Rigid unit modes in the molecular dynamics simulation of quartz and the incommensurate phase transition

A molecular dynamics simulation of quartz at different temperatures both in the a and in the phase has been conducted. The - phase transition could be observed. A phonon analysis of the -phase confirms and rounds out in a quantitative way the origin of the incommensurate (ic) modulated phase. In particular it traces the optic soft mode at becoming (to a good approximation) a so-called rigid unit mode (RUM) at q0, and elucidates its coupling to the transverse acoustic mode which precipitates the incommensurate transition. This success underpins and illuminates the concept of RUMs and their role in structural phase transitions.     

A model of the galactic centre with magnetic monopoles

A model of the galactic centre with magnetic monopole has been presented here. The positron can be produced continuously through magnetic monopoles to induce baryon decay (Rubakov catalytic reaction) and a lot of energy can be released as well. The calculation results show that even if the galactic center contains only a few magnetic monopoles (=N _M/N_B10^–24), this massive object can not collapse into a black hole. This model can explain the observed intensities of the annihilation line and higher energy photons ofE >511 keV from the galactic centre.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Geochemistry of re and trace elements in ferromanganese nodules and their genesis

Trace and RE element geochemistry and genesis have been studied with respect to ferromanganese nodules from the sediments of the Pacific, Atlantic and Indian oceans.     

A possible mechanism of formation of faculae

We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is

$\text{16σT}{}^3{}_{\mathrm{p}}\text{(T}{}_{\mathrm{l}}\text{? T}{}_{\mathrm{p}}\text{)}{}^{\mathrm{n}}\text{HP}{}_{\mathrm{s}}{}^{\mathrm{a}}\text{H}{}^{\mathrm{?}}\text{=}\text{Qn}{}_{\mathrm{s}}\text{m}{}_{\mathrm{i}}\text{u}{}_{\mathrm{x}}{}^2\text{(τ}{}^2{}_{\mathrm{in}}\text{ω}{}_{\mathrm{i}}\text{)}$

.For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae.     

Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume; evidence from the basal alkaline basalts in Dongchuan, Yunnan, Southwestern China

The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO₂ contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high _{Nd (t)} values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P₂O₅ (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low _{Nd (t)} values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume.     

Zircon U–Pb ages, Hf and O isotopes constrain the crustal architecture of the ultrahigh-pressure Dabie orogen in China

The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative ε_Hf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive ε_Hf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ¹⁸O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ¹⁸O rocks. North Dabie shares the same age of Neoproterozoic low δ¹⁸O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower.     

Dehydration and melting during continental collision: Constraints from element and isotope geochemistry of low-T/UHP granitic gneiss in the Dabie orogen

A combined study of petrography, whole-rock major and trace elements as well as Rb?Sr and Sm?Nd isotopes, and mineral oxygen isotopes was carried out for two groups of low-T/UHP granitic gneiss in the Dabie orogen. The results demonstrate that metamorphic dehydration and partial melting occurred during exhumation of deeply subducted continent. Zircon δ¹⁸O values of ? 2.8 to + 4.7‰ for the gneiss are all lower than normal mantle values of 5.3 ± 0.3‰, consistent with ¹⁸O depletion of protolith due to high-T meteoric-hydrothermal alteration at mid-Neoproterozoic. Most samples have extremely low ⁸⁷Sr/⁸⁶Sr ratios at t₁ = 780 Ma, but very high ⁸⁷Sr/⁸⁶Sr ratios at t₂ = 230 Ma. This suggests intensive fluid disturbance due to the hydrothermal alteration of protoliths during Neoproterozoic magma emplacement and the metamorphic dehydration during Triassic continental collision. Rb–Sr isotopes, Th/Ta vs. La/Ta and Th/Hf vs. La/Nb relationships suggest that Group I gneiss experienced lower degrees of hydrothermal alteration, but higher degrees of dehydration, than Group II gneiss. The two groups of gneiss have similar patterns of REE and trace element partition. Group I gneiss displays good correlations between Nb and LREEs but no correlations between Nb and LILEs (Rb, Ba, Pb, Th and U), indicating differential mobilities of LILEs during the dehydration. Thus the correlation between Nb and LREEs is inherited from protolith rather than caused by metamorphic modification. Relative to Group I gneiss, Group II gneiss has stronger negative Eu anomaly, lower contents of Sr and Ba but higher contents of Rb, Th and U. In particular, Nb correlates with LILEs (e.g., Rb, Sr, Ba, Th and U), but not with LREEs (La and Ce). This may indicate decoupling between the dehydration and LILEs transport during continental collision. Furthermore, dehydration melting may have occurred due to breakdown of muscovite during “hot” exhumation. Group II gneiss has extremely low contents of FeO + MgO + TiO₂ (1.04 to 2.08 wt.%), high SiO₂ contents of 75.33 to 78.23 wt%, and high total alkali (Na₂O + K₂O) contents (7.52 to 8.92 wt.%), comparable with compositions predicted from partial melting of felsic rocks by experimental studies. Almost no UHP metamorphic minerals survived; felsic veins of fine-grain minerals occurs locally between coarse-grain minerals, resulting in a kind of metatexite migmatites due to dehydration melting without considerable escape of felsic melts from the host gneiss. In contrast, Group I gneiss only shows metamorphic dehydration. Therefore, the two groups of gneiss show contrasting behaviors of fluid–rock interaction during the continental collision.     

