Minimum Formation Temperature Research Articles

P–T Evolution of the Cyclades Blueschist Unit: Constraints on the Evolution of a Nascent Subduction System From Zr‐In‐Rutile (ZiR) and Quartz‐In‐Garnet (QuiG) Thermobarometry

AbstractNew results that employ Zr‐in‐rutile thermometry (ZiR) and quartz‐inclusion‐in‐garnet (QuiG) barometry constrain the P–T conditions of garnet formation in blueschists and eclogites from the island of Syros, Greece. QuiG barometry reveals that garnet from different regions across the island formed at pressures ranging from 1.1 to 1.8 GPa and ZiR thermometry on rutile inclusions in garnet constrains the minimum temperature of garnet formation to have been 475–550°C. Most importantly, there is no systematic difference in the conditions of garnet formation from different regions across the island and these results are nearly identical to those obtained from the islands of Sifnos and Ios, Greece. A model is proposed whereby the rocks from all three islands were initially metamorphosed along a relatively shallow geotherm of around 11°C/km to a depth of around 45 km and were then subjected to metamorphism along a geotherm of around 7–8°C/km, which could have been caused by either an increase in the dip of the subduction zone or an increase in the rate of subduction. Garnet formed along this steeper geotherm was accompanied by the release of significant H2O from the breakdown of chlorite over a duration of 1 Ma or less based on thermal and diffusion modeling. It is concluded that rocks from Syros, Sifnos and Ios all followed a similar, roughly counter‐clockwise prograde P–T path and that the present outcrop configuration is largely due to a complex exhumation history.

Pressure–temperature evolution of the basement and cover sequences on Ios, Greece: Evidence for subduction of the Hercynian basement

AbstractHigh‐pressure rocks from the island of Ios in the Greek Cyclades were examined to resolve the P–T conditions reached during subduction of the two distinct lithotectonic units that are separated by the South Cycladic Shear Zone (SCSZ)—the footwall complex composed of Hercynian basement gneisses, schists and amphibolites, and the hangingwall complex composed of blueschists and eclogites. A combination of elastic tensor quartz inclusion in garnet (QuiG) barometry and Zr‐in‐rutile (ZiR) trace element thermometry was used to constrain minimum garnet growth conditions. Garnet from the hangingwall (blueschist) unit record formation pressures that range from 1.5 to 1.9 GPa and garnet from the footwall basement complex record garnet formation pressures of 1.65–2.05 GPa. ZiR thermometry on rutile inclusions within garnet establishes the minimum temperature for garnet formation to be ~480–500°C. That is, there is no evidence in the QuiG and ZiR results that the rocks of the blueschist hangingwall and basement experienced different metamorphic histories during subduction. This is the first reported observation of blueschist facies metamorphism in the Hercynian basement complex. A model is proposed in which initial subduction occurred along a relatively shallow P–T trajectory of ~11°C/km and then transitioned to a steeper, nearly isothermal trajectory at a depth of ~45 km reaching similar peak metamorphic conditions of ~500–525°C at 2.0 GPa for all samples. Such a change in the subduction path could be accomplished by either an increase in the rate of subduction or an increase in the angle of the subduction zone. The present juxtaposition of samples with contrasting mineral assemblages and garnet growth histories is interpreted to have arisen from differences in bulk compositions and variations in the preservation of high‐pressure prograde mineral assemblages during exhumation. The existence of similar P–T conditions and prograde paths in the two units does not require that the rocks were all metamorphosed at the same time and that the SCSZ experienced little movement. Rather, it is suggested that the two units experienced prograde and peak metamorphism at different times and were subsequently juxtaposed along the SCSZ.

Hydrothermal silicification and hypogene dissolution of an exhumed Neoproterozoic carbonate sequence in Brazil: Insights from fluid inclusion microthermometry and silicon‐oxygen isotopes

AbstractHypogene dissolution‐precipitation processes strongly affect the petrophysical properties of carbonate rocks and fluid migration pathways in sedimentary basins. In many deep carbonate reservoirs, hypogene cavernous voids are often associated with silicified horizons. The diagenesis of silica in carbonate sequences is still a poorly‐investigated research topic. Studies exploring the complexity of silica dissolution‐precipitation patterns in hypogene cave analogues are therefore fundamental to unravel the diagenetic and speleogenetic processes that may affect this kind of reservoir. In this work, we investigated an exhumed and silicified Neoproterozoic carbonate sequence in Brazil hosting a 1.4 km‐long cave. Quartz mineralization and silicified textures were analyzed with a multidisciplinary approach combining petrography, fluid inclusion microthermometry, silicon‐oxygen stable isotope analyses and U‐Th‐Pb dating of monazite crystals. We found that an early silicification event caused the replacement of the dolostone layers with micro‐crystalline quartz forming chert nodules. This event was likely associated with mixing fluids (ancient Neoproterozoic seawater and hydrothermal solutions sourced from the underlying Mesoproterozoic basement) at relatively low temperatures (ca. 50–100°C) and shallow depth. After the tectonic deformation produced by the Brasiliano orogeny, silica dissolution was promoted by high temperature and alkaline hydrothermal solutions rising from the quartzite basement along deep‐rooted structures. Hypogene hydrothermal alteration promoted the dissolution of the cherty layers and the precipitation of chalcedony and megaquartz. Homogenization temperatures from primary fluid inclusions in megaquartz cement indicate minimum formation temperatures of 165–210°C. Similar temperature estimates (110–200°C) were obtained from the δ30Si and δ18O isotope systematics of quartz precipitated from hydrothermal solutions. The dissolved salts in the fluid inclusions were evaluated as NaCl + CaCl2 from microthermometric data combined with cryogenic Raman spectroscopy, corresponding to salinity ranging between 17 and 25 wt.%. No reliable age constraints for hydrothermal silica dissolution‐precipitation phases were obtained from monazite U‐Th‐Pb dating. However, our results, interpreted in the regional context of the São Francisco Craton, suggest that the Cambrian tectono‐thermal events could have been amongst the possible drivers for this hypogene process in the basin.

