Changes In Bulk Composition Research Articles

Catalytic oxidation of cinnamyl alcohol using Au-Ag nanotubes investigated by surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) enables ultrasensitive detection of adsorbed species at the catalyst surface. However, it is quite difficult to combine catalytic and SERS activities on the same material. Here we report the application of well-defined Au-Ag nanotubes as both SERS substrates and catalysts for the oxidation of cinnamyl alcohol. The species adsorbed on the catalyst surfaces at different reaction times were analyzed by SERS. The bimetallic nanotubes prepared via a simple galvanic replacement reaction are highly active in the oxidation of cinnamyl alcohol, but do not avoid a radical-chain reaction and the cleavage of the carbon-carbon double bond. A comparison between changes in bulk composition and the nature of adsorbed species at the surface of the catalyst over time suggests that cinnamaldehyde is formed on the catalyst surface (metal-catalyzed oxidation) and benzaldehyde is probably formed in the bulk solution via a radical-chain pathway. In the presence of 2,6-di-tert-butyl-4-methylphenol, the radical-chain reaction is suppressed and the oxidation reaction produces cinnamaldehyde.

Carbon accumulation rates in two poor fens with different water regimes: Influence of anthropogenic impact and environmental change

Fens are underestimated carbon sinks. Knowledge about their role in the sequestration of CO2 in the past is limited. The research reported here focused on identifying long-term carbon accumulation rates (CARs) in a drained fen (Bagno Bruch) and a waterlogged fen (Bagno Mikołeska) in southern Poland. On the basis of 210Pb and AMS 14C dates and age–depth modeling, 7000- and 2000-year records of changes in bulk composition and carbon and sulfur content are presented and discussed. Strong human impact is detected, especially in Bagno Bruch. However, minor climatic signals linked to the ‘Little Ice Age’ and to the influence of wind-blown sands are also evident. The sand may have influenced the plant composition, peat accumulation rates (PARs), and CARs, in addition to the bulk composition at Bagno Mikołeska. The mean value of the CAR in the youngest peat layers spanning the last 200 years is generally lower in two cores from Bagno Bruch ( c. 85 and 86 g/m2/yr) than in two cores from Bagno Mikołeska ( c. 140 and 142 g/m2/yr). The fens are characterized by higher CARs compared with boreal peatlands. The reproducibility of the CAR values is the most promising result, suggesting the low mobility of 210Pb and the reliability of this method in assessing the chronology of fens.

Hierarchical Silicoaluminophosphates by Postsynthetic Modification: Influence of Topology, Composition, and Silicon Distribution

AlPO-5, SAPO-5, SAPO-11, and SAPO-34 silicoaluminophosphates (SAPOs) are exposed to various acid and base treatments aimed at mesopore formation and investigation of associated physicochemical modifications. SAPOs amorphize strongly in aqueous NaOH, requiring the use of organic bases (e.g., tetrapropylammonium hydroxide or diethylamine) to preserve the crystallinity during base treatment. In acid media (HCl, H4EDTA, and Na2H2EDTA), SAPO-11 remains fully crystalline, while SAPO-34 strongly amorphize. No clear influence of the framework topology is established. The high resistance in alkaline media and low stability in acid media of SAPO-34 is attributed to its relatively high silicon content. Base treatment of SAPOs leads predominately to the formation of intercrystalline porosity. Still, an up to 4-fold increase in external surface and pore volume in SAPO-11 are achieved. Besides the formation of secondary porosity, base treatment of SAPOs induces a variety of (correlated) physicochemical changes. For example, the silicon distribution clearly influences the dissolution behavior of SAPO-11 in alkaline media, as zeolitic-like Si-domains are more resistant than AlPO domains. As a result, base leaching is selective to phosphorus and leads, depending on the silicon distribution, to either aluminum or silicon enrichment. The resulting changes in bulk composition can be directly related to the secondary porosity, as the Si and Al enrichment takes place predominately on the external surface. Acidity characterization (TPD of ammonia and IR spectroscopy of pyridine or 2,6-di-tert-butylpyridine adsorbed) shows that base treatment of SAPO-11 slightly reduces the concentration of Brønsted sites, while the number of Lewis sites is substantially increased. Moreover, the amount of Brønsted acid sites associated with the external surface is largely enhanced. The behavior of zeotypes, that is, AlPOs, SAPOs, and zeolites, in acid and basic aqueous solutions is generalized, highlighting the role of charge balancing cations. Catalytic evaluation of SAPO-11 shows the potential of base-treated samples in the alkylation of benzyl alcohol with toluene.

