Separate Grains Research Articles

Strath development in small arid watersheds: Case study of South Mountain, Sonoran Desert, Arizona

Analyses of ephemeral granitic drainages of \<5 km^2^ at South Mountain metamorphic core complex, central Arizona, reveal a previously undocumented process of bedrock strath formation in this setting. Granitic channel banks experience a higher degree of mineral decay than that of granitic channel floors. Electron microscope observations show that grussification along the granitic channel banks occurs through abiotic processes of biotite oxidation and biotic processes associated with mycorrhizal fungi and roots of plants preferentially growing along channel banks. Digital image processing of backscattered electron microscope (BSE) images measured: (a) an enhancement of porosity along channel banks 2× to 5× greater than mid-channel positions; and (b) the gradual separation of grains over a 13-year period caused by the roots of Paloverde (*Parkinsonia microphylla*) trees. Ongoing mineral decay along banks facilitates differential erosion similar to Montgomery9s (2004) hypothesis. Ephemeral washes migrate laterally into the decayed granite of their banks and erode the distal end of bounding pediments, expanding beveled bedrock straths. Direct observations of strath widening in six drainages during three distinct flash floods reveal a range from 4 to 23 millimeters of lateral bank erosion and \<1 mm of channel bed abrasion. The widening of straths is likely limited by long-term rates of *in situ* physical separation of granitic minerals.

Influences of die structure on constrained groove pressing of commercially pure Ni sheets

Constrained groove pressing (CGP) is an attractive technique for fabricating ultra-fine grained sheet metals through intense plastic deformation. The design of groove dies is of great importance to the evolutions of microstructure and mechanical properties of materials during CGP. Thus, in this work, the effects of groove width and angle on CGP of commercially pure Ni sheets were investigated by experimental and numerical methods. The results show that an optimum combination of mechanical properties for sheet samples with a thickness of 2mm is obtained by a two-pass CGP with a groove width of 2mm and a groove angle of 45°: the yield and tensile strengths are 476.3 and 532.3MPa, respectively, the elongation to failure is 10.6%, and the average hardness is 218.9HV. In this case, numerous elongated subgrains with a mean width of about 500nm are observed and separate grains having clear boundaries and high misorientation angles begin to appear in the microstructure. CGP with a lower groove angle induces more effective passes but a lower process rate, while it enhances the shear intensity with a smaller groove width. Detailed analysis by a simplified model for flattening establishes the process conditions to maintain the stable shear deformation in CGP: an upper limit of the ratio of groove width to sample thickness is 1.25 when the groove angle is 45°, or an upper limit of groove angle is 50.8° when the ratio is 1.0. Once exceeding the limits, the deformation mode may change from pure shear to bending. Numerical and experimental results reveal that, compared with pure shear, the bending deformation is more likely to cause micro-cracks at the sheet surface due to work hardening and stress concentration. In addition, using groove dies with a width of 3mm and an angle of 45°, a rotated cubic texture {100}〈011〉 is developed from the strong cubic texture {100}〈001〉 of the annealed Ni sheets. The forming load of CGP dies shows exponential decrease with groove width but no significant variation with groove angle.

Investigation of combinatorial coevaporated thin film Cu2ZnSnS4 (II): Beneficial cation arrangement in Cu-rich growth

Cu2ZnSn(S,Se)4 (CZTSSe) is an earth-abundant semiconductor with potential for economical photovoltaic power generation at terawatt scales. In this work, we use Raman scattering to investigate phase coexistence in combinatorial CZTS thin films grown at 325 or 470 °C. The surface of the samples grown at 325 °C is rough except for a prominent specularly reflective band near and along the ZnS-Cu2SnS3 (CTS) tie line in the Cu-Zn-Sn-S quaternary phase diagram. All structurally incoherent secondary phases (SnS2, CuS) exist only as surface phases or are embedded as separate grains, whereas the structurally coherent secondary phase CTS coexists with CZTS in the dense underlying film. In films grown at 325 °C, which are kinetically trapped by the low growth temperature, a change is observed in Cu and Sn site occupancy, evidenced by the shift from cubic-CTS in the Cu-rich region (Cu/Sn &amp;gt; 2) to more tetragonal-CTS in the Sn-rich region (Cu/Sn &amp;lt; 2). For CZTS samples grown at 470 °C, CTS is not observed and regions grown under excess Sn flux are more disordered than Cu-rich regions evidenced by broader CZTS A mode peaks. Therefore, increasing Sn chemical potential results in more CZTS lattice disorder, suggesting, with other evidence, the formation of Sn antisite defects. In contrast, the CZTS A mode breadth is insensitive to Zn richness suggesting that excess Zn does not induce significant disorder within the CZTS lattice. We postulate that initially growing CZTS films Cu-rich (Cu/Sn &amp;gt; 2) results in higher cation ordering meaning fewer antisite defects.

