LASSIE (laser ablation sampler for stable isotope extraction) applied to carbonate minerals

Abstract

LASSIE is an instrument that enables rapid (∼ 30 min) stable isotope analysis of extremely small (∼ 35-μm diameter) areas of carbonates, selected by the operator from a colour TV image of a thin rock slice. This allowspractical routine integration of petrography with isotopic analysis.

The main technical problem—isotopic fractionation during laser ablation—has been overcome by generating correction factors based on analyses of standards (for calcite, correction factors are +1.2‰ forδ¹⁸O, —0.8‰ forδ¹³C. Accuracy is determined by the uncertainty (σ) in these correction factors:±0.4‰ forδ¹⁸O andδ¹³C. Reprocducibility of replicate analyses is also∼ ±0.4‰ (σ) forδ¹⁸O and ∼±0.2‰ forδ¹³C.

An example in which LASSIE analyses were performed on carbonate-cemented sandstones, demonstrated the ability of LASSIE to resolve the various components of a complex carbonate mixture. The study further demonstrated how conventional bulk analyses can give uninterpretable or, worse, misleading results.