Albite Research Articles

Low temperature combustion and ash deposition characteristics of palm oil and forest replanting waste

This study evaluation and analysis the low-temperature combustion characteristics and ash deposition of palm oil waste, including palm kernel shell (PKS) and empty fruit bunch (EFB), as well as forestry waste in the form of rubber wood (RBW) and replanting waste (RPW). The experiments were conducted using a drop tube furnace at 900 ᵒC, which is considered a low temperature compared to the operating temperature of pulverized coal. The thermogravimetric method (TGA) was applied to understand the combustion properties of the biomass, while the ash deposition tendency was assessed through empirical calculations, combustion experiments, and direct observation of the ash produced. The results showed that RBW had the best combustion performance compared to the other samples. Although RPW has the highest ash fusion temperature value among all samples, with a value above 1200 ᵒC, the low-melting-point mineral phase such as fairchildite, produced at low-temperature combustion at 24.74%, increases the risk of ash sticking to metal surfaces. PKS and EFB produce very high albite mineral content of more than 60%, which has a low melting point and could potentially cause ash deposition problems. On the other hand, RBW, with a dominant content of SiO2 (21.79%), Al2O3 (20.24%), and MgO (8.03%), produces minerals dominated by quartz at up to 78% and magnesioferrite at more than 5%, both of which have a high melting point that tends to produce harmless ash. These findings provide insight into the potential of utilizing biomass in low-temperature combustion processes, which is a way of reducing waste and lowering greenhouse gas emissions.

Experimental study on soda granites of the Singhbhum Craton, eastern India, and its petrogenetic significance

The soda granite (~Paleoproterozoic) of the Singhbhum Craton (SC) of eastern India occurs along the entire stretch of the Singhbhum Shear Zone (SSZ; or Copper Belt Thrust Zone). The SSZ (marking a thrust contact between the adjacent North Singhbhum mobile belt and SC) serves as the important locale to host apatite‐magnetite, copper sulphide, and uraniferous mineralization. Typical field occurrence of soda granite is either as tongues (or patches) within a shear zone or as lit‐per‐lit style injections into surrounding country rocks which are generally highly sheared and mylonitized. Experimental studies on granite bodies can potentially throw light on their mineralogical and petrogenetic aspects; however, these studies are hitherto unreported in case of soda granites for almost the last 60 years. In this view, during the present research, experimental studies on soda granites have been carried out and these decipher the nature of the stability relationship of K‐feldspar (and transgression to more disordered anorthoclase), amphibole (both Ca‐amphibole and Fe–Mg–Mn amphibole and breaking down of Ca‐amphibole to Fe–Mg–Mn amphibole + non‐quad pyroxene + quartz at an appropriate temperature), biotite, muscovite, and albite (high albite‐ low albite displacive transformation). Whole‐rock chemistry (deduced from homogenized glass compositions) indicates its peraluminous, S‐type nature with an affinity towards Caledonian post‐collisional plutons. Characteristic geochemical plots suggest a pelitic source material for melting (and subsequent internal differentiation of the melt) and this has given rise to both migmatite as well as patchy soda granite exposures in the field. It is suggested that partial melting of mainly metapelitic (and minor mafic magmatic rocks) source (belonging to Singhbhum Series) gave rise to soda granites in this region.

Host rock peculiarities and influence of major structures on gold and base metal sulfide mineralization in northern Pakistan

For decades, the streams and rivers in northern areas of Pakistan are being explored for gold but the source rock for primary gold is yet to be located. Recent geological surveys have identified several areas for follow-up study for Cu-Au mineralization in Chitral and Gilgit-Baltistan regions. The rocks exposed at various localities are variably altered and/ or mineralized and intensely deformed, which mostly include diorite, granodiorite, greenschists, limestones and undeformed volcanic rocks and granitoids of the Kohistan island arc. The results of petrographic and X-ray diffraction (XRD) analyses of a variety of representative rock samples from a number sites have revealed that mineralization in the Chitral and Gilgit-Baltistan regions is dominantly in the form of pyrite, tetrahedrite, chalcopyrite and galena with subordinate amounts of magnetite, malachite and azurite. The associated/ gangue minerals include albite, quartz, actinolite, biotite, chlorite, epidote, calcite, garnet, illite and titanite (sphene). Diffraction patterns of glycolated samples did not show the existence of swelling clay (e.g., smectite). Sericitic, chloritic and carbonatic alterations have been observed in the studied altered rocks. Mass balance calculations indicate that most of the sulfide-bearing samples are enriched in Cu, Au, Sb, As and Pb and depleted in the rest of the metals reflecting differences in elements mobility during the ore-forming processes. Some of the mineralized rocks especially limestone have experienced a significant volume change due to mobilization of some of the major element oxides e.g. CaO, Fe2O3, SiO2 and ore-forming components e.g. Cu and Pb. The mineralization is of epithermal type in most of the investigated sites, however a few areas show ore formation though orogenic processes and very rarely the ore deposit displays features of the volcanogenic massive sulfide type. Some of the areas are quite promising with respect to their ore element contents and the highly mineralized zones lie in close proximity to major structures in the region. Besides, results from the current study indicate that the mineralization shows close spatial association and hence a strong genetic link with strike slip faults especially where they bend and merge together.