Wear damage of cemented carbides with different combinations of WC mean grain size and Co content. Part II: Laboratory performance tests on rock cutting and drilling

In the present work we carried out laboratory performance tests of cemented carbides with very different WC grain sizes varying from nearly 0.2μm to 5μm and Co contents varying from 6 to 33wt.% in rock cutting and drilling. These tests are determined to well simulate the real operation of cemented carbides in mining and construction applications, particularly in road-planing and rock-cutting as well as in percussive drilling and rotary drilling. The major objective of the present work was to examine the wear damage, wear behavior and wear mechanisms of cemented carbides having a similar hardness but greatly varying with respect to their WC mean grain size and Co content in rock evacuation.Phenomena of micro-fatigue, micro-fracturing and micro-chipping of cemented carbides are found to play the decisive role in rock-cutting. As a result, the wear-resistance of the near-nano carbides having a reduced fracture resistance is significantly lower than that of the medium and coarse grades having similar hardness values. The major wear mechanism of the near-nano grade in rock-cutting is related to micro-cracking and micro-chipping leading to the detachment of huge WC–Co agglomerates. This is presumably a result of reduced fracture toughness of the near-nano cemented carbides containing much grain growth inhibitors, which is caused by the segregation of grain growth inhibitors at the WC–Co and WC–WC interfaces. In contrast to the near-nano grades, the major wear mechanism of the coarse grade in rock-cutting is related to wearing off the binder interlayers among the large WC grains and their micro-chipping and fragmentation.Phenomena of micro-fatigue, micro-fracturing and micro-chipping of cemented carbides also play a very important role in rock-drilling. The wear-resistance of the near-nano grade is noticeably lower than that of the corresponding straight coarse-grain grade having nearly the same hardness but significantly higher fracture resistance. As in the case of rock-cutting, the major wear mechanism of the near-nano grade in rock-drilling is related to micro-cracking and micro-chipping caused by micro-fatigue phenomena, which leads to the detachment of huge WC–Co agglomerates. In contrast to that, the following wear mechanisms take place on the surface of the medium and medium-coarse grades during percussive drilling: (1) wearing the binder among WC grains, which leaves them unsupported, (2) abrasion of the surface of the WC grains, (3) micro-chipping the WC grains, (4) detachment of separate WC grains, and (5) detachment of relatively small WC–Co fragments. There are some regions on the worn surface of the medium and medium-coarse grades, where the WC grains were presumably in direct contact with the rock during drilling (first regions), and there are some regions lying slightly below the first regions (second regions). The worn surfaces in the first regions are characterized by a significantly lower Co content (less than 1wt.%) than on average. The Co contents on the surface of the second regions, which were not presumably in direct contact with the rock when drilling, are noticeably greater and even slightly higher than the average Co content in the bulk of the medium and medium-coarse grades, therefore, the binder was not predominately worn out from the carbide surface in these regions. The second regions presumably comprise Co interlayers on the surface on underlying WC grains after the detachment of WC–Co fragments due to micro-fatigue, as there are no traces of abrasive wear on their surface. Therefore, the presence of the first and the second region on the worn surface with various Co contents is a clear indication of the completely different wear mechanisms in these two regions.

