Melt inclusion

[4] They may contain a number of different constituents, including glass (which represents melt that has been quenched by rapid cooling), small crystals and a separate vapour-rich bubble.

[5] They occur in the crystals that can be found in igneous rocks, such as for example quartz, feldspar, olivine, pyroxene, nepheline, magnetite, perovskite and apatite.

There are various techniques used in analyzing melt inclusion H2O and CO2 contents, major, minor and trace elements including double-sided FTIR micro transmittance,[9] single-sided FTIR micro reflectance,[10] Raman spectroscopy,[11] microthermometry,[12] Secondary Ion Mass Spectroscopy (SIMS), Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), Scanning Electron Microscopy (SEM) and electron microprobe analysis (EMPA).

Raman spectroscopy can also be used to determine the density of CO2 contained in a vapor bubble if present at a high enough concentration within a melt inclusion.

[26][27] Scanning electron microscopy is a useful tool to employ before any of the above analyses that may result in loss of the original material since it can be used to check for daughter minerals or vapor bubbles and help determine the best technique that should be chosen for melt inclusion analysis.

[29] This method can be used to determine the dimensions of different phases present in melt inclusions more precisely than by using visible light microscopy.

[4] Given that melt inclusions form at varying pressures (P) and temperatures (T), they can also provide important information about the entrapping conditions (P-T) at depth and their volatile contents (H2O, CO2, S, Cl and F) that drive volcanic eruptions.

Multiple melt inclusions in an olivine crystal. Individual inclusions are oval or round in shape and consist of clear glass, together with a small round vapor bubble and in some cases a small square spinel crystal. The black arrow points to one good example, but there are several others. The occurrence of multiple inclusions within a single crystal is relatively common
Melt inclusion with accompanying vapor bubble from an olivine crystal. Collected from ash related to the 1992 eruption of Cerro Negro Volcano, Nicaragua
Animation of a melt inclusion viewed in transmitted light.