Na-feldspar: temperature, pressure and the state of order

Abstract. In feldspars, mean tetrahedral T–O bond lengths (T = Al,Si) are the standard measure of the tetrahedral Al content. However, for a sophisticated assessment of the Al,Si distribution, factors have to be accounted for (1) that cause individual T–O bond lengths to deviate from their tetrahedral means and (2) that cause mean tetrahedral lengths to deviate from values specified by the Al content. We investigated low albite, Na[AlSi3O8], from six X-ray crystal structure refinements available in the literature. The Al,Si distribution of low albite is fully ordered so that Al,Si–O bond length variations result only from bond perturbing factors. For the intra-tetrahedral variation ΔT–O≡T–O-〈T–O〉, only two factors turned out to be effective: (1) the sum of bond critical point electron densities in the Na–O and T–O bonds neighbouring the T–O bond under consideration and (2) the fractional s-bond character of the bridging oxygen atom. This model resulted in a root mean square (rms) value for ΔT–O of only 0.002 Å, comparable to the estimated standard deviations (esd's) routinely quoted in X-ray and neutron structure refinements. In the second step, the inter-tetrahedral differences Δ〈T–O〉≡〈T–O〉-〈〈T–O〉〉 were considered. Here, apart from the tetrahedral Al content, the only size-perturbing factor is the difference between the tetrahedral and the grand mean fractional s-characters. The resulting rms value was as small as 0.0003 Å. From this analysis, Al site occupancies, t, can be derived from observed mean tetrahedral distances, 〈T–O〉obs, as t=0.25(1+nAn)+〈T–O〉adj-〈〈T–O〉〉/0.12466(17), with the observed distance 〈T–O〉obs adjusted for the influence of the fractional s-character, 〈T–O〉adj=〈T–O〉obs+0.1907(51)[〈fs(O)〉-〈〈fs(O)〉〉]. This equation served to determine the site occupancies of 16 intermediate to high albites and one analbite from their mean tetrahedral distances. It was found that the individual site occupancies t10, t1m and t20= t2m all vary linearly with the difference Δt1= t10− t1m. Δt1, in turn, varies linearly with the length difference, Δtr[110], between the unit cell repeat distances [1∕2a, 1∕2b, 0] and [1∕2a, -1/2b, 0]. Then, from the Δtr[110] indicator, values of t were obtained as t10=(1-b0)+b0(b1+b2Δtr[110])t1m=(1-b0)-(1-b0)(b1+b2Δtr[110])t20=t2m=(b0-0.5)-(b0-0.5)(b1+b2Δtr[110]), with b0=0.7288(16), b1=0.1103(59) and b2=3.234(32) Å−1. Finally, from an expression that converts the Δ2θ(131) measure of order into Δtr[110] and thus into site occupancies, it was possible to obtain from the unique suite of bracketed high-pressure experiments performed on albites by Goldsmith and Jenkins (1985) the evolution with equilibrium temperature of the thermodynamic order parameter Qod and of the individual Al site occupancies t at a pressure of 1 bar. For that purpose, since the Goldsmith and Jenkins experiments were performed at ≈18 kbar, a procedure was devised that accounts for the effect of pressure on the state of order. At 1 bar, low albite is stable up to 590 ∘C, where it begins to disorder, turning into high albite above 720 ∘C. The highly though not fully disordered monoclinic state (monalbite) is reached at 980 ∘C, 1 bar, and 1055 ∘C, 18 kbar, respectively. Eventually, when applying the determinative equations given above to low microcline, full order is predicted as in low albite.

