A team of Geographical and Earth Scientists at the University of Glasgow have discovered that analysis of one particular type of rock may hold the key to a better understanding of fluids in the Earth's crust.

Dr Tim Dempster and his colleagues have discovered that the surfaces of the mineral, apatite, are capable of preserving potentially useful information about the changes that rocks experience, including unique details of the behaviour of fluids at depth. The find will give geologists new insights into fluid movements in the Earth's crust.

Our knowledge of fluid movements in Earth's crust is important as it impacts a variety of areas of earth science: from the safe storage of nuclear waste to the recovery of hydrocarbons and the concentration of metals to form economic deposits. However, determining the exact history of fluid interaction with rocks at depth by observing rock surfaces has traditionally proved difficult because rocks undergo significant changes as they cool down and become exposed at Earth's surface, where geologists are able to sample them.

Dr Tim Dempster said: "This particular study uses a state-of-the-art electron microscope to examine the surfaces of the minerals at scales of a few microns and represents a new way of examining rocks. In the past, most geologists have examined rocks in cut and polished sections, however this makes it difficult to study the natural edges of minerals, where fluids would move through the rocks. Consequently we have developed methods to study broken rock surfaces where original mineral edges are preserved intact.

"The results of this investigation on rocks from the Outer Hebrides show that one particular mineral, apatite, preserves a unique range of surface textures that allow the history of fluid movements through the rocks to be deciphered. We have now observed similar features in rocks from a wide variety of places. These accessory minerals are providing a wealth of new information on the distribution and movement of fluids within rocks, both at high temperatures and as the rocks cool on their way back to the Earth's surface."

The work, studying the interaction of fluids with rocks in the shallow crust with emphasis on the behaviour of a group of minerals called accessory minerals, will feature in the November edition of the prestigious international journal 'Geology', published by the Geological Society of America.

Martin Shannon (m.shannon@admin.gla.ac.uk)

Further information: Tim Dempster, University of Glasgow, Geographical and Earth Sciences Tel: 0141 330 5445

First published: 26 October 2006