Hydrothermal melting of some New Zealand greywackes and argillites     

J. Rogers 《Bulletin of Volcanology》1966,29(1):173-175

The temperatures at which melting begins of three New Zealand greywackes and two argillites were determined as a function of water pressure up to 3000 atmospheres. The purpose of these experiments was to provide data possibly relevant to the genesis of the North Island ignimbrites and for comparison with the experiments ofBowen andTuttle (1958) on the melting temperatures of granites and the ternary minimum system (NaAlSi₃O₈ — KAlSi₃O₈ — SiO₂ — H₂O). Powdered samples of the rocks were heated in unsealed silver tubes in cold seal bombs, the water pressure being measured on a Bourdon gauge and applied during heating. Temperature control was ± 5°C. Twelve days was the longest heating period, most being for 24 hours, which was sufficient for apparent reaction. At the end of an experiment, the pressure was released, and the sample quickly cooled by removal from the bomb. The samples were crushed and examined by X-ray diffraction and the petrographic microscope. The PT curve for the beginning of melting of the greywackes and argillites is very close toBowen andTuttle’s for granites and the ternary minimum to 1000 atmospheres water pressure. Above this pressure the greywackes melt at slightly higher temperatures than on the granite curve with the argillites a little higher still. These observations are similar to those reported for shales byWyllie andTuttle 1960, 1961, for greywackes byWinkler andvon Platen 1961, and pelitic sediments byWyart andSabatier, 1959. The amount of anatectic melt increases rapidly above the temperature of initial melting and is inversely related to the quartz present in the greywackes. The partially melted products were often notably vesicular. Cordierite, mullite, hypersthene, scapolite and mica were identified in the X-ray diffractograms as coexisting with the melt. These experiments are in agreement with published work in showing that the quartz and alkali feldspars of granites, shales and arkosic sediments can in the presence of water react and begin to melt at 20–25 kilometres depth in the earth assuming a geothermal gradient of 30°C/km. The melt is granitic or granodioritic in composition.  相似文献   

A crustal suture and lineament in North Africa     

Richard M Nagy  Mohamed A Ghuma  John J.W Rogers 《Tectonophysics》1976,31(3-4)

A possible suture between an old craton in West Africa and the Arabian—Nubian shield is marked by a persistent zone of Phanerozoic weakness. This zone extends between the Nile and Niger deltas and passes through the Qattara embayment, along the Bahariya fault, through the Kufra basin, between the Tibesti and Jabal al Uwaynat massifs, through the Bahr el Ghazal and Lake Chad areas, and along the Benoue trough.  相似文献   

The role of social norms in climate adaptation: Mediating risk perception and flood insurance purchase     

Alex Y. Lo 《Global Environmental Change》2013,23(5):1249-1257

Flood insurance plays an important role in climate adaptation by recovering insured losses in the event of catastrophic flooding. Voluntary adoption of flood insurance has been seen as a function of risk perception that is shaped by social norms. This paper attempts to clarify the relationship between these factors. It is based on a household survey conducted in the eastern cities of Australia and involving a total of 501 randomly selected residents. Results of a path analysis show that the likelihood of having flood insurance cover was associated with perceived social norms, but not perceived flood risk. In addition, perceived norms and risk were statistically related to each other. It is concluded that social norms played a mediating role between insuring decision and risk perception. Risk perception might influence the insuring decision indirectly through shaping perception of social norms. This implies that adaptive behaviour is not necessarily a function of risk perception, but an outcome of its impacts upon the ways in which the individuals situate themselves in their social circles or the society. There is a feedback process in which individual perceptions of risk manifest as both a cause and effect, shaping and being shaped by the socio-cultural context.  相似文献   

Land management impacts on runoff sources in small Amazon watersheds     

Joaquín Chaves  Christopher Neill  Sonja Germer  Sérgio Gouveia Neto  Alex Krusche  Helmut Elsenbeer 《水文研究》2008,22(12):1766-1775