Petrogenesis of zoned and unzoned mafic pegmatites: An insight from the Palaeoproterozoic mafic-ultramafic Hamn intrusion, Northern Norway

Mafic pegmatites have been reported from various geological environments, including ophiolites, layered magmatic intrusions, and volcanic arcs, but their petrogenesis stayed poorly constrained. This study brings new mineralogical and geochemical data obtained from unzoned and zoned gabbroic pegmatites hosted by the 1.8 Ga mafic-ultramafic Hamn intrusion, Northern Norway, with an aim to improve our understanding of the primary magmatic physicochemical factors that control the development of pegmatitic textures in mafic rocks. The unzoned mafic pegmatites in the Hamn intrusion are hosted in gabbronorite and gabbro. The pegmatites differ macroscopically from the gabbronorite only by grain size and the color of feldspars. The bulk chemical compositions, including REE concentrations and rock-forming mineral assemblages of both rocks, are identical. The mineral composition of the pegmatite and host gabbro overlap. However, the pegmatite experienced epidotization and scapolitization, suggesting that H 2 O- and chlorine were essential in the formation. Furthermore, the pyroxene of the pegmatite shows a more distinct negative Eu anomaly than the pyroxene of the host gabbronorite. Amphibole dyklets associated with the unzoned pegmatite pockets consist of Cl-rich pargasite and Cl-scapolite, indicating that the fluid pressure during crystallization of the unzoned pegmatites exceeded the confining pressure and resulted in the fracturing of host rocks and expulsion of a Cl- and H 2 O-rich fluid and residual melt that subsequently formed amphibole veins. The zoned pegmatites of the mafic-ultramafic Hamn intrusion are internally differentiated in terms of grain size, texture, and mineral composition. A characteristic comb-like diopside layering shows a change from numerous small to fewer larger grains from the rim towards the core of the pegmatite pocket. This textural change suggests that the pegmatite-forming melt experienced a transition from a high nucleation rate (N) vs. growth rate (G) ratio to a low N/G ratio. A decreasing degree of undercooling with continuous crystallization from the rim to the core of the pockets can explain this transition. Apart from the comb-like layering, the bifurcating texture of some of the diopside grains is another evidence that the pegmatite-forming melt experienced undercooling. The pegmatites could have formed from a remobilized intercumulus or fractionated melt that was emplaced as residual melt into the colder host rock. Fast heat diffusion towards the host rock could have caused undercooling of the pegmatite-forming melt, which led to the formation of the comb-like and partly extremely coarse-grained texture. In contrast to the unzoned pegmatites, the zoned pegmatites lack evidence of significant involvement of chlorine- and H 2 O. Instead, the fluid inclusion study revealed that the pegmatite-forming melt was enriched in CO 2 . Microthermometry of the CO 2 -bearing inclusions indicates a minimum formation pressure of 647 to 734 MPa, and the titanium-in-quartz geothermometer yields a minimum formation temperature of 753 ± 34 °C for the quartz segregation. • The mafic-ultramafic Hamn intrusion hosts unzoned and zoned gabbroic pegmatites. • The unzoned pegmatites crystallized from a H 2 O and Cl rich mafic melt. • Change in degree of undercooling led to a comb-like texture of the zoned pegmatites. • The zoned pegmatites crystallized from a dry but CO2-enriched mafic melt.

Fluid Evolution at the Batu Hijau Porphyry Cu-Au Deposit, Indonesia: Hypogene Sulfide Precipitation from a Single-Phase Aqueous Magmatic Fluid During Chlorite–White-Mica Alteration

