Fine-grained Inclusions Research Articles

Strontium isotope evidence for the repeated formation of refractory inclusions in the Allende meteorite

Calcium-aluminum-rich inclusions (CAIs) in chondrite meteorites are the oldest rocks in the Solar System and were formed by condensation from nebular gas. Recent mass spectrometric measurements have revealed that CAIs possess nucleosynthetic isotopic compositions different from those of terrestrial materials for various elements, indicating a heterogeneous distribution of nuclides from various stellar sources in the early Solar System. CAIs are classified into coarse-grained (CGs) and fine-grained (FGs) inclusions. The former have experienced secondary melting through thermal events after their formation, while the latter evidently avoided the remelting. Thus, FGs are considered to be direct condensates from a high-temperature gas, making them ideal for the investigation of the origin and formation process of CAIs. In this study, the elemental abundances and Sr isotopic compositions in eight FGs from a carbonaceous chondrite Allende were analyzed by utilizing a micromilling technique. These FG samples were found to have rare-earth element (REE) patterns reflecting various degrees of elemental fractionation and variable µ84Sr values ranging from 61 to 844 ppm. It cannot be ruled out that matrix contamination during micromilling or secondary alteration on the Allende parent body has affected the elemental abundances and µ84Sr values observed in FGs to some extent; however, the large variation in µ84Sr values could reflect the variability in the FG formation processes. Importantly, REE-fractionated FGs, which were depleted in heavy REEs relative to light REEs, had relatively high µ84Sr values. This suggests that the formation of REE-fractionated FGs was triggered by rapid heating events, such as FU Orionis that occurred periodically in the early Solar System, and that at least two different heating events probably formed FGs with two different µ84Sr values.

Two- and three-component alloys nanowires: correlation of structural and magnetic properties

Several types of nanowires (NWs) made of alloys of various compositions obtained by the method of matrix synthesis based on track membranes have been studied. Electrolytes were selected to obtain NWs of the desired composition. The control of electrodeposition by chronoamperograms made it possible to systematically change the geometric parameters and morphology. The topographies of the resulting NW arrays and their elemental composition were studied using electron microscopy with an X-ray spectral analyzer. The magnetic properties of the samples were studied on a vibrating magnetometer. The structures of binary alloys were studied: for NWs of FeCo alloys, the dependence of the coercive force on the composition was studied. The obtained dependence has two maxima --- at an equiatomic composition and at a cobalt content of about 90%. For Fe0.3Co0.7 NWs, a sharp increase in the coercive force with decreasing diameter is shown. It is assumed that this effect is due to the formation of single-domain crystallites, the processes of magnetization reversal of which are associated with a uniform rotation of the magnetization. For NWs made of FeNi alloys, the influence of the aspect ratio on the coercive force has been proved. Ternary alloys of the FeCoCu system have been studied: it has been shown that the addition of copper significantly increases the coercive force, which reaches a maximum at a copper content of about 5%. The obtained X-ray data suggest that the effect of an increase in the coercive force is associated with the formation of fine-grained inclusions based on copper, which lead to effective deceleration of the domain walls. The data obtained expand the range of possibilities for controlling the magnetic properties of NW arrays obtained by the method of matrix synthesis. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force.

Нанопроволоки из двух- и трехкомпонентных сплавов: корреляция структурных и магнитных свойств

Several types of nanowires (NWs) made of alloys of various compositions obtained by the method of matrix synthesis based on track membranes have been studied. Electrolytes were selected to obtain NWs of the desired composition. The control of electrodeposition by chronoamperograms made it possible to systematically change the geometric parameters and morphology. The topographies of the resulting NW arrays and their elemental composition were studied using electron microscopy with an X-ray spectral analyzer. The magnetic properties of the samples were studied on a vibrating magnetometer. The structures of binary alloys were studied: for NWs of FeCo alloys, the dependence of the coercive force on the composition was studied. The obtained dependence has two maxima - at an equiatomic composition and at a cobalt content of about 90%. For Fe0.3Co0.7 NWs, a sharp increase in the coercive force with decreasing diameter is shown. It is assumed that this effect is due to the formation of single-domain crystallites, the processes of magnetization reversal of which are associated with a uniform rotation of the magnetization. For NWs made of FeNi alloys, the influence of the aspect ratio on the coercive force has been proved. Ternary alloys of the FeCoCu system have been studied: it has been shown that the addition of copper significantly increases the coercive force, which reaches a maximum at a copper content of about 5%. The obtained X-ray data suggest that the effect of an increase in the coercive force is associated with the formation of fine-grained inclusions based on copper, which lead to effective deceleration of the domain walls. The data obtained expand the range of possibilities for controlling the magnetic properties of NW arrays obtained by the method of matrix synthesis. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force.

