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Sample records for dan feldspar untuk

  1. Elasticity of plagioclase feldspars

    NASA Astrophysics Data System (ADS)

    Brown, J. Michael; Angel, Ross J.; Ross, Nancy L.

    2016-02-01

    Elastic properties are reported for eight plagioclase feldspars that span compositions from albite (NaSi3AlO8) to anorthite (CaSi2Al2O8). Surface acoustic wave velocities measured using Impulsive Stimulated Light Scattering and compliance sums from high-pressure X-ray compression studies accurately determine all 21 components of the elasticity tensor for these triclinic minerals. The overall pattern of elasticity and the changes in individual elastic components with composition can be rationalized on the basis of the evolution of crystal structures and chemistry across this solid-solution join. All plagioclase feldspars have high elastic anisotropy; a* (the direction perpendicular to the b and c axes) is the softest direction by a factor of 3 in albite. From albite to anorthite the stiffness of this direction undergoes the greatest change, increasing twofold. Small discontinuities in the elastic components, inferred to occur between the three plagioclase phases with distinct symmetry (C1>¯, I1>¯, and P1>¯), appear consistent with the nature of the underlying conformation of the framework-linked tetrahedra and the associated structural changes. Measured body wave velocities of plagioclase-rich rocks, reported over the last five decades, are consistent with calculated Hill-averaged velocities using the current moduli. This confirms long-standing speculation that previously reported elastic moduli for plagioclase feldspars are systematically in error. The current results provide greater assurance that the seismic structure of the middle and lower crusts can be accurately estimated on the basis of specified mineral modes, chemistry, and fabric.

  2. The Thermal Expansion Of Feldspars

    NASA Astrophysics Data System (ADS)

    Hovis, G. L.; Medford, A.; Conlon, M.

    2009-12-01

    Hovis and others (1) investigated the thermal expansion of natural and synthetic AlSi3 feldspars and demonstrated that the coefficient of thermal expansion (α) decreases significantly, and linearly, with increasing room-temperature volume (VRT). In all such feldspars, therefore, chemical expansion limits thermal expansion. The scope of this work now has been broadened to include plagioclase and Ba-K feldspar crystalline solutions. X-ray powder diffraction data have been collected between room temperature and 925 °C on six plagioclase specimens ranging in composition from anorthite to oligoclase. When combined with thermal expansion data for albite (2,3,4) a steep linear trend of α as a function of VRT emerges, reflecting how small changes in composition dramatically affect expansion behavior. The thermal expansion data for five synthetic Ba-K feldspars ranging in composition from 20 to 100 mole percent celsian, combined with data for pure K-feldspar (3,4), show α-VRT relationships similar in nature to the plagioclase series, but with a slope and intercept different from the latter. Taken as a group all Al2Si2 feldspars, including anorthite and celsian from the present study along with Sr- (5) and Pb-feldspar (6) from other workers, show very limited thermal expansion that, unlike AlSi3 feldspars, has little dependence on the divalent-ion (or M-) site occupant. This apparently is due to the necessitated alternation of Al and Si in the tetrahedral sites of these minerals (7), which in turn locks the tetrahedral framework and makes the M-site occupant nearly irrelevant to expansion behavior. Indeed, in feldspar series with coupled chemical substitution it is the change away from a 1:1 Al:Si ratio that gives feldspars greater freedom to expand. Overall, the relationships among α, chemical composition, and room-temperature volume provide useful predictive tools for estimating feldspar thermal expansion and give insight into the controls of expansion behavior in

  3. Thermal expansion of plagioclase feldspars

    NASA Astrophysics Data System (ADS)

    Tribaudino, M.; Angel, R. J.; Cámara, F.; Nestola, F.; Pasqual, D.; Margiolaki, I.

    2010-12-01

    The volume thermal expansion coefficient and the anisotropy of thermal expansion were determined for nine natural feldspars with compositions, in terms of albite (NaAlSi3O8, Ab) and anorthite (CaAl2Si2O8, An), of Ab100, An27Ab73, An35Ab65, An46Ab54, An60Ab40, An78Ab22, An89Ab11, An96Ab4 and An100 by high resolution powder diffraction with a synchrotron radiation source. Unit-cell parameters were determined from 124 powder patterns of each sample, collected over the temperature range 298-935 K. The volume thermal expansion coefficient of the samples determined by a linear fit of V/ V 0 = α( T - T 0) varies with composition ( X An in mol %) as: αV = 2.90left( 4 right) × 10^{ - 5} - 3.0left( 2 right) × 10^{ - 7} *X_{text{An}} + 1.8left( 2 right) × 10^{ - 9} *X_{text{An}}2 Two empirical models for the non-linear behaviour of volume with temperature give a better fit to the experimental data. The change with composition in the a° parameter of the non-linear Holland-Powell model V/ V 0 = 1 + a°( T - T 0) + 20a° (√ T - √ T 0) is: a^circ = 4.96left( 5 right) × 10^{ - 5} - 4.7left( 2 right) × 10^{ - 7} *X_{text{An}} + 2.2left( 2 right) × 10^{ - 9} *X_{text{An}}2 For the Berman model, V/ V 0 = a 1( T - T 0) + a 2*( T- T 0)2, the parameters change with composition as: begin{aligned}& a1 = 2.44left( {15} right) × 10^{ - 5} - 3.1left( 6 right) × 10^{ - 7} *X_{text{An}}\\& quad + 1.8left( 5 right) × 10^{ - 9} *X_{text{An}}2 \\& a2 = 9left( 1 right) × 10^{ - 9} - 4left( 2 right) × 10^{ - 11} *X_{text{An}} \\ The thermal expansion of all plagioclases is very anisotropic, with more than 70% of the volume expansion being accommodated by a direction fairly close to the (100) plane normal, whereas perpendicular directions exhibit smaller, and in some cases slightly negative or zero, thermal expansion.

  4. Principles of Thermal Expansion in Feldspars

    NASA Astrophysics Data System (ADS)

    Hovis, Guy; Medford, Aaron; Conlon, Maricate; Tether, Allison; Romanoski, Anthony

    2010-05-01

    Following the recent thermal expansion work of Hovis et al. (1) on AlSi3 feldspars, we have investigated the thermal expansion of plagioclase, Ba-K, and Ca-K feldspar crystalline solutions. X-ray powder diffraction data were collected between room temperature and 925 °C on six natural plagioclase specimens ranging in composition from anorthite to oligoclase, the K-exchanged equivalents of these plagioclase specimens, and five synthetic Ba-K feldspars with compositions ranging from 25 to 99 mol % BaAl2Si2O8. The resulting thermal expansion coefficients (α) for volume have been combined with earlier results for end-member Na- and K-feldspars (2,3). Unlike AlSi3 feldspars, Al2Si2 feldspars, including anorthite and celsian from the present study plus Sr- and Pb-feldspar from other workers (4,5), show essentially constant and very limited thermal expansion, regardless of divalent cation size. In the context of structures where the Lowenstein rule (6) requires Al and Si to alternate among tetrahedra, the proximity of bridging Al-O-Si oxygen ions to divalent neighbors (ranging from 0 to 2) produces short Ca-O (or Ba-O) bonds (7,8) that apparently are the result of local charge-balance requirements (9). Gibbs et al. (10) suggest that short bonds such as these have a partially covalent character. This in turn stiffens the structure. Thus, for feldspar series with coupled substitution the change away from a purely divalent M-site occupant gives the substituting (less strongly bonded) monovalent cations increasingly greater influence on thermal expansion. Overall, then, thermal expansion in the feldspar system is well represented on a plot of α against room-temperature volume, where one sees a quadrilateral bounded by data for (A) AlSi3 feldspars whose expansion behavior is controlled largely by the size of the monovalent alkali-site occupant, (B) Al2Si2 feldspars whose expansion is uniformly limited by partially-covalent bonds between divalent M-site occupants and

  5. The surface chemistry of dissolving labradorite feldspar

    NASA Astrophysics Data System (ADS)

    Casey, William H.; Westrich, Henry R.; Arnold, George W.; banfield, Jillian F.

    1989-04-01

    Elastic recoil detection (ERD) analysis was used in conjunction with Rutherford backscattering (RBS) analysis to determine depth profiles of hydrogen, silicon, aluminum and calcium in labradorite crystals reacted under various pH conditions. The inventory of hydrogen in the mineral is strongly affected by solution pH. Hydrogen extensively infiltrates the mineral during reaction for 264 hours with solutions in the pH range 1-3. Infiltration is accompanied by extensive removal of sodium, calcium and aluminum from the mineral. This incongruent reaction proceeds to several hundreds of angstroms of depth and produces a silicon-rich surface which is amorphous to electron diffraction. The amount of hydrogen in the reacted layer is much less than is predicted from knowledge of the quantity of cations leached from the feldspar. These low inventories of hydrogen suggest that hydrogen-bearing groups in the reacted layer repolymermize subsequent to ion exchange and depolymerization reactions. This repolymerization eliminates hydrogen from the layer. At higher pH conditions (pH > 5), hydrogen inventories in the crystals decrease with time relative to an unreacted reference crystal. Hydrogen does not infiltrate beyond the first few unit cells of feldspar. Thus, dissolution in slightly acid, near-neutral, and basic solutions proceeds at the immediate surface of the feldspar. Within the limit of the RBS technique, there is no evidence for incongruent dissolution at these conditions.

  6. Sintering behaviour of feldspar and influence of electric charge effects

    NASA Astrophysics Data System (ADS)

    Gallala, W.; Gaied, M. E.

    2011-04-01

    The characterization of feldspar for electric porcelain and the behaviour of these materials after heating at 1230°C were studied. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to identify the present phases and the densification level. Feldspar sand was treated by flotation. The floated feldspar is constituted by microcline, quartz, and minor amounts of albite. The microstructure of sintered feldspar at 1230°C is essentially vitreous with open microporosities. The dielectrical properties of composites were characterized by using the induced courant method (ICM), which indicates that the charge trapping capacity depends on the mineralogical and chemical composition of feldspar.

  7. Elastic properties of alkali-feldspars

    NASA Astrophysics Data System (ADS)

    Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.

    2013-12-01

    New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and

  8. A detailed study of ice nucleation by feldspar minerals

    NASA Astrophysics Data System (ADS)

    Whale, T. F.; Murray, B. J.; Wilson, T. W.; Carpenter, M. A.; Harrison, A.; Holden, M. A.; Vergara Temprado, J.; Morris, J.; O'Sullivan, D.

    2015-12-01

    Immersion mode heterogeneous ice nucleation plays a crucial role in controlling the composition of mixed phase clouds, which contain both supercooled liquid water and ice particles. The amount of ice in mixed phase clouds can affect cloud particle size, lifetime and extent and so affects radiative properties and precipitation. Feldspar minerals are probably the most important minerals for ice nucleation in mixed phase clouds because they nucleate ice more efficiently than other components of atmospheric mineral dust (Atkinson et al. 2013). The feldspar class of minerals is complex, containing numerous chemical compositions, several crystal polymorphs and wide variations in microscopic structure. Here we present the results of a study into ice nucleation by a wide range of different feldspars. We found that, in general, alkali feldspars nucleate ice more efficiently than plagioclase feldspars. However, we also found that particular alkali feldspars nucleate ice relatively inefficiently, suggesting that chemical composition is not the only important factor that dictates the ice nucleation efficiency of feldspar minerals. Ice nucleation by feldspar is described well by the singular model and is probably site specific in nature. The alkali feldspars that do not nucleate ice efficiently possess relatively homogenous structure on the micrometre scale suggesting that the important sites for nucleation are related to surface topography. Ice nucleation active site densities for the majority of tested alkali feldspars are similar to those found by Atkinson et al (2013), meaning that the validity of global aerosol modelling conducted in that study is not affected. Additionally, we have found that ice nucleation by feldspars is strongly influenced, both positively and negatively, by the solute content of droplets. Most other nucleants we have tested are unaffected by solutes. This provides insight into the mechanism of ice nucleation by feldspars and could be of importance

  9. Lunar granites with unique ternary feldspars

    NASA Technical Reports Server (NTRS)

    Ryder, G.; Stoeser, D. B.; Marvin, U. B.; Bower, J. F.

    1975-01-01

    An unusually high concentration of granitic fragments, with textures ranging from holocrystalline to glassy, occurs throughout Boulder 1, a complex breccia of highland rocks from Apollo 17, Station 2. Among the minerals included in the granites are enigmatic K-Ca-rich feldspars that fall in the forbidden region of the ternary diagram. The great variability in chemistry and texture is probably the result of impact degradation and melting of a granitic source-rock. Studies of the breccia matrix suggest that this original granitic source-rock may have contained more pyroxenes and phosphates than most of the present clasts contain. Petrographic observations on Apollo 15 KREEP basalts indicate that granitic liquids may be produced by differentiation without immiscibility, and the association of the granites with KREEP-rich fragments in the boulder suggests that the granites represent a residual liquid from the plutonic fractional crystallization of a KREEP-rich magma. Boulder 1 is unique among Apollo 17 samples in its silica-KREEP-rich composition. We conclude that the boulder represents a source-rock unlike the bedrock of South Massif.

  10. APPLICATIONS OF CATHODOLUMINESCENCE OF QUARTZ AND FELDSPAR TO SEDIMENTARY PETROLOGY.

    USGS Publications Warehouse

    Ruppert, Leslie F.

    1987-01-01

    Cathodoluminescence (CL), the emission of visible light during electron bombardment, was first used in sandstone petrology in the mid-1960's. CL techniques are especially useful for determining the origin and source of quartz and feldspar, two of the most common constituents in clastic rocks. CL properties of both minerals are dependent on their temperature of crystallization, duration of cooling, and/or history of deformation. Detrital quartz and feldspar are typically derived from igneous and metamorphic sources and luminesce in the visible range whereas authigenic quartz and feldspar form at low temperatures and do not luminesce. Quantification of luminescent and non-luminescent quartz and feldspar with the scanning electron microscope, electron microprobe, or a commercial CL device can allow for the determination of origin, diagenesis, and source of clastic rocks when used in conjunction with field and other petrographic analyses.

  11. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles

    PubMed Central

    2015-01-01

    Mineral dusts originating from Earth’s crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces. PMID:25584435

  12. Immersion freezing of aqueous suspensions of K-feldspar

    NASA Astrophysics Data System (ADS)

    Peckhaus, Andreas; Kiselev, Alexei; Leisner, Thomas

    2014-05-01

    Recent laboratory measurements showed an increased ice nucleation ability of Kalium-rich feldspar particles in the immersion freezing mode [1]. It was suggested that the proportion of K-feldspar in atmospherically relevant ice nuclei is related to their ice nucleation ability. The importance of K-feldspar is further supported by the field measurements, indicating that it can make a mass fraction of up to 24% in Asian and African mineral dusts [2]. In this contribution we present results of immersion freezing experiments with monodisperse droplets of aqueous suspensions of K-feldspar on a cold stage. We show that the ice nucleation activity strongly depends on i) the particle size distribution (in particular the ice nucleation properties of submicron feldspar particles) ii) the weight concentration of the particles in the aqueous suspension and thus on the total particle surface immersed into the droplets and iii) the age of the particles in an aqueous environment. Further a comparison of different K-feldspars is presented indicating that the origin and the processing methods have a significant impact on the IN activity. The mineralogical composition of feldspar samples is analyzed by means of Raman spectroscopy and a quantification of the particle surface is carried out with environmental scanning electron microscopy (ESEM). The results of freezing experiments are interpreted within the concept of ice nucleation active surface site (INAS) density, which allows a comparison with data obtained with different experimental methods (IN counters, expansion chambers, etc.) 1. Atkinson, J.D., et al., The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds. Nature, 2013. 498(7454): p. 355-358. 2. Nickovic, S., et al., Technical Note: High-resolution mineralogical database of dust-productive soils for atmospheric dust modeling. Atmospheric Chemistry and Physics, 2012. 12(2): p. 845-855.

  13. Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase

    NASA Astrophysics Data System (ADS)

    Biedermann, Andrea R.; Pettke, Thomas; Angel, Ross J.; Hirt, Ann M.

    2016-04-01

    Feldspars are the most abundant rock-forming minerals in the Earth's crust, but their magnetic properties have not been rigorously studied. This work focuses on the intrinsic magnetic anisotropy of 31 feldspar samples with various chemical compositions. Because feldspar is often twinned or shows exsolution textures, measurements were performed on twinned and exsolved samples as well as single crystals. The anisotropy is controlled by the diamagnetic susceptibility and displays a consistent orientation of principal susceptibility axes; the most negative or minimum susceptibility is parallel to [010], and the maximum (least negative) is close to the crystallographic [001] axis. However, the magnetic anisotropy is weak when compared to other rock-forming minerals, 1.53 × 10-9 m3 kg-1 at maximum. Therefore, lower abundance minerals, such as augite, hornblende or biotite, often dominate the bulk paramagnetic anisotropy of a rock. Ferromagnetic anisotropy is not significant in most samples. In the few samples that do show ferromagnetic anisotropy, the principal susceptibility directions of the ferromagnetic subfabric do not display a systematic orientation with respect to the feldspar lattice. These results suggest that palaeointensity estimates of the geomagnetic field made on single crystals of feldspar will not be affected by a systematic orientation of the ferromagnetic inclusions within the feldspar lattice.

  14. Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase

    NASA Astrophysics Data System (ADS)

    Biedermann, Andrea R.; Pettke, Thomas; Angel, Ross J.; Hirt, Ann M.

    2016-01-01

    Feldspars are the most abundant rock-forming minerals in the Earth's crust, but their magnetic properties have not been rigorously studied. This work focuses on the intrinsic magnetic anisotropy of 31 feldspar samples with various chemical compositions. Because feldspar is often twinned or shows exsolution textures, measurements were performed on twinned and exsolved samples as well as single crystals. The anisotropy is controlled by the diamagnetic susceptibility and displays a consistent orientation of principal susceptibility axes; the most negative or minimum susceptibility is parallel to [010], and the maximum (least negative) is close to the crystallographic [001] axis. However, the magnetic anisotropy is weak when compared to other rock-forming minerals, 1.53*10-9 m3 kg-1 at maximum. Therefore, lower abundance minerals such as augite, hornblende or biotite often dominate the bulk paramagnetic anisotropy of a rock. Ferromagnetic anisotropy is not significant in most samples. In the few samples that do show ferromagnetic anisotropy, the principal susceptibility directions of the ferromagnetic subfabric do not display a systematic orientation with respect to the feldspar lattice. These results suggest that paleointensity estimates of the geomagnetic field made on single crystals of feldspar will not be affected by a systematic orientation of the ferromagnetic inclusions within the feldspar lattice.

  15. Can cathodoluminescence of feldspar be used as provenance indicator?

    NASA Astrophysics Data System (ADS)

    Scholonek, Christiane; Augustsson, Carita

    2016-05-01

    We have studied feldspar from crystalline rocks for its textural and spectral cathodoluminescence (CL) characteristics with the aim to reveal their provenance potential. We analyzed ca. 60 rock samples of plutonic, volcanic, metamorphic, and pegmatitic origin from different continents and of 16 Ma to 2 Ga age for their feldspar CL textures and ca. 1200 feldspar crystals from these rocks for their CL color spectra. Among the analyzed rocks, igneous feldspar is most commonly zoned, whereby oscillatory zoning can be confirmed to be typical for volcanic plagioclase. The volcanic plagioclase also less commonly contains twin lamellae that are visible in CL light than crystals from other rock types. Alkali feldspar, particularly from igneous and pegmatitic rocks, was noted to be most affected by alteration features, visible as dark spots, lines and irregular areas. The size of all textural features of up to ca. 150 μm, in combination with possible alteration in both the source area and the sedimentary system, makes the CL textures of feldspar possible to use for qualitative provenance research only. We observed alkali feldspar mostly to luminesce in a bluish color and sometimes in red, and plagioclase in green to yellow. The corresponding CL spectra are dominated by three apparent intensity peaks at 440-520 nm (mainly blue), 540-620 nm (mainly green) and 680-740 nm (red to infrared). A dominance of the peak in the green wavelength interval over the blue one for plagioclase makes CL particularly useful for the differentiation of plagioclase from alkali feldspar. An apparent peak position in red to infrared at < 710 nm for plagioclase mainly is present in mafic rocks. Present-day coastal sand from Peru containing feldspar with the red to infrared peak position mainly exceeding 725 nm for northern Peruvian sand and a larger variety for sand from southern Peru illustrates a discriminative effect of different source areas. We conclude that the provenance application

  16. Differential rates of feldspar weathering in granitic regoliths

    USGS Publications Warehouse

    White, A.F.; Bullen, T.D.; Schulz, M.S.; Blum, A.E.; Huntington, T.G.; Peters, N.E.

    2001-01-01

    Differential rates of plagioclase and K-feldspar weathering commonly observed in bedrock and soil environments are examined in terms of chemical kinetic and solubility controls and hydrologic permeability. For the Panola regolith, in the Georgia Piedmont Province of southeastern United States, petrographic observations, coupled with elemental balances and 87Sr/86Sr ratios, indicate that plagioclase is being converted to kaolinite at depths > 6 m in the granitic bedrock. K-feldspar remains pristine in the bedrock but subsequently weathers to kaolinite at the overlying saprolite. In contrast, both plagioclase and K-feldspar remain stable in granitic bedrocks elsewhere in Piedmont Province, such as Davis Run, Virginia, where feldspars weather concurrently in an overlying thick saprolite sequence. Kinetic rate constants, mineral surface areas, and secondary hydraulic conductivities are fitted to feldspar losses with depth in the Panola and Davis Run regoliths using a time-depth computer spreadsheet model. The primary hydraulic conductivities, describing the rates of meteoric water penetration into the pristine granites, are assumed to be equal to the propagation rates of weathering fronts, which, based on cosmogenic isotope dating, are 7 m/106 yr for the Panola regolith and 4 m/106 yr for the Davis Run regolith. Best fits in the calculations indicate that the kinetic rate constants for plagioclase in both regoliths are factors of two to three times faster than K-feldspar, which is in agreement with experimental findings. However, the range for plagioclase and K-feldspar rates (kr = 1.5 x 10-17 to 2.8 x 10-16 mol m-2 s-1) is three to four orders of magnitude lower than for that for experimental feldspar dissolution rates and are among the slowest yet recorded for natural feldspar weathering. Such slow rates are attributed to the relatively old geomorphic ages of the Panola and Davis Run regoliths, implying that mineral surface reactivity decreases significantly with

  17. Immersion Freezing of Potassium-feldspar and related Natural Samples

    NASA Astrophysics Data System (ADS)

    Zolles, Tobias; Burkart, Julia; Grothe, Hinrich

    2014-05-01

    Ice nucleation activities of mineral dust particles were investigated. The experiments were carried out using cryo-microscopy which is an oil-emulsion based method. The immersion freezing mode was addressed with this experimental setup. The studied samples were common inorganic atmospheric aerosols. Single minerals and natural samples were tested [1]. Mineral dust particles are active ice nuclei in the immersion freezing mode up to 256 K. Only recently potassium-feldspar has been identified as the by far most active ice nucleus followed by other silicates [2, 3]. Natural samples which contain more than 5% K-feldspar are also active. The activity of K-feldspar can be attributed to its surface structure and the presence of potassium ions in the surface. Ice nucleation on mineral dust particles takes place at certain nucleation sites. These sites are domains of molecular sites where water is stabilized in an ice-like structure. To form a good ice nucleation site, the site density of molecular sites needs to be high. More molecular sites are able to form larger domains on the surface, leading to better nucleation sites. This suggests further that the nucleation temperature of mineral dust particles scales with the surface area. The exact configuration of a molecular site is material specific and influenced by the local chemistry and structure of the dust particle surface. A favourable arrangement of the functional groups like surface hydroxyl and oxygen is proposed for the K-feldspar. Potassium ions seem to have a positive or neutral effect on the ice nucleation property of a silicate surface while cations with a higher charge density like calcium and sodium have a negative influence. K-feldspar is abundant in the environment and actually is the most important dust ice nucleus in the atmosphere. The nucleation temperatures of the K-feldspar particles are sufficient to enable further meteorological glaciation processes in high altitude clouds. References [1] Zolles, T

  18. Thermoluminescence signal in K-feldspar grains: Revisited.

    PubMed

    Gong, Gelian; Sun, Weidong; Xu, Hongyun

    2015-11-01

    Recent work has shown that infrared stimulated luminescence (IRSL) signals in sedimentary coarse-grain K-feldspars are derived mainly from high temperature thermoluminescence (TL) peaks around 400°C, and the fading components of the IRSL signal can be preferentially removed by prior IR stimulation at relatively low temperature. Considering the complexity of TL signal for very old samples, we may choose non-fading components from K-feldspar TL signals using the combination of optical and thermal activation methods. This paper examines a protocol of post-IR isothermal TL (i.e. pIRITL) signal for sedimentary coarse-grain K-feldspars, which results from isothermal TL measurements following elevated temperature IR bleaching. We show that a sum of two exponential decay functions can fit well to the pIRITL decay curves, and both the holding temperature for isothermal TL measurements and the prior elevated temperature IR bleaching can affect greatly the fast components of pIRITL signal. The dose response ranges of pIRITL signal are wider than those of post-IR IRSL signals, but the relative high residual pIRITL signal means that it is not appropriate for dating young samples. It is expected that one isothermal TL signal for K-feldspar measured at ~400°C following IR bleaching at 290°C (i.e. pIRITL400) is useful for dating very old samples. PMID:26257084

  19. (Energy related studies utilizing K-feldspar thermochronology)

    SciTech Connect

    Not Available

    1992-01-01

    In our second year of current funding cycle, we have investigated the Ar diffusion properties and microstructures of K-feldspars and the application of domain theory to natural K-feldspars. We completed a combined TEM and argon diffusion study of the effect of laboratory heat treatment on the microstructure and kinetic properties of K-feldspar. We conclude in companion papers that, with one minor exception, no observable change in the diffusion behavior occurs during laboratory extraction procedures until significant fusion occurs at about 1100{degrees}C. The effect that is observed involves a correlation between the homogenization of cryptoperthite lamelle and the apparent increase in retentivity of about 5% of the argon in the K-feldspar under study. We can explain this effect of both as an artifact of the experiment or the loss of a diffusion boundary. Experiments are being considered to resolve this question. Refinements have been made to our experimental protocol that appears that greatly enhance the retrieval of multi-activation energies from K-feldspars. We have applied the multi-domain model to a variety of natural environments (Valles Caldera, Red River fault, Appalachian basin) with some surprising results. Detailed {sup 40}Ar/{sup 39} Ar coverage of the Red River shear zone, thought to be responsible for the accommodation of a significant fraction of the Indo-Asian convergence, strongly suggests that our technique can precisely date both the termination of ductile strike-slip motion and the initiation of normal faulting. Work has continued on improving our numerical codes for calculating thermal histories and the development of computer based graphing tools has significantly increased our productivity.

  20. Energy related studies utilizing K-feldspar thermochronology

    NASA Astrophysics Data System (ADS)

    In our second year of funding, we investigated the Ar diffusion properties and microstructures of K-feldspars and the application of domain theory to natural K-feldspars. We completed a combined TEM and argon diffusion study of the effect of laboratory heat treatment on the microstructure and kinetic properties of K-feldspar. We conclude in companion papers that, with one minor exception, no observable change in the diffusion behavior occurs during laboratory extraction procedures until significant fusion occurs at about 1100 C. The effect that is observed involves a correlation between the homogenization of cryptoperthite lamelle and the apparent increase in retentivity of about 5 percent of the argon in the K-feldspar under study. We can explain this effect of both as an artifact of the experiment or the loss of a diffusion boundary. Experiments are being considered to resolve this question. Refinements have been made to our experimental protocol that appear to enhance the retrieval of multi-activation energies from K-feldspars. We have applied the multi-domain model to a variety of natural environments (Valles Caldera, Red River fault, Appalachian basin) with some surprising results. Detailed Ar-40/Ar-39 coverage of the Red River shear zone, thought to be responsible for the accommodation of a significant fraction of the Indo-Asian convergence, strongly suggests that our technique can precisely date both the termination of ductile strike-slip motion and the initiation of normal faulting. Work has continued on improving our numerical codes for calculating thermal histories and the development of computer based graphing tools has significantly increased our productivity.

  1. Argon Diffusion in Shocked Pyroxene, Feldspar, and Olivine

    NASA Astrophysics Data System (ADS)

    Weirich, J.; Isachsen, C. E.; Johnson, J. R.; Swindle, T.

    2010-12-01

    Background: The diffusion rate of argon (Ar) in unshocked feldspar has been well studied, but studies on pyroxene and olivine are limited or non-existent. Likewise, the effects of shock on these mineral groups is also limited or non-existent. Understanding how shock affects these mineral groups is important for determining the thermal history of shocked meteorites and collisional impact craters. We have analyzed the Ar diffusion rate of an albitite and a pyroxenite at various experimental shock pressures up to ~60GPa, unshocked high-Ca pyroxene, and an olivine mineral separate from the Springwater meteorite. A previous study of shocked feldspar has shown that Ar diffusion in plagioclase (An67) is unaffected by experimental shock [1]. Re-reduction of data from another study [2] suggests naturally shocked K-rich feldspar is affected, though experimentally shocked oligoclase feldspar (An10-30) is not affected. However, previous shock experiments on feldspar were performed with low temperature resolution and only a single extraction at each temperature. This makes determining the diffusion parameters difficult because the presence of multiple grain sizes can compromise the data. By performing our experiments with a higher temperature resolution and with two extractions at each temperature, we can attain higher quality and more reliable data. The effects of shock on pyroxene and olivine have never been studied. Results: We have found that experimental shock undoubtedly raises the diffusivity of albite (Ab97), and lowers the activation energy required for diffusion. Comparison with previous data indicates that the Ca content may be controlling the response to shock. Pyroxene seems to be somewhat variable regardless of shock pressure, even within the same sample. Shock may have an effect on the diffusion rate of pyroxene, but given the variability it is difficult to delineate. The range of pyroxene diffusion rates is similar to previous studies. Olivine is found to have a

  2. Particle size and X-ray analysis of Feldspar, Calvert, Ball, and Jordan soils

    NASA Technical Reports Server (NTRS)

    Chapman, R. S.

    1977-01-01

    Pipette analysis and X-ray diffraction techniques were employed to characterize the particle size distribution and clay mineral content of the feldspar, calvert, ball, and jordan soils. In general, the ball, calvert, and jordan soils were primarily clay size particles composed of kaolinite and illite whereas the feldspar soil was primarily silt-size particles composed of quartz and feldspar minerals.

  3. Visible/Near-Infrared Spectra of Experimentally Shocked Plagioclase Feldspars

    NASA Technical Reports Server (NTRS)

    Johnson, J. R.

    2003-01-01

    Minerals subjected to high shock pressures exhibit structural changes with increasing pressure (e.g., fractures, deformations, formation of diaplectic glass, and complete melting [1-6]). Petrologic and thermal infrared spectroscopic studies have shown that diaplectic glass (maskelynite) formation in feldspars occurs between 25-45 GPa, while significant melting occurs above 45 GPa [7- 12]. Past studies of visible/near-infrared spectra of shocked plagioclase feldspars demonstrated few variations in spectral features with pressure except for a decrease in the absorption feature near 1250 nm and an overall decrease in albedo [13-17]. We report new visible/near-infrared spectra of albite- and anorthiterich rocks experimentally shocked from 17-56 GPa.

  4. Europium anomaly in plagioclase feldspar: experimental results and semiquantitative model.

    PubMed

    Weill, D F; Drake, M J

    1973-06-01

    The partition of europium between plagioclase feldspar and magmatic liquid is considered in terms of the distribution coefficients for divalent and trivalent europium. A model equation is derived giving the europium anomaly in plagioclase as a function of temperature and oxygen fugacity. The model explains europium anomalies in plagioclase synthesized under controlled laboratory conditions as well as the variations of the anomaly observed in natural terrestrial and extraterrestrial igneous rocks. PMID:17806582

  5. Visible/near-infrared spectra of experimentally shocked plagioclase feldspars

    NASA Astrophysics Data System (ADS)

    Johnson, Jeffrey R.; Hörz, Friedrich

    2003-11-01

    High shock pressures cause structural changes in plagioclase feldspars such as mechanical fracturing and disaggregation of the crystal lattice at submicron scales, the formation of diaplectic glass (maskelynite), and genuine melting. Past studies of visible/near-infrared spectra of shocked feldspars demonstrated few spectral variations with pressure except for a decrease in the depth of the absorption feature near 1250-1300 nm and an overall decrease in reflectance. New visible/near-infrared spectra (400-2500 nm) of experimentally shocked (17-56 GPa) albite- and anorthite-rich rock powders demonstrate similar trends, including the loss of minor hydrated mineral bands near 1410, 1930, 2250, and 2350 nm. However, the most interesting new observations are increases in reflectance at intermediate pressures, followed by subsequent decreases in reflectance at higher pressures. The amount of internal scattering and overall sample reflectance is controlled by the relative proportions of micro-fractures, submicron grains, diaplectic glass, and melts formed during shock metamorphism. We interpret the observed reflectance increases at intermediate pressures to result from progressively larger proportions of submicron feldspar grains and diaplectic glass. The ensuing decreases in reflectance occur after diaplectic glass formation is complete and the proportion of genuine melt inclusions increases. The pressure regimes over which these reflectance variations occur differ between albite and anorthite, consistent with thermal infrared spectra of these samples and previous studies of shocked feldspars. These types of spectral variations associated with different peak shock pressures should be considered during interpretation and modeling of visible/near-infrared remotely sensed spectra of planetary and asteroidal surfaces.

  6. Visible/near-infrared spectra of experimentally shocked plagioclase feldspars

    USGS Publications Warehouse

    Johnson, J. R.; Horz, F.

    2003-01-01

    High shock pressures cause structural changes in plagioclase feldspars such as mechanical fracturing and disaggregation of the crystal lattice at submicron scales, the formation of diaplectic glass (maskelynite), and genuine melting. Past studies of visible/ near-infrared spectra of shocked feldspars demonstrated few spectral variations with pressure except for a decrease in the depth of the absorption feature near 1250-1300 nm and an overall decrease in reflectance. New visible/near-infrared spectra (400-2500 nm) of experimentally shocked (17-56 GPa) albite- and anorthite-rich rock powders demonstrate similar trends, including the loss of minor hydrated mineral bands near 1410, 1930, 2250, and 2350 nm. However, the most interesting new observations are increases in reflectance at intermediate pressures, followed by subsequent decreases in reflectance at higher pressures. The amount of internal scattering and overall sample reflectance is controlled by the relative proportions of micro-fractures, submicron grains, diaplectic glass, and melts formed during shock metamorphism. We interpret the observed reflectance increases at intermediate pressures to result from progressively larger proportions of submicron feldspar grains and diaplectic glass. The ensuing decreases in reflectance occur after diaplectic glass formation is complete and the proportion of genuine melt inclusions increases. The pressure regimes over which these reflectance variations occur differ between albite and anorthite, consistent with thermal infrared spectra of these samples and previous studies of shocked feldspars. These types of spectral variations associated with different peak shock pressures should be considered during interpretation and modeling of visible/near-infrared remotely sensed spectra of planetary and asteroidal surfaces.

  7. OSL-thermochronometry of feldspar from the KTB borehole, Germany

    NASA Astrophysics Data System (ADS)

    Guralnik, Benny; Jain, Mayank; Herman, Frédéric; Ankjærgaard, Christina; Murray, Andrew S.; Valla, Pierre G.; Preusser, Frank; King, Georgina E.; Chen, Reuven; Lowick, Sally E.; Kook, Myungho; Rhodes, Edward J.

    2015-08-01

    The reconstruction of thermal histories of rocks (thermochronometry) is a fundamental tool both in Earth science and in geological exploration. However, few methods are currently capable of resolving the low-temperature thermal evolution of the upper ∼2 km of the Earth's crust. Here we introduce a new thermochronometer based on the infrared stimulated luminescence (IRSL) from feldspar, and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions. Specifically, we present a new detailed Na-feldspar IRSL thermochronology from a well-documented thermally-stable crustal environment at the German Continental Deep Drilling Program (KTB). There, the natural luminescence of Na-feldspar extracted from twelve borehole samples (0.1-2.3 km depth, corresponding to 10-70 °C) can be either (i) predicted within uncertainties from the current geothermal gradient, or (ii) inverted into a geothermal palaeogradient of 29 ± 2 °C km-1, integrating natural thermal conditions over the last ∼65 ka. The demonstrated ability to invert a depth-luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing recent ambient temperatures of the shallow crust (<0.3 Ma, 40-70 °C range), or for studying equally recent and rapid transient cooling in active orogens (<0.3 Ma, >200 °C Ma-1 range). Although Na-feldspar IRSL is prone to field saturation in colder or slower environments, the method's primary relevance appears to be for borehole and tunnel studies, where it may offer remarkably recent (<0.3 Ma) information on the thermal structure and history of hydrothermal fields, nuclear waste repositories and hydrocarbon reservoirs.

  8. Naturally weathered feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa, Arizona: Electron microscopic characterization

    NASA Astrophysics Data System (ADS)

    Zhu, Chen; Veblen, David R.; Blum, Alex E.; Chipera, Stephen J.

    2006-09-01

    Naturally weathered feldspar surfaces in the Jurassic Navajo Sandstone at Black Mesa, Arizona, was characterized with high-resolution transmission and analytical electron microscope (HRTEM-AEM) and field emission gun scanning electron microscope (FEG-SEM). Here, we report the first HRTEM observation of a 10-nm thick amorphous layer on naturally weathered K-feldspar in currently slightly alkaline groundwater. The amorphous layer is probably deficient in K and enriched in Si. In addition to the amorphous layer, the feldspar surfaces are also partially coated with tightly adhered kaolin platelets. Outside of the kaolin coatings, feldspar grains are covered with a continuous 3-5 μm thick layer of authigenic smectite, which also coats quartz and other sediment grains. Authigenic K-feldspar overgrowth and etch pits were also found on feldspar grains. These characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems, and may partially contribute to the commonly observed apparent laboratory-field dissolution rate discrepancy. At Black Mesa, feldspars in the Navajo Sandstone are dissolving at ˜10 5 times slower than laboratory rate at comparable temperature and pH under far from equilibrium condition. The tightly adhered kaolin platelets reduce the feldspar reactive surface area, and the authigenic K-feldspar overgrowth reduces the feldspar reactivity. However, the continuous smectite coating layer does not appear to constitute a diffusion barrier. The exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer (leached layer versus re-precipitated silica), which is uncertain at present. However, the nanometer thin layer can be detected only with HRTEM, and thus our study raises the possibility of its wide occurrence in geological systems. Rate laws and proposed mechanisms should consider the

  9. Naturally weathered feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa, Arizona: Electron microscopic characterization

    USGS Publications Warehouse

    Zhu, Chen; Veblen, D.R.; Blum, A.E.; Chipera, S.J.

    2006-01-01

    Naturally weathered feldspar surfaces in the Jurassic Navajo Sandstone at Black Mesa, Arizona, was characterized with high-resolution transmission and analytical electron microscope (HRTEM-AEM) and field emission gun scanning electron microscope (FEG-SEM). Here, we report the first HRTEM observation of a 10-nm thick amorphous layer on naturally weathered K-feldspar in currently slightly alkaline groundwater. The amorphous layer is probably deficient in K and enriched in Si. In addition to the amorphous layer, the feldspar surfaces are also partially coated with tightly adhered kaolin platelets. Outside of the kaolin coatings, feldspar grains are covered with a continuous 3-5 ??m thick layer of authigenic smectite, which also coats quartz and other sediment grains. Authigenic K-feldspar overgrowth and etch pits were also found on feldspar grains. These characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems, and may partially contribute to the commonly observed apparent laboratory-field dissolution rate discrepancy. At Black Mesa, feldspars in the Navajo Sandstone are dissolving at ???105 times slower than laboratory rate at comparable temperature and pH under far from equilibrium condition. The tightly adhered kaolin platelets reduce the feldspar reactive surface area, and the authigenic K-feldspar overgrowth reduces the feldspar reactivity. However, the continuous smectite coating layer does not appear to constitute a diffusion barrier. The exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer (leached layer versus re-precipitated silica), which is uncertain at present. However, the nanometer thin layer can be detected only with HRTEM, and thus our study raises the possibility of its wide occurrence in geological systems. Rate laws and proposed mechanisms should consider the

  10. MDD Analysis of Microtexturally Characterized K-Feldspar Fragments

    NASA Astrophysics Data System (ADS)

    Short, C. H.; Heizler, M. T.; Parsons, I.; Heizler, L.

    2011-12-01

    Multiple diffusion domain (MDD) analysis of K-feldspar 40Ar/39Ar age spectra is a powerful thermochronological tool dating back 25 years, but continued validation of the basic assumptions of the model can be afforded by microanalysis of K-feldspar crystal fragments. MDD theory assumes that diffusion of Ar in K-feldspars is controlled by domains of varying size bounded by infinitely fast diffusion pathways. However, the physical character of these domain boundaries is not fully understood and this issue remains a point of criticism of the MDD model. We have evaluated the relationship between texture, age, and thermal history via step heating and modeling of texturally characterized K-feldspar crystal fragments (250-500 μm). K-feldspar phenocrysts from the Shap granite, chosen for their well-studied and relatively simple microtextures, contain large areas of homogenous regular strain-controlled film perthite with periodicities on the order of ~1 μm and abundant misfit dislocations, as well as areas of much coarser, irregular, slightly turbid, patch and vein perthite. Total gas ages (TGA) for all Shap fragments, regardless of texture, show less than 2% variation, but the shape of the age spectra varies with microtexture. Film perthites produce flat spectra whereas patch/vein perthite spectra have initial steps 5 - 25% older than the age of the emplacement with younger plateau or gently rising steps afterward. Patch/vein perthites have substantial microporosity and their spectral shapes may be a consequence of trapped 40Ar* that has diffused into micropores or other defects that have no continuity with the crystal boundaries. Correlations between spectral shape and heating schedule suggest that initial old ages are produced by the early release of trapped 40Ar* separated from the K parent rather than degassing of excess 40Ar*. The MH-42 K-feldspar from the Chain of Ponds Pluton has two primary microtextures: a coarse patch/vein perthite with lamellae 1-20 μm in

  11. Thermal infrared spectroscopy and modeling of experimentally shocked plagioclase feldspars

    USGS Publications Warehouse

    Johnson, J. R.; Horz, F.; Staid, M.I.

    2003-01-01

    Thermal infrared emission and reflectance spectra (250-1400 cm-1; ???7???40 ??m) of experimentally shocked albite- and anorthite-rich rocks (17-56 GPa) demonstrate that plagioclase feldspars exhibit characteristic degradations in spectral features with increasing pressure. New measurements of albite (Ab98) presented here display major spectral absorptions between 1000-1250 cm-1 (8-10 ??m) (due to Si-O antisymmetric stretch motions of the silica tetrahedra) and weaker absorptions between 350-700 cm-1 (14-29 ??m) (due to Si-O-Si octahedral bending vibrations). Many of these features persist to higher pressures compared to similar features in measurements of shocked anorthite, consistent with previous thermal infrared absorption studies of shocked feldspars. A transparency feature at 855 cm-1 (11.7 ??m) observed in powdered albite spectra also degrades with increasing pressure, similar to the 830 cm-1 (12.0 ??m) transparency feature in spectra of powders of shocked anorthite. Linear deconvolution models demonstrate that combinations of common mineral and glass spectra can replicate the spectra of shocked anorthite relatively well until shock pressures of 20-25 GPa, above which model errors increase substantially, coincident with the onset of diaplectic glass formation. Albite deconvolutions exhibit higher errors overall but do not change significantly with pressure, likely because certain clay minerals selected by the model exhibit absorption features similar to those in highly shocked albite. The implication for deconvolution of thermal infrared spectra of planetary surfaces (or laboratory spectra of samples) is that the use of highly shocked anorthite spectra in end-member libraries could be helpful in identifying highly shocked calcic plagioclase feldspars.

