High pressure transitions in the system KAlSi3O8-NaAlSi3O8

Phase relations in the system KAlSi₃O₈-NaAlSi ₃O₈ have been examined at pressures of 5–23 GPa and temperatures of 700–1200° C. KAlSi₃O₈ sanidine first dissociates into a mixture of wadeite-type K₂Si₄O₉, kyanite and coesite at 6–7 GPa, which further recombines into KAlSi₃O₈ hollandite at 9–10 GPa. In contrast, NaAlSi₃O₈ hollandite is not stable at 800–1200° C near 23 GPa, where the mixture of jadeite plus stishovite directly changes into the assemblage of calcium ferrite-type NaAlSiO₄ plus stishovite. Phase relations in the system KAlSi₃O₈-NaAlSi₃O₈ at 1000° C show that NaAlSi₃O₈ component gradually dissolves into hollandite with increasing pressure. The maximum solubility of NaAlSi₃O₈ in hollandite at 1000° C was about 40 mol% at 22.5 GPa, above which it decreases with pressure. Unit cell volume of the hollandite solid solution decreases with increasing NaAlSi₃O₈ component. The hollandite solid solution in this system may be an important candidate as a host mineral of K and Na in the uppermost lower mantle     

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.     

Types of quaternary volcanic activity in Northeastern Japan

The northeastern Japan forms a typical arcuate structure with a remarkable zonal arrangement of many geologic features, including the distribution of Quaternary volcanoes. Thus two distinct zones of volcanoes are noted here: i. e., Nasu zone on the east and Tyokai zone on the west. Some of the volcanoes of Nasu zone are characterized by the presence of pumice flows or pumice falls, sometimes of very large scales. These pumice flows belong to the calc-alkali rock series. While pumice flows or falls are rare in the Tyokai zone, where they are present though on small scale. Migration of the center of activity is noted along linear fissures, running either from east to west, or north to south at some volcanoes of Nasu zone, and consequently large swarms of volcanoes are common in this zone. While central eruption with definite center is typical of the Tyokai zone. From the petrographical and petrochemical study on the lavas and pyroclastics the original magma of the Nasu zone is estimated to be tholeiitic, and that of the Tyokai zone high-alumina basaltic. Abundant calc-alkali rocks are derived from these parental magmas. Thus the difference in the volcanic activity should be ascribed to the different nature of the parental magmas or the magmas derived from them.     

1996 COMPILATION OF ANALYTICAL DATA ON NINE GSJ GEOCHEMICAL REFERENCE SAMPLES, "SEDIMENTARY ROCK SERIES"

Analytical data compiled on nine Geological Survey of Japan (GSJ) reference samples, "Sedimentary rock series" received by February 1996 are reported. After excluding outliers and examining critically the analytical procedures employed, the data were evaluated statistically. Recommended or preferable values for fifteen major and sixty minor and trace elements are proposed.     

Jurassic and Lower Cretaceous radiolarian zonation in Japan and in the western Pacific

Abstract A radiolarian zonal scheme for the entire Jurassic and Lower Cretaceous using biostratigraphic data from both Japanese Island sections and the western Pacific seafloor is documented. The zonation is applicable to low and middle paleolatitude portions of the Paleo-Pacific ocean. Radiolarian bio-events such as the evolutionary first appearance biohorizon, first occurrence biohorizon, and last occurrence biohorizon were used to define zones. The 11 zones proposed are, in ascending order, Parahsuum simplum, Trillus elkhornensis, Laxtorum(?) jurassicum, Tricolocapsa plicarum, Tricolocapsa conexa, Stylocapsa(?) spiralis, Hsuum maxwelli, Pseudodictyomitra primitiva, Pseudodictyomitra carpatica, Cecrops sep-temporatus, and Acanthocircus carinatus zones. Preliminary age assignments for these zones are presented.     

Numerical simulation of mitigation for liquefaction-induced soil deformations in a sandy ground improved by cement grouting

This paper presents a numerical study of mitigation for liquefaction during earthquake loading. Analyses are carried out using an effective stress based, fully coupled, hybrid, finite element-finite differences approach. The sandy soil behavior is described by means of a cyclic elastoplastic constitutive model, which was developed within the framework of a nonlinear kinematic hardening rule. In theory, the philosophies of mitigation for liquefaction can be summarized as two main concepts, i.e. prevention of excess pore water pressure generation and reduction of liquefaction-induced deformations. This paper is primarily concerned with the latter approach to liquefaction mitigation. Firstly, the numerical method and the analytical procedure are briefly outlined. Subsequently, a case-history study, which includes a liquefaction mitigation technique of cement grouting for ground improvement of a sluice gate, is conducted to illustrate the effectiveness of liquefaction countermeasures. Special emphasis is given to the computed results of excess pore water pressures, displacements, and accelerations during the seismic excitation. Generally, the distinctive patterns of seismic response are accurately reproduced by the numerical simulation. The proposed numerical method is thus considered to capture the fundamental aspects of the problems investigated, and yields results for design purposes. From the results in the case, excess pore water pressures eventually reach fully liquefied state under the input earthquake loading and this cannot be prevented. However, liquefaction-induced lateral spreading of the foundation soils can be effectively reduced by the liquefaction mitigation techniques. An erratum to this article can be found at     

A meta-modeling approach for spatio-temporal uncertainty and sensitivity analysis: an application for a cellular automata-based Urban growth and land-use change model

The paper presents a computationally efficient meta-modeling approach to spatially explicit uncertainty and sensitivity analysis in a cellular automata (CA) urban growth and land-use simulation model. The uncertainty and sensitivity of the model parameters are approximated using a meta-modeling method called polynomial chaos expansion (PCE). The parameter uncertainty and sensitivity measures obtained with PCE are compared with traditional Monte Carlo simulation results. The meta-modeling approach was found to reduce the number of model simulations necessary to arrive at stable sensitivity estimates. The quality of the results is comparable to the full-order modeling approach, which is computationally costly. The study shows that the meta-modeling approach can significantly reduce the computational effort of carrying out spatially explicit uncertainty and sensitivity analysis in the application of spatio-temporal models.     

Next steps in geoengineering scenario research: limited deployment scenarios and beyond

Climate engineering has received increasing attention, but its discussion has remained on the sidelines of mainstream climate policy. The policy relevance of this previously exotic option is poised to rise because of the gap between the temperature goals of the Paris Agreement and slow global mitigation efforts. It is therefore crucial to understand the risks and benefits of the proposed schemes, and the social implications of policy choices. Assessment of the risks and benefits of solar geoengineering strongly depends on scenarios, but previous scenarios have not reflected the full range of social choices. In light of concerns over risks, a newer set of scenarios is desirable, which represents both uncertainties and social choices more fully. Borrowing and extending lessons from recent literature on the new community climate scenario process, we envision a possible scenario-building process that combines interdisciplinary scholarship with the involvement of stakeholders and citizens. The resultant scenarios would better characterize uncertainties of, and policy choices for, solar geoengineering, and foster critical appraisal of its risks and benefits. Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature. The interaction between scenario and governance research would be able to highlight the central issues at stake, including ethical, social, and political dimensions.

Key policy insights

• A more comprehensive assessment of solar geoengineering is necessary to evaluate its risks and benefits, necessitating new scenario research

• It is crucial to reflect the full span of policy choices and uncertainties with interdisciplinary collaboration in such scenarios

• Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature

• Participatory scenario research would enable incorporating the concerns and opinions of stakeholders and citizens in scenario creation