork-style), with the presence of V in high oxidation states suggesting that the hydrothermal fluids responsible were relatively oxidising.

Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss

It is well known that oriented iron and titanium oxide inclusions occur in pyroxenes and plagioclase of anorthosites and granulites, and they are attributed to exsolution at subsolidus conditions. The oxides occur as needles or platelets. In this study, we determine the morphology of oxide needles as well as their orientation in plagioclase (An 30–35) in anorthosite gneiss from the Adirondack mountains (New York). The investigation was done with electron backscatter diffraction (EBSD) in a scanning electron microscope, as well as Laue diffraction with a microfocus synchrotron X-ray beam at the Advanced Light Source in Berkeley. It was observed that the needle direction is [110] in magnetite and [1010] in ilmenite. The needle direction is consistently parallel to [001] of plagioclase. Furthermore, (111) of magnetite and (0001) of ilmenite are sub-parallel to (120) and (120) of plagioclase. We note that for directions [110] in the magnetite structure and [1010] in ilmenite, O atoms are close-packed, and (111) and (0001) are close-packed planes, correspondingly. In plagioclase, [001] is a direction with open channels as well as approximate alignment of Si tetrahedral edges, thus providing nucleation sites with a coincidence lattice relationship. (120) and (120) in this triclinic mineral are planes with approximate tetrahedral sides so that the relationship is structurally plausible. From Laue diffraction, we can determine that the magnetite needle axis is subject to an extensional stress, most likely attained during cooling of the inclusions within the plagioclase host.

Olivine-rich Troctolites from Ligurian Ophiolites (Italy): Evidence for Impregnation of Replacive Mantle Conduits by MORB-type Melts

The gabbroic plutons of the Internal Ligurian ophiolites (Northern Apennines, Italy) include olivine-rich troctolite bodies up to 80 m thick. The rounded to embayed morphology of olivine (Fo ¼ 87^ 88 mol %) and spinel from the olivine-rich troctolites, together with the high Mg-number (88^90) and Cr contents (2400^ 3000 ppm) of associated poikilitic clinopyroxene, indicates their formation through reaction between an olivine^spinel matrix and an infiltrating melt.This interpretation is corroborated by the occurrence of plagioclase-rich veins that exhibit diffuse margins against the host olivine-rich troctolites and centimetre-scale spinel-bearing dunitic clots, which are interpreted as the crystallization products of the infiltrating melts and relics of pre-existing olivine-rich material, respectively. The incompatible element signature of clinopyroxene from the olivine-rich troctolites shows that the infiltrating melts were chemically similar to mid-ocean ridge basalt (MORB). Spinel from the olivine-rich troctolites contains inclusions of Ti-pargasite/ kaersutite, phlogopite/aspidolite and orthopyroxene; inclusions of ilmenite and loveringite are also locally present. These spinels most probably formed from hybrid melts derived from interaction between melts rich in incompatible elements and new injections of primitive melt. We propose that this interaction occurred in the mantle, in melt conduits of replacive origin near the base of the conductive thermal boundary layer, and led to formation of a matrix made up of olivine and minor inclusion-bearing spinel. This matrix was subsequently impregnated by MORB-type melts saturated in plagioclase þ clinopyroxene to produce the olivine-rich troctolites. The amount of melt added to the olivine^spinel matrix to produce the olivine-rich troctolites is estimated to be � 25 wt %.

Tectono-metamorphic history recorded in garnet porphyroblasts: insights from thermodynamic modelling and electron backscatter diffraction analysis of inclusion trails

In a Barrovian metamorphic sequence, garnetiferous mica schists document a heterogeneously developed superposition of sub-orthogonal fabrics and multiple garnet growth episodes. In the variably deformed domains, four types of garnet porphyroblasts have been defined based on inclusion trail patterns. Modelled garnet zoning in the MnNCKFMASHTO system indicates a prograde evolution from 4-4.5 kbar and 490-510 � C to 5-6 kbar and 520-550 � C in the earliest subhorizontal fabric progressing towards 6.5-7.5 kbar and 560-590 � C in the subsequent subvertical foliation. This fabric is heterogeneously deformed into a shallow-dipping retrograde foliation associated with garnet resorption. In situ electron backscatter diffraction measurements of ilmenite inclusions in individual garnet grains yield precise data on included planar and linear elements. Consistent orientations of internal foliations, lineations and foliation intersection axis sets indicate a superposition of three sub-orthogonal foliation systems. Weak variations of internal records with increasing intensity of deformation suggest that a moderate buckling stage occurred, but apparent lack of porphyroblast rotation is interpreted as a result of dominant passive flow. Coupling the orientation of internal fabric sets with P-T estimates is used to complement the tectono-metamorphic evolution of the thickened crust. We demonstrate that garnet porphyroblasts preserve features which reflect large-scale tectonic processes in orogens.

