Isotopic Analysis of Rare Earth Elements in Geological Samples

Isotopic analysis of rare earth elements (REEs) in geological materials has emerged as a powerful tool to trace processes ranging from mantle differentiation and crustal recycling to sedimentary diagenesis and hydrothermal fluid evolution. REEs, a group of 15 lanthanide elements plus yttrium, exhibit coherent chemical behaviour yet display subtle isotopic variations that encode information about temperature, redox conditions and kinetic effects. Advances in sample purification and mass spectrometric techniques have enabled high-precision measurements of both radiogenic systems (for example, Sm–Nd decay series) and non-radiogenic stable isotope systems (for example, Ce, Nd, Gd). These developments allow geoscientists to distinguish mass-dependent fractionation arising from magmatic crystallisation or low-temperature adsorption from mass-independent nuclear field effects associated with valence changes. Applications include constraining the timing of early Earth differentiation, identifying sediment provenance, reconstructing palaeoceanographic redox trends and tracking the mobilisation of anthropogenic REEs in the environment. The growing suite of double-spike and sample-standard bracketing protocols, coupled with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), now attains analytical uncertainties at or below 0.05‰ for many REE isotope ratios. As a result, isotopic signatures of light lanthanides (La, Ce, Nd) and heavy lanthanides (Dy, Er, Yb) can be reliably compared across diverse rock types, meteorites and aqueous systems. The integration of theoretical partition function calculations with empirical data underpins a holistic understanding of REE isotope behaviour in both terrestrial and extraterrestrial contexts, offering unprecedented insight into Earth’s formation, crust–mantle evolution and modern environmental perturbations.

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Isotopic Analysis of Rare Earth Elements in Geological Samples publication trend

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Technical terms

Rare Earth Elements (REEs): A group of 15 lanthanide metals plus yttrium, valued for coherent chemical behaviour and varied isotopic systems in geoscience.

Isotopic fractionation: The process by which isotopes of an element are partitioned between phases or compounds, producing measurable deviations in isotope ratios.

Multi-collector ICP-MS (MC-ICP-MS): A high-precision mass spectrometer employing multiple detectors to acquire isotope ratios simultaneously, reducing instrumental bias.

Double-spike technique: A method using two enriched isotope spikes to correct for mass bias and instrumental drift, enabling highly accurate isotope ratio measurements.

Sample-standard bracketing: An analytical procedure alternating measurements of a sample and a reference standard to correct mass bias and improve accuracy.

Nuclear field shift effect: A mass-independent contribution to isotope fractionation caused by differences in nuclear charge radii, notably in heavy elements.

Reduced partition function ratio (β): A theoretical factor expressing equilibrium isotope fractionation between phases, calculated from molecular vibrations and energy levels.

References

1. The neodymium stable isotope composition of the silicate Earth and chondrites. Earth and Planetary Science Letters (2017).
2. Determination of Rare Earth Element Isotopic Compositions Using Sample-Standard Bracketing and Double-Spike Approaches. ACS Earth and Space Chemistry (2023).
3. Quantifying mass-dependent isotope fractionation and nuclear field shift effects for the light rare Earth elements in hydrous systems. Geochimica et Cosmochimica Acta (2025).