The mobility of the rare earth elements: Evidence and implications from selected terrains affected by burial metamorphism

The mobility of the rare earth element (REE) during hydrous burial metamorphism is described from three localities. Comparison of REE abundances in relict domains and metadomains from flood lavas in the Maddina Volcanics, Fortescue Group, Western Australia shows that, relative to the relict domains, REE may be strongly depleted in certain metadomains. Strong variations in La/Yb, La/Sm and Eu may also occur due to postcrystallization secondary processes. Similar comparisons in flood lavas from Mamainse Point in the Canadian Keweenawan Series show that REE are mobile and increase in abundance in metadomains. Spilites from U.S. Virgin Islands also show evidence for REE mobility during low grade burial metamorphism. In this case light REE (LREE) have been preferentially mobilized with heavy REE (HREE) remaining parallel or sub-parallel on chondrite normalized plots.REE analyses from these locations together with an evaluation of published work suggests that the mobility of REE can be described by: 1. gross REE and selective LREE enrichment; 2. REE movement around a primary mean; 3. gross REE depletion; 4. selective REE mobility. Failure to take into account REE mobility may lead to incorrect conclusions concerning petrogenetic models based on altered basic sequences. The coherence of REE with other key trace elements during alteration is also discussed.     

“Global warming” versus “climate change”: A replication on the association between political self-identification,question wording,and environmental beliefs

Climate change is one of the greatest threats to humanity and requires immediate action. Schuldt, Konrath, and Schwarz (2011) suggested that beliefs in environmental phenomena can be influenced by the terminology used to describe it: changing question wording from global warming to climate change resulted in a 6.3 percentage point increase in belief in environmental phenomena. This association was moderated by political self-identification, with Republicans being 16.2 percentage points more likely to believe in climate change than in global warming, with Democrats showing no difference. The potential for connotative meanings to shift over time and the sociopolitical changes since the original study, potential policy and environmental campaign implications, and an expansion of these findings to other countries, motivated an attempt to replicate this important finding. This pre-registered study repeated the original procedures in the United States of America and two other countries (United Kingdom and Australia; total N = 5,717). Although question wording no longer had a significant effect on beliefs in climate change/global warming, the association of political self-identification with beliefs in environmental phenomena replicated in all three countries, with Conservatives consistently believing less in climate change/global warming than Liberals. The potential impacts of temporal and methodological differences on the discrepancies between this study's and the original's findings are discussed.     

Le Batholite de San Ramon,Cordillère Orientale du Pérou Central

Résumè Le batholite de San Ramon est constitue par un granite à gros grains ou porphyroïde, à biotite et parfois hornblende, de teinte rouge à grise. Il s'étend sur 90 km du Nord au Sud à la bordure est de la Cordillère Orientale du Pérou Central. Il recoupe des terrains carbonifères et on le retrouve en galets dans des conglomérats rouges sous-jacents aux calcaires triasico-liasiques. Son âge est précisé par une isochrone Rb/Sr en roches totales qui le fixe à 238±10 MA. Il s'agit donc d'un granite d'âge permien supérieur à trias inférieur en partie contemporain du volcanisme rhyolitique à andésitique qui accompagne le dépôt des molasses rouges Mitu post-léonardiennes et pré-ladiniennes. Avec d'autre granitoïdes tardi-hercyniens de la Cordillère Orientale, il témoigne de l'importance insuffisamment reconnue jusqu'alors du plutonisme associé à ce volcanisme »permo-triasique«.

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The batholith of San Ramon is made of a coarse-grained to porphyritic granite that bears biotite and also hornblende at some places. It extends over 90 km from north to south along the eastern boundary of the Eastern Cordillera of Central Peru. It intrudes Carboniferous and Lower Permian strata and is included as cobbles into the red conglomerates that underlie Triassic to Liassic carbonates. A Rb/Sr whole-rock isochron gives a Late Permian to Early Triassic age of 238±10 m. y. Thus the San Ramon granite appears to be in part coeval with the andesite to rhyolitic volcanism associated to the red Mitu molasses, that as a whole were deposited after the Late Leonardian and before the Lower Ladinian. Some other radiometric ages from the Eastern Cordillera granitoïds stress the extension of this Late Variscan plutonism.