An AEM study of garnet clinopyroxenite from the Sulu ultrahigh-pressure terrane: formation mechanisms of oriented ilmenite, spinel, magnetite, amphibole and garnet inclusions in clinopyroxene

Optical microscopy, secondary electron microscopy and analytical electron microscopy were used to characterize crystallographic orientation relationships between oriented mineral inclusions and clinopyroxene (Cpx) host from the Hujialing garnet clinopyroxenite within the Sulu ultrahigh-pressure (UHP) terrane, eastern China. One garnet clinopyroxenite sample (2HJ-2C) and one megacrystic garnet-bearing garnet clinopyroxenite (RZ-11D) were studied. Porphyroblastic clinopyroxene from sample 2HJ-2C contains oriented inclusions of ilmenite (Ilm), spinel (Spl), magnetite and garnet, whereas clinopyroxene inclusions within megacrystic garnet from sample RZ-11D contain oriented inclusions of ilmenite and amphibole. Specific crystallographic relationships were observed between ilmenite/spinel plates and host clinopyroxene in sample 2HJ-2C and between ilmenite plates and host clinopyroxene in sample RZ-11D, i.e. [\( 1\bar{1}00 \)]Ilm//[\( 0\bar{1}0 \)]Cpx (0001)Ilm//(100)Cpx; and [110]Spl//[\( 0\bar{1}0 \)]Cpx (\( \bar{1}11 \))Spl//(100)Cpx. These inclusions are suggested to be primary precipitates via solid-state exsolutions. Most of the needle-like magnetite/spinel inclusions generally occur at the rims or along fractures of clinopyroxene within sample 2HJ-2C. Despite the epitaxial relation with host clinopyroxene, these magnetite/spinel needles would have resulted from fluid/melt infiltrations. Non-epitaxial garnet lamellae in clinopyroxene of sample 2HJ-2C were formed via fluid infiltration-deposition primarily along (010) and subordinately along (100) partings. Epitaxial amphibole plates (with a thickness <1 μm) and lamellae (with a thickness = 1–10 μm) in host clinopyroxene of sample RZ-11D were probably results of hydration processes, although amphibole plates could otherwise be interpreted as exsolution products. Temporal relations between mineral inclusions in each sample can be established, and a semi-quantitative P–T path for this garnet clinopyroxenite body was derived accordingly. The present results show that the Hujialing garnet clinopyroxenite may not have subducted to mantle depths as deep as 250 km during UHP metamorphism as suggested by previous studies. This study demonstrates that the crystallographic and temporal/spatial relationships between aligned inclusions and host minerals are essential to a correct genetic interpretation of metamorphic rocks.

Spectral characteristics of lunar impact melts and inferred mineralogy

Abstract– Two suites of lunar impact melt samples have been measured in NASA’s Reflectance Experiment Laboratory (RELAB) at Brown University. Suite 1 comprises seven Apollo 17 crystalline impact melt breccias and seven quenched glass equivalents. Suite 2 is made up of 15 additional impact melt samples (from Apollo 12, 15, 16, and 17) which exhibit a range of textures and compositions related to cooling conditions and glass abundance. A few of these samples have cooled slowly and fully crystallized, and thus have the same spectral properties as igneous rocks of similar texture and composition; they cannot be uniquely distinguished without geologic context. However, most of the impact melts and melt breccias contain either quantities of quenched glass and/or have developed microcrystalline nonequilibrium textures with well‐defined, diagnostic spectral properties. The microcrystalline textures are associated with a distinctive 600 nm absorption feature, apparently due to submicroscopic ilmenite inclusions in a transparent host (typically fine‐grained plagioclase). The reflectance properties of these lunar sample suites contribute to and constrain the identification and characterization of impact melts in remote sensing data.

