Silicate Systems Research Articles

Thermodiffusion driven element and isotope fractionations: A remarkable differentiation mechanism in silicate systems

Thermodiffusion driven element and isotope fractionations: A remarkable differentiation mechanism in silicate systems

Release Kinetics of Nicotine Loaded onto Mesoporous Silicate Materials for Use in Nicotine Replacement Therapy.

In this work, the loading of nicotine onto mesoporous silicate materials and its release into a phosphate buffer solution at 37°C were investigated. The mesoporous silicate materials designated as MCM-41 were prepared with different pore sizes via using alkyltrimethylammonium bromide surfactants with different alkyl chain lengths of carbon atoms 12, 14, and 16. The mesoporous silicate systems were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), N2-adsorption-desorption isotherms, and FT-IR spectroscopy. Loading of nicotine was confirmed by FTIR and thermal gravimetric analysis and was determined by High-Performance Liquid Chromatography (HPLC). A slight increase in loading capacity with increasing pore size was observed, with a loading capacity of about 17% for MCM-41(16). The release of nicotine was monitored by HPLC and was almost complete for MCM-41(14) and MCM-41(16) in 8 h.

Laser-melted surfaces fabricated on MAO films in Al and Si electrolytes

In order to improve the functions of microarc oxidation (MAO) films, the current work investigated the effects of the laser surface melting (LSM) process on MAO films fabricated in different electrolytes. A series of processing experiments was carried out on the composite films. In detail, MAO films using aluminum (Al) and silicon (Si) electrolytes were prepared on a Ti–6Al–4V alloy surface and then treated by using the LSM process. At the same time, the properties of the films, such as phases and morphology, were characterized and analyzed by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that moderate-intensity plasma was more easily obtained on the silicon MAO (Si-MAO) films than on the aluminum MAO (Al-MAO) ones. Similarly, a higher laser power was necessary to liquefy or gasify alumina (Al2O3). Compared with the defective structure of Al-MAO film after LSM, the structure of the Si-MAO film was almost free of defects. The film morphologies showed that an MAO film with low porosity and a smooth surface can be obtained after LSM treatment using proper parameters. In conclusion, the composite silicate system process using the silicon electrolyte had better modification performance.

Influence of electrolyte components on the microstructure and growth mechanism of plasma electrolytic oxidation coatings on 1060 aluminum alloy

Electrolyte systems have a significant impact on plasma electrolytic oxidation (PEO). In this work, the surface, aluminum/coating (A/C) interface and fracture cross-section microstructure and element distribution of PEO coatings prepared in silicate, phosphate and mixed electrolyte were characterized in detail by FESEM, EDS, XRD and XPS. The growth mechanisms of PEO coatings in different electrolytes were also discussed. Results demonstrated that the deposition of silicate dominated the growth of coating in silicate system, many loose nodules were present on the coating surface. Si element occupied almost the entire coating and was enriched at the nodules and cavity edges. In phosphate system, the growth of coating was primarily dependent on the oxidation of aluminum. There are a large number of “hill”-like protrusions at A/C interface. The main component of this coating was a-Al2O3, and a small amount of P was distributed at A/C interface. In the mixed electrolyte, the film-formation process was mainly the matrix oxidation, and supplemented by deposition of electrolytes. Meanwhile, the growth models of PEO coating in different electrolyte were established.

Statistical separation of tectonic and inflation-driven components of deformation on silicic reservoirs, Laguna del Maule volcanic field, Chile

