Partial melting due to breakdown of an epidote‐group mineral during exhumation of ultrahigh‐pressure eclogite: An example from the North‐East Greenland Caledonides     

Wentao Cao  Jane A. Gilotti  Hans‐Joachim Massonne  Simona Ferrando  Charles T. Foster 《Journal of Metamorphic Geology》2019,37(1):15-39

In the North‐East Greenland Caledonides, P–T conditions and textures are consistent with partial melting of ultrahigh‐pressure (UHP) eclogite during exhumation. The eclogite contains a peak assemblage of garnet, omphacite, kyanite, coesite, rutile, and clinozoisite; in addition, phengite is inferred to have been present at peak conditions. An isochemical phase equilibrium diagram, along with garnet isopleths, constrains peak P–T conditions to be subsolidus at 3.4 GPa and 940°C. Zr‐in‐rutile thermometry on inclusions in garnet yields values of ~820°C at 3.4 GPa. In the eclogite, plagioclase may exhibit cuspate textures against surrounding omphacite and has low dihedral angles in plagioclase–clinopyroxene–garnet aggregates, features that are consistent with former melt–solid–solid boundaries and crystallized melt pockets. Graphic intergrowths of plagioclase and amphibole are present in the matrix. Small euhedral neoblasts of garnet against plagioclase are interpreted as formed from a peritectic reaction during partial melting. Polymineralic inclusions of albite+K‐feldspar and clinopyroxene+quartz±kyanite±plagioclase in large anhedral garnet display plagioclase cusps pointing into the host, which are interpreted as crystallized melt pockets. These textures, along with the mineral composition, suggest partial melting of the eclogite by reactions involving phengite and, to a large extent, an epidote‐group mineral. Calculated and experimentally determined phase relations from the literature reveal that partial melting occurred on the exhumation path, at pressures below the coesite to quartz transition. A calculated P–T phase diagram for a former melt‐bearing domain shows that the formation of the peritectic garnet rim occurred at 1.4 GPa and 900°C, with an assemblage of clinopyroxene, amphibole, and plagioclase equilibrated at 1.3 GPa and 720°C. Isochemical phase equilibrium modelling of a symplectite of clinopyroxene, plagioclase, and amphibole after omphacite, combined with the mineral composition, yields a P–T range at 1.0–1. 6 GPa, 680–1,000°C. The assemblage of amphibole and plagioclase is estimated to reach equilibrium at 717–732°C, calculated by amphibole–plagioclase thermometry for the former melt‐bearing domain and symplectite respectively. The results of this study demonstrate that partial melt formed in the UHP eclogite through breakdown of an epidote‐group mineral with minor involvement of phengite during exhumation from peak pressure; melt was subsequently crystallized on the cooling path.  相似文献   

Effect of combined translation and torsion on undrained uplift capacity of plate anchors: Plastic limit analysis (PLA) solution          下载免费PDF全文

Hamid Reza Nouri  Giovanna Biscontin  Charles P. Aubeny 《国际地质力学数值与分析法杂志》2018,42(14):1567-1591

Uplift capacity of plate anchors has been the focus of numerous studies, because anchor plates are designed for pull‐out in normal operating conditions. However, the response of plate anchors under 6‐degrees‐of‐freedom loading caused during extreme loading conditions is poorly understood. The purpose of this study is to propose a simple yet sufficiently accurate analytical solution to investigate the behavior of plate anchor under combined in‐plane translation and torsion and to evaluate its effect on the plate uplift bearing capacity. To this end, a modified plastic limit analysis (PLA) approach is introduced and compared with limit equilibrium and simplified upper bound baseline solutions. The proposed method is verified with 3‐dimensional finite element. The variables considered in this study include plate aspect ratio, plate thickness, as well as load direction and eccentricity. Results of analytical solutions indicate the insensitivity of the “shape” of the shear‐torsion yield envelope to plate thickness. This finding facilitates the use of simplified yet reasonable yield envelope for infinitely thin plate obtained from simplified PLA approach for other plate thicknesses. The “size” of the failure envelope (controlled by pure torsional and translational capacity) could be predicted fairly accurately by PLA and limit equilibrium methods. Combination of these analytical methods offers a simple yet reasonably accurate solution to describe shear‐torsion response of anchor plate. The obtained shear‐torsion yield envelope is then fitted in the generalized 6‐degrees‐of‐freedom yield surface which describes the reducing effect of moment, torsion, and planar forces on the uplift capacity of plate.  相似文献   

Spatial redistribution of Ditrupa arietina (soft bottom Mediterranean epifauna) during a moderate swell event     