Effect of carbon, sulfur and silicon on iron melting at high pressure: Implications for composition and evolution of the planetary terrestrial cores

High-pressure melting experiments in the Fe–S–C ternary and Fe–S–Si–C quaternary systems have been conducted in the range of 3.5–20GPa and 920–1700°C in the multi-anvil press. The mutual solubility, melting relations, and crystallization sequences were systematically investigated with changes of pressure, temperature and bulk composition. Five starting materials of Fe(84.69wt%)–C(4.35wt%)–S(7.85wt%), Fe(84.87wt%)–C(2.08wt%)–S(11.41wt%), Fe(86.36wt%)–C(0.96wt%)–S(10.31wt%), Fe(85.71wt%)–C(0.33wt%)–S(11.86wt%) and Fe(82.95wt%)–C(0.66wt%)–S(13.7wt%)–Si(2.89wt%) were employed. For Fe(84.69wt%)–C(4.35wt%)–S(7.85wt%), the first crystallized phase is Fe3C at 5GPa and Fe7C3 at 10–20GPa. For Fe(84.87wt%)–C(2.08wt%)–S(11.41wt%), Fe3C is the stable carbide at subsolidus temperature at 5–15GPa. For Fe(86.36wt%)–C(0.96wt%)–S(10.31wt%) and Fe(85.71wt%)–C(0.33wt%)–S(11.86wt%), the first crystallized phase is metallic Fe instead of iron carbide at 5–10GPa. The cotectic curves in Fe–S–C ternary system indicate only a small amount of C is needed to form an iron carbide solid inner core with the presence of S. Experiments on Fe(82.95wt%)–C(0.66wt%)–S(13.7wt%)–Si(2.89wt%) showed that a small amount of C does not significantly change the closure pressure of miscibility gap compared with that in Fe–S–Si system. It is observed that S preferentially partitions into molten iron while a significant amount of Si enters the solid phase with temperature decrease. Meanwhile, the C concentration in the liquid and solid iron metal changes little with temperature variations. If S, C and Si partitioning behavior between molten iron and solid iron metal with temperature remains the same under Earth’s present core pressure conditions, the solid inner core should be iron dominated with dissolved Si. On the other hand, the liquid outer core will be S rich and Si poor. Moderate carbon will be evenly present in both solid and liquid cores. Based on our melting data in a multi-component system, no layered liquid core should exist in the Earth, Mars and Mercury.

Staurolite porphyroblast controls on local bulk compositional and microstructural changes during decompression of a St–Bt–Grt–Crd–And schist (Ancasti metamorphic complex, Sierras Pampeanas, W Argentina)

AbstractThe staurolite–biotite–garnet–cordierite–andalusite–plagioclase–muscovite–quartz metapelitic mineral assemblage has been frequently interpreted in the literature as a result of superimposition of various metamorphic events, for example, in polymetamorphic sequences. The assemblage was identified in schists from the Ancasti metamorphic complex (Sierras Pampeanas of Argentina) where previous authors have favoured the polymetamorphic genetic interpretation. A pseudosection in the MnNCKFMASH system for the analysed XRF bulk composition predicts the stability of the sub‐assemblage staurolite–biotite–garnet–plagioclase–muscovite–quartz, and the compositional isopleths also agree with measured mineral compositions. Nevertheless, the XRF pseudosection does not predict any field with staurolite, andalusite and cordierite being stable together. As a result of more detailed modelling making use of the effective bulk composition concept, our interpretation is that the staurolite–biotite–garnet–plagioclase–muscovite–quartz sub‐assemblage was present at peak metamorphic conditions, 590 °C and 5.2 kbar, but that andalusite and cordierite grew later along a continuous P–T path. These minerals are not in mutual contact and are observed in separate microstructural domains with different proportions of staurolite. These domains are explained as a result of local reaction equilibrium subsystems developed during decompression and influenced by the previous peak crystal size and local modal distribution of staurolite porphyroblasts that have remained metastable. Thus, andalusite and cordierite grew synchronously, although in separate microdomains, and represent the decompression stage at 565 °C and 3.5 kbar.

