Aenigmatite,sodic pyroxene,arfvedsonite and associated minerals in syenites from Morotu,Sakhalin

Aenigmatite, sodic pyroxene and arfvedsonite occur as interstitial minerals in metaluminous to weakly peralkaline syenite patches in alkali dolerite, Morotu, Sakhalin. Aenigmatite is zoned from Ca, Al, Fe³⁺-rich cores to Ti, Na, Mn, Si-rich rims reflecting the main substitutions Fe²⁺Ti⁴⁺Fe³⁺, NaSiCaAl and Mn²⁺Fe²⁺. Aenigmatite replaces aegirine and ilmenite supporting the existence of a no-oxide field in — T space. In one case aenigmatite has apparently formed by reaction between ilmenite and arfvedsonite. Titanian aegirine (up to 3.0 wt% TiO₂) and Fe-chlorite may replace aenigmatite. Sodic pyroxene occurs as zoned crystals with cores of aegirine-augite rimmed by aegirine and in turn by pale green aegirine containing 93 mol% NaFe³⁺Si₂O₆. Additional substitution of the type NaAlCaFe²⁺ is indicated by significant amounts (up to 6 mol%) of NaAlSi₂O₆. Arfvedsonite is zoned with rims enriched in Na, Fe and depleted in Ca which parallels the variation of these elements in the sodic pyroxenes.The high peralkalinity of the residual liquid from which the mafic phases formed resulted from the early crystallization of microperthite (which makes up the bulk of the syenites) leading to an increase in the Na₂O/(Na₂O+K₂O) and (Na₂O+K₂O)/Al₂O₃ ratios of the remaining interstitial liquid which is also enriched in Ti, Fe, and Mn. Bulk composition of the melt, , temperature and volatile content were all important variables in determining the composition and stability of the peralkaline silicates. in the residual liquid appears to have been buffered by arfvedsonite-aegirine and later by the arfvedsonite-aenigmatite and aenigmatite-aegirine equilibria under conditions of a no-oxide field. An increase in , above that of the alkali buffer reactions, is inferred by an increase of Ti and Mn in aenigmatite rims. The latest postmagmatic vapour crystallization stage of the syenites is marked by extremely low which may have been facilitated by exsolution of a gas phase. Low is supported by the replacement of aenigmatite by titanian aegirine, and the formation of rare Ti-rich garnet with a very low (Ti⁴⁺+Fe³⁺)/(Ti+Fe) ratio of 0.51, associated with leucoxene alteration of ilmenite.     

Effect of silica concentration on the diopsidic pyroxenes in the system diopside-CaTiAl2O6SiO2

The effect of silica concentration on the solubility of Al and Ti in diopsidic pyroxenes has been investigated at one atmosphere in the system diopside-CaTiAl₂O₆-SiO₂ at temperatures between 1150–1420° C. The composition of pyroxene in the system diopside-CaTiAl₂O₆-SiO₂ is influenced by the total SiO₂ content. Near the join diopside-CaTiAl₂O₆, the pyroxene forms a solid solution with the CaTiAl₂O₆ molecule, and co-exists with perovskite for compositions greater than 11 weight percent CaTiAl₂O₆. Anorthite is an accompanying phase. With increasing total SiO₂ content a series of mineralogical changes involving Ti-bearing phases occur. Sphene solid solution co-exists with diopside solid solution, anorthite, and perovskite in a small compositional range near the diopside-CaTiAl₂O₆ join. Additional total SiO₂ results in the elimination of perovskite and a decrease of solid solution in the pyroxenes. With further increase in SiO₂ content, tridymite appears and the pyroxene is approximately pure diopside. Rutile joins diopside, anorthite, sphene solid solution and tridymite over a broad compositional range in the Ti, Si-rich part of the system. These results demonstrate that increased silica concentration decreases the solubility of Al and Ti in diopsidic pyroxenes and controls the stability of co-existing Ti-bearing phases.     

Finite differencing of the advection term

The advection term in the finite difference diffusion equation can give rise to the false computational oscillation unless the ratio of the grid size to the coefficient of eddy diffusivity is smaller than a critical value. The slightly uncentered differencing scheme is useful for the advection term.     

Internnual variations of water temperature and salinity along the 137°E meridian

Analyses were performed on hydrographic data gathered along the 137°E meridian by the R/V Ryofu Maru of the Japan Meteorological Agency (JMA). Distributions were obtained of the mean and standard deviation of water temperature and salinity along the section. Relationships between interannual variations of these variables and wind forcing were examined. A correlation analysis revealed that temperature change, which occurred in the equatorial region of the western North Pacific accompanied by El Nino and La Nina events, reached about 20°N with the inclination of isotherms across the north equatorial current fluctuating around 20°N. Empirical orthogonal function (EOF) analysis of the winter water temperatures in the section was performed to extract variations following El Nino and La Nina events as the first mode and those corresponding to decadal changes of sea surface temperature (SST) in the North Pacific as the second mode. Interannual variations in the area of the North Pacific tropical saline water (NPTSW) and the North Pacific intermediate water (NPIW) along the section correspond well to interannual variations of the wind-stress curl minimum (negative value) in the area southeast of Japan. A remaining problem is to quantitatively evaluate the lag times of the variations to the wind-stress curl variation. In the equatorial region of the section, the northward extension of saline water is weak, and negative water temperature anomalies have often occurred in connection with El Nino events since the latter half of the 1970s. These changes may be part of the decadal variation of the North Pacific.     

