Melt Depth Research Articles

Detrital zircon evidence for change in geodynamic regime of continental crust formation 3.7–3.6 billion years ago

The nature of the early terrestrial crust and how it evolved through time remains highly controversial. Whether conventional plate tectonics operated in the Hadean and early Archean and when it came into existence remains unclear. Here, we describe U-Pb ages, Hf isotope composition and trace element chemistry of 3.95–3.10 Ga old detrital zircons from the Singhbhum Craton in eastern India. The >3.7 Ga old zircons of this suite have crust-like Hf isotope compositions with strongly negative εHfi and their granitoid sources formed by intra-crustal reworking of a Hadean protolith that was extracted from primitive mantle at 4.4–4.5 Ga. The trace element and Hf isotope compositions of the zircons record a transition from higher Nb/Th (0.070 ± 0.010), Nb/U (0.045 ± 0.005), crust-like Hf isotope compositions, and longer crustal residence times of the protoliths prior to 3.7–3.6 Ga, to lower Nb/Th (0.032 ± 0.012), Nb/U (0.024 ± 0.009; 1σ), mantle-like Hf isotope compositions, and shorter protolith residence times post 3.7–3.6 Ga. The Nb/Th and Nb/U fractionation at 3.7 Ga seen in the detrital zircon record can be explained by transition to granitoid production at greater depths in an oceanic plateau-like regime. However, had that been the case, the crustal residence times of the protoliths of the granitoids from which the detrital zircons were sourced should have progressively increased with time, given the >1.1 billion years protracted history of granitoid magmatism in the craton, which is contrary to what is observed. We suggest that the changes in the granitoid chemistry recorded by the detrital zircons document a significant change in the depth of melting of the protoliths as well as in the tectonic setting of continental crust formation, and argue that it marks the transition to granitoid production from oceanic plateaus to arc-like tectonic environments. Broadly similar transitions at ca. 3.6 Ga have been documented in gneisses from the Acasta Gneiss Complex, the Jack Hills zircons and in detrital zircons from the Wyoming Province, which suggest that the end of the Eoarchean may have been marked by widespread transition in planetary tectonic regime.

Dopant Activation of In Situ Phosphorus‐Doped Silicon Using Multi‐Pulse Nanosecond Laser Annealing

In situ phosphorus‐doped epitaxial silicon films have attracted significant attention as source and drain materials because low specific contact resistivities have been achieved on such films by increasing the active carrier concentration using millisecond laser annealing. However, the active phosphorus concentration that can be achieved using millisecond laser annealing is much less than the incorporated concentration. To increase the activation efficiency, nanosecond laser annealing with a dwell time ≈104 times shorter than that of millisecond laser annealing is investigated and the diffusion, strain, microstructure, and electrical properties of single‐ and multipulse nanosecond laser‐annealed samples are examined. The melting depth simulation classifies the energy density regions and explains the limited diffusion in nanosecond laser annealing. After multipulse nanosecond laser annealing, more phosphorus is activated without diffusion than by millisecond laser annealing. Moreover, almost all the incorporated phosphorus atoms are activated by the nanosecond laser, which melts in situ phosphorus‐doped epitaxial silicon films without major strain loss. The increased active carrier concentration presents an opportunity to achieve low contact resistivity characteristics.

Prediction of Preheating Temperatures for S690QL High Strength Steel Using FEM-Simulation for High Power Laser Welding

This study investigates a method for predicting the effect of preheating temperatures on the resulting hardness for high power laser welding of high strength steel. An FEM model is introduced containing a hardness calculation based on an existing model. Moreover, the hardness values of experimental results have been measured in order to show the performance of the model. The hardness calculation requires the chemical composition and the t8/5-time at the point of measurement. It is claimed that a calibration of the melt pool width and depth at room temperature only is enough to get reasonable results from the FEM-model for higher preheating temperatures. From the experimental result of a single experiment the width of a weld seam and the depth was deducted. In this study experiments have been done at various preheating temperatures in order to show the correlation between the model and the experimental results at various temperatures. The hardness equation provides suitable results in the verification with the measurements. The prediction of preheating temperature can be done with the resulting t8/5-time of the FEM-model. This method can decrease the amount of time and costs within a production according to testing and analyzing a matrix of process parameters. Moreover it is concluded that this methodology might be used for single item production.