PATTERNS IN WOUND HEALING PROCESS AFTER BRANCIAL CLEFT CYST EXCISION IN CHILDREN

The course of the wound healing process after surgical intervention on brancial cleft cyst excision should be considered as a stereotyped inflammatory-reparative reaction of the body, characterized by staged aseptic inflammation, regeneration and fibrosis. Clinically and even morphologically, it is difficult to determine the stages of the wound healing process in the temporal aspect, since they are consistent and interconnected.
 Purpose. The paper is aimed at evaluation of the wound healing process according to clinical indicators in children after branchial cleft cyst excision.
 Methods and Material. 26 children aged from 5 to 17 years old with branchial cleft cysts have been examined and treated. In the postoperative period, the nature, amount of exudate and its cell composition has been determined; skin contact thermometry has been performed at 4 points around the wound at a distance of 1 cm.
 Results. The first manifestations of the disease coincided with the course of acute respiratory viral diseases in 8 children (30.8%); association with ENT pathology was observed in 3 (11.5%) children and the cystic masses emerged spontaneously in 15 cases (57.7%). They were localized with almost the same incidence on the left and right, but the vast majority (21 cases (80.7%)) was located anteriorly the sternocleidomastoid muscle and in 5 (19.3%) cases behind it. Ultrasound examination, made in 21 patients (80.8%), has revealed the presence of cystic masses with clear contours, hypoechoic structure and fine-grained inclusions, and the wall thickness varied from 1 to 3 mm. In 5 doubtful cases (19.2%) a puncture biopsy was performed.
 On 1st day after surgery, hyperemia around the wound was moderate in 15 children (57.7%); it was insignificant in 8 (30.8%) children and it was absent in 3 (11.5%) children. At the same time all children experienced collateral edema of various localization and painful modality. In the impression smears, a significant number of neutrophils, a moderate number of lymphocytes and erythrocytes was detected, which were prominent against the background of a loose substrate. The temperature of the wound area was 36.24 ± 0.07˚C, which was higher compared to the control group (34.71 ± 0.12˚C).
 On 3rd day, the corolla of hyperemia around the wound was not detected in 18 patients (69.2%), and its narrowing was recorded in 6 (23.1%) cases and it was persistent in 2 (7.7%) cases. On palpation, severe, moderate and weak pain on the wound area was experienced by 2 (7.7%), 15 (57.7%) and 9 (36.4%) children, respectively. The cytograms of the exudate showed a reduced quantity of neutrophils, erythrocytes and lymphocytes. Two children showed elevated quantity of destructured neutrophils and local temperature to 37.21 ± 0.16 ° C, which required medical adjustments.
 A narrow corolla of hyperemia around the wound, slight edema and moderate pain was detected on 7th day only in 2 children. In all patients, palpation revealed tissue compaction along the wound canal, onset of epithelialization, and the cytograms revealed the presence of sporadic neutrophils. The temperature of the skin around the wound reached 35.74 ± 0.11˚C, which was almost similar to controls (34.21 ± 0.08˚C). In all cases, the wounds healed with primary tension.
 Thus, the nature of the dynamics of wound healing after brancial cleft cyst extirpation in children can be successfully controlled by the prominence of the main clinical signs, the findings of the study of cellular composition of wound exudate and local temperature measuring.
 The perspectives of further research are associated with availability and simplicity of the methods in terms of their application in everyday clinical practice.

Stability conditions and compositional variations of deerite in high-pressure meta-ironstone during subduction–exhumation processes (SW Tianshan, China)

Index minerals in metamorphic rocks, such as coesite, glaucophane, or lawsonite, are of great importance to understand high-pressure (HP) to ultrahigh-pressure (UHP) metamorphism, the thermal gradient, and the geodynamics of subduction zones. Deerite is thought to be diagnostic for blueschist-facies metamorphism in cold subduction environments and a sensitive indicator of the oxygen fugacity (fO2) in Fe-rich rocks. However, little is known concerning its stability and compositional variation during subduction and exhumation cycles. In this study, we provide the first detailed investigation of deerite in eclogite-facies meta‑ironstones (deerite–garnet riebeckitite) from the Southwestern Tianshan (U)HP metamorphic belt. Petrological observation and textural evidence suggest that the meta‑ironstones –enclosing eclogite blocks– form part of an initially coherent volcano-sedimentary sequence that underwent a common tectono-metamorphic evolution, including HP metamorphism and subsequent exhumation. Two types of deerite, which display a different texture (inclusion vs. matrix) and composition (TiO2 content), occur in the deerite–garnet riebeckitite. Dee_1 and aegirine–augite appear exclusively as fine-grained inclusions in garnet, and together with garnet, riebeckite, quartz and magnetite form the peak metamorphic mineral assemblages at P–T conditions of ~510 °C and 2.6 GPa. Matrix deerite (Dee_2), on the other hand, mainly occurs as coarse-grained rods and acicular needle-like grains in quartz, and rarely as inclusions in riebeckite and garnet intimately in the riebeckitite, representing the blueschist-facies retrogression of the meta‑ironstones during exhumation. The garnet–clinopyroxene oxybarometer and thermodynamic calculations show that the fO2 of the deerite–garnet riebeckitite increases from ΔFMQ–0.64 at the peak eclogite-facies stage to ΔFMQ+1.5 at the blueschist-facies retrogression. This fO2 variation corresponds to the chemical variation of deerite, whereby the TiO2 content increases gradually from <0.1 wt% in the Dee_1 in garnet to about 5 wt% in the matrix Dee_2. Our study reveals the detailed metamorphic P–T–fO2 evolution of the prograde eclogite- and retrograde blueschist-facies deerite-bearing meta‑ironstones during subduction–exhumation processes. This study further emphasizes the potential of deerite to reveal the P–T–fO2 evolution of subduction-related high-pressure rocks.