Occurrence of albitite from Capo Malfatano, SW Sardinia: first report, characterization from mineralogy and whole-rock geochemistry

Within the sedimentary-volcanoclastic succession known as Bithia Unit (SW Sardinia) a decameter-wide albitite lens has been found and is here characterized from a geological, petrographic and geochemical point of view. Albitite is a yellowish, fine-grained body elongated and foliated according to the main schistosity of the hosting rocks (N20-25° - 40° NW). The rock is made up by plagioclase porphyroclasts in a fine-grained matrix of plagioclase (up to 80%) and quartz; both porphyroclasts and small grains in matrix are almost pure albite (Ab 98 ). Accessory phases are ilmenite, rutile, monazite, apatite and zircon. Bulk-rock chemical analyses show that the relative proportions of SiO 2 , Al 2 O 3 and Na 2 O strongly resemble those of pure albite. Major, trace and rare earth element (REE) contents strongly suggest geochemical affinity with the nearby Ordovician metavolcanics and orthogneiss from Capo Malfatano area described in literature. Furthermore, REE, Rb/Sr, Y/Ho and Zr/Hf ratios seem to exclude the involvement of a significant Na-rich fluid metasomatism.

Evolution of the North West Arm and the Central Sector of Mashava Igneous Complex in south central Zimbabwe from an investigation of its silicate minerals compositions

An investigation of the economically important Mashava Igneous Complex (MIC) in Zimbabwe was conducted using petrographic and silicate mineral compositions to gain some insights into its origin. The MIC, an ultramafic-mafic complex located in the western extremity of the Masvingo greenstone belt (MGSB), is composed of amphibole, serpentine, epidote, chlorite, clinopyroxene, orthopyroxene, plagioclase, and olivine. Spinel, sulfide minerals, and minor quartz as well as other opaque minerals are also present.The dominant mineral is serpentine, which displays a wide range in both FeO and SiO2 compositions, and the majority of this mineral belongs to the lizardite, chrysotile, and antigorite varieties. Amphiboles display a wide range in composition from tremolite and actinolite which are both consistent with greenschist facies metamorphism, through magnesiohornblende to tschermakite which are both consistent with amphibolite facies metamorphism. Clinozoisite is the only epidote type occurring in the MIC, whereas chlorite varies widely in composition which reflects the varying concentrations in iron and silica in this mineral. Chlorite types range from talc chlorite through penninite, diabantite, pycnochlorite, brunsvigite, ripidolite, and pseudothuringite.Plagioclase shows a wide compositional range from high albite to bytownite, with only two samples plotting in the alkali feldspar anorthoclase field. Pyroxene ranges in composition from enstatite through pigeonite and augite to diopside whereas olivine is rich in MgO with forsterite contents ranging from 80 to 89. Application of the chlorite geothermometry equation of Kranidiotis and MacLean (1987) yields temperatures ranging from ∼200–320 °C whereas temperatures ranging from 130 to 445 °C are obtained using equations of Lanari et al. (2014) for the formation of this mineral, generally consistent with low- to medium-grade metamorphic conditions.Chlorites in the North West Arm were formed at relatively lower temperatures (97–234 °C) than those at which chlorites in the Central Sector were formed (204–445 °C). Pressure estimates for the metamorphism of the MIC range from 3.8 to 7.3 kbars, which corresponds to depths of ∼13–25 km, respectively. Based on the different silicate mineral compositions of the North West Arm and the Central Sector, it is inferred that these two blocks underwent different petrogenetic and evolutionary histories but they were later juxtaposed, possibly during thrusting of the former onto its present position.

Interação entre magmas graníticos e a origem de epissienitos potássicos estaníferos do granito Madeira, mina Pitinga, Amazonas

O estudo petrográfico de amostras da zona de contato entre as fácies albita-granito de borda e feldspato alcalino-granito hipersolvus porfirítico, na borda oeste do plúton Madeira, identificou rochas com características texturais e composicionais herdadas das duas fácies. Tal feição é interpretada como um processo de interação entre os dois magmas graníticos, colocados e cristalizados contemporaneamente. Em condições subsolidus, fluidos hidrotermais causaram alteração potássica pervasiva, ou epissienitização, caracterizada pela dissolução de quartzo das fácies graníticas, gerando cavidades e aumentando a permeabilidade das rochas alteradas. Paralelamente, a albita da fácies de borda do albita-granito foi desestabilizada e substituída por microclínio hidrotermal e, nos estágios mais tardios, as cavidades foram preenchidas por quartzo, microclínio, fluorita, hematita, cassiterita, fengita, clorita, pirita, esfalerita, galena e calcopirita. Os epissienitos potássicos são rochas de coloração vermelha escura a marrom, granulação fina a média, ricas em microclínio hidrotermal, apresentando-se ora porosas, ora com cavidades preenchidas por quartzo e sulfetos. A cassiterita das rochas epissienitizadas é mais pura e relativamente mais pobre em Nb do que aquela presente no albita-granito magmático. Os fluidos que desencadearam a epissienitização devem ter sido oxidados, ricos em K, alcalinos e subsaturados em sílica. Propõem-se duas hipóteses para a sua origem: 1) por separação de uma fase fluida a partir do líquido magmático formador do granito hipersolvus; 2) pela ação do mesmo fluido que desencadeou o processo de autometassomatismo do albita-granito de núcleo, gerando sua fácies de borda.