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Zusammenfassung Der Batholit von San Ramon besteht aus einem grobkörnigen bis porphyrartigen Granit mit Biotiten und bisweilen Hornblenden von rötlicher bis grauer Farbe. Er erstreckt sich über 90 km in N—S-Richtung längs dem Ostrand der östlichen Cordillere von Zentralperu. Er durchschneidet Karbon- und Permablagerungen und findet sich in Gerollen des triadisch-liassische Kalke unterlagernden Konglomerats. Aus der Rb/Sr-Gesamtisochrone ergibt sich ein Alter von 238±10 M. J. Es handelt sich also um einen Granit aus dem Grenzbereich Perm—Trias, der zum Teil gleichaltrig mit dem rhyolitischen bis andesitischen Vulkanismus ist, der die Ablagerung der postleonardischen und praeladinischen roten Molasse Mitubegleitet. Im Verein mit anderen spätvariszischen Granitoïden weist er auf die bisher ungenügend erkannte Bedeutung des diesen permo-triadischen Vulkanismus begleitenden Plutonismus hin.

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Resumen El batolito de San Ramón esta localizado a lo largo del limite este de la Cordillera Oriental en el Perú Central. Esta compuesto por un granito de grano grueso que puede tambien ser porfiroide, contiene biotita y tambien hornablenda y su color varia de rojo a gris. Dicho granito intruye terrenos carboniferos y eo-pérmicos y se le encuentra formando parte de los cantos en los conglomerados rojos infrayacentes a la serie carbonatada triásico-liásica. Una isocrona Rb/Sr en rocas totales le da una edad de 238±10 m. y. es decir del Permico terminal o de la base del Triásico. Por lo tanto, el granito de San Ramón es contemporáneo con parte del volcanismo riolitico a andesítico asociado a la sedimentacion de las molasas rojas del grupo Mitu, la cual ocure entre el Leonardiano superior y el Ladiniano inferior. Junto con otros granitoïdes de la Cordillera oriental, el batolito de San Ramón demuestra la importancia del plutonismo asociado a este volcanismo »permo-triásico«.

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Uranium series dating of stalagmites from Blanchard Springs Caverns,U.S.A.

Because stalagmites are enriched in ²³⁴U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, ²³⁴U/²³⁸U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP.     

Highly heterogeneous Precambrian basement under the central Deccan Traps, India: Direct evidence from xenoliths in dykes

Crustal or mantle xenoliths are not common in evolved, tholeiitic flood basalts that cover huge areas of the Precambrian shields. Yet, the occasional occurrences provide the most direct and unequivocal evidence on basement composition. Few xenolith occurrences are known from the Deccan Traps, India, and inferences about the Deccan basement have necessarily depended on geophysical studies and geochemistry of Deccan lavas and intrusions. Here, we report two basalt dykes (Rajmane and Talwade dykes) from the central Deccan Traps that are extremely rich in crustal xenoliths of great lithological variety (gneisses, quartzites, granite mylonite, felsic granulite, carbonate rock, tuff). Because the dykes are parallel and only 4 km apart, and only a few kilometres long, the xenoliths provide clear evidence for high small-scale lithological heterogeneity and strong tectonic deformation in the Precambrian Indian crust beneath. Measured ⁸⁷Sr/⁸⁶Sr ratios in the xenoliths range from 0.70935 (carbonate) to 0.78479 (granite mylonite). The Rajmane dyke sampled away from any of the xenoliths shows a present-day ⁸⁷Sr/⁸⁶Sr ratio of 0.70465 and initial (at 66 Ma) ratio of 0.70445. The dyke is subalkalic and fairly evolved (Mg No. = 44.1) and broadly similar in its Sr-isotopic and elemental composition to some of the lavas of the Mahabaleshwar Formation. The xenoliths are comparable lithologically and geochemically to basement rocks from the Archaean Dharwar craton forming much of southern India. As several lines of evidence suggest, the Dharwar craton may extend at least 350–400 km north under the Deccan lava cover. This is significant for Precambrian crustal evolution of India besides continental reconstructions.     

