Magnesiochloritoid: Compressibility and high pressure structure refinement

The response of magnesiochloritoid to pressure has been studied by single crystal X-ray diffraction in a diamond anvil cell, using crystals with composition Mg_1.3Fe_0.7Al₄Si₂O₁₀(OH)₄. The unit cell parameters decrease from a = 9.434 (3), b = 5.452 (2), c = 18.136 (5) Å, β = 101.42° (2) (1 bar pressure) to a = 9.370 (7), b = 5.419 (5), c = 17.88 (1) Å, β = 101.5° (1) (42 kbar pressure), following a slightly anisotropic compression pattern (linear compressibilities parallel to unit cell edges: β _a = 1.85, β _b = 1.74, β_c = 3.05 × 10^?4 kbar^?1) with a bulk modulus of 1480 kbar. Perpendicular to c, the most compressible direction, the crystal structure (space group C2/c) consists of two kinds of alternating octahedral layers connected via isolated SiO₄ tetrahedra. With increasing pressure the slightly wavy layer [Mg_1.3Fe_0.7AlO₂(OH)₄] tends to flatten. Furthermore, the octahedra in this layer, with all cations underbonded, are more compressible than the octahedra in the (A1₃O₈) layer with slightly overbonded aluminum. Comparison between high-pressure and high-temperature data yields the following equations: $$\begin{gathered} a_{P,T} = 9.434{\text{ }}{\AA} - 174 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 9 \cdot 10^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ b_{P,T} = 5.452{\text{ }}{\AA} - 95 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 5 \cdot 65 \cdot 10^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ c_{P,T} = 18.136{\text{ }}{\AA} - 549 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 16 \cdot 2^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ \end{gathered} $$ with P in kbar and T in °C. These equations indicate that the unit cell and bond geometry of magnesiochloritoid at formation conditions do not differ greatly from those at the outcrop conditions, e.g. the calculated unitcell volume is 917.3 ų at P = 16 kbar and T=500 °C, whereas the observed volume at room conditions is 914.4 ų. In addition, they show that the specific gravity increases from formation at depth to outcrop at surface conditions.     

Equilibrium isotopic fractionation in the kaolinite, quartz, water system: Prediction from first-principles density-functional theory

Isotopic fractionation factors for oxygen, hydrogen and silicon have been calculated using first-principles methods for the kaolinite, quartz, water (ice and gas water) system. Good agreement between theory and experiment is obtained for mineral-water oxygen isotope fractionation. This approach gives reliable results on isotopic fractionation factors as a function of temperature, within a relative precision of typically 5%. These calculations provide independent quantitative constraints on the internal fractionation of oxygen in kaolinite, the fractionation of silicon isotopes at equilibrium, or hydrogen fractionation between kaolinite and water. Calculated fractionation factors at 300 K are 12.5‰ for the kaolinite internal-fractionation of oxygen, and 1.6‰ for silicon fractionation between quartz and kaolinite.     

The MgCr2O4–MgFe2O4 solid solution series: effects of octahedrally coordinated Fe3+ on T–O bond lengths

The influence on the spinel structure of Fe³⁺ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr₂O₄–MgFe₂O₄) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe₂O₄), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm^?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe³⁺ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a ₀ and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe³⁺ at the M site on T–O bond lengths in the spinel structure.     

Plan‐form evolution of ancient meandering rivers reconstructed from longitudinal outcrop sections

The mode of channel‐bend transformation (i.e. expansion, translation, rotation or a combination thereof) has a direct bearing on the dimensions, shape, bedding architecture and connectivity of point‐bar sandstone bodies within a fluvial meander belt, but is generally difficult to recognize in vertical outcrops. This study demonstrates how the bend transformation mode and relative rate of channel‐floor aggradation can be deciphered from longitudinal outcrop sections aligned parallel to the meander‐belt axis, as a crucial methodological aid to the reconstruction of ancient fluvial systems and the development of outcrop analogue models for fluvial petroleum reservoirs. The study focuses on single‐storey and multi‐storey fluvial meander‐belt sandstone bodies in the Palaeogene piggyback Boyabat Basin of north‐central Turkey. The sandstone bodies are several hundred metres wide, 5 to 40 m thick and encased in muddy floodplain deposits. The individual channel‐belt storeys are 5 to 9 m thick and their transverse sections show lateral‐accretion bed packages representing point bars. Point bars in longitudinal sections are recognizable as broad mounds whose parts with downstream‐inclined, subhorizontal and upstream‐inclined bedding represent, respectively, the bar downstream, central and upstream parts. The inter‐bar channel thalweg is recognizable as the transition zone between adjacent point‐bar bedsets with opposing dip directions into or out of the outcrop section. The diverging or converging adjacent thalweg trajectories, or a trajectory migrating in up‐valley direction, indicate point‐bar broadening and hence channel‐bend expansion. A concurrent down‐valley migration of adjacent trajectories indicates channel‐bend translation. Bend rotation is recognizable from the replacement of a depositional riffle by an erosional pool zone or vice versa along the thalweg trajectory. The steepness of the thalweg trajectory reflects the relative rate of channel‐floor aggradation. This study discusses further how the late‐stage foreland tectonics, with its alternating pulses of uplift and subsidence and a progressive narrowing of the basin, has forced aggradation of fluvial channels and caused vertical stacking of meander belts.     