Long length scales of element transport during reaction texture development in orthoamphibole-cordierite gneiss: Thor-Odin dome, British Columbia, Canada

First-order factors controlling the textural and chemical evolution of metamorphic rocks are bulk composition and pressure–temperature–time (P–T–t) path. Although it is common to assume that major element bulk composition does not change during regional metamorphism, rocks with reaction textures such as corona structures record evidence for major changes in effective bulk composition (EBC) and therefore provide significant insight into the scale, pathways, and mechanisms of element transport during metamorphism. Quantifying changes in EBC is essential for petrologic applications such as calculation of phase diagrams (pseudosections). The progressive growth of complex corona structures on garnet and Al2SiO5 porphyroblasts in orthoamphibole-cordierite gneiss Thor-Odin dome (British Columbia, Canada) reduced the EBC volume of the rock during metamorphism and therefore had a dramatic effect on the evolution of the stable mineral assemblage. These rocks contain a chemical and textural record of metamorphic reactions and preserve 3D networks (reaction pathways) connecting corona structures. These coronal networks record long (>cm) length scales of localized element transport during metamorphism. P–T, T–X, and P–X pseudosections are used to investigate the control of effective bulk composition on phase assemblage evolution. Despite textural complexity and evidence for disequilibrium, mineral assemblages and compositions were successfully modeled and peak metamorphic conditions estimated at 750°C and 9 kbar. These results illustrate how textural and chemical changes during metamorphism can be evaluated using an integrated petrographic and pseudosection approach, highlight the importance of effective bulk composition choice for application of phase equilibria methods in metamorphic rocks, and show how corona structures can be used to understand the scale of compositional change and element transport during metamorphism.

Quantitative measurements of apoptotic cell properties using acoustic microscopy

Time-resolved acoustic microscopy was used to measure properties of cells such as the thickness, sound velocity, acoustic impedance, density, bulk modulus, and attenuation, before and after apoptosis. A total of 12 cells were measured, 5 apoptotic and 7 non-apoptotic. Measurements made at 375 MHz showed a statistically significant increase in the cell thickness from 13.6 ± 3.1 μm to 17.3 ± 1.6 μm, and in the attenuation from 1.08 ± 0.21 dB/cm/MHz to 1.74 ± 0.36 dB/cm/MHz. The other parameters, such as the sound velocity, density, acoustic impedance, and bulk modulus remained similar within experimental error. Acoustic images obtained at 1.0 GHz showed increased RF-signal backscatter and a clear delineation of the nucleus and cytoplasm from apoptotic cells compared with non-apoptotic cells. Extensive activity was observed optically and acoustically within apoptotic cells. Acoustic measurements made one minute apart showed variations in the ultrasonic backscatter but not attenuation in the cells, which indicated rapid structural changes were occurring but not changes in bulk composition. The normalized crosscorrelation coefficient was used to quantify the variations in the backscatter RF-signal during apoptosis by comparing the first RF signal measured to each successive RF signal every 10 s. A coefficient of 1 indicates strong correlation, whereas a coefficient of 0 indicates no correlation. An average correlation coefficient of 0.93 ± 0.05 was measured for non-apoptotic cells, compared with 0.68 ± 0.17 for apoptotic cells, indicating that the RF signal as a function of time varied rapidly during apoptosis.

WATER/ICY SUPER-EARTHS: GIANT IMPACTS AND MAXIMUM WATER CONTENT

Water-rich super-Earth exoplanets are expected to be common. We explore the effect of late giant impacts on the final bulk abundance of water in such planets. We present the results from smoothed particle hydrodynamics simulations of impacts between differentiated water(ice)-rock planets with masses between 0.5 and 5 M_Earth and projectile to target mass ratios from 1:1 to 1:4. We find that giant impacts between bodies of similar composition never decrease the bulk density of the target planet. If the commonly assumed maximum water fraction of 75wt% for bodies forming beyond the snow line is correct, giant impacts between similar composition bodies cannot serve as a mechanism for increasing the water fraction. Target planets either accrete materials in the same proportion, leaving the water fraction unchanged, or lose material from the water mantle, decreasing the water fraction. The criteria for catastrophic disruption of water-rock planets are similar to those found in previous work on super-Earths of terrestrial composition. Changes in bulk composition for giant impacts onto differentiated bodies of any composition (water-rock or rock-iron) are described by the same equations. These general laws can be incorporated into future N-body calculations of planet formation to track changes in composition from giant impacts.