Katell Guizien  François Charles  David Hurther  Hervé Michallet 《Continental Shelf Research》2010

  相似文献   

Endemic avifaunal biodiversity and tropical forest loss in Makira, a mountainous Pacific island     

Finn Danielsen  Christopher E. Filardi  Knud A. Jønsson  Victor Kohaia  Niels Krabbe  Jan B. Kristensen  Robert G. Moyle  Patrick Pikacha  Michael K. Poulsen  Mikael K. Sørensen  Charles Tatahu  Joseph Waihuru  Jon Fjeldså 《Singapore journal of tropical geography》2010,31(1):100-114

Anthropogenic habitat changes and the introduction of pigs, dogs, cats and rats have caused a catastrophic decline in the terrestrial biodiversity of Pacific archipelagos. At present, economic globalization and an increased demand for timber are promoting industrial logging and plantation expansion. Commercial logging can be sustainable but in practice it more often leads to land degradation, especially on small flat islands. On large and mountainous islands, however, more modest impacts can be expected as the narrowly endemic species tend to inhabit montane forests where logging is difficult. In this study we use ornithological data collected at different elevations to assess the extent to which the avifauna of Makira, a large mountainous island in Melanesia, will be affected by deforestation of the lowlands, most of which are under timber concessions. Our data suggest that a majority of the endemic bird species use lowland forest to some extent and that this may even apply to species hitherto associated with montane forest. If current commercial forestry programmes are continued, the forest habitat may be disturbed or lost over large parts of Makira, potentially undermining the natural resource base for the local subsistence economy, exacerbating climate change and threatening the integrity of one of the most important areas for biodiversity conservation on earth. Our study highlights the importance of understanding the habitat requirements of endemic species and the urgency of establishing and effectively managing community-based protected areas in suitable lowland forests of the Pacific.  相似文献   

Anthropogenic impacts recorded in recent sediments from Otisco Lake,New York,USA     

Revital Bookman  Charles T. Driscoll  Steven W. Effler  Daniel R. Engstrom 《Journal of Paleolimnology》2010,43(3):449-462

Geochemical analysis of ²¹⁰Pb-dated sediment cores from Otisco Lake (New York) combined with analysis of recent land cover change in the watershed revealed the history of land use change, lake management, and industrial pollution since European settlement in the northeastern US. Clearance of forestland for agriculture characterized the early settlement era that was marked in the Otisco Lake sediments by a decline in organic carbon (OC) and OC:N ratios, which indicate a change in the sources of organic matter to the lake. Agricultural land use reached its greatest areal extent in the Otisco watershed around 1900, followed by field abandonment and reforestation over the last century. In the 1920s sediment accumulation rates began to increase coincident with residential development along the lake shore. Nitrogen and organic carbon, which are transported from the watershed, show increased fluxes to the lake in response to this change. Deposition of inorganic carbon increased markedly over a short period from the 1940s to the 1980s, which is consistent with enhanced mobilization of watershed calcium by increased acidic deposition, followed by alkalinization of the lake waters and calcite precipitation. An increase in copper content in the sediments reflects application, since 1942, of the algicide copper sulfate to the lake waters to control algal blooms. This CuSO₄ marker confirmed the accuracy of the ²¹⁰Pb chronology. Atmospheric mercury (Hg) fluxes to the lake were affected by increased sediment transport from the watershed. The maximum Hg peak in the sediment record, however, was dated to the early 1970s and coincides with maximum Hg emissions to the atmosphere in the Great Lakes region.  相似文献   

Modelling of fluid–solid interactions using an adaptive mesh fluid model coupled with a combined finite–discrete element model     

Axelle Viré  Jiansheng Xiang  Frank Milthaler  Patrick Emmet Farrell  Matthew David Piggott  John-Paul Latham  Dimitrios Pavlidis  Christopher Charles Pain 《Ocean Dynamics》2012,62(10-12):1487-1501

Fluid–structure interactions are modelled by coupling the finite element fluid/ocean model ‘Fluidity-ICOM’ with a combined finite–discrete element solid model ‘Y3D’. Because separate meshes are used for the fluids and solids, the present method is flexible in terms of discretisation schemes used for each material. Also, it can tackle multiple solids impacting on one another, without having ill-posed problems in the resolution of the fluid’s equations. Importantly, the proposed approach ensures that Newton’s third law is satisfied at the discrete level. This is done by first computing the action–reaction force on a supermesh, i.e. a function superspace of the fluid and solid meshes, and then projecting it to both meshes to use it as a source term in the fluid and solid equations. This paper demonstrates the properties of spatial conservation and accuracy of the method for a sphere immersed in a fluid, with prescribed fluid and solid velocities. While spatial conservation is shown to be independent of the mesh resolutions, accuracy requires fine resolutions in both fluid and solid meshes. It is further highlighted that unstructured meshes adapted to the solid concentration field reduce the numerical errors, in comparison with uniformly structured meshes with the same number of elements. The method is verified on flow past a falling sphere. Its potential for ocean applications is further shown through the simulation of vortex-induced vibrations of two cylinders and the flow past two flexible fibres.  相似文献   