Danopolonian migmatization of Mesoproterozoic sedimentary rocks in southernmost Sweden: a SIMS zircon study

To assess the age and origin of the metasedimentary migmatites in southernmost Sweden and their relationships with the Mesoproterozoic granitoid magmatism in the area, we have dated migmatite zircon using the secondary ion mass spectrometry U–Pb method. The studied metasedimentary migmatites, here called the Nöteboda migmatites, occur along the southwestern boundary of the 1442 Ma Tåghusa granitoid intrusion in southeastern Skåne. They contain the mineral assemblage garnet+biotite ± muscovite+cordierite+sillimanite+quartz+plagioclase+K-feldspar and were formed during a retrograde evolution from c. 750–720°C and 6 kbar (peak conditions) to c. 675°C and 4 kbar. Zircon is characterized by detrital cores surrounded by U-rich rims and overgrowths. Separate rounded metamorphic grains also exist. The age probability–density distribution peaks for detrital zircon are at c. 1700, 1670, 1650, 1610, 1570 and 1530 Ma. These ages suggest Gothian orogenic rocks in the present west as the most probable principal source. Sedimentation occurred after c. 1530 Ma, the age of the youngest detrital zircon, indicating the existence of a previously unknown period of Mesoproterozoic sedimentation in southernmost Sweden. A homogeneous zircon overgrowth yielded a concordant 207Pb/206Pb age of 1439 ± 5 Ma, which dates the migmatization and is close to the age of the Tåghusa intrusion. We conclude that the burial of the sediments down to c. 20 km, their metamorphism and progressive migmatization took place concurrently with granitic magmatism, NE–SW compression, folding and shearing of the crust between 1460 and 1440 Ma during the Danopolonian orogeny.

Internal friction and evolution of ultrafine-grained structure during annealing of Grade-4 titanium subjected to severe plastic deformation

Electron microscopy, X-ray diffraction, tensile tests, and measurements of internal friction (IF) have been used to study the transformation of the structure and properties of commercial Grade-4 titanium subjected to deformation using equal-channel angular pressing combined with the Conform process (ECAP-Conform), drawing, and subsequent annealing. It has been found that the ECAP-CONFORM with drawing leads to a decrease in the grain size of titanium to about 150 nm. During annealing at 400°C for 1 h, the growth of separate grains was observed; with an increase in the annealing temperature to 450°C or higher, the growth of grains in the whole volume of a specimen occurred. It has been shown that titanium in the ultrafine-grained (UFG) state is characterized by an internal-friction peak at temperatures of 450–500°C (under the selected measurement conditions), which results from the processes of recovery and recrystallization. During repeated heating, no such effect was observed. At higher temperatures, a thermally activated relaxation internal-friction peak was found, which appears to be a grain-boundary internal-friction peak.

Structure and magnetic properties of ultra thin textured EuO films on graphene

We present a straightforward and reproducible method to grow stoichiometric and single phase (100) textured EuO thin films on epitaxial graphene. Depending on coverage, either separated EuO grains or fully closed layers can be prepared. Room temperature preparation followed by annealing in Eu vapor leads to a random distribution of the in-plane orientation, whereas growth under distillation conditions at 720 K induces a fixed orientation with respect to the substrate. Magneto-optical Kerr effect (MOKE) shows that the films are ferromagnetic with an enhanced Curie temperature.

Glacial dispersal and mode of occurrence of metals in till and esker gravel at Kumpuselkä, northern Finland

A Cu-Zn-Pb-Au mineralized quartz-carbonate vein within micaceous schist recently exposed in a gravel pit quarried into the Kumpuselkä esker (Finland) was the impetus of this study, which examines the glacial dispersal of metals in the nearby Quaternary deposits. The oldest ice flow direction in the area was to the SE–SSE, the younger flow in the ice lobe phase to the ESE and the youngest flow to the ENE. Five till and three esker gravel samples were taken for geochemical and heavy mineral studies. The concentrations of base metals in the conventional fine fraction analysis of the till samples are at background level although the samples had been taken from the very proximal part of the glacial dispersal train. Copper and Pb contents in the fine fraction of esker gravel are at higher levels than those in till fines. Base metal sulphides as chalcopyrite, sphalerite, galena and pyrite were found as some separate grains in the heavy mineral concentrates of till. More often, the Cu, Zn and Pb sulphides occur as tiny inclusions in the coarse pyrite grains. Heavy mineral concentrates of the esker gravel contain abundant pyrite grains, but no visible Cu, Zn or Pb sulphides were recovered. In one heavy mineral concentrate of till (KUM 4), Ni-bearing cobaltite and Co-bearing arsenopyrite along with pyrite, chalcopyrite and sphalerite were found. Sulphide minerals have survived even within the upper C-horizon of the till above the groundwater level and therefore sulphide minerals can be used for prospecting sulphide ores by indicator mineral methods. Some chromite grains were also found in the heavy mineral concentrates of the till samples. Their presence reflects multi-phase, long-distance glacial transport (100 km) of the older till material which have subsequently been inherited by the younger till.