Microspectroscopic and Petrographic Comparison of Experimentally Shocked Albite, Andesine, and Bytownite

AbstractPlagioclase feldspars are common on the surfaces of planetary objects in the solar system such as the Moon and Mars, and in meteorites. Understanding their response to shock deformation is important for interpretations of data from remote sensing, returned samples, and naturally shocked samples from impact craters. We used optical petrography, micro‐Raman, and micro–Fourier transform infrared spectroscopy to systematically document vibrational spectral differences related to structural changes in experimentally shocked (0–56 GPa) albite‐, andesine‐, and bytownite‐rich rocks as a function of pressure and composition. Across all techniques, the specific composition of feldspars was confirmed to affect shock deformation, where more Ca‐rich feldspars transform to an amorphous phase at lower shock conditions than more Na‐rich feldspars. Onset of amorphization occurs at ~50 GPa for albite, between 28 and 30 GPa for andesine, and between 25 and 27 GPa for bytownite. Complete amorphization occurred at pressures greater than ~55 GPa for albite, ~47 GPa for andesine, and ~38 GPa for bytownite. Petrographically, these experimentally shocked samples do not exhibit the planar microstructures common in naturally shocked plagioclase, despite showing the expected trends of internal disordering and deformation as seen in the micro‐Raman and infrared spectra. Average spectra of hyperspectral images of these samples mimic macroscale measurements acquired previously. However, we see micro‐scale heterogeneity in the shock response, resulting from variations in either composition, crystal orientation, or the inherent heterogeneity of the shock wave topology. This is an important factor to consider when deducing shock pressures in naturally shocked samples.

The Tanco Pegmatite At Bernic Lake, Manitoba. XVII. Mineralogy and Geochemistry of Alkali Feldspars

Abstract The alkali-feldspar paragenetic sequence in the Tanco pegmatite spans the entire crystallization and cooling history of the pegmatite and includes several different K-feldspar and albite varieties. Total feldspar modal abundance approaches 50% for the entire pegmatite volume. Blocky K-feldspar, aplitic albite, and albite of the cleavelandite habit together account for most of the total feldspar volume, whereas late, low-temperature feldspars in veins and cavities are mostly contained in inner zones associated with pollucite and petalite. In an inward progression through the concentrically zoned pegmatite, average bulk compositional data for blocky K-feldspar reveal steady increases in Rb 2 O (1.45–3.08 wt.%) and Cs 2 O (0.11–0.29 wt.%), increasing followed by decreasing contents of P 2 O 5 (0.34–0.47 wt.%), Li 2 O (0.014–0.095 wt.%), and Tl (105–239 ppm), decreasing Na 2 O (2.5–1.1 wt.%) and CaO (0.13–0.08 wt.%), and variable BaO (0.004–0.17 wt.%) and Ga 2 O 3 (0.006–0.010 wt.%). In aplitic albite and albite of the cleavelandite habit, CaO decreases (0.08–0.03 wt.%) and overall K 2 O and P 2 O 5 contents are variable. Late adularia feldspars from veins and clusters in pollucite exhibit extreme ranges in contents of Rb 2 O (1.80–24.84 wt.%) and Cs 2 O (0.10–1.43 wt.%) and significant P 2 O 5 (up to 0.51 wt.%). X-ray powder-diffraction data indicate near-maximum structural order of the early feldspar varieties as maximum microcline and high albite. Hydrothermal adularia crystals are essentially endmember (Or 100 ) high sanidine. The large and economically significant Tanco pegmatite represents an extreme in terms of petrologic processes involving fractional and disequilibrium crystallization from granitic melts enriched in volatiles and fluxing components (H 2 O, B, F, P), rare alkalis (Li, Rb, Cs), and high field strength elements (Ta, Nb, Zr, Hf). The alkali feldspars are the most significant carriers of P, Li, Rb, Tl, and Cs prior to the stabilization of large volumes of amblygonite–montebrasite, petalite, lepidolite, and pollucite. The rise and fall of trace-element content in feldspars, in relation to the spatial distribution of different zones and mineral assemblages, has implications in terms of the internal evolution of complex granitic pegmatites, as well as on the types and extents of subsolidus readjustments.