A pioneering reputation: Assessing Piers Blaikie’s contributions to political ecology

This paper assesses the key contributions made by Piers Blaikie to the field of political ecology. Those contributions relate to the way in which this scholar has sought to dismantle barriers to thought by: (1) integrating the insights of political economy with those from environmental science, (2) opening up theoretical space in political ecology by engaging fruitfully with post-structural critiques, (3) moving beyond a narrow area-studies and development studies focus, and (4) helping to internationalise the research field beyond its core American base. The paper also highlights ambiguity in the role played by Blaikie in political ecology, as stances that he has taken in his work have provoked wider debate over the field’s purpose and coherence. Ensuing tensions over theory and practice as well as single versus multiple truths persist yet, pace Blaikie and others (e.g. Robbins), a robust political ecology is nonetheless able to consider what people ‘do’ from a healthy diversity of theoretical positions. The multiple contributions of Piers Blaikie underpin a reputation for having produced a pioneering body of work that has inspired scholars across theoretical, empirical and disciplinary boundaries, thereby ensuring that his will be a reputation that is interpreted and re-interpreted for many years to come.     

Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems

Mass fluxes from the ground surface can play a vital role in influencing groundwater ecosystems. Rates of delivery may influence intact ecosystem composition, while fluxes of substances associated with anthropogenic activity may critically alter the functioning of associated microbial assemblages. Field-based tracing experiments offer a valuable means of understanding mass transport rates and mechanisms, particularly in complex heterogeneous epikarst systems overlying vulnerable fissured aquifers. A short-term tracer experiment monitoring solute and particle tracer concentrations after they passed through a 10-m-thick sequence of limestone, capped by a thin soil, revealed rapid travel times and variable attenuation rates for the substances employed. Results demonstrated that particle tracers have shorter average travel times and can reach the subsurface in higher concentrations and over shorter times than non-reactive solutes. High recovery rates for the bacterial tracer Ralstonia eutropha H16 contrasted strongly with those of similarly sized fluorescent polystyrene microspheres, highlighting the importance of physico-chemical surface characteristics of particle tracers. Complementary laboratory batch experiments examined the role played by organic and inorganic soil/rock surfaces on particle tracer attenuation. Findings suggest that biofilms may significantly promote transport of particulate material below ground, i.e., the delivery of allochthonous microorganisms to karst groundwater.     

The effect of leaching on the integrity of a natural clay

Leaching effects on the strength of a natural clay substrate can lead to loss of integrity of pond containment situation — especially if the clay material constitutes the liner system for the containment pond. In this study, the integrity of the clay in the face of five different types of leachates is studied via the creep characteristics of the clay. The resultant effects are evaluated in terms of (a) soil fabric/structure reinforcement or degradation, and/or (b) changes in the relationships established between soil particles and chemical pore fluid. The integrity of the clay is seen to be severely conditioned by (a) factors producing the initial soil structural state, (b) the chemistry of the leachate, (c) local boundary conditions, and (d) time.     

Analysis of the flow in layered fluids at small, but finite, amplitude with application to mullion structures

An analysis of the flow in layered viscous fluids at small, but finite amplitude is illustrated in an application to the shortening of two different viscous fluids parallel to their interface. The analysis extends the familiar infinitesimal amplitude analysis, which retains terms to first-order in the surface slope, to second-order in this quantity. To second-order accuracy, the asymmetry in interface form characteristic of the finite-amplitude lobe-and-cusp structure emerges. Additional results for mullion structures are derived and used to interpret some natural structures.