17 results on '"Department of Earth Sciences [University of Cambridge]"'
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2. Relations between earthquake distributions, geological history, tectonics and rheology on the continents.
- Author
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Jackson J, McKenzie D, and Priestley K
- Abstract
This paper is concerned with the distribution of earthquakes, particularly their depths, with the temperature of the material in which they occur, and with the significance of both for the rheology and deformation of the continental lithosphere. Earthquakes on faults are generated by the sudden release of elastic energy that accumulates during slow plate motions. The nonlinear high-temperature creep that localizes such energy accumulation is, in principle, well understood and can be described by rheological models. But the same is not true of seismogenic brittle failure, the main focus of this paper, and severely limits the insights that can be obtained by simulations derived from geodynamical modelling of lithosphere deformation. Through advances in seismic tomography, we can now make increasingly detailed maps of lithosphere thickness on the continents. The lateral variations are dramatic, with some places up to 300 km thick, and clearly relate to the geological history of the continents as well as their present-day deformation. Where the lithosphere thickness is about 120 km or less, continental earthquakes are generally confined to upper crustal material that is colder than about 350°C. Within thick lithosphere, and especially on its edges, the entire crust may be seismogenic, with earthquakes sometimes extending into the uppermost mantle if the Moho is colder than 600°C, but the continental mantle is generally aseismic. Earthquakes in the continental lower crust at 400-600°C require the crust to be anhydrous and so are a useful guide or proxy to both composition and strength. These patterns and correlations have important implications for the geological evolution of the continents. They can be seen to have influenced features as diverse as the location of post-collisional rifting; cratonic basin formation; the location, origin and timing of granulite-facies metamorphism; and the formation, longevity and strength of cratons. In addition, they have important consequences for earthquake hazard assessment in the slowly deforming edges and interiors of continental shields or platforms, where the large seismogenic thickness can host very large earthquakes. This article is part of a discussion meeting issue 'Understanding earthquakes using the geological record'.
- Published
- 2021
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3. Lightning and charge processes in brown dwarf and exoplanet atmospheres.
- Author
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Helling C and Rimmer PB
- Abstract
The study of the composition of brown dwarf atmospheres helped to understand their formation and evolution. Similarly, the study of exoplanet atmospheres is expected to constrain their formation and evolutionary states. We use results from three-dimensional simulations, kinetic cloud formation and kinetic ion-neutral chemistry to investigate ionization processes that will affect their atmosphere chemistry: the dayside of super-hot Jupiters is dominated by atomic hydrogen, and not H
2 O. Such planetary atmospheres exhibit a substantial degree of thermal ionization and clouds only form on the nightside where lightning leaves chemical tracers (e.g. HCN) for possibly long enough to be detectable. External radiation may cause exoplanets to be enshrouded in a shell of highly ionized, H3 -forming gas and a weather-driven aurora may emerge. Brown dwarfs enable us to study the role of electron beams for the emergence of an extrasolar, weather system-driven aurora-like chemistry, and the effect of strong magnetic fields on cold atmospheric gases. Electron beams trigger the formation of H+ in the upper atmosphere of a brown dwarf (e.g. LSR-J1835), which may react with it to form hydronium, H3 + in the upper atmosphere of a brown dwarf (e.g. LSR-J1835), which may react with it to form hydronium, H3 O+ , as a longer lived chemical tracer. Brown dwarfs and super-hot gas giants may be excellent candidates to search for H3 product. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H+ as an H3 + product. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3 + , H5 + and beyond'.- Published
- 2019
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4. Mafic tiers and transient mushes: evidence from Iceland.
- Author
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Maclennan J
- Abstract
It is well established that magmatism is trans-crustal, with melt storage and processing occurring over a range of depths. Development of this conceptual model was based on observations of the products of magmatism at spreading ridges, including Iceland. Petrological barometry and tracking of the solidification process has been used to show that the Icelandic crust is built by crystallization over a range of depths. The available petrological evidence indicates that most of the active rift zones are not underlain by extensive and pervasive crystal mush. Instead, the microanalytical observations from Iceland are consistent with a model where magmatic processing in the lower crust occurs in sills of decimetric vertical thickness. This stacked sills mode of crustal accretion corresponds to that proposed for the oceanic crust on the basis of ophiolite studies. A key feature of these models is that the country rock for the sills is hot but subsolidus. This condition can be met if the porosity in thin crystal mushes at the margins of the sills is occluded by primitive phases, a contention that is consistent with observations from cumulate nodules in Icelandic basalts. The conditions required for the stabilization of trans-crustal mushes may not be present in magmatic systems at spreading ridges. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
- Published
- 2019
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5. Architecture and dynamics of magma reservoirs.
