Increase Of SiO Research Articles

Novel zeolite transformations: The template-mediated conversion of Cubic P zeolite to SSZ-13

A study of the synthesis of zeolite SSZ-13 (a high-silica chabazite) from sodium silicate solutions showed the transient formation of Cubic P zeolite. The N,N,N,-trimethyl ammonium-I-adamantane organocation converted Cubic P to the secondary zeolite product with an increase in SiO 2 /Al 2 O 3 during the process. pH increase during the secondary zeolite formation was shown to be correlated with SiO 2 /Al 2 O 3 increase in the product. The use of an ion-selective electrode for organocations and its application in kinetic analysis of zeolite crystallization are described. The advantages of a study of this zeolite system in the absence of a hydrogel phase are discussed in terms of mechanisms of zeolite crystallization.

Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the Southern Andes

Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33–46°S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49–54°S) range for 87Sr/ 86Sr from 0.70280 to 0.70591 and for 143Nd/ 144Nd from 0.51314 to 0.51255. The ranges are significantly greater than previously reported from the southern Andes but are different from the isotopic compositions of volcanoes in the central and northern Andes. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have 87Sr/ 86Sr , 143Nd/ 144Nd , La/Yb, Ba/La, and Hf/Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35°S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33° and 34°S, basaltic andesites and andesites have higher 87Sr/ 86Sr , Rb/Cs, and Hf/Lu, and lower 143Nd/ 144Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54°S) has Sr and Nd isotopic compositions and KR/b and Ba/La similar to MORB. The high La/Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO 2, K 2O, Rb, Ba, Ba/La, and 87Sr/ 86Sr/ and decrease in MgO, Sr, KR/b, Rb/Cs, and 143Nd/ 144Nd , suggesting increasingly greater degrees of fractional crystallization and associated intra-crustal contamination.

Structural transformation of the TiO 2SiO 2 system gel during heat-treatment

The gel formation of the (100- x)TiO 2· xSiO 2 ( x = 0–10 mol%) system has been studied. The progressive elimination of residues was followed by DTA and TGA curves. DTA curves showed that the formation of anatase during heat treatment could be sensibly slowed down with the increase of SiO 2. The relationship between the gel composition and crystallization temperature of anatase has been systematically investigated. The X-ray diffraction spectra demonstrated that the crystallization temperature of anatase is 400°C for TiO 2 gel and 430°C for 90TiO 2 - 10SiO 2 gel. The infrared absorption spectra were used to follow the structural transformation of gels heat-treated at different temperatures. With the help of EPR it is evident that titanium ions exist only in tetravalence.

Petrology of nattanen-type granite complexes, northern finland

The Nattanen-type granites form a group of post-tectonic and post-metamorphic 1.77 Ga-old epizonal multiple granite intrusions in the Granulite Belt—granitic gneiss surroundings in northern Finland. The granite complexes (the Tepasto, Pomovaara and Nattanen stocks and the Riestovaara batholith in Finland and the Juvoaivi stock in the U.S.S.R.) are composed of various slightly peraluminous microcline—plagioclasebiotite granites (monzogranites) that contain sphene and magnetite as typical minor constituents. Geochemical evolution within the complexes is demonstrated by the increase of SiO 2, and Rb, and decrease of TiO 2, FeO ∗, MgO, CaO, Sr, Ba and Zr from the oldest to the youngest granite varieties. Molybdenum mineralization is associated with the latest intrusive phases of the Tepasto and Juvoaivi stocks. The isotope geochemical studies indicate a major Archaean crustal component in the source of the Nattanen stock that is situated within the early Proterozoic Granulite Belt.

X-ray diffraction analysis on the structure of the glasses in the system PbOSiO 2

The structures of PbO·SiO 2 and 2PbO·SiO 2 glasses have been analyzed by use of X-ray diffraction data and pair function method. For PbO·SiO 2 glass, a model consisting of chains of PbO 3 pyramids and silicate chains showed good agreement with the observed RDF. For 2PbO·SiO 2 glass, the present authors reported previously a model in which chains of PbO 3 pyramids are connected with SiO 4 tetrahedra, while the chromatographic analyses of silicate anions by Götz et al. and Smart et al. showed that silicate anions are distributed from monomer to polymer in the glass. We reexamined the structure of this glass referring to these results. Three representative models containing isolated SiO 4, Si 4O 12 rings and (SiO 3) n chains respectively as well as PbO 3 chains were constructed and the RDFs were calculated with changing structure parameters. These three models showed satisfactory agreement with the observed data, showing that silicate anions are distributed from monomer to polymer in 2PbO·SiO 2 glass and an increase of SiO 2 content leads to polymerization of silicate anions to longer chains up to PbO·SiO 2 composition, while the chains of PbO 3 pyramids remain unchanged.

