Developments in Halogen Abundance and Isotope Measurements

The four stable halogens (F, Cl, Br, and I) are low-abundance elements that are widely distributed in nature. Two of the halogens, Cl and Br, each have two stable isotopes showing a range in natural isotope variation of up to a few parts per thousand. A variety of analytical techniques have been developed to determine the abundance and isotopic ratios of the halogens: these include in situ techniques for high spatial resolution studies and bulk determinations, and they have been applied to a range of materials, including whole rocks, minerals, glasses, and fluid inclusions. Here, we summarise some of the established methods for determining halogen abundances and isotopes and highlight key advances.

Read More

Experimental and Observational Constraints on Halogen Behavior at Depth

Halogens are volatile elements present in trace amounts in the Earth’s crust, mantle, and core. They show volatile behavior and tend to be incompatible except for fluorine, which makes them key tracers of fluid-mediated and/or melt-mediated chemical transport processes. Even small quantities of halogens can profoundly affect many physicochemical processes such as melt viscosity, the temperature stability of mineral phases, the behavior of trace elements in aqueous fluids, or the composition of the atmosphere through magma degassing. Experiments allow us to simulate deep-Earth conditions. A comparison of experimental results with natural rocks helps us to unravel the role and behavior of halogens in the Earth’s interior.

Read More

Natural Halogen Emissions to the Atmosphere: Sources, Flux, and Environmental Impact

Understanding the atmospheric geochemical cycle of both natural and anthropogenic halogens is important because of the detrimental effect halogens have on the environment, notably on tropospheric and stratospheric ozone. Oceans are the primary natural source for atmospheric Cl, F, Br, and I, but anthropogenic emissions are still important, especially for Cl. While emissions of human-made halocarbons (e.g., chlorofluorocarbons or CFCs) are expected to continue to decrease allowing progressive stratospheric ozone recovery, volcanic activity (e.g., clusters of mid-scale explosive eruptions or large-scale explosive eruptions) might disturb this recovery over the next decades. This review provides a synthesis of natural halogen fluxes from oceanic, terrestrial, and volcanic sources, and discusses the role of natural halogen species on atmosphere chemistry and their environmental impact.

Read More

Sediments, Serpentinites, and Subduction: Halogen Recycling from the Surface to the Deep Earth

Halogens are important elements that participate in a variety of biogeochemical processes and influence the solubility of metals in subduction-zone fluids. Halogens are powerful tracers of subducted volatiles in the Earth’s mantle because they have high abundances in seawater, sediments, and altered oceanic lithosphere but low concentrations in the mantle. Additionally, Br/Cl and I/Cl ratios, as well as Cl-isotope ratios, have characteristic ranges in different surface reservoirs that are not easily fractionated in the mantle. Current data suggest that subduction of serpentinised lithosphere is a major source of halogens in the Earth’s mantle.

Read More

Halogen Record of Fluid Activity in the Solar System

Halogens are mobile in geological fluids, making them excellent tracers of volatile activity. Halogen-bearing minerals in diverse planetary materials, coupled with chlorine isotope compositions of bulk samples and minerals, can be used to infer the presence of fluids on planetary surfaces, crusts, and interiors. Halogen element and isotopic evidence helps define the role that halogens play in diverse planetary environments (e.g., asteroids, the Moon, and Mars), which offers insights into fluid activity in the early Solar System and in the role such fluids have played in volatile transport, alteration processes, and habitability throughout geological history.

Read More

Halogens: Salts of the Earth

The halogen group elements (F, Cl, Br, and I) and the stable isotopes of
Cl and Br collectively are powerful tracers of terrestrial volatile cycling.
Individually, their distinct geochemical affinities inform on a variety of fluid-mediated and magmatic processes. They form a wide-range of halogenbearing minerals whose composition reflects the source fluids from which they evaporated or crystallized. Fluorine’s geochemical cycle is generally decoupled from that of the heavier Cl, Br, and I, which are concentrated into Earth’s surface reservoirs. Throughout history, the salt-forming halogens have been integral to human health and are key constituents of many industries. These common elements have an important role in tracing geochemical processes across many geologic environments – from the surface to the deep planetary interior.

Read More

Tectonic Petrameter

Geologists study the Earth to learn our planet’s natural history. But the reason behind the planet’s birth still remains a mystery. Won’t you join me on a very special journey through geologic time? Four billion, six hundred million years have passed so please don’t mind me if I move somewhat fast through the story. Rocks are the geologist’s inventory of information. They give us clues to their formation. Ever since its creation, the Earth has been dynamic and constantly changing. All of our panoramic views are always rearranging themselves ever so slowly over time. The oldest slice of time is called the Precambrian which is broken into three, beginning with Hadean, and as you can see, our Earth is thought to have been covered by a sea of magma! Could you have handled it? A bombardment of meteorites also hit and continue to hit our planet.

Read More

Radioiodine Contamination Caused

The Great East Japan Earthquake and Tsunami happened on 11 March 2011, which caused the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The accident resulted in a substantial release of radio-nuclides, including 131I, 134Cs, and 137Cs, into the atmosphere, causing significant environmental contamination. This was a particular issue in many parts of eastern Japan, especially in the Fukushima Prefecture (Yoshida and Takahashi 2012). Among the above-mentioned radioactive isotopes, 131I is one of the most critical radionuclides to be monitored after an accidental reactor release due to its tendency to accumulate in the human thyroid gland.

Read More

v18n1 From the Editors

In this issue, we follow the halogen group elements (fluorine, chlorine, bromine, and iodine) from the Earth’s interior to surface—and even beyond! In a similar vein to two previous Elements issues that also explored groups of elements united by common properties (Rare Earth Elements; October 2012 and Platinum Group Elements; August 2008), this issue similarly showcases the wide diversity of research that is encompassed by halogen mineralogy and geochemistry. Over the last several decades, the halogens have increasingly come into the spotlight, possibly due to improving methods for measuring ultra-low abundance bromine and iodine in geologic materials, as well as isotopes of chlorine and bromine. The result of this increased enthusiasm for halogens is deftly covered over six articles by this issue’s authors—from halogens in Earth and planetary systems to experimental petrology and analytical developments, there truly is something for everyone.

Read More

Beware the Bromides

With respect to Br, I was not meaningfully introduced to the term “bromide” until I was an undergraduate at UC Berkeley. Not in chemistry lab, but rather in a Comparative Literature course. The term “bromide!” was scrawled in red, repeatedly, all over my essay on Moby Dick. Apparently, my deep, philosophical musings on Ahab’s obsessive quest were found to be “trite and unoriginal”. Oh dear! A wellearned, if stinging, instruction on how Br-bearing sedatives (no longer available due to their toxicity) entered the English lexicon to refer to boring and meaningless expressions, in large part due to Gelett Burgess’ 1906 essay, Are You a Bromide?

Read More