Enhancing the Sustainability of Household Fe0/Sand Filters by Using Bimetallics and MnO2     

Chicgoua Noubactep  Sabine Caré  Brice Donald Btatkeu K.  Charles Péguy Nanseu‐Njiki 《洁净——土壤、空气、水》2012,40(1):100-109

Filtration systems containing metallic iron as reactive medium (Fe⁰ beds) have been intensively used for water treatment during the last two decades. The sustainability of Fe⁰ beds is severely confined by two major factors: (i) reactivity loss as result of the formation of an oxide scale on Fe⁰ and (ii) permeability loss due to pore filling by generated iron corrosion products. Both factors are inherent to iron corrosion at pH > 4.5 and are common during the lifespan of a Fe⁰ bed. It is of great practical significance to improve the performance of Fe⁰ beds by properly addressing these key factors. Recent studies have shown that both reactivity loss and permeability loss could be addressed by mixing Fe⁰ and inert materials. For a non‐porous additive like quartz, the threshold value for the Fe⁰ volumetric proportion is 51%. Using the Fe⁰/quartz system as reference, this study theoretically discusses the possibility of (i) replacing Fe⁰ by bimetallic systems (e.g., Fe⁰/Cu⁰), or (ii) partially replacing quartz by a reactive metal oxide (MnO₂ or TiO₂) to improve the efficiency of Fe⁰ beds. Results confirmed the suitability of both tools for sustaining Fe⁰ bed performance. It is shown that using a Fe⁰:MnO₂ system with the volumetric proportion 51:49 will yield a filter with 40% residual porosity at Fe⁰ depletion (MnO₂ porosity 62%). This study improves Fe⁰ bed design and can be considered as a basis for further refinement and detailed research for efficient Fe⁰ filters.  相似文献   

Multi-decadal coastal change in New Zealand: Evidence, mechanisms and implications     

Karin R. Bryan  Paul S. Kench  Deirdre E. Hart 《New Zealand geographer》2008,64(2):117-128

Abstract:   Coastal research and monitoring on New Zealand beaches have typically examined seasonal and event-driven (storms) changes in the coast. However, historical records are now of sufficient length to indicate that change occurs at longer timescales. This paper presents examples of multi-decadal change at three case-study locations around New Zealand. Results show that morphological adjustment of the coast occurs at multi-decadal scales and is much larger than short-term dynamics. Physical mechanisms driving changes are ill defined but may be associated with El Niños and La Niña episodes which modulate waves and sea level, as well as changes in sediment supply.  相似文献   

New Zealand coastal system boundaries, connections and management   总被引：1，自引：1，他引：0  

Deirdre E. Hart  Karin R. Bryan 《New Zealand geographer》2008,64(2):129-143

Abstract:    Understanding coastal boundaries, connections and drivers of landscape change is integral to effective coastal planning and management. This concept is explored here through case studies representing two very different New Zealand systems: embayed sand beaches in eastern and western open-coast settings; and mixed sand and gravel coast river-mouth lagoons. When framed within a resource and environmental management context these studies indicate that national recognition of the dynamic and interactive nature of coastal environments is a relatively new and amorphous phenomenon in New Zealand and, as such, has been ineffective in driving integrated regional management practices and sustainable coastal outcomes.  相似文献   

Knowing our own history? Geography department archives in the UK   总被引：1，自引：0，他引：1  

Ron Johnston  Charles W J Withers 《Area》2008,40(1):3-11

The paper presents an analysis of the returns to a questionnaire survey on the state of department archives within UK departments of geography. The results of the survey are discussed in relation to recent work in geography which has examined the archive as a site for knowledge's making but seldom in its own terms as a resource for the history of geography, and studies within the archival sciences which have considered the archive as something more than a 'storehouse' for collective memory. The paper reveals that the archival record for the history of British geography is at best uneven, and in many departments non-existent, although information on departmental history is held, often as memory, by individual geographers. The paper considers the survey's implications for the future histories of British geography and addresses the nature of the UK geography department archive as resource and responsibility.  相似文献