Applied Mineralogical Studies on Iranian Hard Rock Titanium Deposit

The Qara-aghaj hard rock titanium deposit has been located in the 36 Km at the North-West of Euromieh, Iran. Mineralogical studies performed by XRD, XRF, Optical microscopy and SEM studies indicated that ilmenite, magnetite and apatite are main valuable minerals. The gangue minerals consist of the silicate minerals such as pyroxene, olivine, plagioclase and some secondary minerals. Ilmenite in Qara-aghaj ore occurs in three forms: ilmenite grains, exsolved ilmenite lamellae in magnetite and ilmenite particles disseminated in silicate minerals. The grain forms liberated in 150µm are only recoverable by physical methods. The maximum content of TiO2 in ilmenite lattice is determined 48% by EDX. Although the ore has 8.8% average grade of TiO2, the recoverable TiO2 is only about 6.72% the studied sample contained 18.3% ilmenite and the amount of recoverable ilmenite is only about 14% (6.72% TiO2). This is due to the ilmenite exsolutions and inclusions in the magnetite and silicate minerals, and the TiO2 in solid solution in the lattices of these minerals. In fact, about 77% of whole ilmenite content of the ore will be recoverable. EDX analysis showed that Fe is substituted partially in ilmenite by Mn and Mg. Some narrow lamellae of hematite are formed inside ilmenite. By analyzing of magnetite, it was found that the V2O5 content is up to 1%. V 3+ is found in magnetite lattices by replacing Fe 3+ . Analyzing of clinopyroxenes indicated that augite, containing Ti, is the main form of this group. Ilmenite, apatite and magnetite are valuable minerals for production of TiO2, P2O5 and Fe, respectively and the V2O5 can be extracted from magnetite as a by-product.

Petrology of coesite‐bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication

AbstractCoesite inclusions in garnet have been found in eclogite boudins enclosed in coesite‐bearing garnet micaschist in the Habutengsu Valley, Chinese western Tianshan, which are distinguished from their retrograde quartz by means of optical characteristics, CL imaging and Raman spectrum. The coesite‐bearing eclogite is mainly composed of porphyroblastic garnet, omphacite, paragonite, glaucophane and barroisite, minor amounts of rutile and dotted (or banded) graphite. In addition to coesite and quartz, the zoned porphyroblastic garnet contains inclusions of omphacite, Na‐Ca amphibole, calcite, albite, chlorite, rutile, ilmenite and graphite. Multi‐phase inclusions (e.g. Czo + Pg ± Qtz, Grt II + Qtz and Chl + Pg) can be interpreted as breakdown products of former lawsonite and possibly chloritoid. Coesite occurs scattered within a compositionally homogenous but narrow domain of garnet (outer core), indicative of equilibrium at the UHP stage. The estimate by garnet‐clinopyroxene thermometry yields peak temperatures of 420–520 °C at 2.7 GPa. Phase equilibrium calculations further constrain the P–T conditions for the UHP mineral assemblage Grt + Omp + Lws + Gln + Coe to 2.4–2.7 GPa and 470–510 °C. Modelled modal abundances of major minerals along a 5 °C km−1 geothermal gradient suggests two critical dehydration processes at ∼430 and ∼510 °C respectively. Computed garnet composition patterns are in good agreement with measured core‐rim profiles. The petrological study of coesite‐bearing eclogite in this paper provides insight into the metamorphic evolution in a cold subduction zone. Together with other reported localities of UHP rocks from the entire orogen of Chinese western Tianshan, it is concluded that the regional extent of UHP‐LT metamorphism in Chinese western Tianshan is extensive and considerably larger than previously thought, although intensive retrogression has erased UHP‐LT assemblages at most localities.

Enrichment of PGE through interaction of evolved boninitic magmas with early formed cumulates in a gabbro–breccia zone of the Mesoarchean Nuasahi massif (eastern India)