Phase petrographic, thermobarometric and petrochemical significance of Cretaceous mafic dykes along Nongchram Fault Zone of Swangkre–Rongmil area of Shillong plateau, NE India: Implications for genetic link to Kerguelen mantle plume

The present study elucidates the phase petrographic and petrochemical signatures of a group of Cretaceous mafic dykes emplaced in the Precambrian gneissic basement complex in the western part of the Shillong plateau, NE India, in order to trace their petrological, geotectonic, geothermobarometric and oxybarometric status. The whole rock geochemistry discriminates the dykes as basaltic andesites and basaltic trachyandesites genetically related to each other and derived from common parent magma. The enrichment in LREE relative to HREE and HFSE, systematic Nb anomalies, moderate MREE to HREE fractionation suggests variable depths of melting of slightly enriched mantle source in the garnet stability field. As per geochemical modelling, the studied dykes are derived by 3–5% non-modal batch melting of garnet peridotite source at melting depth of ~65–80 km. The clinopyroxene thermobarometry reveals a temperature span of 1250–800°C and < 2 kb pressure of crystallization for the dykes. The oxygen fugacity (16.82–18.25) indicates extremely reducing conditions at the time of cooling. The very good correlation of petrochemical and phase chemical data with Kerguelen plume derived Rajmahal Group II basalt, Sylhet volcanics and some ODP (ocean drilling project) sites from Kerguelen basalts implicate a genetic link of the studied dykes with Kerguelen mantle plume. Finally, the present study deciphers subalkaline nature of the studied dyke rocks that have been generated by tholeiitic magmas probably in an anorogenic extensional environment. But we need more geochemical data especially good isotope geochronologic data to get a clear picture of the studied dyke.

Influence of cusp magnetic field configuration on K-TIG welding arc penetration behavior

Experiments have been carried out to test the improving effect of the cusp magnetic field to K-TIG arc penetration ability. The cusp magnetic field was generated with permanent magnets, the configuration parameters, including pole angle and field direction, were changed. Stationary welding experiments were carried out to measure the melting zone and the melting depth. After compressed with the cusp magnetic field, the anode melting zone changed from a circular shape to an ellipse shape, and the melting zone area was reduced. When the magnetic field direction was perpendicular to the arc column, the constraint effect was better than that when the magnetic field direction was parallel. Arc pressure distributions were experimental measured. Magnetic field with smaller pole angle has better constraint effect to the arc in the aspects of smaller melting zone area, increased melting depth, arc voltage and peak value of the arc pressure. These results indicated that the additional cusp magnetic field with less pole angle could further improve the penetration ability of the K-TIG arc.

Generation and maturation of Mesoarchean continental crust in the Anshan Complex, North China Craton

The mechanisms underlying the generation of tonalite–trondhjemite–granodiorite suites and the transition to K-rich granitoids, which marks the most profound stage of Archean intracrustal differentiation, remain controversial. The Archean Anshan Complex (AAC) of the North China Craton (NCC) preserves diverse 3.8–2.5 Ga granitoids, providing an excellent opportunity to address these problems. We conducted a detailed field, petrological, geochemical, and zircon isotopic study on AAC units, demonstrating that: (1) the Li–Dong–Ying trondhjemite intrudes and encloses ca. 3.3 Ga gneiss–migmatite complex across the Anshan, and crystallized at ca. 3.14 Ga; and (2) the porphyritic and fine-grained Chentaigou monzogranites were emplaced contemporaneously with the trondhjemite, both at ca. 3.14 Ga.The Li–Dong–Ying trondhjemites show high SiO2, Na2O, low MgO, significant variations in Sr, Y, and Yb, REE fractionation (LaN/YbN = 9–140), and variable Eu anomalies (Eu/Eu* = 0.4–1.3). The magmatic zircons yield δ18O of +4.8 ± 0.2‰ to +6.9 ± 0.4‰ and initial εHf of −1.1 ± 0.7 to +4.4 ± 0.9, which translate to TDM ages of 3.6–3.3 Ga. The Chentaigou monzogranites have higher SiO2 and K2O, lower Na2O and CaO, similar δ18O of +5.1 ± 0.3‰ to +7.0 ± 0.3‰, and more negative Eu anomalies as compared with the trondhjemites. The Hf–O isotopes, geochemistry, particularly considerable variations in pressure-sensitive proxies of the trondhjemites, suggest that they were derived by melting of low-temperature altered basaltic rocks at 1.0–1.5 GPa and 900–950 °C, leaving a garnet amphibolite residue with variable amounts of plagioclase but no rutile; the most plausible source is ca. 3.3 Ga basaltic rocks. Polybaric melting of basaltic sources and fractionation of hornblende and plagioclase from trondhjemitic magmas account for the chemical variability of AAC granitoids, providing a mechanism for the coeval emplacement of diverse Archean granitoids. Secular compositional changes in AAC trondhjemites imply that the depth and interval of melting of basaltic sources increased from the Eoarchean to Mesoarchean. Changes in the nature of the source and melting depth characterized the early stage of Archean intracrustal differentiation in the NCC.

