The nanoSIMS as a tool to study zonation around/in melt inclusions

Abstract

Melt inclusions preserve geochemical records of magmatic processes and can provide windows into melt composition prior to near-surface fractionation processes such as degassing, crystal fractionation, and mixing that can influence the compositions of erupted magmas. The compositions of melt inclusions are usually measured near their centers using in-situ analytical techniques such as electron microprobe, ion probe, or LA-ICPMS. However, melt inclusions can experience post-entrapment modifications through crystallization or exchange with the host mineral or the outside melt via diffusion through the host mineral. For example, water loss (or gain) can occur by diffusion of H-bearing species through the host mineral toward (or from) the enclosing melt. Zonation in melt inclusions and their host minerals provide information on such post-entrapment modifications. We present a new approach to the study of such zonation using the nanoSIMS Cameca 50L high-resolution ion microprobe. Our data document mechanisms of chemical evolution of melt inclusion after entrapment and can constrain the nature and timescales of syn-eruptive processes.

Files

Additional details