Abstract Mineralization at the Cu-Au porphyry deposit of Batu Hijau, Indonesia, was previously reported to be associated mainly within stockwork quartz veins accompanied by pervasive biotite-magnetite alteration. We use cathodoluminescence imaging of vein textures followed by microthermometry and laser ablation-inductively coupled plasma-mass spectrometry microanalysis of fluid inclusions to decipher the spatial-temporal evolution of the hydrothermal system. Our results indicate that sulfide precipitation largely postdated the main stockwork quartz veining. Chalcopyrite and bornite were found in three textural positions: (1) within conspicuous quartzpoor veinlets (“paint veins”) that postdate quartz stockwork veins and that also appear to account for the bulk of seemingly disseminated sulfides, (2) as centerlines in B-type veins, and (3) as interstitial grains in A-type veins. In all three textural positions, the sulfides occur together with a volumetrically minor, dull-luminescent quartz generation after local dissolution of the granular quartz dominating the stockwork veins. All three positions are associated with chlorite ± variable phengitic white mica with 3–6 wt % FeO + MgO. In the barren core of the deposit, quartz veins host, almost exclusively, fluid inclusions of intermediate density (~0.6 g/cm3) and near-constant salinity of ~3.7 wt % NaCl equiv, representing the input magmatic fluid. This fluid subsequently separated into a highly saline brine1 and low-density vapor during quartz vein formation in the mineralized parts of the deposit, but we found no textural or fluid-chemical evidence that brine + vapor already reached saturation in sulfides. Within the studied samples, Cu-Fe sulfides are invariably associated with the dull-luminescent quartz hosting only low-salinity (~2–8 wt % NaCl equiv) aqueous fluid inclusions with a density of ~0.8 g/cm3 and minimum formation temperatures of 300°–360°C, in agreement with Ti-inquartz and chlorite thermometry indicating trapping conditions only slightly above the boiling pressure of these liquids. On average, this mineralizing aqueous fluid is compositionally similar to the initial magmatic fluid, suggesting a common source, but some inclusion assemblages deviate to significantly lower or higher salinities (0.5–25 wt % NaCl equiv). We propose a formation model for the Batu Hijau porphyry Cu-Au deposit in which mostly barren quartz veins formed at high temperature (>400°C) in the central part of the system, while sulfide mineralization commences to form peripheral to this zone. The economic ore shell was growing inward and downward as a zone of active sulfide precipitation at 300°–360°C shifted in response to progressive retraction of isotherms, while barren quartz vein formation continued in the system’s core at higher temperature. The aqueous ore-forming liquid is interpreted to have formed by rehomogenization of magmatic brine and vapor that previously formed by phase separation and later became miscible again after cooling over a narrow temperature interval. Vapor condensation into the highly saline brine phase at low pressure and subcritical temperature led to partial dissolution of earlier formed quartz veins and created secondary porosity for subsequent sulfide deposition. We propose that Cu-Fe sulfide precipitation by the low-temperature aqueous fluid was driven by the rehomogenization of S-rich vapor with Cu-rich brine originating from the same input fluid. The selective dissolution of earlier quartz veins in an inward- and downward-growing ore shell explains the positive correlation of ore grades with the density of earlier quartz veining in the ore shell, even though copper mineralization postdates quartz vein formation at any location in the deposit. Late-stage sulfide deposition in paint veins has been noted at other porphyry Cu-(Au-Mo) deposits worldwide, indicating that the proposed fluid evolution model may be applicable to many other porphyry systems.

Observations on the formation and textural properties of “tapiocas”, a traditional cassava-based food from the Northeast of Brazil

“Tapioca” from northeastern Brazil, a starchy, sintered pancake-like product prepared from cassava that is a staple food for much of the regional population. The objective of this work was to propose a specification of tapiocas based on the effects of the water content of cassava starch and the preparation time and temperature of the tapiocas on their physical and structural characteristics. Tapiocas were prepared by sintering defined amounts of cassava gum with a variation in water content between 15% w/w and 45% w/w on a cooking surface that was set at a temperature between 100 °C and 300 °C, for preparation times of 120 s and 210 s. Post-preparation, the tapioca samples were qualitatively evaluated for structure and cohesivity. Based on these observations, temperature-water content diagrams that delimited the regions of tapioca formation were elaborated. Our results demonstrate that tapiocas are thin (2–6 mm) starchy slabs characterized by a continuous gelatinous and translucent core that is formed by starch that is fully or near fully gelatinized. Both the top and bottom crust of the tapiocas are formed by starch particles that have retained their granularity and are thus not or only partially gelatinized. The minimum starch water content for tapioca formation turns out to be 37% w/w for sample thicknesses between 2.5 and 5 mm and at cooking temperatures of 250 °C or higher. The minimum tapioca formation temperature decreases somewhat with increasing water content. However, for the 5 mm thick samples, tapiocas could not be formed at temperatures below 200 °C even at higher water contents. Tapioca texture parameters including hardness (5.4–49 N), springiness index (0.54–0.92), cohesiveness (0.47–0.81), resilience (0.15–0.56) and cutting force (4.1–27 N) were mainly influenced by cooking time and to a lesser degree by the cooking temperature, provided that the temperature was above a minimum threshold. Our results are of importance both for small producers and chefs as well as larger industrial producers, as they allow to rationally develop and optimize tapioca recipes.

