The Hidden Colours Inside Volcanoes

The petrographic microscope is an important tool for geologists. Many generations of us have grappled with thin sections and polarisers in student labs. With luck and perseverance we can learn how to read the record of geological processes that is written in the shapes and sizes of crystals in rocks.

At the very least, most of us quickly appreciate the colourful beauty of thin sections of silicate rocks observed under crossed polars.

Recent rapid advances in the technology of chemical microanalysis and imaging have returned petrography to the leading edge of geological research. These techniques have enormous potential to solve a number of problems in igneous petrology in particular. Quantitative estimates of the spatial characteristics of compositional variation within rocks can be used to test and refine physical models of sub-volcanic processes.

One exciting aspect of this problem is our newfound ability to link the timescales of chemical zonation within individual magmatic crystals to timescales of magmatic evolution prior to large eruptions. The timescales are surprisingly short, bringing the prospect of linking petrological information to monitoring records from active volcanoes.

In John's talk, he will try to show how beautiful images of igneous rocks under the microscope can help to understand the inner workings of volcanoes.