Short-range order in tourmaline: a vibrational spectroscopic approach to elbaite

Polarized Fourier-transform infrared and Raman spectra were acquired on an elbaite sample previously characterized by electron- and ion microprobe analysis, X-ray diffraction and structure refinement. Spectra from the two vibrational spectroscopy techniques reveal a close similarity in the OH-stretching region, with three main absorption bands strongly polarized in the c-axis direction. By means of bond-valence theory arguments, the observed OH bands are interpreted and assigned to specific local cation arrangements around the O1 (≡W) and O3 (≡V) anion sites. In combination with the relatively simple composition of the studied sample, bond-valence constraints are used to identify stable anion-cation arrangements, which permit the occurrence of short-range ordering to be assessed. Evidence for nearly complete short-range order at the O1 site, with the stable arrangements ^Y(LiAlAl)_0.6–^W(OH)_0.6 and ^Y(LiLiAl)_0.4–^W(F)_0.4, are presented. These two local arrangements can be further expanded to obtain the larger ordered clusters [^W(OH)–^Y(LiAl₂)–^V(OH)₃–^Z(Al)₆]_0.6 and [^W(F)–^Y(Li₂Al)–^V(OH)₃–^Z(Al)₆]_0.4.     

Thermal behavior of almandine at temperatures up to 1,200°C in hydrogen

The thermally induced reductive decomposition of a natural near end-member almandine [^VIII(Fe_2.85Mg_0.11Ca_0.05Mn_0.02)^VI(Al_1.99)^IV(Si_2.99)O₁₂] and possible hydrogen diffusion into its structure have been carried out at temperatures up to 1,200°C, monitored by simultaneous thermogravimetric analysis and differential scanning calorimetry (DSC), infrared and ⁵⁷Fe Mössbauer spectroscopy and X-ray powder diffraction. Below 1,000°C, evidence for hydrogen diffusion into almandine structure was not observed. At temperatures above 1,000°C, reductive decomposition sets in, as displayed by a sharp endothermic peak at 1,055°C on the DSC curve accompanied by a total mass loss of 3.51%. We observe the following decomposition mechanism: almandine + hydrogen → α-Fe + cristobalite + hercynite + water. At higher temperatures, fayalite and sekaninaite are formed by consecutive reaction of α-Fe with cristobalite and water, and cristobalite with hercynite, respectively. The metallic α-Fe phase forms spherical and isolated particles (~1 μm).     

Surficial geology indicates early Holocene faulting and seismicity,central Sweden

In Sweden, knowledge of the location and timing of glacially induced faulting and seismicity is critical to effective engineering of a long-term nuclear disposal facility. To improve understanding and modeling of the complex ice-induced and tectonic stresses associated with glacially induced faulting, field studies detailing the location and timing of movement of such structures are required. Although the fault has not been confirmed in the bedrock, multi-proxy surficial geologic evidence indicates that the recently discovered scarp in Bollnäs is such a structure. Machine-excavated trenches across the scarp reveal landsliding down the scarp and, in one location, faulted and vertically offset fine-grained glacial sediments. The presence of water-escape structures in trenches excavated on a topographic high strongly suggests a co-seismic origin derived from earthquake magnitudes >5.5. Numerous landslides in till exist in the region as well. Four slopes with landslides were examined in detail, and the factors of safety for these slopes indicate stable conditions and suggest a seismic trigger. Basal radiocarbon dates from peat bogs located stratigraphically above the landslides provide minimum limiting ages for the co-seismic landslides. The oldest date indicates sliding prior to 10,180 calendar years before the present. The proposed Bollnäs Fault is 400 km south of the so called Lapland Fault Province. To date, it is the southernmost confirmed glacially induced fault in Sweden. The results of this study are consistent with existing modeling results that indicate fault instability in this region of central Sweden following deglaciation.     

An Analysis of the Formation of Interconnecting Loops

Fifty interconnecting loops (ILs) that are induced by new-born active regions are investigated. The formation period of four ILs including two same-hemisphere interconnecting loops (HILs) and two transequatorial loops (TLs) are analyzed. The magnetic flux related with these loops is studied. Considering the active region pairs related with the IL as a magnetic system, the total magnetic flux has a tendency of increasing for this system, the signs of net magnetic flux tend to be opposite for the active region pairs. There is no difference between HILs and TLs in this aspect.