Generating High Mg-numbers and Chemical Diversity in Tonalite-Trondhjemite-Granodiorite (TTG) Magmas during Melting and Melt Segregation in the Continental Crust

Major, trace, and rare earth element compositions of both tonalite^ trondhjemite^granodiorite (TTG) and modern adakite-like magmas are typically used in conjunction with batch melting experiments and models to infer source rock composition, depth of melting and tectonic setting. However, batch melting does not capture the impact of melt segregation processes on magma geochemistry. We have used melting experiments in conjunction with numerical modelling to investigate the impact of melt segregation on TTG arc crust formation. Our melt segregation equilibrium (MSE) experiments are designed to reproduce the local changes in bulk composition that are predicted by the numerical model to occur as buoyant melt migrates upwards along grain boundaries and accumulates to form a magma that leaves the source region. The MSE experimental results show distinct differences in the melt and solid phase compositions and solid phase stability when compared with direct partial melting experiments. They yield a significant reduction in hornblende and plagioclase modal proportions at lower temperatures and partial melt compositions that are lower in An and have higher Mg-numbers. These results suggest that dynamic melt segregation and equilibrium processes may have a significant impact on modes, melt compositions and geochemical indicators such as Mg-numbers. Mantle wedge interaction may not be necessary to generate varying Mg-numbers in TTG and adakite magmas. Moreover, the use of batch melting models or experiments to interpret these geochemical signatures may not be appropriate.

COLLISIONAL STRIPPING AND DISRUPTION OF SUPER-EARTHS

The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to ~5v esc) collisions between 1 and 10 M ⊕ planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.

Metasomatic interaction between disseminated nickel sulphides and reduced metamorphic fluids, Honeymoon Well komatiite complex, Western Australia

Within the Honeymoon Well komatiite complex located within the Archaean Agnew-Wiluna greenstone belt, Western Australia, disseminated Ni sulphide deposits are hosted by completely serpentinised olivine-rich cumulates. These are unusual deposits as they contain large tonnages of mineralisation that are devoid of Cu despite containing up to >2%Ni and having magmatic Co and PGE values. About 55% of the 43 Mt Hannibals deposit consists of this style of mineralisation. The Cu distribution is spatially and geochemically related to bulk-rock changes in S and Fe with the Cu-absent parts of the deposit being variably depleted in these elements. Mimicking these changes in bulk composition is a zonation in sulphide–oxide assemblages of Ni-poor pentlandite-magnetite±pyrrhotite±chalcopyrite, pentlandite-magnetite±chalcopyrite, Ni-rich pentlandite-heazlewoodite±magnetite, and heazlewoodite-only with the latter occurring in zones showing the strongest S and Fe depletion. The sulphide mineral assemblages and bulk compositions correspond to variations in the non-sulphide mineralogy with much of the heazlewoodite mineralisation hosted by lizardite-iowaite±brucite-(magnetite absent) assemblages. Formation of highly reduced fluids during serpentinisation of olivine adcumulate and mesocumulate host sequences resulted in dissolution of sulphides in parts of the disseminated deposits. Copper, Co and Fe, soluble as chloride species, and S in the form of H2S were variably leached and removed from parts of the deposits. Passage of these reduced fluids through barren ultramafic rocks caused partial leaching of Fe and resulted in the formation of lizardite-rich alteration assemblages devoid of magnetite. Metamorphic Fe-Cu±Zn±Ni±Co bearing sulphides are common in pyroaurite-brucite magnetite veins and in former pyroxene-rich lithologies indicating the presence and mobility of these elements in some of the metamorphic fluids at Honeymoon Well. The location of the sulphide deposits immediately adjacent to major shear zones that bound the ultramafic complex allowed the infiltration and passage of large volumes of metamorphic fluids. During the lowermost greenschist facies metamorphism this caused semi-regional scale metasomatism of the ultramafic complex.