The Mesoarchean Nuasahi chromite deposits of the Singhbhum Craton in eastern India consist of a lower chromite-bearing ultramafic unit and an upper magnetite-bearing gabbroic unit. The ultramafic unit is a ∼5 km long and ∼400 m wide linear belt trending NNW-SSE with a general north-easterly dip. The chromitite ore bodies are hosted in the dunite that is flanked by the orthopyroxenite. The rocks of the ultramafic unit including the chromitite crystallized from a primitive boninitic magma, whereas the gabbro unit formed from an evolved boninitic magma. A shear zone (10–75 m wide) is present at the upper contact of the ultramafic unit. This shear zone consists of a breccia comprising millimeter- to meter-sized fragments of chromitite and serpentinized rocks of the ultramafic unit enclosed in a pegmatitic and hybridized gabbroic matrix. The shear zone was formed late synkinematically with respect to the main gabbroic intrusion and intruded by a hydrous mafic magma comagmatic with the evolved boninitic magma that formed the gabbro unit. Both sulfide-free and sulfide-bearing zones with platinum group element (PGE) enrichment are present in the breccia zone. The PGE mineralogy in sulfide-rich assemblages is dominated by minerals containing Pd, Pt, Sb, Bi, Te, S, and/or As. Samples from the gabbro unit and the breccia zone have total PGE concentrations ranging from 3 to 116 ppb and 258 to 24,100 ppb, respectively. The sulfide-rich assemblages of the breccia zone are Pd-rich and have Pd/Ir ratios of 13–1,750 and Pd/Pt ratios of 1–73. The PGE-enriched sulfide-bearing assemblages of the breccia zone are characterized by (1) extensive development of secondary hydrous minerals in the altered parts of fragments and in the matrix of the breccia, (2) coarsening of grain size in the altered parts of the chromitite fragments, and (3) extensive alteration of primary chromite to more Fe-rich chromite with inclusions of chlorite, rutile, ilmenite, magnetite, chalcopyrite, and PGE-bearing chalcogenides. Unaltered parts of the massive chromitite fragments from the breccia zone show PGE ratios (Pd/Ir = 2.5) similar to massive chromitite (Pd/Ir = 0.4–6.6) of the ultramafic unit. The Ir-group PGE (IPGE: Ir, Os, Ru) of the sulfide-rich breccia assemblages were contributed from the ultramafic–chromitite breccia. Samples of the gabbro unit have fractionated primitive mantle-normalized patterns, IPGE depletion (Pd/Ir = 24–1,227) and Ni-depletion due to early removal of olivine and chromite from the primitive boninitic magma that formed the ultramafic unit. Samples of the gabbro and the breccia zone have negative Nb, Th, Zr, and Hf anomalies, indicating derivation from a depleted mantle source. The Cu/Pd ratios of the PGE-mineralized samples of the breccia zone (2.0 × 103–3.2 × 103) are lower than mantle (6.2 × 103) suggesting that the parental boninitic magma (Archean high-Mg lava: Cu/Pd ratio ∼1.3 × 103; komatiite: Cu/Pd ratio ∼8 × 103) was sulfur-undersaturated. Samples of the ultramafic unit, gabbro and the mineralized breccia zone, have a narrow range of incompatible trace element ratios indicating a cogenetic relationship. The ultramafic rocks and the gabbros have relatively constant subchondritic Nb/Ta ratios (ultramafic rocks: Nb/Ta = 4.1–8.8; gabbro unit: Nb/Ta = 11.5–13.2), whereas samples of the breccia zone are characterized by highly variable Nb/Ta ratios (Nb/Ta = 2.5–16.6) and show evidence of metasomatism. The enrichment of light rare earth element and mobile incompatible elements in the mineralized samples provides supporting evidence for metasomatism. The interaction of the ultramafic fragments with the evolved fluid-rich mafic magma was key to the formation of the PGE mineralization in the Nuasahi massif.

Origin of titanite in metarodingite from the Zagros Thrust Zone, Iraq

Three types of metamorphic titanite have been noted in a metarodingite pod within the tectonized and serpentinized peridotite portion of the Penjwin ophiolite sequence within the Iraqi Zagros Thrust Zone (IZTZ), northeastern Iraq. Type I metamorphic titanite occurs as subhedral to anhedral finegrained disseminated crystals within chlorite that was formed during chloritization of biotite as a result of low-temperature (T = 330-340 °C) ocean-floor metamorphism or rodingitization of plagiogranite under a reducing environment. It is characterized by intermediate Al 2 O 3 (Avg: 3.61 wt%), high FeO T (Avg: 0.89 wt%), and intermediate TiO 2 (Avg: 34.7 wt%). Type II metamorphic titanite occurs as a thin rim around ilmenite and has high Al 2 O 3 (Avg: 4.8 wt%), intermediate FeO T (Avg: 0.6 wt%), and low TiO 2 (Avg: 33.7 wt%); it represents a reaction product between grossular and ilmenite, which resulted from an oxidizing high-pressure-high-temperature (P = 1.4-1.6 GPa and T &gt; 750 °C) metamorphic event involving plagiogranite. Type III metamorphic titanite occurs as very coarse, highly fractured grains up to 0.5 mm, with inclusions of ilmenite, and surrounded by albitic plagioclase, analcime, and chlorite. This titanite is characterized by low Al 2 O 3 (Avg: 1.23 wt%), low FeO T (Avg: 0.30 wt%), and high TiO 2 (Avg: 36.98 wt%). It formed during extensive titanitization of ilmenite by a reaction with Ca-plagioclase during moderate pressure and temperature (P &lt; 1.6 GPa and T &lt; 750 °C) conditions, as a result of albitization of Ca-plagioclase in plagiogranite.