  12. Cathodoluminescence Characterization of Maskelynite and Alkali Feldspar in Shergottite (Dhofar 019)

    SciTech Connect

    Kayama, M.; Nakazato, T.; Nishido, H.; Ninagawa, K.; Gucsik, A.

    2009-08-17

    Dhofar 019 is classified as an olivine-bearing basaltic shergottite and consists of subhedral grains of pyroxene, olivine, feldspar mostly converted to maskelynite and minor alkali feldspar. The CL spectrum of its maskelynite exhibits an emission band at around 380 nm. Similar UV-blue emission has been observed in the plagioclase experimentally shocked at 30 and 40 GPa, but not in terrestrial plagioclase. This UV-blue emission is a notable characteristic of maskelynite. CL spectrum of alkali feldspar in Dhofar 019 has an emission bands at around 420 nm with no red emission. Terrestrial alkali feldspar actually consists of blue and red emission at 420 and 710 nm assigned to Al-O{sup -}-Al and Fe{sup 3+} centers, respectively. Maskelynite shows weak and broad Raman spectral peaks at around 500 and 580 cm{sup -1}. The Raman spectrum of alkali feldspar has a weak peak at 520 cm{sup -1}, whereas terrestrial counterpart shows the emission bands at 280, 400, 470, 520 and 1120 cm{sup -1}. Shock pressure on this meteorite transformed plagioclase and alkali feldspar into maskelynite and almost glass phase, respectively. It eliminates their luminescence centers, responsible for disappearance of yellow and/or red emission in CL of maskelynite and alkali feldspar. The absence of the red emission band in alkali feldspar can also be due to the lack of Fe{sup 3+} in the feldspar as it was reported for some lunar feldspars.

  13. Low-temperature multi-OSL-thermochronometry of feldspar

    NASA Astrophysics Data System (ADS)

    King, Georgina; Herman, Frederic; Lambert, Renske; Valla, Pierre; Guralnik, Benny

    2016-04-01

    Constraining exhumation rates and landscape histories over Quaternary timescales represents a major challenge for understanding the interaction between changing climate and erosion processes. Facilitated by closure temperatures of as low as ~30 C, OSL-thermochronometry is able to constrain cooling rates from the top few km of the earth's crust, and offers the potential for recent changes in erosion to be determined. Based on the well-established Quaternary dating technique of optically stimulated luminescence dating, OSL-thermochronometry benefits from a strong methodological and theoretical foundation. A further advantage of OSL-thermochronometry is that it is possible to measure multiple luminescence signals from a single mineral, such as feldspar. Therefore OSL-thermochronometry can be used as a multi-thermochronometer whereby different signals from the same mineral have closure temperatures in the range of 30-70 C, enabling the derivation of very precise cooling histories. However, in contrast to other low-temperature methods, OSL-thermochronometry is limited by signal saturation, restricting its application to either elevated temperature settings (e.g. bore holes, tunnels) or rapidly exhuming terranes. Here we outline the principles of multi-OSL-thermochronometry of feldspar and its potential as a low-temperature thermochronometry system.

  14. In situ feldspar dissolution rates in an aquifer

    NASA Astrophysics Data System (ADS)

    Zhu, Chen

    2005-03-01

    In situ silicate dissolution rates within the saturated Navajo sandstone, at Black Mesa, Arizona were determined from elemental fluxes in the aquifer. The mass transfer between groundwater and mineral matrix along flow paths was calculated from inverse mass balance modeling. The reaction time is bound by 14C-based travel time. BET surface areas were measured with N 2 gas adsorption. Dissolution rates for K-feldspar and plagioclase are 10 -19 and 10 -16 mol (feldspar) m -2 s -1, respectively, which are ˜10 5 times slower than laboratory experiment-derived rates under similar pH and temperature but at far from equilibrium conditions. The rates obtained in this study are consistent with the slower field rates found in numerous watershed and soil profile studies. However, these rates are from saturated aquifers, overcoming some concerns on estimated rates from unsaturated systems. The Navajo sandstone is a quartz-sandstone with a relatively simple and well-studied hydrogeology, groundwater geochemistry, and lithology, a large number of groundwater analyses and 14C groundwater ages, groundwater residence times up to ˜37 ky, groundwater pH from ˜8 to 10, and temperature from ˜15 to 35°C.

  15. Energy related studies utilizing K-feldspar thermochronology

    SciTech Connect

    Not Available

    1993-01-01

    Two distinct sources of information are available from a [sup 40]Ar/[sup 39]Ar step-heating experiment: the age spectrum and Arrhenius plot. Model ages are calculated from the flux of radiogenic argon ([sup 40]Ar*) (assuming trapped argon of atmospheric composition) relative to the reactor produced [sup 39]Ar evolved during discrete laboratory heating steps. With the additional assumption that the [sup 39]Ar is uniformly distributed within the sample, we can infer the spatial distribution of the daughter product. ne associated Arrhenius plot, derived by plotting the diffusion coefficient (obtained from the inversion of the 39[sup Ar] release function assuming a single domain) against the inverse temperature of laboratory heating, are a convolution of the parameters which characterize the individual diffusion domains (whether these be dictated by varying length scale, energetics, etc.). However, many and perhaps Most [sup 40]Ar/[sup 39]Ar age spectra for slowly cooled alkali feldspars are significantly different from model age spectra calculated assuming a single diffusion-domain size. In addition, Arrhenius plots calculated from the measured loss of [sup 39]Ar during the step heating experiment show departures from linearity that are inconsistent with diffusion from domains of equal size. By extending the single diffusion-domain closure model (Dodsontype) to apply to minerals with a discrete distribution of domain sizes, we obtained an internally consistent explanation for the commonly observed features of alkali feldspar age spectra and their associated Arrhenius plots.

  16. Dissolution of K-feldspar at CO2-saturated conditions

    NASA Astrophysics Data System (ADS)

    Rosenqvist, Jörgen; Kilpatrick, Andrew D.; Yardley, Bruce W. D.; Rochelle, Christopher A.

    2014-05-01

    Underground storage of carbon dioxide on a very large scale is widely considered to be an essential part of any strategy to reduce greenhouse gas emissions to the atmosphere. Aquifers in deep sedimentary basins have been identified as suitable targets for geological carbon dioxide storage, especially aquifers located in sandstone host rock. This has led to renewed interest in studying the interaction between sandstone minerals and aqueous fluids, as there is a paucity of data for CO2-containing systems at relevant conditions. In an attempt to improve data coverage for important silicate minerals, we have measured the dissolution kinetics of K-feldspar in CO2-saturated fluids over a range of temperatures. K-feldspar fragments were hand-picked from a larger sample, crushed to a narrow size range and cleaned. The grains were reacted with water in batch-type reactors at temperatures from 20°C to 200°C and pressures up to 200 bar, and the dissolution was followed by periodic withdrawal of aliquots of solution. The mineral grains were allowed to react with pure water for a number of weeks before injection of CO2 into the system. Excess CO2 was provided to ensure CO2 saturation in the experimental systems. While the reaction time before injection was not long enough to attain complete equilibrium, it did considerably lower the degree of undersaturation with respect to K-feldspar and helped highlight the effect of CO2 injection into a rock-equilibrated aqueous fluid. At all temperatures studied, injection of CO2 resulted in a rapid increase in the soluble concentrations of K and Si (and also Na from a plagioclase component). The dissolution then reached apparent steady state conditions after a few days, with observed dissolution rates in the range of 1E-9 to 1E-12 mol/m2/s over the temperature range studied. The CO2-saturated solutions maintained mildly acidic conditions throughout the experiments and the observed rates therefore fall roughly between rates measured in

  17. Thermodynamic Mixing Properties of Rb-K-Na Feldspars and Relevance to Rb-, NH4-, K-, Na-, and Li-Feldspar Thermal Expansion

    NASA Astrophysics Data System (ADS)

    Hovis, G. L.; Morabito, J.; Mott, A.

    2006-12-01

    We have investigated a ten-member Rb-K feldspar solid solution series having an ordered Al-Si distribution. Rb-microcline, or rubicline, was synthesized via repeated ion exchange experiments of microcline in molten RbCl. This resulted in Rb-feldspar containing ~92 mol percent Rb, which appears to be the maximum amount of Rb that ordered feldspars can take up using ion-exchange techniques at 1 kbar. [Similarly synthesized Al-Si disordered Rb-feldspar is even more limited in Rb content (Kovalskii and Kotelnikov, EMPG IX, 2002).] Compositions between 0 and 92 mol percent Rb were synthesized by combining rubicline and microcline in the desired molar proportions, then chemically homogenizing the samples at elevated temperature. Enthalpies of solution (20.1 wt percent HF, 50 °C, isoperibolic conditions) for the series are nearly linear with composition, with the possibility of low-magnitude positive enthalpies of Rb-K mixing at Rb-rich compositions. This behavior contrasts sharply with the considerably greater enthalpies of mixing in K-Na feldspars (Hovis, 1986, Journal of Petrology). Feldspars, therefore, which have but a single alkali site, exhibit larger enthalpies of mixing when there is a clear contrast in the sizes of the ions occupying that site. This is not surprising in light of the tendency of chemically homogeneous K-Na feldspars to undergo exsolution with cooling. In the case of the Rb end member, the feldspar structure appears to be stretched nearly to its limit. This is reflected by the coefficients of thermal expansion for Rb, NH4, K, Na and Li feldspar end members (all of which we have measured) that show a linear relationship with room-temperature unit-cell volume: The larger the unit cell at room temperature, the less potential there is for thermal expansion. [Similar relations are found as a function of K:Na in nepheline - kalsilite framework silicates (Hovis and others, Mineralogical Magazine, 2003).] Thus, even at room temperature the Rb-feldspar

  18. Feldspars Detected by ChemCam in Gale Crater with Implications for Future Martian Exploration

    NASA Astrophysics Data System (ADS)

    Gasda, P. J.; Carlson, E.; Wiens, R. C.; Bridges, J.; Sautter, V.; Cousin, A.; Maurice, S.; Gasnault, O.; Clegg, S. M.

    2015-12-01

    Feldspar is a common igneous mineral that can shed light on parent magma temperatures, pressures, and compositions. During the first 801 sols of the NASA Mars Science Laboratory mission, we have detected 125 possible feldspar grains using the ChemCam LIBS instrument. We analyzed spectra from successive laser shots at the same location and approximate whole rock compositions for each target. Feldspar-containing targets range from tephrite-basanite to trachyandesite. The most common feldspar type is andesine; no targets are >An60. Over 30% are anorthoclase, and ~10% have potassium contents up to Or60. Individual shot measurements in a single spot suggest some feldspars are zoned. Most of these rocks are either float or incorporated into conglomerates, and thus we do not know their provenance. Many of the samples may originate from the Gale crater walls, indicative of Southern Highland ancient crust. Some may also be flung from further away (e.g., emplaced by impact processes). Hence, these rocks may give us a general clue to the variety of evolved igneous materials on Mars. The ubiquity of feldspars at Gale suggests that they have been significantly underestimated for the Southern Highlands, if not for the whole of Mars. For example, significant abundance of andesitic feldspars in both the southern highland and northern lowlands of Mars would imply that Martian volcanism has produced a greater extent of evolved igneous materials to a greater degree than previously thought. Remote sensing instruments are insensitive to plagioclase due to dust cover, lack of exposures, or low feldspar FeO content. However, the Mars 2020 rover will be equipped with 3 new instruments, the arm-mounted SHERLOC Raman, PIXL μXRF, and the mast-mounted SuperCam combined Raman-LIBS instruments, which should help characterize Martian feldspars. Additionally, the SuperCam instrument plans to include three feldspars in its suite of 20+ onboard standards to improve feldspar chemical analysis.

  19. Feldspar basalts in lunar soil and the nature of the lunar continents

    NASA Technical Reports Server (NTRS)

    Reid, A. M.; Ridley, W. I.; Harmon, R. S.; Warner, J.; Brett, R.; Jakes, P.; Brown, R. W.

    1974-01-01

    It is found that 25% on the Apollo-14 glasses have the same composition as the glasses in two samples taken from the Luna-16 column. The compositions are equivalent to feldspar basalt and anorthosite gabbro, and are similar to the feldspar basalts identified from Surveyor-7 analysis for lunar continents.

  20. Aluminum position in Rb-feldspar as determined by X-ray photoelectron spectroscopy.

    PubMed

    Kyono, Atsushi; Kimata, Mitsuyoshi; Hatta, Tamao

    2003-09-01

    Al/Si configurations in some natural and synthetic Rb-feldspars have been examined carefully by EMPA and XPS analyses. Our results indicate that a small amount of H2O and excess Si and Al are incorporated in hydrothermally synthesized Rb-feldspar. The quantities of excess Al are 0.056 atoms per formula unit and are negatively correlated with those of the Rb, suggesting the presence of excess Al occupying non-tetrahedral sites in feldspar structures. This leads to incorporation of Al(Al3Si)O8 endmember into Rb-feldspars, estimated as one appropriate endmember indication for unusual chemistry of feldspars. In addition, Si2p, Al2p and O1s XPS signals of Rb-feldspars shift drastically toward the higher energy side than those of any natural feldspars. These provide conclusive evidence not only for existence of perceptible excess Si and Al, but also for Al at both extra-framework and tetrahedral sites in feldspar structures. PMID:14504785

  1. Oriented feldspar-feldspathoid intergrowths in rocks of the Khibiny massif: genetic implications

    NASA Astrophysics Data System (ADS)

    Ageeva, Olga A.; Abart, Rainer; Habler, Gerlinde; Ye. Borutzky, Boris; Trubkin, Nikolay V.

    2012-09-01

    Poikilitic megacrysts of alkali feldspar with abundant inclusions of feldspar-nepheline and feldspar-kalsilite micrographic or lamellar intergrowths are characteristic for the rischorrites of the Khibiny massif. Strict crystallographic orientation relations were identified among the intergrowth phases based on optical investigation using a 4-axes universal stage and crystal orientation imaging using electron back scatter diffraction. The most frequently observed orientation relation is the parallel orientation of the kalsilite and nepheline [001] directions with the [010] direction of the alkali feldspar host and concomitant coincidence of the feldspathoid [100] directions with the [100]-, [101]- and [001] directions of the alkali feldspar. The presence of relic nepheline within intergrowth domains and the successive replacement of precursor nepheline by alkali feldspar and associated formation of feldspar-feldspathoid intergrowth suggest development of the rischorrites from feldspar urtites, in which nepheline is the dominant felsic phase. The metasomatic nature of the transformation of urtites to rischorrites is identified from massive introduction of potassium and silica and removal of sodium. Metasomatism occurred at high temperature; the gigantic apatite deposits of the Khibiny massif seem to be related to this metasomatic event.

  2. Dissolution rates and surface chemistry of feldspar glass and crystal. Final technical report, June 15, 1995 - August 14, 2001

    SciTech Connect

    Brantley, S.; Pantano, C.

    2002-06-11

    Final report summarizing the completed work of the project entitled 'Dissolution of Feldspar in the Field and Laboratory.' One of the highly debated questions today in low-temperature geochemical kinetics centers upon the rate and mechanism of dissolution of feldspar, the most common mineral in the crust. In this project, the mechanisms of feldspar dissolution were investigated by emphasizing experiments with feldspar glass and crystal while comparing surface and solution chemistry. Specifically, laboratory work focused on the structure of altered surface layers on feldspars, the rate of dissolution of feldspar crystal and glass, and the presence of porosity and surface coatings on feldspars. In a complementary field project, the use of Sr concentrations and isotopic ratios were used to calculate feldspar dissolution rates.

  3. Characterization and Thermodynamics Studies of Feldspar and Feldspathoid Minerals

    NASA Astrophysics Data System (ADS)

    Rudow, M.; Lilova, K.

    2015-12-01

    The application of thermal analysis and calorimetry for the studies of minerals has a history as long as the existence of the thermal methods themselves. New advanced calorimetric techniques have been developed for more accurate characterization of both bulk and nano materials thus impacting their design, processing, and applications. TG-DTA and TG-DSC are used to characterize the composition of complex minerals (e.g. [KxNa1-x(AlSi3)O8]) based on the weight changes and phase transformations observed with temperature increase. Additionally, those techniques allow to determine the quantity of the different types of water contained in natural feldspars and feldspathoids (absorbed, interlayer, structural). The results for several clays will be discussed. The geochemical properties and thermal stability of another class of minerals - aluminosilicate frameworks (alkali sodalities, natrolites, etc.) as related to high-level nuclear waste treatment facilities, radioactive waste storage and management were studied. The natural sodalite Na8[Al6Si6O24]Cl2 and similar frameworks with different anions are part of sodium-aluminosilicate (NAS) low activity radioactive waste produced during steam reforming process treatment. The enthalpies and entropies of formation and the hydration enthalpies of the above-mentioned feltspathoids are obtained and the effect of the different cations and anions on the thermodynamic stability was studied. The results will allow to predict the long term behavior of the compounds in the environment under different conditions.

  4. Formation of halloysite from feldspar: Low temperature, artificial weathering versus natural weathering

    USGS Publications Warehouse

    Parham, W.E.

    1969-01-01

    Weathering products formed on surfaces of both potassium and plagioclase feldspar (An70), which were continuously leached in a Soxhlet extraction apparatus for 140 days with 7.21 of distilled water per day at a temperature of approximately 78 ??C, are morphologically identical to natural products developed on potassium feldspars weathered under conditions of good drainage in the humid tropics. The new products, which first appear as tiny bumps on the feldspar surface, start to develop mainly at exposed edges but also at apparently random sites on flat cleavage surfaces. As weathering continues, the bumps grow outward from the feldspar surface to form tapered projections, which then develop into wide-based thin films or sheets. The thin sheets of many projections merge laterally to form one continuous flame-shaped sheet. The sheets formed on potassium feldspars may then roll to form tubes that are inclined at a high angle to the feldspar surface. Etch pits of triangular outline on the artificially weathered potassium feldspars serve as sites for development of continuous, non-rolled, hollow tubes. It is inferred from its morphology that this weathering product is halloysite or its primitive form. The product of naturally weathered potassium feldspars is halloysite . 4H2O. The flame-shaped films or sheets formed on artificially weathered plagioclase feldspar do not develop into hollow tubes, but instead give rise to a platy mineral that is most probably boehmite. These plates form within the flame-shaped films, and with continued weathering are released as the film deteriorates. There is no indication from this experiment that platy pseudohexagonal kaolinite forms from any of these minerals under the initial stage of weathering. ?? 1969.

  5. Feldspar diagenesis in the Frio Formation, Brazoria County, Texas Gulf Coast

    SciTech Connect

    Land, L.S.; Milliken, K.L.

    1981-07-01

    Tremendous quantities of detrital feldspar have been dissolved or albitized below about 14000 ft (4267 m) in the Frio Formation (Oligocene), Chocolate Bayou Field, Brazoria County, Texas. Some sandstones no longer contain any unmodified detrital feldspar grains. Material transfer involved in these reactions is immense, affecting at least 15% of the rock volume. Thus, albitization has important implications for several other diagenetic processes that involve feldspars or their components. These processes include formation of secondary porosity, precipitation of quartz and carbonate cements, and the evolution of Na-Ca-Cl formation water.

  6. Authigenic potassium feldspar in Cambrian carbonates: Evidence of Alleghanian brine migration

    USGS Publications Warehouse

    Hearn, P.P., Jr.; Sutter, J.F.

    1985-01-01

    The shallow-water limestones and dolostones of the Conococheague Limestone (Upper Cambrian) of western Maryland contain large amounts of authigenic potassium feldspar. The presence of halite daughter crystals in breached fluid inclusions, low whole-rock ratios of chlorine to bromine, and thermochemical data suggest that the potassium feldspar formed at low temperature by the reaction of connate brines with intercalated siliciclastic debris. Analyses of argon age spectra indicate that the authigenic feldspar probably formed during Late Pennsylvanian to Early Permian time. These results may indicate mobilization and migration of connate brines brought about by Alleghanian folding. The widespread occurrence of authigenic potassium feldspar in Cambrian and Ordovician carbonate rocks throughout the Appalachians suggests that this may have occurred throughout the entire basin.

  7. Feldspar-Bearing Igneous Rocks at Gale: A ChemCam Campaign

    NASA Astrophysics Data System (ADS)

    Sautter, V.; Fabre, C.; Toplis, M.; Wiens, R. C.; Gasnault, O.; Forni, O.; Mangold, N.

    2014-09-01

    We present the first in situ evidences of feldspar-rich rocks ranging from granodioritic and alkalin effusive rocks (trachy basalts and syenitic liquids). Implication for primitive noachain crust will be discussed.

  8. Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Bryan, C.R.; Helean, K.B.; Marshall, B.D.; Brady, P.V.

    2009-01-01

    Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (???60 wt%) and quartz polymorphs (???35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10-16 to 10-17 mol s-1 kg tuff-1 with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10-15 to 10-16 mol s-1 kg tuff-1 for percolation fluxes of 15 mm a-1 and 1 mm a-1, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a-1 or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (???50 mg L-1) may inhibit feldspar dissolution. ?? 2009 Elsevier Ltd. All rights reserved.

  9. Evidence for Coordination and Redox Changes of Iron in Shocked Feldspar from Synchrotron MicroXANES

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Dyar, M. D.; Hoerz, F.; Johnson, J. R.

    2003-01-01

    Shock modification of feldspar has been documented and experimentally reproduced in many studies since the recognition of maskelynite in Shergotty. Experimentally shocked feldspar samples have been well studied using chemical and crystallographic techniques. The crystallographic, site-specific characterization of major and minor elements is less well documented. We present early x-ray absorption (XAS) spectral data for a suite of albitite samples that were experimentally shocked at pressures between 17 and 50 Gpa.

  10. [Study on the fine structure of K-feldspar of Qichun granite].

    PubMed

    Du, Deng-Wen; Hong, Han-Lie; Fan, Kan; Wang, Chao-Wen; Yin, Ke

    2013-03-01

    Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR), and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization. The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry. K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening [131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp [131] peak and is honiogeneously monoclinic. The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer (1974). The 640 cm-1 absorption band increases while the 540 cm-' absorption band decreases with increase in K-feldspar ordering index, also, the 1,010 cm-1 absorption band separates into 1,010 and 1,046 cm-1 absorption bands, with a change in the band shape from widening to sharp outline. The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements, and the granite exhibits better mineralization background, K-feldspar of the potassic alteration veins has markedly lower Sr and Ba, indicating that the alteration fluid originated from the granitic magmatism, and hence, potassic alteration is a good indicator for molybdenite exploration. PMID:23705418

  11. Feldspar concentrations in lower Cambrian limestones of the Moroccan Atlas: Pyroclastic vs authigenic processes

    NASA Astrophysics Data System (ADS)

    Álvaro, J. Javier; Bauluz, Blanca

    2008-02-01

    Carbonate strata containing abundant euhedral feldspar, usually considered as authigenic, are characteristic of some lower Cambrian exposures in the Atlas Mountains, Morocco. Impure limestones are abundant in the Issendalenian Amouslek Formation of the western Anti-Atlas, and in the Banian Lemdad Formation of the southern High Atlas. Some of their limestone beds contain up to 40% acid insoluble residue, of which feldspar comprises as much as 65% in some samples, the remainder consisting of detrital and authigenic quartz, apatite, pyrite, and clay minerals. The host limestones are bioclastic tempestites, ooidal-oncoidal-bioclastic shoal complexes, archaeocyathan-microbial peri-reef settings (mainly flanks but not reef cores), and microbial reefs. A volcanic origin is adopted for the feldspars based on: (i) fluctuations in feldspar concentration paralleling bedding, but unrelated to host-facies (except for the aforementioned archaeocyathan-microbial reef cores that were controlled by turbidity); (ii) the local association with glassy fragments (with feldspars embedded in glass shards); and (iii) the scattered occurrence of gradational lithofacies from silty tuff to tuffitic limestone. The mineral and chemical composition of the host-rock and diagenetic fluids was the determining factor for the kind of feldspar preservation. Although the primary type of K-feldspar replacement is albitization, secondary albite subsequently suffered from illitization, chloritization, and/or replacement by calcite. A direct implication of this work is the possible geochronological dating of both volcanic eruptions and archaeocyath- and trilobite-bearing host-rocks based on radiometric analyses within unaltered K-feldspar pyroclasts extracted after etching.

  12. Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent

    SciTech Connect

    Duffin, M.E. )

    1989-08-01

    Authigenic K-feldspar occurs in alteration profiles in uppermost Precambrian igneous and metamorphic basement rocks of the midcontinent. The K-feldspar is widespread and has been identified in six states. The profiles occur directly below the Cambrian-Precambrian unconformity and range from about <1 to 8 m in thickness. Authigenic K-feldspar occurs throughout the profile. The K-feldspar is monoclinic or triclinic by X-ray diffraction, of end-member composition, and may compose 63% of rock volume. Much of the K-feldspar formed by replacement of primary feldspar. A sample of wholly authigenic K-feldspar from altered basement in southern Illinois gives a K/Ar data of 549 {plus minus} 18 Ma (Early Cambrian). This data is in agreement with Early Cambrian Rb/Sr dates for potassic alteration of uppermost Precambrian basement in Ohio. Dated authigenic K-feldspars from both Ohio and Illinois give identical {delta}{sup 18}O values of 17.5, suggesting formation from a very similar fluid. Concordancy of both dates and {delta}{sup 18}O values suggests that the K-feldspar formed during an episode of potassic alteration during Early Cambrian time that affected much of midcontinent North America. The dates and {delta}{sup 18}O values for K-feldspar, when considered together, do not fit any of the hypotheses presented here.

  13. Systematic variations of argon diffusion in feldspars and implications for thermochronometry

    DOE PAGESBeta

    Cassata, William S.; Renne, Paul R.

    2013-03-07

    Coupled information about the time-dependent production and temperature-dependent diffusion of radiogenic argon in feldspars can be used to constrain the thermal evolution attending a host of Earth and planetary processes. To better assess the accuracy of thermal models, an understanding of the mechanisms and pathways by which argon diffuses in feldspars is desirable. Here we present step-heating Ar diffusion experiments conducted on feldspars with diverse compositions, structural states, and microstructural characteristics. The experiments reveal systematic variations in diffusive behavior that appear closely related to these variables, with apparent closure temperatures for 0.1–1 mm grains of ~200–400 °C (assuming a 10more » °C/Ma cooling rate). Given such variability, there is no broadly applicable set of diffusion parameters that can be utilized in feldspar thermal modeling; sample-specific data are required. Diffusion experiments conducted on oriented cleavage flakes do not reveal directionally-dependent diffusive anisotropy to within the resolution limits of our approach (approximately a factor of 2). Additional experiments aimed at constraining the physical significance of the diffusion domain are presented and indicate that unaltered feldspar crystals with or without coherent exsolution lamellae diffuse at the grain-scale, whereas feldspars containing hydrothermal alteration and/or incoherent sub-grain intergrowths do not. Arrhenius plots for argon diffusion in plagioclase and alkali feldspars appear to reflect a confluence of intrinsic diffusion kinetics and structural transitions that occur during incremental heating experiments. These structural transitions, along with sub-grain domain size variations, cause deviations from linearity (i.e., upward and downward curvature) on Arrhenius plots. An atomistic model for Arrhenius behavior is proposed that incorporates the variable lattice deformations of different feldspars in response to heating and

  14. Systematic variations of argon diffusion in feldspars and implications for thermochronometry

    SciTech Connect

    Cassata, William S.; Renne, Paul R.

    2013-03-07

    Coupled information about the time-dependent production and temperature-dependent diffusion of radiogenic argon in feldspars can be used to constrain the thermal evolution attending a host of Earth and planetary processes. To better assess the accuracy of thermal models, an understanding of the mechanisms and pathways by which argon diffuses in feldspars is desirable. Here we present step-heating Ar diffusion experiments conducted on feldspars with diverse compositions, structural states, and microstructural characteristics. The experiments reveal systematic variations in diffusive behavior that appear closely related to these variables, with apparent closure temperatures for 0.1–1 mm grains of ~200–400 °C (assuming a 10 °C/Ma cooling rate). Given such variability, there is no broadly applicable set of diffusion parameters that can be utilized in feldspar thermal modeling; sample-specific data are required. Diffusion experiments conducted on oriented cleavage flakes do not reveal directionally-dependent diffusive anisotropy to within the resolution limits of our approach (approximately a factor of 2). Additional experiments aimed at constraining the physical significance of the diffusion domain are presented and indicate that unaltered feldspar crystals with or without coherent exsolution lamellae diffuse at the grain-scale, whereas feldspars containing hydrothermal alteration and/or incoherent sub-grain intergrowths do not. Arrhenius plots for argon diffusion in plagioclase and alkali feldspars appear to reflect a confluence of intrinsic diffusion kinetics and structural transitions that occur during incremental heating experiments. These structural transitions, along with sub-grain domain size variations, cause deviations from linearity (i.e., upward and downward curvature) on Arrhenius plots. An atomistic model for Arrhenius behavior is proposed that incorporates the variable lattice deformations of different feldspars in response to heating and

  15. Asbestos contamination in feldspar extraction sites: a failure of prevention? Commentary.

    PubMed

    Cavariani, Fulvio

    2016-01-01

    Fibrous tremolite is a mineral species belonging to the amphibole group. It is present almost everywhere in the world as a natural contaminant of other minerals, like talc and vermiculite. It can be also found as a natural contaminant of the chrysotile form of asbestos. Tremolite asbestos exposures result in respiratory health consequences similar to the other forms of asbestos exposure, including lung cancer and mesothelioma. Although abundantly distributed on the earth's surface, tremolite is only rarely present in significant deposits and it has had little commercial use. Significant presence of amphibole asbestos fibers, characterized as tremolite, was identified in mineral powders coming from the milling of feldspar rocks extracted from a Sardinian mining site (Italy). This evidence raises several problems, in particular the prevention of carcinogenic risks for the workers. Feldspar is widespread all over the world and every year it is produced in large quantities and it is used for several productive processes in many manufacturing industries (over 21 million tons of feldspar mined and marketed every year). Until now the presence of tremolite asbestos in feldspar has not been described, nor has the possibility of such a health hazard for workers involved in mining, milling and handling of rocks from feldspar ores been appreciated. Therefore the need for a wider dissemination of knowledge of these problems among professionals, in particular mineralogists and industrial hygienists, must be emphasized. In fact both disciplines are necessary to plan appropriate environmental controls and adequate protections in order to achieve safe working conditions. PMID:27033611

  16. Progressive deformation of feldspar recording low-barometry impact processes, Tenoumer impact structure, Mauritania

    NASA Astrophysics Data System (ADS)

    Jaret, Steven J.; Kah, Linda C.; Harris, R. Scott

    2014-06-01

    The Tenoumer impact structure is a small, well-preserved crater within Archean to Paleoproterozoic amphibolite, gneiss, and granite of the Reguibat Shield, north-central Mauritania. The structure is surrounded by a thin ejecta blanket of crystalline blocks (granitic gneiss, granite, and amphibolite) and impact-melt rocks. Evidence of shock metamorphism of quartz, most notably planar deformation features (PDFs), occurs exclusively in granitic clasts entrained within small bodies of polymict, glass-rich breccia. Impact-related deformation features in oligoclase and microcline grains, on the other hand, occur both within clasts in melt-breccia deposits, where they co-occur with quartz PDFs, and also within melt-free crystalline ejecta, in the absence of co-occurring quartz PDFs. Feldspar deformation features include multiple orientations of PDFs, enhanced optical relief of grain components, selective disordering of alternate twins, inclined lamellae within alternate twins, and combinations of these individual textures. The distribution of shock features in quartz and feldspar suggests that deformation textures within feldspar can record a wide range of average pressures, starting below that required for shock deformation of quartz. We suggest that experimental analysis of feldspar behavior, combined with detailed mapping of shock metamorphism of feldspar in natural systems, may provide critical data to constrain energy dissipation within impact regimes that experienced low average shock pressures.

  17. Shock effects in plagioclase feldspar from the Mistastin Lake impact structure, Canada

    NASA Astrophysics Data System (ADS)

    Pickersgill, Annemarie E.; Osinski, Gordon R.; Flemming, Roberta L.

    2015-09-01

    Shock metamorphism, caused by hypervelocity impact, is a poorly understood process in feldspar due to the complexity of the crystal structure, the relative ease of weathering, and chemical variations, making optical studies of shocked feldspars challenging. Understanding shock metamorphism in feldspars, and plagioclase in particular, is vital for understanding the history of Earth's moon, Mars, and many other planetary bodies. We present here a comprehensive study of shock effects in andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada. Samples from a range of different settings were studied, from in situ central uplift materials to clasts from various breccias and impact melt rocks. Evidence of shock metamorphism includes undulose extinction, offset twins, kinked twins, alternate twin deformation, and partial to complete transformation to diaplectic plagioclase glass. In some cases, isotropization of alternating twin lamellae was observed. Planar deformation features (PDFs) are notably absent in the plagioclase, even when present in neighboring quartz grains. It is notable that various microlites, twin planes, and compositionally different lamellae could easily be mistaken for PDFs and so care must be taken. A pseudomorphous zeolite phase (levyne-Ca) was identified as a replacement mineral of diaplectic feldspar glass in some samples, which could, in some instances, also be potentially mistaken for PDFs. We suggest that the lack of PDFs in plagioclase could be due to a combination of structural controls relating to the crystal structure of different feldspars and/or the presence of existing planes of weakness in the form of twin and cleavage planes.

  18. Rock-Forming feldspars of the Khibiny alkaline pluton, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Ivanyuk, G. Yu.; Pakhomovsky, Ya. A.; Konopleva, N. G.; Kalashnikov, A. O.; Korchak, Yu. A.; Selivanova, E. A.; Yakovenchuk, V. N.

    2010-12-01

    This paper describes the structural-compositional zoning of the well-known Khibiny pluton in regard to rock-forming feldspars. The content of K-Na-feldspars increases inward and outward from the Main foidolite ring. The degree of coorientation of tabular K-Na-feldspar crystals sharply increases in the Main ring zone, and microcline-dominant foyaite turns into orthoclase-dominant foyaite. The composition of K-Na-feldspars in the center of the pluton and the Main ring zone is characterized by an enrichment in Al. This shift is compensated by a substitution of some K and Na with Ba (the Main ring zone) or by an addition of K and Na cations to the initially cation-deficient microcline (the central part of the pluton). Feldspars of volcanosedimentary rocks occurring as xenoliths in foyaite primarily corresponded to plagioclase An15-40, but high-temperature fenitization and formation of hornfels in the Main ring zone gave rise to the crystallization of anorthoclase subsequently transformed into orthoclase and albite due to cooling and further fenitization. Such a zoning is the result of filling the Main ring fault zone within the homogeneous foyaite pluton with a foidolite melt, which provided the heating and potassium metasomatism of foyaite and xenoliths of volcanosedimentary rocks therein. The process eventually led to the transformation of foyaite into rischorrite-lyavochorrite, while xenoliths were transformed into aluminum hornfels with anorthoclase, annite, andalusite, topaz, and sekaninaite.

  19. Raman Spectroscopic Characterization of the Feldspars: Implications for Surface Mineral Characterization in Planetary Exploration

    NASA Technical Reports Server (NTRS)

    Freeman, J. J.; Wang, Alian; Kuebler, K. E.; Haskin, L. A.

    2003-01-01

    The availability in the last decade of improved Raman instrumentation using small, stable, intense lasers, sensitive CCD array detectors, and advanced fast grating systems enabled us to develop the Mars Microbeam Raman Spectrometer (MMRS), a field-portable Raman spectrometer with precision and accuracy capable of identifying minerals and their different compositions. For example, we can determine Mg cation ratios in pyroxenes and olivines to +/-0.1 on the basis of Raman peak positions. Feldspar is another major mineral formed in igneous systems whose characterization is important for determining rock petrogenesis and alteration. From their Raman spectral pattern, feldspars can be readily distinguished from ortho- and chain-silicates and from other tecto-silicates such as quartz and zeolites. We show here how well Raman spectral analysis can distinguish among members within the feldspar group.

  20. Regional and local correlations of feldspar geochemistry of the Peach Spring Tuff, Alvord Mountain, California

    USGS Publications Warehouse

    Buesch, David C.

    2016-01-01

    The chemical composition of feldspar grains in an ignimbrite from the Spanish Canyon Formation in the Alvord Mountain area, California, have been used to confirm similarities in three measured sections locally, and they are similar to exposures of the Peach Spring Tuff (PST) regionally. Feldspar grains were identified on the basis of texture (zoning, as mantled feldspars, or in crystal clusters), whether the grains were attached to glass or were in pumice clasts, or were simply crystal fragments with no textural context. Chemistry was determined by electron microprobe analysis, and each analysis is calculated in terms of the percent endmember and plotted on orthoclase (Or) versus anorthite (An) plots. In general, the PST has sanidine and plagioclase compositions that are consistent with having formed in high-silica rhyolite and trachyte within a zoned magma chamber. Feldspars from the PST in Spanish Canyon area cluster along the rhyolitic trend with no grains along the trachytic trend. Similar clustering of feldspars along the rhyolitic trend with no grains along the trachytic trend also occur in the PST from Granite Spring and Providence Mountains to the east of the Alvord Mountain area, and the ranges in compositions are also similar in these locations. In contrast, the PST in the Kane Wash area of the Newberry Mountains has feldspars only from the rhyolitic trend in the basal deposits, but some grains from the trachytic trend are in the upper part of the deposit, and the range in compositions are greater than in the Spanish Canyon area. The variations in vertical compositional zoning and compositional range in these different deposits suggests there were probably different flow paths (or timing of the delivery) during the eruption and runout of the pyroclastic flow(s) generated from the climactic eruption of the PST magma chamber.

  1. Natural radioactivity and rare earth elements in feldspar samples, Central Eastern desert, Egypt.

    PubMed

    Walley El-Dine, Nadia; El-Shershaby, Amal; Afifi, Sofia; Sroor, Amany; Samir, Eman

    2011-05-01

    The pegmatite bodies of the Eastern Desert of Egypt are widely distributed especially along the Marsa-Alam-Idfu road. The Abu Dob area covers about 150km(2) of the Arabian Nubian shield at the central part of the Eastern Desert of Egypt. Most of the pegmatite is zoned; the zonation starts with milky quartz at the core followed by alkali feldspar at the margins. The feldspars vary in color from rose to milky and in composition from K-feldspar to Na-feldspar, sometimes interactions of both types are encountered. Thirteen feldspar samples were collected from different locations in the Abu Dob area for measuring the natural radioactivity of (238)U, (232)Th and (40)K using an HPGe detector. The variation in concentration of radionuclides for the area under investigation can be classified into regions of high, medium and low natural radioactivity. The average concentration in BqKg(-1) has been observed to be from 9.5 to 183675.7BqKg(-1) for (238)U, between 6.1 and 94,314.2BqKg(-1) for (232)Th and from 0 to 7894.6BqKg(-1) for (40)K. Radium equivalent activities (Ra(eq)), dose rate (D(R)) and external hazard (H(ex)) have also been determined. In the present work, the concentration of rare earth elements are measured for two feldspar samples using two techniques, Environmental Scanning Electron microscope XIL 30 ESEM, Philips, and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The existence of rare earth elements in this area are very high and can be used in different important industries. PMID:21324705

  2. Atmospheric weathering and silica-coated feldspar: Analogy with zeolite molecular sieves, granite weathering, soil formation, ornamental slabs, and ceramics

    PubMed Central

    Smith, Joseph V.

    1998-01-01

    Feldspar surfaces respond to chemical, biological, and mechanical weathering. The simplest termination is hydroxyl (OH), which interacts with any adsorption layer. Acid leaching of alkalis and aluminum generated a silica-rich, nanometers-thick skin on certain feldspars. Natural K, Na-feldspars develop fragile surfaces as etch pits expand into micrometer honeycombs, possibly colonized by lichens. Most crystals have various irregular coats. Based on surface-catalytic processes in molecular sieve zeolites, I proposed that some natural feldspars lose weakly bonded Al-OH (aluminol) to yield surfaces terminated by strongly bonded Si-OH (silanol). This might explain why some old feldspar-bearing rocks weather slower than predicted from brief laboratory dissolution. Lack of an Al-OH infrared frequency from a feldspar surface is consistent with such a silanol-dominated surface. Raman spectra of altered patches on acid-leached albite correspond with amorphous silica rather than hydroxylated silica–feldspar, but natural feldspar may respond differently. The crystal structure of H-exchanged feldspar provides atomic positions for computer modeling of complex ideas for silica-terminated feldspar surfaces. Natural weathering also depends on swings of temperature and hydration, plus transport of particles, molecules, and ionic complexes by rain and wind. Soil formation might be enhanced by crushing granitic outcrops to generate new Al-rich surfaces favorable for chemical and biological weathering. Ornamental slabs used by architects and monumental masons might last longer by minimizing mechanical abrasion during sawing and polishing and by silicifying the surface. Silica-terminated feldspar might be a promising ceramic surface. PMID:9520371

  3. Experimental alkali feldspar dissolution at 100 degree C by carboxylic acids and their anions

    SciTech Connect

    Stoessell, R.K. ); Pittman, E.D. )

    1990-05-01

    Feldspar dissolution will enhance sandstone porosity if the released aluminum can be transported away in the subsurface waters. Carboxylic acids have been proposed to provide hydrogen ions to promote dissolution and anions to complex aqueous aluminum to keep it in solution. However, the hydrogen ions should react quickly following acid generation in source beds, leaving monocarboxylic anions with lesser amounts of dicarboxylic acids and their anions on feldspar dissolution and the apparent complexing of aluminum in solution. Two-week dissolution experiments of alkali feldspar were run at 100{degree}C and 300 bars in acetic acid, oxalic acid, and sodium salt solutions of chloride, acetate, propionate, oxalate, and malonate. Extrapolation of the results, to reservoir conditions during sandstone diagenesis, implies that concentrations of aluminum-organic complexes are not significant for acetate and propionate and are possibly significant for oxalate and malonate, depending upon fluid compositions. Propionate appeared to inhibit feldspar dissolution and hence might decrease secondary porosity formation. Increases in aluminum concentrations in the presence of oxalic and acetic acid solutions appear to be due to enhanced dissolution kinetics and greater aluminum solubility under low-pH conditions. Such low-pH fluids are generally absent in subsurface reservoirs, making this an unlikely mechanism for enhancing porosity. Furthermore, the observed thermal instability of oxalate and malonate anions explains their general low concentrations in subsurface fluids which limits their aluminum complexing potential in reservoirs during late diagenesis.