Rare earth element geochemistry of Australian Paleozoic graywackes and mudrocks: Provenance and tectonic control

In the Paleozoic graywackes of eastern Australia there is an increase in the total abundance of rare earth elements (REE), a light to heavy REE ratio and a decrease in the chondrite normalized Eu anomaly with the increase in SiO 2/Al 2O 3 and K 2O/Na 2O ratios. This is due to the change in the dominant source rocks from andesite to dacite to granite-gneiss and sedimentary rocks. Similarly, an increase in total REE and a decrease in Eu anomaly is also seen in the associated mudrocks with the increase in total clay content. This correlation in Paleozoic sedimentary rocks suggests that the REE characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin. The oceanic island-arc-type graywackes are characterised by their lower total REE abundance, only slight enrichment of LREE over HREE, and the absence of a negative Eu anomaly on chondrite-normalised plots. The continental island arc type graywackes are discriminated by their higher REE abundance and La/Yb ratio, the presence of a small negative Eu anomaly on the chondrite normalised plots and the significant enrichment of Eu compared to PAAS (Post-Archean Average Australian Shale). The sedimentary rocks deposited on Andean-type active continental margins, passive margins, platform and cratonic basins are all characterised by the high enrichment of LREE over HREE and the presence of a pronounced negative Eu anomaly on chondrite-normalised plots and can not be discriminated from each other by REE patterns alone.

Geochemistry of Dras volcanics and the evolution of the Indus Suture ophiolites

The Indus Suture Zone, with many ophiolite occurrences, represents the northern limit of the Tethyan Himalaya. The volcanic rocks of the Dras ophiolite zone exhibit low TiO 2, K 2O, P 2O 5, SiO 2, Pb, Rb, Ba, Sr and Zr concentrations and lower La Yb ratios than the intraplate tholeiites. Intercalation of marine sediments, presence of pillow lavas, low K 2O, low to moderate TiO 2, high MgO, CaO TiO 2 and Al 2O 3 TiO 2 , flat REE patterns with lower La N Sm N ratios and increase of SiO 2, FeO (T) and TiO 2 with the fractionation indicate that they are island-arc tholeiites similar to lavas of late Cretaceous age in Cyprus and Oman. These volcanics are postulated to have been derived from a tholeiitic magma generated by a high degree of partial melting and fractionation of mafic phases prior to the crystallization of plagioclase. The island-arc tholeiitic volcanism, the lack of major CA volcanic activity and the reported blueschist metamorphism of the Indus ophiolites suggest a palaeo-island arc development along the Indus Suture Zone along which the Tethys oceanic crust was consumed.

A geochemical study of metabasalts from a subduction complex in eastern Australia

East of the Peel Fault System, in the New England Fold Belt of eastern Australia, a base faulted sequence of mafic igneous rocks conformably overlain by chert, siltstone and minor sandstone, occurs in repeated slices forming a stacked sequence, tens of kilometres thick. The mafic rocks show extensive mineralogical alteration, but apart from the highly mobile alkali elements, bulk whole-rock compositions retain a strong igneous imprint. Two metabasalt groups are recognised. Group A shows a distinct tholeiitic fractionation trend with increasing FeO★, TiO 2, P 2O 5, FeO★ MgO , Zr and Y relative to only a small increase in SiO 2. The mean concentration of incompatible and immobile elements, and the composition of relict endiopsidic and augitic pyroxenes is similar to mid-ocean ridge tholeiites, particularly the more evolved ferrobasalts. Group-B metabasalts are alkalic in composition. They tend to have higher Al 2O 3, MgO, P 2O 5 and Zr, and lower FeO★ and Sr than Group-A basalts. Relict pyroxenes have high Ti and Al concentrations and are salites. These rocks were probably the product of oceanic within-plate volcanism. Both groups represent fragments of oceanic crust incorporated into a subduction complex along the eastern margin of the Australian continent.