The reconstruction of the structural history of inflating silicic systems is challenging because their faulting record encompasses tectonic and inflation-driven deformation, and separating the two can rarely be accomplished. Here, we present and utilize a statistical methodology to differentiate tectonic from inflation-driven deformation in the Laguna del Maule (LdM), a post-glacial rhyolitic volcanic field (Southern Volcanic Zone, Chile, latitude 36° S). LdM is cut by the Troncoso fault, a major normal fault that strikes NE and dips to the NW. The Troncoso hanging wall contains abundant, young (< 23 ka) NE-striking normal faults, whereas the footwall is largely unfaulted, with few NNW-striking faults. Activity within the shallow (<8 km) LdM reservoir has caused two inflation events, both centered in different areas of the footwall: 1) a geodetic-based (InSAR) inflation, acting since 2007; and 2) a shoreline-based inflation, evidenced by warping of a 9.4 ka high-stand shoreline. To separate tectonic and inflation-driven faults in the Troncoso hanging wall, we perform a statistical analysis of fault orientation to compare them to the elongation direction predicted by tectonics. The orientation of normal faults is consistent with NW-SE tectonic elongation recorded outside the inflating area. To evaluate if either inflation event has reactivated these tectonic faults, we perform a statistical analysis of orientation-and-heave (horizontal offset on a fault): we calculate the maximum elongation direction (the accumulated horizontal offset) and compare it to elongation predicted by tectonics, shoreline-based inflation and geodetic-based inflation. The maximum elongation direction is sub-parallel to elongation predicted by shoreline-based inflation and is statistically different from tectonic elongation. We interpret a first stage of tectonic extension (>19–9.4 ka) where normal faults are developed on the Troncoso hanging wall. During shoreline-based inflation (<9.4 ka), faults on the hanging wall are reactivated, suppressing uplift; the largely unfaulted footwall uplifts instead. The differential uplift is accommodated by slip on the Troncoso fault. The current, geodetic based uplift, nucleates few faults with large offsets, and potentially reactivates the Troncoso fault. From the structural history, we suggest that the structural architecture is associated with surface volcanism: deformation of the Troncoso hanging wall appears to facilitate repeated, small volume, post-glacial rhyodacitic and andesitic eruptions, whereas the largely unfaulted Troncoso footwall seems to favor rhyolite accumulation and eruption during the late Holocene.

Contemporary CAD/CAM Materials in Dentistry

To present an update on the current CAD/CAM materials in restorative dentistry. Important contributions are seen in updated mechanical properties of CAD/CAM materials, new insights in lithium silicate systems, and development in translucent zirconia. Many materials are arriving at optimized processing procedures and further development will come from new strategies and systems. Increasing our understanding of CAD/CAM materials will improve their use and indications and drive innovation. A general update was provided by classifications, mechanical properties, and clinical considerations by providing commentary on recent significant contributions.

Effects of electrolyte system on the microstructure and properties of MAO ceramics coatings on 7050 high strength aluminum alloy

Purpose This paper aims to investigate the effects of different electrolyte systems on the properties of micro-arc oxidation coating on 7050 high strength aluminum alloy. Design/methodology/approach The coatings were prepared in silicate system with Na2SiO3 as main component, borate system with Na2B4O7 as main component and aluminate solution with Na2AlO2 as main salt, respectively. Findings The results show that the 7050 high strength aluminum alloy shows the best properties in silicate system. Originality/value This manuscript studied the crucial influence of different electrolyte systems on the microstructure and properties of the aluminum alloy micro-arc oxidation layer.

An experimental study of dissolution and precipitation of forsterite in a thermal gradient: implications for cellular growth of olivine phenocrysts in basalt and melt inclusion formation

The morphology of crystals in magmas strongly depends on the temperature regime of the system, in particular the degree of undercooling and the cooling rate. To simulate low degrees of undercooling, we developed a new experimental setup based on thermal migration, in which large cylinders of forsterite (single crystals) immersed in haplobasaltic melt were subjected to a temperature gradient. As forsterite solubility is sensitive to temperature, the forsterite on the high-temperature side undergoes dissolution and the dissolved components are transported toward the low-temperature side where a layer of newly grown forsterite forms (up to 340 μm thick after 101 h). A striking feature is that the precipitation process does not produce a planar front of forsterite advancing at the expense of liquid: the growth front shows a fingered outline in planar section, with solid lobes separated by glass tubes that are perpendicular to the growth front. We ascribe this texture to cellular growth, a type of growth that had not been experimentally produced so far in silicate systems. We find that the development of cellular growth requires low degrees of undercooling (a few °C) and large crystal–liquid interfaces (~ 1 mm across or more), and that it occurs at a growth rate of the order of 10−9 m/s. We found natural occurrences of cellular growth on the rims of olivines from basanites, but otherwise cellular textures are poorly documented in natural volcanic rocks. Melt inclusions were produced in our experiments, showing that they can form in olivine at relatively slow rates of growth (10−9 m/s or lower).