  4. Secondary porosity revisited: The chemistry of feldspar dissolution by carboxylic acids and anions

    SciTech Connect

    Stoessell, R.K. ); Pittman, E.D. )

    1990-12-01

    Carboxylic acids in subsurface waters have been proposed as agents for dissolving feldspars and complexing aluminum to create secondary porosity in sandstones. Previously published experimental work indicated high aluminum mobility in the presence of carboxylic acid solutions. In order to further evaluate aluminum mobility, alkali feldspar dissolution experiments were run at 100C and 300 bars in the presence of mono- and dicarboxylic acids and their anions. Experimental results imply that under reservoir conditions, aluminum-organic anion complexes are insignificant for acetate and propionate and possibly significant for oxalate and malonate. Propionate appeared to inhibit alkali feldspar dissolution and, hence, may retard aluminum mobility. Dissolution of feldspar in the presence of oxalic and acetic acid can be explained by enhanced dissolution kinetics and greater aluminum mobility under low-pH conditions. The general absence of such low-pH fluids in subsurface reservoirs makes this an unlikely mechanism for creating secondary porosity. Also, the thermal instability of oxalate and malonate limits their aluminum-complexing potential in reservoirs at temperatures above 100C.

  5. Preferential cataclastic grain size reduction of feldspar in deformation bands in poorly consolidated arkosic sands

    NASA Astrophysics Data System (ADS)

    Exner, Ulrike; Tschegg, Cornelius

    2012-10-01

    This study presents microstructural as well as bulk and mineral chemical investigations of deformation bands in uncemented, friable arkosic sands of Miocene age (Vienna Basin, Austria). Our microstructural study indicates grain size reduction by grain flaking in deformation bands with small offsets (0.5-8 cm), and dominant intragranular fracturing and cataclasis of altered feldspar grains at larger displacements (up to 60 cm). Relative to quartz, the sericitized feldspar grains are preferably fractured and abraded, which additionally leads to an enrichment of mainly phyllosilicates by mechanical expulsion from feldspar. Both cataclasis of quartz and feldspar grains and enrichment of phyllosilicates result in grain size reduction within the deformation bands. The measured reduction in porosity of up to 20% is in some cases associated with a permeability reduction, reflected in the retention of iron-oxide rich fluids along deformation bands. These deformation bands formed at very shallow burial depths in unconsolidated sediments indicate that fault sealing may occur in the absence of chemical alteration of the deformation bands and lead to a compartmentalization of a groundwater or hydrocarbon reservoir.

  6. I-Xe Record of Cooling in K-Feldspar Inclusion from the Colomera (IIE) Iron

    NASA Technical Reports Server (NTRS)

    Pravdivtseva, Olga; Meshik, Alex; Hohenberg, Charles M.; Wasserburg, Gerald J.

    2000-01-01

    Individual mineral grains from a silicate inclusion of the Colomera IIE iron meteorite were studied by laser extraction to find suitable host phases for I-Xe dating. K-feldspar separate yields an I-Xe age of 4.552 Ga and a cooling rate of 4-16 C/Ma.

  7. Re-Examination of Anomalous I-Xe Ages: Orgueil and Murchison Magnetites and Allegan Feldspar

    NASA Technical Reports Server (NTRS)

    Hohenberg, Charles M.; Pravdivtseva, Olga V.; Meshik, Alex P.

    2000-01-01

    Old I-Xe age for Orgueil (and Murchison) magnetite is not confirmed. New results show closure 2.8 Ma after Shallowater/Bjurbole standard, 10.3 Ma later than previously reported. The anomalously old I-Xe age of Allegan feldspar is attributed to shock.

  8. SCR neon and argon in Kapoeta feldspar: Evidence for an active ancient Sun

    NASA Technical Reports Server (NTRS)

    Rao, M. N.; Garrison, D. H.; Bogard, D. D.

    1993-01-01

    From etched feldspar size-fractions of Kapoeta, we determine a significant excess of cosmogenic Ne-21 and Ar-38 over that produced by galactic cosmic rays. This excess component is attributed to early production by energetic solar protons and suggest that the energetic proton flux from the ancient Sun was several hundred times more intense than that of the contemporary Sun.

  9. Preferential cataclastic grain size reduction of feldspar in deformation bands in poorly consolidated arkosic sands

    PubMed Central

    Exner, Ulrike; Tschegg, Cornelius

    2012-01-01

    This study presents microstructural as well as bulk and mineral chemical investigations of deformation bands in uncemented, friable arkosic sands of Miocene age (Vienna Basin, Austria). Our microstructural study indicates grain size reduction by grain flaking in deformation bands with small offsets (0.5–8 cm), and dominant intragranular fracturing and cataclasis of altered feldspar grains at larger displacements (up to 60 cm). Relative to quartz, the sericitized feldspar grains are preferably fractured and abraded, which additionally leads to an enrichment of mainly phyllosilicates by mechanical expulsion from feldspar. Both cataclasis of quartz and feldspar grains and enrichment of phyllosilicates result in grain size reduction within the deformation bands. The measured reduction in porosity of up to 20% is in some cases associated with a permeability reduction, reflected in the retention of iron-oxide rich fluids along deformation bands. These deformation bands formed at very shallow burial depths in unconsolidated sediments indicate that fault sealing may occur in the absence of chemical alteration of the deformation bands and lead to a compartmentalization of a groundwater or hydrocarbon reservoir. PMID:26523078

  10. Modeling H, Na, and K diffusion in plagioclase feldspar by relating point defect parameters to bulk properties

    NASA Astrophysics Data System (ADS)

    Zhang, Baohua; Shan, Shuangming; Wu, Xiaoping

    2016-02-01

    Hydrogen and alkali ion diffusion in plagioclase feldspars is important to study the evolution of the crust and the kinetics of exsolution and ion-exchange reactions in feldspars. Using the available PVT equation of state of feldspars, we show that the diffusivities of H and alkali in plagioclase feldspars as a function of temperature can be successfully reproduced in terms of the bulk elastic and expansivity data through a thermodynamic model that interconnects point defect parameters with bulk properties. Our calculated diffusion coefficients of H, Na, and K well agree with experimental ones when uncertainties are considered. Additional point defect parameters such as activation enthalpy, activation entropy, and activation volume are also predicted. Furthermore, the electrical conductivity of feldspars inferred from our predicted diffusivities of H, Na, and K through the Nernst-Einstein equation is compared with previous experimental data.

  11. [Energy related studies utilizing K-feldspar thermochronology]. Progress report, 1991--1992

    SciTech Connect

    Not Available

    1992-03-01

    In our second year of current funding cycle, we have investigated the Ar diffusion properties and microstructures of K-feldspars and the application of domain theory to natural K-feldspars. We completed a combined TEM and argon diffusion study of the effect of laboratory heat treatment on the microstructure and kinetic properties of K-feldspar. We conclude in companion papers that, with one minor exception, no observable change in the diffusion behavior occurs during laboratory extraction procedures until significant fusion occurs at about 1100{degrees}C. The effect that is observed involves a correlation between the homogenization of cryptoperthite lamelle and the apparent increase in retentivity of about 5% of the argon in the K-feldspar under study. We can explain this effect of both as an artifact of the experiment or the loss of a diffusion boundary. Experiments are being considered to resolve this question. Refinements have been made to our experimental protocol that appears that greatly enhance the retrieval of multi-activation energies from K-feldspars. We have applied the multi-domain model to a variety of natural environments (Valles Caldera, Red River fault, Appalachian basin) with some surprising results. Detailed {sup 40}Ar/{sup 39} Ar coverage of the Red River shear zone, thought to be responsible for the accommodation of a significant fraction of the Indo-Asian convergence, strongly suggests that our technique can precisely date both the termination of ductile strike-slip motion and the initiation of normal faulting. Work has continued on improving our numerical codes for calculating thermal histories and the development of computer based graphing tools has significantly increased our productivity.

  12. Biochemical evolution II: origin of life in tubular microstructures on weathered feldspar surfaces.

    PubMed

    Parsons, I; Lee, M R; Smith, J V

    1998-12-22

    Mineral surfaces were important during the emergence of life on Earth because the assembly of the necessary complex biomolecules by random collisions in dilute aqueous solutions is implausible. Most silicate mineral surfaces are hydrophilic and organophobic and unsuitable for catalytic reactions, but some silica-rich surfaces of partly dealuminated feldspars and zeolites are organophilic and potentially catalytic. Weathered alkali feldspar crystals from granitic rocks at Shap, north west England, contain abundant tubular etch pits, typically 0.4-0.6 microm wide, forming an orthogonal honeycomb network in a surface zone 50 microm thick, with 2-3 x 10(6) intersections per mm2 of crystal surface. Surviving metamorphic rocks demonstrate that granites and acidic surface water were present on the Earth's surface by approximately 3.8 Ga. By analogy with Shap granite, honeycombed feldspar has considerable potential as a natural catalytic surface for the start of biochemical evolution. Biomolecules should have become available by catalysis of amino acids, etc. The honeycomb would have provided access to various mineral inclusions in the feldspar, particularly apatite and oxides, which contain phosphorus and transition metals necessary for energetic life. The organized environment would have protected complex molecules from dispersion into dilute solutions, from hydrolysis, and from UV radiation. Sub-micrometer tubes in the honeycomb might have acted as rudimentary cell walls for proto-organisms, which ultimately evolved a lipid lid giving further shelter from the hostile outside environment. A lid would finally have become a complete cell wall permitting detachment and flotation in primordial "soup." Etch features on weathered alkali feldspar from Shap match the shape of overlying soil bacteria. PMID:9860941

  13. CO2 Sequestration in Feldspar-Rich Sandstone: The Importance of Saturation State and Fluid Composition

    NASA Astrophysics Data System (ADS)

    Tutolo, B. M.; Luhmann, A. J.; Kong, X. Z.; Seyfried, W. E., Jr.; Saar, M. O.

    2014-12-01

    To investigate CO2 Capture, Utilization, and Storage (CCUS) in sandstones, we performed 150°C flow-through experiments on K-feldspar rich cores from the Eau Claire Formation. We observed mass transfer processes operating on a range of scales by measuring sample porosity, permeability, and surface area and fluid and solid chemistry. The close agreement between our measured K-feldspar dissolution rates and literature values demonstrate that feldspar-fluid interaction can be confidently modeled using our chosen rate parameters and characterization methods, but other hydrogeochemical processes evolve somewhat less predictably. Specifically, a sandstone core through which CO2-rich deionized water was recycled for 52 days decreased in porosity and permeability and increased in surface area while an Al hydroxide mineral, such as boehmite, precipitated within its pore space. However, two samples subjected to ~3 day single-pass experiments run with CO2-rich NaCl brines generally increased in porosity and surface area and decreased in permeability as K-feldspar was converted to a phase with kaolinite-like stoichiometry. Notably, boehmite remained two orders of magnitude less supersaturated than kaolinite in all samples from all experiments, and we therefore hypothesize that the identity of the secondary phase is related to the presence of NaCl in solution. Regardless of their identity, long-lived secondary phase supersaturations and low measured Al molalities suggest that Al is precipitated at approximately the same rate at which it is released to solution through feldspar hydrolysis. Finally, we note that, although core permeability measurably decreased in all three experiments, the magnitude of these changes is unlikely to impact CO2 injectivity over a CCUS reservoir's lifetime. The observations produced here are critical to the application of reactive transport models to CCUS systems, yet more work will be required in order to improve model predictions.

  14. Authigenic K-feldspar in salt rock (Haselgebirge Formation, Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Leitner, Christoph

    2015-04-01

    The crystallisation of authigenic quartz under low temperature, saline conditions is well known (Grimm, 1962). Also the growth of low temperature authigenic feldspar in sediments is a long known phenomenon (Kastner & Siever, 1979; Sandler et al., 2004). In this study we intend to show that halite (NaCl) is a major catalyser for authigenic mineral growth. During late Permian (c. 255-250 Ma), when the later Eastern Alps were located around north of the equator, the evaporites of the Haselgebirge Formation were deposited (Piller et al., 2004). The Haselgebirge Fm. consists in salt mines of a two-component tectonite of c. 50 % halite and 50 % sedimentary clastic and other evaporite rocks (Spötl 1998). Most of the clastic rocks are mud- to siltstones ("mudrock"). During this study, we investigated rare sandstones embedded in salt rock form four Alpine salt mines. Around 40 polished thin sections were prepared by dry grinding for thin section analysis and scanning electron microscopy. The sandstones consist mainly of quartz, K-feldspar, rock fragments, micas, accessory minerals and halite in the pore space. They are fine grained and well sorted. Mudrock clasts in sandstone were observed locally, and also coal was observed repeatedly. Asymmetric ripples were found only in the dimension of millimeters to centimeters. Euhedral halite crystals in pores indicate an early presence of halite. During early diagenesis, authigenic minerals crystallized in the following chronological order. (1) Where carbonate (mainly magnesite) occurred, it first filled the pore space. Plant remains were impregnated with carbonate. (2) Halite precipitated between the detritic sandstone grains. Carbonate grains can be completely embedded in halite. (3) K-feldspar and quartz grains usually expose a detritic core and a later grown euhedral inclusion free rim. Euhedral rims of K-feldspar often also enclose a halite core. K-feldspar replaced the pre-existing halite along former grain boundaries of

  15. Structure-dependent interactions between alkali feldspars and organic compounds: implications for reactions in geologic carbon sequestration.

    PubMed

    Yang, Yi; Min, Yujia; Jun, Young-Shin

    2013-01-01

    Organic compounds in deep saline aquifers may change supercritical CO(2) (scCO(2))-induced geochemical processes by attacking specific components in a mineral's crystal structure. Here we investigate effects of acetate and oxalate on alkali feldspar-brine interactions in a simulated geologic carbon sequestration (GCS) environment at 100 atm of CO(2) and 90 °C. We show that both organics enhance the net extent of feldspar's dissolution, with oxalate showing a more prominent effect than acetate. Further, we demonstrate that the increased reactivity of Al-O-Si linkages due to the presence of oxalate results in the promotion of both Al and Si release from feldspars. As a consequence, the degree of Al-Si order may affect the effect of oxalate on feldspar dissolution: a promotion of ~500% in terms of cumulative Si concentration was observed after 75 h of dissolution for sanidine (a highly disordered feldspar) owing to oxalate, while the corresponding increase for albite (a highly ordered feldspar) was ~90%. These results provide new insights into the dependence of feldspar dissolution kinetics on the crystallographic properties of the mineral under GCS conditions. PMID:22978468

  16. Age of K-feldspar authigenesis in Lower Paleozoic and uppermost Precambrian rocks of the Mississippi Valley area

    SciTech Connect

    Hay, R.L.; Liu, J. . Dept. of Geology); Deino, A. . Geochronology Center); Kyser, T.K. . Dept. of Geology)

    1992-01-01

    Published K-Ar dates (n = 12) of authigenic K-feldspar in Cambrian and Ordovician rocks of the Mississippi Valley area range from 448 to 375 Ma (Late Ordovician to Middle Devonian), suggesting a lengthy episode of K-feldspar authigenesis. Here the authors report an age span of 465--400 Ma (Middle Ordovician to Early Devonian) for authigenic K-feldspar of two samples from the alteration profile widely developed over Precambrian rocks at the unconformity with Cambrian deposits. This dating was done on 42 to 48 mesh grains of K-feldspar by the laser incremental-heating Ar-40/Ar-39 method. One sample, from west-central Wisconsin, is from a vein formed along a fracture in kaolinitic altered granite. Three grains nearest the fracture yielded plateau ages with a range of 9 Ma and an average of 430 Ma. Three grains distant from the fracture yielded a similar range of 10 Ma but with an average age of 397 Ma. Thus the grains grew over an extended period from at least 430 to 400 Ma. The other sample, from the St. Francois Mts. of Missouri, is of diabase replaced by K-feldspar. Three grains yielded plateau ages ranging over 20 Ma and apparently recording an extended history of K-feldspar growth. The average age of these grains is 454 Ma, compared to a K-Ar date of 444 [+-] 9 Ma obtained from a split of the same sample. The period(s) of K-feldspar authigenesis does not support its linkage with orogenic activity. Oxygen-isotope values of authigenic K-feldspar from lower Paleozoic and uppermost Precambrian rocks range from +19.8 to +23.0 [per thousand] and average 21.4 [per thousand] (N = 11). These values are compatible with formation of the K-feldspar from similar fluids and comparable temperatures.

  17. Effects of chemical surface modification on the ice nucleation ability of feldspar and illite

    NASA Astrophysics Data System (ADS)

    Augustin, Stefanie; Wex, Heike; Kanter, Sandra; Ebert, Martin; Niedermeier, Dennis; Stratmann, Frank

    2014-05-01

    Mineral dust is the most abundant ice nuclei (IN) in the atmosphere and thus it is thought to be important for ice nucleation in clouds (Murray et al. [2012]). The clay minerals contribute approximately two thirds of the mineral dust mass (Atkinson et al. [2013]), and illite is the most abundant clay mineral found in the atmosphere [Broadley et al., 2012]. In the past years a lot of the ice nucleation research focused on proxies for clay minerals like Arizona Test Dust (ATD), kaolinite and illite (see reviews by Murray et al. [2012] and Hoose and Möhler. [2012]). In most experiments, these substances acted as IN only at relatively low temperatures (lower than -25°C). Very recently Atkinson et al. (2013) showed that K-feldspar, which is a common crustal material, is the most active mineral dust with freezing temperatures above -20°C. In the present study we compared the immersion freezing behavior of size segregated illite and feldspar particles. We used illite-NX (Arginotec) and a feldspar sample from Minas Gerais, Brazil (consisting to roughly 80% of a K-feldspar with the remainder being a Na-feldspar). Both substances were examined in the framework of the INUIT research project. For the illite-NX particles freezing onset was observed at temperatures around -34°C. The feldspar sample already induced freezing at -23°C. The data obtained was in agreement to those reported in Broadley el al. [2012] and Atkinson et al. [2013]. To simulate chemical aging of the particle surface we coated the particles with sulfuric acid and repeated the measurements. The illite-NX showed a rather small change in the ice nucleation ability, whereas the freezing ability of the feldspar was strongly reduced and became similar to that of illite-NX. It seems that the sulfuric acid destroyed those sites on the particle surface which are responsible for the initiation of freezing. We continue our work in trying to better understand what exactly it is that gives K-feldspar its good IN

  18. Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar.

    PubMed

    Ciceri, Davide; Allanore, Antoine

    2015-01-01

    The rate of K+ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K+ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K+ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~101-102 μm), time (~101-102 min) and fluid volume (~100-101 mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils. PMID:26485160

  19. Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar

    PubMed Central

    Ciceri, Davide; Allanore, Antoine

    2015-01-01

    The rate of K+ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K+ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K+ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~101-102 μm), time (~101-102 min) and fluid volume (~100-101 mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils. PMID:26485160

  20. Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

    NASA Astrophysics Data System (ADS)

    Pagonis, Vasilis; Ankjærgaard, Christina; Jain, Mayank; Chithambo, Makaiko L.

    2016-09-01

    Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IRSL signals, both during and after short infrared stimulation pulses. The equations are developed using a recently proposed kinetic model, which describes localized electronic recombination via tunneling between trapped electrons and recombination centers in luminescent materials. Recombination is assumed to take place from the excited state of the trapped electron to the nearest-neighbor center within a random distribution of luminescence recombination centers. Different possibilities are examined within the model, depending on the relative importance of electron de-excitation and recombination. The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results.

  1. 40Ar/39Ar ages in deformed potassium feldspar: evidence of microstructural control on Ar isotope systematics

    NASA Astrophysics Data System (ADS)

    Reddy, Steven M.; Potts, Graham J.; Kelley, Simon P.

    2001-05-01

    Detailed field and microstructural studies have been combined with high spatial resolution ultraviolet laser 40Ar/39Ar dating of naturally deformed K-feldspar to investigate the direct relationship between deformation-related microstructure and Ar isotope systematics. The sample studied is a ~1,000 Ma Torridonian arkose from Skye, Scotland, that contains detrital feldspars previously metamorphosed at amphibolite-facies conditions ~1,700 Ma. The sample was subsequently deformed ~430 Ma ago during Caledonian orogenesis. The form and distribution of deformation-induced microstructures within three different feldspar clasts has been mapped using atomic number contrast and orientation contrast imaging, at a range of scales, to identify intragrain variations in composition and lattice orientation. These variations have been related to thin section and regional structural data to provide a well-constrained deformation history for the feldspar clasts. One hundred and forty-three in-situ 40Ar/39Ar analyses measured using ultraviolet laser ablation record a range of apparent ages (317-1030 Ma). The K-feldspar showing the least strain records the greatest range of apparent ages from 420-1,030 Ma, with the oldest apparent ages being found close to the centre of the feldspar away from fractures and the detrital grain boundary. The most deformed K-feldspar yields the youngest apparent ages (317-453 Ma) but there is no spatial relationship between apparent age and the detrital grain boundary. Within this feldspar, the oldest apparent ages are recorded from orientation domain boundaries and fracture surfaces where an excess or trapped 40Ar component resides. Orientation contrast images at a similar scale to the Ar analyses illustrate a significant deformation-related microstructural difference between the feldspars and we conclude that deformation plays a significant role in controlling Ar systematics of feldspars at both the inter- and intragrain scales even at relatively low

  2. Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

    PubMed Central

    Smith, Joseph V.

    1998-01-01

    Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; = Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars. PMID:9520372

  3. Preparation of ultrafine silica from potash feldspar using sodium carbonate roasting technology

    NASA Astrophysics Data System (ADS)

    Liu, Jia-nan; Shen, Xiao-yi; Wu, Yan; Zhang, Jun; Zhai, Yu-chun

    2016-08-01

    A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.

  4. Gamma activity of stream sediment feldspars as ceramic raw materials and their environmental impact.

    PubMed

    Aboelkhair, Hatem; Ibrahim, Tarek; Saad, Ahmed

    2012-08-01

    In situ gamma spectrometric measurements have been performed to characterise the natural radiation that emitted from the stream sediment feldspars in Wadi El Missikat and Wadi Homret El Gergab, Eastern Desert, Egypt. The measurements of potassium (K, %), equivalent uranium (eU, ppm) and equivalent thorium (eTh, ppm) were converted into specific activities and equivalent dose rate. The average specific activities were 1402 Bq kg(-1) for K, 113 Bq kg(-1) for eU and 108 Bq kg(-1) for eTh in Wadi El Missikat, while they were 1240, 104 and 185 Bq kg(-1) in Wadi Homret El Gergab. The calculated outdoor average effective dose rates was 1.1 mSv y(-1) in wadi El Missikat and 1.3 mSv y(-1) in Wadi Homret El Gergab. The terrestrial-specific activities and effective dose rate levels of the natural radioactivity in the two areas lie within the international recommended limits for occupational feldspar quarry workers. On the other hand, these results indicated that irradiation is higher than the allowable level for members of the public. Therefore, quarrying the feldspar sediments from these locations as ceramic raw materials may yield an undesired impact on the environment, especially through the indoor applications. PMID:22171098

  5. Isochron dating of sediments using luminescence of K-feldspar grains

    NASA Astrophysics Data System (ADS)

    Li, Bo; Li, Sheng-Hua; Wintle, Ann G.; Zhao, Hui

    2008-06-01

    A new method for dating well-bleached sediments is presented, with results for thirteen samples from China. The method uses an isochron constructed from the measurement of natural radiation doses received by potassium-feldspar grains in a range of grain sizes using the infrared stimulated luminescence (IRSL) signal. The age of deposition of the sediment is calculated from this isochron and from the internal dose rate to the grains from 40K and 87Rb in the crystal lattice. This procedure appears to overcome age underestimation due to anomalous fading, a phenomenon that has precluded conventional luminescence dating of K-feldspars and would be applicable to K-feldspars for which the natural dose is beyond the linear dose response region. Also, since the isochron IRSL method is reliant on only the internal dose rate, it overcomes problems related to (1) changes in past dose rate due to postdepositional migration of radionuclides, (2) changes in water content as water-lain sediments dry out, (3) spatial heterogeneity in the gamma dose rate, and (4) uncertainties in the cosmic ray dose rate during the period of sample burial.

  6. Sorption Mechanisms of Antibiotic Cephapirin onto Quartz and Feldspar by Raman Spectroscopy

    SciTech Connect

    Peterson, Jonathan; Wang, Wei; Gu, Baohua

    2009-01-01

    Raman spectroscopy was used to investigate the sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO2) and feldspar (KAlSi3O8) at different pH values. Depending on the charge and surface properties of the mineral, different reaction mechanisms including electrostatic attraction, monodentate and bidentate complexation were found to be responsible for CHP sorption. The zwitterion (CHPo) adsorbs to a quartz(+) surface by electrostatic attraction of the carboxylate anion group ( COO-) at a low pH, but adsorbs to a quartz(-) surface through electrostatic attraction of the pyridinium cation and possibly COO- bridge complexes at relatively higher pH conditions. CHP- bonds to a quartz(-) surface by bidentate complexation between one oxygen of COO- and oxygen from the carbonyl (C=O) of the acetoxymethyl group. On a feldspar surface of mixed charge, CHPo forms monodentate complexes between C=O as well as COO- bridging complexes or electrostatically attached to localized edge (hydr)oxy-Al surfaces. CHP- adsorbs to feldspar(-) through monodentate C=O complexation, and similar mechanisms may operate for the sorption of other cephalosporins. This research demonstrates, for the first time, that Raman spectroscopic techniques can be effective for evaluating the sorption processes and mechanisms of cephalosporin antibiotics even at relatively low sorbed concentrations (97-120 μmol/kg).

  7. Igneous phenocrystic origin of K-feldspar megacrysts in granitic rocks from the Sierra Nevada batholith

    USGS Publications Warehouse

    Moore, J.G.; Sisson, T.W.

    2008-01-01

    Study of four K-feldspar megacrystic granitic plutons and related dikes in the Sierra Nevada composite batholith indicates that the megacrysts are phenocrysts that grew in contact with granitic melt. Growth to megacrystic sizes was due to repeated replenishment of the magma bodies by fresh granitic melt that maintained temperatures above the solidus for extended time periods and that provided components necessary for K-feldspar growth. These intrusions cooled 89-83 Ma, are the youngest in the range, and represent the culminating magmatic phase of the Sierra Nevada batholith. They are the granodiorite of Topaz Lake, the Cathedral Peak Granodiorite, the Mono Creek Granite, the Whitney Granodiorite, the Johnson Granite Porphyry, and the Golden Bear Dike. Megacrysts in these igneous bodies attain 4-10 cm in length. All have sawtooth oscillatory zoning marked by varying concentration of BaO ranging generally from 3.5 to 0.5 wt%. Some of the more pronounced zones begin with resorption and channeling of the underlying zone. Layers of mineral inclusions, principally plagioclase, but also biotite, quartz, hornblende, titanite, and accessory minerals, are parallel to the BaO-delineated zones, are sorted by size along the boundaries, and have their long axes preferentially aligned parallel to the boundaries. These features indicate that the K-feldspar megacrysts grew while surrounded by melt, allowing the inclusion minerals to periodically attach themselves to the faces of the growing crystals. The temperature of growth of titanite included within the K-feldspar megacrysts is estimated by use of a Zr-in-titanite geothermometer. Megacryst-hosted titanite grains all yield temperatures typical of felsic magmas, mainly 735-760 ??C. Titanite grains in the granodiorite hosts marginal to the megacrysts range to lower growth temperatures, in some instances into the subsolidus. The limited range and igneous values of growth temperatures for megacryst-hosted titanite grains support the

  8. Age and thermochronology of K-feldspars from the Manson Impact Structure

    NASA Technical Reports Server (NTRS)

    Zeitler, P. K.; Kunk, M. J.

    1993-01-01

    As a contribution to the effort to obtain a precise age for the Manson Impact Structure, we are approaching the problem from a thermo chronological perspective, with the goal of extracting an age from Ar-40/Ar-39 age-spectrum analysis of partially overprinted K-feldspars taken from granitoid clasts. We find that shocked feldspars from Manson generally show a strong overprint in their age spectra, with more than 50 percent of each spectrum being reset. The reset portions of the age spectra correspond to gas lost from very small diffusion domains, and a characteristic of the Manson samples is the very large range in apparent diffusion dimensions that they display, with the smallest domains being some 400 times smaller than the largest domains. It is also noteworthy that the small domains comprise a substantial portion of the volume of the feldspars (50 percent or more). These observations are consistent with the extreme shock experienced by these samples. In detail, the spectra we have measured to date are saddle-shaped and show minimum ages of between 67 and 72 Ma, which we interpret to be maximum estimates for the age of the impact. In the case of one sample (M1-678.3; K-feldspar from a large syenite block located well below the apparent melt-matrix breccia in the M1 borehole), isotope correlation analysis suggests the presence of a non-atmospheric trapped Ar component (Ar-40/Ar-36 of 660 plus or minus 40), and an age of about 65.3 plus or minus 0.5 Ma (2 sigma). Our interpretation of our results is that the shock of impact greatly reduced the diffusion-domain sizes of our samples, making them susceptible to significant Ar loss during heating associated with impact. It appears that while our feldspars were partially open to Ar loss, they equilibrated with a non-atmospheric Ar component, probably related to impact-related degassing of old basement around the impact site.

  9. Age and thermochronology of K-feldspars from the Manson Impact Structure

    NASA Astrophysics Data System (ADS)

    Zeitler, P. K.; Kunk, M. J.

    1993-03-01

    As a contribution to the effort to obtain a precise age for the Manson Impact Structure, we are approaching the problem from a thermo chronological perspective, with the goal of extracting an age from Ar-40/Ar-39 age-spectrum analysis of partially overprinted K-feldspars taken from granitoid clasts. We find that shocked feldspars from Manson generally show a strong overprint in their age spectra, with more than 50 percent of each spectrum being reset. The reset portions of the age spectra correspond to gas lost from very small diffusion domains, and a characteristic of the Manson samples is the very large range in apparent diffusion dimensions that they display, with the smallest domains being some 400 times smaller than the largest domains. It is also noteworthy that the small domains comprise a substantial portion of the volume of the feldspars (50 percent or more). These observations are consistent with the extreme shock experienced by these samples. In detail, the spectra we have measured to date are saddle-shaped and show minimum ages of between 67 and 72 Ma, which we interpret to be maximum estimates for the age of the impact. In the case of one sample (M1-678.3; K-feldspar from a large syenite block located well below the apparent melt-matrix breccia in the M1 borehole), isotope correlation analysis suggests the presence of a non-atmospheric trapped Ar component (Ar-40/Ar-36 of 660 plus or minus 40), and an age of about 65.3 plus or minus 0.5 Ma (2 sigma). Our interpretation of our results is that the shock of impact greatly reduced the diffusion-domain sizes of our samples, making them susceptible to significant Ar loss during heating associated with impact. It appears that while our feldspars were partially open to Ar loss, they equilibrated with a non-atmospheric Ar component, probably related to impact-related degassing of old basement around the impact site.

  10. Comment on “Systematic variations of argon diffusion in feldspars and implications for thermochronometry” by Cassata and Renne

    NASA Astrophysics Data System (ADS)

    Lovera, Oscar M.; Harrison, T. Mark; Boehnke, Patrick

    2015-02-01

    Cassata and Renne (2013) is a data-rich paper potentially providing opportunities to systematically test long-standing models of argon diffusion behavior in feldspars and we congratulate them on a heroic achievement. That said, several of their interpretations are highly problematic due to misconceptions of both the nature of their sample and diffusion modeling. Evidence of grain-scale diffusion in an exsolved feldspar

  11. What classic greywacke (litharenite) can reveal about feldspar diagenesis: An example from Permian Rotliegend sandstone in Hessen, Germany

    NASA Astrophysics Data System (ADS)

    Molenaar, Nicolaas; Felder, Marita; Bär, Kristian; Götz, Annette E.

    2015-08-01

    Rotliegend siliciclastic sediments in southern Hessen (Germany) are a good example of dissolution of detrital feldspars, which is a common feature in many sandstones. Dissolution occurred after mechanical compaction of the lithic-rich sandstone, which experienced framework collapse with pores and pore connections filled and obstructed by deformed ductile lithic grains (pseudomatrix) thereby reducing pore space to microporosity., The advanced degree of compaction and reduced porosity caused low permeability and low hydraulic conductivity of the rock mass. This is further reduced by the presence of wackes and shales that occur intercalated with the sandstones. Feldspar dissolution thus took place in low permeable sediments when large-scale flow of meteoric or acidic fluids is ruled out as a cause of feldspar dissolution. Mineral precipitation (illite, kaolinite, and albite) took place within pseudomatrix and detrital matrix as well as in secondary pores created by feldspar dissolution. Feldspar was the source for the authigenesis. The system was thus closed during burial after framework collapse, and diagenetic reactants in the form of detrital components were already present within the system. The original mass was preserved, but redistributed and diagenetic minerals were the local sinks for the dissolved reactants, precipitating within the system. This also suggests that burial diagenesis in general might be more mass conservative than usually assumed. Rotliegend sandstones thus form a case where, despite of the lack of external exchange of mass by fluid flow, major diagenetic processes did take place and significantly modified the original mineralogy and texture. Feldspar diagenesis can take place from other processes than mere large-scale flushing of open systems as often supposed. It implies that the volumes of rock affected by feldspar diagenesis may be much larger than anticipated based upon the common hold believe that feldspar diagenesis is linked to

  12. AUthigenic feldspar as an indicator of paleo-rock/water interactions in Permian carbonates of the Northern Calcareous Alps, Austria

    USGS Publications Warehouse

    Spotl, C.; Kralik, M.; Kunk, M.J.

    1996-01-01

    Dolostones interbedded with Upper Permian evaporites at the base of the Northern Calcareous Alps contain abundant authigenic K-feldspar. Two petrographically, structurally, and isotopically distinct generations of K-feldspar can be distinguished: crystals composed of an inclusion-rich core and a clear rim, and optically unzoned, transparent crystals. Both feldspar types have essentially identical K-feldspar end-member compositions with ??? 99.5 mole % Or component. Low oxygen isotope ratios (+16.1??? to +18.1??? SMOW) suggest precipitation from 18O-enriched, saline fluids at temperatures in excess of ??? 140??C. 40Ar/39Ar plateau-age spectra of five samples range from 145 ?? 1 to 144 ?? 1 Ma (Early Berriasian) and suggest that both types of feldspar were formed within an interval that did not exceed ??? 2 m.y. Rb/Sr model ages range from 152 to 140 Ma, assuming that the burial diagenetic regime was buffered with respect to strontium by the associated marine Permian evaporites. Authigenic K-feldspar records two distinct events of hot brine flow, most likely triggered by tectonic movements (detachment) and by an increase in the subsurface temperature in response to thrust loading.

  13. Surface chemistry of labradorite feldspar reacted with aqueous solutions at pH = 2, 3, and 12

    NASA Astrophysics Data System (ADS)

    Casey, William H.; Westrich, Henry R.; Arnold, George W.

    1988-12-01

    The reaction of feldspar with an aqueous solution is examined by complementing dissolution rate measurements with analysis of mineral surface chemistry. Rates of feldspar dissolution were measured in H 2O - HCl and D 2O - DCl solutions. These measurements were combined with elastic recoil detection (ERD) analysis of hydrogen isotope concentration, and Rutherford backscattering analysis (RBS) of silicon, aluminum and calcium concentrations near the surface of the mineral. Dissolution rates of labradorite feldspar in H 2O - HCl solutions ( pH = 1.7) are 33% more rapid than in D 2O - DCl mixtures ( pD = 1.7). The depth of penetration and inventory of hydrogen in the feldspar is a strong function of solution pH, temperature, and reaction time. Hydrogen infiltrates the feldspar more extensively from an acidic solution than from a basic solution, and complete isotopic exchange between the hydration layer and water proceeds in time on the order of hours. The hydrolysis of bridging Si - O - Al bonds by reaction with a strongly acidic solution for several hundreds of hours progresses to depths of several hundreds of Angstroms into the mineral. Calcium is also removed from the mineral to this depth during reaction with an acidic solution. The composition of the reacted surface, however, cannot be explained solely on the basis of ion exchange or depolymerization reactions. The data suggest that the silicon-rich surface of feldspar continually repolymerizes during reaction, and that this repolymerization eliminates hydrogen from the hydration layer.

  14. Solution-precipitation of K-feldspar in deformed granitoids and its relationship to the distribution of water

    NASA Astrophysics Data System (ADS)

    Fukuda, Jun-ichi; Okudaira, Takamoto; Satsukawa, Takako; Michibayashi, Katsuyoshi

    2012-04-01

    We have investigated K-feldspar recrystallisation in granitoid mylonites within a ductile shear zone from the Ryoke metamorphic belt, SW Japan. Fine-grained K-feldspar (20 μm on average) occurs in the matrix and in pull-apart areas within fractured K-feldspar porphyroclasts. These fine grains are elongated and oriented parallel to the main foliation in the matrix, and their grain surfaces, observed with the scanning electron microscope, are not smooth, but rough due to the development of very fine (< 1 μm) round grains of K-feldspar on the surface of each grain. In pull-apart areas, the crystallographic orientation of fine-grained K-feldspar, as measured by electron backscatter diffraction (EBSD), is strongly controlled by that of the host porphyroclast, and shows rotations with shear components parallel to fractures. In the matrix, the crystallographic orientation of fine-grained K-feldspar is not consistent with intracrystalline plasticity, but rather with a growth rate that is slightly controlled by nearby porphyroclasts. All this, together with the growth features on grains, suggests that solution-precipitation of K-feldspar from K-rich aqueous fluid occurred during progressive deformation. Infrared (IR) mapping was performed to evaluate the distribution of water in pull-apart areas and the matrix. Water is heterogeneously distributed within K-feldspar porphyroclasts, which contain 150-2200 ppm H2O. In contrast, the water content is low (150-300 ppm H2O) and homogeneously distributed in fine-grained K-feldspar in the matrix and pull-apart areas, even though included in these analyses are grain boundaries that can generally contain abundant aqueous fluid. The results of EBSD analysis and IR mapping indicate that water is released during solution-precipitation of K-feldspar under mid-crustal conditions. The solution-precipitation process under a water-rich environment in the middle crust results in the formation of fine grains, possibly deforming dominantly by

  15. Feldspar-fluid interactions in braid microperthites: pleated rims and vein microperthites

    NASA Astrophysics Data System (ADS)

    Lee, Martin R.; Waldron, Kim A.; Parsons, I.; Brown, William L.

    Braid microperthitic alkali feldspars in the Klokken, South Greenland and Coldwell, Ontario syenite intrusions have bulk-compositional variations along grain boundaries called pleated rims. These, together with vein microperthites in aplites which cross-cut the syenites, have been investigated by SEM and TEM. We distinguish two main types of pleated rims, ``arched '' and ``parallel-sided '', consisting of alternating Ab- and Or-rich areas on (001), which are 0.5-300 μm in length normal to (010) and 0.2-20 μm in width along (010). The smallest pleats, which occur on intracrystalline boundaries in Klokken feldspars, are fully coherent and composed of low albite and low microcline. Above the heads of some of the coarser pleats, braid microperthite grades into a film crypto- and micro-perthite and antiperthite microtexture called a ``transitional zone'' containing roughly planar lamellae of low albite and tweed orthoclase. During pleat development, local alternating volumes form in which the proportions of the phases differ ( phase separation) and the morphology of the intergrowths changes from braided to straight in response to this change in local bulk composition. Straightening is also accompanied by transformation of low microcline to tweed orthoclase. The coarsest pleats, which occur along grain boundaries in feldspars from the Coldwell syenite, are semi- or in-coherent and have a thick coherent and semicoherent transitional zone. Coarsening of pleats and development of the transitional zone has been facilitated by diffusion of ``water'' into grain interiors. In many cases, pleated rims have suffered deuteric alteration, by dissolution-reprecipitation processes, through the action of a water-rich fluid from the grain boundary, in which tweed orthoclase was transformed into irregular microcline and micropores developed. Vein microperthites in aplites from Klokken, and by extension the vein microperthites almost universal in most alkali granites, are interpreted

  16. Feldspar microtextures and multistage thermal history of syenites from the Coldwell Complex, Ontario

    NASA Astrophysics Data System (ADS)

    Waldron, Kim A.; Parsons, Ian

    1992-06-01

    Optical and TEM (transmission electron microscopy) observations of perthites from augite syenites in the Coldwell Complex (Ontario) reveal a complex set of microtextures that outline a multistage thermal history. Regular microtextures (linear or braid texture, straincontrolled, coherent intergrowths) show a progressive evolution from the margin of the intrusion inwards with lamellar spacings in the range 40 100 nm. The textures evolve in a manner similar to those for the Klokken intrusion and reflect differences in cooling rates and bulk composition. Superimposed upon the regular microtexture are 10 μm scale compositional fluctuations which we call “ripples”. The boundary relationships and bulk composition of ripples, which are themselves Ab-rich and Or-rich linear coherent cryptoperthites, suggest that they formed by coarsening during a phase of high-temperature (˜530°C) fluid-feldspar interaction. This was followed by a return to coherent exsolution in which fluid was not involved. Coarse, irregular, patch microperthite cross-cuts all other microtextures. These final “deuteric” intergrowths are believed to result from a further low-temperature (< 380° C) fluid-feldspar interaction and are associated with subgrain formation and the presence of micropores. The outermost syenite sample, against a gabbro ring structure, has distinctive, modified microtextures, indicating that the gabbro is, at least in part, a later intrusion. Our findings show that TEM work on alkali feldspar microtextures can identify discrete thermal events in the cooling history of igneous plutons and illustrates the potential of such microtextures for establishing the relative ages of intrusive rocks.

  17. Crystallization kinetics of alkali feldspars in cooling and decompression-induced crystallization experiments in trachytic melt

    NASA Astrophysics Data System (ADS)

    Arzilli, Fabio; Carroll, Michael R.

    2013-10-01

    Cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar, the effect of the degree of undercooling ( ΔT = T liquidus - T experimental) and time on nucleation and crystal growth process. This experimental work gives us new data about crystallization kinetics of trachytic melts, and it that will be useful to better understand the natural system of Campi Flegrei volcanoes. Experiments have been conducted using cold seal pressure vessel apparatus, at pressure between 30 and 200 MPa, temperature between 750 and 855 °C, time between 7,200 and 57,600 s and redox condition close to the NNO +0.8 buffer. These conditions are ideal to reproducing pre- and syn-eruptive conditions of the Campi Flegrei volcanoes, where the "conditions" pertain to the complete range of pressures, temperatures and time at which the experiments were performed. Alkali feldspar is the main phase present in this trachyte, and its abundance can strongly vary with small changes in pressure, temperature and water content in the melt, implying appreciable variations in the textures and in the crystallization kinetics. The obtained results show that crystallization kinetics are strictly related to ΔT, time, final pressure, superheating (- ΔT) and water content in the melt. ΔT is the driving force of the crystallization, and it has a strong influence on nucleation and growth processes. In fact, the growth process dominates crystallization at small ΔT, whereas the nucleation dominates crystallization at large ΔT. Time also is an important variable during crystallization process, because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations. This is an important aspect to understand magma evolution in the magma chamber and in the conduit, which in turn has strong effects on magma rheology.