Real–time prediction of penetration depths of laser surface melting based on coaxial visual monitoring

Laser surface melting (LSM) is an important laser processing technique that can be used in laser conduction welding, laser remelting, and defect elimination. Penetration depths are essential to determine LSM qualities. To enhance the ability to predict penetration depths, a real-time prediction method based on coaxial visual characteristics and the convection state of a molten pool is reported. First, the coaxial visual characteristics of the molten pool are analyzed, and its image is divided into convection, transition, and boundary regions. Based on these region characteristics, the convection state can be indicated. Then, the relationships among process parameters, coaxial visual characteristics, and penetration depths are presented. Finally, we attempt to predict the penetration depths based on these coaxial visual characteristics. The results show that the convection region characteristics are more sensitive to the changes in process parameters. The oscillation amplitude of the convection region can be considered monitored objects to indicate the convection state. The convection region can predict the penetration depths better than the entire molten pool. Furthermore, this work will be beneficial to understanding the experimental phenomenon and enhance the monitoring ability of other laser processing techniques, such as laser alloying, laser cladding, and laser-based additive manufacturing.

Neoarchean arc basaltic magmatism and associated sulfide mineralization in the North China Craton: Evidence from the Taoke mafic-ultramafic complex in Shandong Province

The Neoarchean Taoke mafic-ultramafic complex is located in the eastern block of the North China Craton. We report the first geochronological and geochemical data for the complex, and use these data to unravel the fundamental tectonic-magmatic processes involved in the formation of this complex. The Taoke complex comprises a large elongated gabbronorite intrusion, a small sulfide-mineralized olivine websterite body in the center, and many dolerite dikes. The U-Pb isotope ages of magmatic zircon from the mafic and ultramafic intrusions are 2520.3 ± 6.5 Ma and 2537 ± 12 Ma, respectively, which are contemporaneous with abundant granitoids and boninitic basalts but ~620 myr older than the collision-related, granulite-facies metamorphism in the region. Like the coeval boninitic basalts, the Taoke mafic-ultramafic rocks are characterized by light-REE enrichments and negative Nb-Ta anomalies, which are characteristic of modern arc basalts. The εNd(t) values of the Taoke mafic-ultramafic rocks are from 1.0 to 3.3, within the range of the coeval basalts in the region. The εHf(t) values of zircon from the Taoke mafic-ultramafic complex are from 0.2 to 2.3. The integrated Nd-Hf isotope data indicate that crustal contamination is absent to negligible. No correlation between Th/Nb ratios and εNd(t) values are present, implying that the negative Nb-Ta anomalies of these rocks are not the result of crustal contamination but are original features of the magma. Our new data support the interpretation that the complex is a Neoarchean arc-type mafic-ultramafic complex. Liquid inversion using the La/Yb and Gd/Yb ratios of the associated dolerite dikes and coeval boninitic basalts indicates a garnet-bearing lherzolite mantle source. The depth of partial melting is estimated to be >85 km, which is within the range of mafic magma generation in modern arc settings. The results from this study demonstrate that by Neoarchean the style of arc basaltic magmatism already closely resembled the modern counterpart. Based on the presence of sulfide mineralization in the Neoarchean arc-type mafic-ultramafic complex at Taoke and the association of major magmatic Ni-Cu sulfide ore deposits with post-Archean arc-type mafic-ultramafic complexes elsewhere in the world, we suggest that exploration for this type of deposit in the Neoarchean arc-type mafic-ultramafic complexes including the Taoke complex in western Shandong, should continue.

