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REE Patterns in Geochemistry

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rare-earth-elements REE chondrite-normalized Eu-anomaly

Core Idea

The rare earth elements (La through Lu, plus Y) form a coherent geochemical group with smoothly varying ionic radii, making their chondrite-normalized abundance patterns powerful diagnostic tools. Because all REE are trivalent (except Eu2+ and Ce4+ under specific conditions), their relative behavior during geological processes reflects systematic size-dependent partitioning rather than dramatic chemical differences. The slope of the REE pattern (LREE/HREE ratio) indicates the depth and degree of melting (garnet retains HREE). Anomalies at Eu (controlled by plagioclase fractionation in the crust) and Ce (controlled by redox in marine environments) provide additional process-specific information. REE patterns are among the most widely used geochemical fingerprints in igneous, sedimentary, and environmental geochemistry.

Explainer

The rare earth elements are the geochemist's most versatile pattern-recognition tool. Their coherent geochemical behavior -- all trivalent, similar bonding properties, smoothly decreasing ionic radius from La to Lu -- means that any deviation from a smooth chondrite-normalized pattern records a specific geological process.

Chondrite normalization removes the odd-even abundance variation (the Oddo-Harkins effect, where even-Z elements are more abundant) inherited from stellar nucleosynthesis. After normalization, any remaining pattern is geological. A flat pattern at 10x chondrite indicates a source with chondritic REE ratios. A steep LREE-enriched pattern indicates either a LREE-enriched source or a process that preferentially concentrated LREE. The slope of the pattern, quantified by La_N/Yb_N (where N = chondrite-normalized), ranges from ~1 (flat, like MORB) to >30 (steep, like kimberlites).

The two diagnostic anomalies -- Eu and Ce -- arise from unique redox chemistry. Europium can exist as Eu2+ in reducing conditions (silicate melts, lower crust). Eu2+ has the same charge and similar radius to Ca2+ and enters plagioclase readily. Plagioclase fractionation produces negative Eu anomalies in evolved magmas and complementary positive Eu anomalies in cumulate anorthosites. The magnitude of the Eu anomaly quantifies the role of plagioclase in the magmatic history. Cerium can be oxidized to Ce4+ in surface environments, making it insoluble and causing it to be removed from seawater onto oxide surfaces. Seawater has a pronounced negative Ce anomaly; marine precipitates inherit this signature.

In sedimentary geochemistry, REE patterns trace provenance. Sediments derived from felsic continental sources have negative Eu anomalies, LREE enrichment, and high total REE. Sediments from mafic sources have flatter patterns without Eu anomalies. Marine authigenic minerals (phosphorites, carbonates, iron formations) inherit the REE pattern of the seawater from which they precipitated, preserving a record of marine chemistry -- including Ce anomalies as a proxy for ocean oxygenation -- through geological time.

Practice Questions 3 questions

Prerequisite Chain

Counting to 10 → Counting to 20 → Understanding Zero → The Number Zero → Counting to Five → One-to-One Correspondence → Combining Small Groups Within 5 → Addition Within 10 → Addition Within 20 → Two-Digit Addition Without Regrouping → Two-Digit Addition with Regrouping → Addition Within 100 → Repeated Addition as Multiplication → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Two-Digit by One-Digit Division → Division with Remainders → Remainders and Quotients in Division → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Reading and Writing Decimals → Comparing and Ordering Decimals → Adding and Subtracting Decimals → Multiplying Decimals → Dividing Decimals → Dividing Fractions → Mixed Number Arithmetic → Order of Operations → Integer Order of Operations → Variable Expressions → Combining Like Terms → One-Step Equations → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Iterated Integrals and Fubini's Theorem → Double Integrals in Cartesian Coordinates → Double Integrals over Rectangular Regions → Double Integrals in Polar Coordinates → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Green's Theorem → Surface Integrals and Flux of Vector Fields → Surface Integrals and Flux of Vector Fields → Divergence Theorem: Flux and Outflow → Divergence Theorem → Electric Flux → Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → The Electromagnetic Spectrum → Blackbody Radiation and Planck's Law → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → Heisenberg Uncertainty Principle → Wavefunction and the Born Rule → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → Quantum Entanglement → Bell Theorem and Bell Inequalities → Postulates of Quantum Mechanics → Scattering Theory → Introduction to Scattering Theory → Partial Wave Analysis in Scattering → Spin Angular Momentum → Electron Spin and Intrinsic Magnetic Moment → Stern-Gerlach Experiment: Spin Quantization and Measurement → Electron Diffraction and Matter Wave Properties → Davisson-Germer Experiment: Crystal Diffraction of Electrons → Electron Diffraction and Matter Wave Interference → Wavefunctions and Probability Density Interpretation → Quantum Superposition and Linear Combinations of States → Quantum Operators and Observables → Canonical Commutation Relations and Uncertainty → Heisenberg Uncertainty Principle and Measurement Limits → Time-Independent Schrödinger Equation and Eigenvalues → Hydrogen Atom in Quantum Mechanics → Spectral Lines and Energy Transitions → Selection Rules for Atomic Transitions → LS and jj Coupling Schemes in Multi-Electron Atoms → Pauli Exclusion Principle and Antisymmetric Wavefunctions → Electron Configuration and the Aufbau Principle → The Periodic Table and Atomic Electronic Structure → The Periodic Table → Electron Configuration → Periodic Trends → Ionization Energy → Ionic Bonding → Lewis Structures → Resonance Structures and Delocalized Electrons → Resonance and Formal Charge → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Solubility Equilibria → Phase Diagrams and Clausius-Clapeyron Equation → Chemical Potential and Thermodynamic Equilibrium → Geochemical Thermodynamics → Trace Element Geochemistry → Partition Coefficients → REE Patterns in Geochemistry

Longest path: 172 steps · 774 total prerequisite topics

Prerequisites (2)

Trace Element Geochemistryhard Partition Coefficientshard

Leads To (1)

Sedimentary Geochemistrysoft