  18. Effect of ageing of K-feldspar on its ice nucleating efficiency in immersion, deposition and contact freezing modes

    NASA Astrophysics Data System (ADS)

    Peckhaus, Andreas; Bachmann, Felix; Hoffmann, Nadine; Koch, Michael; Kiselev, Alexei; Leisner, Thomas

    2015-04-01

    Recently K-feldspar was identified as one of the most active atmospheric ice nucleating particles (INP) of mineral origin [1]. Seeking the explanation to this phenomena we have conducted extensive experimental investigation of the ice nucleating efficiency of K-feldspar in three heterogeneous freezing modes. The immersion freezing of K-feldspar was investigated with the cold stage using arrays of nanoliter-size droplets containing aqueous suspension of polydisperse feldspar particles. For contact freezing, the charged droplets of supercooled water were suspended in the laminar flow of the DMA-selected feldspar-containing particles, allowing for determination of freezing probability on a single particle-droplet contact [2]. The nucleation and growth of ice via vapor deposition on the crystalline surfaces of macroscopic feldspar particles have been investigated in the Environmental Scanning Electron Microscope (ESEM) under humidified nitrogen atmosphere. The ice nucleation experiments were supplemented with measurements of effective surface area of feldspar particles and ion chromatography (IC) analysis of the leached framework cations (K+, Na+, Ca2+, Mg2+). In this contribution we focus on the role of surface chemistry influencing the IN efficiency of K-feldspar, in particular the connection between the degree of surface hydroxylation and its ability to induce local structural ordering in the interfacial layer in water molecules (as suggested by recent modeling efforts). We mimic the natural process of feldspar ageing by suspending it in water or weak aqueous solution of carbonic acid for different time periods, from minutes to months, and present its freezing efficiency as a function of time. Our immersion freezing experiments show that ageing have a nonlinear effect on the freezing behavior of feldspar within the investigated temperature range (-40°C to -10°C). On the other hand, deposition nucleation of ice observed in the ESEM reveals clear different pattern

  19. Investigation of Potassium Feldspar Reactivity in Wet Supercritical CO2 by In Situ Infrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Thompson, C.; Widener, C.; Schaef, T.; Loring, J.; McGrail, B. P.

    2014-12-01

    Capture and subsequent storage of CO2 in deep geologic reservoirs is progressively being considered as a viable approach to reduce anthropogenic greenhouse gas emissions. In the long term, injected CO2 may become permanently entrapped as silicate minerals react with CO2 enriched fluids to form stable carbonate minerals. Potassium feldspars are highly abundant in the earth's crust and are present in the caprocks and storage formations of many target reservoirs. While the dissolution kinetics and carbonation reactions of feldspars have been well studied in the aqueous phase, comparatively little work has focused on K-feldspar reactivity in the CO2-rich fluid. In this study, we used in situ infrared spectroscopy to investigate the carbonation reactions of natural microcline samples. Experiments were carried out at 50 °C and 91 bar by circulating dry or wet supercritical CO2 (scCO2) past a thin film of powdered sample. Water concentrations ranged from 0% to 125% relative to saturation, and transmission-mode absorbance spectra were recorded as a function of time for 48 hours. No discernible reaction was detected when the samples were exposed to anhydrous scCO2. However, in fully water-saturated scCO2, a thin film of liquid-like water was observed on the samples' surfaces, and up to 0.6% of the microcline was converted to a carbonate phase. Potassium carbonate is the most likely reaction product, but minor amounts of sodium carbonate and siderite may also have formed from minor sample impurities. The extent of reaction appears to be related to the thickness of the water film and is likely a consequence of the film's ability to solvate and transport ions in the vicinity of the mineral surface. Other features observed in the spectra correspond to microcline dissolution and precipitation of amorphous silica. Implications about the role of water in these reactions and the relative effectiveness of alkali feldspars for mineral trapping of CO2 will be discussed.

  20. Age of authigenic K-feldspar in Lower Paleozoic and uppermost Precambrian rocks of the Mississippi Valley area

    SciTech Connect

    Hay, R.L.; Liu, J. . Dept. of Geology); Deino, A. . Geochronology Center); Kyser, T.K. . Dept. of Geology)

    1993-03-01

    Published K-Ar dates of authigenic K-feldspar in Cambrian and Ordovician rocks of the Mississippi Valley area range from 448 to 375 Ma (Late Ordovician to Middle Devonian), suggesting a lengthy episode of K-feldspar authigenesis. Here the authors report an age span of [approximately]464--400 Ma (Middle Ordovician to Early Devonian) for authigenic K-feldspar of two samples from the alteration profile widely developed over Precambrian rocks at the unconformity with Cambrian deposits. This dating was done on 42 to 48 mesh grains of K-feldspar by the laser incremental-heating [sup 40]Ar/[sup 39]Ar method. One sample, from west-central Wisconsin, is from an 8-mm-thick vein formed along a fracture in kaolinitic altered granite. Three grains nearest the fracture yielded plateau ages with a range of [approximately]9 Ma and an average of 430 Ma. Three grains distant from the fracture yielded a similar range of 10 Ma but with an average age of 397 Ma. Thus the grains grew over an extended period from at least [approximately]430 to 400 Ma. A K-Ar date of 411 Ma was obtained from a sample representing the entire thickness of the vein. The other sample, from the St. Francois Mts. of Missouri, is of diabase replaced by K-feldspar. Three grains yielded plateau ages ranging from [approximately]444 to 464 Ma. Oxygen-isotope values of authigenic K-feldspar from lower Paleozoic and uppermost Precambrian rocks range from +19.8 to +22.2[per thousand] and average 21.4[per thousand] (n = 11). These values are compatible with formation of the K-feldspar from similar fluids and comparable temperatures.

  1. Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

    USGS Publications Warehouse

    Spotl, C.; Kunk, M.J.; Ramseyer, K.; Longstaffe, F.J.

    1998-01-01

    This paper is included in the Special Publication entitled 'Dating and duration of fluid flow and fluid-rock interaction', edited by J. Parnell. Feldspar is a common authigenic constituent in Permian carbonate rocks which occur as tectonically isolated blocks within the evaporitic Haselgebirge melange in the Northern Calcareous Alps (NCA). Coexisting with pyrite, anhydrite, (saddle) dolomite, magnesite, fluorite and calcite, K-feldspar and minor albite record an event of regionally extensive interaction of hot brines with carbonate rocks. Detailed petrographic, crystallographic and geochemical studies reveal a variability in crystal size and shape, Al-Si ordering, elemental and stable isotopic compositions of the K-feldspar, which is only partially consistent with the traditional view of authigenic feldspar as a well-ordered, compositionally pure mineral. 40Ar-39Ar step- heating measurements of authigenic potassium feldspar from several localities yield two age populations, an older one of 145-154 Ma, and a younger one of c.90-97 Ma. Most age spectra reflect cooling through the argon retention temperature interval, which was rapid in some localities (as indicated by plateau ages) and slower in others. Rb-Sr isotope data are more difficult to interpret, because in many K-feldspar samples they are controlled largely by Sr-bearing inclusions. The Jurassic 40Ar-39Ar dates are interpreted as minimum ages of feldspar growth and hence imply that fluid-rock interaction is likely to be simultaneous with or to slightly predate melange formation. Deformation associated with the closure and subduction of the Meliata-Hallstatt ocean south of the NCA during the Upper Jurassic is regarded as the principal geodynamic driving force for both enhanced fluid circulation and melange formation. Some localities were reheated beyond the argon retention temperature for microcline during mid-Cretaceous nappe stacking of the NCA, thus obliterating the older signal.

  2. Origin of alkali-feldspar granites: An example from the Poimena Granite, northeastern Tasmania, Australia

    SciTech Connect

    Mackenzie, D.E.; Black, L.P.; Sun, Shensu )

    1988-10-01

    The Lottah Granite is a composite pluton of tin mineralized strongly peraluminous alkali-feldspar granite which intrudes the Poimena Granite, a major component of the mid-Devonian Blue Tier Batholith of northeastern Tasmania. Earlier workers interpreted the Lottah Granite as a metasomatised differentiate of the Poimena Granite. The Poimena Granite is a slightly peraluminous, felsic, I-type biotite granite which contains restite minerals and shows linear trends on Harker plots, both consistent with restite separation. The mineralogy, chemical variation, and isotopic characteristics of the Lottah Granite are consistent with origin as a magma genetically unrelated to the host granite. The Lottah Granite contains sanidine, albite, topaz, zinnwaldite and other minerals consistent with crystallization from a melt. Furthermore, Rb-Sr isotopic dating indicates that the Lottah Granite was emplaced about 10 Ma after the Poimena Granite, and initial Sr and Nd isotope ratios indicate that the Lottah Granite was derived from a higher-{sup 87}Sr/{sup 86}Sr, higher-{epsilon}Nd source composition. Chemical and mineralogical evolution of the Lottah Granite conform to the experimental behavior of Li-F-rich melts, and indicate a possible crystallization temperature range as extreme as 750-430{degree}C. Many other examples of alkali-feldspar granite, and much of the associated mineralization, are probably also of essentially primary magmatic origin rather than of metasomatic or hydrothermal origin as commonly interpreted. They may also be genetically unrelated to granites with which they are associated.

  3. Energy related studies utilizing K-feldspar thermochronology. Progress performance report, 1990--1993

    SciTech Connect

    Not Available

    1993-05-01

    Two distinct sources of information are available from a {sup 40}Ar/{sup 39}Ar step-heating experiment: the age spectrum and Arrhenius plot. Model ages are calculated from the flux of radiogenic argon ({sup 40}Ar*) (assuming trapped argon of atmospheric composition) relative to the reactor produced {sup 39}Ar evolved during discrete laboratory heating steps. With the additional assumption that the {sup 39}Ar is uniformly distributed within the sample, we can infer the spatial distribution of the daughter product. ne associated Arrhenius plot, derived by plotting the diffusion coefficient (obtained from the inversion of the 39{sup Ar} release function assuming a single domain) against the inverse temperature of laboratory heating, are a convolution of the parameters which characterize the individual diffusion domains (whether these be dictated by varying length scale, energetics, etc.). However, many and perhaps Most {sup 40}Ar/{sup 39}Ar age spectra for slowly cooled alkali feldspars are significantly different from model age spectra calculated assuming a single diffusion-domain size. In addition, Arrhenius plots calculated from the measured loss of {sup 39}Ar during the step heating experiment show departures from linearity that are inconsistent with diffusion from domains of equal size. By extending the single diffusion-domain closure model (Dodsontype) to apply to minerals with a discrete distribution of domain sizes, we obtained an internally consistent explanation for the commonly observed features of alkali feldspar age spectra and their associated Arrhenius plots.

  4. Saddle-shaped 40Ar /39Ar age spectra from young, microstructurally complex potassium feldspars

    NASA Astrophysics Data System (ADS)

    Zeitler, Peter K.; Fitz Gerald, John D.

    1986-06-01

    A suite of young potassium feldspars show markedly saddle-shaped 40Ar /39Ar age spectra as a result of incorporating 10 -10 to 10 -9 mol/g of excess 40Ar. The minima of these age spectra record reasonable cooling ages, based on the known thermal history and geology of the samples. Acid etching of one sample indicates that excess 40Ar is concentrated near grain margins. The release of a substantial portion of this excess Ar at high temperatures in the laboratory requires that this component be situated in a more retentive site than radiogenic 40Ar. Anion vacancies have been proposed to act in this role in plagioclase, and we speculate that this is so in K-feldspar as well. Such a mechanism would explain the observation that relative to radiogenic 40Ar, excess 40Ar is incorporated at low temperatures in nature but is released at high temperatures in the laboratory. Oxygen diffusion provides an appropriate analogy for this phenomenon, being relatively fast under natural, hydrothermal conditions, but extremely slow in anhydrous environments such as an Ar-extraction system. TEM observations made on two of the samples confirm that their effective grain sizes for diffusion are likely to be on the order of ten microns, due to the presence of such microstructures as incoherent exsolution lamellae, dislocations, and stepped twins. TEM observations also reveal the presence in one sample of orthoclase enclaves in a microcline host.

  5. CO2 sequestration in feldspar-rich sandstone: Coupled evolution of fluid chemistry, mineral reaction rates, and hydrogeochemical properties

    NASA Astrophysics Data System (ADS)

    Tutolo, Benjamin M.; Luhmann, Andrew J.; Kong, Xiang-Zhao; Saar, Martin O.; Seyfried, William E.

    2015-07-01

    To investigate CO2 Capture, Utilization, and Storage (CCUS) in sandstones, we performed three 150 °C flow-through experiments on K-feldspar-rich cores from the Eau Claire formation. By characterizing fluid and solid samples from these experiments using a suite of analytical techniques, we explored the coupled evolution of fluid chemistry, mineral reaction rates, and hydrogeochemical properties during CO2 sequestration in feldspar-rich sandstone. Overall, our results confirm predictions that the heightened acidity resulting from supercritical CO2 injection into feldspar-rich sandstone will dissolve primary feldspars and precipitate secondary aluminum minerals. A core through which CO2-rich deionized water was recycled for 52 days decreased in bulk permeability, exhibited generally low porosity associated with high surface area in post-experiment core sub-samples, and produced an Al hydroxide secondary mineral, such as boehmite. However, two samples subjected to ∼3 day single-pass experiments run with CO2-rich, 0.94 mol/kg NaCl brines decreased in bulk permeability, showed generally elevated porosity associated with elevated surface area in post-experiment core sub-samples, and produced a phase with kaolinite-like stoichiometry. CO2-induced metal mobilization during the experiments was relatively minor and likely related to Ca mineral dissolution. Based on the relatively rapid approach to equilibrium, the relatively slow near-equilibrium reaction rates, and the minor magnitudes of permeability changes in these experiments, we conclude that CCUS systems with projected lifetimes of several decades are geochemically feasible in the feldspar-rich sandstone end-member examined here. Additionally, the observation that K-feldspar dissolution rates calculated from our whole-rock experiments are in good agreement with literature parameterizations suggests that the latter can be utilized to model CCUS in K-feldspar-rich sandstone. Finally, by performing a number of reactive

  6. Lattice strain across Na-K interdiffusion fronts in alkali feldspar: an electron back-scatter diffraction study

    NASA Astrophysics Data System (ADS)

    Schäffer, Anne-Kathrin; Jäpel, Tom; Zaefferer, Stefan; Abart, Rainer; Rhede, Dieter

    2014-11-01

    Cation exchange experiments between gem quality sanidine and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na-K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a- c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na-K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a- c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.

  7. 3D distribution and evolution of porosity during albitization and patch perthitization of alkali feldspars

    NASA Astrophysics Data System (ADS)

    Norberg, N.; Neusser, G.; Wirth, R.; Harlov, D. E.

    2010-12-01

    Fluid-mediated replacement of minerals and rocks often results in the formation of an extensive porosity. This reaction-induced porosity is generally assumed to be pervasive enabling the constant progress of the alteration process and fluid infiltration of initially impermeable rocks (e.g. Putnis, 2009 Rev Min Geochem, 70, 87). This hypothesis was tested utilizing state-of-the-art micro- to nano-analytical techniques including FIB in combination with SEM and TEM. For this study two different alkali feldspar replacement reactions common in natural rocks were reproduced experimentally; (i) albitization of K-rich alkali-feldspar (Or85-95) and (ii) patch perthitization of intermediate (exsolved) alkali feldspars (Ab60Or40). 3D analysis of the pore distribution was done by a combination of alternate removal of 100 nm slices using FIB followed by SE imaging of the dissected surface. Series of 100-200 SE images were obtained from 20 × 8 × 20 µm3 sample blocks and translated into a 3-dimensional model using Fiji software package (resolution ~0.03 × 0.03 × 0.1 µm3). Analyses of the experimentally albitized and patch-perthitized alkali feldspar demonstrate that in both cases single-crystalline starting materials are replaced by highly porous, polycrystalline replacement products. In the case of albitization the replacement rim consists of two generations of polycrystalline intergrowths of slightly tilted albite sub-grains visible in TEM. These are a fine-grained, highly porous and a coarse-grained, almost non-porous albite that seems to progressively replace the former. The total reaction-induced porosity clearly exceeds the difference in the molar volume of the reaction of ~ -7.5%. Pores are mostly elongated forming several micron long channels. However, despite the abundance of porosity within the albitized areas, neither 3D analysis nor TEM could detect any significant interconnection between these channels. The same holds true in the case of patch perthitization

  8. An FTIR Calibration for Structural Hydrogen in Feldspars Using 1H MAS NMR

    NASA Astrophysics Data System (ADS)

    Johnson, E. A.; Rossman, G. R.

    2002-05-01

    It is important to know how to determine the speciation and concentration of H in feldspars because this information could be used to determine primary magmatic water activity or to estimate the degree of hydrothermal alteration in igneous rocks. FTIR spectroscopy is sensitive to changes in speciation of hydrogen, and can be calibrated for quantitative determination of H concentration using 1H MAS (magic-angle spinning) NMR spectroscopy. Three pegmatitic albites, one metamorphic albite, three volcanic plagioclases (albite, andesine, and anorthite) and one pegmatite oligoclase were used in this study to provide a range of plagioclase compositions. Two pegmatitic microclines and one sanidine were also studied. Polarized infrared spectra were obtained in the three principal optical directions for each specimen. Samples were prepared for 1H MAS NMR experiments at 12 kHz spinning speed in a dry box, without the use of a liquid grinding aid. A spectrum from anhydrous synthetic corundum was used as a baseline for feldspar NMR spectra. The pegmatitic and metamorphic albites are transparent, but contain submicroscopic fluid inclusions as evidenced by a broad band at 3400 cm-1 and an asymmetric band at 5200 cm-1 in the IR spectra that shift to bands characteristic of ice upon cooling to 77 K. These albites have a very sharp band at 4.7 ppm (relative to TMS) in their NMR spectra consistent with fluid inclusion water. In addition to the broad fluid inclusion band, the pegmatitic albites have sharp bands in the mid-IR similar the OH bands found in quartz. All other plagioclases have broad, anisotropic bands around 3200 cm-1 in the mid-IR and MOH combination stretch-bend bands near 4500 cm-1 in the near-IR, indicative of structural OH. The NMR spectra of these plagioclases have a broad band at 4.7 to 4.9 ppm TMS. The OH vector in plagioclases is preferentially aligned parallel to the a crystallographic axis. The concentration of structural OH in the plagioclases ranges from 50

  9. Effects of Al/Si ordering on feldspar dissolution: Part II. The pH dependence of plagioclases' dissolution rates

    NASA Astrophysics Data System (ADS)

    Yang, Yi; Min, Yujia; Jun, Young-Shin

    2014-02-01

    The rate of mineral dissolution in an aquatic environment is sensitive to the pH of the contacting solution. The pH dependence of mineral dissolution rate has been interpreted by the Transition State Theory-Surface Complexation Model (TST-SCM) formalism in terms of pH-sensitive variability in surface chemistry. In this study, we provide an alternative interpretation for the experimentally observed nonlinear pH dependence of feldspar dissolution rates. The interpretation is based on a new formalism for feldspar dissolution which, while compatible with the TST-SCM formalism, incorporates the effects of both surface chemistry and bulk chemistry on feldspar dissolution into the quantification of dissolution rate. The pH dependence of dissolution rate varies from one feldspar specimen to another because different TOT linkages within one solid matrix can respond differently to the attack of proton. Our results suggest that the pH dependence of feldspar dissolution rate is not a constant in general, and could be affected by pH, substitutional Al/Si ordering, chemical composition of the specimen, and the relative rapidness of linkage hydrolysis according to different mechanisms. The rate law proposed in this study is able to capture the experimentally observed pH dependence of the dissolution rates of a series of plagioclases, including albite, andesine, labradorite, bytownite, and anorthite. The effectiveness of the newly proposed formalism for feldspar dissolution, hence, suggests that dissolution reactions of minerals are combinations of surface renewal and heterogeneous chemical reactions. The currently widely used TST-SCM-based rate laws can be further improved by taking into account the effects of bulk chemistry and surface renewal in the prediction of mineral dissolution rates. An improved formalism for mineral dissolution will be mineral-specific, and will reflect the effects of the temporal decay in the availability of reactive surface sites as well as the

  10. Characterization of Quartz and Feldspar Deformation in the Mid-crust: Insights from the Cordillera Blanca Shear Zone, Peru

    NASA Astrophysics Data System (ADS)

    Hughes, C. A.; Jessup, M. J.; Shaw, C. A.

    2014-12-01

    Deformation mechanisms within shear zones from various crustal levels must be characterized to develop accurate models of lithospheric rheology. The Cordillera Blanca Shear Zone (CBSZ) in the central Peruvian Andes records changes in temperature, microstructures, and deformation mechanisms that occurred during exhumation through the brittle-ductile-transition during normal-sense slip over the last ~5 m.y. The 100-500-m-thick mylonitic shear zone occupies the footwall of a 200-km-long normal detachment fault, marking the western boundary of the 8 Ma, leucogranodiorite Cordillera Blanca Batholith. Though local variations do occur, including recrystallized quartz veins and local, decimeter- to meter- scale shear zones, the CBSZ follows a general trend of increasing strain towards the detachment. Structurally lowest positions are weakly deformed and transition to protomylonite, mylonite, and ultramylonite at higher positions, truncating at a cataclasite nearest the detachment. We characterize strain using EBSD analyses of quartz lattice preferred orientations and deformation temperatures using quartz and feldspar textures and two-feldspar thermometry of asymmetric strain-induced myrmekite. At the deepest structural positions, feldspar grains record a complex history characterized by bulging recrystallization, myrmekite formation, and brittle fracture, while quartz exhibits dominant grain-boundary migration recrystallization (T> 500 °C) and prism slip. Intermediate samples exhibit more prevalent strain-induced myrmekite, brittle fracture in feldspar, and reaction-associated recrystallization of K-feldspar to mica; quartz records mainly subgrain-rotation recrystallization (400-500 °C) and dominant prism slip with a rhomb component. Shallower positions preserve fewer, smaller, and more rounded feldspar porphyroclasts with no myrmekite, and dominant bulging recrystallization (280-400 °C) in quartz that records prism , rhomb , and some basal slip.

  11. Ar Ar dating of authigenic K-feldspar: Quantitative modelling of radiogenic argon-loss through subgrain boundary networks

    NASA Astrophysics Data System (ADS)

    Mark, D. F.; Kelley, S. P.; Lee, M. R.; Parnell, J.; Sherlock, S. C.; Brown, D. J.

    2008-06-01

    We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon. The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian. Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention.

  12. Igneous origin of K-feldspar Megacrysts in Granitic Rocks of the Sierra Nevada Batholith

    NASA Astrophysics Data System (ADS)

    Moore, J. G.; Sisson, T. W.

    2007-12-01

    Study of the four principal K-feldspar megacrystic granitic plutons and related porphyrys in the Sierra Nevada composite batholith indicates that the included megacrysts are phenocrysts that grew in contact with granitic melt in long-lasting magma chambers. These 89-83 Ma plutons or intrusions are the youngest in the range, and represent the culminating magmatic phase of the batholith. They are the: Granodiorite of Topaz Lake; Cathedral Peak Granodiorite, Mono Creek Granite, Whitney Granodiorite, Johnson Granite Porphyry, and Golden Bear Dike. The zoned megacrysts in each of these igneous bodies attain 4-10 cm in length and all display oscillatory zoning with each zone beginning with a sharp increase followed by a gradual decrease in the concentration of BaO - commonly from 3 to 1 weight percent. Some of the more pronounced zones overlie resorption and channeling features on the underlying zone. Trains of small mineral inclusions (plagioclase, biotite, hornblende, quartz, sphene, and accessory minerals) are parallel to the BaO-delineated zones. The long axes of the inclusions are preferentially aligned parallel to the zone boundaries and inclusions are sorted by size from zone to zone. The growth temperature of sphene included in K-feldspar megacrysts is estimated by use of a Zr-in-sphene geothermometer. The sphene grains all yield igneous temperatures, mainly 735 - 760 °C. Sphene grains in the granodiorite host marginal to the megacrysts range to lower growth temperatures, in some instances into the subsolidus range. The zoning of the megacrysts, their presence in quenched porphry dikes, and the limited range and igneous values of growth temperatures of sphene inclusions within them, support the interpretation that the megacrysts formed as igneous sanidine phenocrysts, and that intrusion temperatures varied by only small amounts while the megacrysts grew. Each Ba- enriched zone was apparently formed by a repeated surge of new, hot melt injected into the large

  13. Potassium Feldspar Megacrysts in Granites: Passive Markers of Magma Dynamics or Products of Textural Coarsening?

    NASA Astrophysics Data System (ADS)

    Johnson, B. R.; Glazner, A. F.; Coleman, D. S.

    2006-12-01

    Megacrysts of potassium feldspar (K-spar) in granitic rocks are commonly interpreted as early-crystallizing phases whose textural relationships record flow, settling, and diapirism within evolving magma chambers. However, experimental studies on granitic magmas show that K-spar does not begin to nucleate until the system is at least 30% crystalline, and that much of the final crystallization history records co-crystallization of K-spar, quartz, and sodic plagioclase. These data require that the megacrysts cannot have reached large sizes until the magma was largely crystallized and incapable of flow. We have made chemical and textural observations of K-spar megacrysts from the Tuolumne Intrusive Suite (TIS), California. Cathodoluminescence images show sawtooth oscillatory zoning in K-spars, albite-rich rims on plagioclase, reaction zones at boundaries between plagioclase and K-spar, and almost no perthite. Electron microprobe analyses of the sawtooth zones reveal a sharp outward increase in Ba concentration at each zone boundary. Plagioclase core compositions follow whole-rock compositions, becoming increasingly albitic toward the center of the TIS, but K-spar in all units is highly potassic (Or80-95). A three-feldspar assemblage (An15-35, An1-7, and Or80-95) occurs in several megacrystic samples. Stained rock slabs reveal tentacles of interstitial K-spar radiating from megacryst edges far into the adjacent matrix, and a deficit of smaller K-spar crystals in megacrystic units. K-spar size measurements across the contacts of the TIS from the 10 largest crystals within a 1 m2 area show a steady increase in the average megacryst area from 0.2 to 30 cm2. In contrast, bulk rock K2O and K-spar mode (vol%) are constant across this same transect (at 3.7± 0.5 wt% and 22± 5 vol% respectively). Extreme feldspar compositions, phase equilibria, and textural observations argue for late development of K- spar megacrysts during the prolonged and probably cyclic cooling history of

  14. Mesoscale Approach to Feldspar Dissolution: Quantification of Dissolution Incongruency Based on Al/Si Ordering State

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Min, Y.; Jun, Y.

    2012-12-01

    Dissolution mechanism of aluminosilicates is important for understanding natural and anthropogenic carbon cycles. The total mass of atmospheric CO2 is regulated by the weathering of silicate minerals, and the fate of geologically sequestered CO2 is affected by the interactions between brine, sandstone, caprock, and CO2, which is initiated by mineral dissolution. It has been shown through both experimental and ab initio studies that the dissolution/weathering reactivities of Al and Si in the matrix of an aluminosilicate can be different under many conditions. A subsequent observation is that the release rates of Al and Si, both from the same mineral, may not be stoichiometric when compared to the bulk chemistry of the mineral. For a very long time, the relationship between mineral dissolution incongruency and mineral crystallographic properties remain largely qualitative and descriptive. Here we study the dissolution incongruency of feldspars, the most abundant aluminosilicate on earth. Mineral dissolution experiments for a series of alkali feldspars (albite, anorthoclase, sanidine, and microcline) and plagioclases (oligoclase, andesine, labradorite, bytownite, and anorthite) were conducted at pH 1.68 under ambient conditions. Synchrotron-based X-ray diffraction (HR-XRD), Fourier transform infrared spectroscopy (FTIR), and water chemistry analysis (ICP-MS) are combined to examine the effect of Al/Si ordering on mineral dissolution. Our analysis based on a C1 structure model shows that the incongruency, stemming from the different reactivities of Al-O-Si and Si-O-Si linkages in feldspar's framework, is quantifiable and closely related to the Al/Si ordering state of a feldspar. Our results also suggest that the more random the Al/Si distribution of a mineral, the greater the dissolution incongruency. Our results have significant implications for understanding water-rock interactions. First, when studying the effect of water chemistry on water-rock interaction, smaller

  15. Evidence for 26Al in Feldspars from the H4 Chondrite Ste. Marguerite

    NASA Astrophysics Data System (ADS)

    Zinner, E.; Gopel, C.

    1992-07-01

    One of the important questions for the history of the early solar system is whether or not there was enough ^26Al to melt small planetary bodies through the heat released by its decay. Although there is ample evidence for the existence of live ^26Al in refractory inclusions (Wasserburg and Papanastassiou, 1982; Hutcheon, 1982; Podosek et al., 1991), CAIs are special objects with peculiar properties and their Al is not necessarily representative of that of their host meteorites nor the early solar systems. Furthermore, some inclusions do not show any evidence for ^26Al (Wasserburg and Papanastassiou, 1982; Ireland, 1990; Virag et al., 1991), raising the possibility of ^26Al heterogeneity. The only previous observation of ^26Mg excesses attributed to the decay of ^26Al outside of CAIs was in an igneous clast from Semarkona (Hutcheon and Hutchison, 1989) leading to the conclusion that ^26Al indeed could have been a heat source for planetary melting. We have measured Al-Mg in plagioclase grains from the H4 chondrite Ste. Marguerite by ion microprobe mass spectrometry. Feldspars from H4 chondrites are good samples for addressing the problem of ^26Al as heat source because most Al resides in this phase and some H4s experienced fast cooling (Pellas and Storzer, 1981); in fact, the possibility of live ^26Al in feldspars from H4 chondrites that cooled fast has been predicted by Pellas and Storzer (1981). Furthermore, extremely precise absolute Pb/Pb ages exist for these meteorites (Gopel et al., 1991). Figure 1 shows the measurements on five feldspar crystals. All show ^26Mg excesses. A fit through the data points and the normal ^26Mg/^24Mg ratio of 0.13962 obtained from Lake County plagioclase measured under the same instrumental conditions as the Ste. Marguerite samples yields a (^26Al/^27Al)(sub)0 ratio of (2.0 +- 0.6) x 10^-7. If interpreted chronologically this ratio dates the retention of radiogenic ^26Mg in Ste. Marguerite feldspar to 5.6 +- 0.4 Ma after the

  16. Laboratory measurements of upwelled radiance and reflectance spectra of Calvert, Ball, Jordan, and Feldspar soil sediments

    NASA Technical Reports Server (NTRS)

    Whitlock, C. H.; Usry, J. W.; Witte, W. G.; Gurganus, E. A.

    1977-01-01

    An effort to investigate the potential of remote sensing for monitoring nonpoint source pollution was conducted. Spectral reflectance characteristics for four types of soil sediments were measured for mixture concentrations between 4 and 173 ppm. For measurements at a spectral resolution of 32 mm, the spectral reflectances of Calvert, Ball, Jordan, and Feldspar soil sediments were distinctly different over the wavelength range from 400 to 980 nm at each concentration tested. At high concentrations, spectral differences between the various sediments could be detected by measurements with a spectral resolution of 160 nm. At a low concentration, only small differences were observed between the various sediments when measurements were made with 160 nm spectral resolution. Radiance levels generally varied in a nonlinear manner with sediment concentration; linearity occurred in special cases, depending on sediment type, concentration range, and wavelength.

  17. Elemental content of feldspar from Eastern Desert, Egypt, determined by INAA and XRF.

    PubMed

    El-Taher, A

    2010-06-01

    Instrumental neutron activation analysis (INAA) and HPGe detector gamma-spectroscopy were used to determine a total of 16 elements qualitatively and quantitatively for the first time from feldspar rock samples collected from Gabel El Dubb, Eastern desert, Egypt. The elements determined are (Na, Mg, K, Sc, Ga, Cr, Fe, Co, Zn, Nb, Ba, Ce, Eu, Hf, Th and U). The samples were properly prepared together with their standard reference material and simultaneously irradiated by thermal neutrons at the TRIGA Mainz research reactor at a neutron flux of 7x10(11)n/cm(2)s. XRF was also used. Comparison of the results obtained by both techniques showed good agreement for such elements as K, Na, Fe, Mg, Ba and Cr. PMID:20185321

  18. Diffusion dans les liquides

    NASA Astrophysics Data System (ADS)

    Dianoux, A. J.

    2003-09-01

    Après une brève introduction qui rappelle les concepts détaillés dans le cours de M. Bée, nous présentons un aperçu de trois de nos travaux sur l'étude de la diffusion. Tout d'abord la dynamique de l'eau, dans son état normal ou surfondu, révèle la complexité apportée par le réseau de liaisons hydrogène. Ensuite l'effet du confinement sur la dynamique de l'eau sera étudié dans le cas de la membrane Nafion. Enfin la diffusion dans les phases nématique et smectique A d'un cristal liquide permet d'obtenir la valeur du potentiel qui maintient les couches dans la phase smectique.

  19. Exchange of Na+ and K+ between water vapor and feldspar phases at high temperature and low vapor pressure

    USGS Publications Warehouse

    Fournier, R.O.

    1976-01-01

    In order to determine whether gas (steam) containing a small amount of dissolved alkali chloride is effective in promoting base exchange of Na+ and K+ among alkali feldspars and coexisting brine or brine plus solid salt, experiments were carried out at 400-700??C and steam densities ranging down to less than 0.05. For bulk compositions rich in potassium, the low pressure results are close to previous high-pressure results in composition of the fluid and coexisting solid phase. However, when the bulk composition is more sodic, alkali feldspars are relatively richer in potassium at low pressure than at high pressure. This behaviour corresponds to enrichment of potassium in the gas phase relative to coexisting brine and precipitation of solid NaCl when the brine plus gas composition becomes moderately sodic. The gas phase is very effective in promoting base exchange between coexisting alkali feldspars at high temperature and low water pressure. This suggests that those igneous rocks which contain coexisting alkali feldspars out of chemical equilibrium either remained very dry during the high-temperature part of their cooling history or that the pore fluid was a gas containing very little potassium relative to sodium. ?? 1976.

  20. Magnetic Properties Of Feldspars And Other Rock-forming Minerals: Evaluation Of Their Potential As Paleointensity Recorders

    NASA Astrophysics Data System (ADS)

    Cottrell, R. D.; Smirnov, A. V.; Tarduno, J. A.

    The continued development of highly sensitive SQUID magnetometers has opened the way for paleomagnetic and paleointensity studies of individual rock forming miner- als. The motivation for these studies is the desire to avoid contamination of magnetic data related to secondary minerals that commonly form in the ground mass of igneous rocks on geologic timescales or during laboratory experiments. As part of a survey of various mineral phases we have examined magnetic hysteresis data of olivine, py- roxene and feldspar separated from mafic lavas flows, quartz separated from tuffs and zircon separated from granites. Our studies of optically clear plagioclase feldspar have shown them to have several properties favorable for paleointensity investigations. Hys- teresis properties indicate that the domain state of magnetic inclusions in the feldspar crystals is single or pseudosingle domain while that of the groundmass is pseudosingle to multidomain. High resolution SEM and TEM analyses indicate that the magnetic inclusions are equant to slightly elongated and are 50 to 350 nm in size. Low tempera- ture data and magnetic unblocking temperatures indicate that the overall composition of the inclusions is similar to that of the bulk volcanic rocks from which they were separated. These properties, together with the relatively rapid cooling characteristics of lavas, suggest that Thellier analyses of plagioclase feldspars will continue to yield important paleointensity data. The potential of other mineral phases for paleomagnetic and paleointensity studies will be discussed.

  1. Fractionation of Stable Si Isotopes During in-situ Dissolution of Feldspars and Formation of Secondary Clay Minerals

    NASA Astrophysics Data System (ADS)

    Georg, R. B.; Reynolds, B. C.; Halliday, A. N.; Zhu, C.

    2005-12-01

    It has been proposed that weathering of igneous silicate minerals may fractionate Si isotopes (Douthitt 1982, de la Rocha et al. 2000). This is supported by the observation that clays yield δ30Si compositions between +0.5‰ and -2.5‰ compared to the igneous range for δ30Si between +0.1‰ and -1‰ respectively (Douthitt 1982). The difference may relate to a discrimination against heavier Si isotopes during clay mineral formation. However, no study has yet shown a direct Si isotope fractionation between coexisting primary igneous and secondary clay mineral phases. We have measured the stable Si isotope fractionation during in-situ feldspar dissolution and formation of secondary clay minerals in the Navajo Sandstone, Black Mesa, Arizona. The Jurassic Navajo Sandstone is composed of about 94% quartz and 2-4% K-feldspar. The K-feldspar grains are covered with kaolinite, and both quartz and feldspars are covered with a mantle of smectite coating. Petrographic studies demonstrate that the clay minerals formed in situ as alteration products of feldspar, and the smectite is of a low-temperature variety (Zhu, 2005). Therefore, the Si isotope fractionation at low temperature (15-35°C) can be evaluated - something that is difficult to replicate in the laboratory. For the Si isotope analyses we used 20-30 mg of 5 separated clay samples, and 0.36 mg of hand picked feldspars. The silicates were fused with an alkaline flux and dissolved in a weak HCl acid. The dissolved Si was then separated by ion-exchange chromatography. The relative Si isotope compositions were measured using a high-resolution MC-ICP-MS (The Nu1700 at ETH Zurich) and are reported in δ notation relative to the international Si standard NBS 28. The bulk rock and separated feldspar fraction have Si isotope compositions are -0.09 ± 0.03‰ and -0.15 ±0.03 ‰ (±2σSEM) δ30Si, respectively. The clay samples have δ30Si values of -0.24 ±0.05‰, -0.16 ±0.03‰, -0.30 ±0.03‰, -0.42 ±0.03‰ and -0

  2. Distribution and textures of K-feldspar grains in the George Ashley Block layered-aplite pegmatite intrusive

    NASA Astrophysics Data System (ADS)

    Kleck, W. D.

    2013-12-01

    Both Johns & Tuttle (1963) and London (2008) note that the distribution of potassium is neither uniform nor symmetrical in some pegmatite bodies. A detailed chemical and mineral analysis of the George Ashley Block (Kleck & Foord 1999) shows that the distribution of K-feldspar over the entire body is generally uniform, but not symmetrical. The amounts of quartz, plagioclase, muscovite, and garnet are neither uniform nor symmetrical. It is noted that layered-aplite, pegmatite intrusives (terminology of Jahns & Tuttle 1963) are intruded horizontally, and it is suggested that these are the pegmatite bodies which have this non-uniform distribution of minerals. These types of pegmatite bodies are distinctly different from other pegmatite bodies in several ways. The core zone in these bodies is not centrally located and typically divides these bodies into a pegmatitic top and an aplitic bottom; the top and bottom appear to be contemporaneous. The features and content of the border- and core-zones are not included in this discussion. The texture of the K-feldspar in the top of these bodies is generally pegmatitic; some of the K-feldspar grains may exist as ultra-large grains which have a teardrop shape or minor-crystal surfaces. In the bottom of these bodies, the K-feldspar is commonly rounded grains approximately 1 mm in diameter; rarely, some K-feldspar grains here are centimeter-grained with crystal surfaces indicating growth. In the George Ashley Block, the concentration and distribution of K-feldspar is inversely symmetrical in the top vs. bottom. In the top it increases toward the core zone; K-feldspar--20 increasing to 60 vol% (all values one significant figure) and K2O--3 increasing to 8 wt%. In the bottom it decreases toward the core zone; K-feldspar--40 decreasing to 0 vol% and K2O--4 decreasing to 0 wt%. The two trends are approximately parallel and the total amounts are approximately constant. The suggested conditions and mechanisms (with the added condition of

  3. The effect of SEM imaging on the Ar/Ar system in feldspars

    NASA Astrophysics Data System (ADS)

    Flude, S.; Sherlock, S.; Lee, M.; Kelley, S. P.

    2010-12-01

    Complex microtextures form in K-feldspar crystals as they cool and are affected by deuteric alteration. This complex structure is the cause of variable closure temperatures for Ar-Ar, a phenomenon which has been utilized in multi domain diffusion (MDD) modelling to recover thermal histories [1]. However, there has been substantial controversy regarding the precise interaction between feldspar microtextures and Ar-diffusion [2,3]. A number of studies have addressed this issue using coupled SEM imaging and Ar/Ar UV laser ablation microprobe (UV-LAMP) analysis on the same sample, to enable direct comparison of microtextures with Ar/Ar age data [4]. Here we have tested the idea that SEM work may affect Ar/Ar ages, leading to inaccurate results in subsequent Ar/Ar analyses. Three splits of alkali feldspar from the Dartmoor Granite in SW England were selected for Ar/Ar UV-LAMP analysis. Split 1 (“control”) was prepared as a polished thick section for Ar/Ar analysis. Split 2 (“SEM”) was prepared as a polished thick section, was chemically-mechanically polished with colloidal silica and underwent SEM imaging (uncoated) and focussed ion beam (FIB) milling (gold coated); electron beam damage in the SEM was maximised by leaving the sample at high magnification for eight minutes. Split 3 (“Etch”) is a cleavage fragment that was etched with HF vapour and underwent low to moderate magnification SEM imaging. The control split gave a range of laser-spot ages consistent with the expected cooling age of the granite and high yields of radiogenic 40Ar* (>90%). The area of the “SEM” split that experienced significant electron beam damage gave younger than expected ages and 40Ar* yields as low as 57%. These are interpreted as a combination of implantation of atmospheric Ar and local redistribution of K within the sample. The area of “SEM” that underwent FIB milling gave ages and 40Ar* yields comparable to the control split, suggesting that the Au-coat minimises FIB

  4. Contact freezing induced by biological (Snomax) and mineral dust (K-feldspar) particles

    NASA Astrophysics Data System (ADS)

    Hoffmann, N.; Schäfer, M.; Duft, D.; Kiselev, A. A.; Leisner, T.

    2013-12-01

    The contact freezing of supercooled cloud droplets is one of the potentially important and the least investigated heterogeneous mechanism of ice formation in tropospheric clouds [1]. On the time scales of cloud lifetime the freezing of supercooled water droplets via contact mechanism may occur at higher temperature compared to the same IN immersed in the droplet. In our experiment we study single water droplets freely levitated in an Electrodynamic Balance [2]. We have shown previously that the rate of freezing at given temperature is governed only by the rate of droplet -particle collision and by the properties of the contact ice nuclei [2, 3]. Recently, we have extended our experiments to feldspar, being the most abundant component of the atmospheric mineral dust particles, and Snomax, as a proxy for atmospheric biological Ice Nuclei (IN). In this contribution we show that both IN exhibits the same temperature, size and material dependency observed previously in immersion mode [4, 5]. Based on these results, we limit the number of mechanisms that could be responsible for the enhancement of contact nucleation of ice in supercooled water. [1] - Ladino, L. A., Stetzer, O., and Lohmann, U.: Contact freezing: a review, Atmos. Chem. Phys. Discuss., 13, 7811-7869, doi:10.5194/acpd-13-7811-2013, 2013. [2] - Hoffmann, N., Kiselev, A., Rzesanke, D., Duft, D., and Leisner, T.: Experimental quantification of contact freezing in an electrodynamic balance, Atmos. Meas. Tech. Discuss., 6, 3407-3437, doi:10.5194/amtd-6-3407-2013, 2013. [3] - Hoffmann, N., Duft, D., Kiselev, A., and Leisner, T.: Contact freezing efficiency of mineral dust aerosols studied in an electrodynamic balance: quantitative size and temperature dependence for illite particles, Faraday Discuss., doi: 10.1039/C3FD00033H, 2013. [4] - Atkinson, James D., Murray, Benjamin J., Woodhouse, Matthew T., Whale, Thomas F., Baustian, Kelly J., Carslaw, Kenneth S., Dobbie, Steven, O'Sullivan, Daniel, and Malkin, Tamsin

  5. Fluvial terrace gravels of the "Hochterrasse" (N-Alpine Foreland, Austria): luminescence characteristics of quartz and feldspar

    NASA Astrophysics Data System (ADS)

    Bickel, L.; Lomax, J.; Fiebig, M.