A procedure to estimate the seismic hazard in an urban area: an application to Acireale (Eastern Sicily)

A “standard procedure” to characterize the seismic hazard of a given area was proposed. It is based on a multidisciplinary approach implying: (1) the knowledge of the seismic history of the area; (2) detailed geological surveys; (3)seismic noise measurements; (4) simulations of earthquake scenarios. The downtown of Acireale, a typical baroque town located on Eastern Sicily, was chosen as the “test area”. A catalog of the local seismogenic faults (able to generate earthquakes in historical times) has been compiled, as well as a seismic catalog for the effects of both local and regional earthquakes. The analysis of both catalogs allowed us to make the following conclusions: (1) the most important seismogenic faults affecting the Acireale municipality do not affect the downtown, while the related local earthquakes attenuate their energy (and intensity) in short (few km) distances; (2) the highest seismic intensity (degree X) experienced in Acireale downtown was caused by the 1693 regional earthquake; (3) over the last 140 years, the downtown has experienced the highest intensity value of VII only once, while six times the intensity was VI. On the whole, this implies a moderate seismic hazard. The estimation of the seismic hazard has been also approached by the experimental method of recording seismic noise. Measurements have been performed at seven different sites, where drills gave detailed information on the shallow subsurface geology to obtain HV (horizontal/vertical) spectral ratios. On the whole, the highest site amplification factor was moderate (about 7). A further investigation based on synthetic seismograms (and spectra) produced by simulating two given earthquake scenarios was also performed. The two scenarios are, respectively, representative of the largest expected earthquake in the area (the 1693 shock) and of a moderate (magnitude ca. 5.5) local earthquake (as the 1818 one). Moderate to strong locally expected accelerations were evidenced.     

Rhythms of feeding activity and food consumption of two Mediterranean burrowing fishes: Gnathophis mystax (Delaroche) and Chlopsis bicolor Rafinesque

Data on the food consumption, feeding activity and periodicity of two burrowing fish, the congrid eel Gnathophis mystax (Delaroche, 1809) and the false moray Chlopsis bicolor Rafinesque, 1810 are presented. In all, 455 specimens were collected by bottom trawl in the central Mediterranean Sea at depths ranging from 140 to 160 m during four 24‐h day–night sampling cycles. The diet of G. mystax and C. bicolor was investigated by means of stomach content analysis. Diet varied significantly with length and maturity stage. During ontogenetic development G. mystax occupied different trophic levels: diet shifted from amphipods, predominantly in the smaller congrid eels [<25 cm total length (TL)] to fish in the larger individuals (>30 cm TL). Before the transition to the icthyophagous phase, the congrid eel showed a more generalistic foraging behaviour where decapods (Solenocera membranacea, Parapenaeus longirostris, Alpheus glaber), cephalopods (Sepiola spp. and Alloteuthis media), benthic (Gobiidae, Callionymus maculatus, Arnoglossus laterna) and benthopelagic fish (Argentina sphyraena) dominated the diet. Smaller C. bicolor (<25 cm TL) fed primarily on amphipods and cephalopods; bigger specimens fed also on decapods both natantian (A. glaber, Processa canaliculata) and reptantian (Medorippe lanata, Goneplax rhomboides). Daily ration values, computed from the Eggers method, ranged from 2.48% to 2.99% wet body weight for C. bicolor and G. mystax, respectively. Diel patterns in stomach fullness and the trophic niche overlap between the two species were also discussed.     

High-temperature rapid pyrometamorphism induced by a charcoal pit burning: The case of Ricetto,central Italy

Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The ¹⁴C analysis of a coal fragment from bottom of the body yields the conventional age of 227(±50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000–1,100 °C when melilite crystallization conditions were reached at appreciable P(CO₂) and high f(O₂). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+BtMel+Melt+2H₂O+3CO₂+0.5O₂. Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O₂3Di+2An+7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.An erratum to this article can be found at     

Job losses and political acceptability of climate policies: why the ‘job-killing’ argument is so persistent and how to overturn it

Political acceptability is an essential issue in choosing appropriate climate policies. Sociologists and behavioural scientists recognize the importance of selecting environmental policies that have broad political support, while economists tend to compare different instruments first on the basis of their efficiency, and then by assessing their distributional impacts and thus their political acceptability. This paper examines case-study and empirical evidence that the job losses ascribed (correctly or incorrectly) to climate policies have substantial impacts on the willingness of affected workers to support these policies. In aggregate, the costs of these losses are significantly smaller than the benefits, both in terms of health and, probably, of labour market outcomes, but the losses are concentrated in specific areas, sectors and social groups that have been hit hard by the great recession and international competition. Localized contextual effects, such as peer group pressure, and politico-economic factors, such as weakened unions and tightened government budgets, amplify the strength and the persistence of the ‘job-killing’ argument. Compensating for the effects of climate policies on ‘left-behind’ workers appears to be the key priority to increase the political acceptability of such policies, but the design of compensatory policies poses serious challenges.

Key policy insights

• Public perception of, and support for, climate policies is substantially reduced in the presence of large negative shocks, especially job losses.

• Climate policies can be perceived as negative for employment, especially in areas where polluting industries represent a large share of employment and in occupations and sectors already damaged by globalization and automation.

• Policymakers should distinguish between small and large distributional effects of climate policies, and find the appropriate combination of revenue recycling schemes, industrial and retraining policies as well as compensation packages to increase the support for such policies.