Natural age dispersion arising from the analysis of broken crystals. Part I: Theoretical basis and implications for the apatite (U–Th)/He thermochronometer

Over the last decade major progress has been made in developing both the theoretical and practical aspects of apatite (U–Th)/He thermochronometry and it is now standard practice, and generally seen as best practice, to analyse single grain aliquots. These individual prismatic crystals are often broken and are fragments of larger crystals that have broken during mineral separation along the weak basal cleavage in apatite. This is clearly indicated by the common occurrence of only 1 or no clear crystal terminations present on separated apatite grains, and evidence of freshly broken ends when grains are viewed using a scanning electron microscope. This matters because if the 4He distribution within the whole grain is not homogeneous, because of partial loss due to thermal diffusion for example, then the fragments will all yield ages different from each other and from the whole grain age. Here we use a numerical model with a finite cylinder geometry to approximate 4He ingrowth and thermal diffusion within hexagonal prismatic apatite crystals. This is used to quantify the amount and patterns of inherent, natural age dispersion that arises from analysing broken crystals. A series of systematic numerical experiments were conducted to explore and quantify the pattern and behaviour of this source of dispersion using a set of 5 simple thermal histories that represent a range of plausible geological scenarios. In addition some more complex numerical experiments were run to investigate the pattern and behaviour of grain dispersion seen in several real data sets. The results indicate that natural dispersion of a set of single fragment ages (defined as the range divided by the mean) arising from fragmentation alone varies from c. 7% even for rapid (c. 10°C/Ma), monotonic cooling to over 50% for protracted, complex histories that cause significant diffusional loss of 4He. The magnitude of dispersion arising from fragmentation scales with the grain cylindrical radius, and is of a similar magnitude to dispersion expected from differences in absolute grain size alone (spherical equivalent radii of 40–150μm). This source of dispersion is significant compared with typical analytical uncertainties on individual grain analyses (c. 6%) and standard deviations on multiple grain analyses from a single sample (c. 10–20%). Where there is a significant difference in the U and Th concentration of individual grains (eU), the effect of radiation damage accumulation on 4He diffusivity (assessed using the RDAAM model of Flowers et al. (2009)) is the primary cause of dispersion for samples that have experienced a protracted thermal history, and can cause dispersion in excess of 100% for realistic ranges of eU concentration (i.e. 5–100ppm). Expected natural dispersion arising from the combined effects of reasonable variations in grain size (radii 40–125μm), eU concentration (5–150ppm) and fragmentation would typically exceed 100% for complex thermal histories. In addition to adding a significant component of natural dispersion to analyses, the effect of fragmentation also acts to decouple and corrupt expected correlations between grain ages and absolute grain size and to a lesser extent between grain age and effective uranium concentration (eU). Considering fragmentation explicitly as a source of dispersion and analysing how the different sources of natural dispersion all interact with each other provides a quantitative framework for understanding patterns of dispersion that otherwise appear chaotic. An important outcome of these numerical experiments is that they demonstrate that the pattern of age dispersion arising from fragmentation mimics the pattern of 4He distribution within the whole grains, thus providing an important source of information about the thermal history of the sample. We suggest that if the primary focus of a study is to extract the thermal history information from (U–Th)/He analyses then sampling and analytical strategies should aim to maximise the natural dispersion of grain ages, not minimise it, and should aim to analyse circa 20–30 grains from each sample. The key observations and conclusions drawn here are directly applicable to other thermochronometers, such as the apatite, rutile and titanite U–Pb systems, where the diffusion domain is approximated by the physical grain size.

