Rare Earth Elements (REE) The rare earth elements (REE) are the most useful of all trace elements, with significant applications in igneous, sedimentary, and metamorphic petrology. The REE comprise the series of metals with atomic numbers 57 to 71 (La to Lu). Additionally, the element Y, which has an ionic radius similar to that of […]
What is an Oxygen Isotope Thermometry One of the first applications of the study of oxygen isotopes to geological problems was geothermometry. Urey (1947) suggested that the enrichment of 18O in calcium carbonate relative to seawater was temperature-dependent and could be used to determine the temperature of ancient ocean waters. The idea was quickly adopted, and
Sulphur Isotopes There are four stable isotopes of sulphur: The ratio between the two most abundant isotopes, 34S/32S, is essential in geochemistry. It is expressed in parts per thousand relative to the troilite (FeS) reference standard from the Canyon Diablo iron meteorite (CDT) as follows: 34S/32S=( 34S/32S (sample) – 34S/32S (standard) ) / 34S/32S (standard)
Carbon Isotopes Carbon has two stable isotopes with the following abundances: Measurements are made relative to a standard belemnite sample known as PDB – Belemnitella americana from the Cretaceous Peedee formation, South Carolina. The original material of the PDB standard is now exhausted, and current standard materials are a carbonatite (NBS-18) and a marine limestone
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Hydrogen Isotopes There are two naturally occurring stable isotopes of hydrogen, which occur in the following proportions: Hydrogen isotopes show the largest relative mass difference between two stable isotopes. This leads to significant variations in hydrogen isotope ratios in naturally occurring materials. These isotopes are widespread in nature, present in forms like H₂O, OH⁻, H₂,
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What are the stable isotopes of oxygen and their abundances? There are three stable isotopes of oxygen which have the following abundances: The isotope ratio 18O/16O is typically measured in oxygen isotope studies, and δ values are calculated from this ratio. There are two main isotopic standards used for these measurements: PDB and SMOW. PDB
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Understanding the physical and chemical controls on stable isotope fractionation is vital to a correct interpretation of measured stable isotope ratios. When the fractionation processes are well understood, the measured δ-values can be used to correctly identify the source of the element in question and the geological processes involved. In this section, we examine briefly
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What is Isotope Fractionation? Isotope fractionation is the process by which stable isotopes are separated based on their mass rather than their chemical properties. This natural process occurs in three main ways: 1. Isotopic Exchange Reactions Isotope fractionation can occur during conventional exchange reactions, such as when oxygen isotopes exchange between quartz and magnetite. The
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