Elements Covers

Thematic Articles

Flyby Missions to Comets and Return Sample Analysis

Images from flyby missions show comets to be geomorphically diverse bodies that spew jets of gas, dust, and rocks into space. Comet surfaces differ from other small bodies because of their ejection of mass into space. Comet solids >2 µm are similar to primitive meteorite ingredients and include the highest temperature materials made in the early solar system. The presence of these materials in ice-rich comets is strong evidence for large-scale migration of solid grains in the early solar system. Cometary silicates appear to have formed in numerous hot solar system regions. Preserved interstellar grains are rare, unless they have eluded identification by having solar isotopic compositions

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Seeing Snails in a New Light

Luminescence is exhibited by many common minerals, some of which have been exploited for dating. Calcite has the potential to date events that occurred over millions of years, but a series of challenges has hindered its use in dating limestone building stones, speleothems, and mollusk shells. Now, however, promising results from calcite luminescence dating have been achieved from an unexpected source: the opercula grown by certain species of snail. Coupled with innovations in luminescence imaging systems, snail opercula offer an exciting new approach that may finally unlock calcite’s potential for dating.

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Luminescence Thermochronometry: Investigating the Link between Mountain Erosion, Tectonics and Climate

Luminescence thermochronometry is a recently developed method that can constrain erosion histories at sub-Quaternary timescales. Luminescence thermochronometry determines the timing and rate at which electrons are trapped and thermally released in minerals, in response to in situ radiation and rock cooling. Erosion histories can be inferred by translating rock cooling rates into an erosion rate using knowledge of the Earth’s thermal field. In this article, we use examples of luminescence thermochronometry applied to the Himalaya mountains, the New Zealand Alps and the Japanese Alps to infer (and link together) wider aspects of regional erosion, climate and tectonic activity.

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Timelines for Human Evolution and Dispersals

Luminescence dating has been instrumental in constraining the age of archaeological and human skeletal remains. Thermoluminescence dating was applied originally to heated pottery and burnt flint, and optical dating was developed subsequently to estimate the depositional age of sun-bleached sediments associated with artefacts and fossils. These methods have helped establish numerical timelines for human evolution and dispersals over the last half million years, including the earliest evidence for modern humans in Africa, Asia and Australia, and the comings and goings of archaic humans in Eurasia and Indonesia. Here, we recount the major role that luminescence dating has played recently in enriching our understanding of global human history.

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Dates and Rates of Earth-Surface Processes Revealed using Luminescence Dating

Understanding rates and variability of Earth-surface processes is vital to assessing natural hazards, landscape response to climate change and addressing concerns related to food security and water supply. Surface processes affect the critical zone, where life interacts with the land surface, and are archived in sediment records. Luminescence dating provides an age estimate for sediment deposition and can provide dates to calculate rates and recurrence intervals of natural hazards and Earth-surface processes. This method has produced robust age estimates from a wide range of terrestrial, marine, tectonic, and archaeological settings. Importantly, luminescence dating covers an age range that spans the last several decades to the last several hundred thousand years, providing critical rates and dates for evaluating processes that are important to society.

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Innovative Dose Rate Determinations for Luminescence Dating

Luminescence dating relies on the fact that mineral grains (crystals) are exposed to sources of natural radiation, which causes charge to be stored in electron traps within the crystal lattice. The radiation dose rate from the grain’s local environment, which ideally should be homogeneous, is what is routinely measured for luminescence dating. However, there are often local, sub-millimetre, sources of radiation heterogeneity that adversely affect a desired luminescence age. For the past 15 years, researchers have been developing Monte Carlo simulations and computer software that can correct for these heterogeneities. These new computer modelling techniques, and concomitant advances in statistics, allow more accurate luminescence dates to be obtained and also allow researchers access to a wider range of samples for an even greater number of dating applications.

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Telling the Time with Dust, Sand and Rocks

Luminescence dating plays a major role in reconstructing environments of Earth’s recent geological history. Since its proposal in 1953, luminescence dating has developed into a versatile geochronological technique that can be applied to material up to 2 million years old. Luminescence dating has many novel applications because it can utilize the most ubiquitous minerals in the Earth’s crust (quartz and feldspar) to determine the timing of sediment burial or exposure. The technique can be applied to grain sizes from silt to boulder, and to sediments that occur in a wide range of settings, e.g. deserts, rivers, lakes, glaciers, caves. This issue discusses the latest technical developments of luminescence dating and the key scientific discoveries that it has facilitated over the last few decades.

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Layered Mafic–Ultramafic Intrusions of Fennoscandia: Europe’s Treasure Chest of Magmatic Metal Deposits

Northeastern Fennoscandia hosts a rich diversity of mafic–ultramafic intrusions of variable shape and size, emplaced in different tectonic regimes over a period spanning ~600 million years (between 1.88 Ga and 2.5 Ga). Several of the bodies contain world-class ore deposits, notably the Kemi chromium deposit and the Pechenga nickel deposits. Other deposits include nickel and copper at Kevitsa, Kotalahti and Sakatti; vanadium at Koillismaa; and platinum-group elements at Portimo and Penikat. These deposits constitute important resources that could shield Europe from potential future supply shortages of these key industrial metals.

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Quantitative Textural Insights into the Formation of Gabbro in Mafic Intrusions

Rock textures provide a key to deciphering the physical processes by which gabbro forms in mafic intrusions. Developments in both direct optical and crystallographic methods, as well as indirect magnetic fabric measurements, promise significant advances in understanding gabbroic textures. Here, we illustrate how bulk magnetic fabric data, particularly from intrusions with sparse silicate-hosted magnetite, may be used to extend direct crystallographic observations from thin sections. We also present a scheme for characterizing crystallographic foliation and lineation and use this to suggest that the strength of gabbro plagioclase foliations and lineations varies significantly with geodynamic environment.

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