Estimation of groundwater recharge using the soil moisture budget method and the base-flow model

A detailed characterization of the site is crucial to designing an efficient method of managing the risks associated with tailings from abandoned mines. Therefore, samples collected from various depths within tailings in Guryong mine, Korea, were analyzed for their chemical, physical and mineralogical characteristics. All samples of the Guryong tailings had acid-generating potential. However, in the oxidation zone, the net acid generation (NAG) was low (30 kg H₂SO₄ t⁻¹) although the acid neutralization potential (ANP) was less than zero. The ANP values in the unoxidation zone were higher (> −56.0 kg CaCO₃ t⁻¹) than in the other zones. As a result, the amount of alkali ions that are needed to neutralize the acid needs to be considered. In this experiment G3, G4 and G6 drill cores containing fine tailings particles near the unoxidation zone were observed to contain calcite (CaCO₃) with acid-neutralizing capacity. A low pH (2−4) in the oxidation zone of the tailings changed to a neutral pH in the unoxidation zone of the tailings. These results suggest that the acid-neutralizing capacity of the tailings was controlled by particle and mineral composition of tailings.     

Numerical modeling of rainstorm-induced shallow landslides in saturated and unsaturated soils

For the assessment of shallow landslides triggered by rainfall, the physically based model coupling the infinite slope stability analysis with the hydrological modeling in nearly saturated soil has commonly been used due to its simplicity. However, in that model the rainfall infiltration in unsaturated soil could not be reliably simulated because a linear diffusion-type Richards’ equation rather than the complete Richards’ equation was used. In addition, the effect of matric suction on the shear strength of soil was not actually considered. Therefore, except the shallow landslide in saturated soil due to groundwater table rise, the shallow landslide induced by the loss in unsaturated shear strength due to the dissipation of matric suction could not be reliably assessed. In this study, a physically based model capable of assessing shallow landslides in variably saturated soils is developed by adopting the complete Richards’ equation with the effect of slope angle in the rainfall infiltration modeling and using the extended Mohr–Coulomb failure criterion to describe the unsaturated shear strength in the soil failure modeling. The influence of rainfall intensity and duration on shallow landslide is investigated using the developed model. The result shows that the rainfall intensity and duration seem to have similar influence on shallow landslides respectively triggered by the increase of positive pore water pressure in saturated soil and induced by the dissipation of matric suction in unsaturated soil. The rainfall duration threshold decreases with the increase in rainfall intensity, but remains constant for large rainfall intensity.     

Shear strength characterization of municipal solid waste at the Suzhou landfill, China

The current practice of slope stability analysis for a municipal solid waste (MSW) landfill usually overlooks the dependence of waste properties on the fill age or embedment depth. Changes in shear strength of MSW as a function of fill age were investigated by performing field and laboratory studies on the Suzhou landfill in China. The field study included sampling from five boreholes advanced to the bottom of the landfill, cone penetration tests and monitoring of pore fluid pressures. Twenty-six borehole samples representative of different fill ages (0 to 13 years) were used to perform drained triaxial compression tests. The field and laboratory study showed that the waste body in the landfill can be sub-divided into several strata corresponding to different ranges of fill age. Each of the waste strata has individual composition and shear strength characteristics. The triaxial test results showed that the MSW samples exhibited a strain-hardening and contractive behavior. As the fill age of the waste increased from 1.7 years to 11 years, the cohesion mobilized at a strain level of 10% was found to decrease from 23.3 kPa to 0 kPa, and the mobilized friction angle at the same strain level increasing from 9.9° to 26°. For a confinement stress level greater than 50 kPa, the shear strength of the recently-placed MSW seemed to be lower than that of the older MSW. This behavior was consistent with the cone penetration test results. The field measurement of pore pressures revealed a perched leachate mound above an intermediate cover of soils and a substantial leachate mound near the bottom of the landfill. The measurements of shear strength properties and pore pressures were utilized to assess the slope stability of the Suzhou landfill.