Complex speleothem growth processes revealed by trace element mapping and scanning electron microscopy of annual layers

Closely-spaced transects measured by excimer laser ablation inductively-coupled plasma mass spectrometry (ELA-ICPMS) at 5 and 32 μm spatial resolution are used to generate trace element composition maps (Ba, Sr, Mg, U, Na, P and Al) from MND-S1, a previously studied modern stalagmite from southwest Australia (Treble et al., 2003: EPSL216: 141). Rainfall at the site is highly seasonal, and trace elements in MND-S1 show strong seasonal variation. Trace element maps show that Ba, Sr, U and Na concentrations coherently follow annual growth layers identified from Scanning Electron Microscopy (SEM) images. The SEM images also reveal that stalagmite growth did not proceed uniformly: growth layers vary in thickness and locally pinch out. Highly preferential crystal growth, determined by nucleation sites left by the previous year’s growth, may be responsible for this uneven growth layering. Differential crystal growth apparently causes variability of trace element concentrations along each annual layer, although additional disequilibrium processes affect Mg, which is less distinctly banded than Ba, Sr, U and Na. Uneven and discontinuous growth layers influence the number of annual cycles, their wavelengths and seasonal amplitudes measured in any one transect. This has clear implications for studies that use annual trace element cycles as chronological markers, growth rate or seasonality proxies.     

COUNTIES,STATES, SECTIONS,AND PARTIES IN THE 1984 PRESIDENTIAL ELECTION

County scale cartographic analysis of Ronald Reagan's reelection landslide of 1984 shows the geographical core of his electoral strength to be in the Interior West, non-ethnic areas of the South, and suburbs across the nation. Examination of spatio-temporal variations using factor analysis at a state scale shows this to be a continuation and reinforcement of recent electoral-geographical cleavages. T-mode factor analysis traces the emergence of a contemporary Conservative Normal Vote during the past several presidential elections and the manifestation of this cleavage in the election of 1984.     

Quartz and sheet-silicate preferred orientations of low symmetry, Pikikiruna Schist, New Zealand

The Pikikiruna Schist of Nelson, New Zealand, displays a fabric in which the patterns of quartz c-axes, the poles to planes of inequidimensional quartz grains, and the statistical maxima of poles to sheet-silicate cleavages are oblique to each other. The quartz c-axes patterns consist of type-1 and type-2 crossed-girdles. The triclinic fabric can be explained in terms of one complex rotational deformation of an essentially plane strain nature. Rotation of approximately 90° about the intermediate strain-axis was combined at a late stage with subsidiary rotations about the extension axis. The quartz c-axes patterns can be related to the kinematic framework rather than the finite strain-axes. On the other hand, the dimensional quartz preferred orientation may be closely related to the finite strain-axes, though the quantity of strain can not be measured because of recrystallisation.     

Quartz [0001]-axes preferred orientation, Bluff, New Zealand: Origin elucidated by grain-size measurements

Permian volcanic sediments at Bluff have been strained and thermally metamorphosed by Permian intrusives to metasediments of hornblende—hornfels facies. Quartz, which crystallised as a secondary mineral during metamorphism, has an unusual preferred orientation with c-axes either forming paired maxima in the plane containing the lineation (=maximum principal strain axis = direction of extension) and the perpendicular to schistosity (=minimum principal strain axis = shortening direction) or a broad maximum parallel to the lineation; the paired maxima are approximately 30° either side of the lineation. Some quartz grains are markedly elongate parallel to the lineation, and according to hypotheses of preferred orientation involving crystal plasticity, there should be some correlation between the shape of such grains and their c-axis orientations. Grain-size and shape analysis of Bluff quartz demonstrate that no such correlation exists; the analyses show that the preferred orientation results from oriented nucleation in the residual stress field immediately following the bulk straining of the rocks, with the distribution of c-axes as predicted by Kamb's hypothesis (1959). The time relationships of rock deformation, thermal metamorphism, and nucleation and growth of quartz are discussed.     

Merging science into community adaptation planning processes: a cross-site comparison of four distinct areas of the Lower Mekong Basin

Climate change is increasingly affecting rural areas worldwide. The Lower Mekong Basin (LMB) is at particular risk due to heat stress, changing rainfall patterns, rising sea levels, and more frequent and extreme climatic events. It is imperative that local-level adaptation plans are developed in a manner that builds resilience to these growing threats. Strategies for developing adaptation plans tend to comprise predominantly science-led or predominantly community-led processes. This study examines an approach that balances inputs from both processes in characterizing community vulnerability as a component of the adaptation planning workflow. Evaluation sites are located within four distinct sub-regions of the LMB: the Vietnam Mekong Delta, the Annamite Mountains of Lao PDR, the Cambodia central lowlands, and the mid-elevation forests of northern Thailand. Our results indicate that by merging science-based data with community-level perspective, knowledge gaps from both sides are filled and a more comprehensive understanding of vulnerability is factored into adaptation planning.     