    2012-04-01

    The Northern Alpine Foreland has played a major role in the investigation of glacial and furthermore paleo-climatic events. It was at the beginning of the 20th century, when Albrecht Penck developed the idea of four big alpine glaciations which extended into the alpine foreland. He developed the model of the glacial series in which he correlated terminal moraines with distinguishable terrace bodies. In the case of the fluvial sediments of the Hochterrasse (correlated with marine isotope stage (MIS) 6 in Austrian geological maps) the existence of numerical ages in the Austrian Alpine Foreland is sparse. This study is aimed at shedding light on the luminescence properties of quartz and feldspar derived from Hochterrasse systems in foreland valleys (Traun, Enns and Ybbs valley) so far attributed to the penultimate glaciation. Coarse grain (100-200 µm) K-feldspar and quartz are analyzed by Infrared stimulated luminescence (IRSL), post-Infrared Infrared stimulated luminescence (pIRIR) and optically stimulated luminescence (OSL) methods. One of the issues that arise when dating glaciofluvial quartz from this area is the apparent underestimation of the quartz ages which can vary up to 50% from the calculated IRSL ages. Linearly modulated OSL shows a big contribution of thermally unstable components to the overall equivalent dose (De) which can add to the general underestimation of quartz. Also the measurement of feldspar aliquots is anything but trivial. Luminescence signal intensities are very viable for the samples from the Enns and Traun valley. The samples derived from the Ybbs valley in contrast show very low feldspar signal intensities on most aliquots. Thermal transfer has shown to have negligible impact on the overall paleodose for the feldspar samples (maximum 1% of the paleodose attributed to thermal transfer). In contrast anomalous fading seems to be affecting all feldspar samples. However an assessment of the amount of signal loss in time is difficult to

  6. Accretion and canal impacts in a rapidly subsiding wetland II: Feldspar marker horizon technique

    USGS Publications Warehouse

    Cahoon, D.R.; Turner, R.E.

    1989-01-01

    Recent (6-12 months) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in a Spartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr-1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr-1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackish Spatina patens marsh on Louisiana's chenier plain, vertical accretion rates were the same along natural and canal waterways (3-4 mm yr-1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr-1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.

  7. Adsorption mechanism of mixed cationic/anionic collectors in feldspar-quartz flotation system.

    PubMed

    Vidyadhar, A; Hanumantha Rao, K

    2007-02-15

    The adsorption mechanism of mixed cationic alkyl diamine and anionic sulfonate/oleate collectors at acidic pH values was investigated on microcline and quartz minerals through Hallimond flotation, electrokinetic and diffuse reflectance FTIR studies. In the presence of anionic collectors, neither of the minerals responded to flotation but the diamine flotation of the minerals was observed to be pH and concentration dependent. The presence of sulfonate enhanced the diamine flotation of the minerals by its co-adsorption. The difference in surface charge between the minerals at pH 2 was found to be the basis for preferential feldspar flotation from quartz in mixed diamine/sulfonate collectors. The infrared spectra revealed no adsorption of sulfonate collector when used alone but displayed its co-adsorption as diamine-sulfonate complex when used with diamine. The presence of sulfonate increased the diamine adsorption due to a decrease in the electrostatic head-head repulsion between the adjacent surface ammonium ions and thereby increasing the lateral tail-tail hydrophobic bonds. The mole ratio of diamine/sulfonate was found to be an important factor in the orientation of alkyl chains and thus the flotation response of minerals. The increase in sulfonate concentration beyond diamine concentration leads to the formation of soluble 1:2 diamine-sulfonate complex or precipitate and the adsorption of these species decreased the flotation since the alkyl chains are in chaotical orientation with a conceivable number of head groups directing towards the solution phase. PMID:17098246

  8. Xenon diffusion following ion implantation into feldspar - Dependence on implantation dose

    NASA Technical Reports Server (NTRS)

    Melcher, C. L.; Burnett, D. S.; Tombrello, T. A.

    1982-01-01

    The diffusion properties of xenon implanted into feldspar, a major mineral in meteorites and lunar samples, are investigated in light of the importance of xenon diffusion in the interpretation of early solar system chronologies and the retention time of solar-wind-implanted Xe. Known doses of Xe ions were implanted at an energy of 200 keV into single-crystal plagioclase targets, and depth profiles were measured by alpha particle backscattering before and after annealing for one hour at 900 or 1000 C. The fraction of Xe retained following annealing is found to be strongly dependent on implantation dose, being greatest at a dose of 3 x 10 to the 15th ions/sq cm and decreasing at higher and lower doses. Xe retention is also observed to be unaffected by two-step anneals, or by implantation with He or Ar. Three models of the dose-dependent diffusion properties are considered, including epitaxial crystal regrowth during annealing controlled by the extent of radiation damage, the creation of trapping sites by radiation damage, and the inhibition of recrystallization by Xe during annealing

  9. A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

    NASA Astrophysics Data System (ADS)

    Duffield, Wendell A.; Ruiz, Joaquin

    1998-12-01

    Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.

  10. Deformation behaviour of feldspar in greenschist facies granitoide shear zones from the Austroalpine basement to the south of the western Tauern window, Eastern Alps

    NASA Astrophysics Data System (ADS)

    Hentschel, Felix; Trepmann, Claudia

    2015-04-01

    Objective of this study is to elucidate the feldspar deformation behaviour at greenschist facies conditions relevant for the long-term rheological properties of continental crust. Uncertainties in models for the rheological properties are partly due to a poor knowledge of the deformation mechanisms taking place in granitoid rocks at inaccessible depth. The deformation behaviour of feldspar, the most abundant mineral in the continental crust, is characterized by an interaction of brittle, dissolution-precipitation and crystal-plastic processes, which is difficult to evaluate in experiments given the problematic extrapolation of experimental conditions to reasonable natural conditions. However, microfabrics of metamorphic granitoid rocks record the grain-scale deformation mechanisms and involved chemical reactions proceeding during their geological history. This usually includes deformation and modification through several stages in space (depth, i.e., P, T conditions) and/or time. For deciphering the rock's record this implies both, challenge and chance to resolve these different stages. Here, we use the deformation record of mylonitic pegmatites from the Austroalpine basement south to the western Tauern window. The structural, crystallographic and chemical characteristics of the feldspar microfabrics are determined via micro-analytical techniques (polarized light microscopy, scanning electron microscopy, SEM, electron back scatter diffraction, EBSD) to identify the relevant deformation mechanisms and deformation conditions. The pegmatites represent a relatively simple Ca-poor granitoid system, mineralogically dominated by albite-rich plagioclase, K-feldspar and quartz. The matrix of the mylonitic pegmatites is composed of alternating monomineralic albite and quartz ribbons defining the foliation. Fragmented tourmaline and K-feldspar porphyroclasts occur isolated within the matrix. At sites of dilation along the stretching lineation K-feldspar porphyroclasts show

  11. Buffering capability of mineral assemblage (feldspar + kaolinite + quartz) and its application to predicting illite occurrence in arkosic sandstones

    SciTech Connect

    Huang, W.L.

    1986-05-01

    Studies of phase relationships using the activity diagrams involving feldspar, illite, kaolinite, and gibbsite (or boehmite) reveal that the common mineral assemblage of feldspar, kaolinite, and quartz found in arkosic sandstone provides a strong driving force to change the fluid chemistry to conditions thermodynamically favoring illite formation. The driving force involves three major diagenetic reactions: the hydrolysis of feldspar with acidic fluid, the reaction of kaolinite with alkaline fluid, and the saturation of the fluid with respect to quartz. The first and second reactions result in, respectively, the increase and decrease of K/sup +//H/sup +/ activity ratio, whereas the third reaction tends to maintain the Si(OH)/sub 4/ activity in the pore fluid. The resultant fluid chemistry of these reactions coincidentally falls in the stability field of illite. This relationship occurs over a wide range of pressure and temperature conditions with low fluid to rock ratio. Experimental results show that an increase in the fluid to rock ratio will decrease the rate that the fluid chemistry approaches the illite stability field. The effectiveness of the buffering capability, therefore, depends on the relative rate of fluid movement and fluid/rock reaction. This study demonstrates that the most likely condition for illite formation is a quartzofeldspathic system involving the presence of kaolinite and low fluid movement. In the absence of these conditions, the opportunity to precipitate illite in the pore space is significantly reduced. The commonly observed illitization of kaolinite or feldspar during burial diagenesis could be caused simply by the reduced influx of fluid (with any compositions: alkaline, neutral, or acidic) due to deep burial of the sandstone.

  12. Alkali feldspar dissolution and secondary mineral precipitation in batch systems: 3. Saturation states of product minerals and reaction paths

    NASA Astrophysics Data System (ADS)

    Zhu, Chen; Lu, Peng

    2009-06-01

    In order to evaluate the complex interplay between dissolution and precipitation reaction kinetics, we examined the hypothesis of partial equilibria between secondary mineral products and aqueous solutions in feldspar-water systems. Speciation and solubility geochemical modeling was used to compute the saturation indices (SI) for product minerals in batch feldspar dissolution experiments at elevated temperatures and pressures and to trace the reaction paths on activity-activity diagrams. The modeling results demonstrated: (1) the experimental aqueous solutions were supersaturated with respect to product minerals for almost the entire duration of the experiments; (2) the aqueous solution chemistry did not evolve along the phase boundaries but crossed the phase boundaries at oblique angles; and (3) the earlier precipitated product minerals did not dissolve but continued to precipitate even after the solution chemistry had evolved into the stability fields of minerals lower in the paragenesis sequence. These three lines of evidence signify that product mineral precipitation is a slow kinetic process and partial equilibria between aqueous solution and product minerals were not held. In contrast, the experimental evidences are consistent with the hypothesis of strong coupling of mineral dissolution/precipitation kinetics [e.g., Zhu C., Blum A. E. and Veblen D. R. (2004a) Feldspar dissolution rates and clay precipitation in the Navajo aquifer at Black Mesa, Arizona, USA. In Water-Rock Interaction (eds. R. B. Wanty and R. R. I. Seal). A.A. Balkema, Saratoga Springs, New York. pp. 895-899]. In all batch experiments examined, the time of congruent feldspar dissolution was short and supersaturation with respect to the product minerals was reached within a short period of time. The experimental system progressed from a dissolution driven regime to a precipitation limited regime in a short order. The results of this study suggest a complex feedback between dissolution and

  13. [The characteristics of microstructure and chemical compositions of K-feldspar, sphene and zircon with zoning structure].

    PubMed

    Liu, Chun-Hua; Wu, Cai-Lai; Lei, Min; Qin, Hai-Peng; Li, Ming-Ze

    2013-08-01

    K-feldspar, sphene and zircon in quartz monzonite from Shahewan, south Qinling, showing strong zoning structure. Characteristics of microstructure and chemical compositions of K-feldspar, sphene and zircon with zoning structure were investigated using advanced instruments of electron probe micro analyses equipped with wavelength dispersive spectrometer (EPM-WDS), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and laser ablation--inductively coupled plasma--mass spectrometry (LA-ICP-MS). Our study suggests that K+ could be substituted by small amounts of Na+, Ca2+, Ba2+, Fe2+ and Ce3+. Ca2+ in sphene could be replaced by V3+, Ce3+, Ba2+ and Ti4+ could be substituted by both Fe2+ and Al3+. Zircon contains trace elements like Fe, Th, U, Nb, Ta, Y, Hf, Yb and Pb. Concentration of Si, Al, K, Ca, Na, Mg and Ba in K-feldspar ranked from high to low, among which the contents of K and Na are negatively correlated, the lighter part of BSE images featuring K-feldspar is attributed to comparably higher Ba content, additionally, Si and K contents are elevated while Na content decreased rimward. Ca, Si, Ti, Ba, V, Ce, Al and Fe concentration listed downward, among which higher iron content corresponds to brighter portion of BSE images. Element concentration of zircon could be ranked from high to low as Zr, Si, Nd, Ce, Hf, U, Pb and Th, in which Hf and Zr exhibit negatively correlated. Zr concentration increased while Hf, U and Th concentration decreased from core to rim. PMID:24159884

  14. In situ 40K-40Ca ‘double-plus’ SIMS dating resolves Klokken feldspar 40K-40Ar paradox

    NASA Astrophysics Data System (ADS)

    Harrison, T. Mark; Heizler, Matthew T.; McKeegan, Kevin D.; Schmitt, Axel K.

    2010-11-01

    The 40K- 40Ca decay system has not been widely utilized as a geochronometer because quantification of radiogenic daughter is difficult except in old, extremely high K/Ca domains. Even these environments have not heretofore been exploited by ion microprobe analysis due to the very high mass resolving power (MRP) of 25,000 required to separate 40K + from 40Ca +. We introduce a method that utilizes doubly-charged K and Ca species which permits isotopic measurements to be made at relatively low MRP (~ 5000). We used this K-Ca 'double-plus' approach to address an enduring controversy in 40Ar/ 39Ar thermochronology revolving around exsolved alkali feldspars from the 1166 Ma Klokken syenite (southern Greenland). Ion microprobe 40K- 40Ca analysis of Klokken samples reveal both isochron and pseudoisochron behaviors that reflect episodic isotopic and chemical exchange of coarsely exsolved perthites and a near end-member K-feldspar until ≤ 719 Ma, and perhaps as late at ~ 400 Ma. Feldspar microtextures in the Klokken syenite evolved over a protracted interval by non-thermal processes (fluid-assisted recrystallization) and thus this sample makes a poor model from which to address the general validity of 40Ar/ 39Ar thermochronological methodologies.

  15. Ionic conductivity in gem-quality single-crystal alkali feldspar from the Eifel: temperature, orientation and composition dependence

    NASA Astrophysics Data System (ADS)

    El Maanaoui, Hamid; Wilangowski, Fabian; Maheshwari, Aditya; Wiemhöfer, Hans-Dieter; Abart, Rainer; Stolwijk, Nicolaas A.

    2016-05-01

    We measured the ion conductivity of single-crystal alkali feldspar originating from two different locations in the Eifel/Germany, named Volkesfeld and Rockeskyller sanidine and having potassium site fractions C_K of 0.83 and 0.71, respectively. The dc conductivities resulting from electrochemical impedance spectroscopy over the temperature range of 300-900°C show a weak composition dependence but pronounced differences between the b-direction [perp (010)] and c^{*}-direction [perp (001)] of the monoclinic feldspar structure. Conductivity activation energies obtained from the observed linear Arrhenius plots are close to 1.2 eV in all cases, which is closely similar to the activation energies of the ^{22}Na tracer diffusivity in the same crystals. Taking into account literature data on K tracer diffusion and diffusion correlation effects, the present results point to a predominance of the interstitialcy mechanism over the vacancy mechanism in mass and charge transport on the alkali sublattice in potassium-rich alkali feldspar.

  16. Correlation of basic TL, OSL and IRSL properties of ten K-feldspar samples of various origins

    NASA Astrophysics Data System (ADS)

    Sfampa, I. K.; Polymeris, G. S.; Pagonis, V.; Theodosoglou, E.; Tsirliganis, N. C.; Kitis, G.

    2015-09-01

    Feldspars stand among the most widely used minerals in dosimetric methods of dating using thermoluminescence (TL), optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL). Having very good dosimetric properties, they can in principle contribute to the dating of every site of archaeological and geological interest. The present work studies basic properties of ten naturally occurring K-feldspar samples belonging to three feldspar species, namely sanidine, orthoclase and microcline. The basic properties studied are (a) the influence of blue light and infrared stimulation on the thermoluminescence glow-curves, (b) the growth of OSL, IRSL, residual TL and TL-loss as a function of OSL and IRSL bleaching time and (c) the correlation between the OSL and IRSL signals and the energy levels responsible for the TL glow-curve. All experimental data were fitted using analytical expressions derived from a recently developed tunneling recombination model. The results show that the analytical expressions provide excellent fits to all experimental results, thus verifying the tunneling recombination mechanism in these materials and providing valuable information about the concentrations of luminescence centers.

  17. Highly retentive core domains in K-feldspar preserve argon ages from high temperature stages of granite exhumation

    NASA Astrophysics Data System (ADS)

    Forster, Marnie; Lister, Gordon

    2016-04-01

    Retentive core domains are characterized by diffusion parameters that imply K-feldspar should be able to retain argon even at temperatures near or above the granite solidus. In this case it should be possible to date granite emplacement using argon geochronology, and the same answer should be obtained as by using other methods. We present one case study where this is the case, from the elevated Capoas granite stock on Palawan, in the Philippines, and another where it is not, from the South Cyclades Shear Zone, on Ios, Greece. We attempt to determine the factors such as the role of fluid ingress in triggering the in situ recrystallization that can eliminate and/or modify the core domains, leading to relatively youthful ages. Thermochronology is still possible, because less retentive diffusion domains exist, but different methods need to be applied to interpret the data. The work also demonstrates that K-feldspar can be sufficiently retentive as to allow direct dating of processes that reduce the dimensions of diffusion domains, e.g., cataclased and/or recrystallized K-feldspar in fault rock and/or mylonite. These are important developments in the methodology of 40Ar/39Ar geochronology, but to further advance we need to clarify the nature of these highly retentive core domains. In particular, we need better understand how they are modified by microstructural processes during deformation and metamorphism. We need also to assess the role of any crystal structural changes during step-heating in vacuo.

  18. Dan Johnson the mentor

    NASA Astrophysics Data System (ADS)

    McKinley, Richard

    2003-04-01

    I first met Dan Johnson in early 1975 as I was interviewing for an engineering job with Henning von Gierke's bioengineering and bionics laboratory at Wright-Patterson Air Force Base. From the very beginning Dan was always direct and forthright. Over the ensuing next 27 years my knowledge and respect of Dan constantly grew. This presentation will review Dan's technical and personal contributions while at the laboratory at Wright-Patterson Air Force Base. He was instrumental in the development of a national noise exposure criteria with the equal-energy-rule, an accurate single number hearing protector attenuation measure based on ``C-A,'' an impulse noise exposure criteria, a longitudinal study of hearing loss in children, development of noise dosimeters, and description of hearing damage risk from nonoccupational noise exposures such as disco's, bowling alleys, lawn mowers, and school buses. Dan has had a significant effect on my career. I and the many people who knew him at the laboratory miss him greatly.

  19. Climate dependence of feldspar weathering in shale soils along a latitudinal gradient

    NASA Astrophysics Data System (ADS)

    Dere, Ashlee L.; White, Timothy S.; April, Richard H.; Reynolds, Brian; Miller, Thomas E.; Knapp, Elizabeth P.; McKay, Larry D.; Brantley, Susan L.

    2013-12-01

    Although regolith, the mantle of physically, chemically, and biologically altered material overlying bedrock, covers much of Earth’s continents, the rates and mechanisms of regolith formation are not well quantified. Without this knowledge, predictions of the availability of soil to sustain Earth’s growing population are problematic. To quantify the influence of climate on regolith formation, a transect of study sites has been established on the same lithology - Silurian shale - along a climatic gradient in the northern hemisphere as part of the Susquehanna Shale Hills Critical Zone Observatory, Pennsylvania, USA. The climate gradient is bounded by a cold/wet end member in Wales and a warm/wet end member in Puerto Rico; in between, mean annual temperature (MAT) and mean annual precipitation (MAP) increase to the south through New York, Pennsylvania, Virginia, Tennessee and Alabama. The site in Puerto Rico does not lie on the same shale formation as the Appalachian sites but is similar in composition. Soils and rocks were sampled at geomorphologically similar ridgetop sites to compare and model shale weathering along the transect. Focusing on the low-concentration, non-nutrient element Na, we observe that the extent and depth of Na depletion is greater where mean annual temperature (MAT) and precipitation (MAP) are higher. Na depletion, a proxy for feldspar weathering, is the deepest reaction documented in the augerable soil profiles. This may therefore be the reaction that initiates the transformation of high bulk-density bedrock to regolith of low bulk density. Based on the shale chemistry along the transect, the time-integrated Na release rate (QNa) increases exponentially as a function of MAT and linearly with MAP. NY, the only site with shale-till parent material, is characterized by a QNa that is 18 times faster than PA, an observation which is attributed to the increased surface area of minerals due to grinding of the glacier and kinetically limited

  20. Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

    NASA Technical Reports Server (NTRS)

    Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

    2014-01-01

    Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

  1. Feldspar dissolution kinetics and Gibbs free energy dependence in a CO 2-enriched groundwater system, Green River, Utah

    NASA Astrophysics Data System (ADS)

    Kampman, Niko; Bickle, Mike; Becker, John; Assayag, Nelly; Chapman, Hazel

    2009-07-01

    Reactions between CO 2-charged brines and reservoir minerals might either enhance the long-term storage of CO 2 in geological reservoirs or facilitate leakage by corroding cap rocks and fault seals. Modelling the progress of such reactions is frustrated by uncertainties in the absolute mineral surface reaction rates and the significance of other rate limiting steps in natural systems. Here we use the chemical evolution of groundwater from the Jurassic Navajo Sandstone, part of a leaking natural accumulation of CO 2 at Green River, Utah, in the Colorado Plateau, USA, to place constraints on the rates and potential controlling mechanisms of the mineral-fluid reactions, under elevated CO 2 pressures, in a natural system. The progress of individual reactions, inferred from changes in groundwater chemistry is modelled using mass balance techniques. The mineral reactions are close to stoichiometric with plagioclase and K-feldspar dissolution largely balanced by precipitation of clay minerals and carbonate. Mineral modes, in conjunction with published surface area measurements and flow rates estimated from hydraulic head measurements, are then used to quantify the kinetics of feldspar dissolution. Maximum estimated dissolution rates for plagioclase and K-feldspar are 2 × 10 - 14 and 4 × 10 - 16 mol m - 2 s - 1 , respectively. Fluid ion-activity products are close to equilibrium (e.g. Δ Gr for plagioclase between - 2 and - 10 kJ/mol) and lie in the region in which mineral surface reaction rates show a strong dependence on Δ Gr. Local variation in Δ Gr is attributed to the injection and disassociation of CO 2 which initially depresses silicate mineral saturation in the fluid, promoting feldspar dissolution. With progressive flow through the aquifer feldspar hydrolysis reactions consume H + and liberate solutes to solution which increase mineral saturation in the fluid and rates slow as a consequence. The measured plagioclase dissolution rates at low Δ Gr of 2 × 10

  2. Progressive hydrothermal alteration of feldspars from the Comstock Lode Region, Nevada: Submicron elemental imaging by Time of Flight-SIMS

    NASA Astrophysics Data System (ADS)

    Handler, M. R.; Vicenzi, E. P.; Sorensen, S. S.

    2002-05-01

    Time of Flight-Secondary Ionization Mass Spectrometry (ToF-SIMS) allows elemental mapping and depth profiling at lateral and depth resolutions of several hundred nanometers, with near-simultaneous acquisition of the entire elemental mass range and extending to larger hydrocarbon molecules. ToF-SIMS has been greatly utilized by surface scientists, but has rarely been used in terrestrial geosciences (e.g. [1]). Essentially a surface imaging technique, with shallow depth profiling abilities, it is ideal for investigating the distribution of elements and molecules (e.g. OH) on mineral surfaces, thin films [1], around fluid inclusions, and to trace chemical changes during weathering or hydrothermal alteration. To illustrate the potential of this analytical technique we highlight the progressive hydrothermal alteration of feldspars in the host andesites of the Comstock Lode paleohydrothermal system, Nevada. The Miocene Comstock Lode and related Ag-Au deposits are hosted mainly within Miocene Alta andesites, which were extensively sampled in the 1880s by G.F. Becker[2]. A sub-suite of these samples from the Sutro Tunnel document progressive hydrothermal alteration, with whole rock δ 18O values progressing from ~ +6 ‰ in distal andesites to -1.5 ‰ at the Coryell Lode [3]. The andesites are porphyritic with up to 50% feldspar phenocrysts, and minor mafic phases. Feldspar phenocrysts show systematic progression of alteration and replacement textures with decreasing whole rock δ 18O values and increasing proximity to the Coryell Lode. Relatively fresh igneous zoned phenocrysts (An35-55) grade into grains with fluid inclusions, crosscutting calcite +/- quartz veins, and increasingly complex reaction rims. Chemical alteration of feldspar progresses along cracks filled with fluid inclusions. Within 400 m of the Coryell Lode, feldspar phenocrysts have fully recrystallized, following crystallographic controls: Ab98-90 + An58-68, +/- sericite +/- calcite. A combination of BSE

  3. Quartz and feldspar zoning in the eastern Erzgebirge volcano-plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing

    NASA Astrophysics Data System (ADS)

    Müller, Axel; Breiter, Karel; Seltmann, Reimar; Pécskay, Zoltán

    2005-03-01

    Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks. Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre

  4. Grain size reduction of feldspar and pyroxene, phase mixing, and strain localization in lower crustal shear zones (Lofoten, Norway)

    NASA Astrophysics Data System (ADS)

    Menegon, L.; Stunitz, H.; Nasipuri, P.; Svahnberg, H.; Heilbronner, R.

    2011-12-01

    High temperature shear zones are common in the magmatic suite of the granulite facies Lofoten basement of Norway, and typically consist of narrow structures (1 cm to 1 m in thickness) showing a mylonite-to ultramylonite transition from the shear zone boundary to the shear zone center. In this contribution we examine the deformation microstructures and synkinematic mineral assemblages of shear zones developed from a mangerite (=monzonite) protolith. The mineral assemblage in the host mangerite indicates anhydrous conditions (mesoperthite + clinopyroxene ± orthopyroxene), whereas the mineral assemblage in the shear zones consists of plagioclase + K-feldspar + quartz + hornblende + calcite + biotite ± clinopyroxene and indicates hydrated conditions. Hornblende-plagioclase geothermobarometry yields upper amphibolite- to granulite facies conditions during shearing (730-760° C, 0.55-0.8 GPa). The mylonite consists of two distinct compositional domains: a pyroxene-derived aggregate and a feldspar-derived aggregate. The pyroxene-derived aggregate consists of the products of the following breakdown reaction: clinopyroxene + plagioclase ± K-feldspar ± orthopyroxene + H2O + CO2 --> quartz + hornblende + calcite ± biotite. In the feldspar-derived aggregate fractured fragments of mesoperthite are surrounded by a bi-phase mixture of recrystallized plagioclase and K-feldspar. EBSD analysis indicates that the recrystallized grains originated as micro-fragments from fracturation, and recrystallization was compositionally-induced (e.g. An22 average composition of plagioclase in the mesoperthite, An14 in the recrystallized aggregate). Detailed grain size, grain shape and EBSD analysis indicate that diffusion creep was the dominant deformation mechanism in both aggregates. Spatial distribution of K-feldspar and plagioclase shows a well dispersed aggregate and may serve as a tool to characterize diffusion creep deformation in phase mixtures. In the ultramylonite the two

  5. Grain boundary diffusion of oxygen, potassium and calcium in natural and hot-pressed feldspar aggregates

    NASA Astrophysics Data System (ADS)

    Farver, John R.; Yund, Richard A.

    1995-01-01

    Grain boundary diffusion rates of oxygen, potassium and calcium in fine-grained feldspar aggregates were determined experimentally. The starting materials were a natural albite rock from the Tanco pegmatite and aggregates hot-pressed from fragments of Amelia albite or Ab, Or and An composition glasses. The technique employed isotopic tracers (18O, 41K, 42Ca) either evaporated onto the surface or in an aqueous solution surrounding the sample, and depth profiling using an ion microprobe (SIMS). From the depth profiles, the product of the grain boundary diffusion coefficient (D') and effective boundary width (δ) was calculated using numerical solutions to the appropriate diffusion equation. The experimental reproducibility of D'δ is a factor of 3. A separate determination of D' independent of δ yields an effective grain boundary width of ˜3 nm, consistent with high resolution TEM observations of a physical grain boundary width <5 nm. Oxygen (as molecular water) grain boundary diffusion rates were determined in the Ab and Or aggregates at 450°-800°C and 100 MPa (hydrothermal), potassium rates in Or aggregates at 450°-700°C both at 0.1 MPa (in air) and at 100 MPa (hydrothermal), and calcium rates in An aggregates at 700°-1100°C and 0.1 MPa (in air). Oxygen grain boundary diffusion rates are similar in all three of the Ab aggregates and in the Or aggregate. Potassium and oxygen depth profiles measured in the same samples yield different D'δ values, confirming a diffusional transport mechanism. Potassium diffusion in the Or aggregate has a greater activation energy (216 vs 78 kJ/mol) than oxygen, and the Arrhenius relations cross at ˜625°C. Potassium D'δ values in Or aggregates are about a factor of five greater in hydrothermal experiments at 100 MPa than in experiments at 0.1 MPa in air. Calcium grain boundary diffusion rates in An aggregates are 4 to 5 orders of magnitude slower than potassium in Or and have a greater (291 kJ/mol) activation energy. This

  6. Thermal diffusivity of pyroxene, feldspar, and silica melts, glasses, and single-crystals at high temperature

    NASA Astrophysics Data System (ADS)

    Pertermann, M.; Branlund, J.; Whittington, A.; Hofmeister, A.

    2007-12-01

    Thermal diffusivity (D) due to phonon transport (the lattice component) was measured using laser-flash analysis from oriented single-crystals and of glasses above the glass transition, which proxy as melts. Compositions include SiO2, CaMgSi2O6, LiAlSi2O6, NaAlSi3O8, and CaAl2Si2O8. KAlSi3O8 was studied previously. Viscosity measurements of the supercooled liquids, in the range 106.8 to 1012.3 Pas, confirm near-Arrhenian behavior. For all compositions and for crystal and glass, D decreases with T, approaching a constant generally near 1000 K: Dsat, which is larger in the crystal than in the glass. A rapid decrease in D as T is increased further (ca 1400 K for orthoclase) is consistent with crossing the glass transition, verified from our viscosity data on these systems. The amount of the decrease depends on the chemical composition and similar to the relative decrease observed in heat capacity. Orthoclase values for Dsat are 0.65± 0.3 mm2/s for bulk crystal and 0.53+/-0.03 mm2/s for the glass. Constant D = 0.475+/-.01 mm2/s represents melt. Thermal conductivity (klat) of orthoclase glass, calculated using previous results for heat capacity (CP) and our density data, increases with T due to CP strongly increasing with T, reaching a plateau near 1.45 W/m-K for melt, but is always below klat of the crystal. Similar results were obtained from the other systems studied. Melting of silica, pyroxene, and feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in the continental crust. The consistency of the behavior for these different compositions and structures suggests that our results are universal, holding for oceanic lithosphere as well. Melts, due to being disordered, are poor transporters of heat via vibrations. However, d(ln klat)/dP depends inversely on bulk modulus, suggesting that at some high pressure, the thermal conductivity of the melt and corresponding crystal become equal so that retention of heat by melts

  7. Resolving the gap between laboratory and field rates of feldspar weathering

    NASA Astrophysics Data System (ADS)

    Gruber, Chen; Zhu, Chen; Georg, R. Bastian; Zakon, Yevgeny; Ganor, Jiwchar

    2014-12-01

    Weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies. The differences between experimental conditions in the laboratory and natural conditions in the field have been thoroughly discussed in previous studies, however, the discrepancy was never fully resolved. It has been shown in past work that if the field conditions are fully simulated in standard laboratory experiments, it is not possible to measure the slow rates of mineral dissolution that are observed in the field using standard laboratory experiments. Therefore, a novel method that uses the change of Si isotopes ratio in spiked solutions is used in the present study to measure weathering rates of feldspar under close-to-natural conditions. A single-point batch experiment (SPBE) of albite dissolution was performed in the present study with an “untreated” albite sample. During the SPBE the dissolution rate was affected by the change of deviation from equilibrium and by the change in the mineral surface reactivity. In order to quantify the effect of the change in surface reactivity on the measured dissolution rates, two multi-point batch experiments (MPBE) were conducted. In those experiments, surface reactivity was found to depend on the amount of dissolved mineral. The decrease in surface reactivity as a function of the amount of dissolved mineral may be described using empirical power laws. Another MPBE was used to measure far-from-equilibrium dissolution rate of albite using a sample that lost most of the highly reactive sites and highly reactive fine crystal during the initial stage of the experiment. Therefore, the change of its surface reactivity is small over the duration of the laboratory experiment (henceforth, “treated” albite sample). Another SPBE was conducted to quantify the effect of deviation from equilibrium on albite dissolution rate under close-to-equilibrium using the

  8. Time-temperature evolution of microtextures and contained fluids in a plutonic alkali feldspar during heating

    NASA Astrophysics Data System (ADS)

    Parsons, Ian; Fitz Gerald, John D.; Lee, James K. W.; Ivanic, Tim; Golla-Schindler, Ute

    2010-08-01

    Microtextural changes brought about by heating alkali feldspar crystals from the Shap granite, northern England, at atmospheric pressure, have been studied using transmission and scanning electron microscopy. A typical unheated phenocryst from Shap is composed of about 70 vol% of tweed orthoclase with strain-controlled coherent or semicoherent micro- and crypto-perthitic albite lamellae, with maximum lamellar thicknesses <1 μm. Semicoherent lamellae are encircled by nanotunnel loops in two orientations and cut by pull-apart cracks. The average bulk composition of this microtexture is Ab27.6Or71.8An0.6. The remaining 30 vol% is deuterically coarsened, microporous patch and vein perthite composed of incoherent subgrains of oligoclase, albite and irregular microcline. The largest subgrains are ~3 μm in diameter. Heating times in the laboratory were 12 to 6,792 h and T from 300°C into the melting interval at 1,100°C. Most samples were annealed at constant T but two were heated to simulate an 40Ar/39Ar step-heating schedule. Homogenisation of strain-controlled lamellae by Na↔K inter-diffusion was rapid, so that in all run products at >700°C, and after >48 h at 700°C, all such regions were essentially compositionally homogeneous, as indicated by X-ray analyses at fine scale in the transmission electron microscope. Changes in lamellar thickness with time at different T point to an activation energy of ~350 kJmol-1. A lamella which homogenised after 6,800 h at 600°C, therefore, would have required only 0.6 s to do so in the melting interval at 1,100°C. Subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted for >5,000 h at 700°C. Homogenisation T is in agreement with experimentally determined solvi for coherent ordered intergrowths, when a 50-100°C increase in T for An1 is applied. Homogenisation of lamellae appears to proceed in an unexpected manner: two smooth interfaces, microstructurally sharp

  9. The Nature of Feldspar Clouding and Its Paleomagnetic Significance With Reference To The 2.45 Ga Matachewan Dyke Swarm, Canada

    NASA Astrophysics Data System (ADS)

    Halls, Henry C.; Zhang, Baoxing; Garland, Mary

    Clouding in calcic plagioclase is a common occurrence in Precambrian diabase dyke swarms worldwide, particularly those of Paleoproterozoic age. The occurrence of this clouding in 2.45 Ga Matachewan dykes within uplifted blocks of the Kapuskasing Zone (KZ) in Canada, and not in dykes of the same swarm at shallower crustal levels in surrounding terranes, suggests that the clouding is produced as a re- equilibration of the felspar in response to declining temperatures but in the presence of pressures appropriate to mid - to lower- crustal levels. We have made the following observations on feldspar separates extracted from the dykes: (1) Curie Balance, and low temperature SIRM acquisition studies show Curie temperarures of 580° C and a Verwey transition at 110-120K appropriate for Ti-poor magnetite; (2) Saturation magnetization is proportional to clouding intensity as determined from image analysis techniques; (3) Hysteresis and SEM studies indicate that the particles are small, typically about 1 micron (PSD) in size; (4) A baked contact test on cloudy feldspar dykes within the KZ is negative, but positive for dykes outside the KZ; (5) Magnetite in cloudy feldspars carries a high coercivity N component of magnetization which increases with clouding intensity, whereas dykes outside the KZ mostly carry an older R remanence; (6) Since sets of R dykes become N along strike on entering the KZ, the magnetization carried by cloudy feldspars is secondary; (7) The presence of R host rocks adjacent to an N cloudy dyke and the occasional survival of lower Hc and lower Tub R components in N cloudy dykes within the KZ suggests that the N magnetization of the feldspar magnetite is a CRM; (8) SEM shows that feldspars of different clouding intensity (from image analysis) have a near constant atomic percentage of Fe, so that the degree of clouding is determined in part by the concentration of magnetite rather than by total Fe and indicates that from 30-90% of the total Fe is used in

  10. Sr and Pb isotopic geochemistry of feldspars and implications for the growth of megacrysts in plutonic settings.

    NASA Astrophysics Data System (ADS)

    Munnikhuis, J.; Glazner, A. F.; Coleman, D. S.; Mills, R. D.

    2015-12-01

    Why megacrystic textures develop in silicic igneous rocks is still unknown. One hypothesis is that these crystals nucleate early in a magma chamber with a high liquid content. A supportive observation of this hypothesis is areas in plutons with high concentrations of megacrysts suggesting flow sorting. Another group of hypotheses suggest megacrystic textures form during protracted late-stage coarsening in a low-melt, interlocked matrix due to either thermal oscillations from incremental pluton emplacement, or Ostwald ripening. Isotopic analyses of large, euhedral K-feldspar megacrysts from the Cretaceous intrusive suites of the Sierra Nevada batholith (SNB) provide new insight into their origin. Megacrysts from the SNB reach the decimeter scale, are Or rich (85-90%), are perthitic, and host mineral inclusions of nearly all phases in the host rock. In-situ micro-drilling of transects, from core to rim, of the alkali feldspars provides material for Sr and Pb isotopic analyses by thermal ionization mass spectrometry (TIMS). Preliminary 87Sr/86Sr(i) isotopic data from samples from the Cathedral Peak Granodiorite, of the Tuolumne Intrusive Suite range from 0.706337 to 0.706452 (~1.6ɛSr) near the cores, whereas a sawtooth pattern with larger variability, 0.706179 to 0.706533 (~5ɛSr), occurs nears the rims. We interpret these preliminary data to indicate that the late portion of growth (i.e. crystal rim) was dominated by either cannibalism of small K-feldspar crystals with isotopic variability, or by addition of isotopically diverse late components to the magma. By comparing the Sr and Pb isotopic stratigraphy of megacrysts from a variety of rock matrices and different granitoids in the SNB isotopic trends can be evaluated to determine if crystals sizes are dependent on disequilibrium processes or grow at a steady state.

  11. A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

    USGS Publications Warehouse

    Duffield, W.A.; Ruiz, J.

    1998-01-01

    Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a

  12. Electron microprobe study of lunar and planetary zoned plagioclase feldspars: An analytical and experimental study of zoning in plagioclase

    NASA Technical Reports Server (NTRS)

    Smith, R. K.; Lofgren, G. E.

    1982-01-01

    Natural and experimentally grown zoned plagioclase feldspars were examined by electron microprobe. The analyses revealed discontinuous, sector, and oscillary chemical zoning superimposed on continuous normal or reverse zoning trends. Postulated mechanisms for the origin of zoning are based on either physical changes external to the magma (P, T, H2O saturation) or kinetic changes internal to the magma (diffusion, supersaturation, growth rate). Comparison of microprobe data on natural zoned plagioclase with zoned plagioclase grown in controlled experiments show that it may be possible to distinguish zonal development resulting from physio-chemical changes to the bulk magma from local kinetic control on the growth of individual crystals.

  13. Shock melting of K-feldspar and interlacing with cataclastically deformed plagioclase in granitic rocks at Toqqusap Nunaa, southern West Greenland: Implications for the genesis of the Maniitsoq structure

    NASA Astrophysics Data System (ADS)

    Keulen, Nynke; Garde, Adam A.; Jørgart, Tommy

    2015-11-01

    Folded sheets of Mesoarchaean, leucocratic plagioclase-K-feldspar-mesoperthite-bearing granitic rocks in the Toqqusap Nunaa area of the Maniitsoq structure, West Greenland, are characterised by their very fine grain sizes and microstructures without normal igneous or planar/linear tectonic fabrics. Quartz forms equidimensional and branching, ductilely deformed aggregates and bifurcating panels with protrusions, constrictions and chains of ball-shaped grains with healed, radiating intergranular fractures. Plagioclase (An10-20) was cataclastically deformed and comminuted, whereas K-feldspar and mesoperthite are devoid of cataclastic microstructures. K-feldspar forms dispersed, highly irregular grains with numerous cusps and saddles, indicating almost ubiquitous direct (shock) melting of this mineral. It is commonly located along former fractures in plagioclase, resulting in an 'interlaced' feldspar microstructure with contact shapes indicating subsequent melting of plagioclase directly adjacent to K-feldspar. Mesoperthite forms separate, rounded, and irregular grains with protrusions and cusped margins indicating crystallisation from melts. Some mesoperthite grains are texturally and compositionally heterogeneous and contain internal lenses of K-feldspar and/or plagioclase. Other mesoperthite grains comprise coarsened, 'unzipped' areas, presumably due to localised, fluid-controlled dissolution-reprecipitation processes. The ternary feldspar precursor of the mesoperthite is interpreted as having crystallised from variably effectively mixed K-feldspar shock melts and plagioclase contact melts. Direct melting of K-feldspar, but no whole-rock melting, requires shock metamorphism with a short-lived temperature excursion to above the melting temperature of K-feldspar (~ 1300 °C). The presence of three different feldspar species and absence of chemical zonation, magmatic mantling, or metamorphic coronas furthermore hinders interpretations solely by means of endogenic

  14. Thermal history and origin of the Tanzanian Craton from Pb isotope thermochronology of feldspars from lower crustal xenoliths

    NASA Astrophysics Data System (ADS)

    Bellucci, Jeremy J.; McDonough, William F.; Rudnick, Roberta L.

    2011-01-01

    Common and radiogenic Pb isotopic compositions of plagioclase and anti-perthitic feldspars from granulite-facies lower crustal xenoliths from the Labait Volcano on the eastern margin of the Tanzanian Craton have been measured via laser ablation MC-ICP-MS. Common Pb in plagioclase and a single stage Pb evolution model indicate that the lower crust of the Tanzanian Craton was extracted from mantle having a 238U/ 204Pb of 8.1 ± 0.3 and a 232Th/ 238U of 4.3 ± 0.1 at 2.71 ± 0.09 Ga (all uncertainties are 2σ). Since 2.4 Ga, some orthoclase domains within anti-perthites have evolved with a maximum 238U/ 204Pb of 6 and 232Th/ 238U of 4.3. The spread in Pb isotopic composition in the anti-perthitic feldspars yields single crystal Pb-Pb isochrons of ˜ 2.4 Ga, within uncertainty of U-Pb zircon ages from the same sample suite. The Pb isotopic heterogeneities imply that these granulites resided at temperatures < 600 °C in the lower crust of the Tanzanian Craton from ca. 2.4 Ga to the present. In concert with the chemistry of surface samples, mantle xenoliths, and lower crustal xenoliths, our data imply that the cratonic lithosphere in Tanzania formed ca. ˜ 2.7 Ga, in a convergent margin setting, and has remained undisturbed since 2.7 Ga.

