Microsampling and Isotopic Analysis of Igneous Rocks: Implications for the Study of Magmatic Systems

Abstract

Isotopic fingerprinting has long been used to trace magmatic processes and the components that contribute to magmas. Recent technological improvements enable us to measure the isotopic composition of progressively smaller samples. This has provided an opportunity to analyze isotopic compositions on the scale of individual crystals, their growth zones, and their trapped melt inclusions, and consequently, to integrate isotopic and geochemical tracing with textural and petrographic observations. Over the past decade, as a result of these advances, it has become clear that mineral phases are commonly not in isotopic equilibrium with their host glass/groundmass. Isotopic ratios recorded from core to rim of a mineral grain reflect the progressive changes in the magma composition from which the mineral crystallized. The sense of these changes and the relationship between isotopic composition and petrographic features, such as dissolution surfaces, can be used to constrain magma evolution pathways involving open system processes such as magma mixing, contamination and recharge.