Catalytic functionalities of supported sulfides: I. Effect of support and additives on the CoMo catalyst

CS hydrogenolysis (HDS) of thiophene, hydrogenation (HYD) of 1-hexene, and hydrocracking (HCG) of 2,4,4-trimethyl-1-pentene, were used as separate model test reactions to differentiate and assess the catalytic functionalities of sulfided CoMo catalysts, and their dependence on the nature of the support and incorporation of additives. Rate constants and relative catalyst activities for these three reaction types were determined. HDS and HYD activities of CoMo supported on different types of Al 2O 3 were higher, while the HCG activity was lower compared with CoMo supported on SiO 2Al 2O 3, SiO 2MgO, or TiO 2. For SiO 2Al 2O 3 supports both HDS and HYD activities decreased with increase in SiO 2 content from 10 to 75%, while HCG activity showed the opposite trend. Additives to a finished CoMo catalyst at 0.5% level caused variations in HDS and HCG activities, while HYD was essentially unaffected. HDS was promoted by NH 4HF 2 and NH 4Cl, but depressed by NaNO 3, Ca(NO 3) 2, and H 3BO 3. HCG was promoted by NH 4HF 2, NH 4Cl, and H 3BO 3. Additives at 5% level, prior to or after CoMo impregnation, showed a strong depressing effect on HDS and a lesser effect on HYD, while HCG was strongly promoted by NH 4HF 2, Ti isopropoxide, and H 3BO 3. The changes in catalytic functionalities are rationalized in terms of different interactions between CoMo phase, support, and additives.

Geochemistry of the Chakradharpur granite—Gneiss complex—A Precambrian trondhjemite body from West Singhbhum, Eastern India

The Chakradharpur Granite—Gneiss complex (CKPG) is exposed as an elliptical body within the arcuate metamorphic belt sandwiched between the Singhbhum Granite in the south and the Chotonagpur Granite—Gneiss to the north. It consists of an older bimodal suite of grey gneiss and amphibolites, intruded by a younger unit of pegmatitic granite. The bimodal suite represents the basement to the enveloping metasediments. The average major-element chemistry of the grey gneiss conforms to the definition of trondhjemite and includes both low-Al 2O 3 and high-Al 2O 3 types. The amphibolites can be grouped into a low-MgO and a high-MgO type. Rocks of the younger unit range in composition from granodiorite to quartz monzonite. The two granitic units also differ significantly in their Rb, Sr and Ba contents, and in the REE distribution pattern. The grey gneiss shows a highly fractionated REE pattern and a distinct positive Eu anomaly, with Eu/Eu * values increasing with increase in SiO 2 %. In samples of the younger granite, the REE pattern is less fractionated, with higher HREE abundance relative to the grey gneiss and usually shows a negative Eu anomaly. The two types of REE patterns in amphibolites are interpreted to represent the two broad groups identified on the basis of major element chemistry. On the basis of chemical data, a two-stage partial melting model for the genesis of grey gneiss is suggested, involving separation of hornblende and varying amounts of plagioclase in the residual phase. Varying amounts of plagioclase in the residuum result in the wide range of Al 2O 3 content of the partial melt from which the trondhjemites crystallised. Residual hornblende produces the highly fractionated REE pattern, but a relatively higher HREE content of the trondhjemites compared to those produced by separation of garnet in the residual phase. The high level of Ba together with moderate levels of Sr in the trondhjemites can also be explained by plagioclase in the residue, whose effectiveness in partitioning Ba compared to Sr is lower. Of the two groups of amphibolites, the low-MgO type shows relative depletion of LREE compared to the high-MgO type. It contains varying amounts of plagioclase and is tentatively suggested to represent the residue. The other group, with a slightly fractionated REE pattern (Ce N/ Yb N = 2.01), is generally considered to represent the source material for the trondhjemites. This may have been generated by 5–15% partial melting of mantle peridotites, containing higher concentrations of LIL elements than those which produced average Precambrian tholeiites. This first phase of partial melting resulted in the slightly fractionated REE pattern of these amphibolites. Derivation of the younger granitic unit from the trondhjemites can be ruled out on the basis of REE data alone. REE data suggest partial melting of metasediments to be the origin of these rocks. It is also possible that deeply buried volcanic rocks, similar to calc-alkaline components of greenstone belts, are the parent for this component.

Petrology, geochemistry and geochronology of the Chilka Lake igneous complex, Orissa state, India