- Author
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Edmonds M, Cashman KV, Holness M, and Jackson M
- Abstract
This introductory article provides a synopsis of our current understanding of the form and dynamics of magma reservoirs in the crust. This knowledge is based on a range of experimental, observational and theoretical approaches, some of which are multidisclipinary and pioneering. We introduce and provide a contextual background for the papers in this issue, which cover a wide range of topics, encompassing magma storage, transport, behaviour and rheology, as well as the timescales on which magma reservoirs operate. We summarize the key findings that emerged from the meeting and the challenges that remain. The study of magma reservoirs has wide implications not only for understanding geothermal and magmatic systems, but also for natural oil and gas reservoirs and for ore deposit formation. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
- Published
- 2019
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6. Magma chambers versus mush zones: constraining the architecture of sub-volcanic plumbing systems from microstructural analysis of crystalline enclaves.
- Author
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Holness MB, Stock MJ, and Geist D
- Abstract
There are clear microstructural differences between mafic plutonic rocks that formed in a dynamic liquid-rich environment, in which crystals can be moved and re-arranged by magmatic currents, and those in which crystal nucleation and growth are essentially in situ and static. Crystalline enclaves, derived from deep crustal mushy zones and erupted in many volcanic settings, afford a unique opportunity to use the understanding of microstructural development, established from the study of intrusive plutons, to place constraints on the architecture of sub-volcanic systems. Here, we review the relevant microstructural literature, before applying these techniques to interrogate the crystallization environments of enclaves from the Kameni Islands of Santorini and Rábida Volcano in the Galápagos. Crystals in samples of deep-sourced material from both case studies preserve evidence of at least some time spent in a liquid-rich environment. The Kameni enclaves appear to record an early stage of crystallization during which crystals were free to move, with the bulk of crystallization occurring in a static, mushy environment. By contrast, the Rábida enclaves were sourced from an environment in which hydrodynamic sorting and re-arrangement by magmatic currents were common, consistent with a liquid-rich magma chamber. While presently active volcanoes are thought to be underlain by extensive regions rich in crystal mush, these examples preserve robust evidence for the presence of liquid-rich magma chambers in the geological record. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
- Published
- 2019
- Full Text
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7. Some fluid mechanical constraints on crystallization and recharge within sills.
- Author
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Woods AW and Stock MJ
- Abstract
The injection of hot magma into a sill can lead to heating and melting of the walls and roof of the reservoir while the injected magma cools and crystallizes. If the crystals are relatively dense, they will try to sediment from the injected magma to form a cumulate layer. In this cumulate layer, the crystals form a porous framework which traps the melt as it is built up. As the melt within the sill continually cools and precipitates dense crystals, there will be a gradual reduction in the density of the remaining silicate liquid. As a result, the melt which is progressively trapped in the pore space of the cumulate layer will become stably stratified in density. Using an idealized model of the fluid mechanical and thermodynamical principles, we explore some of the controls on the thickness and density stratification of cumulate layers following replenishment of a sill-like magma chamber. We show the balance between jamming of the crystal laden melt to form a homogeneous layer and the formation of a stratified cumulate zone depends on the cooling time scale compared to the sedimentation time scale. A key finding is that the composition and stratification in a packed crystal-melt suspension and the associated cumulate layer formed by cooling an intrusion of hot melt injected into the crust may have considerable variability, depending on the properties of the overlying roof melt and the size and hence fall speed of crystals which form in the melt. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
- Published
- 2019
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8. Feedbacks on climate in the Earth system: introduction.
- Author
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Wolff EW, Shepherd JG, Shuckburgh E, and Watson AJ
- Published
- 2015
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9. Multi-scaling and mesoscopic structures.
- Author
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Salje EK
- Abstract
Multi-scaling and the systematic investigation of mesoscopic structures represent a field of fruitful cooperation in physics, chemistry, mineralogy and life sciences. The increasing miniaturization of devices as well as the emphasis of recent research on microstructures with length scales of a few nanometres lead to paradigm changes that may impact not only on our scientific understanding of fine-grained structures but also on the way we will develop device materials in the future. Here the role of interfaces becomes more important, and developments in areas such as 'domain boundary engineering' are evidence of this scientific evolution. In addition, nano-porous materials are particularly important in geology and in the development of artificial bones and ultra-light metals. Some of these developments are reviewed in this paper.
- Published
- 2010
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10. eScience for molecular-scale simulations and the eMinerals project.
- Author
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Salje EK, Artacho E, Austen KF, Bruin RP, Calleja M, Chappell HF, Chiang GT, Dove MT, Frame I, Goodwin AL, Kleese van Dam K, Marmier A, Parker SC, Pruneda JM, Todorov IT, Trachenko K, Tyer RP, Walker AM, and White TO
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- Computer Simulation, Climate, Internet, Minerals chemistry, Models, Chemical, Models, Molecular, Science methods, Software
- Abstract
We review the work carried out within the eMinerals project to develop eScience solutions that facilitate a new generation of molecular-scale simulation work. Technological developments include integration of compute and data systems, developing of collaborative frameworks and new researcher-friendly tools for grid job submission, XML data representation, information delivery, metadata harvesting and metadata management. A number of diverse science applications will illustrate how these tools are being used for large parameter-sweep studies, an emerging type of study for which the integration of computing, data and collaboration is essential.