Discrimination of molten pool penetration based on genetic algorithm optimization of BP neural network

The metal spatter and light intensity of CO2 welding in the vicinity of the melt pool during the short transition of the melt droplet seriously affect the realtime and reliability of weld feature extraction. The mapping relationship between welding pool characteristic parameters and melting depth is established by using BP neural network optimized by genetic algorithm. The results show that the training results and test results of the optimized BP neural network model of genetic algorithm have little error and meet the requirements of precision. The model can well reflect the relationship between the melting depth and the characteristic parameters of the melting pool.

Numerical prediction of solid-liquid front during laser melting of fused quartz

A 2-D transient model is explored for knowing the process of melting with laser in a Fused Quartz work piece. The work piece is irradiated with a single Gaussian laser pulse. The temporal variation is trapezoidal in nature. The laser source is considered as volumetric instead of surface laser source to match more closely with experiment. The convection and radiation heat losses are considered from the irradiated surface. By using the FVM (Finite Volume Method), the energy equation is discretized. The resulting algebraic equation is explained with the help of Tridiagonal matrix algorithm (TDMA) and it is to find the temperature field in the work piece. To capture the solid liquid front during the melting process the enthalpy-porosity method is used. With the help of available experimental results, the temperature field obtained is validated and a good agreement is found. The temperature field, the progress of the solid liquid front at different heating times and the melt depth is analysed to control the melting with laser intensity value.

A huzalelektródás aktív védőgázos ívhegesztés korszerű eljárásváltozatainak összehasonlítása varratgeometria alapján

In the present work I present the results obtained by investigating the influence of different pulse modes (pulse, double pulse) and the welding parameters in case of gas metal arc welding. Two different welding machines were used in the tests. In both devices, the same material transitions were selected as far as possible and their effect on the joint was investigated. The base material, the filler material and the gas mixture were same in every case. The relationship between metal transfer modes, welding parameters and weld geometry characteristics (external and internal form factor, melt depth, weld width) has been revealed.

Scaling melt pool geometry over a wide range of laser scanning speeds during laser-based Powder Bed Fusion

Generating dense parts from laser-based Powder Bed Fusion of metals often requires the adaption of laser scanning speed. Thereby, scanning speed is lost as a degree of freedom for tailoring the microstructure. This paper addresses this issue by using an analytical model from literature to achieve equal melt pool width and depth for a range of factor 12 for laser scanning speeds and by examining the resulting specimen densities for this range of scanning speeds. The melt pool width and the melt pool depth of a dense reference specimen are measured. The measured melt pool width and melt pool depth are defined as the target sizes of the melt pool for all examined scanning speeds, as this is expected to result in dense specimens from a geometrical point of view. The target size shall be achieved by using an analytical model from the literature. This strategy is chosen to estimate the necessary energy input for creating dense specimens while avoiding incomplete fusion and keyholing. Defects mechanisms like splatters and cracks are excluded from this initial examination.

ГЕТЕРОГЕННОЕ СТРОЕНИЕ ПОЛИГОНАЛЬНО-ЖИЛЬНЫХ ЛЬДОВ В ТОРФЯНИКАХ ПУР-ТАЗОВСКОГО МЕЖДУРЕЧЬЯ

Structure of arctic peatlands with massive ice and structure-forming ice were studied in drained lake («khasyrey») of the Pur-Taz interfluves (the north of West Siberia). The period of accumulation of two-meter thickness of the peat was established to be changed from 8413±90 to 897±90 years BP. Composition of the peat deposits is represented by Betula nana, Sphagnum sp., Vaccinium oxycoccos, Eriophorum sp., Equisetum sp. The massive ice is represented by ice wedges with large shoulders and young ice wedges. The central part of the ice wedge is composed by recrystallized crystals of ice veins. Melting zones (elongated crystals of segregated ice and closed-cavity ice) were found in the shoulders of the ice wedge and in the upper part of the young ice wedge. Young ice wedges in the central and lateral parts the main wedge have a similar structure in the cross-section, but they are built by different genetic types of ice: the ice veins or closed-cavity ice with segregated ice. Ice-rich peat contains different types of ice inclusions and subhorizontal ice belts and ice lenses. Ice lenses in the peat can be formed by the segregated ice and/or infiltrated-segregated ice. The hydrochemical composition of the ice wedges, ice lenses, surface water samples and the aqueous extract from peat was analyzed. Hydrochemical analysis did show that polygonal-core ice has basically similar composition with the present-day atmospheric precipitation and surface waters of the polygonal bath; in the area of the shoulder – the composition is intermediate between the ground waters of peat and the central part of the vein. The hydrochemical composition of the ice lenses is similar to the composition of the lake water and peat underlying the active layer. The methane concentrations and its distribution within the ice wedges, peat and lens ice were determined. The closed-cavity ice doesn’t contain methane; the ice wedges with ice veins have minimal methane concentrations; large ice lenses have differentiation of methane concentrations. High concentrations of methane are typical for the frozen peat with inclusions of closed-cavity ice in the uppermost part of permafrost layer; the maximum methane concentration was determined inside the peat with ice lenses. The heterogeneous ices inside the ice wedges, distribution of hydrochemical compounds and methane distribution were conditioned by dynamics of the melting depth during the peatland formation under changing climate of the Holocene in the Arctic.

