Revised activity–composition models for clinopyroxene and amphibole

Recent activity–composition models for clinopyroxene and amphibole are revised to provide better consistency with observed phase relations in natural rocks. For clinopyroxene, the calibration in NCFMAS is retained, but the incorporation of acmite is revised to improve the partitioning of ferric iron between coexisting clinopyroxenes. For amphibole, the NCFMASH calibration is retained, but the addition of ferric iron is changed to provide consistency with the clinopyroxenes. The thermodynamics of orthoamphibole (gedrite) is also adjusted to resolve an unrelated inconsistency. The effects of these improvements are illustrated through comparison of calculated pseudosections produced with the existing and new models with natural data from lawsonite eclogites.     

An examination of snow redistribution over smooth land‐fast sea ice

An understanding of temporal evolution of snow on sea ice at different spatial scales is essential for improvement of snow parameterization in sea ice models. One of the problems we face, however, is that long‐term climate data are routinely available for land and not for sea ice. In this paper, we examine the temporal evolution of snow over smooth land‐fast first‐year sea ice using observational and modelled data. Changes in probability density functions indicate that depositional and drifting events control the evolution of snow distribution. Geostatistical analysis suggests that snowdrifts increased over the study period, and the orientation was related to the meteorological conditions. At the microscale, the temporal evolution of the snowdrifts was a product of infilling in the valleys between drifts. Results using two shore‐based climate reporting stations (Paulatuk and Tuktoyuktuk, NWT) suggest that on‐ice air temperature and relative humidity can be estimated using air temperature recorded at either station. Wind speed, direction and precipitation on ice cannot be accurately estimated using meteorological data from either station. The temporal evolution of snow distribution over smooth land‐fast sea ice was modelled using SnowModel and four different forcing regimes. The results from these model runs indicate a lack of agreement between observed distribution and model outputs. The reasons for these results are lack of meteorological measurements prior to the end of January, lack of spatially adequate surface topography and discrepancies between meteorological variables on land and ice. Copyright © 2009 John Wiley & Sons, Ltd.     

Permian volcanism and its relation to the tectonic development of Sumatra

The Permian volcanic deposits covering an extensive area southeast of Lake Singkarak, Central Sumatra, have been mapped in detail and studied in relation to the structural development of the pre-Tertiary Sumatra orogene. During the Permian time, Central Sumatra was occupied by an elongated sea basin in which thick sequence of bathyal and neritic sediments were deposited. Pelitic sediments dominated, but at the same time volcanic activity started in this area. The volcanic products comprise mainly flow of hornblende and augite andesites with their tuffs. In some parts of Southern Sumatra the volcanic activity lasted till Cretaceous time. The main phase of folding took place about 120 m.y. ago accompanied by an emplacement of granitic rocks. After an uplift in younger Cretaceous time, the area was strongly attacked by erosion. The regional geologic history of Sumatra revealed clearly a divergent behaviour from the classical concept of magmatic evolution in an orogenic belt as demonstrated by the dominantly andesitic character of the geosynclinal volcanism. Other examples of volcanism associated with geosynclinal subsidence, possessing an andesitic rather than a basaltic character, could also be observed in the Tertiary Sunda mountain system of Sumatra. The Indonesian examples and similar occurrences of andesitic volcanism during a geosynclinal subsidence in other parts of the world, show that much work still will have to be done in order to gain a better undestanding regarding the relationship between volcanism and orogenesis.     

The origin and response of zircon in eclogite to metamorphism during the multi-stage evolution of the Huwan Shear Zone,China: Insights from Lu–Hf and U–Pb isotopic and trace element geochemistry

