Boron Isotope Analysis of Geological Materials

Abstract

Over the last twenty years applications of the boron isotope system have expanded from the analysis of boron-rich phases (e.g., tourmaline, borates) to include other materials with low B concentrations (e.g., carbonates, basaltic glass). The accurate and precise determination of the boron isotopic composition of geological materials is however a difficult task, particularly for those where boron is present in low-concentration. For solution methods, this difficulty arises principally from the near ubiquitous level of boron contamination in most standard clean laboratories, the light mass of the element, the occurrence of only two stable isotopes, and the large mass difference between them. For in situ approaches, such as secondary-ion mass spectrometry, additional difficulties arise from the restricted availability of well-characterized reference materials, from surface contamination, from limited precision in low-concentration samples, and limitations in reproducibility in high-concentration samples that may partly arise from small-scale heterogeneities in the analyzed materials. Nevertheless, a variety of novel techniques, strategies and methodologies have been developed over the past two decades to meet these challenges. We describe here some of these developments and focus on those that we feel are going to play a major role in the growing use of the boron isotope system in the earth and planetary sciences in decades to come.