Forest clearing and conversion to cattle pasture in the lowland Amazon region has been linked to soil compaction and increased soil water storage, which combine to diminish soil infiltration, enhance quick lateral flows and increase the stream flow response to precipitation. Quantifying the importance of quick surficial flow in response to this land use change requires identification of water sources within catchments that contribute to stream flow. Using an end member mixing analysis approach, potential contributing sources of stream flow were evaluated during an entire rainy season in a forest and a pasture watershed drained by ephemeral‐to‐intermittent streams in the south‐western Amazon. Water yield was 17% of precipitation in the pasture and 0·8% of precipitation in the forest. During the early rainy season, throughfall, groundwater, and soil water contributed 79%, 18%, and 3%, respectively, to total forest stream flow. Over the entire rainy season, throughfall, groundwater, and shallow soil water provided 57%, 24%, and 19%, respectively, of stream flow. In the pasture watershed, overland flow dominated stream flow both in the early (67%) and late (57%) rainy season, with a mean contribution of 60% overland flow, 35% groundwater, and 5% soil water. The uncertainty associated with those estimates was studied using a Monte Carlo approach. In addition to large changes in total surface flow, marked differences were found in the proportions of total stream flow in the second half of the rainy season between the forest and pasture watershed. These results suggest that (1) there is great potential for alteration of the hydrological budgets of larger watersheds as the proportion of deforested land in the Amazon increases, and (2) as more rainfall is diverted into fast flowpaths to streams in established pastures, the potential to deliver water with higher solute concentrations generated by erosion or by bypassing sites of solute removal increases. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Genetic structure of the tall sea pen Funiculina quadrangularis in NW Scottish sea lochs          下载免费PDF全文

Erin P. Wright  Kirsty Kemp  Alex D. Rogers  Chris Yesson 《Marine Ecology》2015,36(3):659-667

The tall sea pen Funiculina quadrangularis has a patchy distribution around the UK, being found in sheltered waters below 20 m depth on the northwest coast of Scotland and Ireland. The limited distribution and sensitivity to bottom fishing activities make F. quadrangularis vulnerable to reduction in population numbers that may lead to genetic isolation and reduced diversity. Because of this vulnerability and low resilience to physical disturbance, the tall sea pen is recognised as a Species of Principle Importance under the Natural Environment and Rural Communities Act, 2006, UK. ( http://www.legislation.gov.uk/ukpga/2006/16/contents ) and is also on the Biodiversity Action Plan list of Priority Species for the UK. In the Mediterranean it is recognised as a sensitive and essential fish habitat because it forms habitat for several commercially important crustaceans. The aim of this study was to understand the current state of the genetic structure and gene flow of F. quadrangularis in areas of NW Scotland. We developed 10 microsatellite markers and used them to genotype 176 samples from four populations. Overall, our results suggest that there is high genetic diversity and high gene flow between colonies of F. quadrangularis in and among locations in Loch Linnhe and Loch Duich. As a result of the high rates of gene flow, genetic differentiation between sites was low. This may provide resilience to human impacts if distant populations have a high connectivity. However, care must be taken, as small but significant isolation by distance was found between the most geographically distant sites and only a small part of the species range was examined in this study. The genetic tools developed here will provide a foundation for wider studies of this vulnerable species.  相似文献   

Reflection and Ducting of Gravity Waves Inside the Sun     

K. B. MacGregor  T. M. Rogers 《Solar physics》2011,270(2):417-436

Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward traveling wave energy flux from reaching the deep solar interior. If a highly reflecting magnetized layer is located some distance below the convection zone base, a duct or wave guide can be set up, wherein vertical propagation is restricted by successive reflections at the upper and lower boundaries. The presence of both upward and downward traveling disturbances inside the duct leads to the existence of a set of horizontally propagating modes that have significantly enhanced amplitudes. We point out that the helical structure of these waves makes them capable of generating an α-effect, and briefly consider the possibility that propagation in a shear of sufficient strength could lead to instability, the result of wave growth due to over-reflection.  相似文献   