The Chilka Lake igneous complex of Orissa, the largest known anortosite massif of the Indian Shield, occurs in a catazonal environment of high-grade metamorphics of the Eastern Ghats Precambrian Orogenic Province. The syntectonic massif consists of the anorthositic Balugaon dome, leuconoritic Rambha lobe and quartz-mangeritic Kallikota cover. A completely gradational suite comprising anorthosite-leuconorite-norite-minor jotunite (the anorthositic suite) constitutes most of the complex. The subordinate of suite of acid rocks spatially associated with this is of a broad quartz-mangeritic lithology with minor granitic rocks (the acidic suite). Geochemical evolution of the complex in the sequence anorthosite-leuconorite-norite-jotunite-acidic rocks shows moderate iron enrichment in the noritic-jotunitic stage and is marked by an overall decrease in Al 2O 3, CaO, MgO, Ni/Co, Sr/Ba, K/Rb and increase in SiO 2, K 2O, V/Ni, K/Ba and Rb/Sr. Such progressive variation in geochemical parameters appears (i) essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and (ii) rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies. RbSr whole rock isochron studies indicate that the complex was emplaced ca. 1400 Ma ago. The initial 87Sr/ 68Sr (0.70661) implies limited hybridisation of the parent magma prior to emplacement. A critical appraisal of all the available evidence suggests that (i) the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and (ii) the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes (the latter brought about by contact anatexis of the host rocks). The complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 Ma ago.

Contrasting fractionation patterns for sequential magmas from two calc-alkaline volcanoes in Central America

Two sequences of alternating units of lavas and pyroclastic rocks from two volcanoes in Central America were sampled and analysed. The rocks from Izalco, the smaller, more mafic cone, show a continuous increase in SiO 2, K 2O, Zr and La, and a decrease in CaO, MgO, Co and Cr with time. These trends are shown to be consistent with progressive crystal fractionation. Atitlán, a larger and more silicic volcano, displays a discontinuous trend in which geochemical reversals are thought to reflect the development of a series of small bodies of zoned magma. The lavas of each zoned section show decreases in SiO 2, K 2O, Hf and Ba, and increases in CaO, MgO, Co and V from the bottom of the section to its top. The different trends at Izalco and Atitlán are believed to reflect the restrictions cone height places on the effects of crystal fractionation. As cone height increases, the intervals between eruptions progressively lengthen, allowing more time for crystal fractionation to proceed. The two volcanoes may represent an early and a later stage in the general evolutionary development of large composite cones. Despite the remarkable regularity of the alternating flows and pyroclastic eruptions, no systematic chemical variations were recognized between the two types of lava.

Optical properties of the anisotropic C 3A

This study deals with optical properties of the anisotropic C 3A-form. With an increase in SiO 2 or Fe 2O 3 in the orthorhombic form of C 3A dispersion formula varies from v > r to v < r with different optic planes (010 and 100 respectively), so that for a certain intermediate content the optic planes for colors at the extremes of the visible spectrum are crossed. In the case of the monoclinic phase dispersion takes place by a rotation of the optic plane around the acute bisectrix X(= c). The characteristic abnormal interference color of the anisotropic C 3A can be explained by these various types of dispersion.

Petrology and chemistry of a Columbia River basalt section, Rocky Canyon, west-central Idaho

Field characteristics, petrography, and major-element analyses are given for 17 of the 19 flows of the Columbia River Group present in a canyon in the southeast corner of the Columbia Plateau. The 17 flows are divided into 4 flows of Imnaha Basalt at the base, 12 flows of lower Yakima Basalt above, and 1 flow of middle Yakima Basalt at the top. The 4 Imnaha Basalt members are feldsparphyric with lower SiO 2 (48.0 to 52.0 percent) and lower K 2 O (0.60 to 1.14 percent) than the lower Yakima Basalt. They may be subdivided into the upper two flows of Rock Creek chemical type that have less SiO 2 (48.8 to 50.5 percent) than the other two members. The Rock Creek flow has uniquely high values of Al 2 O 3 and MgO associated with high modal olivine. The lower two members may be distinguished from each other by their TiO 2 contents. The lower Yakima Basalt flows are fine grained and nonporphyritic with an intergranular to intersertal texture, SiO 2 varies from 52.0 to 56.6 percent and K 2 O varies from 1.14 to 2.00 percent. The earlier nine members show an increase in SiO 2 and K 2 O and a decrease in MgO upward; the top three members show a reversal of this trend. The less siliceous flows contain small subhedral olivine crystals or their pseudomorphs, and the more siliceous contain a pigeonitic in addition to an augitic clinopyroxene. Each member has a unique set of properties that is consistent vertically through the thickness of a flow and laterally between two sections 4 km apart and separated by a major fault. The top flow exposed, with phenocrysts of plagioclase and olivine, falls within the Pomona chemical type previously recorded only from upper Yakima Basalt. Flow-by-flow correlation can be made of the lower Yakima Basalt with the Whitebird section 20 km to the south. Thinning and cutting out of flows from north to south suggests that many flows are local in origin. Similar types of Imnaha Basalt occur at Rocky Canyon and Whitebird, but flow-by-flow correlation is less convincing.

