Biological and hydrological activity cause volatiles to be rapidly exchanged between surface reservoirs, forming the life-sustaining water, carbon and nitrogen cycles; however, volatiles are also exchanged between the surface and the Earth’s interior as a result of plate tectonic processes. As the Earth’s mantle - the essentially solid silicate region of the interior - comprises by far the largest terrestrial reservoir for most volatile elements, it has an enormous capacity to influence the surface availability of these elements over geological time. Volatiles within the Earth also influence physical properties that likely regulate the very plate tectonic processes responsible for their deep transport cycle. Understanding the interdependence between the geochemical and geodynamic behaviour of volatiles, in addition to quantifying how volatiles are transported, stored and expelled from the interior, are key challenges in illuminating the unique long-term sustaining mechanisms of our planet and form the research focus of this IRTG.

The cycling of water

The cycling of water between potential
reservoirs in the interior along with those
that might have developed in the Hadean.

Large gaps exist in our understanding of Earth´s deep volatile cycles, because (i) some important volatiles have hardly been studied due to analytical problems; (ii) data are limited mostly to the crust and upper mantle for other volatiles, (iii) current models of volatile cycles ignore the feedback of mantle volatile contents on mantle dynamics, (iv) the same models do not appropriately treat the interaction between different volatiles, including the effect of oxygen fugacity. Projects within this IRTG are aimed at addressing these issues using experimental and computational modelling strategies.

An important aspect is the involvement of researchers, principally from the university of Tohoku who complement the experimental strength of BGI through observational expertise in the study of volatiles entering and exiting the mantle and in interpreting geochemical and geophysical evidence for the passage of volatiles within the Earth. Their involvement powerfully extends the competence of the IRTG by allowing experimental researchers to be in close contact with the observational studies. This competence is essential for the design and execution of experimental studies, for the evaluation of models and training of students. Through 6 to 12 month exchange visits, doctoral researchers are exposed to complementary aspects of experimental and observational volatiles research. Although high-pressure research has always been motivated by outstanding questions concerning Earth and planetary interiors, it has been continuously facilitated by advances in technology. Technique development is therefore a crucial aspect of many IRTG projects.

A new multianvil press

A new multianvil press facility
for experiments in excess of 25 GPa

The structured qualification programme provides doctoral researchers with (i) an integrated understanding of global volatile cycles and (ii) trains them in modern methods of high-pressure/high-temperature experimentation that can be applied to various branches of physical sciences and materials science. Due to natural synergies in expertise between the principal researchers a range of courses are offered that are specifically relevant to the research focus. Through workshops and short courses, key topics from experts at the University of Tohoku also provide background in volatile cycles.

A thin section in polarised light

A thin section in polarised light
showing a series of water bearing
lower mantle minerals.

Many types of experiments for investigating properties at extreme conditions can only be performed at large centralised facilities, such as neutron and synchrotron X-ray sources, which are consequently an increasingly important component of modern research. Many of these techniques provide the only mechanism for the analysis of small high-pressure samples. Doctoral researchers also receive training in key new technologies specifically chosen to augment their principal research topic. Complementary methods are also made available thought the use of Japanese centralised facilities during research visits. Knowledge of these techniques and their applications provide important tools for the next generation of researchers in academia and industry.