COMPREHENSIVE INVESTIGATION OF PHASE FORMATION MECHANISM AND PHYSICO-MECHANICAL PROPERTIES OF Ca-Mg-SILICATE

This study aimed to investigate extensively the full phase formation mechanism from the lowest temperature to form the phases to the optimum temperature to crystallize akermanite. The effects of various milling speeds and sintering temperatures on physico-mechanical properties of akermanite prepared using high-energy planetary milling method were also investigated. The minimum formation temperature of akermanite phase (above 800°C) was determined by X-Ray diffraction (XRD) and differential thermal analysis. XRD analysis revealed akermanite had formed through gradual phase development with the increase in temperature. Below 700C, akermanite was structurally unstable while multiple transient compounds (low clinoenstatite, wollastonite, monticellite, and diopside) coexisted, as indicated by low peak intensities. Single phase akermanite was obtained by heat-treating at 1100C. Physical studies suggested the densest akermanite ceramic feature, with tensile strength range of 25.26 ± 1.41 MPa32.10 ± 2.13 MPa and Vickers microhardness range of 1.39 ± 0.04 GPa4.94 ± 0.26 GPa could be obtained at 1250°C.

Reconstruction of Hydrothermal Processes in the Cyprus Type Fe-Cu-Zn Deposits of the Italian Northern Apennines: Results of Combined Fluid Inclusion Microthermometry, SEM-CL Imaging and Trace Element Analyses by LA-ICP-MS

Quartz from the stockwork zone of various Cyprus type volcanogenic massive sulfide deposits (Boccassuolo, Reppia, Campegli, Bargone and Vigonzano) from the unmetamorphosed, Jurassic Northern Apennine ophiolites was studied in order to provide details on the submarine hydrothermal conditions and the characteristics for ore formation. Our detailed SEM-CL investigation of quartz contributed to a robust characterization and interpretation of primary fluid inclusions and microthermometry data. SEM-CL imaging was also useful for reconstructing the consecutive steps of quartz precipitation. The determination of trace element contents according to growth zoning in quartz by LA-ICP-MS constrained the compositional variations of parent fluids during the hydrothermal activity. A continuously cooling fluid regime characterized each studied volcanogenic massive sulfide (VMS) occurrence although the minimum formation temperatures were different (Bargone: 110–270 °C; Boccassuolo: 60–360 °C; Campegli: 110–225 °C; Reppia: 50–205 °C; Vigonzano: 260–330 °C), the range of temperature most probably depends on the original position of sampling in relation to the centers of the hydrothermal systems. Compositional changes are reflected by variations in the methane content (0.13–0.33 mol/kg) and salinity (2.6–9.3 NaCl equiv. wt. %) in the fluid inclusions of quartz and calcite as well as a changeable Al content (11–1526 ppm) in quartz. This study demonstrates that the combined use of SEM-CL imaging and LA-ICP-MS analyses, coupled with fluid inclusion microthermometry, can constrain the different fluid conditions of ore forming and the barren stages of evolving submarine hydrothermal systems.

Parametric Study of Mechanical Stresses within Cement Sheath in Geothermal Wells

A cement sheath, placed between the casing and the formation, is an important barrier that establishes a hydraulic seal and provides zonal isolation, preventing fluid communication in the wellbore. In geothermal wells, stress induced by high bottom-hole temperature is one of the major factors triggering failure in the cement sheath. However, the influence of heat flow direction and differential temperature, relative to other design and operating factors, is not well understood. The objective of this paper is to investigate these two important factors.In this study, an analytically verified 2D numerical model was used to perform a parametric study of mechanical stress within a cement sheath. Loading conditions applied to the model included maximum and minimum horizontal formation stresses, wellbore pressures, and temperature differences. Sensitivity analysis was conducted to understand the effect of cement properties, temperature difference between the casing and the formation, and casing pressure on stresses in the cement sheath. Sensitivity response curves demonstrated the relative influence of investigated parameters on radial and hoop stresses. Results showed that heat transfer from the formation to the casing (Ti < Tf) is more detrimental to cement integrity than the opposite scenario (Ti> Tf). When heat flows away from the wellbore, hoop stress in cement is mainly dependent on temperature difference, while radial stress is primarily dependent on temperature difference as well as wellbore pressure. When heat flows toward the wellbore, radial stress in cement is primarily a function of temperature difference and wellbore pressure. Hoop stress, on the other hand, is mainly dependent on temperature difference and the cement’s thermal expansion coefficient.

Quantifying production of hot firebrands using a fire-resistant fabric

Identifying the number of firebrands generated during wildfires is an important aspect of understanding their propagation. A key challenge in quantifying the number of firebrands released is to distinguish those that are ‘hot’ and could lead to further fire spread from the total number released. Recently, a fire-resistant fabric was used to quantify the number of ‘hot’ firebrands released from different species of trees (based on char marks). However, information regarding the temperatures of the firebrands leaving the char marks was not reported. In this paper, we demonstrate a methodology for characterising the charring behaviour of fire-resistant fabrics and illustrate how the fabric can be used for firebrand generation studies. The results established a minimum temperature (300°C) for char mark formation. The sensitivities of charring to temperature and time of contact between the fabric and heater are reported. A first-order analysis estimated the char mark area to be an exponential function of the temperature, power input and time of exposure. Illustrating the usefulness of the approach, the fire-resistant fabric was deployed to study hot firebrand production rates for trees treated with and without a fire retardant. The number of hot firebrands produced was lower for trees coated with fire retardant.