MOLECULAR DYNAMIC SIMULATION OF THE MELT OF OXIDE-FLUORIDE INDUSTRIAL SLAG-FORMING MIXTURE

The paper discusses the results of molecular dynamic simulation of a melt of the multicomponent oxide-fluoride system CaO – SiO2 – – Al2O3 – MgO – Na2O – K2O – CaF2 – FeO, corresponding to composition of industrial slag-forming mixture (SFM) used in steel casting for slag targeting in the mold of a continuous casting machine (in wt %: 35.35 % SiO2 , 30.79 % CaO, 8.58 % Al2O3 , 1.26 % MgO, 13.73 % CaF2 , 7.57 % Na2O, 0.88 % K2O, and 1.82 % FeO). These concentrations were converted to mole fractions, and the number of ions was calculated for each of the components in the model. An eightcomponent oxide-fluoride melt containing 2003 ions in the main cube with a side length of 31.01 Å was simulated under periodic boundary conditions at an experimentally determined solidification onset temperature of 1257 K at constant volume. Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608·10–14 s is the internal unit of time. The melt density was taken to be 3.04 g/cm3 based on our experimental data. The interparticle interaction potentials were chosen in the Born–Mayer form. Based on the simulation results, the structure of subcrystalline groups of atoms present in the melt at the temperature of solidification onset was determined. A discussion of the simulation results and their comparison with the literature data was held. It is shown that the computer model allows one to obtain a fairly realistic picture of atomic structure of the slag melt, indicating that the main structural component of all silicate systems is silicon-oxygen tetrahedron. Tetrahedra in silicates are either in the form of structural units isolated from each other, or, connecting together through peaks, they form complex anions. It is consistent with the theory of slag melts. Molecular-dynamic simulation allows one to obtain adequate information on structure of the melt of a certain chemical composition.

Ge/Si Partitioning in Igneous Systems: Constraints From Laser Ablation ICP‐MS Measurements on Natural Samples

AbstractMineral/melt and intermineral Ge/Si exchange coefficients for nine common rock‐forming silicate minerals were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Ge/Si mineral/melt exchange coefficients were found to vary by up to a factor of 10. In mafic and ultramafic systems, Ge/Si mineral/melt exchange coefficients are less than 1 for plagioclase (0.48) and olivine (0.72), close to 1 for clinopyroxene (1.17) and orthopyroxene (1.07), and greater than 1 for garnet (2.69). In felsic and silicic systems, the Ge/Si mineral/melt exchange coefficient is less than 1 for quartz (0.23), plagioclase (0.67), and potassium feldspar (0.67) but much greater than 1 for biotite (4.80) and hornblende (3.95). We show that early, olivine‐dominated fractionation of primitive basalts does not fractionate Ge/Si significantly, but subsequent cotectic crystallization of plagioclase and pyroxene can increase the Ge/Si ratio from 6 × 10−6 to 7 × 10−6. We show that the only way to decrease Ge/Si during magmatic differentiation is by crystallization of hornblende or biotite (though biotite is typically a late crystallizing phase), consistent with hornblende being a major fractionating phase in hydrous intermediate magmas. The high compatibility of Ge in hornblende makes this element, in conjunction with Si, a potentially useful approach for distinguishing between hornblende and garnet in the source regions of intermediate magmas. The high compatibility of Ge in micas suggests that Ge/Si systematics may also be useful in understanding the origin of ultrapotassic magmas, which are often thought to derive from phlogopite‐rich sources.

Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10-3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

Mineral binding material with the use of paper manufacturing wastes

The possibility of making of mineral astringent material of the low temperature burning at utilization of wastes of production of paper – scope is shown. The analysis of compositions of raw material mixtures on the basis of the system chalk -clay-scope is conducted with varying of concentration of scope at the set descriptions of product of burning. The compositions of mixtures with introduction of 25 - 51 % scope is determinated. The features of phase composition and indexes of properties for mineral astringent with the use of scope as technogenic raw material are shown at the maximal temperature 1100 0С of burning.&#x0D; Industrial use of multi-tonnage waste of various industries, including scopes from paper production, allows to solve complex issues of technology of production of silicate materials, resource conservation and ecology.&#x0D; The feasibility of using scopes as man-made raw materials in the technology of mineral binders is determined by the peculiarities of the chemical and mineralogical composition - the presence of a complete complex of oxides necessary for the formation of a given phase composition during firing and the possibility of intensification of the sintering increase in the reactivity of the silicate system at.&#x0D; The efficiency of practical use of an osprey on the basis of the above developments is defined as the prospect of increasing the volume of utilization of industrial waste, as well as obtaining a new kind of mineral binder material in the low-temperature firing, which differs from romance with improved strength indicators.