  15. Evidence for the compaction of feldspar-rich cumulates in the Pleasant Bay layered intrusion, coastal Maine

    SciTech Connect

    Horrigan, E.K. )

    1993-03-01

    The Pleasant Bay intrusion is roughly 12 km by 20 km. It consists of prominent rhythmic layers, up to 100 m thick, that grade from chilled gabbro on the base, to coarse-grained gabbroic, dioritic, or granitic rocks on the top. These layers were formed by multiple injections of basalt into a large chamber of silicic magma. The focus of this study is on one layer that is about 100 m thick, and is overlain by another basally chilled gabbroic layer at least 50 m thick. Silicic pipes and veins extend upward into the overlying gabbroic chill. The lower part of the layer has dominant calcic plagioclase, An60, augite, and olivine, with subordinate hornblende and biotite. The uppermost part has dominant sodic plagioclase, An20, and two pyroxenes with subordinate quartz, K-feldspar and hornblende. SiO[sub 2] and MgO vary from 49% and 5% at the base to 58% and 1% at the top, respectively. The top 7 m of this layer are characterized by variably deformed minerals. The deformation grades from bent biotite and plagioclase near the bottom to sutured plagioclase at the top. Pockets of undeformed quartz and K-feldspar in the uppermost rocks demonstrate that interstitial liquid was present during a after compaction. The pipes and veins probably represent trapped liquid and some crystals that were expelled into the overlying gabbroic chill.

  16. Preparation and Characterization of Chitosan/Feldspar Biohybrid as an Adsorbent: Optimization of Adsorption Process via Response Surface Modeling

    PubMed Central

    Yazdani, Maryam; Bahrami, Hajir; Arami, Mokhtar

    2014-01-01

    Chitosan/feldspar biobased beads were synthesized, characterized, and tested for the removal of Acid Black 1 dye from aquatic phases. A four-factor central composite design (CCD) accompanied by response surface modeling (RSM) and optimization was used to optimize the dye adsorption by the adsorbent (chitosan/feldspar composite) in 31 different batch experiments. Independent variables of temperature, pH, initial dye concentration, and adsorbent dose were used to change to coded values. To anticipate the responses, a quadratic model was applied. Analysis of variance (ANOVA) tested the significance of the process factors and their interactions. The adequacy of the model was investigated by the correlation between experimental and predicted data of the adsorption and the calculation of prediction errors. The results showed that the predicted maximum adsorption amount of 21.63 mg/g under the optimum conditions (pH 3, temperature 15°C, initial dye concentration 125 mg/L, and dose 0.2 g/50 mL) was close to the experimental value of 19.85 mg/g. In addition, the results of adsorption behaviors of the dye illustrated that the adsorption process followed the Langmuir isotherm model and the pseudo-second-order kinetic model. Langmuir sorption capacity was found to be 17.86 mg/g. Besides, thermodynamic parameters were evaluated and revealed that the adsorption process was exothermic and favourable. PMID:24587722

  17. Do ages of authigenic K-feldspar date the formation of Mississippi valley-type Pb-Zn deposits, central and southeastern United States?: Pb isotopic evidence

    USGS Publications Warehouse

    Aleinikoff, J.N.; Walter, M.; Kunk, M.J.; Hearn, P.P., Jr.

    1993-01-01

    Pb concentrations and isotopic compositions have been determined for authigenic overgrowths and detrital cores of K-feldspar from Cambrian sedimentary rocks in Texas, Tennessee, and Pennsylvania (group 1) and southeastern Missouri (group 2). Overgrowths and cores were separated by abrasion and analyzed separately. The disparity in Pb isotopic ratios of group 1 overgrowths and Pb in nearby Mississippi Valley-type deposits implies that the regional authigenic K-feldspar event was not synchronous with ore deposition in the southeastern United States. In contrast, Pb isotopic ratios from group 2 authigenic K-feldspar are similar to ratios in ores of southeastern Missouri, suggesting a genetic relation in late Paleozoic time. -from Authors

  18. Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 4. Numerical modeling of kinetic reaction paths

    NASA Astrophysics Data System (ADS)

    Zhu, Chen; Lu, Peng; Zheng, Zuoping; Ganor, Jiwchar

    2010-07-01

    This paper explores how dissolution and precipitation reactions are coupled in batch reactor experimental systems at elevated temperatures. This is the fourth paper in our series of "Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems". In our third paper, we demonstrated via speciation-solubility modeling that partial equilibrium between secondary minerals and aqueous solutions was not attained in feldspar hydrolysis batch reactors at 90-300 °C and that a strong coupling between dissolution and precipitation reactions follows as a consequence of the slower precipitation of secondary minerals ( Zhu and Lu, 2009). Here, we develop this concept further by using numerical reaction path models to elucidate how the dissolution and precipitation reactions are coupled. Modeling results show that a quasi-steady state was reached. At the quasi-steady state, dissolution reactions proceeded at rates that are orders of magnitude slower than the rates measured at far from equilibrium. The quasi-steady state is determined by the relative rate constants, and strongly influenced by the function of Gibbs free energy of reaction ( ΔG) in the rate laws. To explore the potential effects of fluid flow rates on the coupling of reactions, we extrapolate a batch system ( Ganor et al., 2007) to open systems and simulated one-dimensional reactive mass transport for oligoclase dissolution and kaolinite precipitation in homogeneous porous media. Different steady states were achieved at different locations along the one-dimensional domain. The time-space distribution and saturation indices (SI) at the steady states were a function of flow rates for a given kinetic model. Regardless of the differences in SI, the ratio between oligoclase dissolution rates and kaolinite precipitation rates remained 1.626, as in the batch system case ( Ganor et al., 2007). Therefore, our simulation results demonstrated coupling among dissolution, precipitation, and flow rates

  19. Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-03-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse-grained (> 50 µm) feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 µm) localized in C' shear bands. Detailed microstructural observations and electron backscatter diffraction (EBSD) analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (˜ 1-2 mm) monomineralic veins transposed along the shear zone foliation or as thin ribbons ( ≤ 25 µm width) dispersed in the feldspathic mixture. The microstructure and c axis crystallographic-preferred orientation are similar in the thick monomineralic veins and in the thin ribbons, and they suggest dominant subgrain rotation recrystallization and activity of prism < a > and rhomb < a > slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the quartz monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 µm vs. 5 µm respectively). The fine-grained feldspar mixture has a weak crystallographic-preferred orientation interpreted as the result of shear zone parallel-oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Once C' shear bands were generated and underwent viscous deformation at constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate 1 order of magnitude faster than the monophase quartz monomineralic veins, as evidenced by applying experimentally and theoretically calibrated flow laws for dislocation creep in quartz and diffusion creep in

  20. The evolution and significance of microfracturing within feldspars in low-grade granitic mylonites: A case study from the Eastern Ghats Mobile Belt, India

    NASA Astrophysics Data System (ADS)

    Sinha, Suspa; Alsop, G. Ian; Biswal, T. K.

    2010-10-01

    Patterns of microfracturing are investigated in plagioclase and K-feldspar porphyroclasts formed within granitic mylonites along the boundary of the Eastern Ghats Mobile Belt, India. The mineral assemblage comprising quartz, feldspar, biotite and hornblende suggests lower greenschist facies conditions during mylonitisation, with the contrasting ductile behaviour of quartz and brittle fracturing of feldspars restricting the temperature range during deformation to 300-350 °C. Microfracturing of feldspars takes place by concentration of pure shear within the feldspar-rich layers. This may reflect strain partitioning into dominantly pure and simple shear due to the competency contrasts between the two major constituent minerals (quartz and feldspar). The microfractures occur in conjugates (here designated T 1 and T 2) with T 1 inclined in the same direction as the S-fabric and showing an antithetic sense to the NW verging shear, while T 2 is inclined in an opposite sense to the S-fabric and displays synthetic shear. The direction of maximum compression occurs at high angles to the C-fabric, and the T 1 and T 2 fractures are the result of pure shear localized into brittle layers within the mylonite. With progressive shear, the fractures along with their host feldspar grains are rotated. Theoretical graphs are plotted between bulk shear ( γ) and the angle of initiation ( α) of T 1 and T 2 with respect to C-planes, for fractures hosted in a circular or elliptical objects. The kinematics of these fractures are also analyzed with regard to variations in shear strain and sense of shear along them. The sense of shear may vary or remain stable within fractures, depending on their initial angle of inclination with respect to the C-fabric. As T 1 is inclined at low angles to the XY plane and in the same direction as the S-fabric, it undergoes maximum shear strain compared to T 2 and may even exceed the bulk shear. This facilitates breakdown of feldspar porphyroclasts during

  1. Kinetics of feldspar and quartz dissolution at 70-80°C and near-neutral pH: effects of organic acids and NaCl

    NASA Astrophysics Data System (ADS)

    Blake, R. E.; Waltera, L. M.

    1999-07-01

    Effects of the organic acid (OA) anions, oxalate and citrate, on the solubility and dissolution kinetics of feldspars (labradorite, orthoclase, and albite) at 80°C and of quartz at 70°C were investigated at pH 6 in separate batch experiments and in media with different ionic strength (0.02-2.2 M NaCl). Although it has been shown that OAs can increase rates of feldspar dissolution, prior experiments have focused primarily on dilute, highly undersaturated and acidic conditions where feldspar dissolution kinetics are dominated by H + adsorption and exchange reactions. Many natural waters, however, are only weakly acidic and have variable ionic strength and composition which would be expected to influence mineral surface properties and mechanisms of organic ligand-promoted reactions. Oxalate and citrate (2-20 mM) increased the rate of quartz dissolution by up to a factor of 2.5. Quartz solubility, however, was not increased appreciably by these OAs, suggesting that Si-OA complexation is not significant under these conditions. The lack of significant OA-SiO 2 interaction is important to understanding the effects of OAs on the release of both Si and Al from feldspars. In contrast to quartz, both the rates of dissolution and amounts of Si and Al released from the three feldspars studied increased regularly with increasing OA concentration. Feldspar dissolution was congruent at all but the lowest OA concentrations. Total dissolved Al concentrations increased by 1-2 orders of magnitude in the presence of oxalate and citrate, and reached values as high as 43 mg/l (1.6 mM). Si concentrations reached values up to 65 mg/l (2.3 mM) in feldspar-OA experiments. Precipitation of authigenic clays was observed only in experiments without or at very low concentrations of OAs. The high concentrations of dissolved Si attained during dissolution of feldspars in OA solutions, relative to Si concentrations in quartz-OA experiments, is attributed to concomitant release of Si driven by

  2. Brittle grain size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-04-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse (> 50 μm) grained feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 μm in size) localized in C' shear bands. Detailed microstructural observations and EBSD analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (˜ 1-2 mm) monomineralic bands or as thin ribbons dispersed in the feldspathic mixture. The microstructure and c-axis crystallographic preferred orientation are similar in the thick monomineralic band and in the thin ribbons, and suggest dominant subgrain rotation recrystallization and activity of prism and rhomb slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 μm vs 5 μm, respectively).The fine-grained feldspar mixture has a weak crystallographic preferred orientation interpreted as the result of oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Assuming that the C' shear bands deformed under constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate one order of magnitude faster than the monophase quartz ribbons. Overall, our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystalline plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the feldspathic material

  3. Brittle grain size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, G.; Menegon, L.; Archanjo, C. J.

    2015-10-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse (> 50 μm) grained feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (~ < 15 μm in size) localized in C' shear bands. Detailed microstructural observations and EBSD analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (~ 1-2 mm) monomineralic bands or as thin ribbons dispersed in the feldspathic mixture. The microstructure and c axis crystallographic preferred orientation are similar in the thick monomineralic band and in the thin ribbons, and suggest dominant subgrain rotation recrystallization and activity of prism ⟨a⟩ and rhomb ⟨a⟩ slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the transposed veins to the thin ribbons embedded in the feldspathic C' bands (14 μm vs. 5 μm, respectively). The fine-grained feldspar mixture has a weak crystallographic preferred orientation interpreted as the result of oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Assuming that the C' shear bands deformed under constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate one order of magnitude faster than the monophase quartz ribbons. Overall, our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase

  4. Systematic analysis of K-feldspar 40Ar/ 39Ar step heating results II: relevance of laboratory argon diffusion properties to nature

    NASA Astrophysics Data System (ADS)

    Lovera, Oscar M.; Grove, Marty; Harrison, T. Mark

    2002-04-01

    We examine a database containing the results of 40Ar/ 39Ar step-heating experiments performed on 194 basement K-feldspars to recover thermal history information. Qualitative examination of 40Ar/ 39Ar systematics reveals that about half of the K-feldspars examined are sufficiently well behaved to be suitable for thermal history analysis. Correlation algorithms are developed to quantitatively assess the degree to which age and 39Ar release spectra are compatible with the same volume diffusion process. Upon applying these methods, we find that 65% of all samples yield correlation coefficients in excess of 0.8, whereas roughly 40% give values above 0.9. We further compare the observed correlation behavior with that predicted from the multidiffusion domain model and find good agreement for samples with correlation coefficients above 0.9. In contrast, hydrous phases unstable under in vacuo heating and K-feldspars with highly disturbed age spectra yield poorly correlated age and diffusion properties. The high degree of correlation exhibited by the majority of K-feldspars we have analyzed validates extrapolation of experimentally determined diffusion properties to conditions attending natural Ar loss within the crust. Despite this, a significant number of basement K-feldspars analyzed by the step-heating method yield 40Ar/ 39Ar systematics that are clearly problematic for thermal history analysis. We numerically explore the effects of low-temperature alteration of K-feldspar on thermochronological analysis and identify a range of conditions under which information is progressively lost. Finally, we demonstrate the insensitivity of thermal history calculations to detailed knowledge of the diffusion mechanism by introducing the heterogeneous diffusion model. We find that the multidiffusion domain approach can successfully recover imposed thermal histories from heterogeneous diffusion-type crystals and conclude that most details of the interpretive model employed are of

  5. Rheasilvia provenance of the Kapoeta howardite inferred from ∼ 1 Ga40Ar/39Ar feldspar ages

    NASA Astrophysics Data System (ADS)

    Lindsay, Fara N.; Delaney, Jeremy S.; Herzog, Gregory F.; Turrin, Brent D.; Park, Jisun; Swisher, Carl C.

    2015-03-01

    We report 40Ar/39Ar ages for several lithological components of the brecciated howardite Kapoeta and compare the ages with results for asteroid 4 Vesta as observed by the Dawn mission. Our Kapoeta sample has an unusual, millimeter wide glass vein that intruded into a complex breccia. The plateau ages of three lithic clasts of basaltic composition that were remote from the glass vein range from 4.2 to 4.5 Ga. Such ages are typical of eucritic material; the oldest reflects early magmatic crystallization (∼ 4.5 Ga), the younger (4.2-4.5 Ga) reflect magmatism associated with protracted cooling. Samples of the glass vein itself, which include relict grains, give apparent ages between 3.1 and 3.9 Ga as do chips from the matrix. We consider both glass and bulk matrix ages as mixing ages; not marking the time of a single event, but dating regolith activity (< 3.1- 4.1 Ga). Eight feldspar grains close to the glass vein give markedly younger plateau ages averaging 1.4 Ga. The Ar release spectra for glass vein and breccia subsamples indicate a disturbance in the last 1.4 Ga. Taken together, these younger ages suggest a recent, major thermal event in the history of howardites that has been under-reported - perhaps the impact that formed the Rheasilvia basin on Vesta.

  6. 40Ar/39Ar dating of microgram feldspar grains from the paired feldspathic achondrites GRA 06128 and 06129

    NASA Astrophysics Data System (ADS)

    Lindsay, Fara N.; Herzog, Gregory F.; Park, Jisun; Delaney, Jeremy S.; Turrin, Brent D.; Swisher, Carl C.

    2014-03-01

    40Ar/39Ar ages of single feldspar grains from the paired meteorites Graves Nunatak 06128 (GRA8; 8 grains) and 06129 (GRA9; 26 grains) are presented. Plateau ages (⩾70% of the 39Ar released) ranged from 4000 to 4600 Ma with an average 1-σ uncertainty of ±90 Ma. The most precise ages obtained were 4267 ± 17 Ma for a grain from GRA8 and 4437 ± 19 Ma and 4321 ± 18 Ma for two grains from GRA9. Isotope correlation diagrams yield less precise ages ranging from 3800 to 5200 Ma with an average 1-σ uncertainty of 250 Ma; they indicate a negligible trapped component. Plateau ages, integrated total fusion ages, and isochron ages are internally concordant at the 95% confidence level. The distribution of the plateau ages for GRA9 is bimodal with peaks at 4400 and 4300 Ma. In contrast, the plateau age distribution for GRA8 peaks at about 4260 Ma with broad wings extending toward younger and older ages. To explain the distributions of grain ages we prefer a scenario that includes a major post-formation event about 4400 Ma ago and a later melt intrusion event that heated GRA8 more than some parts of GRA9.

  7. NPPy With Dan DeVito

    NASA Video Gallery

    The NPP mission mascot NPPy was found by the NPP Ground Project Manager Dan DeVito in a place called Svalbard, located 600 miles from the North Pole. Since then, Dan and other people on the NPP pro...

  8. The destruction of quartz, amorphous silica minerals, and feldspars in model experiments and in soils: Possible mechanisms, rates, and diagnostics (the analysis of literature)

    NASA Astrophysics Data System (ADS)

    Sokolova, T. A.

    2013-01-01

    The dissolution of quartz and amorphous SiO2 proceeds via the adsorption of water molecules on the surface of these minerals with the further formation of four silanol groups around the silicon atom and the detachment of the molecules of orthosilicic acid from the surface. The rates of quartz dissolution at pH 7 and 3 constitute 10-15.72 and 10-16.12 mol/m2 s, respectively. They increase by three orders of magnitude upon the rise in pH from 7 to 10; they also increase in the solutions of strong electrolytes and in the presence of the anions of polybasic organic acids. The dissolution of feldspars begins from the release of alkali metals and calcium from the surface of crystal lattices of these minerals into the solution in the course of the cation exchange reaction. This is a fast process, and it does not control the rate of the feldspar dissolution that depends on the concentrations of protonated (in the acid medium) and deprotonated (in the alkaline medium) complexes with participation of the surface Si-O-Si and Al-O-Si groups of the mineral lattices. The rate of dissolution of K-Na feldspars decreases from n × 10-11 to n × 10-12 mol/m2 s upon the rise in pH from 3 to 5; it also increases in the plagioclase series with an increase in the portion of anorthite molecules and in the presence of the anions of polybasic organic acids in the solution. The rate of dissolution of feldspars in the model experiments is by 1-3 orders of magnitude higher than that obtained by different methods for native soils. This may be related to the adequacy of determination of the specific surface and its changes with time in native soils.

  9. P- T conditions of crystallization and origin of plagioclase-mantled alkali feldspar megacrysts in the Mesozoic granitoids in the Qinling orogen (China)

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Wang, Tao; Haapala, Ilmari; Mao, Jingwen

    2008-07-01

    The Qinling orogen between the North China and South China cratons was intruded at 211-217 Ma by calc-alkaline quartz monzonitic to monzogranitic plutons characterized by I- to A-type geochemistry and in many places contain plagioclase-mantled alkali feldspar megacrysts (rapakivi texture sensu lato). The felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas. The P- T conditions of crystallization have been determined for early mineral assemblages (inner parts of alkali feldspar megacrysts and their plagioclase, quartz, amphibole and biotite inclusions) and late assemblages (matrix minerals) of the rapakivi-textured granitoids. Al contents in amphibole from the early and late mineral assemblages yield pressures of 1.2-3.0 and 0.7-3.0 kbar, respectively, and indicate only minor pressure change between the crystallization of the early and late assemblages. Amphibole-plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 °C for both the early and late assemblages indicating nearly isothermal conditions. Feldspar thermometers yield lower temperatures. Relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in MgO, Na 2O and CaO than the early assemblages. Rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas. Small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts.

  10. Cationic polyelectrolyte induced separation of some inorganic contaminants and their mixture (zirconium silicate, kaolin, K-feldspar, zinc oxide) as well as of the paraffin oil from water.

    PubMed

    Ghimici, Luminita

    2016-03-15

    The flocculation efficiency of a cationic polyelectrolyte with quaternary ammonium salt groups in the backbone, namely PCA5 was evaluated on zirconium silicate (kreutzonit), kaolin, K- feldspar and zinc oxide (ZnO) suspensions prepared either with each pollutant or with their mixture. The effect of several parameters such as settling time, polymer dose and the pollutant type on the separation efficacy was evaluated and followed by optical density and zeta potential measurements. Except for ZnO, the interactions between PCA5 and suspended particles led to low residual turbidity values (around 4% for kreutzonit, 5% for kaolin and 8% for K-feldspar) as well as to the reduction of flocs settling time (from 1200 min to 30 min and 120 min in case of kaolinit and K-feldspar, respectively), that meant a high efficiency in their separation. The negative value of the zeta potential and flocs size measurements, at the optimum polymer dose, point to contribution from charge patch mechanism for the particles flocculation. A good efficiency of PCA5 in separation of paraffin oil (a minimum residual turbidity of 9.8%) has been also found. PMID:26716571

  11. Corner Office: Google's Dan Clancy

    ERIC Educational Resources Information Center

    Albanese, Andrew Richard; Oder, Norman

    2009-01-01

    This article presents an interview with Dan Clancy, engineering director for Google Book Search. In this interview, Clancy talks about the pending Google Book Search settlement, involving millions of volumes digitized from libraries, which drew a lawsuit from the Association of American Publishers and the Authors Guild. He also discusses pricing,…

  12. Isothermal thermoluminescence dating of K-feldspar from sediments to determine fault slip rates: development and assessment

    NASA Astrophysics Data System (ADS)

    Rhodes, E. J.; Roder, B. J.; Lawson, M. J.; Dolan, J. F.; McGill, S. F.; McAuliffe, L.

    2012-04-01

    Faults in California accommodate most of the relative motion between the Pacific and North American tectonic plates, along either one main strike-slip fault, - the San Andreas fault - or a network of sub-parallel faults (e.g., the San Jacinto, Elsinore and San Andreas faults). Slip is also accommodated along many other associated faults and folds, and the region suffers frequent damaging earthquakes. Contemporary movements of different fault-bounded blocks are relatively well established on decadal timescales using remote sensing and GPS, and on timescales of 106 to 107 years, by dating offset geologic features with radiometric methods. However, on timescales of decades to several hundred thousand years, determining total fault offset and mean slip rate is harder. Critical questions for understanding fault dynamics and improving earthquake risk assessment include the degree to which slip is clustered into episodes of more rapid movement, and how slip is accommodated by different sub-parallel faults. In many cases, streams with offset courses can be recognised, and in some cases offset terrace surfaces can be located, especially when using LiDAR data to complement field mapping. Radiocarbon and terrestrial cosmogenic nuclides have been used to date these features, but both have limitations of age range, sample suitability and availability. OSL (optically stimulated luminescence) and IRSL (infra-red stimulated luminescence) have great potential to complement these techniques, though the characteristics of quartz in some parts of southern California are suboptimal, displaying low sensitivity and other limitations. In order to overcome these limitations encountered using quartz OSL, we are developing a new geochronometer based on the isothermal thermoluminescence (ITL) signal of K feldspar measured at 250°C. Preliminary ITL age estimates from the paleoseismic site of El Paso Peaks on the Central Garlock fault in the Mojave Desert, California, agree well with a well

  13. Tectonic burial and exhumation cycles tracked by muscovite and K-feldspar 40Ar/39Ar thermochronology in a strike-slip fault zone, central Turkey

    NASA Astrophysics Data System (ADS)

    Idleman, Lauren; Cosca, Michael A.; Heizler, Matthew T.; Thomson, Stuart N.; Teyssier, Christian; Whitney, Donna L.

    2014-02-01

    Muscovite and K-feldspar 40Ar/39Ar ages from the eastern margin of the Niğde massif in central Anatolia track the timing of initial exhumation, reburial, and final exhumation and cooling of metamorphic rocks deformed within a strike-slip fault zone. Although the ages of initial and final cooling were known from previous studies, our new results document the timing of the reheating/reburial event. Muscovite from four of eight gneiss samples have Late Cretaceous 40Ar/39Ar ages that date initial cooling at ~ 75 Ma. The remaining samples have perturbed spectra that climb to Late Cretaceous ages with increasing extraction temperatures during analysis. These perturbed samples are located beneath a faulted unconformity overlain by Paleogene sedimentary deposits that were derived in part from the metamorphic rocks, then buried, metamorphosed, and deformed under greenschist facies conditions. Samples close to the faulted unconformity are more perturbed than structurally deeper samples. The age of the thermal perturbation is determined at 30 ± 5 Ma using multi-diffusion domain modeling of K-feldspar 40Ar/39Ar data from two gneiss samples, one located close to the unconformity and one at a structurally deeper level. Muscovite 40Ar/39Ar results and modeled K-feldspar temperature-time histories show that the eastern margin of the Niğde massif experienced a reheating event that peaked at ~ 30 Ma. The thermal pulse has been attributed to reburial associated with transpression in the Ecemiş segment of the Central Anatolian Fault Zone along the eastern margin of the Niğde massif. Activity of this fault zone may represent a far-field expression of the onset of collision of Arabia with Eurasia in SE Anatolia.

  14. Constraints on the formation of the Bitterroot Lobe of the Idaho Batholith, Idaho and Montana, from U-Pb zircon geochronology and feldspar Pb isotopic data

    SciTech Connect

    Toth, M.I.; Stacey, J.S.

    1992-01-01

    This paper reports on zircons from tonalite emplaced along the western periphery of the Bitterroot Lobe of the Idaho Batholith yield an almost concordant age of 94 {plus minus} 1.4 Ma; monozogranite and granodiorite plutons along the northern edge of the lobe yield ages of 75 to 71 ma. The volumetrically more dominant plutons in the central and western parts of the lobe were emplaced between 59 and 54 Ma. Upper intercept data, combined with Pb isotopic data from feldspars, confirm that the magmas of the Bitterroot Lobe were derived mainly from an early Proterozoic lower continental crust.

  15. Metasomatism in the Chain of Ponds K-feldspars: Reassessing Discrete Domain 39Ar-40Ar Modelling

    NASA Astrophysics Data System (ADS)

    Villa, I. M.; Chafe, A. N.; Hanchar, J. M.; Wirth, R.

    2012-12-01

    The post-crystallization petrology of K-feldspar (Kfs) is mostly controlled by fluids. Accordingly, [1] documented that successive mineral generations in Kfs grains of the Aar metagranite can be concordantly identified by both cathodoluminescence (CL) and back-scattered electron (BSE) imaging, elemental, and multi-isotope techniques. Imaging microstructures is a particularly powerful tool appreciated by many U-Pb geochronologists, and its use in 39Ar-40Ar dating is beginning to show beneficial progress [2]. However, a dissenting reviewer of [1] argued that the Aar sample was not typical of "orthodox" Kfs and the results could not be generalized to all Kfs [3]. On a different front, [4] demonstrated that the mathematical modeling that assumed Fickian diffusion in discrete domains, defined once and for all by [5], lacked internal consistency on several counts. As Chain of Ponds Pluton (CPP) Kfs sample MH-10 played a foundational role in the development of the mathematical model by [5], we decided to obtain direct evidence whether the numerous internal inconsistencies of the model are due to the previously undescribed petrological history of MH-10. We collected sample JH-02-01 on the same CPP outcrop as MH-10 [6]. All age spectra of different sieve fractions of the Kfs separate, both handpicked and unpicked, show a staircase shape. The Arrhenius diagram of apparent diffusivity agrees with the original MH-10 [5] and shows the same apparent r/r0 behavior. However, Arrhenius trajectories for all size fractions are parallel to each other and self-similar, as predicted by [4], instead of being joined at low temperature ("small domains") and diverging only at high T ("largest domain"), as would be implicit in the model by [5]. The CL and BSE images demonstrate several successive Kfs generations of diverse luminescence and chemical and isotopic properties. Microchemical analyses document patchy Ba enrichment, a tell-tale fingerprint of deuteric fluid interaction and

  16. Crystal-chemical controls on the partitioning of Sr and Ba between plagioclase feldspar, silicate melts, and hydrothermal solutions

    NASA Astrophysics Data System (ADS)

    Blundy, Jonathan D.; Wood, Bernard J.

    1991-01-01

    The isothermal (750°C) experiments of LAGACHE and DUJON (1987) reveal that the partitioning of Sr between plagioclase feldspar and hydrothermal solutions is a funtion of the anorthite (An) content of the plagioclase, indicating that crystal chemistry may exert a powerful influence on trace element partitioning. In order to compare these results with those on trace element partitioning between plagioclase and silicate melts we have compiled from the literature a large dataset of experimental and volcanic distribution coefficients ( D's) for Sr (and Ba). These data, which span a compositional range from lunar basalt to high silica rhyolite and a temperature range of over 650°C, show a relationship between DSr (and DBa) and mole fraction An ( XAn) which is similar to that exhibited by the hydrothermal results obtained at constant temperature. Plots of In DSr and In DBa versus XAn are linear with negative slope, indicating that both elements are more compatible in albite than anorthite. In terms of molar distribution coefficients ( D Sr∗) the hydrothermal and silicate melt data display an identical linear relationship between RT In D Sr∗ (where T is the absolute temperature in K and R is the gas constant, 8.314 JK -1 mol -1) and XAn. We conclude therefore that crystal chemistry provides the dominant control on partitioning of Sr and Ba into plagioclase and that the effects of temperature, pressure, and fluid composition are minor. Apparent relationships between DSr (and DBa) and the reciprocal temperature (1/ T) are artefacts of the linear relationships between XAn and 1/ T in the experimental studies. By defining a Henry's law standard state for the silicate melts and hydrothermal solutions, and considering plagioclases to be ternary regular solutions, we are able to relate the observed relationships between RT In D i∗ (where i is Ba or Sr) and XAn to the excess free energies of the trace element partitioning reactions between plagioclase and melt or

  17. Magnetic susceptibility and feldspar zonations in the Peoria Loess and Roxana Silt of southwestern Illinois and eastern Missouri: Correlation tools and provenance indicators

    SciTech Connect

    Grimley, D.A. . Dept. of Geology)

    1993-03-01

    Magnetic susceptibility zonations within the Peoria Loess and Roxana Silt are useful for correlations across several counties in southwestern Illinois and eastern Missouri. The Roxana Silt and lower Peoria Loess (60--80 [times] 10[sup [minus]5] SI units) contain a greater concentration of primary magnetite in all silt fractions than the middle Peoria Loess (40--55 [times] 10[sup [minus]5] SI units). Similarly, feldspar contents (as determined from X-ray diffraction of micronized silts) are 30% to 40% higher in the high susceptibility zones, while the bulk grain size distributions do not vary significantly. Therefore, the origin of these mineralogical zones is best explained by the changing proportion of silt derived from igneous and metamorphic rocks as compared with silt derived from sedimentary rocks. During deposition of the Roxana Silt and lower Peoria Loess, an ice margin in Upper Michigan, Wisconsin, Minnesota, or the Canadian Shield, would be responsible for the erosion of a greater proportion of shield lithologies. During the Wisconsinan glacial maximum, the erosion of Paleozoic sedimentary rocks by the advance of the Lake Michigan Lobe diluted the contribution of shield lithologies to the middle Peoria Loess. Higher magnetite and feldspar contents, present in the upper Peoria Loess when relatively unweathered, coincide with a receding ice margin during the latest Wisconsinan.

  18. Radiations cosmiques : danger dans l'Espace

    NASA Astrophysics Data System (ADS)

    Bonnet-Bidaud, J. M.; Dzitko, H.

    2000-06-01

    Au sol, l'atmosphere nous protege plus ou moins bien. Mais dans l'espace ou a bord des avions de ligne, l'homme est directement expose aux rayonnements cosmiques qui peuvent etre mortels. Un veritable frein a la presence humaine prolongee dans l'espace. Une menace que les agences spatiales prennent tres au serieux.

  19. Provenance of sands from the confluence of the Amazon and Madeira rivers based on detrital heavy minerals and luminescence of quartz and feldspar

    NASA Astrophysics Data System (ADS)

    do Nascimento, Daniel R.; Sawakuchi, André O.; Guedes, Carlos C. F.; Giannini, Paulo C. F.; Grohmann, Carlos H.; Ferreira, Manuela P.

    2015-03-01

    Source-to-sink systems are poorly known in tropical rivers. For the Amazonian rivers, the majority of the provenance studies remain focused on the suspended load, implying a poor understanding of the processes governing production and distribution of sands. In this study, we perform heavy mineral and optically stimulated luminescence (OSL) analysis to cover the entire spectrum (heavy and light minerals fraction) of 29 sand samples of the Lower Madeira river region (Amazon and Madeira rivers), of which the main goal was to find provenance indicators specific to these rivers. Despite the tropical humid climate, the sands of the Amazon and Lower Madeira rivers are rich in unstable heavy minerals as augite, hypersthene, green hornblende and andalusite. The Madeira river is highlighted by its higher content of andalusite, with source attributed to the Amazon Craton (medium-to-high grade metamorphic rocks), while the Amazon river, upstream of the Madeira river mouth, has a signature of augite and hypersthene, that suggests an Andean provenance (volcanic rocks). Sands from the Madeira river can be tracked in the Amazon river by the increasing concentration in andalusite. OSL analysis of the light minerals fraction was used as an index of feldspar concentration and sedimentary history of quartz grains. Lower feldspar concentration and quartz grains with longer sedimentary history (higher OSL sensitivity) also point to a major contribution of cratonic sources for the sands in the Madeira river. While the sands from the Lower Madeira would be mainly supplied by cratonic rocks, previous work recognised that suspended sediments (silt and clay) are derived from Andean rocks. Therefore, we interpret a decoupling between the sources of sand and mud (silt and clay) under transport in the Madeira river. Andean sands (rich in augite and hypersthene) would be trapped in the foreland zones of the Beni and Mamoré tributaries. In the Amazon river sands, the low OSL sensitivity of the

  20. Mineral dissolution in the Cape Cod aquifer, Massachusetts, USA: I . Reaction stoichiometry and impact of accessory feldspar and glauconite on strontium isotopes, solute concentrations, and REY distribution

    NASA Astrophysics Data System (ADS)

    Bau, Michael; Alexander, Brian; Chesley, John T.; Dulski, Peter; Brantley, Susan L.

    2004-03-01

    To compare relative reaction rates of mineral dissolution in a mineralogically simple groundwater aquifer, we studied the controls on solute concentrations, Sr isotopes, and rare earth element and yttrium (REY) systematics in the Cape Cod aquifer. This aquifer comprises mostly carbonate-free Pleistocene sediments that are about 90% quartz with minor K-feldspar, plagioclase, glauconite, and Fe-oxides. Silica concentrations and pH in the groundwater increase systematically with increasing depth, while Sr isotopic ratios decrease. No clear relationship between 87Sr/ 86Sr and Sr concentration is observed. At all depths, the 87Sr/ 86Sr ratio of the groundwater is considerably lower than the Sr isotopic ratio of the bulk sediment or its K-feldspar component, but similar to that of a plagioclase-rich accessory separate obtained from the sediment. The Si- 87Sr/ 86Sr-depth relationships are consistent with dissolution of accessory plagioclase. In addition, solutes such as Sr, Ca, and particularly K show concentration spikes superimposed on their respective general trends. The K-Sr- 87Sr/ 86Sr systematics suggests that accessory glauconite is another major solute source to Cape Cod groundwater. Although the authigenic glauconite in the Cape Cod sediment is rich in Rb, it is low in in-grown radiogenic 87Sr because of its young Pleistocene age. The low 87Sr/ 86Sr ratios are consistent with equilibration of glauconite with seawater. The impact of glauconite is inferred to vary due to its variable abundance in the sediments. In the Cape Cod groundwater, the variation of REY concentrations with sampling depth resembles that of K and Rb, but differs from that of Ca and Sr. Shale-normalized REY patterns are light REY depleted, show negative Ce anomalies and super-chondritic Y/Ho ratios, but no Eu anomalies. REY input from feldspar, therefore, is insignificant compared to input from a K-Rb-bearing phase, inferred to be glauconite. These results emphasize that interpretation of

  1. New ages for Middle and Later Stone Age deposits at Mumba rockshelter, Tanzania: optically stimulated luminescence dating of quartz and feldspar grains.

    PubMed

    Gliganic, Luke A; Jacobs, Zenobia; Roberts, Richard G; Domínguez-Rodrigo, Manuel; Mabulla, Audax Z P

    2012-04-01

    The archaeological deposits at Mumba rockshelter, northern Tanzania, have been excavated for more than 70 years, starting with Margit and Ludwig Köhl-Larsen in the 1930s. The assemblages of Middle Stone Age (MSA) and Later Stone Age (LSA) artefacts collected from this site constitute the type sequences for these cultural phases in East Africa. Despite its archaeological importance, however, the chronology of the site is poorly constrained, despite the application since the 1980s of several dating methods (radiocarbon, uranium-series and amino acid racemisation) to a variety of materials recovered from the deposits. Here, we review these previous chronologies for Mumba and report new ages obtained from optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) measurements on single grains of quartz and multi-grain aliquots of potassium (K) feldspar from the MSA and LSA deposits. Measurements of single grains of quartz allowed the rejection of unrepresentative grains and the application of appropriate statistical models to obtain the most reliable age estimates, while measurements of K-feldspars allowed the chronology to be extended to older deposits. The seven quartz ages and four K-feldspar ages provide improved temporal constraints on the archaeological sequence at Mumba. The deposits associated with the latest Kisele Industry (Bed VI-A) and the earliest Mumba Industry (Bed V) are dated to 63.4 ± 5.7 and 56.9 ± 4.8 ka (thousands of years ago), respectively, thus constraining the time of transition between these two archaeological phases to ~60 ka. An age of 49.1 ± 4.3 ka has been obtained for the latest deposits associated with the Mumba Industry, which show no evidence for post-depositional mixing and contain ostrich eggshell (OES) beads and abundant microlithics. The Nasera Industry deposits (Bed III) contain large quantities of OES beads and date to 36.8 ± 3.4 ka. We compare the luminescence ages with the previous chronologies for

  2. Calorimetric investigation of the excess entropy of mixing in analbite-sanidine solid solutions: lack of evidence for Na,K short- range order and implications for two-feldspar thermometry.

    USGS Publications Warehouse

    Haselton, H.T., Jr.; Hovis, G.L.; Hemingway, B.S.; Robie, R.A.

    1983-01-01

    Heat capacities (5-380 K) have been measured by adiabatic calorimetry for five highly disordered alkali feldspars (Ab99Or1, Ab85Or15, Ab55Or45, Ab25Or75 and Ab1Or99). The thermodynamic and mineralogical implications of the results are discussed. The new data are also combined with recent data for plagioclases in order to derive a revised expression for the two-feldspar thermometer. T calculated from the revised expression tend to be higher than previous calculations.-J.A.Z.

  3. The temperature dependence of bytownite feldspar dissolution in neutral aqueous solutions of inorganic and organic ligands at low temperature (5-35 deg C)

    SciTech Connect

    Welch, Susan A.; Ullman, William J.

    2000-06-15

    The temperature dependence of silica release from bytownite, a Ca,Al-rich feldspar, was determined in solutions of inorganic and organic ligands at neutral pH from 5 deg C to 35 deg C. The apparent activation energy of dissolution in the inorganic (distilled water and KNO3) solutions was approximately 10 Kcal/mole. The rates and temperature dependence in acetate solutions was indistinguishable from the inorganic solutions. In contrast, both oxalate and gluconate, ligands that form strong complexes with Al in solution and presumably with Al at the mineral surface, enhanced the dissolution rates relative to the inorganic controls and had a significantly lower apparent activation energy consistent with a catalytic effect on the dissolution process.

  4. Mineralogy of silicate inclusions of the Colomera IIE iron and crystallization of Cr-diopside and alkali feldspar from a partial melt

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroshi; Hsu, Weibiao; Huss, Gary R.

    2003-06-01

    We studied the mineralogy, mineral chemistry, and compositions of 48 interior silicate inclusions and a large K-rich surface inclusion from the Colomera IIE iron meteorite. Common minerals in the interior silicate inclusions are Cr diopside and Na plagioclase (albite). They are often enclosed by or coexist with albitic glasses with excess silica and minor Fe-Mg components. This mineral assemblage is similar to the "andesitic" material found in the Caddo County IAB iron meteorite for which a partial melt origin has been proposed. The fairly uniform compositions of Cr diopside (Ca 44Mg 46Fe 10) and Na plagioclase (Or 2.5Ab 90.0An 7.5 to Or 3.5Ab 96.1An 0.4) in Colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near-equilibrium conditions from a common melt before emplacement into molten metal. The melt-crystal assemblage has been called "crystal mush." The bulk compositions of the individual composite inclusions form an array between the most diopside-rich inclusion and plagioclase. This is consistent only with a simple mechanical mixing relationship, not a magmatic evolution series. We propose a model in which partly molten metal and crystal mush were mixed together by impact on the IIE parent body. Other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and Na plagioclase, followed by rapid cooling. In the K-rich surface inclusion, K feldspar, orthopyroxene, and olivine were found together with diopside for the first time. K feldspar (sanidine, Or 92.7Ab 7.2An 0.1 to Or 87.3Ab 11.0An 1.7) occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition (Ca 1.3Mg 80.5Fe 17.8 to Ca 3.1Mg 78.1Fe 18.9) and intruding into a relict olivine with deformed-oval shape. Silica and subrounded Cr diopside are

  5. Large-scale fluid movement through crustal rocks by transition porosity generation: Feldspar replacement reactions within the Larvik Plutonic Complex, SE-Norway

    NASA Astrophysics Data System (ADS)

    Los, Karin; Verberne, Rick; Plümper, Oliver; Jamtveit, Bjørn; Austrheim, Håkon

    2014-05-01

    Fluid flow through rocks transports heat and mass across the grain to tectonic plate scale. Fluids promote mineral reactions, redistribute elements to form ore deposits, cool the planet and form habitats for life. A fundamental understanding of fluid flow through rocks is central to interpreting geodynamic and geochemical interactions between the geosphere, hydrosphere and biosphere. Some geological systems are open to fluids, but the majority are nearly impermeable. Surprisingly though, even in rocks that are impermeable, evidence for widespread fluid-rock interactions are observed leading to the question: How can fluids migrate through vast amounts of initially impermeable rocks? Here we present work on the Larvik Plutonic Complex (SE-Norway) that provides an ideal natural laboratory to study fluid movement and feldspar re-equilibration reactions. The Larvik Plutonic Complex shows fluid-rock interactions on tens of kilometres. In the field, this is observed as a colour change: the blue larvikite rock is (partly) replaced by red tønsbergite. On the grain scale, mineral replacement is visible as porous crystals surrounding larvikite feldspar relicts. Chemical analysis shows that the alteration is zoned, from non-porous larvikite feldspar at the core to porous albite and orthoclase at the rim. A possible explanation would be infiltration of several fluids; another possibility is a changing fluid activity for Na+ and K+, resulting in a front which shifts during the reaction. The mineral replacement looks pervasive, starting with fluid flowing around the grain boundaries over a long distance. This is followed by slower consumption of the old mineral; the degree of alteration varies throughout the area of interest. Locally, alteration is related to fracture zones with pseudotachylites, which are overprinted by fluids in the vicinity of feldspars. Fluid flow and element mobilisation is controlled by an interaction between grain boundary diffusion and reaction front

  6. Sr-Isotope Composition of Feldspar: Implication for age and Evolution of Gabbros from Uralian-Alaskan Type Complexes in the Ural Mountains, Russia

    NASA Astrophysics Data System (ADS)

    Bruegmann, G. E.; Krause, J.; Pushkarev, E.