Thermoluminescence measurements of trap depth in alkali feldspars extracted from bedrock samples

Various measurements of thermal trap depth are evaluated for K-feldspar grains extracted from a bedrock sample. The initial rise method and the various heating rates method yield consistent results for both the natural signal (E = 1.23 and 1.16 eV, respectively) and for a regenerative dose of 64 Gy (0.83 and 0.78 eV). For the fractional glow curve, apparent E-values range from 0.39 eV to a plateau around 1.50 eV. The highest values for the natural and regenerative signals are obtained using the newly-developed post-isothermal TL (pI-TL) method wherein the isothermal loss curves (gotten by subtracting TL curves obtained after different preheat durations) are fitted in the initial rise region on an Arrhenius plot. For a dose of 12.8 Gy, this method measures apparent E-values ranging from 0.73 eV to a plateau near 1.84 ± 0.06 eV. We repeat this analysis on three additional feldspar samples (two perthites and a high albite) to get a mean value of E = 1.86 ± 0.03 eV. The same analysis of natural aliquots of the K-feldspar sample yields similar results, with the two highest E-values at 1.81 and 1.86 eV. The kinetic order does not systematically vary with isothermal holding temperature or duration but remains relatively constant at 1.6 ± 0.3 (regenerative dose) and 1.5 ± 0.5 (natural dose). The apparent frequency factor, measured assuming a single E-value of 1.86 eV, decreases systematically (∼1023−1012s−1) with hold temperature and duration, a result which is consistent with a thermally-activated, distance-dependent tunneling model for feldspar thermoluminescence (i.e., a single trap depth and a continuum of apparent frequency factors). Frequency factor values measured following identical isothermal treatments are comparable between the natural and regenerative post-isothermal TL curves. By contrast, if different E-values are assumed, the apparent frequency factor values appear stochastic. Finally, it is speculated that the plateau of pI-TL E-values may be interpreted as the thermal depth of the main dosimetric trap measured with IRSL protocols.

Record of S-rich vapors on asteroid 4 Vesta: Sulfurization in the Northwest Africa 2339 eucrite

In the Northwest Africa (NWA) 2339 eucrite, a few high-Fe pigeonite fragments were partially replaced by fine-grained troilite, Mg-rich augite, silica, with minor ilmenite and Mg-rich ferrosilite. The relict pigeonite has distinctly lower Fe/Mn values (17–18) than those (∼30) of augite and Mg-rich ferrosilite in the fine-grained replacement textures and other eucritic pyroxenes in NWA 2339. The few plagioclase grains associated with these Fe-rich pigeonite fragments contain high albite components (Ab17–31). Similar replacement textures are also present in a lithic clast consisting of pyroxene and Na-rich plagioclase (Ab20–25). In this lithic clast, high-Fe subcalcic augite was replaced by troilite, Mg-rich hedenbergite, silica, and minor ilmenite whereas Mg-rich pigeonite remains intact. Troilite also occurs as tiny inclusions in porous regions of plagioclase. Moreover, the porous regions of plagioclase are enriched in Si and depleted in Al, Ca, and Na, compared to relict plagioclase. These textures indicate that the formation of troilite-rich mineral assemblages is related to the reaction between FeSiO3 component in pyroxene and S-rich vapors; whereas, the formation of tiny troilite in porous regions of plagioclase is related to the reaction between Fe2+ in plagioclase and S-rich vapors. X-ray mapping results reveal that during sulfurization of pyroxene and plagioclase, lithophile elements Mn, Al, Ca, Na, and Mg were removed to various extents, very likely by the S-rich vapors. Based on our observations, the S-rich vapors could be dry S–O–P vapors, which most likely have been formed by volatilization of pre-existing S,P-bearing materials due to impact heating on the surface of asteroid 4 Vesta.