Kulikovskiyia gen. nov. (Bacillariophyceae) from the lateritic rock pools of the Western Ghats, India and from Hainan Province, China

ABSTRACTA new triundulate naviculoid diatom genus is described from the Western Ghats of Peninsular India and Hainan Province, China. The new taxon, Kulikovskiyia gen. nov. has robust conical spines along its margin and at the apices and the external valve face has longitudinally‐oriented siliceous slat system extending the length of the valve. The external distal raphe ends bifurcate and terminates on the valve face. There appear to be superficial similarities between this Asian genus and species and Playaensis, a genus comprised of two species found only in the western USA. The systematic position of Kulikovskiyia is discussed, and other than noting its similarities to other biraphid naviculoid diatoms due to symmetry features and the position of the raphe, we are uncertain about its systematic placement at finer levels of classification.

Molecular–Dynamic Simulation of the Melt of an Industrial Oxide–Fluoride Mold Flux

Abstract—The paper discusses the results of molecular–dynamic simulation of a melt of the multicomponent oxide–fluoride CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system that corresponds to the composition of an industrial mold flux (MF) used in steel casting for slag targeting in the mold of a continuous casting machine as: (wt %) 35.35% SiO2, 30.79% CaO, 8.58% Al2O3, 1.26% MgO, 13.73% CaF2, 7.57% Na2O, 0.88% K2O, and 1.82% FeO. These concentrations were converted to mole fractions and the number of ions was calculated for each of the components in the model. An eight-component oxide–fluoride melt containing 2003 ions in the main cube with an edge length of 31.01 A was simulated under periodic boundary conditions at an experimentally determined solidification onset temperature of 1257 K at a constant volume. The Coulomb interaction was considered by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7.608 × 10–14 s is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on experimental data obtained by the authors. The interparticle interaction potentials were chosen in the Born–Mayer form. Based on the simulation results, the structure of subcrystalline groups of atoms present in the melt at the temperature of solidification onset was determined. A discussion of the simulation results and their comparison with the literature data was held. It is shown that the computer model allows one to obtain a fairly realistic picture of the atomic structure of the slag melt, which indicates that the basic structural component of all silicate systems is silicon–oxygen tetrahedron. Tetrahedra in silicates either are in the form of structural units isolated from each other or, being connected together through vertices, form complex anions, which is consistent with the theory of slag melts. Molecular–dynamic simulation allows one to obtain adequate information on the structure of a melt of a certain chemical composition.

The Lower Paleozoic Plutonic-Volcanic connection in the Eastern Magmatic Belt, SW Gondwana, northern Puna Argentina

The relationship between plutonic and volcanic rocks is key to understanding the geochemical evolution of silicic magma systems. In order to untangle the plutonic and volcanic connection and contribute to the reconstruction of the Lower Paleozoic Arc at the SW Gondwana margin, in this study we describe the Sey Plutonic-Volcanic Unit, located in Eastern Magmatic Belt, northern Puna, Argentina. Additionally, we present zircon U-Pb ages by LA-MC-ICP-MS and geochemical data. The studied unit is comprised of monzogranites, granodiorites, gabbros, dacites, and rhyodacites, cropping out as plutonic bodies, laccoliths, sills, subaqueous domes, and lava flows. Following the analyses of the different zircon age populations, the granodiorites bodies crystallized at ∼480 Ma, the monzogranites followed at ∼470 Ma. Lastly, the rhyodacites crystallized at ∼446 Ma. Afterward the age groups analyses, in the Eastern Magmatic Belt, northern Puna, the magmatic activity started from ∼520 to 515 Ma until ∼446 Ma, with the magmatic activity peak at ∼485-475 Ma. The age groups, besides with the geochemistry data, isotope, and magma source similarities of the Eastern Magmatic Belt, both north and southern Puna, underline that the formation of the granitoids and volcanites in the Eastern Magmatic Belt was perhaps through a long-lived magmatic event, represented by low and high volume magmatic episodes.