Petrological evolution of silica-undersaturated sapphirine-bearing granulite in the Paleoproterozoic Salvador–Curaçá Belt, Bahia, Brazil

The Salvador–Curaçá Belt, located in São Francisco Craton, Brazil, was subjected to granulite facies metamorphism during the Paleoproterozoic orogeny ( c. 2.0 Ga). Well preserved in enclaves of silica-undersaturated sapphirine-bearing granulite occur in a charnockite outcrop located along a kilometric-scale shear zone. The sapphirine-bearing granulite preserves domains with distinct mineral assemblages that record interactions between melt and peritectic phases (orthopyroxene 1 + spinel 1 + biotite 1). Sapphirine was crystallized in the Si-poor cores of the enclaves, sillimanite and spinel–cordierite symplectites in the intermediate Si-rich domains between cores and margins, and garnet and quartz-bearing cordierite/biotite symplectites in Si-rich margins of the enclaves. Melt-rock interactions and metamorphism occurred at ultrahigh temperatures of 900–950 °C at 7.0–8.0 kbar pressures. The mineralogical evolution of the domains reflects not only the influence of changes in bulk composition in the equilibrium volume of the reactions but also P– T changes during orogeny evolution. Electron microprobe dating of monazite both in the sapphirine-bearing granulite and charnockite indicates UHT metamorphism timing at c. 2.08–2.05 Ga that is related to global Paleoproterozoic UHT metamorphic events that occurred during the Columbia supercontinent assembly.

Comparison of eruptive and intrusive samples from Unzen Volcano, Japan: Effects of contrasting pressure–temperature–time paths

Core samples from the conduit of Unzen Volcano, obtained only 9 years after cessation of the 1991–1995 eruption, exhibit important differences in physical characteristics and mineralogy, and subtle differences in bulk chemistry from erupted samples. These differences in the conduit samples reflect emplacement under a confining pressure where about half of the original magmatic water was retained in the melt phase, maintenance at hypersolidus temperature for some unknown but significant time span, and subsequent subsolidus hydrothermal alteration. In contrast, magma that extruded as lava underwent decompression to 1 atm with nearly complete loss of magmatic water and cooling at a sufficiently rapid rate to produce glass. The resulting hypabyssal texture of the conduit samples, while clearly distinct from eruptive rocks, is also distinct from plutonic suites. Given the already low temperature of the conduit (less than 200 °C, [Nakada, S., Uto, K., Yoshimoto, M., Eichelberger, J.C., Shimizu, H., 2005. Scientific Results of Conduit Drilling in the Unzen Scientific Drilling Project (USDP), Sci. Drill., 1, 18–22]) when it was sampled by drilling, this texture must have developed within a decade, and perhaps within a much shorter time, after emplacement. The fact that all trace-element concentrations of the conduit and the last-emplaced lava of the spine, 1300 m above it, are identical to within analytical uncertainty provides strong evidence that both were produced during the same eruption sequence. Changes in conduit magma that occurred between emplacement and cooling to the solidus were collapse of vesicles from less than or equal to the equilibrium value of about 50 vol.% to about 0.1 vol.%; continued resorption of quartz and reaction of biotite phenocrysts due to heating of magma prior to ascent by intruding mafic magma; breakdown of hornblende; and micro-crystallization of rhyolitic melt to feldspar and quartz. Subsolidus changes were deposition of calcite and pyrite, growth of sericite in anorthite-rich zones of plagioclase, and development of montmorillonite as an alteration product. Significant changes in bulk composition were depletion of Mg, Fe and Na and enrichment in C and S. These changes were due mainly to the breakdown of hornblende and plagioclase, and addition of carbonate and pyrite, respectively. The identical concentrations of REEs in the conduit and surface lava are consistent with low water to rock ratios during alteration. This suggests to us that despite convective hydrothermal removal of heat from the conduit, chemical open-system effects were limited to early loss of magmatic water and later addition of magmatic CO 2 and SO 2 and/or H 2S streaming up the conduit from deeper levels.

Bulk-compositional changes of Ni 2Al 3 and NiAl 3 during ion etching

Bulk-compositional changes of Ni 2Al 3 and NiAl 3 in a Ni-50 wt% Al alloy during ion etching have been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopic analyses. After etching with 7, 5 and 3 keV Ar + ions for 15, 24 and 100 h nickel contents in both Ni 2Al 3 and NiAl 3 exceeded greatly those in the initial compounds and increased with the decrement of the sputtering energy. After 100 h etching with 3 keV Ar + ions the compositions of these two compounds reached a similar value, about Ni 80–83Al 12–15Fe 3–4Cr 1–2 (at%). A synergistic action of preferential sputtering, radiation-induced segregation and radiation-enhanced diffusion enables the altered-layers at the top and bottom of the film extend through the whole film. The bulk-compositional changes are proposed to occur in the unsteady-state sputtering regime of ion etching and caused by an insufficient supply of matter in a thin film.