Mineralogical, IR-spectral and geochemical monitoring of hydrothermal alteration in a deformed and metamorphosed Jurassic VMS deposit at Arroyo Rojo, Tierra del Fuego, Argentina

Fil: Biel, C.. Universidad de Zaragoza; Espana. Productos Minerales para la Industria S.A.; Espana

Microstructural evolution during experimental albitization of K-rich alkali feldspar

Crystals of K-feldspar (C2/m), in contact with highly concentrated aqueous NaCl solutions at 500°C and 200 MPa, are pseudomorphically replaced by high albite $$ (C\bar{1}) $$ as a result of an interface-coupled dissolution/reprecipitation process. The reaction occurs at an extremely sharp reaction front (<10 nm) and involves the complete breakdown of the initial framework structure. This results in the release of tetrahedrally incorporated elements such as Fe3+ and Ti4+ and a significant increase in Si/Al disorder across the reaction interface. The evolving microstructure is controlled by crystallographic relations between the phases. This leads to highly anisotropic, sawtooth-shaped intergrowths of albite and initial K-feldspar, resulting in the least structural misfit between the two framework structures. As a result, the newly formed interfaces appear to be semicoherent, and cracks across the reaction fronts even indicate elastic strain. The reaction produces 2 distinctive albite types (albite-1 and albite-2). Both are polycrystalline, with albite-2 showing significantly larger subgrain sizes. This indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product. The reaction also produces a highly porous rim. However, the porosity is not evenly distributed resulting in a porous albite-1 and a non-porous albite-2 that mostly surrounds large, euhedral pores. Despite the substantial volume fraction of porosity in albite-1, no significant 3D interconnectivity could be detected, making the presence of a pervasive porosity unlikely. However, the result of coarsening is the continuous modification of the 3D porosity distribution. This could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved.

Transport properties of high albite crystals, near-endmember feldspar and pyroxene glasses, and their melts to high temperature

Thermal diffusivity (D) was measured using laser-flash analysis (LFA) from oriented single-crystal albite and glasses near LiAlSi3O8, NaAlSi3O8, CaAl2Si2O8, LiAlSi2O6 and CaMgSi2O6 compositions. Viscosity measurements of the supercooled liquids, over 2.6 × 108 to 8.9 × 1012 Pa s, confirm strongly non-Arrhenian behavior for CaAl2Si2O8, and CaMgSi2O6, and near-Arrhenian behavior for the others. As T increases, D glass decreases, approaching a constant near 1,000 K. Upon crossing the glass transition, D decreases rapidly. For feldspars, D for the melt is ~15% below D of the bulk crystal, whereas for pyroxenes, this difference is ~40%. Thermal conductivity (k lat = ρC P D) of crystals decreases with increasing T, but k lat of glasses increases with T because heat capacity (C P ) increases with T more strongly than density (ρ) and D decrease. For feldspars, k lat for the melt is ~10% below that of the bulk crystal or glass, whereas this decrease for pyroxene is ~50%. Therefore, melting substantially impedes heat transport, providing positive thermal feedback that could promote further melting.

Microstructure Defects in Ultrahigh-pressure Metamorphic Rock: Evidence from TEM and FTIR Studies

Defect microstructures of minerals are a potential indicator of extremely rapid and episodic exhumation of ultrahigh-pressure (UHP) metamorphic rock. The microstructure defects in the minerals from UHP jadeite quartzite at Shuanghe, Dabie Mountains, China, have been investigated using transmission electron microscope (TEM) and Fourier transform infrared spectroscopy (FTIR). TEM observations indicate that three polymorphs, namely, submicron-scale nature monalbite (MA, C2/ m) (about 0.8 μm), high albite (HA, CĪ), and low albite (LA, CĪ) occur in jadeite inclusions from jadeite quartzite. The existence of monalbite (MA) implies that high-temperature metamorphism (>930 °C) takes place during exhumation and rapid cooling, during retrogression. The occurrence of nanoscale coesite (about 80 nm) and halite daughter minerals in quartz inclusions provide evidence for the transformation of the original coesite to quartz and the existence of high-salty fluids at peak metamorphic conditions. Structural water (OH/H 2O) in nominally anhydrous minerals (NAMs) exists in the structures of these minerals as defects. The FTIR results show that the average contents of structural water in jadeite, garnet, rutile, and quartz are 1000 × 10 −6, (900–1600) × 10 −6, > 2000 × 10 −6, and < 4 × 10 −6, respectively, and the estimated whole-rock water content is (490–600) × 10 −6. The results reveal that the water in crust or protolith can transport into the earth's depth through NAMs during HP-UHP metamorphism. These unique defect microstructures can be rationalized by a high strain rate at local weakening and deep faulting of continental collision orogens.

