Thematic Articles

Isotopic Microsampling of Magmatic Rocks

Radiogenic isotope ratios can be used as a kind of petrogenetic “DNA” to identify the source components of magmas. Technical advances allowing us to measure isotopic compositions at the sub-crystal scale have led to the realisation that many magmatic rocks are isotopically heterogeneous. Crystals traditionally regarded as phenocrysts grown from the host magma have now been shown to be wholly or partly out of isotopic equilibrium with the glass or groundmass in which they are contained. Many of these crystals are likely to be recycled from earlier cumulates. Combining these fingerprinting techniques with the other approaches described in this issue offers an unprecedented opportunity to understand the processes and timescales through which magmas are assembled, differentiated and delivered to sites of eruption or emplacement.

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Igneous Textures: On the Kinetics behind the Words

That igneous textures can be collectively described, classified, and related to magma composition, style of emplacement, and spatial position speaks deeply to the existence of a specific set of fundamental kinetic processes controlling all magma crystallization. Textures record magma life history, telling the most recent, local conditions of cooling and also where the magma has been. Yet it is largely a mystery how silicate melts crystallize, how they become what they are, and, especially, how the final texture relates to the early transient textures more closely linked to the governing kinetics of nucleation and growth. These rich and intriguing processes can be understood by deciphering textures. This is done by first dismantling and quantifying them, then by rebuilding them and simulating magma crystallization and transport, and last by taking the results to the final court of appeal, the rocks themselves.

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3D Analysis of Rock Textures: Quantifying Igneous Microstructures

An important goal of petrographers is to analyse rock textures (microstructures) and compositions in three dimensions, and thus fully quantify rock properties (porosity and permeability, geochemistry, crystal abundance, etc.). With the advent of serial sectioning techniques, X-ray tomography analysis and advanced image analysis, it is becoming increasingly easy to reconstruct rock textures in three dimensions. An exciting consequence is the potential to reconstruct crystal populations in three dimensions and relate their distribution to the chemical budget of a rock. Here we review the current state of the art in textural analysis techniques and consider the possibilities of virtual three-dimensional models of rock textures.

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Frontiers in Textural and Microgeochemical Analysis

Igneous rocks display a large and varied range of textures and compositions, reflecting complex magma pathways, differentiation processes and cooling histories. Integrating geochemical analyses with petrographic and textural information allows us to gain valuable insights into the details of the magma system: the rock’s texture serves as a window into the crystallization history of the magma, while the compositions of the components (crystals and glass) document the conditions and pathways of evolution. In this issue of Elements we take a look at the frontiers in igneous petrology, focussing on the state of the art in textural and microgeochemical analysis and on how we can use some of the latest approaches to unravel the complexities of the magmatic system.

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Tapping Methane Hydrates for Unconventional Natural Gas

Methane hydrate is an icelike form of concentrated methane and water found in the sediments of permafrost regions and marine continental margins at depths far shallower than conventional oil and gas. Despite their relative accessibility and widespread occurrence, methane hydrates have never been tapped to meet increasing global energy demands. With rising natural gas prices, production from these unconventional gas deposits is becoming economically viable, particularly in permafrost areas already being exploited for conventional oil and gas. This article provides an overview of gas hydrate occurrence, resource assessment, exploration, production technologies, renewability, and future challenges

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Nuclear Energy and Uranium Resources

The amount of electricity generated by nuclear power plants may increase in the next few decades, as this form of energy is one of the few that are proven, reliable, and relatively carbon dioxide free. A question often asked about nuclear power is how long its main resource, uranium, will last. In the face of a large expansion of nuclear power to deal with climate change considerations, we revisit the question of the adequacy of the uranium resource and show that there is adequate supply for at least the next century and probably more.

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Geological Carbon Dioxide Sequestration

Akey means of reducing greenhouse gas emissions from fossil fuels is to separate and concentrate CO2 from large point sources and inject it underground. The injection process, so-called “geological carbon sequestration”, uses off-the-shelf technology from the hydrocarbon industry and can be deployed at a useful scale. Widespread deployment will require a greater understanding of processes that trap CO2 underground, improved means of monitoring the injection stream, and a small number of large-scale experiments in settings with the most important representative geology. If successful, geological sequestration could greatly reduce greenhouse gas emissions while we continue to benefit from fossil fuels until true alternatives emerge.

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Confronting the Climate–Energy Challenge

Combustion of coal, oil, and gas has raised the amount of carbon dioxide in the atmosphere to levels higher than they have been for millions of years. A brief review of the history of Earth’s climate puts the next hundred years in its natural context, suggesting that most predictions based on climate models may be underestimating the problem. Reducing risks of future climate change requires changes in existing energy systems. These changes will be in three areas: increasing energy efficiency, increasing the stock of non-fossil energy generation, and adopting technologies for capturing and storing carbon dioxide from fossil fuels.

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Energy: The Issue of the 21st Century

Energy usage makes modern life possible. Without it we would have no communications, transportation, food, health, and many other services and products that we rely on daily. Energy issues are moving to the forefront in the 21st century because of constraints imposed by increasing energy needs, climate change, energy security, and the apparent decline of fossil fuel resources. The main challenge is how to provide more energy for more people worldwide while at the same time reducing greenhouse gas and pollution emissions and providing secure and plentiful energy supplies. There is no silver bullet, so a variety of energy resources and technologies will be required.

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Environmental and Biomedical Applications of Natural Metal Stable Isotope Variations

Metal stable isotopes are now being used to trace metal contaminants in the environment and as indicators of human systemic function where metals play a role. Stable isotope abundance variations provide information about metal sources and the processes affecting metals in complex natural systems, complementing information gained from surrogate tracers, such as metal abundance ratios or biochemical markers of metal metabolism. The science is still in its infancy, but the results of initial studies confirm that metal stable isotopes can provide a powerful tool for forensic and biomedical investigations.

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