Garnet fractionation, progressive melt loss and bulk composition variations in anatectic metabasites: Complications for interpreting the geodynamic significance of TTGs

Tonalite-trondhjemite-granodiorite (TTG) suites constitute a large proportion of the Archean geological record; however, the geodynamic processes that generated them, and Archean continental crust in general, remain a subject of debate. The concentrations and ratios of Sr, Y, La, Yb, Nb, and Ta in TTGs are commonly used to determine the depth of melting of their metabasic sources. The trace element composition of melt produced by metabasic source rocks during anatexis is strongly affected by the presence and abundance of pressure-sensitive minerals, such as plagioclase (Sr-bearing), garnet (Y- and HREE-bearing), and rutile (Nb- and Ta-bearing). Elevated Sr/Y and La/Yb ratios and low concentrations of Nb and Ta in TTGs are generally considered to indicate melting at high pressures (≥2.0 ​GPa). The depth of melting is a key factor in determining the origin of TTGs as this provides critical information on the tectonic setting of their generation. We use phase equilibrium and trace element modelling to explore the effects of three potential influences on TTG trace element compositions: fractionation of trace elements into peritectic garnet cores, progressive melt loss from the source, and source bulk composition. We model three different compositions of Archean basalts along thermal gradients of 500 ​°C/GPa, 750 ​°C/GPa, and 1000 ​°C/GPa. The models produce major and trace element melt compositions that are generally consistent with measured compositions of TTGs. Although Sr/Y, La/Yb, Nb, and Ta exhibit pressure-dependent behaviour, other factors also affect these values. Garnet fractionation causes Sr/Y and La/Yb to reach much greater values and in this scenario, the values also increase with increasing temperature. Source bulk composition has an effect in all scenarios and most strongly influences La/Yb, Nb, and Ta. Overall, these results show that Sr/Y, La/Yb, Nb, and Ta can reach values generally considered to be indicative of high pressure melting at a range of P–T conditions including P ​< ​2.0 ​GPa. Consequently, trace element compositions of TTGs alone may provide a misleading impression of the depth of melting of metabasites and the geodynamic environment of Archean crustal growth and reworking.

Physical Characteristics of Coupled Plasma and Its Influence on Weld Formation in Hybrid Laser-Double-Arc Welding.

Hybrid laser-double-arc welding (HLDAW) is an efficient welding method with multi-heat sources comprised of two arcs and a laser beam, which is an intricate process with much randomness and uncertainty due to the mutual effect between multi-plasmas. Compared with double-arc welding (DAW), HLDAW can generally obtain a more stable welding process and deeper weld penetration, which is directly affected by the synergistic effect of multiple heat sources; however, the mechanism has not been systematically studied. In this study, the multi-information analysis method is adopted to study the distribution of electron temperatures, electron densities and electrical conductivity of double-arc welding (DAW) and HLDAW by utilizing synchronous radiation spectrum, high-speed photography and electrical signal sensing technology. The results indicated that the high concentration of charged particles provided a conductive channel for the two arcs to achieve a more stable welding process in HLDAW. The synergy between the laser and the arc changed the flow mode of the weld pool, which facilitated the molten metal flowing toward the bottom of the molten pool. Obtaining the same melting depth, the line energy input of HLDAW was 13% lower than that of DAW; the heat affected zone is narrower and the grain size is smaller. The weld penetration depth was improved in HLDAW, which was 1.8 times that of DAW and 1.5 times that of pure laser welding under the laser power of 1.5 kW. The weld penetration of HLDAW increased with laser power.