Crystallographic orientation of ilmenite inclusions in amphibole – an electron backscatter diffraction study

AbstractOrientated ilmenite inclusions have been discovered in amphibole of hornblendite from the Zhujiapu area, Dabie ultra-high-pressure (UHP) metamorphic terrane, China. In order to characterize the crystallographic orientation relationships between ilmenite inclusions and amphibole host and reconstruct the mechanism of their formation, we present an electron backscatter diffraction (EBSD) analysis combined with energy dispersive spectroscopy (EDS) analysis and electron microprobe analysis (EPMA) for ilmenite inclusions and amphibole host. The inclusions can be subdivided into four groups: (1) 60.2% of ilmenites have the crystallographic orientation {0001}Ilm// {100}Amp, (101̅0)Ilm// {010}Amp, [112̅0]Ilm// &lt;001&gt; Ampand [112̅0]Ilm// &lt;012 &gt; Amp. (2) 16.5% of ilmenites have &lt;0001&gt; Ilm// &lt;001&gt; Amp, (101̅0)Ilm// {010}Amp, (112̅0)Ilm// {100}Ampand [3̅031]Ilm// &lt;012&gt; Amp. (3) 13.8% of ilmenites have &lt;0001&gt; Ilm// &lt;012&gt; Amp, (112̅0)Ilm// {100}Ampand [3̅031]Ilm// &lt;001&gt; Amp. (4) 9.5% of ilmenites have &lt;0001&gt; Ilm// [1̅12]Amp, (101̅0)Ilm// {201}Amp, [112̅0]Ilm// [1̅12]Ampand[1121¯]Ilm${[11\overline {21} ]_{Ilm}}$// &lt;010&gt; Amp. By comparing the lattice relationship between ilmenite inclusions and amphibole hosts, it is shown that the frequency of the ilmenite inclusions in different groups is related to the lattice coherency and oxygen packing. Group-1 of the ilmenite inclusions was most likely be formed via a solid-state exsolution process by cooling of the hornblendite after the intrusion was emplaced. The other three groups of ilmenite inclusions were probably formed via reduction reaction in an open system. The formation temperature of the ilmenite inclusions is estimated by using the TiO2solubility geothermeter in amphibole. The minimum formation temperature of the ilmenite inclusions is about 1025 °C, and the maximum formation temperature of the ilmenite inclusions is about 1126 °C.

Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/SiO2 core–shell structure particles during fluidised bed chemical vapour deposition

In the synthesis of ferromagnetic/SiO2 core–shell structures, the minimum formation conditions and evolution mechanism are worth investigating. In the present study, to determine the minimum formation temperature of an integrated Fe–Si/SiO2 core–shell structure during chemical vapour deposition in a fluidised bed, the effects of deposition temperature on the structural and magnetic performances of SiO2 insulation coatings on Fe–Si particles were investigated. Thermodynamic calculations and differential scanning calorimetry were used to understand the thermal decomposition of C8H20O4Si. The results of the theoretical and structural studies showed that the minimum deposition temperature of the amorphous SiO2 insulation coating on the Fe–Si particle surface was ~880 K and that the Fe–Si/SiO2 composite structure started to convert into an integrated Fe–Si/SiO2 core–shell structure after the deposition temperature was raised above 920 K. The increase in the thickness of the SiO2 insulation layer due to the increased deposition temperature was studied using X-ray diffraction and scanning electron microscope analyses. The results of X-ray photoelectron spectroscopy showed that four and five types of electronic structures existed in the SiO2 insulation shell for silicon and oxygen, respectively, and that only 32.74 at.% of the oxygen from the Si(OSi)3(OH) group interacted with the Fe–Si alloy surface. The results of the performance test indicated that the integrated Fe–Si/SiO2 core–shell structure led to a substantial enhancement in the electrical resistivity of the particles and reduction in their saturation magnetisation, but hardly affected the coercive force.

The Effect of SrCrO4 Impurity Phase in (La0.75Sr0.25)0.95CrxFe1-XO3-Δ (LSCrF) Nanoceramic Powder Series As Catalyst during the Propane Dehydrogenation

Lanthanum strontium chromite based materials are promising candidate for use as electrode components in Intermediate Temperature Proton Conductive Fuel Cell (IT-PCFC)[1]. In this work, (La0.75Sr0.25)0.95CrxFe1-xO3-δ(LSCrF) with x=0.3, 0.4, 0.5, 0.6 and 0.7 perovskite nano-ceramic powder series considered as anode material for IT-PCFCs [2] were focused on due to its structural, physical & chemical and also electrochemical properties corresponding with Cr amount, such as catalytic activities under the operation conditions. The nano-sized LSCrF perovskite powders were systematically synthesized by using sol-gel method[3], to understand whether the increment of Cr amount have any positive or negative effect in terms of catalytic performance, impurity, particle size and surface area. In this regard, all powders were annealed at the different temperatures changing from 500oC to 700oC in order to determine the minimum formation temperature of the powders having different amounts of Cr and Fe in order to enhance smaller particle size with higher surface area. LSCrF nano-powders were structurally characterized by means of X-ray Powder Diffraction (XRD) with Reitveld refinement by using GSAS software [4]. Cr rich samples shows more SrCrO4 impurity phase and bigger crystallite size than Fe-rich samples which leads to poor catalytic performance in the propane dehydrogenation process. Ex-situ X-ray Absorption Spectroscopy study was also performed for Fe (7112 eV) and Cr (5989 eV) K-edge in the fluorescence mode by using a 4-elements Vortex detector. When we looked at the XANES region of both Fe and Cr K edge XAS data to understand the electronic structure of Fe and Cr in the LSCrF powders, Cr K edge XAS data shows a sharp pre-edge peak resulting from SrCrO4 impurity phase having tetrahedral geometry of Cr+6 with 4-fold Oxygen atoms, whereas Fe K-edge XAS data does not show any pre-edge feature due to the octahedral geometry of Fe+3 in LSCrF perovskite structure, as we expect. the C3H8 conversion of Fe rich LSCrF samples (x<0) having more SrCrO4 pre-edge intensity and higher surface area is found higher than Cr-rich samples (x>0). Especially, Fe rich LSCr0.4Fe0.6O3 sample having wt.frac.~13.14% SrCrO4 impurity phase considered as better catalyst shows much lower carbon balance than other samples unsurprisingly due to its higher surface area with smaller crystallite size and having more catalytically active SrCrO4 pre-edge intensity proved by XANES analysis. Morphological analysis of the LSCrF powders was done by Scanning Electron Microscopy (SEM/EDX). BET measurements were also performed to calculate their surface area.