An unusual radiation dose dependent EPR line at g{sub eff} = 2.54 in feldspars: possible evidence of Fe{sup 3+}O{sup 2-} {r_reversible} Fe{sup 2+}O{sup -} and exchange coupled Fe{sup 3+}-Fe{sup 2+}-nO{sup -}

We report electron paramagnetic resonance (EPR) results on natural feldspar grains extracted from sediment samples of three widely different source regions. The XRD analysis indicated that the samples had albite, microcline and Ca/Ba-orthoclase as the major constituents. The EPR spectrum of all the samples exhibited an intense line around g{sub eff} = 4.3. This is characteristic of Fe{sup 3+} with a zero field splitting that is significantly larger than the microwave quantum. More interesting was the presence of a strong EPR signal in the region of g{sub eff} = 2.54-2.7. On irradiation with gamma rays the position of the line shifted to higher magnetic field. The possible origin of this line and its unusual behavior with dose is explained as being due to the interaction of a hopping 'hole' on oxygen with iron centers. The possibilities considered include (1) the valence fluctuation of an Fe{sup 3+} center at a tetrahedral site (2) oscillation of FeO{sub 4}{sup -} between two resonant forms, Fe{sup 2+}O{sup -} and Fe{sup 3+}O{sup 2-}, and (3) exchange coupling between Fe{sup 3+}, Fe{sup 2+} and O{sup -}. The concentration of the latter is dose dependent and, consequently, it results in the observed dose dependent line shift.

The albite fusion curve re-examined: New experiments and the high-pressure density and compressibility of high albite and NaAlSi3O8 liquid

Experimental brackets on the melting temperature of high albite (NaAlSi3O8) were determined at 2.33 ± 0.03 GPa (1360-1370 °C) and 2.79 ± 0.03 GPa (1370-1389 °C) in a piston-cylinder apparatus. All run products that quenched to a glass were analyzed by Fourier-transform infrared spectroscopy and found to contain ≤500 ppm H2O. In addition, new X-ray diffraction experiments on fully disordered albite are reported to 7.6 GPa; the Þ tted results lead to a zero-pressure bulk modulus (K0) of 56.4 ± 0.7 and a pressure derivative (K0) of 3.9 ± 0.3 in a third-order Birch-Murnaghan equation of state. Revised values for the enthalpy and entropy of fusion of high albite at one bar and 1100 °C (∆HTf = 64.5 ± 2.1 kJ/mol and ∆STf = 47.0 J/(mol·K)) are recommended on the basis of improved heat capacity equations for NaAlSi3O8 glass and liquid. On the basis of these new results on the fusion curve and thermody- namic data for high albite, the pressure dependence of the NaAlSi3O8 liquid compressibility (K0) is constrained to be 10.8 ± 1.5 in a third-order Birch-Murnaghan equation of state. The uncertainty in K0 of ±1.5 contributes an error to melt density at 3 GPa (2.543 ± 0.010 g/cm 3 at 1500 °C) of ±0.4%.

Petrology and mineralogy of granulite-facies mafic xenoliths (Sardinia, Italy): Evidence for KCl metasomatism in the lower crust

Here new mineralogical data is presented on the occurrence of K-feldspar in granulite-facies metagabbronorite xenoliths found in recent alkaline lavas from Western Sardinia, Italy. The xenoliths originated from the underplating of variably evolved subduction-related basaltic liquids, which underwent cooling and recrystallisation in the deep crust ( T = 850–900 °C, P = 0.8–1.0 GPa). They consist of orthopyroxene + clinopyroxene + plagioclase porphyroclasts (An = 50–66 mol%) in a granoblastic, recrystallised, quartz-free matrix composed of pyroxene + plagioclase (An = 56–72 mol%) + Fe–Ti oxides ± K-feldspar ± biotite ± fluorapatite ± Ti-biotite. Texturally, the K-feldspar occurs in a variety of different modes. These include: (1) rods, blebs, and irregular patches in a random scattering of plagioclase grains in the form of antiperthite; (2) micro-veins along plagioclase–plagioclase and plagioclase–pyroxene grain rims; (3) myrmekite-like intergrowths with Ca-rich plagioclase along plagioclase–plagioclase grain boundaries; and (4) discrete anhedral grains (sometimes microperthitic). The composition of each type of K-feldspar is characterized by relatively high albite contents (16–33 mol%). An increasing anorthite content in the plagioclase towards the contact with the K-feldspar micro-vein and myrmekite-like intergrowths into the K-feldspar along the plagioclase–K-feldspar grain boundary are also observed. Small amounts of biotite (TiO 2 = 4.7–6.5 wt.%; F = 0.24–1.19 wt.%; Cl = 0.04–0.20 wt.%) in textural equilibrium with the granulite-facies assemblage is present in both K-feldspar-bearing and K-feldspar-free xenoliths. These K-feldspar textures suggest a likely metasomatic origin due to solid-state infiltration of KCl-rich fluids/melts. The presence of such fluids is supported by the fluorapatite in these xenoliths, which is enriched in Cl (Cl = 6–50% of the total F + Cl + OH). These lines of evidence suggest that formation of K-feldspar in the mafic xenoliths reflects metasomatic processes, requiring an external K-rich fluid source, which operated in the lower crust during and after in-situ high- T recrystallisation of relatively dry rocks.