Impact of melt segregation on tonalite-trondhjemite-granodiorite (TTG) petrogenesis

Abstract“In searching for the origin of granites, it is tempting to view them as purely chemical systems”(Pitcher 1979, p. 90)Although sophisticated geochemical studies tell us that tonolite-trondhjemite-granodiorite (TTG) plutonic complexes must be formed by partial melting of metabasaltic source material, they cannot tell us the tectonic regime in which this crust was formed, nor how large volumes of TTG magma can be generated. This study suggests that a solution to TTG arc crust formation requires a strongly interdisciplinary approach, to resolve the tectonic setting (slab melt verses mafic lowermost crust sources), the time and length scales for melting and extraction, and the role of melt segregation mechanisms in the formation of both Archean TTGs and more recent adakite-like magmas. The aim of this paper is to present an experimental approach which, when coupled with numerical models, allows some of these issues to be addressed. The experiments are designed to reproduce the local changes in bulk composition that are predicted to occur in response to buoyancy-driven melt segregation along grain edges and associated compaction of the solid residue. The preliminary study presented here documents the changes we observe in the melt composition and melt and solid phase modes between earlier direct partial melting and the new segregation equilibration experiments on metabasalt bulk compositions. The results suggest that if dynamic melt segregation and equilibrium processes are active, they may modify the normally robust geochemical indicators, such as Mg-numbers, which are typically used to develop models of TTG petrogenesis.

XRMapAnal: A program for analysis of quantitative X-ray maps

Software for processing quantitative X-ray maps collected on an electron probe microanalyzer is described. The techniques used in collection of maps and capabilities of the software to produce data useful for petrologic analysis are illustrated using three examples from pelitic schists from Mica Creek, British Columbia. The program utilizes a Bence-Albee algorithm to convert raw X-ray counts at each map pixel to wt% oxide, and allows for spectrometer deadtime corrections and background subtraction. Additional features include phase identification, modal analysis, calculation of cations, calculation of integrated rock composition over specified regions of the map, display of maps and compositional graphs, output of compositional statistics, and the ability to remove pixels and screen for bad analyses. The first example utilizes a sample lacking phases with significant chemical zonation, and outlines the basic functionality of the program. The second example compares an integrated map composition to an X-ray fluorescence analysis on the same rock chip. The results indicate it is possible to obtain integrated map compositions approaching that obtained from an X-ray fluorescence analysis. The third example compares mean X-ray map compositions for individual phases to means obtained using routine point analysis procedures, and the results indicate mean phase compositions obtained from the X-ray maps are of generally high quality. The sample in this example contains compositionally zoned garnet, and is used to show the ability to remove selective portions of garnet to model the approximate change in effective bulk composition during garnet growth.

Compatibility of high pressure cleaning mixtures with a porous low dielectric constant film: A positronium annihilation lifetime spectroscopic study

High pressure CO2 based cleaning mixtures have recently been proposed as an environmentally benign approach for postplasma etch residue removal. These mixtures must remove etch residues without damaging the low-k dielectric film that will be used to isolate interconnect structures in future generation devices. In this work, the compatibility of a CO2-based mixture with a porous low-k film is evaluated. Positronium annihilation lifetime spectroscopy (PALS) is used to monitor the change in pore size and film chemistry in a porous methyl silsesquioxane film after treatments under several different elevated pressure conditions. Spectroscopic ellipsometry and infrared spectroscopy are used to complement the PALS technique in order to better understand cleaning mixture effects on the dielectric film. CO2–TMAHCO3–methanol mixtures cause negligible changes in pore dimensions and bulk composition of the film. The high pressure treatments cause a small decrease in positronium formation which may be attributed to co...

THE HYPABYSSAL 5034 KIMBERLITE OF THE GAHCHO KUE CLUSTER, SOUTHEASTERN SLAVE CRATON, NORTHWEST TERRITORIES, CANADA: A GRANITE-CONTAMINATED GROUP-I KIMBERLITE