Microstructure and magnetic properties of FePt(B4C) and FePt(B4C–Ag) granular films with perpendicular magnetization

Abstract Multilayers [FePt/B 4 C ( t nm)] 10 ( t = 0–0.4) and [FePt/(B 4 C) y Ag 1− y (0.1 nm)] 10 ( y = 0.2–0.8) films were deposited on a glass substrate and subsequently annealed by a rapid thermal process (RTP) at 800 °C for 3 min. After RTP, the granular FePt(B 4 C) and FePt(B 4 C–Ag) films with perpendicular magnetization were formed. The FePt grains were interconnected in FePt(B 4 C) films and further broken into the small round grains in FePt(B 4 C–Ag) films. In FePt(B 4 C) films, the maze-like structure with worm shape FePt grains but the grains boundaries were still defined. The granular structure with well defined boundaries was formed when the minor Ag was added to partial replace B 4 C. The immiscible (B 4 C, Ag) were demonstrated as segregant to separate FePt grains without affecting c -axis alignment. The FePt grains were separated uniformly with size distribution 19% and the average grains size was 13.5 nm in (Fe 0.48 Pt 0.52 ) 90 [(B 4 C) 0.6 Ag 0.4 )] 10 film. The average grains size of FePt was 10. 6 nm in (Fe 0.48 Pt 0.52 ) 90 [(B 4 C) 0.2 Ag 0.8 )] 10 film. The grains were more distanced and show magnetostatic coupling.

Schlegel description of grain form evolution in grain growth

The paths of evolution of topological grain forms during grain growth are described in terms of number of faces, edges per face and face arrangements, as depicted by Schlegel diagrams and the topological events that change them. This “Schlegel tree” describes transitions to higher face classes by grain encounters at corners and to lower face classes by grain-pair separation at three-edged faces. Transitions within face classes are described through rearrangements that occur to neighboring grains during these events. The process is further described by probabilities of the different paths in terms of numbers of edges, corners and three-edged faces at which face gain and loss events occur. Schlegel data from separated grains and three-dimensional Monte Carlo and front-tracking simulations show good comparison. Grain form frequencies increase with increasing number of transition paths into them from other forms. The highest frequency forms have few or no three-edged faces, while those with the most three-edged faces are present the least. These observations suggest that three-edged faces are catalysts for topological change, and forms with higher frequencies of these have shorter residence times before transitioning to lower classes.

Experimental simulation of orthopyroxene enrichment and carbonation in the suprasubduction mantle under the influence of H2O, CO2, and SiO2

Thermal and chemical gradients at the boundary of a subducting plate and suprasubduction mantle lead to a variety of poorly understood geologic processes. This paper reports the results of experiments simulating interaction between olivine (Ol, mantle analog) and carbonated glaucophane schist (Gls, analog of the upper layer of the subducted crust) under the P-t conditions of a ‘hot’ subduction zone. The experiments were carried out at a pressure of P = 25 kbar under temperature gradient conditions (tminGls = 720°C and tmaxOl = 1000°C) and at a constant temperature of t = 800°C corresponding to the boundary between the materials in the gradient experiment. A comparison of experimental data obtained using two different methods showed that the temperature gradient experiment reproduced the character of schist-olivine interaction under isothermal conditions and provided additional information on the effect of temperature on mineral reactions. Orthopyroxene occurs in the experimental products in different textural positions, forming a layer (with or without magnesite) at the base of the olivine zone or separate grains and intergrowths with magnesite at the boundary of olivine grains. The development of orthopyroxene and carbonate redeposition are described by reactions between olivine and aqueous fluid components, SiO2 and CO2, at \(a_{SiO_2 } = 0.23\) and \(a_{CO_2 } = 0.07\). The calculated silica content in the fluid under such thermodynamic conditions is 0.39 mol/kg H2O. Given these parameters, the estimated SiO2 flux at a depth of ∼80 km from the downgoing slab of the Cascadia subduction zone in the northwester United States is 180 t/yr at a very moderate (for the considered depth level) aqueous fluid flux of one million moles per year per kilometer. Modern concepts on convective flows initiated by a subducting slab in the mantle wedge allow us to suggest that orthopyroxene-enriched ultramafic rocks must occur both above the areas of the release of volatile components and silica from the slab and at deeper levels of subduction zones.