    2006-12-01

    Compared to whole-rock or bulk mineral analyses single mineral composition could reveal disequilibrium features between crystals or within individual crystals which provide important information on magma chamber processes. We applied a LA-ICPMS technique to determine Sr isotopes in plagioclase and K-feldspar of gabbroic rocks from the Nizhnii Tagil and Kytlym complexes in the Ural Mountains in Russia. These complexes are Uralian-Alaskan-type zoned mafic-ultramafic complexes, consisting of dunite, clinopyroxenite and gabbro bodies. The rock association is considered to represent a cumulate sequence of a single parental melt feeding a magma chamber system. The instruments used were a NU Plasma MC-ICPMS and a solid-state 193 and 213 nm Nd:YAG laser ablation system from New Wave. The data of the present study includes up to five spot analyses (100-120 μm spot size) of each mineral in a thin section. Baselines for analyses were measured on-peak for 20 s while flushing the sample chamber with He. About 300 to 500 isotope ratios were measured during the ablation time of 80-100 s. Raw data were exported to an external data reduction spreadsheet and corrected for interferences (Kr, Rb) and mass bias using 87Sr/^{88}Sr=0.1194. During the time of analyses we measured the Sr isotope composition of an in-house marine carbonate reference material. Its 87Sr/86Sr of 0.70923±6 (2SD) agrees within error limits with our TIMS measurements. The gabbros have porphyric textures with clinopyroxene phenocrysts in a matrix of olivine, clinopyroxene and spinel. Two gabbro types can be distinguished based on additional matrix minerals. One type of gabbro is silica saturated, contains plagioclase (An57-88) and in places orthopyroxene as matrix phases. The second gabbro type is silica undersaturated and contains in the matrix plagioclase (An29-56) and pseudoleucite, a fine grained intergrowth of nepheline and K-feldspar (Or30-81). In this gabbro plagioclase has generally higher Sr

  7. 40Ar/39Ar Data for White Mica, Biotite, and K-Feldspar Samples from Low-Grade Metamorphic Rocks in the Westminster Terrane and Adjacent Rocks, Maryland

    USGS Publications Warehouse

    Kunk, Michael J.; McAleer, Ryan

    2008-01-01

    This report contains reduced 40Ar/39Ar data of white mica and K-feldspar mineral separates and matrix of a whole rock phyllite, all from low-grade metamorphic rocks of the Westminster terrane and adjacent strata in central Maryland. This report presents these data in a preliminary form, but in more detail than can be accommodated in todays professional journals. Also included in this report is information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by readers unfamiliar with argon isotopic data in the use of these results; many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context.

  8. Zircon U-Pb and K-feldspar megacryst Rb-Sr isotopic ages and Sr-Hf isotopic composition of the Mesozoic Heyu pluton, eastern Qingling orogen, China

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Yan; Chen, Fukun; Liu, Bing-Xiang; Siebel, Wolfgang

    2013-01-01

    Mesozoic granitoids are ubiquitous in China and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material, emplacement mechanisms and crustal architecture. Most of the plutons were created by multi-stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history. A multi-isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings. This study presents Rb-Sr isotope data for K-feldspar megacrysts and U-Pb ages and Hf isotopic composition for zircons from the composite Heyu pluton exposed in eastern Qinling orogen, central China. Zircon U-Pb concordia ages of 150 and 140 Ma and single K-feldspar Rb-Sr isochron ages between 133 and 121 Ma were obtained from early and late magmatic stages, respectively, consistent with slow cooling or isotopic re-equilibration of the Rb-Sr K-feldspar system. The distinct K-feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth, likely to be associated with a gravity-driven sinking model. Corresponding zircon ɛHf(t) values are - 21.8 to - 18.0 and - 17.2 to - 10.3 for early and late intrusive phases, respectively, indicating different magma sources.

  9. Experimental calibration of cotectic melt compositions coexisting with quartz and feldspar in rhyolitic systems - Application to Snake River Plain rhyolites,Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Holtz, F.; Klahn, C.; Bolte, T.; Almeev, R. R.; Christiansen, E. H.; Nash, B. P.

    2013-12-01

    The depth of magma storage prior to eruption is difficult to constrain for rhyolitic systems and remains often unknown because the typical mineral assemblages in rhyolite magmas are not suitable for geobarometry. As an alternative to mineral compositions, the silica content of rhyolitic melts can be used to constrain pressure, provided that the silicate melts have cotectic compositions (melts coexisting with quartz and feldspar). From studies in synthetic haplogranitic systems, it is well known that the silica content of cotectic melts decreases with increasing pressure and that it may be used as barometer. However, the evolution of silica content with pressure is not calibrated for natural rhyolitic systems containing up to 2 wt% CaO and 4 wt% FeO. Crystallization experiments in Fe-, Ca- and Ti-bearing rhyolitic systems have been performed at 200 MPa and a temperature range of 790 to 850°C to calibrate the position of cotectic compositions in natural rhyolitic systems and the results have been projected onto the haplogranitic quartz-albite-orthoclase diagram (Qz-Ab-Or). The starting materials were glasses with various proportions of the Qz, Ab and Or components; all glasses contained 1 wt% FeO, 3.4 wt% An component and 0.2 wt% TiO2. The glasses were pre-hydrated with 3 wt% H2O in an internally heated pressure vessel. The crystallization experiments were conducted in cold seal pressure vessels. The water contents of the pre-hydrated starting glasses were checked by Fourier Transform Infrared Spectroscopy (FTIR) and Karl Fischer titration. The experimental products (glasses and crystals) were analyzed via electron microprobe. Results at 200 MPa show that the cotectic line separating the quartz primary field from the feldspar primary field is shifted towards the Qz apex by 6 wt% when compared with the water-undersaturated haplogranitic system (containing 3 wt% water). The minimum composition is shifted towards the Qz-Or sideline when compared with the haplogranitic

  10. Massive Red-Staining and Albitization of Feldspars in Paleozoic Basement Rocks of Western Europe and Their Association with the Triassic Palaeogeography

    NASA Astrophysics Data System (ADS)

    Fabrega, C.; Parcerisa, D.; Franke, C.; Thiry, M.; Yao, K.; Gómez-Gras, D.

    2013-12-01

    Albitization of feldspars is a widespread mineral replacement process of the upper crust. An ubiquitous and pervasive red-staining albitization of feldspars has been observed in the feldspathic rocks of the Variscan basement in the Sudetes, Armorican, Morvan, Roc de Frausa and Montseny-Guilleries Massifs (Western Europe). These crystalline massifs were strongly eroded during Permian and Triassic times and suffered a long-lasting exposition in the Permian-Triassic palaeosurface. The albitized rocks contain minute Fe-oxides hoisted within the microporosity of the secondary albite. The intimate textural relationship between the Fe-oxides and the albite strongly suggest that they are coetaneous with albitization. The microscope, cathodoluminescence, SEM and EMPA analyses reveal that almost all plagioclases and some K-feldspars are albitized in those areas close to the Permian-Triassic palaeosurface. Moving downwards the palaeosurface the albitization of Variscan rocks progressively disappears. Field mapping of the albitized areas points to estimated thickness about 100-200m. In the uppermost parts of the profile almost all plagioclases are totally albitized and the rock shows a strong and pervasive reddening, whereas in the lowermost parts the mineral replacement is restricted to fractures and neighbouring walls and the rock in tinted with a soft pink colour. These observations suggest that albitization is linked to that palaeosurface and constitutes a paleoalteration profile beneath the Permian-Triassic palaeosurface. All these observations suggest that the mineral replacement could have been driven by descending Na+ rich brines related with or coming from the Permian-Triassic palaeosurface. Ricodel et al. (2007) determined a Triassic age for the paleomagnetic signature of the Fe-oxides hoisted within the microporosity of albite in the Morvan Massif. The narrow textural relationship between the Fe-oxides and the albite support the idea that this is the age of

  11. Origin of hydrous alkali feldspar-silica intergrowth in spherulites from intra-plate A2-type rhyolites at the Jabal Shama, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Surour, Adel A.; El-Nisr, Said A.; Bakhsh, Rami A.

    2016-03-01

    Miocene rhyolites (19.2 ± 0.9 Ma) at the Jabal Shama in western Saudi Arabia represent an example of rift-related silicic volcanism that took place during the formation of the Red Sea. They mostly consist of tuffaceous varieties with distinct flow banding, and pea-sized spherulites, obsidian and perlitized rhyolite tuffs. Although they have the geochemical signature of A2-type rhyolites, these silicic rocks are not typically alkaline but alkali-calcic to calc-alkaline. They developed in a within-plate regime and possibly derived from a recycled mafic subducted slab in depleted sub-continental mantle beneath the western Arabian plate. The Jabal Shama rhyolites are younger in age than their Miocene counterparts in Yemen and Ethiopia. The Jabal Shama spherulites consist of hydrous alkali feldspar-silica radial intergrowths with an occasional brown glass nucleus. Carbonate- and glass-free spherulites give up to 4.45 wt% L.O.I. The hydrous nature of these silicates and the absence of magnetite in the spherulites is a strong indication of oxidizing conditions. The spherulites contain hydrous feldspars with up to ∼6 wt% H2O, and they develop by diffusion and devitrification of glass in the rhyolite tuff at ∼800 °C. Owing to higher undercooling due to supersaturation, the radial hydrous phases within spherulites might grow faster and led to coagulation. The polygonal contacts between spherulites and the ∼120° dihedral angle suggest solid-state modification and recrystallization as the process of devitrification proceeds as low as ∼300 °C. The sum of FeO + MgO is positively correlated with total alkalies along with magnetite oxidation in the matrix to Fe-oxyhydroxides, and to the incorporation of OH- into silicates within the spehrulites themselves. Structural H2O in glass of the Jabal Shama perlite (obsidian) is considerable (∼9-12 wt%) with 3.72-5.6 wt% L.O.I. of the whole-rock. The presence of deleterious silica impurities would lower the ore grade due to

  12. Dan Johnson's impact on hearing research

    NASA Astrophysics Data System (ADS)

    Shotland, Lawrence I.

    2003-04-01

    Daniel L. Johnson is well known for his many technical contributions to noise research. Throughout a long and distinguished career at Wright-Patterson Air Force Base, Dan published the results of several significant experiments, including his landmark experiments on asymptotic threshold shift and exposure to impulse noise. His work in the area of noise exposure laid much of the groundwork for a greater understanding of the physiologic response to hazardous noise, much of which has since been incorporated in national and international standards. Dan is highly regarded for his tireless work on technical and advisory committees in noise, and most recently, ototoxicity. Throughout his career, Dan has adhered to a self-imposed standard of intellectual honesty and discovery. Dan's most recent endeavor, the development of a personal noise dosimeter designed for self-monitoring by the employee, is characteristic of his creativity and energy. Perhaps less well known are his contributions over the years to the success of his younger colleagues. He has accomplished this in an unselfish and egalitarian manner, oftentimes challenging and even contradicting his own research. The focus of this talk will elaborate on these facets of Dan's professional contributions.

  13. Reactions of the feldspar surface with metal ions: Sorption of Pb(II), U(VI) and Np(V), and surface analytical studies of reaction with Pb(II) and U(VI)

    NASA Astrophysics Data System (ADS)

    Chardon, Emmanuelle S.; Bosbach, Dirk; Bryan, Nicholas D.; Lyon, Ian C.; Marquardt, Christian; Römer, Jürgen; Schild, Dieter; Vaughan, David J.; Wincott, Paul L.; Wogelius, Roy A.; Livens, Francis R.

    2008-01-01

    Feldspar minerals are thermodynamically unstable in the near-surface environment and their surfaces are well known to react readily with aqueous solutions, leading to incongruent dissolution at low pH values, but congruent dissolution at neutral and high pH values. Interactions with mineral surfaces are an important control on the environmental transport of trace elements and detrital feldspars are abundant in soils and sediments. However, the interactions of metal ions in solution with the reacting feldspar surface have not been widely explored. The interactions of Pb(II), U(VI) and Np(V) ions with the feldspar surface have therefore been studied. Lead is taken up by the microcline surface at pH 6 and 10, but no uptake could be measured at pH 2. There was measurable uptake of Pb(II) on the plagioclase surface at pH 2, 6 and 10. Uptake always increased with pH. In most conditions, Pb(II) reacts through cation exchange process although, at high pH, a discrete phase, probably hydrocerrusite, is observed by atomic force microscopy (AFM) to precipitate on the plagioclase surface. Supersaturation with hydrocerrusite in these conditions is expected from thermodynamic calculations. Uptake of uranyl ion (UO22+), generally through surface complex formation, could only be measured at pH 6 and 10. At pH 6 and an initial U(VI) concentration above 21.0 μM, precipitation of becquerelite (Ca[(UO2)3O2(OH)3]2·8H2O), identified by AFM and characterised by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy, is observed on plagioclase. The U(VI) concentration range in which becquerelite precipitation begins (dissolved U(VI) 1-5 μM) is consistent with that predicted from thermodynamic modelling. On plagioclase feldspar, secondary ion mass spectrometry showed diffusion of uranium into the altered surface layer. Uptake of the neptunyl ion (Np(V)) was found at pH 6 and 10 for microcline and at pH 2, 6 and 10 for plagioclase, and was generally lower than uptake of

  14. Origin of minor and trace element compositional diversity in anorthitic feldspar phenocrysts and melt inclusions from the Juan de Fuca Ridge

    USGS Publications Warehouse

    Adams, David T.; Nielsen, Roger L.; Kent, Adam J.R.; Tepley, Frank J., III

    2011-01-01

    Melt inclusions trapped in phenocryst phases are important primarily due to their potential of preserving a significant proportion of the diversity of magma composition prior to modification of the parent magma array during transport through the crust. The goal of this investigation was to evaluate the impact of formational and post-entrapment processes on the composition of melt inclusions hosted in high anorthite plagioclase in MORB. Our observations from three plagioclase ultra-phyric lavas from the Endeavor Segment of the Juan de Fuca Ridge document a narrow range of major elements and a dramatically greater range of minor and trace elements within most host plagioclase crystals. Observed host/inclusion partition coefficients for Ti are consistent with experimental determinations. In addition, observed values of DTi are independent of inclusion size and inclusion TiO2 content of the melt inclusion. These observations preclude significant effects from the re-homogenization process, entrapment of incompatible element boundary layers or dissolution/precipitation. The observed wide range of TiO2 contents in the host feldspar, and between bands of melt inclusions within individual crystals rule out modification of TiO contents by diffusion, either pre-eruption or due to re-homogenization. However, we do observe comparatively small ranges for values of K2O and Sr compared to P2O5 and TiO2 in both inclusions and crystals that can be attributed to diffusive processes that occurred prior to eruption.

  15. Preparation and characterization of new dental porcelains, using K-feldspar and quartz raw materials. Effect of B2O3 additions on sintering and mechanical properties.

    PubMed

    Harabi, Abdelhamid; Guerfa, Fatiha; Harabi, Esma; Benhassine, Mohamed-Tayeb; Foughali, Lazhar; Zaiou, Soumia

    2016-08-01

    The aim of this work was to determine the effect of temperature and boric oxide (B2O3) addition on sintering and mechanical properties of a newly developed dental porcelain (DP) prepared from local Algerian raw materials. Based on a preliminary work, the new selected composition was 75wt.% feldspar, 20wt.% quartz and 5wt.% kaolin. It was prepared by sintering the mixture at different temperatures (1100-1250°C). The optimum sintering conditions gave a relatively higher density (2.47g/cm(3)) and excellent mechanical properties. The three point flexural strength (3PFS) and Martens micro-hardness of dental porcelains were 149MPa and 2600MPa, respectively. This obtained 3PFS value is more than four times greater than that of hydroxyapatite (HA) value (about 37MPa) sintered under the same conditions. However, the sintering temperature was lowered by about 25 and 50°C for 3 and 5wt.% B2O3 additions, respectively. But, it did not improve furthermore the samples density and their mechanical properties. It has also been found that B2O3 additions provoke a glass matrix composition variation which delays the leucite formation during sintering. PMID:27157725

  16. Dan jiang kou hydropower station turbine refurbishment

    NASA Astrophysics Data System (ADS)

    Zhang, R. Y.; Nie, S. Q.; Bazin, D.; Cheng, J. H.

    2012-11-01

    Dan jiangkou hydropower station refurbished project, isan important project of Chinese refurbishment market. Tianjin Alstom Hydro Co., ltd won this contract by right of good performance and design technology,Its design took into account all the constraints linked to the existing frame. It results in a specific and highly advanced shape.The objective of this paper is to introduce the successful turbine hydraulic design, model test and mechanical design of Dan jiangkou project; and also analyze the cavitation phenomena occurred on runner band surface of Unit 4 after putting into commercial operation. These technology and feedback shall be a good reference and experience for other similar projects

  17. K-feldspar megacrysts growth and their link to the granitic mush: insight from high precision U-Pb dates (ID-TIMS) and trace elements (TIMS-TEA) on zircon

    NASA Astrophysics Data System (ADS)

    Barboni, M.; Schoene, B.

    2012-12-01

    K-feldspar megacrysts are common in granitic to granodioritic rocks though their origin and evolution is still poorly understood. Their occurrence seems to reflect a low nucleation rate relative to growth rate at low degrees of supersaturation. Though K-feldspar has been argued to be one of the last minerals to saturate in felsic magma, crystal mush may still contain 60-70% liquid at the initiation of crystallization. Therefore, abundant liquid might be available for development of large crystals early in the magma cooling process. The recent recognition that many granitoid plutons are built incrementally by many magma injections open new perspectives for K-feldspar megacrysts formation. Repeated replenishment, reheating and reinvigoration of the mush might play a significant role in making and preserving K-feldspar megacrysts. The Miocene Elba island intrusives (Italy) are famous for having some of the largest K-feldspar megacrysts ever found (up to 25 cm.). This young plutonic body emplaced incrementally at shallow crustal level (ca. 3km) and displays extensive evidence of interactions between magmas of contrasting compositions. We have sampled three different families of K-feldspar megacrysts occurring in different host rock and have combined U/Pb high precision dates (ID-TIMS) with trace elements (TIMS-TEA) and Hf isotopes of zircons that are included within the K-feldspar megacrysts and compared them to zircons from the host rock. Ages of zircon included in the megacrysts could document whether the crystals grew early in the magmatic system (inclusions older than the host rock) or late during the cooling history (similar ages within inclusions and host rock). Ti-in zircon thermometer combined with trace-elements signature could record slight differences between megacrysts and host rock zircons, documenting the development of the megacrysts in comparison with the one of the host granite. Strong field evidence support a magmatic/ phenocrystic origin for the Elba

  18. Peralkaline fluid composition in equilibrium with K-feldspar, muscovite and quartz at 10 kbar and 700°C: Al transport in crustal fluids

    NASA Astrophysics Data System (ADS)

    Wohlers, A.; Manning, C. E.

    2012-04-01

    Aluminum is commonly regarded as one of the least soluble elements during metamorphic and metasomatic processes. However, abundant field evidence suggests that aluminum transport can occur in natural hydrothermal processes. For example, late formed aluminumsilicate-bearing and muscovite-bearing veins are widely observed in high-grade metamorphic rocks, and provide a persuasive argument for considerable mobility of aluminum in aqueous fluid. The present study explores the fluid composition coexisting with K-feldspar (K-fsp), muscovite (ms), corundum (co) and quartz (qz) at deep crustal metamorphic conditions, using a piston cylinder device at 10 kbar and 700°C. Starting materials of natural microcline, quartz, synthetic corundum, reagent Al2O3 and KSi3O6.5 glass was used. Ms and K-fsp dissolve incongruently to co + fluid and ms + fluid, respectively. Fluid composition in equilibrium with co + ms and ms + K-fsp were located in experiments with and without qz. In quartz-absent experiments fluid composition with co+ms (I1) is mAl = 0.11, mK = 0.15, mSi = 0.44, and with K-fsp + ms (I2) mAl = 0.18, mK = 0.28 and mSi = 0.81, where mi is molality of the subscripted element. Fluid compositions with qz are: mAl = 0.08, mK = 0.11 and mSi = 1.18 (co + ms + qtz; II1) and mAl = 0.18, mK = 0.29 and mSi = 1.58 for (K-fsp + ms +qtz; II2). Measured fluid compositions are peralkaline (K/Al < 1.4). Bulk solubility of Al in pure H2O at this P and T is reported to be ~0.3 wt% [1], and increase to ~1.9 wt % Al in the presence of SiO2 [2]. This study shows that Al solubility is further enhanced by the presence of K and Si, increasing from ~4.07 wt% for (I1) to ~ 7.14 wt% at (I2). Presence of quartz enhances the bulk solubility from ~ 7.63 wt% (II1) to ~ 12.05 wt % at (II2). Results indicate that substantial aluminum transfer may occur at deep-crust metamorphic conditions in aqueous solutions equilibrated with common crustal bulk compositions such as metapelites and granites. Such high Al

  19. Petrogenesis of mid-Miocene rhyolites from the Idaho-Oregon-Nevada region, USA: Implications from feldspar Sr and Pb isotope data

    NASA Astrophysics Data System (ADS)

    Wypych, A.; Hart, W. K.

    2012-12-01

    between the silicic centers [4]. The samples demonstrate involvement of fractional crystallization of less evolved mafic material along with assimilation of partial crustal melts, however the degree of involvement of each process remains difficult to quantify, as do the contributions from mantle and crustal reservoirs. To further investigate these issues, we here present petrological, major and trace element, along with lead and strontium isotopic examination of feldspar crystals from three selected silicic centers: 1) westernmost, off-craton, 2) central region of transitional lithosphere, and 3) eastern transition zone to on-craton. The textural evidence for open system behavior is only partially supported by bulk feldspar Pb and Sr isotopic compositions where the differences between whole rock, glass and crystal separate aliquots of the same eruptive units are a maximum of 0.3 in 208Pb/204Pb, 0.2 in 206Pb/204Pb and 0.002 in 87Sr/86Sr. Models combining these results with the spatial availability of geochemically distinct magma source reservoirs will be discussed. [1] Brueseke et al. (2008) Bull. Volc. 70, 343-360. [2] Nash et al. (2006) Earth Plant. Sci. Lett. 247, 143-156. [3] Christiansen and McCurry (2008) Bull. Volc., 70, 251-267. [4] Wypych and Hart (2011) Min. Magazine, 75 (3), 2186.

  20. A re-examination of petrogenesis and 40Ar/39Ar systematics in the Chain of Ponds K-feldspar: "diffusion domain" archetype versus polyphase hygrochronology

    NASA Astrophysics Data System (ADS)

    Chafe, Alex N.; Villa, Igor M.; Hanchar, John M.; Wirth, Richard

    2014-05-01

    K-feldspar (Kfs) from the Chain of Ponds Pluton (CPP) is the archetypal reference material, upon which thermochronological modeling of Ar diffusion in discrete "domains" was founded. We re-examine the CPP Kfs using cathodoluminescence and back-scattered electron imaging, transmission electron microscopy, and electron probe microanalysis. 40Ar/39Ar stepwise heating experiments on different sieve fractions, and on handpicked and unpicked aliquots, are compared. Our results reproduce the staircase-shaped age spectrum and the Arrhenius trajectory of the literature sample, confirming that samples collected from the same locality have an identical Ar isotope record. Even the most pristine-looking Kfs from the CPP contains successive generations of secondary, metasomatic/retrograde mineral replacements that post-date magmatic crystallization. These chemically and chronologically distinct phases are responsible for its staircase-shaped age spectra, which are modified by handpicking. While genuine within-grain diffusion gradients are not ruled out by these data, this study demonstrates that the most important control on staircase-shaped age spectra is the simultaneous presence of heterochemical, diachronous post-magmatic mineral growth. At least five distinct mineral species were identified in the Kfs separate, three of which can be traced to external fluids interacting with the CPP in a chemically open system. Sieve fractions have size-shifted Arrhenius trajectories, negating the existence of the smallest "diffusion domains." Heterochemical phases also play an important role in producing nonlinear trajectories. In vacuo degassing rates recovered from Arrhenius plots are neither related to true Fick's Law diffusion nor to the staircase shape of the age spectra. The CPP Kfs used to define the "diffusion domain" model demonstrates the predominance of metasomatic alteration by hydrothermal fluids and recrystallization in establishing the natural Ar distribution among different

  1. The isotopic composition of lead in potassium feldspars from some 1.0-b.y. old North American igneous rocks

    USGS Publications Warehouse

    Zartman, R.E.; Wasserburg, G.J.

    1969-01-01

    The isotopic composition of lead and the uranium, thorium and lead concentrations in potassium feldspars are determined for more than 30 1.0-b.y. old North American igneous rocks. Samples representing a broad spectrum in petrographic type and mode of occurrence were chosen; an effort was made to include only rocks having well-documented ages from 950 to 1140 m.y. and showing minimal evidence of subsequent metamorphism. Most samples, including those from extensive terranes of contemporaneous age, have limited lead isotope variations ( Pb206 Pb204 = 16.74-17.38; Pb207 Pb204 = 15.39-15.59; Pb208 Pb204 = 36.38-37.10), which yield model ages close to the radiometric ages. Granite, pegmatite, and rhyolite from within the Grenville province of Canada and age-equivalent rocks of New York, Virginia, Texas, and Colorado and granophyric units associated with the Duluth Gabbro Complex of Minnesota are among the materials yielding this main isotopic spectrum. Several samples were encountered which had isotopic compositions very different from the above group. Lead showing a marked deficiency in radiogenic isotopes was found in two granitic bodies associated with older Labrador Trough rocks from Quebec, in a rapakivi granite from southern Nevada, and in a small granite stock from Mellen, Wisconsin. These occurrences all involve small intrusions of granite which lie near considerably older areas of basement rock. Model ages calculated from the Pb206 Pb204 ratio are older than the age of the intrusions and approach the age of the host basement rock. Several possible interpretations are offered to explain the isotopic behavior encountered in this study. In particular, a "vertically differentiated crust" model is proposed which will account for both the main spectrum and the anomalous lead. The significance of lead isotopic studies in understanding crustal structure in continental regions is discussed. ?? 1969.

  2. Stable Isotope Variability of Altered Sanidine Feldspars within the Bear Lodge Alkaline Intrusive Complex, Wyoming: Implications for Mineral Exploration Near a Late-Stage Carbonatite Ore Body

    NASA Astrophysics Data System (ADS)

    Mulvaney-Norris, J. L.; Larson, P. B.

    2015-12-01

    In a brecciated intrusive complex, mineral assemblages from non-ore-stage hydrothermal alteration may be mistakenly associated with ore body emplacement during exploration. The ability to differentiate mineralizing from non-mineralizing alteration by stable isotope analysis, and to map the fluid pathways, is a useful tool for future exploration. The Bull Hill diatreme, central Bear Lodge Mountains, contains porphyritic alkaline clasts and cross-cutting megacrystic sanidine trachyte dikes. The K feldspar (Kfs) phenocrysts reacted with and recorded the passage of hydrothermal fluids, likely derived from post-diatreme carbonatite intrusions. A study of the δ18O values of Kfs in the complex can assist mineralization mapping by revealing the late hydrothermal fluid pathways and provenance. Dike and breccia samples were split from three drill holes at regular distances, moving away from carbonatite dikes and large veins. Eighteen samples were prepared for oxygen isotope analysis by physical separation of megacrysts, or by crushing and hand-picking Kfs fragments from the breccia. A carbonatite Kfs sample was prepared by partial HCl digestion. Oxygen isotope ratios were measured at the Washington State University GeoAnalytical Laboratory using a Finnegan Delta S Mass Spectrometer. Kfs δ18O values range between 7.69‰ and 9.09‰ in the diatreme breccia xenocrysts, 5.28‰ to 8.12‰ in the megacrystic dike phenocrysts, and 7.15‰ in the carbonatite phenocrysts. Results suggest no clear relationship between the δ18O values in Kfs and the different phases of intrusion. This may be due to δ18O variability introduced by zoned and multi-crystal samples, limited variations of δ18O values among intrusion fluids, or that the final carbonatite intrusion pervasively altered all samples within the study area. Therefore, this method may not be particularly useful for identifying potential ore-bearing units in the Bear Lodge Intrusive Complex.

  3. MSL DAN Passive Data and Interpretations

    NASA Astrophysics Data System (ADS)

    Tate, C. G.; Moersch, J.; Jun, I.; Ming, D. W.; Mitrofanov, I. G.; Litvak, M. L.; Behar, A.; Boynton, W. V.; Drake, D.; Lisov, D.; Mischna, M. A.; Hardgrove, C. J.; Milliken, R.; Sanin, A. B.; Starr, R. D.; Martín-Torres, J.; Zorzano, M. P.; Fedosov, F.; Golovin, D.; Harshman, K.; Kozyrev, A.; Malakhov, A. V.; Mokrousov, M.; Nikiforov, S.; Varenikov, A.

    2014-12-01

    In its passive mode of operation, The Mars Science Laboratory Dynamic Albedo of Neutrons experiment (DAN) detects low energy neutrons that are produced by two different sources on Mars. Neutrons are produced by the rover's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and by interactions of high energy galactic cosmic rays (GCR) within the atmosphere and regolith. As these neutrons propagate through the subsurface, their energies can be moderated by interactions with hydrogen nuclei. More hydrogen leads to greater moderation (thermalization) of the neutron population energies. The presence of high thermal neutron absorbing elements within the regolith also complicates the spectrum of the returning neutron population, as shown by Hardgrove et al. DAN measures the thermal and epithermal neutron populations leaking from the surface to infer the amount of water equivalent hydrogen (WEH) in the shallow regolith. Extensive modeling is performed using a Monte Carlo approach (MCNPX) to analyze DAN passive measurements at fixed locations and along rover traverse segments. DAN passive WEH estimates along Curiosity's traverse will be presented along with an analysis of trends in the data and a description of correlations between these results and the geologic characteristics of the surfaces traversed.

  4. Registration of 'Dan' winter hulless barley

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dan’ (Reg. No. CV- , PI 659066) six-rowed winter hulless barley (Hordeum vulgare L.) was developed and released by the Virginia Agricultural Experiment Station in March 2009. Dan was derived from the cross VA96-41-17 / SC872143. It was released for production in the eastern United States, as a poten...

  5. Dan Marino Helping Those with Autism Spectrum Disorders | NIH MedlinePlus the Magazine

    MedlinePlus

    ... Marino Foundation. Photo: Dan Marino Foundation Former NFL star quarterback Dan Marino and his wife Claire experienced ... to succeed in life,'" says the former NFL star. "That's where the focus for The Dan Marino ...

  6. The role of magma mixing in the formation of the Kuna Crest lobe of the Tuolumne batholith, Sierra Nevada, USA: Lessons from minor and trace element distributions in K-feldspar

    NASA Astrophysics Data System (ADS)

    Krause, Joachim; Memeti, Valbone; Paterson, Scott

    2010-05-01

    Geochemical and geochronologic studies emphasize the role of incremental growth of large magma chambers and associated complex magma processes. One of the major results of these studies is that volcanic and plutonic rocks tend to consist of different crystal populations recording complex individual histories. Detailed geochemical observations of individual minerals provide direct access to petrogenetic processes such as magma mixing, assimilation and fractionation and their role for the evolution of the magma chamber. Recent field, U/Pb zircon geochronology and geochemistry data on the 95-85 Ma Tuolumne batholith (TB), Sierra Nevada, CA, have shown ample evidence for extensive mixing between different magmas and internal magma chamber recycling of older marginal units into younger central units within the long lived, main batholith. Field, geochronologic, whole rock geochemical, and isotopic data have been examined in four magmatic lobes extending out from the main batholith. The lobes are interpreted to represent shorter lived and simpler magma bodies since their composition is attributed to fractionation and some remixing of magma derived from a single isotopically similar source. In order to test this hypothesis on the mineral scale, X-ray element distribution maps and quantitative analyses for minor and trace elements have been performed with the electron microprobe and LA-ICPMS on samples from different structural positions in the southern Kuna Crest lobe of the TB. Ophitic, ≤ 5 mm large K-feldspars, of the Kuna Crest lobe show simple Ba zoning patterns with elevated contents in the center (Ba = 0.8-1.2 wt.%) decreasing towards the rim (Ba = 0.4-0.5 wt.%). Other hypidiomorphic to xenomorphic K-feldspars ≤ 1.5 mm within the same thin section have reversed zoning with low Ba contents in the core (Ba = 0.1-0.2 wt.%) increasing towards the rim (Ba = 0.4-0.6 wt.%). The larger, ophitic K-feldspars show decreasing La/Y and Y concentrations from the core (La/Y = 5

  7. Tracking the provenance of Greenland-sourced, Holocene aged, individual sand-sized ice-rafted debris using the Pb-isotope compositions of feldspars and 40Ar/39Ar ages of hornblendes

    NASA Astrophysics Data System (ADS)

    White, Lee F.; Bailey, Ian; Foster, Gavin L.; Allen, Georgina; Kelley, Simon P.; Andrews, John T.; Hogan, Kelly; Dowdeswell, Julian A.; Storey, Craig D.

    2016-01-01

    The provenance of sand-sized ice-rafted debris (IRD) sourced from Greenland is currently difficult to determine. Such knowledge, if it could be ascertained with a high degree of certainty, could be applied to the Greenland-proximal marine records to improve both our understanding of modern-day spatial patterns of iceberg rafting and the past history of the Greenland Ice Sheet (GIS). Recent studies have highlighted the utility of the Pb-isotope composition of individual sand-sized feldspars and the 40Ar/39Ar ages of individual sand-sized hornblendes in this regard. However, before any such provenance toolkit can be applied to the palaeo-record, it is necessary first to determine whether this approach can be used to track the sources of known recent Greenland-proximal IRD deposition. To this end we present new records of the Pb-isotope composition and the 40Ar/39Ar ages of individual sand-sized grains of feldspars and hornblendes, respectively, from modern Greenland glacifluvial and fjord sands and Holocene to modern Greenland-proximal marine sediments. These new data demonstrate that sand-sized feldspars and hornblendes glacially eroded by the GIS exhibit distinct intra- and inter-tectonic terrane differences in their Pb-isotope compositions and ages and that these differences are clearly expressed in the geochemistry and geochronology of sand-sized IRD deposited in marine sediments around Greenland. Although overlap exists between some Greenland-proximal IRD 'source fields' defined by these data, our approach has the potential to both better understand spatial patterns of Greenland-derived IRD in the modern day as well as during past episodes of iceberg calving.

  8. Pb, Nd and Sr isotopic compositions of feldspar, apatite and sphene as a guide to the nature of the sub-Andean mantle and crust-mantle interaction in the coastal batholith, Peru

    SciTech Connect

    Mukasa, S.B.; Barreiro, B.A.

    1985-01-01

    Common Pb isotopic compositions for 65 feldspar samples from the 188-37 Ma gabbroic to monzogranitic plutons of the Peruvian Coastal batholith (PCB) show changes along strike that can be related to variable contamination of mantle-derived magmas by Precambrian basement (PB). The dominant Pb component in mafic plutons of the Lima segment (LS) is similar to the isotopically homogeneous reservoir (IHR) identified by others for rocks in central and southern Chile. It has been suggested that the IHR is enriched subcontinental mantle. More siliceous rocks in the LS have considerably higher Pb ratios, suggesting that they have a component of supracrustal materials. Feldspars from plutons in the Arequipa and Toquepala segments (ATS) of the PCB have low PB ratios. The data plot between the PB and IHR fields on Pb correlation diagrams, indicating that these end members were the principal magma sources in southern Peru. /sup 143/Nd//sup 144/Nd and /sup 87/Sr//sup 86/Sr compositions for a small group of apatite and sphene samples selected on the basis of extreme PB ratios in coexisting feldspars are negatively correlated and support the magmagenetic models proposed using the more thorough Pb analyses. Also, mass balance considerations using Nd and Sr concentrations suggest that contamination of IHR magmas by PB was magmatic and not the result of subsolidus diffusion. Contamination of plutons in the ATS by PB and lack of it in the LS supports crustal models by Couch et al. (1981) and Jones (1981) which show a thick PB layer in southern Peru and an extremely thin layer beneath the LS.

  9. 8. Wabash Ave. North. View of Loop and Dan Ryan ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Wabash Ave. North. View of Loop and Dan Ryan Line. Curve at Van Buren St. and Wabash Ave. at center. Dan Ryan line starts at center and runs south (toward bottom of picture). Photo by Jet Lowe. - Union Elevated Railroad, Union Loop, Wells, Van Buren, Lake Streets & Wabash Avenue, Chicago, Cook County, IL

  10. Paragenesis and chemical characteristics of the celsian-hyalophane-K-feldspar series and associated Ba-Cr micas in barite-bearing strata of the Mesoarchaean Ghattihosahalli Belt, Western Dharwar Craton, South India

    NASA Astrophysics Data System (ADS)

    Raith, Michael M.; Devaraju, Tadasore C.; Spiering, Beate

    2014-04-01

    The upper greenschist - lower amphibolite facies, argillaceous to chemical-exhalative metasedimentary sequence of the Mesoarchaean Ghattihosahalli Schist Belt (GHSB), southern India, has been examined with a special focus on the paragenesis and solid solution characteristics of barian feldspars and associated dioctahedral Ba-Cr-bearing micas. Barian feldspars occur as untwinned porphyroblasts in a recrystallized finely banded matrix of barite, quartz and minor white mica. Idioblastic celsian (Cls98-76Or2-20Ab1-8) and hyalophane (Cls55-39Or35-51Ab10) predate the greenschist-facies foliation, whereas xenoblastic hyalophane (Cls44-35Or45-59Ab8-17) and mantles on celsian (Cls45-35Or42-60Ab13-5) as well as xenoblastic barian K-feldspar (Cls6Or90Ab2) postdate the last fabric-defining event. The preservation of extremely complex zoning patterns down to the micron-scale shows that diffusional homogenization did not operate at fluid-present low to medium-grade conditions (350-550 °C, 3-5 kb). Microstructures indicate that at these conditions barian feldspars deform exclusively by brittle fracturing and do not undergo recrystallization. Barian feldspar compositions confirm the positive correlation of Na-content with temperature and the existence of a narrow asymmetric compositional gap (Cls90-85↔Cls55, ~350 °C) which probably closes at lower amphibolite facies conditions (Xc ~Cls75; Tc ~550 °C). White micas are solid solutions of the end-members muscovite, ganterite (Ba0.5 K0.5)Al2(Al1.5Si2.5)O10(OH)2, paragonite, celadonite with a significant substitution of [VI]Al by Cr. Zoning is a common feature with cores being enriched in Ba. The data document extensive Ba substitution for K from muscovite to ganterite, exclusively controlled by the coupled substitution [XII]K + [IV]Si ↔ [XII]Ba + [IV]Al and strongly dependent on bulk composition. The extent of solid solution from (Ms+Gnt) towards paragonite and celadonite end-members is controlled by the miscibility gap in the

  11. L'astronomie dans le monde

    NASA Astrophysics Data System (ADS)

    Manfroid, J.

    2014-06-01

    Future lune ? - L'âge de la Lune - Des volcans actifs sur Vénus - Un lac dans le cratère Gusev ? - Météorites et atmosphère martiennes - L’hexagone de Saturne - Pluton - Exo-Terre - Bêta Pictoris b - Cérès et Vesta depuis Mars - Naine froide - Parallaxes par Hubble - L2 Puppis et le sort du Soleil - Supernova et lentille gravitationnelle - Champ magnétique galactique - L’objet de Sakurai - Fermi et la matière noire - Lentille naine

  12. Field Calibration Studies of Continuous Thermal Histories Derived From Multiple Diffusion Domain (MDD) Modeling of 40Ar/39Ar K-feldspar Analyses at the Grayback and Gold Butte Normal Fault Blocks, U.S. Basin and Range

    NASA Astrophysics Data System (ADS)

    Wong, M.; Roesler, D.; Gans, P. B.; Zeitler, P. K.; Idleman, B. D.

    2014-12-01

    Most thermochronometers provide point constraints on a temperature-time path. Thermochronometers that record a continuous thermal history over a range of temperatures can provide more robust constraints, but only a few have such potential. One such system is multiple diffusion domain (MDD) modeling of 40Ar/39Ar K-feldspar analyses, which is interpreted to record thermal histories between ~150-300°C. Although this approach has been applied in numerous studies, some workers have questioned its accuracy in some applications. This study tests whether MDD K-feldspar modeling produces an accurate thermal history that is calibrated to other thermochronometers. Samples were collected from the Grayback normal fault block in central Arizona and the Gold Butte block in Nevada. Both blocks were exhumed during Oligo-Miocene extension and the timing and pre-extensional paleogeothermal gradient are well constrained from prior work. At the Grayback block, MDD thermal histories from shallow paleodepths show rapid cooling from 55-65 Ma following ~75 Ma pluton emplacement, slow cooling from 27-55 Ma at middle paleodepths, and rapid cooling at deep structural levels after 27 Ma during tectonic exhumation. The start of rapid cooling and residence temperatures at 27 Ma from MDD models match expected results from prior fission track work at all structural levels. In the Gold Butte block, MDD thermal models at moderate paleodepths also record slow cooling throughout the Mesozoic to early Tertiary, with deeper structural levels recording rapid cooling at 17 Ma, identical to previous work. Samples from the deepest paleodepths yield MDD thermal histories that repeat this pattern, suggesting that the Gold Butte block is not intact but cut by at least one normal fault at relatively deep paleodepths, which was not evident from prior thermochronologic data. Taken as a whole, the results provide strong confirmation that MDD modeling of K-feldspar 40Ar/39Ar analyses can provide accurate

  13. 40Ar/39Ar age-spectrum data for hornblende, biotite, white mica, and K-feldspar samples from metamorphic rocks in the Great Smoky Mountains of North Carolina and Tennessee

    USGS Publications Warehouse

    Kunk, Michael J.; McAleer, Ryan

    2011-01-01

    This report contains reduced 40Ar/39Ar data of hornblende, biotite, white mica and (or) sericite, and potassium-feldspar mineral separates and phyllite groundmass samples from metamorphic rocks of the Great Smoky Mountains in North Carolina and Tennessee. Included in this report are information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by users unfamiliar with argon isotopic data in the use of these results. No geological meaning is implied for any of the apparent ages presented below, and many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context. All the samples in this report were collected in and around the Great Smoky Mountain National Park in western North Carolina and eastern Tennessee.

  14. Pat Thiel talks about Nobel Prize winner Dan Shechtman

    SciTech Connect

    Thiel, Pat

    2012-01-01

    Ames Laboratory senior scientist and Iowa State University Distinguished Professor of Chemistry Pat Thiel talks about her friend and colleague Dan Shechtman who received the 2011 Nobel Prize for Chemistry.

