June 2023 - Volume 19, Number 3

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Olivine

Emily C. First, Philipp Ruprecht, and Benoit Welsch – Guest Editors

Overview

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2023 Topics

Overview

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2023 Topics

Thematic Articles

Olivine—The Little Green Science Machine

By Benoît Welsch, Emily C. First, Philipp Ruprecht, Michael C. Jollands

In some ways, olivine has driven the evolution of the Solar System and likely beyond. As one of the earliest-crystallizing silicate minerals, olivine controls the initial chemical evolution of planet-wide magma oceans and individual lava flows alike. In solid aggregate form, it controls and records deformation of the mantle and smaller-scale intrusive complexes. The components of its crystal structure are mobile at high temperatures and their migration can be used to explore the timing of magmatic events. During chemical weathering, these olivine crystals capture carbon dioxide from the atmosphere as secondary minerals are formed. All of these processes take place not only on Earth, but also on other planetary bodies, making olivine ideally suited to shed light on both primordial planet-building processes and current-day volcanism and surface processes.

Hide and Seek— Trace Element Incorporation and Diffusion in Olivine

By Michael C. Jollands, Ralf Dohmen, José Alberto Padrón-Navarta

Olivine, once overlooked as a host of trace elements, is becoming increasingly important for our understanding of the kinetic and equilibrium behaviour of these elements. Much of our understanding of trace element substitution and diffusion in geological materials comes as a result of experimental and petrological studies of olivine. Here, we consider trace element concentrations and incorporation mechanisms, and how these relate to diffusive behaviour. If we understand trace element behaviour in olivine, we have a powerful tool kit that can be directly applied to address many problems in petrology and volcanology. Perhaps more importantly, what we have learned from olivine can be applied to other minerals and aid us in addressing other far-reaching questions from across the Earth sciences.

Deforming the Upper Mantle—Olivine Mechanical Properties and Anisotropy

By Sylvie Demouchy, Qin Wang, Andréa Tommasi

The interior of the Earth remains our last terra incognita, inaccessible to direct observations. Our understanding of the deformation of the mantle, which shapes our planet through convection and plate tectonics, is based on analysis of: (1) rare mantle rocks carried to the Earth’s surface by volcanic or tectonic processes, (2) the consequences of this deformation on the planet’s surface, and (3) geophysical data. These observables combined with laboratory experiments and numerical modeling imply that olivine deforms via the motion of defects within its crystalline structure and along grain boundaries. Ductile deformation by these crystal-scale processes results in anisotropic propagation of seismic waves, which allows us to probe upper-mantle deformation at scales of tens to hundreds of kilometers.

Olivine Exit Interviews—Piecing Together Magmatic Puzzles

By Philipp Ruprecht, Benoît Welsch

When magmas erupt at the surface, they may have undergone many changes since their inception. While olivine drives some of these changes through crystallization and fractionation, it also records the magma evolution via mineral chemistry and by trapping mineral and melt inclusions. Olivine is an effective recorder of intensive parameters, such as temperature and melt composition, and provides an outstanding petrological tool for constraining dynamic processes, such as ascent, mixing, and cooling. Olivine sheds light on magmatic puzzles that involve both mafic and more evolved magmas, with protracted and complex magmatic histories that often obscure earlier and deeper processes. This contribution summarizes the current state of how olivine helps reconstruct source-to-surface magma assembly through its chemistry, inclusions, and textures.

Olivine—The Alteration Rock Star

By Oliver Plümper, Juerg Matter

Olivine is the main component of the Earth’s upper mantle, on which our tectonic plates rest. As such, olivine has been studied since the dawn of geology and is regarded as the storyteller of the Earth’s interior. Its physical and chemical properties provide insight into its creation in magmas and its voyage through the upper mantle. However, when olivine is exposed to aqueous fluids, it adopts a more rebellious, rock star–like disposition. Here, we show that the discord, or disequilibrium, between olivine, its reaction products, and fluids containing water and carbon dioxide is so significant that it has been instrumental in changing the Earth throughout the planet’s history and will continue to do so well into the future.

Galaxy of Green

By Emily C. First, Christopher Kremer, Myriam Telus, David Trang

Olivine occurs across the galaxy, from Earth to extraterrestrial bodies including the Moon, Mars, and asteroids, to particles of comet dust and distant debris disks. The mineral is critical to our understanding of early Solar System chronology, planetary formation processes (e.g., magma ocean solidification), crustal evolution (e.g., volcanic eruptions), and surface weathering. Olivine’s ability to shed light on these processes lies in the linkage of small, physical samples and satellite-derived data. Laboratory spectra become the basis for olivine detection and compositional interpretation in remotely sensed spectra ranging from high-resolution planetary maps to single extra-solar datapoints. In turn, petrologic studies of olivine underpin the geologic interpretations of these spectral datasets. Finally, olivine chemistry records Solar System formation conditions and relative chronology. Olivine is our bridge across time and space.