Ultraprecise age and formation temperature of the Australasian tektites constrained by40Ar/39Ar analyses

AbstractThe Australasian tektites are quench melt glass ejecta particles distributed over the Asian, Australian, and Antarctic regions, the source crater of which is currently elusive. New40Ar/39Ar age data from four tektites: one each from Thailand, China, Vietnam, and Australia measured using three different instruments from two different laboratories and combined with published40Ar/39Ar data yield a weighted mean age of 788.1 ± 2.8 ka (±3.0 ka, including all sources of uncertainties) (P = 0.54). This age is five times more precise compared to previous results thanks, in part, to the multicollection capabilities of theARGUS VInoble gas mass spectrometer, which allows an improvement of almost fourfold on a single plateau age measurement. Diffusion experiments on tektites combined with synthetic age spectra and Monte Carlo diffusion models suggest that the minimum temperature of formation of the Thai tektite is between 2350 °C and 3950 °C, hence astrict minimumvalue of 2350 °C.

The Effect of SrCrO4 Impurity Phase in (La​0.75​Sr0.25​)​0.95​Cr​X​Fe​1-X​O​3-Δ (LSCrF) Nano-Ceramic Powder Series As Catalyst for the Propane Dehydrogenation

Lanthanum strontium chromite based materials are promising candidate for use as electrode components in Intermediate Temperature Proton Conductive Fuel Cell (IT-PCFC)[1]. In this work, (La0.75Sr0.25)0.95CrxFe1-xO3-δ (LSCrF) with x=0.3, 0.4, 0.5, 0.6 and 0.7 perovskite nano-ceramic powder series considered as anode material for IT-PCFCs[2] were focused on due to its structural, physical & chemical and also electrochemical properties corresponding with Cr amount, such as catalytic activities under the operation conditions. The nano-sized LSCrF perovskite powders were systematically synthesized by using sol-gel method[3], to figure out whether the increment of Cr amount have any positive or negative effect in terms of catalytic performance, impurity, particle size and surface area. In this regard, all powders were annealed at the different temperatures changing from 500°C to 700°C in order to determine the minimum formation temperature of the powders having different amounts of Cr and Fe in order to enhance smaller particle size with higher surface area. LSCrF nano-powders were structurally characterized by means of X-ray Powder Diffraction (XRD) with Reitveld refinement by using GSAS software[3]. Cr rich samples shows more SrCrO4 impurity phase and bigger crystallite size than Fe-rich samples which leads to poor catalytic performance in the propane dehydrogenation process. Ex-situ X-ray Absorption Spectroscopy study was also performed for Fe (7112eV) and Cr (5989eV) K-edge in the fluorescence mode by using a 4-elements Vortex detector. When we looked at the XANES region of both Fe and Cr K edge XAS data to understand the electronic structure of Fe and Cr in the LSCrF powders, Cr K edge XAS data shows a sharp pre-edge peak resulting from SrCrO4 impurity phase having tetrahedral geometry of Cr+6 with 4-fold Oxygen atoms, whereas Fe K-edge XAS data does not show any pre-edge feature due to the octahedral geometry of Fe+3 in LSCrF perovskite structure, as we expect. the C3H8 conversion of Fe rich LSCrF samples (x<0) having more SrCrO4 pre-edge intensity and higher surface area is found higher than Cr-rich samples(x>0). Especially, Fe rich LSCr0.4Fe0.6O3 sample having ~13.14wt.frac.%SrCrO4 impurity phase considered as better catalyst shows much lower carbon balance than other samples unsurprisingly due to its higher surface area with smaller crystallite size and having more catalytically active SrCrO4 pre-edge intensity proved by XANES analysis. Morphological analysis of the LSCrF powders was done by Scanning Electron Microscopy (SEM/EDX). BET measurements were also performed to calculate their surface area.

