Polyorogenic reworking of ore‐controlling shear zones at the South Range of the Sudbury impact structure: A telltale story from in situ U–Pb titanite geochronology

The post‐impact orogenic evolution of the world class Ni–Cu–PGE Sudbury mining camp in Ontario remains poorly understood. New temporal constraints from ore‐controlling, epidote–amphibolite facies shear zones in the heavily mineralised Creighton Mine (Sudbury, South Range) illuminate the complex orogenic history of the Sudbury structure. In situ U–Pb dating of shear‐hosted titanite grains by LA‐ICP‐MS reveals new evidence for shear zone reworking during the Yavapai (ca. 1.77–1.7 Ga), Mazatzalian–Labradorian (1.7–1.6 Ga) and Chieflakian–Pinwarian (1.5–1.4 Ga) accretionary events. The new age data show that the effects of the Penokean orogeny (1.9–1.8 Ga) on the structural architecture of the Sudbury structure have been overestimated. At a regional scale, the new titanite age populations corroborate that the Southern Province of the Canadian Shield documents the same tectonothermal episodes that are recorded along orogenic strike within the accretionary provinces of the Southwestern United States.     

Dense Gas, Chemistry and Star Formation in Luminous Galaxies

The molecular phase of the ISM constitutes the main source of fuel for the activity in starburst and AGNs. The physical conditions and chemical constitution of the molecular gas will change with, and respond to, the evolution of the activity. This paper includes a short discussion of the ¹²CO/¹³CO 1–0 line intensity ratio as a diagnostic tool of the molecular gas properties of luminous galaxies – paired with examples of high-resolution studies of how the line ratio varies within galaxies. A possible connection between the OH megamasers and galaxies with unusually high ¹²CO/¹³CO 1–0 line intensity ratios are also briefly discussed.The relative intensities of the dense gas tracers HNC, HCN, HCO⁺ and CN are a result of both chemistry and starburst evolution. The discussion on the interpretation of HNC 1–0 emission includes the importance of ion-neutral chemistry in a luminous starburst region. Finally, simple cartoon ISM models and how they can be applied to LIRGs and ULIRGs, are presented.     

Very low grade metamorphism of the Taveyanne formation of western Switzerland

The andesitic early Oligocene Taveyanne metagreywacke of the Helvetic nappes of western Switzerland shows an increase of metamorphic grade from zeolite facies through lower greenschist facies. Electron microprobe analysis, fluid inclusion thermometry, stable isotope analysis, coal rank, illite and chlorite crystallinity and thermodynamic calculations were carried out to determine metamorphic conditions. Evaluation of all techniques used in this study suggest that only combinations of different parameters yield reliable information to constrain very low-grade metamorphic conditions. Electron microprobe analyses are presented for actinolite, chlorite, epidote, phengite, laumontite, prehnite, pumpellyite, and titanite. With increasing metamorphic grade, chlorite is enriched in tetrahedral Al, pumpellyite becomes poorer in Fe_tot and more homogeneous in chemical composition, and titanite tends to incorporate Ti at the expense of Al and Fe³⁺. Metamorphic P-T conditions were determined by a combination of fluid inclusion microthermobarometry, stable isotope thermometry on quartz-calcite veins, chlorite “geothermometry” and thermodynamic calculations. Peak temperatures range from 210–250 °C for zeolite facies to 270–300 °C for prehnite-pumpellyite facies to 300–360 °C for pumpellyite-actinolite facies. An evaluation of 289 chlorite analyses indicates that the tetrahedral Al content is negatively correlated with the saponite component. Temperatures derived from chlorite “geothermometry” match maximum temperature conditions mentioned above. Illite crystallinity data for shales and slates intercalated with the Taveyanne metagreywacke indicate that the diagenetic zone correlates with the zeolite facies, the upper anchizone with the prehnite-pumpellyite facies, and the lower epizone with the pumpellyite-actinolite facies. A comparison of coal rank and illite crystallinity data (n=12,r=0.91) yielded R _max values of 2.9 and 5.5% for the lower and upper boundary of the anchizone, respectively. Received: 2 August 1996 / Accepted: 16 July 1997     

