Determination of Rare Earth Element Isotopic Compositions Using Sample-Standard Bracketing and Double-Spike Approaches

Justin Y Hu; Francois L H Tissot; Reika Yokochi; Thomas J Ireland; Nicolas Dauphas; Helen M Williams

doi:10.1021/acsearthspacechem.3c00172

Determination of Rare Earth Element Isotopic Compositions Using Sample-Standard Bracketing and Double-Spike Approaches

ACS Earth Space Chem. 2023 Nov 6;7(11):2222-2238. doi: 10.1021/acsearthspacechem.3c00172. eCollection 2023 Nov 16.

Authors

Justin Y Hu^{1

2}, Francois L H Tissot^{1

3}, Reika Yokochi¹, Thomas J Ireland^{1

4}, Nicolas Dauphas¹, Helen M Williams⁵

Affiliations

¹ Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637, United States.
² Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom.
³ The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125, United States.
⁴ Department of Earth and Environment, Boston University, 685 Commonwealth Avenue, Boston, Massachusetts 02215, United States.
⁵ Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kindgom.

Abstract

Rare earth elements (REEs) have been found to have numerous uses to trace geological and cosmochemical processes through analyses of elemental patterns, radioactive decay, nucleosynthetic anomalies, and cosmogenic effects. Stable isotopic fractionation is one aspect of REE geochemistry that has been seldom studied, with most publications focusing on the development of analytical methodologies for individual REEs, and most applications concerning terrestrial igneous rocks. In this study, we present a method to systematically analyze stable isotopic fractionations of 8 REEs, including Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb, using sample-standard bracketing (SSB) and double-spike (DS) approaches. All REEs are separated and purified using a fluoropolymer pneumatic liquid chromatography (FPLC) system. We introduce procedures for identifying and correcting some isobaric interferences in double-spike data reduction. Several geostandards, including igneous rocks and sediments, are analyzed using SSB and DS methods. The results indicate that REE isotopic fractionation in igneous processes is limited, except for Eu. Other REEs can still be isotopically fractionated by low-temperature processes and kinetic effects at a high temperature.