The P-T-t path of pelitic gneisses in the Zanhuang Complex: Further constraints on the Palaeoproterozoic tectonic evolution of the Trans-North China Orogen, North China Craton

The Zanhuang Complex, situated on the eastern margin of the central section of the Trans-North China Orogen (TNCO), North China Craton, mainly comprises Archean-Palaeoproterozoic tonalite-trondhjemite-granodiorite (TTG) gneisses, migmatites, granites, metavolcanic rocks, and metasedimentary rocks. Petrographic observations of garnet-bearing pelitic gneisses from the south-eastern Zanhuang Complex show three distinct mineral assemblages (M1-M3) that correspond to three different metamorphic stages. The interpreted prograde metamorphic stage (M1) is mainly represented by the cores of garnet porphyroblasts with fine-grained inclusions of biotite + plagioclase + staurolite + kyanite + quartz + ilmenite. The peak metamorphic stage (M2) is mainly represented by garnet mantles and a matrix-type mineral assemblage of kyanite + biotite + plagioclase + quartz + ilmenite + melt. The retrograde metamorphic stage (M3) is represented by the presence of sillimanite with garnet rims + biotite + plagioclase + quartz + ilmenite + magnetite. Quantitative phase equilibria modelling constrains the pressure–temperature (P–T) conditions of the M1 and M2 stages to 640–670 °C/7.3–7.5 kbar and 705–760 °C/7.9–9.1 kbar, respectively. The zircons and monazites in the Zanhuang pelitic gneisses all record consistent ages of 1839–1831 Ma, which most likely represent the near-peak metamorphic age. Thus, a clockwise P-T-time (P-T-t) path is determined for the garnet-bearing pelitic gneisses from the Zanhuang Complex. The petrological and geochronological evidence from the pelitic gneisses in the Zanhuang Complex in this paper suggests that the TNCO might have experienced continuous continental collision and rapid tectonic uplift at ca. 1839–1831 Ma, thereby providing a metamorphic constraint on the Palaeoproterozoic tectonic evolution of the TNCO.

Modeling the evaporation of CAI-like melts, and constraining the origin of CH-CB CAIs

To address the bulk compositions of CAIs from CH-CB chondrites we have used a new thermodynamic method to model the evaporation of CAI-like melts. The model calculations agree closely with the results of evaporation experiments on individual bulk compositions, and thus could provide a general means of predicting the evaporation trajectory of any CAI bulk composition melt. The model calculations and evaporation experiments show that the initial stages of CAI melt evaporation are controlled by the relative evaporation rates of MgO and SiO2, whereas the late stages are dominated by the initial CaO/Al2O3 ratio of the melt. Application of the model to the puzzling bulk compositions of very refractory CAIs from CH-CB chondrites, many of which are grossite-, hibonite-, and spinel-rich, shows that such compositions can be derived via evaporation of precursors unusually enriched in Al2O3 with CaO/Al2O3 ratios (weight %) < 0.3. This rules out most silicate-rich CAI varieties. Only spinel- and spinel-hibonite-rich fine-grained inclusions with group II REE patterns (common in CV3 chondrites), which may have been present in the region where CH CAIs formed, could be precursors for the grossite- and hibonite-rich igneous CAIs.

Inclusion's distribution pattern's influence on mixture's effective permittivity in two dimension utilizing finite difference method (FDM)

In this paper, a numerical technique based on two dimensional finite difference method (FDM) is utilized to study the effective permittivity of mixtures with various patterns of inclusions’ distributions. The inclusions are assumed to be periodically distributed in the host medium. The influence of the inclusions’ shape, permittivity, volume fraction and randomness are investigated in the simulation. Three categories of inclusions’ types are considered, which are solid, hollow and randomly distributed inclusion. The shapes of solid inclusion type include square, cylinder, diamond and plus. The shapes of hollow inclusion type include square, cylinder, diamond and grid. The shapes of randomly distributed inclusion type include fine-grained inclusions and coarse-grained inclusions. The results of FDM methods are also compared with that of the analysis. Several analysis formulas are considered, such as Maxwell-Garnett, Bruggeman, Birchak, Looyenga and Lichtenecker. For all shapes of solid patterns except the plus, the simulated effective dielectric properties of mixtures are in good agreement with that obtained by Maxwell-Garnett prediction formula. When the contrast of permittivities between the inclusions and the environment is high, the numerical results for the square solid pattern match well with the analytical results provided by the Maxwell-Garnett formula. For other patterns, no analytical formulas can be implemented appropriately. The FDM results of hollow patterns deviate from the theoretical results significantly. In addition, for mixtures with randomly distributed inclusions, the effective permittivity achieved by the numerical technique varies almost linearly with volume fraction, which does not agree well with any analysis formula.