THE ORIGIN OF THE KAHNUJ OPHIOLITIC COMPLEX, SE OF IRAN: CONSTRAINTS FROM WHOLE ROCK AND MINERAL CHEMISTRY OF THE BANDE-ZEYARAT GABBROIC COMPLEX

The Upper Jurassic-Lower Cretaceous Kahnuj ophiolite complex, a part of Jazmurian ophiolitic belt, is situated in the southeastern part of Iran and represents a remnant of the Mesozoic Neotethyan Ocean. The oceanic lithospheric section of the Kahnuj ophiolite comprises from bottom to top: a plutonic unit (Bande-Zeyarat Complex); a diabase sheeted dyke unit; and a volcanic unit (Dare-Anar Complex). Although it is extensively faulted and fractured, the internal relationships have been preserved. The Bande-Zeyarat gabbroic complex consists of layered gabbroic cumulates and isotropic gabbros. The cumulate gabbro shows adcumulate, mesocumulate and orthocumulate textures and is represented exclusively by olivine gabbro, gabbro, melagabbro, leucogabbro, anorthosite, with minor troctolite, gabbronorite, pegmatoid and tectonic rafts of dunite. The cumulate gabbro is characterized by well-developed magmatic layering, defined by variation in mode /or size of plagioclase and mafic minerals, and by a tectonic foliation which is marked by preferred flattening of all mineral phases. These two structures for most parts are sub-parallel to each other. Rhythmic layering is also present. The isotropic gabbro consists of hypidiomorphic granular uralitized pyroxene gabbro and hornblende gabbro with minor ilmenite-rich gabbro, olivine gabbro, diorite and trondhjemite. They are the most fractionated part of the gabbros, plagioclase is more albite rich, clinopyroxene and olivine are more iron rich. The layered gabbro shows strong positive Eu anomalies, attributable to high modal abundances of plagioclase, whereas the isotropic gabbro with hornblende predominant over plagioclase does not have any Eu anomalies. The isotropic gabbros are crystallized from influxes of slightly different less magnesiferous parental melts. They are related to the cumulate gabbro by crystal fractionation and represent late differentiation products which formed as the rate of the magma influx slowed and finally ceased. Mineral assemblages, mineral chemistry (i.e., Fo67.8-78.54, low Mg# < 84.16 and high Si relative to tetrahedral Al in clinopyroxenes), crystallization order (olivine-plagioclase-clinopyroxene) and whole rock chemistry suggest that the Bande-Zeyarat gabbroic complex has been produced by low to moderate pressure crystal fractionation from a tholeiitic basaltic magma similar to MORB. These data indicate that the Kahnuj ophiolite complex may represent an oceanic basin developed in the Mesozoic between the Lut block of Central Iran and the Bajgan-Dur-Kan microcontinents.

Occurrence of “monalbite” in nature: a TEM study

Natural “monalbite” (MA) has been observed on a submicron-scale in jadeite along with high albite (HA) and low albite (LA) in jadeite quartzite in the Dabie ultrahigh-pressure (UHP) metamorphic terrane, China. Transmission electron microscope (TEM) observation of inclusions in jadeite crystals has revealed mineral phases with C2/ m and C1̄ structures. The cell parameters of the C2/ m crystal structure correspond to those of MA, whereas the cell parameters of C1̄ structure are identical to those of HA and LA. The existence of the C2/ m structure shows that the jadeite underwent partial change to MA on a submicron-scale during retrograde metamorphism. Albite transformation twinning of HA suggests the transformation of MA into HA. MA occurrence provides powerful evidence of high-temperature metamorphism during exhumation, probably above 930 °C. The preservation of MA may be due to the armouring by the jadeite and implies a very rapid cooling (quenching) during retrogression.