Glass-bearing plutonic fragments from ignimbrites of the Okataina caldera complex, Taupo Volcanic Zone, New Zealand: remnants of a partially molten intrusion associated with preceding eruptions

Glass-bearing plutonic fragments occur as rare accessory lithics within the ca. 64 ka Rotoiti and Earthquake Flat ignimbrites that were erupted from Okataina caldera complex, Taupo Volcanic Zone, New Zealand. Granitoid lithic fragments are only found in the Rotoiti ignimbrite and fall into two groups. Group 1 granitoids have textures consistent with a period of slow cooling followed by rapid quenching, and were excavated by the Rotoiti eruption from a single incompletely solidified magma body. Although isotopic ratios for the Group 1 granitoids are similar to the host ignimbrite, they are not cognate, having different chemistry, mineralogy, mineral chemistry and crystallisation history. It is more likely that they represent fragments of a separate incompletely solidified magma chamber that was intercepted by the erupting Rotoiti ignimbrite magma. Low LILE and high HFSE abundances favour a comagmatic link with the ca. 0.28 Ma Matahina ignimbrite and it is suggested they are derived from an isolated cupola of the Matahina magma chamber that remained at depth (between 3.5 and 5 kbar pressure) after eruption of the Matahina ignimbrite. Migration toward the surface probably accompanied development of the Rotoiti magma system in the upper crust. Most geochemical variation in Group 1 granitoids is related to the abundance of biotite, the concentration of which is controlled by differential shear. REE abundance is controlled by light REE-enriched accessory minerals preferentially included within biotite. Although Eu_n remains constant in the Group 1 granitoids, Eu/Eu^* varies systematically with (La/Yb)_n and is controlled by variations in Sm and Gd rather than in Eu. Group 2 granitoid fragments have a wide range of composition, comparable to many Okataina rhyolites, including those found as lithic fragments in the Rotoiti ignimbrite. Rare microdiorite fragments occur in both Rotoiti and Earthquake Flat ignimbrites and typically contain vesicular interstitial glass indicating that they were incompletely solidified prior to eruption. Those from the Rotoiti ignimbrite are comparable to the (>64 ka) Matahi basaltic tephra and probably represent part of the same magmatic event which generated the Matahi tephra.     

Geographic EducationResearch and the Changing Institutional Structure of American Education

Professional geographers are paying increasing attention to the development of a research agenda concerning geographic education. In doing so, it is essential that geographers pay close attention to fundamental changes in the structure of education itself. Traditional educational methods and procedures associated with industrial society are being replaced by new and innovative modes of education that are linked to post-industrial social organization. This article explores the implications of these changes for understanding the teaching and learning of geography in the future.     

Mutual replacement reactions in alkali feldspars II: trace element partitioning and geothermometry

Perthitic alkali feldspar primocrysts in layered syenites in the Klokken intrusion in South Greenland, underwent dissolution–reprecipitation reactions in a circulating post-magmatic aqueous fluid at ~450°C, and are to a large degree pseudomorphs. These ‘mutual replacement’ reactions provide a perfect natural experiment with which to study trace element partitioning between sodium and potassium feldspars growing simultaneously. The reactant ‘phase’ was a cryptoperthitic feldspar consisting of low albite and low microcline in a coherent sub-μm ‘braid’ intergrowth and the product phases were ‘strain-free’ incoherent subgrains of low albite and low microcline forming microporous patch perthites on scales up to 200 μm. The driving force for the reaction was reduction of coherency strain energy. The mechanisms of this process are described in Part I. Five mixed braid perthite–patch perthite crystals were analysed for major and trace elements using laser ablation-inductively coupled plasma mass spectrometry with a 19 μm beam diameter. This gave bulk analyses of the braid texture, which were in the range Ab_73–54Or_45–27An_4.3–0.8, but could resolve Ab- and Or-rich patches in patch perthite. The major element bulk compositions of the crystals were retained during the replacement reactions. Major components in patches plot on tielines in the Ab–Or–An ternary system that pass through or very close to the parent braid perthite composition and indicate local equilibrium on the scale of a few tens of mm. Many trace elements, including REE, were lost to the fluid during the deuteric reactions, but the effect is large only for Fe and Ti. Cs, Pb and Sr were added to some crystals. Plots of log distribution coefficient D for Rb, Ba, Pb, Eu²⁺, La and Ce between Or- and Ab-rich patches against ionic radius are straight lines, assuming eightfold coordination, and to a first approximation are independent of ionic charge. K also lies on these lines, and the smaller ions Na and Ca lie close to them. The best linear fits were obtained using ionic radii for ^[8]K and ^[8]Ca, but there is ambiguity as to whether ^[7]Na or ^[5]Na is most appropriate. The linear relationship shows that the listed trace elements are in the feldspar M-site rather than in inclusions. Tl is in M although an exact D could not be obtained. The very large Cs ion partitions strongly into the Or-rich phase but its D value appears to be less than predicted by extrapolation. The near-linearity arises because partitioning is occurring between two solids into sites which have similar Young’s moduli, so that the parabolas that normally represent trace element partitioning between crystals and liquids (which have negligible shear strength) approximately cancel out. Ga and Be are in T-sites, as well as some of the Fe and Ti present, although part is in oxide inclusions. The site of Sc is unclear, but if structural it is likely to be T. Partitioning on M-sites is a potential geothermometer but because the effective size of the irregular M-site is defined by its K and (Na + Ca) contents, which are controlled by ternary solvus relationships, its calibration is not independent of conventional two-feldspar geothermometers. Trace elements may however provide a useful means of confirming that feldspar pairs are in equilibrium, and of recognising feldspar intergrowths produced by non-isochemical replacement rather than exsolution. Two-feldspar geothermometry for the ternary phases in the low-albite microcline patch perthites gives temperatures above the stability range of microcline, markedly so if a correction is made for Si–Al ordering. This is probably because current geothermometers are too sensitive to low concentrations of An in ordered Or-rich feldspars. This interpretation is supported by two-feldspar assemblages growing at known temperatures in geothermal systems and sedimentary basins. This paper and the earlier Part I are dedicated in the memory of J. V. Smith and W. L. Brown, both of whom died in 2007, in acknowledgement of their unrivalled contributions to the study of the feldspar minerals over more than half a century. An erratum to this article can be found at