The Huwan Shear Zone (HSZ) is an eclogite bearing transpressive wrench zone located along the Shangdan Suture that juxtaposes the Paleozoic Qinling and Mesozoic Hong'an–Dabie orogenic terrains. The region preserves a complex history that bridges the gap between adjacent orogenic terrains. Simultaneous in-situ trace element, U–Th–Pb and Lu–Hf‐isotope analysis of zircon grains from samples of the Xiongdian and Sujiahe eclogite identify a late Carboniferous to early Permian period of high pressure metamorphism, ca. 283 to 306 Ma. Zircon grains are observed to respond to metamorphic overprint via a two stage process: (1) An initial prograde stage of fluid catalyzed interface coupled dissolution–reprecipitation, involving exsolution of a non-ideal solid solution thorite (ThSiO₄) end member and loss of highly incompatible components (LREE and Pb), (2) A second stage of coupled zircon dissolution, coarsening, and new rim growth in equilibrium with garnet at high pressure conditions.We identify Proterozoic whole rock Sm–Nd and zircon grain Lu–Hf isotopic evidence which challenges the traditional interpretation that the Xiongdian and Sujiahe eclogite formed in response to early Paleozoic mantle melting and oceanic crust generation. We argue the Huwan Shear Zone contains no conclusive evidence of early/middle Paleozoic oceanic crust, but rather Proterozoic crustal components analogous to those found in the Northern Qinling Terrain and associated with formation of the Shangdan Suture. We present a simpler geodynamic model involving continuous convergence and accretion of terrains onto the southern margin of the North China Block during the Paleozoic Qinling and Mesozoic Dabie orogenies.     

Ranking of national-level adaptation options. An editorial comment

de Bruin et al. (Clim Change, 2009) report on an expert assessment aimed at prioritizing adaptation options in several climate-sensitive sectors of the Netherlands. Their results show that even in a country with high economic, institutional and technical capacity, it is not currently feasible to prioritize national-level adaptation options based on social cost-benefit analysis because of methodological difficulties and insufficient quantitative data. Multi-criteria analysis based on qualitative indicators can help prioritizing adaptation options but the analysis detected strong conflicts between priority and feasibility criteria. The specific results of the ranking exercise should be treated with caution due to weaknesses in the selection of adaptation options and the definition of evaluation criteria. The authors assert that their methods can be transferred to other regions but substantial modifications are likely required in developing countries with large current climate risks, fewer economic resources, and substantial social inequalities.     

Soil amplification of plane seismic waves

Amplitudes of surface particle velocities are calculated when time-harmonic seismic waves of uniform amplitude are incident upon an arbitrary stratified elastic soil layer from the underlying bedrock. Whereas previous workers have mainly treated normally incident S waves, we allow the waves to be of SV, P, or SH types and to have arbitrary angles of incidence. Following standard practice the problem is set up as a matrix differential system, but in such a way that incident SV and P waves may be treated together (the system for SH decoupling). Though complicated, the 4 × 4 SVP system has considerable structure which is elucidated in Appendices 1 and 2. These results, though not altogether new, are of independent interest, and are gathered together in concise form for reference. The theory for low- and for high-frequency approximations is given. The main results of the work are illustrated by two numerical examples: Model 1 where the soil layer is homogeneous; and Model 2 where the soil layer has a linear velocity profile.     

Diet of a fossorial rodent (Octodontidae), above-ground food availability,and changes related to cattle grazing in the Central Monte (Argentina)

Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle.     

Trace metals in fish and invertebrates of three California coastal Wetlands

Metal concentrations were measured in selected fish and invertebrate species from Mugu Lagoon, Malibu Lagoon and Ballona Wetlands in southern California in order to assess the extent of metal contamination in these three wetlands. Ranges of element concentrations (in microgram/g) found in biota were: Zn 12-650; Cu 1.9-440; Ni < 1-37; Cr < 1-55; Pb < 0.5-6.8; As < 1-8.5; Se < 1-3.8; Cd < 0.2-0.90; and Ag < 0.3-5.9. Relative to previous studies of California biota, the highest metal concentrations found were for chromium and nickel. The highest levels were in one of the two bottom-dwelling fish (juvenile Leptocottus armatus) (55 micrograms/g) and the two water-column fish sampled (Fundulus parvipinnis and Atherinops affinis) (30 and 24 micrograms/g). At Ballona Lagoon, elevated levels of copper and silver were found in the bivalve Tagelus californianus (440 and 5.9 micrograms/g). Chromium and nickel appeared to be most persistent in fish from Mugu (4.6-55 and 2.6-37 micrograms/g), the most northern site and an active military base, and Ballona (< 1-30 and < 1-16 micrograms/g), believed to be the most metal-contaminated site. Compared to previously measured metal concentrations in species of California coastal waters, these regions revealed higher levels of chromium, nickel, silver, arsenic, zinc, copper and, to a lesser extent, cadmium and selenium. Chromium and silver were present at high enough levels at all three sites to be considered environmental health hazards.