Monazite and xenotime solubility in hydrous, boron-bearing rhyolitic melt

Abstract We conducted a series of monazite and xenotime dissolution experiments in a boron-bearing silicic melt at 1000–1400 °C and 800 MPa in a piston-cylinder apparatus. We present new measurements of monazite and xenotime solubility in hydrous (~3 wt% water), boron-bearing rhyolitic melts, as well as the diffusivities of the essential structural constituents of those minerals (LREE, P, and Y). We compare our results to the previous studies and discuss the implications of this study on the understanding of natural, silicic (granitic/rhyolitic) systems. We propose one equation describing the relationship between the solubility of xenotime and temperature in hydrous rhyolitic melts: ln ⁡ Y = 18.3 ± 0.3 − 125499 ± 3356 R T and another for monazite: ln ⁡ Σ LREE = 18.6 ± 1.5 − 129307 ± 18163 R T . In the presence of sufficient phosphorous, the concentration of LREE needed for monazite saturation is within the uncertainty of the Y concentration needed from xenotime saturation and indicates that in the case of equilibrium crystallization the mineral that forms will only depend on the availability of LREE and Y and HREE. Given the similarity of the solubility of xenotime to that of monazite, we propose that previously published models of monazite solubility in silicic melts can potentially be applied to xenotime, and could, like monazite, serve as a geothermometer. In the case of disequilibrium crystallization in front of rapidly growing crystals, Y will diffuse faster than LREE and xenotime will only crystallize when LREE are depleted. We also found that the diffusion of Y is greater than the diffusion of P from dissolving xenotime, unlike the similar diffusivities of LREE and P during monazite dissolution. The significant difference between Y and P diffusivities suggests that the components forming xenotime diffuse as separate entities rather than molecular complexes. The dissolution of phosphates (monazite, xenotime, apatite) in hydrous, silicic melts with the addition of boron leads to liquid-liquid immiscibility at high temperatures where the saturation values of P and either light rare earth elements or Y are in the weight percent range. Immiscibility is not observable at low, magmatic temperatures, most probably due to the lower concentrations of P2O5 necessary for phosphate saturation at these conditions; however addition of other components, notably F, may result in liquid-liquid immiscibility at magmatic temperatures.

Adaptation of the dynamic mechanical analysis to determine the gel point during the setting of liquid alkali silicates

AbstractThe gel point is one of the relevant parameters for the characterization of materials that undergo a sol‐to‐gel‐transition during their setting. A test method for its determination could be the Dynamic Mechanical Analysis, currently used in the field of polymer science. For the first time this measuring principle has been adapted to the group of liquid alkali silicates, thus verifying the possibility to describe their setting process. Three analytical methods for the determination of the gel point were studied with regard to their applicability and consistency for a compound alkali silicate system used as chemical hardener.

Viscoelastic relaxation: A mechanism to explain the decennial large surface displacements at the Laguna del Maule silicic volcanic complex

Silicic systems generate the most explosive eruptions on Earth. In contrast to basaltic systems, they can accumulate large volumes of magma without systematically erupting, confronting the classical interpretation that a volcano inflates when a magmatic intrusion occurs. Understanding the mechanisms of volcanic inflation and unrest is thus one of the most important challenges in volcanic risk assessment. Laguna del Maule (LdM) in the Southern Volcanic Zone (SVZ) of Chile, is one of the most active Holocene silicic complexes in the world and it has been inflating since 2007, accumulating 2 m of uplift without erupting. Several geophysical and geochemical studies conclude that a large crystal rich reservoir would be residing beneath LdM, in consistency with other multi-disciplinary studies showing that such crystal-rich reservoirs (“mush zones”) can be maintained beneath silicic volcanoes, fed by mafic magma recharge from below. Nevertheless, the mechanical state of such reservoirs remains unclear. Here, we characterize for the first time the mechanical properties of such a mush reservoir, able to promote large surface displacements such as those measured at LdM. Using a 3D finite element method we simulate a recharge of magma at the base of a crystal rich reservoir, by assuming an overpressurized source surrounded by a large viscoelastic shell. Inversion results show that this model fits the observed temporal and spatial evolution of ground displacements measured with InSAR data and GNSS data between 2007 and 2017. We interpret the temporal behavior of ground displacement at LdM as resulting from two contributions. A magma recharge occurred within the first 4 yr of the active inflation, followed by the viscous response of the large viscoelastic shell, set to a viscosity of 1017 Pas. Compared to a purely elastic solution, our model suggests that up to 50% of the accumulated surface displacement during the ten-year period can be explained by this viscous response, and predicts ongoing displacements 50 yr after the onset of inflation. This model agrees with geophysical and geochemical observations and offers a simple explanation of the temporal evolution of surface displacements. It further allows to reconsider the mechanical behavior of large partially crystallized domains in the upper crust; such significant transient stress transfer over large viscoelastic areas should thus be accounted for in other studies of silicic volcanic complexes.