Sulfur isotope compositions of pyrite from high-pressure metamorphic rocks and related veins (SW Tianshan, China): Implications for the sulfur cycle in subduction zones

A detailed petrographic, microstructural and geochemical investigation of pyrites from four eclogites / blueschists and their veins in the Tianshan (NW China) have revealed the occurrence of four types of pyrites: δ34S values of the pyrites range from −24.7 to +13.2‰, whereby three populations can be distinguished that have distinct δ34S ranges corresponding to different paragenetic stages. Py1 pyrite grains contain micro- to nanoscale inclusions of pyrrhotite, chalcopyrite, bornite, sphalerite, galena, arsenopyrite, cobalt-pentlandite, enargite, titanite, biotite, barite, and have δ34S values of −3.8 to +2.7‰ (average δ34S = −0.6 ± 0.9‰), which is inherited from a magmatic and hydrothermal fluid input during alteration of the oceanic crust. Py2 pyrite occurs as inclusions within the cores of garnet where it coexists with fine-grained inclusions of rutile, glaucophane and rarely with omphacite. Thus, these pyrite inclusions likely formed during prograde evolution. Py2 is too small to be analyzed by SIMS and thus no isotopic compositions could be determined. The Py3 pyrite grains contain eclogite-facies mineral inclusions, such as omphacite, glaucophane, epidote, rutile and lawsonite, and are inferred to have formed during the late prograde evolution close to or at peak eclogite-facies conditions. Py3 pyrite display positive δ34S values ranging from +3.6 to +13.2‰ (average δ34S = +9.7 ± 2.8‰), suggesting the source of sulfur was either anhydrite incorporated during seafloor alteration or 34S-enriched sulfide from lower sections of the oceanic lithosphere. Py4 pyrite occurs as irregular patches, isolated euhedral to subhedral grains or as rims around Py1 or Py3 pyrites, associated with magnetite and ilmenite. Py4 grains have δ34S values of −24.7 to −3.9‰ (average δ34S = −5.0 ± 2.1‰), with the most likely source of sulfur being 32S-enriched pelagic sediments that in the Tianshan are interlayered with the metavolcanic lithologies and underwent amphibolite facies metamorphism during exhumation. This study provides insight into the sulfur cycle within subduction zones. We document that during subduction and exhumation fluids with distinct sulfur isotopic compositions driven by dehydration reactions in the downgoing slab cause metasomatism in the surrounding lithologies. In particular, we suggest that at least locally the plate interface is characterized by sediment-derived fluids that are characterized by 32S-enriched sulfur and comparatively higher oxygen fugacities.

Combined mass-dependent and nucleosynthetic isotope variations in refractory inclusions and their mineral separates to determine their original Fe isotope compositions.

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials that provide crucial information about the isotopic reservoirs present in the early Solar System. For a variety of elements, CAIs have isotope compositions that are uniform yet distinct from later formed solid material. However, despite being the most abundant metal in the Solar System, the isotopic composition of Fe in CAIs is not well constrained. In an attempt to determine the Fe isotopic compositions of CAIs, we combine extensive work from a previously studied CAI sample set with new isotopic work characterizing mass-dependent and mass-independent (nucleosynthetic) signatures in Mg, Ca, and Fe. This investigation includes work on three mineral separates of the Allende CAI Egg 2. For all isotope systems investigated, we find that in general, fine-grained CAIs exhibit light mass-dependent isotopic signatures relative to terrestrial standards, whereas igneous CAIs have heavier isotopic compositions relative to the fine-grained CAIs. Importantly, the mass-dependent Fe isotope signatures of bulk CAIs show a range of both light (fine-grained CAIs) and heavy (igneous CAIs) isotopic signatures relative to bulk chondrites, suggesting that Fe isotope signatures in CAIs largely derive from mass fractionation events such as condensation and evaporation occurring in the nebula. Such signatures show that a significant portion of the secondary alteration experienced by CAIs, particularly prevalent in fine-grained inclusions, occurred in the nebula prior to accretion into their respective parent bodies. Regarding nucleosynthetic Fe isotope signatures, we do not observe any variation outside of analytical uncertainty in bulk CAIs compared to terrestrial standards. In contrast, all three Egg 2 mineral separates display resolved mass-independent excesses in 56Fe compared to terrestrial standards. Furthermore, we find that the combined mass-dependent and nucleosynthetic Fe isotopic compositions of the Egg 2 mineral separates are well correlated, likely indicating that Fe indigenous to the CAI is mixed with less anomalous Fe, presumably from the solar nebula. Thus, these reported nucleosynthetic anomalies may point in the direction of the original Fe isotope composition of the CAI-forming region, but they likely only provide a minimum isotopic difference between the original mass-independent Fe isotopic composition of CAIs and that of later formed solids.