Shock and thermal history of Northwest Africa 4859, an annealed impact‐melt breccia of LL chondrite parentage containing unusual igneous features and pentlandite     

Niina JAMSJA  Alex RUZICKA 《Meteoritics & planetary science》2010,45(5):828-849

Abstract– Northwest Africa 4859 (NWA 4859) is a meteorite of LL chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite. The most obvious unusual feature is a high proportion of large (≤3 cm diameter) igneous‐textured enclaves (LITEs), interpreted as shock melts that were intruded into an LL chondrite host. One such LITE appears to have been produced by whole rock melting of LL chondrite, initial rapid partial crystallization, and subsequent slow cooling of the residual melt in the host to produce a differentiated object. Other unusual features include mm‐sized “overgrowth objects,” fine‐grained plagioclase‐rich bands, and coarse troilite (≤7 mm across) grains. All these features are interpreted as having crystallized from melts produced by a single transient shock event, followed by slow cooling. A subsequent shock event of moderate (S3) intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype. Pentlandite (together with associated troilite) in NWA 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature (≤230 °C) following the second shock event. NWA 4859 is interpreted to be an unusual impact‐melt breccia that contains shock melt which crystallized in different forms at depth within the parent body.  相似文献   

Pencil-beam surveys for trans-neptunian objects: Limits on distant populations     

Alex H. Parker  J.J. Kavelaars 《Icarus》2010,209(2):766-770

Two populations of minor bodies in the outer Solar System remain particularly elusive: Scattered Disk Objects and Sedna-like objects. These populations are important dynamical tracers, and understanding the details of their spatial- and size-distributions will enhance our understanding of the formation and on-going evolution of the Solar System. By using newly-derived limits on the maximum heliocentric distances that recent pencil-beam surveys for trans-neptunian objects were sensitive to, we determine new upper limits on the total numbers of distant SDOs and Sedna-like objects. While generally consistent with populations estimated from wide-area surveys, we show that for magnitude-distribution slopes of α ? 0.7-1.0, these pencil-beam surveys provide stronger upper limits than current estimates in literature.  相似文献   

On the interaction of internal gravity waves with a magnetic field – I. Artificial wave forcing     

T. M. Rogers  K. B. MacGregor 《Monthly notices of the Royal Astronomical Society》2010,401(1):191-196

We present results from numerical simulations of the interaction of internal gravity waves (IGW) with a magnetic field. In accordance with the dispersion relation governing IGW in the presence of magnetism and rotation, when the IGW frequency is approximately that of the Alfvén frequency, strong reflection of the wave occurs. Such strong reflection markedly changes the angular momentum transport properties of the waves. In these simple models a strong, time-independent shear layer develops, in contrast to the oscillating shear layer that develops in the purely hydrodynamic case.  相似文献   

Functional diversity of nematode communities in the southwestern North Sea     

Schratzberger M  Warr K  Rogers SI 《Marine environmental research》2007,63(4):368-389

A range of biological traits of nematode species were combined to identify patterns in the functional composition of their assemblages collected at 19 soft-bottom stations in the southwestern North Sea with the primary aim to determine which environmental variables control communities. We used 19 categories of five biological traits thought or known to represent an important ecological function. These were related to buccal morphology, tail shape, body size, body shape and life history strategy. Data on trait membership was provided by biological information on species and genera. A total of 79 different trait combinations were recorded. Results from correlation analyses revealed several significant relationships between traits. Some trait combinations were shared by different species and genera, and the ratio of realised versus total number of possible trait combinations of < 1 suggested that some trait combinations were not represented by the nematode fauna from this region. The functional composition of nematodes was strongly linked to median particle diameter and silt content of the sediment and water depth. The approach adopted and our attempts at defining and analysing functional attributes of nematode communities raised a number of conceptual and methodological issues which are discussed.  相似文献