Experimental examination of two-pyroxene graphical thermometers using natural pyroxenes with application to metaigneous pyroxenes from the Adirondack Mountains,New York

Clinopyroxene with exsolved orthopyroxene and coexisting orthopyroxene with exsolved clinopyroxene (inverted pigeonite) in metaigneous rocks from the Adirondacks, New York, were experimentally homogenized at temperatures near those inferred for their original crystallization. The purposes were several: (1) to test the graphical two-pyroxene geothermometer of Lindsley (1983); (2) to test the hypothesis of Bohlen and Essene (1978) that these were originally igneous pyroxenes; and (3) to test whether modal recombination of complexly exsolved pyroxenes yields realistic compositions. Experiments on Fe-rich compositions at 930° and 870° C (1 GPa) are compatible with the graphical thermometer of Lindsley (1983); however, this graphical thermometer yields apparent temperatures approximately 50° C too high for experiments at 1050° C and 1100° C (0 MPa). This suggests that at intermediate Mg/Fe the augite isotherms for these temperatures lie at lower wollastonite compositions than shown by Lindsley. The results are, however, in good agreement with isotherms derived from the solution model of Davidson (1985). When these isotherms are applied to a variety of terrestrial and lunar igneous rocks and the metaigneous rocks from the Adirondacks, temperatures given by augite and pigeonite compositions from coexisting pairs are similar. Comparison of the experimentally homogenized compositions with modally recombined compositions of Bohlen and Essene (1978) show that discrepancies between augite and pigeonite temperatures may nevertheless arise if pyroxene grains formed by granular exsolution are not correctly reintegrated.     

X-ray spectra of iron atoms in minerals

The results of X-ray fluorescence Ka _1,2 and Kβ₁,β′-spectra of iron in 54 samples, including 23 minerals, are presented. Spectrum characteristics are mainly dependent on the environment of iron in the sample, the most susceptible parameter being the chemical shift δβ₁. For the compounds investigated δβ₁ varies between ?1.58 eV and +1.56 eV when referring to metallic iron. Chemical shifts of compounds with predominantly covalent bonds exhibit more negative values, compounds with metallic bonds nearly vanishing values and compounds with predominantly ionic bonds more positive values. The FeKβ₁,β′-group of lines is actually a superposition of three lines: the long-wave line β′ and two overlapping lines β ₁ ⁵ and β ₁ ⁷ of which the superposition is conventionally denoted as β₁. The relative intensity of β ₁ ⁵ increases with ionicity of the bond, while that of β ₁ ⁷ decreases. The effective charge of iron has been determined for a group of iron-bearing minerals.     

Trophic Resource Overlap Between Small Elasmobranchs and Sympatric Teleosts in Mid-Atlantic Bight Nearshore Habitats

Small, abundant elasmobranchs use shallow marine areas (<20 m depth) of the US Middle Atlantic coast as nurseries and adult foraging habitat, an area also used by a diverse assemblage of economically important juvenile and adult teleost species. Specimens of three small elasmobranch species (smooth dogfish Mustelus canis, clearnose skate Raja eglanteria, and bullnose ray Myliobatis freminvillii) were collected in August 2007 and 2008 from a study area of ∼150 km², extending 22 km south from Ocean City, Maryland, USA (38° 19′ N) and offshore from 5- to 20-m depth. Stomach contents indicated that fish were part of the diets of smooth dogfish and clearnose skate at a level comparable with sympatric piscivorous teleosts. However, stable isotope data suggest that piscivory is likely an opportunistic foraging behavior in this habitat. Studied elasmobranchs were secondary-tertiary consumers with diets composed primarily of decapod crustaceans, fish, and mollusks. There was significant overlap in diet composition, spatial distribution, and diel stomach fullness patterns between clearnose skate, southern kingfish Menticirrhus americanus (teleost) and, to a lesser extent, smooth dogfish. Despite this evidence for piscivory, their relatively low densities suggest that predation by these elasmobranchs is unlikely to affect teleost populations in shallow coastal ocean habitats. If shared prey were to become scarce, then competitive interactions are possible.     

Relationships between the color and chemical composition of quaternary bottom sediments from the southern part of the Mendeleev Rise and the continental slope of the East Siberian Sea

This paper addresses the problem of relationships between the chemical composition and color of Quaternary marine sediments using the data of X-ray fluorescence analysis for the region of the Mendeleev Rise (Arctic Ocean). The contributions of sedimentation and diagenetic factors to color formation were estimated. It was shown that lithostratigraphic correlations should be performed (with certain limitations) using only sediment layers of dark brown and pink color.     