Petrological and geochronological evidence for Paleoproterozoic granulite-facies metamorphism of the South Liaohe Group in the Jiao-Liao-Ji Belt, North China Craton

To better understand the formation of high-temperature metamorphic rocks, we present a detailed petrological and geochronological study of recently discovered cordierite-bearing granulites of the South Liaohe Group in the Jiao-Liao-Ji Belt, North China Craton. Petrographic observations indicate that four distinct mineral assemblages are present in the granulites: pre-peak amphibolite facies (M1), peak granulite facies (M2), post-peak decompression (M3), and late cooling retrogression (M4). M1 is preserved as fine-grained inclusions in the cores of garnet grains, represented by quartz + plagioclase + biotite + ilmenite. M2 is interpreted to have comprised garnet + sillimanite + plagioclase + quartz + biotite + ilmenite + melt. M3 was characterized by the formation of cordierite + sillimanite symplectites and cordierite + quartz coronas replacing garnet. M4 is indicated by the formation of staurolite, accompanied by the crystallization of melt. A combination of multi-equilibria geothermobarometers and pseudosection modeling constrains the P–T conditions of the M1, M2, M3, and M4 stages to P = 0.66–0.71 GPa and T = 620–650 °C, P = 0.96–1.10 GPa and T = 790–840 °C, P = 0.62–0.65 GPa and T = 725–785 °C, and P = 0.43–0.55 GPa and T = 595–625 °C, respectively. Zircon and monazite U–Pb dating yields three distinct and meaningful ages for the granulites: (1) 2200–2100 Ma for the granulite protoliths, (2) ca. 1945 Ma for the near-peak metamorphism, and (3) 1851–1839 Ma for the post-peak and late retrogressive metamorphism. Thus, a clockwise P–T–t path is determined for the cordierite-bearing granulites of the South Liaohe Group. Petrological and geochronological evidence from regional metamorphic rocks in the Jiao-Liao-Ji Belt suggests that the belt experienced a continuous orogenesis from 1950 to 1800 Ma.

SIMULATION OF 3D TRANSIENT FLOW PASSING THROUGH AN INTESTINAL ANASTOMOSIS BY LATTICE-BOLTZMANN METHOD

Context. Recently, the number of reconstructive operations on the digestive tract has significantly increased. Such operations have predictable negative consequences associated with disruptions of hydrodynamic processes in the anastomosis area. These negative consequences can be partially avoided by choosing anastomosis anatomical form based on mathematical modeling. Known mathematical models are cumbersome and do not allow to obtain results in real time. The proposed approach using lattice Boltzmann method allows solving this problem. Objective. The purpose of the work is to develop a three-dimensional mathematical model of anastomosis for research of hydrodynamic parameters of fluids with complex structure in real time. Method. The method of constructing and analyzing the mathematical model of anastomosis of the digestive tract based on lattice Boltzmann method is proposed. The method differs in that it provides simultaneous analysis of hydrodynamic parameters of the liquid and determines the nature of movement of fine-grained inclusions in the anastomosis area. The main stages of the method are the development of technology for determining the modeling area, discretization of the three-dimensional Boltzmann equation with the choice of lattice and the nature of the collision operator, taking into account the complex structure of the liquid; development of the technology of transition from the density distribution function to the distribution of pressure at the mesoscopic level, taking into account the properties of the liquid, the creation of the process of transforming the set of mesoscopic parameters into the macroscopic parameters of the liquid. Results include determining the distribution of the velocity field in the anastomosis area to modify its geometry. The study of the influence of gravity on the nature of motion of fine-grained inclusions has been carried out. The quantitative characteristics of the delay of particles in the area of anastomosis, depending on the dynamic viscosity of the liquid, are determined. Conclusions. The three-dimensional mathematical model discussed in this paper is based on the application of the lattice Boltzmann method for calculating the hydrodynamic parameters of the motion of fluid in the study area. The distinctive feature of the model is that it accounts for the complex nature of the liquid having fine-grained inclusions. The model allows determining the behavior of these inclusions and the field of speed with sufficient accuracy in real time.

Metamorphic P–T–t paths of the Zanhuang metamorphic complex: Implications for the Paleoproterozoic evolution of the Trans-North China Orogen