- Published
- 2009
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11. Lessons in scientific data interoperability: XML and the eMinerals project.
- Author
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White TO, Bruin RP, Chiang GT, Dove MT, Tyer RP, and Walker AM
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- Computer Simulation, Ecology trends, Information Dissemination methods, User-Computer Interface, Database Management Systems trends, Databases, Factual trends, Ecology methods, Information Storage and Retrieval trends, Internet, Minerals chemistry, Models, Chemical, Software
- Abstract
A collaborative environmental eScience project produces a broad range of data, notable as much for its diversity, in source and format, as its quantity. We find that extensible markup language (XML) and associated technologies are invaluable in managing this deluge of data. We describe Fo X, a toolkit for allowing Fortran codes to read and write XML, thus allowing existing scientific tools to be easily re-used in an XML-centric workflow.
- Published
- 2009
- Full Text
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12. Integrating computing, data and collaboration grids: the RMCS tool.
- Author
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Walker AM, Bruin RP, Dove MT, White TO, Kleese van Dam K, and Tyer RP
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- Computer Simulation, Ecology trends, Information Dissemination methods, Systems Integration, User-Computer Interface, Cooperative Behavior, Database Management Systems trends, Databases, Factual trends, Ecology methods, Information Storage and Retrieval trends, Internet, Models, Theoretical, Software
- Abstract
We describe RMCS as one of the first tools for grid computing that integrates data and metadata management into a single job submission system. The system is easy to use, with client tools that are easy to install. Although the RMCS system was developed as a prototype, it is now in production use and a number of scientific studies have been completed using it.
- Published
- 2009
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13. New tools to support collaboration and virtual organizations.
- Author
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Frame I, Austen KF, Calleja M, Dove MT, White TO, and Wilson DJ
- Subjects
- Computer Simulation, Ecology trends, Information Dissemination methods, Cooperative Behavior, Database Management Systems trends, Databases, Factual trends, Ecology methods, Information Storage and Retrieval trends, Internet, Models, Theoretical, Software, User-Computer Interface
- Abstract
We describe the use of new eScience tools to support collaboration, including the use of XML data representations to support shared viewing of the information content of data, metadata tools for documenting data and Web 2.0 social networking tools for documenting ideas and the collaboration process. This latter work has led to the development of the http://SciSpace.net Web resource.
- Published
- 2009
- Full Text
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14. New geochemical insights into volcanic degassing.
- Author
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Edmonds M
- Subjects
- Disasters, Spectrum Analysis, Gases chemistry, Volcanic Eruptions
- Abstract
Magma degassing plays a fundamental role in controlling the style of volcanic eruptions. Whether a volcanic eruption is explosive, or effusive, is of crucial importance to approximately 500 million people living in the shadow of hazardous volcanoes worldwide. Studies of how gases exsolve and separate from magma prior to and during eruptions have been given new impetus by the emergence of more accurate and automated methods to measure volatile species both as volcanic gases and dissolved in the glasses of erupted products. The composition of volcanic gases is dependent on a number of factors, the most important being magma composition and the depth of gas-melt segregation prior to eruption; this latter parameter has proved difficult to constrain in the past, yet is arguably the most critical for controlling eruptive style. Spectroscopic techniques operating in the infrared have proved to be of great value in measuring the composition of gases at high temporal resolution. Such methods, when used in tandem with microanalytical geochemical investigations of erupted products, are leading to better constraints on the depth at which gases are generated and separated from magma. A number of recent studies have focused on transitions between explosive and effusive activity and have led to a better understanding of gas-melt segregation at basaltic volcanoes. Other studies have focused on degassing during intermediate and silicic eruptions. Important new results include the recognition of fluxing by deep-derived gases, which buffer the amount of dissolved volatiles in the melt at shallow depths, and the observation of gas flow up permeable conduit wall shear zones, which may be the primary mechanism for gas loss at the cusp of the most explosive and unpredictable volcanic eruptions. In this paper, I review current and future directions in the field of geochemical studies of volcanic degassing processes and illustrate how the new insights are beginning to change the way in which we understand and classify volcanic eruptions.
- Published
- 2008
- Full Text
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15. Facing future climate change: is the past relevant?