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics

ObjectiveThe study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests. MethodsXRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization. ResultsThe two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD. SignificanceAccurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.

40Ar/39Ar and paleomagnetic constraints on the age and areal extent of the Picabo volcanic field: Implications for the Yellowstone hotspot

AbstractThe Picabo volcanic field is one of the key silicic volcanic fields in the time-transgressive track of the Yellowstone hotspot. The Picabo volcanic field is also one of the most poorly defined volcanic fields along the track of the Yellowstone hotspot. Determining the age and areal extent of the Picabo volcanic field ignimbrites is one of the primary objectives of this study. In our effort to correlate ignimbrites within the Picabo volcanic field as well as identify those from the neighboring Twin Falls and Heise volcanic fields, we present new petrographic, 40Ar/39Ar, and paleomagnetic data. With these data, we correlated several ignimbrites within the Picabo volcanic field. In some cases, we correlate units previously thought to be in the Picabo volcanic field to older volcanic fields. This includes the Picabo Tuff, which we suggest originates from the Twin Falls volcanic field rather from its namesake volcanic field. The first and best documented major silicic eruption of the volcanic field, the Arbon Valley Tuff, is also the largest ignimbrite in the Picabo volcanic field. There is disagreement as to whether the Arbon Valley Tuff is the result of a single ignimbrite eruption or multiple eruptions. We previously have suggested that the Arbon Valley Tuff is the result of two eruptions, one at 10.41 ± 0.01 Ma and the other at 10.22 ± 0.01 Ma (Anders et al., 2014). Those combining radiometric dates into a single eruption age report ages of 10.2 Ma, 10.27 ± 0.01 Ma, 10.34 ± 0.03 Ma, and 10.44 ± 0.27 Ma. We also suggest the final eruption of the Picabo volcanic field was the tuff of American Falls dated at 7.58 ± 0.02 Ma. Estimates of the location of Picabo volcanic field have been used to mark a major change in the migration rate of the Yellowstone–Snake River Plain silicic volcanic system. Based on our new data, we found only minor changes of the boundaries of the Picabo volcanic field from previous studies. Using the age of the Arbon Valley Tuff (10.41 Ma), we calculated an extension-corrected migration rate of 2.27 ± 0.2 cm/yr between the position of the Picabo volcanic field and that of the Yellowstone volcanic field over the past ∼10 m.y. This estimate is close to the extension corrected 2.38 ± 0.21 cm/yr value based on the migration of the hotspot deformation field. These rates are consistent with independent estimates of North American plate velocity over the past 10 m.y. and therefore consistent with a fixed reference frame for the Yellowstone hotspot. These results stand in contrast with several recent models for the evolution of the Yellowstone–Snake River Plain volcanic system.We also discovered a new ignimbrite from the Heise volcanic field, the 4.37 ± 0.08 Ma tuff of Birch Creek Sinks, in core from the U.S. Geological Survey (USGS) borehole 2-2A, which now represents the youngest outflow ignimbrite of the Heise volcanic field. Although recently, several intracaldera ignimbrites younger than 4 Ma have been identified in the volcanic field, the age range of outflow ignimbrites from the Heise volcanic field is now extended from 6.66 Ma to at least 4.37 Ma.