Plate-driven micro-hotspots and the evolution of the Dragon Flag melting anomaly, Southwest Indian Ridge

Micro hotspots represent excess volcanism at the ultraslow spreading Southwest Indian Ridge (SWIR) unrelated to mantle hotspots, but to focused melt flow in the mantle, wide volcano spacing, and/or increased mantle fertility. Individual micro hotspot can reflect variations in regional mantle fertility, simultaneously affecting 100's of km of ridge, or extreme melt focusing to isolated segments in regions with unusually thick lithosphere. The Dragon Flag melting anomaly, erupting isotopically moderately depleted low-K tholeiite, is the best example of the former: an enormous ridge-centered volcano at 50.5°E. It is far from Crozet, and lies at the apex of a V-shaped trace consisting of ∼1 km anomalously elevated seafloor that extends ∼400 km to the northwest and southeast, indicating a sudden onset of excess volcanism at ∼11-8 Ma. This trend is opposite to that predicted by the hotspot framework, with inconsistent geochemistry. Narrowgate at 14.7°E is one of many micro hotspots that represent isolated large volcanic centers bounded by long amagmatic ridge sections. It also lies at the apex of an eastward V-shaped bathymetric trend, but erupts large volumes of alkali basalt.Both micro hotspot varieties are an order of magnitude smaller than Wilson's classic hotspots, and are not fixed in the hotspot referenced frame. They can grow and remain stationary for extended periods, or migrate freely with respect to each other; driven by the evolving plate tectonic stress field. Dragon Flag, represents a plate reorganization during a prolong period of enhanced melt supply. Narrowgate, on the other hand represents excess volcanism due to extreme deep melt focusing of low degree melt from an unusually wide region in the mantle to an isolated volcanic segment where thick lithosphere caps melting at great depth. To constrain the origins of the micro hotspots six examples are evaluated in terms of their major and isotopic composition, prior plate history, depth and extent of melting and tectonic context. This includes new major, trace element, and heavy isotope data for the Dragon Flag Supersegment, and unpublished data for the Joseph Mayes and Narrowgate segments.

Study on Short-Circuiting GMAW Pool Behavior and Microstructure of the Weld with Different Waveform Control Methods

In order to study internal relation among the behavior of the weld pool, the microstructure of weld bead and the waveform of short-circuiting gas metal arc welding (S-GMAW), a high speed photograph-images analysis system was formed to extract characteristics of weld pool behavior. Three representative waveform control methods were used to provide partly and fully penetrated weld pools and beads. It was found that the behavior of the weld pool was related to the instantaneous power density of the liquid bridge at the break-up time. Weld pool oscillation was triggered by the explosion of the liquid bridge, the natural oscillation frequencies were derived by the continuous wavelet transform. The change of weld pool state caused the transition of oscillation mode, and it led to different nature oscillation frequencies between partial and full penetration. Slags flow pattern could be an indication of the weld pool flow. Compared with the scattered slags on fully penetrated weld pool, slag particles accumulated on partially penetrated weld pools. The oscillating promoted the convection of the welding pool and resulted in larger melting width and depth, the grain size, and the content of pro-eutectoid ferrite in the weld microstructure of S235JR increased, the content of acicular ferrite decreased.

Transient global modeling for the pulling process of Czochralski silicon crystal growth. II. Investigation on segregation of oxygen and carbon

Abstract We conducted the transient global simulations for the crystal pulling process of Czochralski silicon (CZ-Si) growth with the cusp-shaped magnetic field (CMF). The generation, transport, and segregation of oxygen (O) were considered for the crystal growing process. Further, the incorporation, accumulation, and segregation of carbon (C) were also predicted based on our previous studies on CZ-Si growth. The distributions of O and C at the growth interface were dynamically predicted for the diameter pulling stages, and their segregations were plotted as a function of solidified fraction and crystal length. The O level and uniformities at the growth interface exhibit a strong correlation with the depth of melt in the crucible and the flow structures inside the melt. The comparisons of different CMFs indicated that adjustments of the zero-Gauss plane (ZGP) have the potential to optimize the O segregation into the pulling crystal from the level, axial, and radial uniformities. Further, the C concentration increased with the increase in the crystal length because of the continuous contamination and the lower segregation coefficient. Hence, the developed dynamic global model also has applications in the segregation prediction of other dopants and impurities in the CZ-Si growing process.