Allocycles and Autocycles in the Upper Part of the Limestone Coal Group (Pendleian E1) in the Glasgow–Stirling Region of the Midland Valley of Scotland

The upper part of the Limestone Coal Group (Pendleian E₁), between the major marine transgressions of the Black Metals and the Index Limestone, represents an early example of ‘coal measures’ facies. It comprises a distal and a proximal facies association. The distal facies association, which was subject to relatively strong marine influences and included both deltaic and fluvial elements, is characterized by a regular ‘layer-cake’ succession with laterally-persistent lithological members. By contrast, the proximal association, which was more subject to fluvial influences and is typified by the variable Bannockburn Main Complex, is characterized by abrupt lateral changes in lithofacies. The distal facies association is dominant in the west of the Kilsyth Trough, but proximal facies intercalations increase eastwards, so that they constitute a fairly high proportion of the succession in the Kincardine Basin, particularly in areas of locally-increased tectonic subsidence that were frequently occupied by major channel belts. Some of the sheet sandstones within the distal association have a lower, upward-coarsening portion succeeded by a coarser-grained, erosive-based, upward-fining portion. The resulting ‘two-storey’ profile may reflect deltaic sand bodies having been suceeded by fluvial sand bodies, following a general fall in base level. Linear regression lines showing the relationship between the number of horizons colonized by vegetation and net subsidence, suggest that local autocyclic, tectonosedimentary processes, such as delta switching, channel migration, and avulsion, were superimposed upon a widespread allocyclic, probably glacial-eustatic, process. The former processes were most effective within the proximal facies association and in the Kincardine Basin and the latter in the distal association and the Kilsyth Trough.     

Dynamics of the soil water and solute in the sodic saline soil in the Songnen Plain,China

According to the field experiment in the sodic saline soil region in the Songnen Plain, the dynamics of the soil water and solute affected by the shallow groundwater were explored during the growing season in 2004. The results presented that, influenced by the strongly evaporative demand, the soil water tended to transport to the upper soil layer with salt. The layered soil water balance model (LSWB model) revealed that the ratio of the water exchange between the groundwater and upper layer of the soil was 11.7:1. The groundwater discharge was 53.86 mm, but the groundwater recharge from the upper layer of soil was only 5.04 mm from 11 July to 06 September, which indicated that the groundwater could discharge to upper layer of soil and influence the soil salinization through capillary rise. The observed values of the salt content from July to mid-October presented that the soil solute was more changeable influenced by the climatic condition at 30 cm depth. As the field saturated hydraulic conductivity was low, the salts mainly accumulated in about 50–70 cm depth soil layer and hardly leached into deeper soil layer. Furthermore, the salt content was mainly controlled by the groundwater in the subsoil below 100 cm depth, the salt content decreased with the groundwater level receding. As influenced by the shallow groundwater and freeze-thaw action, further studies should be performed on the mechanism of soil salinization in the sodic saline soil region in the Songnen Plain of China.     

Water diffusion in Mount Changbai peralkaline rhyolitic melt

Diffusion couple experiments with wet half (up to 4.6 wt%) and dry half were carried out at 789–1,516 K and 0.47–1.42 GPa to investigate water diffusion in a peralkaline rhyolitic melt with major oxide concentrations matching Mount Changbai rhyolite. Combining data from this work and a related study, total water diffusivity in peralkaline rhyolitic melt can be expressed as:

$ D_{{{\text{H}}_{ 2} {\text{O}}_{\text{t}} }} = D_{{{\text{H}}_{ 2} {\text{O}}_{\text{m}} }} \left( {1 - \frac{0.5 - X}{{\sqrt {[4\exp (3110/T - 1.876) - 1](X - X^{2} ) + 0.25} }}} \right), $

$ {\text{with}}\;D_{{{\text{H}}_{ 2} {\text{O}}_{\text{m}} }} = \exp \left[ { - 1 2. 7 8 9- \frac{13939}{T} - 1229.6\frac{P}{T} + ( - 27.867 + \frac{60559}{T})X} \right], $

where D is in m² s^?1, T is the temperature in K, P is the pressure in GPa, and X is the mole fraction of water and calculated as X = (C/18.015)/(C/18.015 + (100 ? C)/33.14), where C is water content in wt%. We recommend this equation in modeling bubble growth and volcanic eruption dynamics in peralkaline rhyolitic eruptions, such as the ~1,000-ad eruption of Mount Changbai in North East China. Water diffusivities in peralkaline and metaluminous rhyolitic melts are comparable within a factor of 2, in contrast with the 1.0–2.6 orders of magnitude difference in viscosities. The decoupling of diffusivity of neutral molecular species from melt viscosity, i.e., the deviation from the inversely proportional relationship predicted by the Stokes–Einstein equation, might be attributed to the small size of H₂O molecules. With distinct viscosities but similar diffusivity, bubble growth controlled by diffusion in peralkaline and metaluminous rhyolitic melts follows similar parabolic curves. However, at low confining pressure or low water content, viscosity plays a larger role and bubble growth rate in peralkaline rhyolitic melt is much faster than that in metaluminous rhyolite.

     

New Chronological,Paleontological, and Geochemical Data on the Formation of Glacier-Dammed Lakes in the Kurai Depression (Southeastern Russian Altai) at the End of the Late Pleistocene

Doklady Earth Sciences - One of the debated problems in Pleistocene paleogeography of the Altai region is the extent and time of existence of the last glacier-dammed lakes. For the first time...