Garnet-bearing metapelites are cropped out in the Zanhuang metamorphic complex located in the central section of the N–S trending Trans-North China Orogen. Petrological studies indicate that these garnet-bearing metapelites preserve three distinct metamorphic assemblages (M1–M3). The cores of garnet porphyroblasts and fine-grained inclusions of plagioclase+quartz±biotite±apatite±magnetite±rutile±ilmenite define the prograde metamorphic stage (M1). The assemblage of the peak metamorphic stage (M2) consists of biotite+plagioclase+quartz±kyanite±hornblende±magnetite±ilmenite in equilibrium with the lowest-XMn garnet rims. The peak metamorphism was followed by a near-isothermal decompressional stage (M3) and the development of symplectitic coronas of biotite+plagioclase+quartz±hornblende±magnetite surrounding garnet porphyroblasts. Quantitative phase equilibria modeling and traditional thermobarometric estimations were applied to yield P–T conditions of 4.5–5.9kbar and 551–596°C for stage M1, 9.6–12.3kbar and 770–830°C for stage M2, and ∼4.7kbar and ∼635°C for stage M3. The combination of the mineral inclusions, mineral compositions, and metamorphic reactions in the Zanhuang metapelites defines a clockwise P–T path with nearly isothermal decompression, which is considered to have been related to the amalgamation of the Eastern and Western Blocks to form the North China Craton. Abundant U–Pb spot analyses of metamorphic zircons from the gneiss and amphibolite reveal two discrete, meaningful ages of metamorphism within the Zanhuang complex: the first age dates to ∼2507Ma, and the second age dates to ∼1839Ma. The first age group (∼2507Ma) was most likely associated with a regional Neoarchean granulite-facies metamorphic event within the North China Craton, whereas the second age group (∼1839Ma) is interpreted as the result of a Paleoproterozoic orogenic event that occurred in the Trans-North China Orogen (TNCO).

Petrochemistry of ultrapotassic tephrites and associated cognate plutonic xenoliths with carbonatite affinities from the late Quaternary Qa’le Hasan Ali maars, central Iran

The Quaternary Qa’le Hasan Ali (QHA) maars in central Iran occur at the intersection of the north–south Nayband fault, which defines the western boundary of the Lut micro-continental block, and a system of northwest–southeast faults, subparallel to the Zagros suture zone, that formed during the Arabian–Eurasian collision. These post-collisional maars intrude Eocene volcanic rocks of the Urumieh–Dokhtar magmatic belt, which was generated by the subduction of Neotethys oceanic lithosphere below Iran. The highly potassic, Ti-phlogopite+Mg-rich (Fo89–92) olivine+diopside-augite+aegirine–augite basanite tephrites forming the tuff rims of the QHA maars contain tephrite-coated plutonic xenoliths, some of which are interpreted as co-genetic with the tephrites based on their similar mineralogy and Sr isotopic composition (87Sr/86Sr=0.70590). Cognate plutonic xenoliths have up to ∼20vol% calcite, considered to be magmatic calcite because of (1) its grain size, which is similar to feldspars and aegirine–augite pyroxenes in these rocks, (2) the occurrence of fine-grained inclusions of pyroxene and apatite within these calcite grains, and (3) the similarity of the Sr-isotopic composition of this calcite with the other minerals in these rocks. The fact that the magmatic calcite has remained intact and did not volatilize during the transport of these xenoliths to the surface in the hot tephrite magma implies a short transit time, indicating that they are samples of a shallow plutonic complex, as does the presence of anorthoclase in these plutonic xenoliths. Their high modal proportion of magmatic calcite suggests that this shallow plutonic complex has affinities with carbonatites. The magmatic calcite-bearing plutonic xenoliths have high LREE/HREE ratios and contain REE-rich allanite (with up to ∼20wt% LREE) and britholite (∼60wt% LREE) that make up ∼3 modal percent of the most calcite-rich samples. Similar to many post-collisional highly potassic rocks formed in the Alpine–Himalayan collision zone, the highly potassic basanite tephrites of the QHA maars have high 87Sr/86Sr and low C̵Nd (−1.3 to −3.4), distinct from convecting asthenosphere, and they are depleted in Nb and Ta relative to Ba and La. They formed by small degrees of partial melting of lower continental lithospheric mantle metasomatized by both H2O and CO2-rich fluids derived from subducted Neotethys oceanic crust and sediments during the collision of the Arabian and Eurasian plates.

Metamorphic P–T path and tectonic implications of pelitic granulites from the Daqingshan Complex of the Khondalite Belt, North China Craton

Pelitic granulites are cropped out in the Daqingshan Complex of the Khondalite Belt, a Paleoproterozoic tectonic belt in the Western Block of the North China Craton. Petrological studies show that these granulites contain four distinct metamorphic assemblages. The core of a garnet porphyroblast, along with fine-grained inclusions of biotite+plagioclase+K-feldspar+quartz±sillimanite±ilmenite, defines the prograde metamorphic (M1) stage. The peak (M2) assemblage consists of garnet (mantle)+biotite+K-feldspar+plagioclase+quartz±sillimanite±orthopyroxene±ilmenite±magnetite±rutile. Peak metamorphism was followed by a near-isothermal decompression (M3) and the development of coronae of garnet+biotite+cordierite+plagioclase+quartz±K-feldspar±sillimanite±spinel±ilmenite±magnetite (M3) in the Crd–Grt–Bt gneisses during the following garnet breakdown reactions: garnet+sillimanite+melt→cordierite+biotite+Fe-oxide and garnet+melt→biotite+quartz+plagioclase. Retrograde cooling (M4) assemblages are represented by biotite+muscovite+sillimanite+quartz+plagioclase+K-feldspar±ilmenite. Quantitative phase equilibria modeling in the system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 was applied to obtain P–T conditions of <780°C and <9kbar for M1, 840–880°C and 9–11kbar for M2, 800–870°C and 5.0–7.5kbar for M3, and <660°C and 4.1–6.9kbar for M4. The combination of the mineral assemblages, mineral compositions, and metamorphic reaction histories in the Daqingshan pelitic granulites defines a clockwise P–T path that involves periods of near-isothermal decompression and late cooling that followed the peak granulite-facies metamorphism. This result is consistent with the tectonic history of the Daqingshan Complex in the Khondalite Belt, which involved continent–continent subduction and collision followed by exhumation and cooling. This suggests a continent–continent collisional event between the Yinshan and Ordos blocks, which became amalgamated to form the Paleoproterozoic Khondalite Belt in the Western Block of the North China Craton.