Bandgap in Al1−xScxN

Aluminum scandium nitride (Al1−xScxN) layers deposited by reactive magnetron co-sputtering on sapphire 0001 substrates at 850 °C are epitaxial single-crystals for x ≤ 0.20. Their in-plane lattice constant increases linearly (3.111 + 0.744x Å) while the out-of-plane constant remains at 4.989 ± 0.005 Å. Optical absorption indicates a band gap of 6.15–9.32x eV and a linearly increasing density of defect states within the gap. The average bond angle decreases linearly with x, suggesting a trend towards the metastable hexagonal-ScN structure. However, an anomalous decrease at x = 0.20 indicates a structural instability which ultimately leads to phase separated rock-salt ScN grains for x &amp;gt; 0.4.

Model of garnet oxygen barometer for mantle peridotites and potential diamodiferous ability estimation on its basis

191 The elaboration of monomineral thermobarome ters based on the composition of one phase is a chal lenging task in modern petrology. This is because xenoliths are lacking or rare, and only xenocrysts are available in many mantle derived rocks. Prospecting and exploration for diamonds are commonly con ducted with separate grains of mantle derived associ ated minerals. The estimation of their formation oxy gen fugacity is important both for theoretical petrol ogy and applied purposes. Nowday the oxygen fugacity estimation sensors for garnet olivine orthopyroxene parageneses are known [8, 10]. There is a model of garnet olivine orthopy roxene oxybarometer [4, 10] based on the equilibrium from [2]:

Geology, mineralogy, and genesis of PGE mineralization in the South Sopcha massif, Monchegorsk complex, Russia

New data are reported on the localization and genesis of PGE mineralization at the South Sopcha deposit situated in the southern framework of the Monchegorsk pluton. Disseminated PGE-Cu-Ni mineralization, the thickness of which in particular boreholes exceeds 100 m, is hosted in the zone of alternating peridotite, pyroxenite, norite, and gabbronorite. The PGE grade does not exceed 1–2 gpt with Pd/Pt = 3–4 at Ni and Cu contents from 0.2 to 1.5 wt %. The PGE contents up to 4–6 gpt and Pd/Pt = 4–8 are noted at local sites of hydrothermally altered rocks. Another type of PGE mineralization is established in the outcrops of the southeastern marginal group of the massif. Pyroxenite, norite, and gabbronorite fragments are incorporated here in the gabbroic matrix, making up a complex zone of magmatic breccia complicated by mylonites and late injections. Elevated PGE contents (1.0–6.5 gpt) are detected in all types of rocks in the zone of brecciation, mainly in the matrix. Platinum-group minerals (PGM) occur in association with magmatic and late sulfides, amphibole, mica, and chlorite. PGM vary in composition depending on the petrographic features of rocks. In rocks of the layered series and in pegmatoid pyroxenite PGM are extremely diverse comprising PGE compounds with As, Sb, Bi, Te, Se, and S. In the brecciated rocks of the marginal group, Pd bismuthotellurides (mainly merenskyite), sperrylite, hollingworthite, and Pd- and Rh-bearing cobaltite and gersdorffite are predominant. The PGE mineralization in rocks of the layered series and pegmatoid pyroxenite was formed from the magmatic melt enriched in volatiles and with subsequent transformation of PGE assemblages under the influence of hydrothermal fluids at a lower temperature. In gabbroic rocks of the marginal group, PGM are associated with the latest sulfides (chalcopyrite, bornite, chalcocite), forming separate grains and thin veinlets in hydrothermally altered rocks. The gabbroic melt affected incompletely crystallized rocks of the layered series by formation of contact-type PGE mineralization, deposition and redeposition of ore matter.

A new garnet thermometer for mantle peridotites and estimation of the diamond potential on its basis

The elaboration of monomineral thermobarome� ters based on the composition of one phase is a chal� lenging task in modern petrology. This is because xenoliths are lacking or rare, and only xenocrysts are available in many mantlederived rocks. Prospecting and exploration for diamonds are commonly con� ducted with separate grains of mantlederived associ� ated minerals. The estimation of their formation tem� perature is important both for theoretical petrology and applied purposes. The methods of temperature estimation by nickel concentration in garnet are known (13); however, their application requires addi� tional expensive ion-proton analyses.