Effect of temperature and ceramic bonding on BC oxidation behavior in plasma-sprayed thermal barrier coatings

This study was conducted to investigate formation and growth of thermally grown oxide (TGO) and mixed oxide clusters of Chromia, Spinel, and Nickel oxide (CSN) under the influence of temperature and the absence of top coat (TC). For this purpose, 21 plasma-sprayed thermal barrier coating (TBC) samples underwent isothermal loading at various temperatures with different time exposures and the effect of temperature and time exposure on the formation of TGO and CSN oxides were explored. It was concluded that the minimum temperature for formation of TGO and CSNs were 900 and 1040 °C, respectively, and the minimum time exposure for CSNs to start the formation process was 12 h. Furthermore, an isothermal loading at 1070 °C was applied on 5 samples without TC to study the formation trend of TGO growth and found that the growth rate of TGO is lower when TC exists in the samples. In order to explain the behavior of TGO growth in this state, a finite element model was executed and the applied stresses to TGO from bond coat (BC) were calculated. Results show that the order of stresses in the state with TC is much lower than the state without TC, which consequently leads to TGO separation in the latter state and, as a result, a weaker adhesion to the BC and lower TGO growth rate.

Origin and evolution of microporosity in packstones and grainstones in a Lower Cretaceous carbonate reservoir, United Arab Emirates

Abstract Microporosity in carbonate reservoirs is generated by the complex interplay between depositional and diagenetic processes. This petrographical, SEM, fluid-inclusion and isotopic study of a Lower Cretaceous carbonate reservoir, Abu Dhabi, UAE, revealed that: (1) micritization of ooids and skeletal fragments, which resulted in spheroidal (rounded) micrite, accounts for most microporosity in peloidal packstones and grainstones; and (2) transformation of spheroidal micrite into subhedral/euhedral micrite and microspar, known as aggrading neomorphism, could happen via precipitation of syntaxial calcite overgrowths around micrite (micro-overgrowths) and not only, as suggested previously in the literature, by recrystallization involving the dissolution (of micrite) and reprecipitation (of microspar). Precipitation of calcite cement around micrite (i.e. destruction of microporosity) is more extensive in the water zone than in the oil zone, which is possibly contributing to the lower porosity and permeability of the carbonate reservoir in the water zone. Similarity in bulk oxygen isotopic values of micritized packstones and grainstones in the water and oil zones (average δ 18 O V-PDB = −7.2‰ and −7.8‰, respectively) is attributed to: (1) a small difference in temperatures between the crest (oil zone) and the flanks (water zone); and (2) calcite precipitation around micrite occurred prior and subsequent to oil emplacement. Bulk carbon and strontium isotopic compositions of micritized packstones and grainstones in the water and oil zones (average δ 13 C V-PDB = +3.7‰ and average 87 Sr/ 86 Sr ratios = 0.707469) indicate that calcite cement was derived from marine porewaters and/or dissolution of the host limestones. The minimum formation temperatures of bulk micrite/microspar, which are inferred based on paragenetic relationships, fluid-inclusion microthermometry and oxygen isotope data, are around 58–78°C.

Fe–O stable isotope pairs elucidate a high-temperature origin of Chilean iron oxide-apatite deposits

Iron oxide–apatite (IOA) ore deposits occur globally and can host millions to billions of tons of Fe in addition to economic reserves of other metals such as rare earth elements, which are critical for the expected growth of technology and renewable energy resources. In this study, we pair the stable Fe and O isotope compositions of magnetite samples from several IOA deposits to constrain the source reservoir of these elements in IOAs. Since magnetite constitutes up to 90 modal% of many IOAs, identifying the source of Fe and O within the magnetite may elucidate high-temperature and/or lower-temperature processes responsible for their formation. Here, we focus on the world-class Los Colorados IOA in the Chilean iron belt (CIB), and present data for magnetite from other Fe oxide deposits in the CIB (El Laco, Mariela). We also report Fe and O isotopic values for other IOA deposits, including Mineville, New York (USA) and the type locale, Kiruna (Sweden). The ranges of Fe isotopic composition (δ56Fe, 56Fe/54Fe relative to IRMM-14) of magnetite from the Chilean deposits are: Los Colorados, δ56Fe (±2σ)=0.08±0.03‰ to 0.24±0.08‰; El Laco, δ56Fe=0.20±0.03‰ to 0.53±0.03‰; Mariela, δ56Fe=0.13±0.03‰. The O isotopic composition (δ18O, 18O/16O relative to VSMOW) of the same Chilean magnetite samples are: Los Colorados, δ18O (±2σ) = 1.92±0.08‰ to 3.17±0.03‰; El Laco, δ18O=4.00±0.10‰ to 4.34±0.10‰; Mariela, δ18O=(1.48±0.04‰). The δ18O and δ56Fe values for Kiruna magnetite yield an average of 1.76±0.25‰ and 0.16±0.07‰, respectively. The Fe and O isotope data from the Chilean IOAs fit unequivocally within the range of magnetite formed by high-temperature magmatic or magmatic–hydrothermal processes (i.e., δ56Fe 0.06–0.49‰ and δ18O=1.0–4.5‰), consistent with a high-temperature origin for Chilean IOA deposits. Additionally, minimum formation temperatures calculated by using the measured Δ18O values of coexisting Los Colorados magnetite and actinolite separates (630°C) as well as Fe numbers of actinolite grains (610–820°C) are consistent with this interpretation. We also present Fe isotope data from magmatic magnetite of the Bushveld Complex, South Africa, where δ56Fe ranges from 0.28±0.04‰ to 0.86±0.07‰. Based on these data and comparison to published Fe and O stable isotope values of igneous magnetite, we propose extending the magmatic/high-temperature δ56Fe range to 0.86‰. Considering that the Chilean IOAs and Kiruna deposit are representative of IOA deposits worldwide, the Fe and O stable isotope data indicate that IOAs are formed by high-temperature (magmatic) processes.