Chemistry, microstructure, and alpha decay damage of natural brannerite

To investigate the long-term stability of brannerite with respect to alpha decay damage and interaction with aqueous fluids, we have undertaken a study of twelve natural samples from a range of geological environments. Our results indicate that seven of the samples exhibit only minor alteration, usually located within veinlets or around the rim of the sample. The remaining five samples consist of variable amounts of unaltered and altered brannerite. Based on a total of 3 metal cations, the Ti and U contents of unaltered brannerite range from 1.8 to 2.1 and 0.4 to 0.9 atoms per formula unit (apfu), respectively. Maximum amounts of the other major cations on the A-site are 0.48 Ca, 0.22 Th, 0.14 Y, and 0.07 Ln (lanthanide = Ce, Nd, Gd, Sm) atoms pfu. Maximum values of other cations on the B-site are 0.15 Fe, 0.14 Si, 0.09 Al, 0.06 Nb, 0.04 Mn, and 0.04 Ni atoms pfu. Altered regions of brannerite contain significant amounts of Si and other elements incorporated from an aqueous fluid phase, and up to 40–90% of the original amount of U has been lost as a result of alteration. SEM-EDX results also provide evidence for TiO 2 phases, galena, and a thorite-like phase as alteration products. Electron diffraction patterns of all samples typically consist of two broad, diffuse rings that have equivalent d-spacings of 0.31 nm and 0.19 nm, indicating that brannerite is rendered completely amorphous by alpha decay damage. Many of the grains also exhibit weak diffraction spots due to fine-grained inclusions of a uranium oxide phase and galena. Using the available age data, these samples have accumulated alpha decay doses in the range of 0.7–200 × 10 16 α mg −1. Although imprecise, the U–Th–Pb chemical ages determined by microanalysis are generally consistent with the known ages and geological histories of the brannerite host rocks. To a first approximation, it is possible to understand the results of chemical and isotopic dating of brannerite by treating each sample as a complex system composed of nominally unaltered, altered, and recrystallised areas. The dominant effects are U loss from altered areas and Pb loss from unaltered brannerite and, to a lesser extent, altered brannerite, the structure of which approximates to a Ti–Si–O glass-like network wherein Pb is more comfortable as a network modifier.

Geochemistry, mineralogy and genesis of the Ayazmant Fe–Cu skarn deposit in Ayvalik, (Balikesir), Turkey

The Ayazmant Fe–Cu skarn deposit is located approximately 20 km SE of Ayvalık or 140 km N of Izmir in western Turkey. The skarn occurs at the contact between metapelites and the metabasites of the Early Triassic Kınık Formation and the porphyritic hypabyssal intrusive rocks of the Late Oligocene Kozak Intrusive Complex. The major, trace, and rare earth-element geochemical analysis of the igneous rocks indicate that they are I-type, subalkaline, calc-alkaline, metaluminous, I-type products of a high-level magma chamber, generated in a continental arc setting. The 40Ar– 39Ar isochron age obtained from biotite of hornfels is 20.3 ± 0.1 Ma, probably reflecting the age of metamorphic–bimetasomatic alteration which commenced shortly after intrusion into impure carbonates. Three stages of skarn formation and ore development are recognized: (1) Early skarn stage (Stage I) consisting mainly of garnet with grossular-rich (Gr 75–79) cores and andradite-rich (Gr 36–38) rims, diopside (Di 94–97), scapolite and magnetite; (2) sulfide-rich skarn (Stage II), dominated by chalcopyrite with magnetite, andraditic garnet (Ad 84– 89), diopside (Di 65– 75) and actinolite; and (3) retrograde alteration (Stage III) dominated by actinolite, epidote, orthoclase, phlogopite and chlorite in which sulfides are the main ore phases. 40Ar– 39Ar age data indicate that potassic alteration, synchronous or postdating magnetite–pyroxene–amphibole skarn, occurred at 20.0 ± 0.1 Ma. The high pyroxene/garnet ratio, plus the presence of scapolite in calc-silicate and associated ore paragenesis characterized by magnetite (± hematite), chalcopyrite and bornite, suggests that the bulk of the Ayazmant skarns were formed under oxidized conditions. Oxygen isotope compositions of pyroxene, magnetite and garnet of prograde skarn alteration indicate a magmatic fluid with δ 18O values between 5.4 and 9.5‰. On the basis of oxygen isotope data from mineral pairs, the early stage of prograde skarn formation is characterized by pyroxene (Di 94–97)-magnetite assemblage formed at an upper temperature limit of 576 °C. The lower temperature limit for magnetite precipitation is estimated below 300 °C, on the basis of magnetite–calcite pairs either as fracture-fillings or massive ore in recrystallized limestone-marble. The sulfide assemblage is dominated by chalcopyrite with subordinate molybdenite, pyrite, cubanite, bornite, pyrrhotite, galena, sphalerite and idaite. Gold–copper mineralization formed adjacent to andradite-dominated skarn which occurs in close proximity to the intrusion contacts. Native gold and electrum are most abundant in sulfides, as fine-grained inclusions; grain size with varying from 5 to 20 µm. Sulfur isotope compositions obtained from pyrrhotite, pyrite, chalcopyrite, sphalerite and galena form a narrow range between − 4.8 and 1.6‰, suggesting the sulfur was probably mantle-derived or leached from magmatic rocks. Geochemical data from Ayazmant shows that Cu is strongly associated with Au, Bi, Te, Se, Cd, Zn, Pb, Ni and Co. The Ayazmant mineralizing system possesses all the ingredients of a skarn system either cogenetic with, or formed prior to a porphyry Cu(Au–Mo) system. The results of this study indicate that the Aegean Region of Turkey has considerable exploration potential for both porphyry-related skarns and porphyry Cu and Au mineralization.