Comparative Geothermometry in High-Mg Magmas from the Etendeka Province and Constraints on their Mantle Source

Abstract There is still debate whether Large Igneous Provinces (LIPs) are caused by high mantle temperatures induced by thermal plumes or by other factors that enhance melt production from the mantle. A prerequisite for assessing the thermal plume model is a reliable estimate of liquidus temperatures of the magmas produced, preferably based on more than one method of geothermometry. The study reported here compares multiple geothermometers for the Etendeka LIP, which is among the largest Phanerozoic examples and one that shows several features suggestive of a plume origin (continental flood basalt province linked via an age-progressive volcanic ridge to an active hotspot). Magnesium (Mg)-rich magmas emplaced as dikes in NW Namibia are the most primitive rocks known from this province and are thus best suited to determine the composition and melting conditions of their mantle source. Earlier studies of the Etendeka Mg-rich dikes reported high liquidus temperatures based on olivine-melt Mg–Fe equilibria. We extend that work to a larger set of samples and compare the results of olivine-melt Mg–Fe thermometry with other methods based on spinel-melt and spinel–olivine equilibria (Al-in-olivine thermometry), as well as olivine-melt trace-element exchange (Sc/Y thermometry and V oxybarometry). All methods used the same starting assumptions of nominally anhydrous melts and a crystallization pressure of 0·5 GPa. Only mineral-melt or mineral-mineral pairs consistent with compositional equilibrium were used for calculating temperatures. The trace-element compositions of olivine are also used to discuss the relative proportion of peridotite and pyroxenite in the mantle source for these magmas. Twelve dike samples were studied, with whole-rock MgO concentrations ranging from 8·4 to 19·4 wt %. Diagnostic element ratios of transition metals in olivine (e.g., Mn/Fe, Mn/Zn, Zn/Fe) indicate a peridotite-dominated mantle source for the magmas, which is consistent with the other indicators based on whole-rock data e.g., 10 000×Zn/Fe, CaO–MgO trend, FeO/MnO and FC3MS (FeO/CaO–3×MgO/SiO2). The temperature variations show a positive correlation with the Fo-content of host olivines, and values from high-Fo olivine agree well with olivine and spinel liquidus temperatures calculated from thermodynamic models of bulk-rock composition. All methods and most samples yielded a temperature range between 1300 °C and 1400 °C. An exceptional few samples returned temperatures below 1300 °C, the minimum being 1193 °C, whereas several samples yielded temperatures above 1400 °C, the upper range being 1420–1440°C, which we consider to be a robust estimate of the maximum liquidus temperatures for the high-Mg magmas studied. The conversion to mantle potential temperatures is complicated by uncertain depth and degree of melting, but the functional relationship between Tp and primary melt MgO contents, using melt inclusions from olivine phenocrysts with of Fo &amp;gt; 90, indicate a Tp range from 1414 to 1525 °C ( 42 °C), which is 100–150°C higher than estimates of ambient upper mantle Tp in the South Atlantic today.

Microstructural control in metal laser powder bed fusion additive manufacturing using laser beam shaping strategy

Additive manufacturing (AM) promises to revolutionize manufacturing by producing complex parts with tailored mechanical properties through local microstructure control. The main challenge is to control or prevent columnar (elongated) growth morphology which is prevalent in AM parts. Here, we elucidate mechanisms of microstructure control that promote favorable equiaxed grains (aspect ratio close to 1) using a laser beam shaping strategy. This requires an accurate thermal profile that is only captured using advanced predictive simulation that couples full laser ray tracing, ultra-fast hydrodynamic melt flow and the cellular automata method for grain growth. We investigate columnar to equiaxed microstructure transition during single-track laser powder bed fusion processing of 316 L stainless steel using Gaussian (circular) and elliptical (transverse and longitudinal) laser beam shapes. We demonstrate that the propensity to produce equiaxed grains through nucleation events correlates with large beam width as delivered by an elliptical transverse laser beam. In addition, we reveal different microstructure evolution mechanisms during transient states such as at start and end of a scan track when the laser is respectively turned on and off. Columnar growth is hard to prevent at the start of a track and the growth morphology in the absence of heat input is dictated by the melt pool width and depth achieved and the degree of thermal undercooling. We expect this fundamental understanding of the physics of local beam shaping for microstructural control would have implications on future complex beam shape designs as well as beam modulation.