The 40Ar/39Ar and Rb–Sr chronology of the Precambrian Aksu blueschists in western China

Three metapelite samples from the Aksu blueschist terrane, Xinjiang, China, were dated by the 40Ar/39Ar method on separated phengite grains, obtaining plateau ages in the range of 741−757Ma. In contrast, the measured Rb and Sr isotope data for the three samples yielded isochron ages ranging from 630Ma to 900Ma, suggesting large heterogeneity in the blueschist protolith and suppression of diffusional exchange owing to the low-temperature metamorphic conditions. Because the protolith of Aksu blueschist is composed of oceanic materials that formed 40Ar-free phengite during HP and UHP metamorphism and the apparent 40Ar/39Ar plateaus ages in this study are similar to previous K–Ar and Rb–Sr ages, the existence of excess argon in these rocks is considered to be insignificant. As a result, the 40Ar/39Ar plateau ages in this study (ca. 750Ma) likely represent the approximate time for peak metamorphism, given the low peak metamorphic temperatures for the Aksu blueschist terrane (300−400°C). This strongly implies that modern style, cold subduction tectonics operated along the margin of the Aksu terrane no later than 750Ma, in Neoproterozoic time.

Effect of large strain cold rolling and subsequent annealing on microstructure and mechanical properties of an austenitic stainless steel

Abstract The microstructural evolution of an S304H steel during bar rolling to a strain of 4 and subsequent annealing as well as its effect on the mechanical properties were investigated. The cold working was accompanied by a strain-induced martensitic transformation, leading to the development of lamellar-type microstructure consisting of highly elongated austenite/ferrite subgrains with a mean transverse size of approximately 50 nm; the austenite volume fraction was approximately 0.35. This material exhibited a yield strength above 2000 MPa. The subsequent annealing resulted in grain coarsening following the ferrite → austenite reversion, which led to almost full austenitization at temperatures above 700 °C. The formation of the austenite/ferrite lamellar structure that mixed with separate equiaxed grains occurred after annealing at temperatures of T ≤ 700 °C. The grain coarsening was accompanied by a degradation in strength, although the yield strength of above 1000 MPa remained after 2 h of annealing at 700 °C. The discontinuous recrystallization of austenite resulted in the development of a relatively coarse-grained microstructure at T ≥ 800 °C.

Multiple age components in individual molybdenite grains

Re–Os geochronology of fractions composed of unsized, coarse, and fine molybdenite from a pod of unusual monazite–xenotime gneiss within a granulite facies paragneiss, Hudson Highlands, NY, yielded dates of 950.5±2.5, 953.8±2.6, and 941.2±2.6Ma, respectively. These dates are not recorded by co-existing zircon, monazite, or xenotime. SEM–BSE imagery of thin sections and separated grains reveals that most molybdenite grains are composed of core and rim plates that are approximately perpendicular. Rim material invaded cores, forming irregular contacts, probably reflecting dissolution/reprecipitation. EPMA and LA-ICP-MS analyses show that cores and rims have different trace element concentrations (for example, cores are relatively enriched in W). On the basis of inclusions of zircon with metamorphic overgrowths, we conclude that molybdenite cores and rims formed after high-grade regional metamorphism. The discovery of cores and rims in individual molybdenite grains is analogous to multi-component U-Pb geochronometers such as zircon, monazite, and titanite; thus, molybdenite should be carefully examined before dating to ensure that the requirement of age homogeneity is fulfilled.

Comparative Study of the Nutritional Value of Four Types of Egyptian Palm Pollens

Pollen grains are good sources of vitamins, minerals and amino acids with a high nutritional value that can be used as human food supplement. Date palm pollens are used in the Middle East especially Egypt in herbal mixtures as a folk medicine remedy for curing male infertility and promoting fertility in women .The raw materials purchased from the market are found to be a mixture of several palm pollens. The main objective of this study was to determine the nutritional value of four local Egyptian date pollen grains {Amhat(A), Hiani(H), Sewy(S)&amp; Zaghlol(Z)} by microscopical and chemical means. These differences could determine the quality of separate pollen grains and show to what extent they affect the quality of the natural products manufactured from them? Each of the pollen samples were treated identically: collected from locations of similar clay loamy soils, in March 2011 at an early time of the day, subjected to electron microscope examination and chemical analysis of trace elements, amino acids &amp; vitamins. The results showed that there are clear differences in the quality of the four Egyptian palm pollens which could be distinguished microscopically and chemically by the percentage of the trace elements, amino acids &amp; vitamins.