Annealing Time-Scale of the Cratonic Lithosphere of Southern Africa Inferred from the Shape of Inclusion Minerals

The change in shape of inclusion minerals is a time-dependent process that is controlled by grain-boundary diffusion to minimize the interfacial free energy between inclusion and host minerals. We analyzed olivine inclusions in the orthopyroxene matrix in mantle xenoliths erupted by kimberlites in the Kalahari craton, southern Africa. Most fine-grained inclusions are rounded, whereas coarse-grained ones show a polyhedral outline with slightly rounded edges. The critical radius of the largest rounded inclusion is in the size range 240-280 μm in several kimberlite suites in this craton; this corresponds to a minimum annealing time-scale of the order of billions of years, which agrees with the isotopic model ages of the mantle xenoliths. The coincidence of the annealing time-scale of the mantle xenoliths with the major age of the crust formation in this region suggests a coupled link between the formation of the Archean craton and that of the underlying lithospheric mantle.

Effects of the Li-evaporation on the Czochralski growth of γ-LiAlO 2

Two-inch-diameter γ-LiAlO 2 single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the γ-LiAlO 2 growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li 2O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50 mol% Li 2O to obtain transparent LiAlO 2 crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl 5O 8 crystallites.

Fine‐grained, spinel‐rich inclusions from the reduced CV chondrites Efremovka and Leoville: I. Mineralogy, petrology, and bulk chemistry

Abstract— Fine‐grained, spinel‐rich inclusions in the reduced CV chondrites Efremovka and Leoville consist of spinel, melilite, anorthite, Al‐diopside, and minor hibonite and perovskite; forsterite is very rare. Several CAIs are surrounded by forsterite‐rich accretionary rims. In contrast to heavily altered fine‐grained CAIs in the oxidized CV chondrite Allende, those in the reduced CVs experienced very little alteration (secondary nepheline and sodalite are rare). The Efremovka and Leoville fine‐grained CAIs are 16O‐enriched and, like their Allende counterparts, generally have volatility fractionated group II rare earth element patterns. Three out of 13 fine‐grained CAIs we studied are structurally uniform and consist of small concentrically zoned nodules having spinel ± hibonite ± perovskite cores surrounded by layers of melilite and Al‐diopside. Other fine‐grained CAIs show an overall structural zonation defined by modal mineralogy differences between the inclusion cores and mantles. The cores are melilite‐free and consist of tiny spinel ± hibonite ± perovskite grains surrounded by layers of anorthite and Al‐diopside. The mantles are calcium‐enriched, magnesium‐depleted and coarsergrained relative to the cores; they generally contain abundant melilite but have less spinel and anorthite than the cores. The bulk compositions of fine‐grained CAIs generally show significant fractionation of Al from Ca and Ti, with Ca and Ti being depleted relative to Al; they are similar to those of coarsegrained, type C igneous CAIs, and thus are reasonable candidate precursors for the latter. The finegrained CAIs originally formed as aggregates of spinel‐perovskite‐melilite ± hibonite gas‐solid condensates from a reservoir that was 16O‐enriched but depleted in the most refractory REEs. These aggregates later experienced low‐temperature gas‐solid nebular reactions with gaseous SiO and Mg to form Al‐diopside and ±anorthite. The zoned structures of many of the fine‐grained inclusions may be the result of subsequent reheating that resulted in the evaporative loss of SiO and Mg and the formation of melilite. The inferred multi‐stage formation history of fine‐grained inclusions in Efremovka and Leoville is consistent with a complex formation history of coarse‐grained CAIs in CV chondrites.