  15. 4. Historic American Buildings Survey Dan Leyrer, Photographer, July 10, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. Historic American Buildings Survey Dan Leyrer, Photographer, July 10, 1963 ENTRANCE HALL & STAIRWAY with BRASS NEWEL POST - Herman-Grima House, 820 Saint Louis Street, New Orleans, Orleans Parish, LA

  16. 1. Historic American Buildings Survey Dan Leyrer, Photographer August 1963 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey Dan Leyrer, Photographer August 1963 PATIO AND GARCONNIERE--VIEW FROM EAST - Herman-Grima House, Garconniere & Kitchen, 820 Saint Louis Street, New Orleans, Orleans Parish, LA

  17. 2. Historic American Buildings Survey Dan Leyrer, Photographer August 1963 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey Dan Leyrer, Photographer August 1963 KITCHEN (SOUTHEAST ELEVATION) ATTACHED TO GARCONNIERE - Herman-Grima House, Garconniere & Kitchen, 820 Saint Louis Street, New Orleans, Orleans Parish, LA

  18. Environmental Scientist/Chemist Dan Gazda Speaks With Students

    NASA Video Gallery

    From NASA's International Space Station Mission Control Center, Environmental Scientist/Chemist Dan Gazda participates in a Digital Learning Network (DLN) event with students at from St. Peter's Pr...

  19. 1. Historic American Buildings Survey Dan Leyrer, Photographer Summer 1964 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey Dan Leyrer, Photographer Summer 1964 FRONT ELEVATION, OVERLOOKING BAYOU ST. JOHN - Michel-Pitot House, 1370 Moss Street (moved to 1440 Moss Street), New Orleans, Orleans Parish, LA

  20. Pat Thiel talks about Nobel Prize winner Dan Shechtman

    ScienceCinema

    Thiel, Pat

    2013-03-01

    Ames Laboratory senior scientist and Iowa State University Distinguished Professor of Chemistry Pat Thiel talks about her friend and colleague Dan Shechtman who received the 2011 Nobel Prize for Chemistry.

  1. Formation of a Phyllosilicate-, K-feldspar-, and Sulfate-Bearing Hematite Ridge on Mauna Kea Volcano, Hawaii, Under Hydrothermal, Acid-Sulfate Conditions: Process and Mineralogical Analog for the Hematite Ridge on Mt. Sharp, Gale Crater, Mars.

    NASA Astrophysics Data System (ADS)

    Ming, D. W.; Morris, R. V.; Adams, M. E.; Catalano, J. G.; Graff, T. G.; Arvidson, R. E.; Guinness, E. A.; Hamilton, J. C.; Mertzman, S. A.; Fraeman, A.

    2015-12-01

    The Mars Science Laboratory rover Curiosity is currently moving upslope on Mt. Sharp in Gale Crater toward a hematite-bearing ridge. This hematite exposure was originally detected in CRISM spectra and subsequently mapped as part of a ~200 m wide, 6.5 km long ridge extending roughly parallel to the base of Mt. Sharp. CRISM spectra in the region suggest that hematite, smectite, and hydrated sulfates occur as secondary phases in lower layers of Mt. Sharp, separated by an unconformity from overlying anhydrous strata. A potential process and mineralogical analog is a hematite-bearing and weathering-resistant stratum (ridge) is exposed on the Puu Poliahu cinder cone on Mauna Kea (MK) volcano, Hawaii. The MK ridge is the product of hydrothermal alteration of basaltic precursors under acid-sulfate conditions. We are acquiring chemical and mineralogical (VNIR, Mid-IR, and backscatter Moessbauer spectroscopy, and transmission XRD) data on the MK ridge area that correspond to rover and orbiting spacecraft measurements at Gale Crater and elsewhere. The hematite-bearing stratum does not have detectable sulfate minerals by XRD, and hematite is variably present as up to mm-sized black crystals which, together with associated trioctahedral smectite and K-feldspar (from XRD), imply hydrothermal conditions. Adjacent to the MK hematite-bearing stratum are sulfates (jarosite and alunite) that are evidence for aqueous alteration under acid-sulfate conditions, and more soluble sulfates are absent but such phases would not persist if formed because of annual precipitation. Dioctahedral smectite is associated with red hematite and alunite-rich samples. The black and red hematite zones have the highest and lowest MgO/Al2O3 and K2O/Na2O ratios, respectively. Hematite, smectite, jarosite, and K-feldspar have been detected by Curiosity XRD downslope from the Mt. Sharp hematite ridge. MK field work and samples were obtained with PISCES partnership and OMKM, MKMB, BLNR, and KKMC permissions.

  2. STS-108 Crew Interviews: Dan Tani

    NASA Technical Reports Server (NTRS)

    2001-01-01

    STS-108 Mission Specialist Dan Tani is seen during a prelaunch interview. He answers questions about the mission's goals and significance, explaining the meaning of 'utilization flight 1' (UF-1) as opposed to an 'assembly flight'. He gives details on the payload (Starshine Satellite, Avian Development Facility, and Rafaello Multipurpose Logistics Module (MPLM)), his role in the rendezvous, docking, and undocking of the Endeavour Orbiter to the International Space Station (ISS), how he will participate in the unloading and reloading of the MPLM, and the way in which the old and new resident crews of ISS will exchanged. Tani ends with his thoughts on the short-term and long-term future of the International Space Station.

  3. L'astronomie dans le monde

    NASA Astrophysics Data System (ADS)

    Manfroid, J.

    2007-09-01

    Anions interstellaires; S Orionis; Altaîr; Courants stellaires; Etoiles jeunes; 2MASSW J1207334-393254; Alpha Andromède; Etoiles à neutrons (1); LH54-425; AGNs invisibles; Deux supernovae; Les GRBs seon Swift; Peser les trous noirs; Formation de trous noirs; Trou noir; ondes gravitationnelles : Virgo entre dans sa phase d'exploitation scientifique; Amas de galaxies actifs; Amas de galaxies; Galaxies actives d'amas; L'univers statique: le retour; Macho; Exoplanètes; Exoplanètes habitables?; Exoplanètes habitables? (suite); Une année d'un an; Une année de 31 heures; Valse des Jupiters; Disque de HD 15115; Impact majeur; Planètes isolées; Super-Jupiter; Impact et mini-extinction; L'effet Pioneer; Toungouska; Spéléo martienne; Autres lunes dactives; Encelade; Hypérion; Pluton dépassé; Satellites d'Uranus; Titan

  4. Place du Lambeau Interosseux Posterieur dans sa Variante Aponevrotique dans le Traitement des Sequelles de Brulure de la Face Dorsale de la Main

    PubMed Central

    Achbouk, A.; Khales, A.; Oufkir, A.; Ihrai, H.

    2010-01-01

    Summary Le lambeau interosseux postérieur dans sa variante aponévrotique est un outil très intéressant dans le traitement des séquelles de brûlures de la face dorsale de la main. Les Auteurs cherchent, à travers un cas clinique et une revue de la littérature, à replacer cette variante dans l'arsenal thérapeutique. PMID:21991207

  5. Kyste hydatique du foie rompu dans la paroi abdominale et dans le muscle psoas : à propos d'une rare observation

    PubMed Central

    En-Nafaa, Issam; Moujahid, Mountassir; Alahyane, Abdelouahabe; Amil, Touria; Hanine, Ahmed; Ziadi, Tarik

    2011-01-01

    Le kyste hydatique du foie est une parasitose qui sévit à l′état endémique au maroc. La rupture dans la paroi abdominale et dans le psoas est une complication exceptionnelle. Nous rapportons un cas de kyste hydatique du foie rompu dans la paroi et dans le muscle psoas. Le diagnostic a été établi sur les données de l′échographie et surtout de la tomodensitométrie. Le patient a été opéré avec des suites simples. PMID:22187585

  6. Dan Poskevich demonstrates experiment for STS student involvement project

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Dan Poskevich, a college student, demonstrates an experiment he developed for the Space Transportation System (STS) student involvement project. In the aluminum box are thousands of honeybees constructing a honeycomb. Poskevich gave a brief demonstration for news media representatives in the Space Shuttle one-G trainer in JSC's mockup and integration lab.

  7. ADFL Award for Distinguished Service in the Profession: Dan Davidson.

    ERIC Educational Resources Information Center

    Dabars, Zita D.

    1999-01-01

    Discusses the influence of Dan Davidson on the Russian language teaching profession, concentrating on the NEH-CORLAC Institutes in Russian Language and Culture and materials development projects and on Davidson's role in programs involving high schools that teach Russian, the high school exchange program, and two national contests to stimulate…

  8. Transport de paires EPR dans des structures mesoscopiques

    NASA Astrophysics Data System (ADS)

    Dupont, Emilie

    Dans cette these, nous nous sommes particulierement interesses a la propagation de paires EPR1 delocalisees et localisees, et a l'influence d'un supraconducteur sur le transport de ces paires. Apres une introduction de cette etude, ainsi que du cadre scientifique qu'est l'informatique quantique dans lequel elle s'inscrit, nous allons dans le chapitre 1 faire un rappel sur le systeme constitue de deux points quantiques normaux entoures de deux fils supraconducteurs. Cela nous permettra d'introduire une methode de calcul qui sera reutilisee par la suite, et de trouver egalement le courant Josephson produit par ce systeme transforme en SQUID-dc par l'ajout d'une jonction auxiliaire. Le SQUID permet de mesurer l'etat de spin (singulet ou triplet), et peut etre forme a partir d'autres systemes que nous etudierons ensuite. Dans le chapitre 2, nous rappellerons l'etude detaillee d'un intricateur d'Andreev faite par un groupe de Bale. La matrice T, permettant d'obtenir le courant dans les cas ou les electrons sont separes spatialement ou non, sera etudiee en detail afin d'en faire usage au chapitre suivant. Le chapitre 3 est consacre a l'etude de l'influence du bruit sur le fonctionnement de l'intricateur d'Andreev. Ce bruit modifie la forme du courant jusqu'a aboutir a d'autres conditions de fonctionnement de l'intricateur. En effet, le bruit present sur les points quantiques peut perturber le transport des paires EPR par l'intermediaire des degres de liberte. Nous montrerons que, du fait de l'"intrication" entre la charge de la paire et le bruit, la paire est detruite pour des temps longs. Cependant, le resultat le plus important sera que le bruit perturbe plus le transport des paires delocalisees, qui implique une resonance de Breit-Wigner a deux particules. Le transport parasite n'implique pour sa part qu'une resonance de Breit-Wigner a une particule. Dans le chapitre 4, nous reviendrons au systeme constitue de deux points quantiques entoures de deux fils

  9. Multi-method low-temperature geochronology from the bergell pluton, italian alps: Utilizing K-feldspar 40Ar/39Ar multidiffusion domain modeling, conventional 40Ar/39Ar biotite dating, U-Th-He apatite and fission-track dating.

    NASA Astrophysics Data System (ADS)

    Page, L.; Dunai, T.; Wijbrans, J.; Andriessen, P.

    2003-04-01

    The Bergell batholith of SE Switzerland and NE Italy is a deep-seated igneous body which intruded previously emplaced and metamorphosed Alpine nappes at c. 32 Ma (U-Pb Zircon, von Blanckenburg 1990) The intrusion is located at the junction between the Eastern, Southern and Central Alps and is located along the late Alpine Insubric Fault Zone which has been linked with deep crustal lithospheric processes in the Alps. .K-Feldspar 40Ar/39Ar MDD geochronology from a suite of samples from different elevations in the Bergell Pluton has been obtained as part of an on-going multi-method geochronology study which also includes conventional 40Ar/39Ar step-heating of biotites, U-Th-He dating and Fission Track dating to 1) fully constrain the tectonothermal history of the region and 2) test the different isotopic methods against each other. The results to date from high-resolution K-Feldspar samples from a vertical profile of c. 1300 m demonstrate that the first-order characteristics of the release spectra are consistent with different splits and show a trend with elevation with highest elevations leveling out at a 30 Ma maximum and lower elevations reaching 25 Ma. K-Feldspar multidiffusion domain modeling confirms the height vs. cooling age relationship and yields discernable changes in the cooling rate from c. 10 C/MY to c. 60 C/MY which may represent discrete tectonic episodes. The 40Ar/39Ar biotite ages range from 23-26 Ma and are generally consistent with the K-Feldspar results. U-Th-He apatite ages from the region range from 7-15 Ma. New fission-track ages from these samples will be presented.

  10. Dissolution of Quartz, Albite and K-feldspar Into H2O-Saturated Haplogranitic Melt at 800oC and 200 MPa: Diffusive Transport Properties of Granitic Melts at Crustal Anatectic Temperatures

    NASA Astrophysics Data System (ADS)

    Acosta, A.; London, D.; Dewers, T.; Morgan, G.

    2002-12-01

    With the aim of investigating the diffusive transport properties of granitic melts at crustal anatectic conditions and obtaining some constraints on speciation and coordination in the melt, we conducted albite, K-feldspar and quartz dissolution experiments in H2O-saturated metaluminous haplogranitic glass (nominal composition of the 200 MPa H2O-saturated haplogranite eutectic of Tuttle and Bowen, 1958) at 800oC and 200 MPa. Mineral and glass cylinders were juxtaposed against flat polished surfaces inside platinum or gold capsules, then run for durations in the range 120-960 h. Based on the time dependence of interface retreat dissolution is interface reaction-controlled up to 700 h, and becomes diffusion-controlled afterwards. Upon dissolution of albite, Al and Na entering the melt decouple and Na diffuses away from the interface to maintain a constant Al/Na molar ratio throughout the entire melt column. Potassium from the bulk melt diffuses uphill towards the albite-melt interface to maintain a constant Aluminum Saturation Index (ASI=molar Al2O3/Na2O+K2O) of 1.00 throughout the entire melt column. Dissolution of K-feldspar results in migration of K away from the interface and uphill diffusion of Na from the bulk melt towards the interface, again maintaining constant Al/Na and ASI ratios in the bulk melt. Dissolution of quartz produces enrichment in SiO2 versus dilution of the rest of components in the interface melt. These results indicate that in the five-component H2O-saturated metaluminous haplogranite system, uncoupled diffusion takes place along the following four directions in composition space: SiO2; Na2O; K2O; and a combination of Al2O3 and alkalis such that the Al/Na molar ratio is equal to that in the bulk melt, and the Al2O3/Na2O+K2O molar ratio is equal to the equilibrium ASI of the melt. These observations are in accord with results obtained from corundum and andalusite dissolution experiments in the same system and P-T-X conditions (Acosta-Vigil et

  11. Apport de l'imagerie dans le diagnostic des sacroiliites infectieuses : à propos de 19 cas

    PubMed Central

    Abid, Hanen; Chaabouni, Salim; Frikha, Faten; Toumi, Nozha; Souissi, Basma; Lahiani, Dorra; Bahloul, Zouhir; Ben Mahfoudh, Khaireddine

    2014-01-01

    Les sacro-iliites infectieuses méritent d’être mieux connues. Leur diagnostic est souvent retardé en raison d'une symptomatologie trompeuse et des diffcultés d'exploration de l'articulation sacro-iliaque. Notre travail est basé sur une étude rétrospective portant sur les cas de SII, recueillis sur une période comprise entre 1997 et 2008 dans notre centre universitaire Sfax-Tunisie. Le diagnostic de sacro-iliite était retenu en présence d'arguments cliniques et radiologiques d'atteinte sacroiliaque. Nous rapportons dix neuf cas de sacroiliites infectieuses (10 hommes et 9 femmes), avec un âge moyen de 32 ans. L'atteinte était unilatérale dans tous les cas. Les radiographies standard faites dans tous les cas ont été suggestives dans 14 cas et normales dans les autres cas. La TDM faite dans 13 cas a montré, un abcès des parties molles dans 8 cas et un séquestre osseux dans 2 cas. L'IRM réalisée dans 8 cas, a objectivé une infiltration des parties molles dans tous les cas et un abcès dans 3 cas. Le germe a été identifié dans 9 cas (3 cas de tuberculose, 3 cas de brucellose, 2 sacro-iliites à pyogène et un cas de candidose). Cette identification était faite par biopsie dans 3 cas, hémocultures dans 2 cas, prélèvement au niveau de la porte d'entrée dans 1 cas et sérodiagnostic dans 3 cas. Pour les autres cas, l'origine pyogène a été retenue sur des arguments cliniques et biologiques. L'imagerie joue un rôle primordial dans le diagnostic précoce et l'orientation étiologique d'une sacroiliite infectieuse. PMID:25120884

  12. NASA Administrator Dan Goldin talks with STS-78 crew

    NASA Technical Reports Server (NTRS)

    1996-01-01

    NASA Administrator Dan Goldin (left) chats with STS-78 Mission Commander Terence 'Tom' Henricks (center) and KSC Director Jay Honeycutt underneath the orbiter Columbia. Columbia and her seven-member crew touched down on Runway 33 of KSC's Shuttle Landing Facility at 8:36 a.m. EDT, July 7, bringing to a close the longest Shuttle flight to date. STS-78, which also was the 78th Shuttle flight, lasted 16 days, 21 minutes and 47 seconds.

  13. Dissolution de la matiere lignocellulosique dans les liquides ioniques

    NASA Astrophysics Data System (ADS)

    Rebiere, Jeremy

    De nos jours, avec la raréfaction des ressources fossiles, le développement de procédés entrant dans le cadre de la chimie verte s'accentue. De plus, ces procédés utilisent comme ressources, des matériaux d'origine végétale, abondants et biodégradables. Au cours de ces 20 dernières années, la littérature utilisant les liquides ioniques (LI) connait une importante croissance. Ces solvants sont de plus en plus employés dans des réactions chimiques classiques. Cependant le coût de leur synthèse en fait un solvant réactionnel cher dont l'application en tant que tel dans l'industrie ne peut être raisonnablement envisagée. Ces liquides ioniques permettent la dissolution des matériaux lignocellulosiques (lignine ou cellulose) et possèdent des propriétés physico-chimiques intéressantes. Nous savons également que la dissolution de la cellulose par des procédés d'hydrolyse classique s'effectue dans des conditions dures, dues à la structure cristalline de la cellulose, (fortes concentrations en acide) qui paraissent limitées pour une utilisation à grande échelle. Il est donc nécessaire de rechercher des méthodes moins onéreuses et plus efficaces écologiquement. S'appuyant sur des recherches démontrant que la dissolution de la cellulose dans les LI, diminue la cristallinité de la cellulose, nous allons chercher à démontrer au cours de ces travaux, la possibilité d'utiliser les LI comme moyen de prétraitement pour la dissolution de la cellulose. Nous allons nous attacher à dissoudre la cellulose, et à étudier les proportions pouvant être dissoutes. Puis nous chercherons à récupérer puis à réutiliser ces LI. Enfin nous cherchons à caractériser les modifications apportées à notre cellulose. Mots Clés liquide ionique, cellulose, cristallinité, réactivité, dissolution, régénération, non-solvant, purification, prétraitement, zone amorphe.

  14. 77 FR 75628 - STS Hydropower, Ltd., Dan River, Inc., and City of Danville, VA; Notice of Application for...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-21

    ... Energy Regulatory Commission STS Hydropower, Ltd., Dan River, Inc., and City of Danville, VA; Notice of..., 2012, Jeoffrey L. Burtch, as Chapter 7 Bankruptcy Trustee for Dan River, Inc. and STS Hydropower, Ltd... the license for the Schoolfield Hydroelectric Project from Dan River, Inc. and STS Hydropower, Ltd....

  15. Dan Olweus: Award for Distinguished Contributions to Research in Public Policy

    ERIC Educational Resources Information Center

    American Psychologist, 2012

    2012-01-01

    Presents a short biography of the winner of the American Psychological Association's Award for Distinguished Contributions to Research in Public Policy. The 2012 winner is Dan Olweus for his rigorous scientific research on bullying among children and youth and his early and tireless attention to its public policy implications. Dan Olweus's…

  16. MALDI-MS analysis and imaging of small molecule metabolites with 1,5-diaminonaphthalene (DAN)

    SciTech Connect

    Korte, Andrew R; Lee, Young Jin

    2014-07-08

    1,5-diaminonaphthalene (DAN) has previously been reported as an effective matrix for matrix-assisted laser desorption ionization-mass spectrometry of phospholipids. In the current work, we investigate the use of DAN as a matrix for small metabolite analysis in negative ion mode. DAN was found to provide superior ionization to the compared matrices for MW < ~400 Da; however, 9-aminoacridine (9-AA) was found to be superior for a uridine diphosphate standard (MW 566 Da). DAN was also found to provide a more representative profile of a natural phospholipid mixture than 9-AA. Finally, DAN and 9-AA were applied for imaging of metabolites directly from corn leaf sections. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

  17. Blocage de Coulomb dans une boite quantique laterale contenant un faible nombre d'electrons

    NASA Astrophysics Data System (ADS)

    Gould, Charles

    Dans ce travail on utilise une nouvelle geometrie pour augmenter le controle sur le nombre d'electrons contenus dans une boite quantique laterale, et ainsi atteindre un regime de petit nombre d'electrons. Ces echantillons permettent une etude du blocage de Coulomb quand les electrons sont injectes a partir d'un gaz electronique a deux dimensions (2DEG). Les mesures a faible champ magnetique demontrent la grande flexibilite des echantillons et montrent que l'on peut faire varier le nombre d'electrons dans une boite quantique a partir de plus de 40 electrons jusqu'a un seul electron, ce qui est assez courant dans les boites quantiques verticales, mais ce qui n'avait jamais ete reussi dans une boite quantique laterale. Nos resultats montrent egalement que dans les boites quantiques laterales il est possible de determiner le spin du niveau qui participe au transport a l'aide du phenomene de blocage de spin. De plus, dans certaines circonstances il est meme possible de determiner le spin total de la boite quantique, ce qui peut avoir des applications pratiques dans des domaines tels l'informatique quantique. Les mesures dans le regime de renversement de spin a un champ magnetique plus eleve montrent l'importance des correlations electrons---electrons dans ces boites quantiques, qui menent a des depolarisations et a des structures de spins qui ont un effet sur le transport. En particulier, ces correlations menent a l'existence de niveaux excites de basse energie qui causent une dependance anormale de l'amplitude des pics de blocage de Coulomb en fonction de la temperature. Nos experiences demontrent egalement la possibilite d'utiliser ces boites quantiques comme sondes pour etudier les proprietes du bord d'un 2DEG. Une voie de recherche a etre exploree.

  18. Residence times of alkali feldspar phenocrysts from magma feeding the Agnano-Monte Spina Eruption (4.7 ka), Campi Flegrei caldera (Napoli, southern Italy) based on Ba-zonation modelling

    NASA Astrophysics Data System (ADS)

    Iovine, Raffaella Silvia; Wörner, Gerhard; Carmine Mazzeo, Fabio; Arienzo, Ilenia; Fedele, Lorenzo; Civetta, Lucia; D'Antonio, Massimo; Orsi, Giovanni

    2016-04-01

    Timescales governing the development of crustal magma reservoirs are a key for understanding magmatic processes such as ascent, storage and mixing event. An estimate of these timescales can provide important constraints for volcanic hazard assessment of active volcanoes. We studied the Agnano-Monte Spina eruption (A-MS; 4.7 ka; VEI = 4; 0.85 km3 D.R.E. of magma erupted) of the Campi Flegrei caldera, one of the most dangerous volcanic areas on Earth. The A-MS eruption has been fed by magmas varying from more to less evolved trachyte whose variable 87Sr/86Sr and trace elements features suggest magma mixing between two end-members. Ba zonation profiles of alkali feldspar phenocrysts have been determined through combined energy-dispersive and wavelength-dispersive electron microprobe analyses (EDS-WDS-EMPA). We focused on distinct compositional breaks near the rim of the crystals that likely represent the last mixing event prior to eruption. We always chose the steepest gradients close to the crystal rims, taking into account that any effects related to cutting angles or crystal orientation should give longer apparent diffusion times. Two different approaches were undertaken: (1) a quantitative Ba compositional profiles were measured by point analyses along a short transect crossing growth discontinuities and (2) grey-scale profiles were taken parallel to the acquired point profiles. Assuming that Ba dominates the backscattered electron intensities in sanidines, greyscale gradients can be used as a diffusive tracer. BSE images were processed using the ImageJ® software, in order to extract a numerical greyscale profile. In both cases, each profile was interpolated through a non-linear Boltzmann fit curve with the Mathematica® software. A few traverses done at angles smaller than 90° to the compositional boundary interface were corrected by multiplying the distance values by the sinus of the traverse angle relative to the vertical on the interface. Our preliminary

  19. NASA Administrator Dan Goldin greets 10-year-old VIP.

    NASA Technical Reports Server (NTRS)

    2000-01-01

    NASA Administrator Dan Goldin (left) shares a light moment during his meeting with 10-year-old Jonathan Pierce (right), who is garbed in a protective cooling suit designed by NASA. Behind Goldin is astronaut Doug Wheelock; behind Jonathan is his mother, Penny. Jonathan suffers from erythropoietic protoporphyria, a rare condition that makes his body unable to withstand ultraviolet rays. The suit allows him to be outside during the day, which would otherwise be impossible. Jonathan's trip was funded by the Make-A-Wish Foundation and included a visit to Disney World. He and his family were among a dozen VIPs at KSC to view the launch of STS-99.

  20. Transition de phase quantique de type verrouillage-deverrouillage dans les canaux lineaires coherents des phases en rayures dans les doubles puits quantiques sous champ magnetique perpendiculaire

    NASA Astrophysics Data System (ADS)

    Faribault, Alexandre

    On peut creer un gaz electronique bidimensionnel en utilisant le potentiel de confinement d'une couche mince d'un semiconducteur dans un substrat fait d'une autre semiconducteur de gap plus eleve. L'ajout d'un champ magnetique perpendiculaire au plan de confinement modifie de facon drastique les proprietes du gaz electronique. Pour des densites et des valeurs du champ magnetique adequatement choisies, on obtient un etat fondamental en onde de densite de charge. Dans un systeme compose de deux de ces gaz bidimensionnels suffisamment rapproches l'un de l'autre, on prevoit theoriquement l'existence d'un etat fondamental compose d'une onde de densite de charge dans chacun des puits et d'une serie de regions lineaires ou l'on a une delocalisation coherente des electrons entre les deux puits. Dans cette these, on etudie le comportement a temperature nulle de cet etat fondamental en rayures coherentes. L'etude numerique des modes collectifs de ces phases laisse croire qu'un deverrouillage des canaux coherents est envisageable dans ce systeme. Afin d'etudier cette possibilite, nous construisons d'abord un modele effectif de canaux quasi-unidimensionnels couples qui permettent de reproduire correctement les excitations collectives a basse energie de la phase en rayures coherentes du double puits quantique. Dans un systeme de coordonnees adequatement choisi, ces excitations peuvent etre decrites par des ondes de pseudospin. Les parametres de ce modele effectif simple peuvent etre extraits des calculs des fonctions de reponse realises dans l'approximation Hartree-Fock dependante du temps (appelee aussi Generalized Random Phase Approximation). On constate l'efficacite de ce modele a decrire la dynamique basse energie du systeme pour une certaine plage de distances inter-puits. En retirant de ce modele les contributions a l'hamiltonien provenant des couplages de type Josephson entre les canaux, on obtient alors un systeme ou les canaux sont deverrouilles. Un traitement en

  1. Structure of Protein Related to DAN and Cerberus (PRDC): Insights into the Mechanism of BMP Antagonism

    PubMed Central

    Nolan, Kristof; Kattamuri, Chandramohan; Luedeke, David M.; Deng, Andy; Jagpal, Amrita; Zhang, Fuming; Linhardt, Robert; Kenny, Alan P.; Zorn, Aaron M.; Thompson, Thomas B.

    2013-01-01

    Summary The Bone Morphogenetic Proteins (BMP) are secreted ligands largely known for their functional roles in embryogenesis and tissue development. A number of structurally diverse extracellular antagonists inhibit BMP ligands to regulate signaling. The DAN family of antagonists represents the largest group of BMP inhibitors, however, little is known for how they mechanistically inhibit BMP ligands. Here, we present the structure of the DAN family member Protein Related to Dan and Cerberus (PRDC) solved by X-ray crystallography. The structure reveals an unexpected growth factor-like appearance with a novel dimerization mechanism that is formed through extensive β-strand contacts. Using site-directed mutagenesis coupled with in vitro and in vivo activity assays, we identified a BMP binding epitope on PRDC. We also determined that PRDC binds heparin with high affinity and that heparin binding to PRDC interferes with BMP antagonism. These results offer insight for how DAN family antagonists functionally inhibit BMP ligands. PMID:23850456

  2. Tuberculome de Bouchut dans la tuberculose multi focale: à propos de quatre cas

    PubMed Central

    Janah, Hicham; Alami, Ahmed; Souhi, Hicham; Zegmout, Adil; Naji-Amrani, Hicham; Raoufi, Mohamed; Elouazzani, Hanane; Rhorfi, Ismail Abderrahmani; Abid, Ahmed

    2014-01-01

    La tuberculose multifocale a connu un regain de fréquence avec la pandémie du SIDA, elle s'observe encore chez des sujets non infectés par le VIH surtout dans les pays en voie de développement notamment au Maroc. Nous rapportons quatre observations de tuberculose multifocale chez trois patients immunocompétents et un patient immunodéprimé. Quatre patients ont bénéficié d'un bilan phtisiologique, biologique, sérologique(HIV), radiologique et d'angiographie à la fluorescéine pour suspicion de tuberculose multifocale. Il s'agit de trois hommes et une femme, d’âge moyen de 44 ans, trois patients sont immunocompétents et un patient séropositif. La tuberculose intéressait trois localisations chez les quatre patients: pulmonaire dans quatre cas, ophtalmique dans quatre cas, digestive dans un cas, urinaire dans un cas, cérébrale dans un cas et un cas d'atteinte de la moelle osseuse. L'atteinte ophtalmologique est représentée par des nodules choroïdiens de Bouchut dans quatre cas et un nodule papillaire de Bouchut dans un cas; aucun des ces patients ne présentait une uvéite granulomateuse. Nos malades ont reçu un traitement anti-tuberculeux d'une durée de neuf mois avec une bonne évolution clinique, biologique, radiologique et angiographique. Au Maroc, la tuberculose continue à surprendre aussi bien par son extension touchant le sujet débilité et le sujet immunocompétent, que par ses présentations diverses y compris l'atteinte oculaire qu'elle faut rechercher par un examen ophtalmologique soigneux et systématique. PMID:25478047

  3. The Dynamic Albedo of Neutrons (DAN) experiment for NASA's 2009 Mars Science Laboratory.

    PubMed

    Litvak, M L; Mitrofanov, I G; Barmakov, Yu N; Behar, A; Bitulev, A; Bobrovnitsky, Yu; Bogolubov, E P; Boynton, W V; Bragin, S I; Churin, S; Grebennikov, A S; Konovalov, A; Kozyrev, A S; Kurdumov, I G; Krylov, A; Kuznetsov, Yu P; Malakhov, A V; Mokrousov, M I; Ryzhkov, V I; Sanin, A B; Shvetsov, V N; Smirnov, G A; Sholeninov, S; Timoshenko, G N; Tomilina, T M; Tuvakin, D V; Tretyakov, V I; Troshin, V S; Uvarov, V N; Varenikov, A; Vostrukhin, A

    2008-06-01

    We present a summary of the physical principles and design of the Dynamic Albedo of Neutrons (DAN) instrument onboard NASA's 2009 Mars Science Laboratory (MSL) mission. The DAN instrument will use the method of neutron-neutron activation analysis in a space application to study the abundance and depth distribution of water in the martian subsurface along the path of the MSL rover. PMID:18598140

  4. Les fluctuations supraconductrices dans le compose praseodyme-cerium-oxyde de cuivre

    NASA Astrophysics Data System (ADS)

    Renaud, Jacques

    Ce travail etudie les fluctuations supraconductrices dans le compose supraconducteur a haute temperature critique dope aux electrons Pr2-xCe xCuO4+delta. La technique utilisee pour sonder ces fluctuations est le transport electrique DC dans le plan ab. Il s'agit, a notre connaissance, de la premiere etude de ce type dans la classe generale des supraconducteurs a haute temperature critique dopes aux electrons et, plus particulierement, dans Pr2-xCe xCuO4+delta. De plus, l'etude est effectuee pour trois regimes de dopage, soit sous-dope x = 0.135, dopage optimal x = 0.15 et surdope x = 0.17. Les echantillons etudies sont des couches minces d'epaisseur plus grande que 100 nm crues par ablation laser. Les mesures electriques DC effectuees dans ce travail sont la resistance en reponse lineaire et les courbes IV en reponse non lineaire en fonction de la temperature. La mise en oeuvre experimentale de ces mesures a necessite une grande attention au filtrage et aux effets de chauffage a haut courant. Nous montrons que, sans cette attention, les donnees experimentales sont toujours erronees dans le regime pertinent pour nos echantillons. Les resultats pour le dopage optimal x = 0.15 sont expliques de facon tres convaincante dans le cadre de fluctuations purement 2D. D'abord, le regime des fluctuations gaussiennes est tres bien decrit par le modele d'Aslamazov-Larkin en deux dimensions. Ensuite, le regime de fluctuations critiques, se trouvant a plus basse temperature que le regime gaussien, est tres bien decrit par la physique 2D de Kosterlitz-Thouless. Dans cette analyse, les deux regimes ont des temperatures critiques coherentes entre elles, ce qui semble confirmer ce scenario 2D. Une analyse des donnees dans le cadre de fluctuations 3D est exploree mais donne des conclusions incoherentes. Les resultats pour les autres dopages sont qualitativement equivalents avec le dopage optimal et permettent donc une explication purement 2D. Par contre, contrairement au dopage optimal

  5. Transitions de phase dans le oxyde de yttrium vanadium

    NASA Astrophysics Data System (ADS)

    Roberge, Benoit

    Dans le mémoire qui suit, les ordres structural, magnétiques et orbital dans le YVO3 sont étudiés avec l'aide de la diffraction des rayons X,de la spectroscopie Raman et de la technique de la cavité résonnante hyperfréquence. L'objectif premier consiste à observer l'évolution de ces ordres en fonction de la température. Le mémoire met ensuite en évidence le couplage entre les différents ordres cohabitants dans le YVO3 . Les mesures effectuées par la diffraction des rayons X permettent de mesurer le caractère polycrystallin des échantillons du YVO 3. Une comparaison de nos mesures avec des mesures de diffraction des rayons X faites sur la poudre de YVO3 indique la faible présence de maclage. Les mesures effectuées avec la technique de résonnance hyperfréquence permettent de suivre l'évolution de la constante diélectrique en fonction de la température. Les changements impliquant l'ordre orbital se manifestent de manière évidente dans la constante diélectrique à 200 K et à 77 K. La transition diélectrique détectée à 77 K est une transition de premier ordre. Un couplage entre les propriétés diélectriques et magnétiques est observable à la température de Néel à 114 K. L'effet d'un champ magnétique fixe sur la température de transition de l'ordre orbital survenant à 77 K est également remarquable. Cela indique un couplage magnétodiélectrique démontrant ainsi le caractère multiferroïque du YVO 3. Finalement, l'observation d'un mécanisme de relaxation pouvant être modélisé par le modèle d'Havriliak-Negami est observé en dessous de 77 K. En utilisant le modèle d'Arrhénius et le modèle d'Havriliak-Negami, on peut caractériser le mécanisme avec son énergie d'activation et son temps de relaxation. Les mesures effectuées en spectroscopie Raman permettent de suivre l'évolution de la structure du YVO3 en fonction de la température. Les deux changements structuraux survenant à 200 K et 77 K sont observés. Le

  6. DAN Active Parameters and Mastcam Hydration Survey Imaging: Comparisons Across Yellowknife Bay, Gale Crater, Mars

    NASA Astrophysics Data System (ADS)

    Hardgrove, C. J.; Rice, M. S.; Moersch, J.; Mitrofanov, I. G.; Litvak, M.; Wellington, D. F.; Behar, A.; Bell, J. F.; Boynton, W. V.; DeFlores, L.; Drake, D.; Fedosov, F.; Golovin, D.; Jun, I.; Harshman, K.; Kozyrev, A.; Malakhov, A.; Milliken, R.; Kuzmin, R.; Mischna, M. A.; Mokrousov, M.; Nikiforov, S.; Sanin, A.; Tate, C.; Team, M.

    2013-12-01

    The Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) rover Curiosity has recorded variability in neutron counts along traverses in and around Yellowknife Bay that suggest variable amounts of hydrogen (H) are present. At the locations of several DAN observations, Mastcam 'hydration survey' mosaics have been acquired with the R0 (493 nm, 551 nm and 638 nm), R5 (937 nm) and R6 (1013 nm) science filters to characterize RGB color and look for potential hydration as indicated by an absorption near 1000 nm. Whereas DAN is sensitive to H abundance down to 60cm depth, the Mastcam hydration index is sensitive to the presence of certain hydrated minerals (bound-OH and/or H2O) exposed in the upper hundreds of micrometers of the surface. Furthermore, many light-toned, Ca-sulfate-bearing features (i.e. veins and nodules within the outcrop) exposed at the surface in Yellowknife Bay have a high hydration index, consistent with a hydrated mineral such as gypsum. Other light-toned features do not have a high hydration index, suggesting they are composed of anhydrous or lower hydration state phases such as anhydrite or bassanite. The distribution of light-toned features within the outcrop at Yellowknife Bay is also highly variable within a DAN footprint. Given that there is variability in both the DAN signal and Mastcam hydration index throughout Yellowknife Bay, this work investigates whether or not increases or decreases in H seen by DAN correlate to areas of high hydration index as derived from Mastcam observations. Positive correlations of the DAN H signal and Mastcam hydration index may indicate that the observed densities of light-toned features (hydrated or dehydrated) extend to at least 60cm depth. Conversely, negative correlations could indicate that either the veins/nodules are only present at very shallow depths (a few cm), that the hydration of the phases changes with depth (e.g., gypsum at the surface and anhydrite at depth), or that there

  7. Sacroiliites infectieuses dans le centre tunisien: étude rétrospective de 25 cas

    PubMed Central

    Bellazreg, Foued; Alaya, Zeineb; Hattab, Zouhour; Lasfar, Nadia Ben; Ayeche, Mohamed Laziz Ben; Bouajina, Elyes; Letaief, Amel; Hachfi, Wissem

    2016-01-01

    Les sacroiliites infectieuses sont rares mais peuvent se compliquer de séquelles fonctionnelles invalidantes. Décrire les caractéristiques cliniques et bactériologiques des sacroiliites infectieuses chez les patients suivis à Sousse, Centre Tunisien. Etude rétrospective, descriptive, des cas de sacroiliites infectieuses chez les patients hospitalisés à Sousse entre 2000 et 2015. Le diagnostic a été retenu devant des signes cliniques, d'imagerie, et microbiologiques évocateurs. Vingt-cinq patients, 10 hommes et 15 femmes, d’âge moyen 41 ans (19-78) ont été inclus. Les sacroiliites étaient dues à des bactéries pyogènes dans 14 cas (56%), brucelliennes dans 6 cas (24%), et tuberculeuses dans 5 cas (20%). La durée moyenne d’évolution était de 61, 45 et 402 jours respectivement. Les signes cliniques les plus fréquents étaient les douleurs fessières (92%) et la fièvre (88%). La radiographie standard était anormale dans 75% des cas. La TDM et l'IRM sacro-iliaques dans tous les cas. Le diagnostic a été confirmé bactériologiquement dans 24 cas (96%). La durée moyenne d'antibiothérapie était de 83 jours dans les sacroiliites à pyogènes, et de 102 jours dans les SI brucelliennes. L’évolution était favorable chez 12 patients (48%), 9 patients (36%) ont gardé une douleur sacro-iliaque séquellaire, et 4 patients (16%) sont décédés. Dans notre étude, la durée d’évolution de la sacroiliite infectieuse ne permettait pas de prédire la bactérie responsable, d'où la nécessité d'obtenir une documentation bactériologique afin de prescrire une antibiothérapie appropriée. PMID:27583067

  8. Spectres d'absorption X dans les plasmas femtosecondes

    NASA Astrophysics Data System (ADS)

    Bastiani-Ceccotti, S.; Audebert, P.; Renaudin, P.; Chenais-Popovics, C.; Geindre, J. P.; Tzortzakis, S.; Nagels-Silvert, V.; Shepherd, R.; Matsushima, I.; Gary, S.; Girard, F.; Peyrusse, O.; Gauthier, J. C.

    2005-06-01

    Nous avons mesuré le spectre d'absorption en couche K de plasmas d'aluminium à haute densité. Deux faisceaux de la chaîne laser femtoseconde 100 TW du LULI (de durée 300 fs) ont été utilisés pour produire le plasma absorbant sur une feuille mince d'Al (830 Å ou 500 Å), et la source de radiographie sur du samarium massif. Les spectres X étaient résolus spatialement dans une direction perpendiculaire à la direction de la dispersion spectrale. Les spectres ont été mesurés pour différents retards entre la source deradiographie et le plasma d'Al. Des simulations des spectres et de l'ionisation en fonction du temps et de l'intensité, obtenues au moyen de codes hydrodynamiques et de structure atomique, montrent un bon accord avec les résultats expérimentaux.

  9. Migration pelvienne de broche guide dans la chirurgie des fractures de hanche: à propos de 3 cas

    PubMed Central

    Guèye, Mohamadou Lamine; Thiam, Ousmane; Touré, Alpha Oumar; Seck, Mamadou; Cissé, Mamadou; Kâ, Ousmane; Dieng, Madieng; Dia, Abderahmane; Touré, Cheikh Tidiane

    2015-01-01

    La migration de matériel d'ostéosynthèse est une complication bien connue du traitement chirurgical des fractures. Toutefois, la migration pelvienne de broche guide dans la chirurgie des fractures de la hanche est un incident rare et potentiellement grave. Nous rapportons 3 observations dans lesquelles on notait une migration de broche guide dans le pelvis lors d'une ostéosynthèse dela hanche de type DHS. L'indication chirurgicale était une fracture per-trochantérienne dans 2 cas et une fracture du col fémoral type 4 de Garden dans 1 cas. Une minilaparotomie permettait d'objectiver une plaie du ligament large gauche et un hématome ligamentaire dans 1 cas, tandis que dans les 2 autres cas, il n'y avait pas de lésion viscérale. L'extraction de la broche a été effectuée dans les 3 cas. Les suites opératoires ont été simples chez tous les patients. PMID:26327949

  10. The local subsurface water and chlorine distributions evaluated by DAN/MSL in Curiosity observational campaigns

    NASA Astrophysics Data System (ADS)

    Litvak, Maxim; Mitrofanov, Igor; Hardgrove, Craig; Sanin, Anton; Lisov, Denis; Golovin, Dmitry; Jun, Insoo; Kozyrev, Alexander; Malakhov, Alexey; Mischna, Michael; Moersch, Jeffrey; Nikiforov, Sergey; Tate, Cristopher; Vostrukhin, Andrey

    2016-04-01

    The measurements with the Dynamic Albedo of Neutrons (DAN) instrument onboard the Mars Science Laboratory (MSL) Curiosity rover are presented and analyzed as a summary of observations acquired during several special observational campaigns at the Yellowknife Bay area (first discovery of habitability environment), at the striated units of Kimberley formation, at outcrops studied in Pahrump Hills (at the base of Mt Sharp) and in high silica area discovered in Marias Pass (Mudstone facies of the Murray formation). DAN data were analyzed to test local and global variability in the distribution of bulk hydrogen and neutron-absorbing elements, characterized as chlorine-equivalent concentration. Using multi instrument approach in the data analysis we have compared DAN estimations of subsurface H and Cl distributions with inhomogeneity of local geological context, top surface measurements of chlorine with APXS and with SAM measurements of absorbed H2O extracted from the drilled samples based on low temperature evolved gas analysis.