Geochemical and mineralogical characteristics of ion-adsorption type REE mineralization in Phuket, Thailand

Geochemical and mineralogical studies were conducted on the 12-m-thick weathering profile of the Kata Beach granite in Phuket, Thailand, in order to reveal the transport and adsorption of rare earth elements (REE) related to the ion-adsorption type mineralization. The parent rock is ilmenite-series biotite granite with transitional characteristics from I type to S type, abundant in REE (592 ppm). REE are contained dominantly in fluorocarbonate as well as in allanite, titanite, apatite, and zircon. The chondrite-normalized REE pattern of the parent granite indicates enrichment of LREE relative to HREE and no significant Ce anomaly. The upper part of the weathering profile from the surface to 4.5 m depth is mostly characterized by positive Ce anomaly, showing lower REE contents ranging from 174 to 548 ppm and lower percentages of adsorbed REE from 34% to 68% compared with the parent granite. In contrast, the lower part of the profile from 4.5 to 12 m depth is characterized by negative Ce anomaly, showing higher REE contents ranging from 578 to 1,084 ppm and higher percentages from 53% to 85%. The negative Ce anomaly and enrichment of REE in the lower part of the profile suggest that acidic soil water in an oxidizing condition in the upper part mostly immobilized Ce⁴⁺ as CeO₂ and transported REE³⁺ downward to the lower part of the profile. The transported REE³⁺ were adsorbed onto weathering products or distributed to secondary minerals such as rhabdophane. The immobilization of REE results from the increase of pH due to the contact with higher pH groundwater. Since the majority of REE in the weathered granite are present in the ion-adsorption fraction with negative Ce anomaly, the percentages of adsorbed REE are positively correlated with the whole-rock negative Ce anomaly. The result of this study suggests that the ion-adsorption type REE mineralization is identified by the occurrence of easily soluble REE fluorocarbonate and whole-rock negative Ce anomaly of weathered granite. Although fractionation of REE in weathered granite is controlled by the occurrence of REE-bearing minerals and adsorption by weathering products, the ion-adsorption fraction tends to be enriched in LREE relative to weathered granite.     

Generalized method for non-linear seismic response analysis of a three dimensional soil–structure interaction system

Previous achievements using the dynamic non-linear analysis of an interaction system are reviewed briefly, after which a three dimensional (3D) model of the stress redistribution of soil based on the Mohr–Coulomb failure law is presented to evaluate the unbalanced tensor at every iteration in the load transfer method. A 3D, full non-linear analysis was used to examine the validity and accuracy of results obtained by 2D analysis by combining the model of redistributed stresses proposed here with the joint element model. Based on the numerical solution reported here, we concluded that both the 3D and 2D models of stress redistribution work well and reflect the yielding pattern of soil during excitation, but the former is more realistic. The failure area in the structural zone obtained by 3D analysis is slightly larger but similar to that obtained by 2D analysis. The ratio of maximum strain to yield strain and non-linear time ratio, β_s, for the soil elements in the structural zone are also a little larger. In contrast, the maximum separation values for the joint elements are much smaller and the separation pattern for the x-side wall interface is the reverse of that found by 2D analysis. These values, however, affect only responses in the short period range and the regions close to the interface. In general, the tendencies shown by 2D analysis for the effects of non-linear behaviour on structural responses are confirmed for the parameters investigated.     

Dynamic behaviour and identification of non-uniform ground by the discrete wave number method

Powell's method for minimizing a function of several variables without calculating derivatives is applied to recorded earthquake motion on the ground surface to identify ground characteristics that have irregular profiles. The identifications are made by designating the shear wave velocity depth and width of the irregularity of surface ground as unknown parameters and are based on the least square fit between the amplitude of the transfer function determined from accelerograms recorded at two observation sites and the corresponding transfer function calculated from the response analysis of a ground model. The discrete wave number method is used to analyze the response of ground with a non-uniform profile for the incidence of SH waves. The effect of the initial assumed values on the convergence is studied by evaluating the square error between the theoretical transfer function and that calculated from the parameters identified. The dispersive trend found for the accelerograms is explained by the calculated response of a ground model with a non-uniform profile.     

Welded tuffs and related pyroclastic deposits in northeastern Japan

Welded tuffs and related pyroclastic deposits are distributed at many localities in northeastern Japan, especially around the volcanoes of the Nasu volcanic zone running from north to south, but they are absent from the region along the Japan Sea. Their geological age varies from the Miocene to the Holocene, those of the Pleistocene being predominant in amount. Petrographically they cover rather a wide range from andesite to rhyolite, among which dacite is most common. The welded tuffs are always compact and hard, with well-developed columnar jointing, carrying parallel-layered obsidian lenticules; and various stages are observed from loose pyroclastic deposits to lava-like welded tuffs. Petrological, petrochemical, and physical properties of these deposits are studied in some detail. From these data some genetic consideration is given for the mechanism of welding, and also for the relation between the nature of parental magma and the formation of such pyroclastic deposits.     

Separation and sliding between soil and structure during strong ground motion

This paper presents an approach to the problem of separation and sliding between soil and structure in the finite element analysis of dynamic soil-structure interaction problems. Joint elements are arranged along the contact surface between soil and structure and they have a property such that tensile forces are not transmitted between the planes representing structure and soil in the finite element analysis. The dynamic properties governing the sliding are determined by the Mohr-Coulomb failure law determined from the cohesion and the friction angle between soil and structure. The proposed method is applied to (i) a model of a reactor building resting on the free surface of layered ground and (ii) a buried foundation structure. The numerical computations reveal the following results: that the translation is dominant in the motion of the structure when sliding is taking place between soil and structure, and that the rocking is dominant in the rest of the response. The amplitude of the response during sliding is increased on any one point of the structure and decreased on any one point of the ground compared with that of the fixed condition at the interface. In the case of the buried structure, it is observed in the computed results that the structure and soil move in the opposite direction along the vertical contact surface and are separated from each other in the near surface region during the strong phase of the excitation.