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Skinner L
- Subjects
- Climate, Geology, Models, Theoretical, Uncertainty, Climate Change, Forecasting
- Abstract
From a socio-economic perspective, the 'sharp end' of climate research is very much about looking forward in time. As far as possible, we need to know what to expect and approximately when to expect it. However, it is argued here that our approach to climate change (including its scientific basis and its policy implications) is firmly linked to our understanding of the past. This is mainly due to the role played by palaeoclimate reconstructions in shaping our expectations of the climate system, in particular via their ability to test the accuracy of our climate models. Importantly, this includes the intuitive models that each of us carries around in our mind, as well as the more complex numerical models hiding inside supercomputers. It is through such models that palaeoclimate insights may affect the scientific and political judgements that we must make in the face of persistent and ultimately irreducible predictive uncertainty. Already we can demonstrate a great deal of confidence in our current understanding of the global climate system based specifically on insights from the geological record. If further advances are to be made effectively, climate models should take advantage of both past and present constraints on their behaviour, and should be given added credence to the extent that they are compatible with an increasingly rich tapestry of past climatic phenomena. Furthermore, palaeoclimate data should be accompanied by clearly defined uncertainties, and organized in arrays that are capable of speaking directly to numerical models, and their limitations in particular.
- Published
- 2008
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16. Deep flow in the Madagascar-Mascarene Basin over the last 150,000 years.
- Author
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McCave IN, Kiefer T, Thornalley DJ, and Elderfield H
- Abstract
The SW Indian Ocean contains at least four layers of water masses with different sources: deep Antarctic (Lower Circumpolar Deep Water) flow to the north, midwater North Indian Deep Water flow to the south and Upper Circumpolar Deep Water to the north, meridional convergence of intermediate waters at 500-1500 m, and the shallow South Equatorial Current flowing west. Sedimentation rates in the area are rather low, being less than 1 cm ka(-1) on Madagascar Ridge, but up to 4 cm ka(-1) at Amirante Passage. Bottom flow through the Madagascar-Mascarene Basin into Amirante Passage varies slightly on glacial-interglacial time-scales, with faster flow in the warm periods of the last interglacial and minima in cold periods. Far more important are the particularly high flow rates, inferred from silt grain size, which occur at warm-to-cold transitions rather than extrema. This suggests the cause is changing density gradient driving a transiently fast flow. Corroboration is found in the glacial-interglacial range of benthic delta18O which is ca. 2 per thousand, suggesting water close to freezing and at least 1.2 more saline and thus more dense glacial bottom waters than present. Significant density steps are inferred in isotope stage 6, the 5e-5d, and 5a-4 transitions. Oxygen isotope data suggest little change by mixing in glacial bottom water on their northward path. Benthic carbon isotope ratios at Amirante Passage differ from glacial Southern Ocean values, due possibly to absence of a local productivity effect present in the Southern Ocean.
- Published
- 2005
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17. The future of the carbon cycle: review, calcification response, ballast and feedback on atmospheric CO2.
- Author
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Barker S, Higgins JA, and Elderfield H
- Subjects
- Atmosphere chemistry, Calcium Compounds chemistry, Calcium Compounds metabolism, Carbon metabolism, Carbon Dioxide metabolism, Climate, Computer Simulation, Evolution, Planetary, Feedback, Geologic Sediments chemistry, Oceans and Seas, Atmosphere analysis, Calcium Compounds analysis, Carbon analysis, Carbon Dioxide analysis, Geologic Sediments analysis, Greenhouse Effect, Models, Theoretical
- Abstract
The operation of the carbon cycle forms an important part of the processes relevant to future changes in atmospheric carbon dioxide. The balance of carbon between terrestrial and oceanic reservoirs is an important factor and here we focus in particular on the oceans. Future changes in the carbon cycle that may affect air-sea partitioning of CO(2) are difficult to quantify but the palaeoceanographic record and modern observational studies provide important evidence of what variations might occur. These include changes in surface nutrient use, the oceanic inventory of nutrients, and the elemental composition and rain-rate ratio of marine particles. Recent work has identified two inter-linked processes of potential importance that we consider in some detail: the response of marine calcification to changes in surface water CO(2) and the association of particulate organic carbon with ballast minerals, in particular biogenic calcite. We review evidence from corals, coccolithophores and foraminifera, which suggests that the response of reduced calcification provides a negative feedback on rising atmospheric CO(2). We then use a box model to demonstrate how the calcification response may affect the organic carbon rain rate through the ballast effect. The ballast effect on export fluxes of organic and inorganic carbon acts to counteract the negative calcification response to increased CO(2). Thus, two oceanic buffers exert a significant control on ocean-atmosphere carbonate chemistry: the thermodynamic CO(2) buffer; and the ballast/calcification buffer. Just how tightly coupled the rain-rate ratio of CaCO(3)/C(org) is to fluxes of ballast minerals is an important question for future research.
- Published
- 2003
- Full Text
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