We present petrographic, mineralogical, geochemical and isotopic data on the 5034 kimberlite of the Cambrian Gahcho Kue kimberlite cluster (Slave craton, northern Canada). This Group-IA kimberlite is a multiphase intrusion composed of the diatreme-facies magmatic and hypabyssal kimberlite, which intruded in at least four magmatic phases. The dominant hypabyssal phase is composed of macrocrystal monticellite – phlogopite – serpentine kimberlite. Occasional samples with diopside ± melilite may reflect local heterogeneities in the bulk composition or separate intrusive phases. Aphanitic monticellite – serpentine kimberlite forms as early and contemporaneous small-volume magmas and is present in autoliths and in cross-cutting dykes. The subsequent explosive magmatic phase formed tuffisitic kimberlite breccia, which in turn is cut by macrocrystal phlogopite – serpentine kimberlite. The phlogopite in all recognized hypabyssal rock-types has distinct compositional trends, but within a given rock-type, it also varies significantly in response to local chemical heterogeneities and to the composition of minerals adjacent to it. The large variability in phlogopite compositions is due to very local diffusion-controlled crystallization, and not to changes in bulk composition of the magma. All varieties of the 5034 kimberlite show strong evidence of contamination by host granitic rocks. Pectolite, diopside, melilite and phlogopite have replaced and crystallized around partly assimilated granitic xenoliths from a hybrid melt enriched in Si and Na. A high activity of Si may be the major factor controlling the presence of melilite in kimberlites. The mineralogical character of the 5034 kimberlite, which is intermediate between Group-I and Group-II kimberlites, can be explained by its strong contamination by granites. The composition of the kimberlite in terms of Sr and Nd isotopes suggests an asthenospheric origin of the melt and allows for incorporation of no more than 8–12% granitic material into the parental magma.

Experimental Constraints on the Conditions of Formation of Highly Calcic Plagioclase Microlites at the Soufrire Hills Volcano, Montserrat

High-pressure and -temperature experiments on a bulk-rock composition representative of the groundmass of the Soufrière Hills Volcano andesite have allowed the phase equilibria of the system to be determined; these are then compared with the natural samples. Experimental conditions varied from 825 to 1100°C and from 5 to 225 MPa; the main phases observed were clinopyroxene, crystalline silica, amphibole and plagioclase. A relationship between plagioclase microlite size and anorthite content is identified in samples of the natural andesite. Large crystals (>60 µm2 in area) have cores of An60–75, whereas small crystals (<60 µm2 in area) have cores of An40–60. Experimental results show that if the magma is heated to >950°C the high-anorthite microlite crystals can form at magma chamber pressures without any need for a change in bulk composition. It is proposed that convective self-mixing occurs within the magma chamber. Geothermometry of coexisting plagioclase–amphibole pairs confirms the complex crystallization history of the natural samples. Analysis of natural glass samples has identified compositional variations that can be related to the crystallinity of the sample and also the groundmass plagioclase composition. Rapidly erupted pumice samples have high glass contents, lower SiO2 glass compositions and plagioclase microlites that are large in size (>60 µm2) and have a high anorthite content (>An60). Slowly erupted dome samples are highly crystalline and contain numerous plagioclase microlites of variable size and composition.

Chemical and physical responses to deformation in micaceous quartzites from the Tauern Window, Eastern Alps

AbstractMicaceous quartzites from a subvertical shear zone in the Tauern Window contain abundant quartz clasts derived from dismembered quartz‐tourmaline veins. Bulk plane strain deformation affected these rocks at amphibolite facies conditions. Shape changes suggest net shortening of the clasts by 11–64%, with a mean value of 35%. Quartz within the clasts accommodated this strain largely via dislocation creep processes. On the high‐stress flanks of the clasts, however, quartz was removed via solution mass transfer (pressure solution) processes; the resulting change in bulk composition allowed growth of porphyroblastic staurolite + chlorite ± kyanite on the clast flanks. Matrix SiO2 contents decrease from c. 83 wt% away from the clasts to 49–58% in the selvages on the clast flanks. The chemical changes are consistent with c. 70% volume loss in the high‐stress zones. Calculated shortening values within the clast flanks are similar to the volume‐loss estimates, and are greatly in excess of the shortening values calculated from the clasts themselves. Flow laws for dislocation creep versus pressure solution imply large strain‐rate gradients and/or differential stress gradients between the matrix and the clast selvages. In a rock containing a large proportion of semirigid clasts, weakening within the clast flanks could dominate rock rheology. In our samples, however, weakening within the selvages was self limiting: (1) growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution; and (2) overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix, which would have reduced the driving force for solution‐transfer creep. Extreme chemical changes nonetheless occurred over short distances. The necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities, and overall weakening of the rocks may result. Solution‐transfer creep may be a major process whereby weakening and strain localization occur during deep‐crustal metamorphism of polymineralic rocks.