Computer reconstruction of the physicochemical conditions of sulfide formation for the Krasnov and Ashadze hydrothermal systems (Mid-Atlantic Ridge)

Computer-based reconstruction of the physicochemical conditions of formation of the Krasnov (16° N) and Ashadze (13° N) submarine systems in the Mid-Atlantic Ridge (MAR) has been performed using the equilibrium-thermodynamic approach to study samples from these sites. In the first case, a sphalerite-pyrite-barite association was considered, and in the second case, a sphalerite-pyrite association. In the modeling conducted, the composition of the sphalerite solid solution corresponding to the nonideal mixing of ZnS and FeS was used as a correlation parameter with the total composition of the Fe-Zn-Ba-S-H2O-NaCl-HCl hydrothermal system depending on temperature (200-300°C) and a given pressure of 100bar. The calculation results predict that at an iron content of 0.17-0.36wt.% in sphalerite, the minimum formation temperatures of the equilibrium sphalerite-pyrite-barite association should correspond to the interval of 280-300°C (Krasnov site). As the iron content in sphalerite increases to 4.15-13.28wt.%, the occurrence of barite in the systems studied becomes impossible and the formation temperatures of the sphalerite-pyrite association become equal to or higher than 300°C (Ashadze site).

Hydrothermal controls on iron and lead mineralization on the farms Leeuwbosch and Cornwall, Thabazimbi District, South Africa

The Paleoproterozoic Malmani Subgroup and Penge Formation (Transvaal Supergroup) exposed on the farms Leeuwbosch and Cornwall north of Thabazimbi (Limpopo Province, South Africa) host hydrothermal Pb–Ag–Cu–Zn and high-grade hematite iron ore deposits which include the historic Leeuwbosch lead mine. Based on ore petrography, fluid inclusion and stable isotope analyses and geochemical modeling, the structurally controlled, stratabound Leeuwbosch Pb–Ag–Cu–Zn–Fe deposits formed from high salinity NaCl–CaCl2-rich basinal brines with total salinities from 18 to 24wt.% NaCl equivalent which are similar to those found in the Mississippi Valley Type (MVT) Pb–Zn deposits. The minimum formation temperatures (homogenization temperatures) for the lead deposits range between 120 and 185°C and the estimated formation conditions are 200°C at 1kbar pressure. Stable isotope analyses of gangue siderite and calcite indicate that the deposits formed from base metal-enriched brines derived from recycled seawater with δ13Cvs. PDB from 0.46 to 3.17‰ and δ18Ovs. SMOW from −2.95 to −1.79‰. Hydrothermal transport of lead and silver as PbCl3− and AgCl2− respectively took place at mildly acidic pH and elevated fO2 in the SO42− predominance field. Extensive host rock interaction neutralized and reduced the ore fluid to precipitate galena hosting Ag with chalcopyrite and sphalerite. Fluid inclusions in gangue quartz and calcite in the extensive structurally controlled and pervasive stratabound hydrothermal iron ore deposits on the farms Leeuwbosch and Cornwall, chiefly consisting of high-grade hematite with rare relict magnetite, show a wide compositional variability due to episodic fluid mixing and successive hydrothermal activity in the presence of several distinct fluid end members. Total salinities of fluid inclusions in quartz from the hematite deposits range from 9.2 to 39.9wt.% NaCl eq. with highly variable proportions of NaCl and CaCl2 and minimum formation temperatures are between 100 and 190°C. The estimated formation conditions for the iron ore deposits are 175°C and 1kbar. Stable isotopes of gangue calcite indicate that diagenetic fluids with δ13Cvs. PDB from −3.33 to −2.09 and δ18Ovs. SMOW from 2.52 to 5.60‰ and a second fluid with δ13Cvs. PDB of −7.45 and δ13Cvs. PDB of 17.45 were controlling the formation of the hematite deposits. In agreement with oxidized conditions during hematite formation and characteristic host rock alteration patterns traced by carbon and oxygen isotopes, the second low salinity fluid was derived from the overlying Waterberg Group sandstones and played an important role in the formation of the iron ore deposits, in addition to high salinity diagenetic brines. Iron was leached from the BIFs of the Penge Formation, transported as FeCl+ under mildly acidic conditions and likely deposited in response to the oxidation of the iron-bearing fluids. The lead and iron ore deposits formed by combinations of structural controls which influenced the regional fluid flow patterns and fluid compositions, and fluid–rock interaction with reactive carbonate lithologies of the Malmani Subgroup which acted as a sink for metals transported in acidic hydrothermal solutions.