‘Ageing in place’: experiences of older adults in Amsterdam and Portland

This article addresses the importance and meanings of formal and informal social support relationships and neighbourhood ties for older adults ‘ageing in place’ in urban neighbourhoods in two different welfare state settings: Portland (Oregon, the United States) and Amsterdam (the Netherlands). The rising number of people growing old(er) in urban environments raises new demands and pressing challenges for urban development. The majority of older adults are and will be ageing in their homes and communities, as opposed to institutionalized care facilities and settings. At the same time, the provision of formal and public care is being increasingly challenged by government cutbacks. On top of this, the formerly strong welfare states in many European countries have weakened. In-depth interviews with 40 older adults and key informants in two neighbourhoods in each city provide the empirical basis for this study. In Portland, there are widespread local civic initiatives related to care provision for older adults. The city has a long tradition both of individual responsibility and community culture, which has emerged from and appears to compensate for the overall lack of state services and support. Amsterdam has a long tradition of state provision, but is experiencing a policy shift towards a stronger reliance on private market-led services, and an emphasis on family and community as providers of support. Although a few emerging local initiatives for elderly care in Amsterdam were identified, it is unclear whether this form of community support can compensate for decreasing state provision in Amsterdam. This study raises concerns about the future of care provision for older adults living in unsupportive urban neighbourhoods, without financial resources or nearby relatives.     

Differential recruitment of introduced Pacific oysters and native mussels at the North Sea coast: coexistence possible?

Pacific oysters (Crassostrea gigas Thunberg 1793) have been introduced into the Wadden Sea (North Sea), where they settle on native mussel beds (Mytilus edulis L.), which represent the only extensive insular hard substrata in this soft-sediment environment. As abundances of C. gigas rose, some mussel beds became increasingly overgrown with oysters, whereas others did not. Field experiments revealed that recruitment of C. gigas was higher in the lower intertidal than in the upper subtidal zone, that it was higher on conspecifics than on mussels, and that it was not affected by barnacle epigrowth except when settling on mussels. Mussel recruitment is known from inter- and subtidal zones. It occurred equally on oyster and mussel shells but showed a clear preference for barnacle epigrowth over clean shells. Assuming that settlement and recruitment are key processes for species abundances on the North Sea coast, it is predicted that the positive feedback in oyster settlement will lead to rapid reef formation of this invader at the expense of mussel beds. Mussels, however, may escape competitive exclusion by settling between or on the larger oysters especially when barnacles are abundant. Experimental patches with mussels were more often covered by fucoid algae (Fucus vesiculosus forma mytili Nienburg) than patches with oysters, and oyster recruitment was poor underneath such algal canopies. Thus, fucoids may provide the native mussels with a refuge from the invading oysters and the two bivalves may coexist, provided food is not limiting.     

Stream network expansion: a riparian water quality factor

Little is known about how active stream network expansion during rainstorms influences the ability of riparian buffers to improve water quality. We used aerial photographs to quantify stream network expansion during the wet winter season in five agricultural catchments in western Oregon, USA. Winter stream drainage densities were nearly two orders of magnitude greater than summer stream densities, and agricultural land use was much more abundant along transient portions (e.g. swales, road ditches) of stream networks. Water moving from agricultural fields into expanded stream networks during large hydrologic events has the opportunity to bypass downstream riparian buffers along perennial streams and contribute nonpoint‐source pollutants directly into perennial stream channels. Copyright © 2005 John Wiley & Sons, Ltd.     

An ice-core based history of Siberian forest fires since AD 1250

Forest fires play a key role in the global carbon cycle and thus, can affect regional and global climate. Although fires in extended areas of Russian boreal forests have a considerable influence on atmospheric greenhouse gas and soot concentrations, estimates of their impact on climate are hampered by a lack of data on the history of forest fires. Especially regions with strong continental climate are of high importance due to an intensified development of wildfires. In this study we reconstruct the fire history of Southern Siberia during the past 750 years using ice-core based nitrate, potassium, and charcoal concentration records from Belukha glacier in the continental Siberian Altai. A period of exceptionally high forest-fire activity was observed between AD 1600 and 1680, following an extremely dry period AD 1540–1600. Ice-core pollen data suggest distinct forest diebacks and the expansion of steppe in response to dry climatic conditions. Coherence with a paleoenvironmental record from the 200 km distant Siberian lake Teletskoye shows that the vegetational shift AD 1540–1680, the increase in fire activity AD 1600–1680, and the subsequent recovery of forests AD 1700 were of regional significance. Dead biomass accumulation in response to drought and high temperatures around AD 1600 probably triggered maximum forest-fire activity AD 1600–1680. The extreme dry period in the 16th century was also observed at other sites in Central Asia and is possibly associated with a persistent positive mode of the Pacific Decadal Oscillation (PDO). No significant increase in biomass burning occurred in the Altai region during the last 300 years, despite strongly increasing temperatures and human activities. Our results imply that precipitation changes controlled fire-regime and vegetation shifts in the Altai region during the past 750 years. We conclude that high sensitivity of ecosystems to occasional decadal-scale drought events may trigger unprecedented environmental reorganizations under global-warming conditions.