Effect of [formula omitted] ratio on physicochemical properties of mordenite and activity for n-pentane isomerization

A series of acid mordenites having SiO 2 Al 2O 3 ratios from 12 to 97 was prepared for a study of their physical and catalytic properties. The removal of alumina by acid extraction results in a shrinkage in the unit cell. This is indicated by an increase in the frequency of the infrared lattice vibrations and a shift in the position of the X-ray diffraction lines. Infrared spectra show OH groups absorbing at 3740 and 3590 cm −1. The latter are no longer present on severely acid extracted mordenites. NH 3 adsorption isobars at 8 mm show that the surface acidity decreases in a regular manner with an increase in SiO 2 Al 2O 3 ratio. At the same time, acid treatment opens up more of the channels to permit the adsorption of Decalin. The mordenite becomes less resistant to the adsorptive diffusion of these large molecules. Catalysts containing 0.5% Pd were tested for the hydroisomerization of n-pentane. In this reaction, surface acidity appears to be the dominant factor and the catalyst activity decreases with an increase in SiO 2 Al 2O 3 ratio of the mordenite.

Boulder Creek Batholith, Colorado Part II: Isotopic Age of Emplacement and Morphology of Zircon

Zircon separated from six rocks whose compositions spanned the range of differentiation in the Boulder Creek batholith yielded a “discordia” age of emplacement of 1725 m.y., close to the average PB 207 /Pb 206 age 1720 m.y.) and indicating that the constituent rocks are cogenetic within approximately ± 20 m.y. Statistical studies show that from 20 to 80 percent of the zircon in any one sample (1) is no-neuhedral, (2) has lower (length/width) ratios than the associated euhedral zircon, and (3) in direct contrast to the euhedral, increases markedly interior of the batholith toward contacts with the older metasediments and internal zones of contamination; it is inferred to have been “inherited” via assimilation. Unlike the noneuhedral fraction the euhedral zircon shows a linear decrease in length/width ratio with an increase in SiO 2 content of the containing rocks; it is inferred to be magmatic in origin. Regardless of the relative abundance of inherited versus magmatic zircon, all samples closely fit a single discordia chord, indicating that both zircon fractions formed at about the same time. This conclusion is compatible with field relationships that indicate the emplacement of the syntectonic Boulder Creek rocks took place during a period of metamorphism notable for the widespread development of new minerals in the country rocks. (1) Zircon from a Silver Plume Granite dike intruding the Boulder Creek batholith, (2) zircon from Silver Plume correlatives immediately to the north (Tilton and co-workers), and (3) uraninite from a probable Silver Plume correlative in the Central City district, together yield a sharply defined discordia age of emplacement of 1415 m.y. The separate “discordia” chords for the Boulder Creek and Silver Plume zirconconverge close to their lower intercepts with “concordia” indicative of a one-step lead loss during the Laramide disturbance. The Silver Plume “thermal event” left no age imprint on the Boulder Creek zircon, presumably because insufficient time had elapsed to produce significant metamictization.

The contact phenomena on the north-west of the Crossdoney Complex, Co. Cavan

On the north-west of the Crossdoney Complex two gradational contacts are well exposed. The first, in the quarry north-west of Bellahillan Bridge, is between biotite-plagioclase-hornfels and porphyritic granodiorite with quartz-bearing monzonite and melanocratic granodiorite as linking rocks. The second, at Drummora Great, is between metamorphosed argillaceous greywacke and porphyritic granodiorite with quartz-diorite and biotite-hornblende-diorite as intermediate rocks. Also developed are small irregular lenticles and pods of hornfelso-tonalite within plagioclase-biotite-hornfels. Field relations and study of thin sections show that the irregular bodies are the result of metasomatic replacement. Textural, mineralogical and chemical evidence, and the gradational contacts between porphyritic granodiorite and the metamorphosed country rocks provide ample evidence that the igneous-looking rocks have developed as a replacement of country rocks without passing through a liquid state. The processes responsible for the transformation of greywackes are interpreted as desilication (feldspathisation and/or basification) followed by granitisation. Near the contact the hornfelses are enriched in biotite and hornblende, implying a chemical enrichment in Fe, Mg, Ca and K, that is, basification. The culmination of this enrichment is shown by the dioritic and monzonitic rocks. These basic enrichments are accompanied by enrichment and culmination of minor elements such as Ti, Mn and P. The results of feldspathisation are also illustrated by the rocks described. It is shown that the basified and feldspathised rocks approach and reach the composition either of tonalite by increase of SiO 2 or of granodiorite by increase of SiO 2 and alkalis, accompanied in each case by decrease of cafemic constituents.