Monday, 11 January - 15.30 h, Kleine Collegezaal Earth Sciences

'The cycling and detection of volatiles in the Earth's interior' by
Dr. Daniel Frost
(Bayerisches Geoinstitut, University of Bayreuth, Germany)

All are welcome - There will be drinks afterwards

Abstract:

Volatiles such as H2O and CO2 play an important role in many physical and chemical processes in the Earth's mantle.
The mantle is also a major reservoir for volatiles, with bulk concentrations that are likely comparable to that at
the Earth's surface. Understanding the volatile content of the mantle and the flux of volatiles through the interior
is a major challenge requiring the assimilation of evidence from geochemistry, mantle petrology and seismology
and interpretation using results of high-pressure experiments and geodynamic modeling. Subducting slabs are initially
enriched in volatiles due to alteration of the oceanic lithosphere at the surface. The passage of volatile components
through the mantle can be assessed through high-pressure experiments on the stability of volatile minerals.
Many volatile minerals breakdown in subduction zones at depths below 150 km causing metasomatism of the mantle wedge,
as inferred in island arc magmas. Some proportion of volatiles, however, likely remains within the subducting slab
to be transported to greater depths. The key to understanding this deep mantle volatile content lies in the interpretation
of seismic observations. Observations of slow seismic wave velocities in the deep mantle have been attributed
to the presence of deep volatile rich melts. It has been argued that melting beneath mid ocean ridges commences with
the production of small degree volatile rich melts at conditions much deeper in the mantle than the main phase
of silicate partial melting. It may also be possible to detect the presence of H2O in the mantle from its influence
on transition zone phase transformations that can be detected in seismic studies. Ultimately sufficient volatiles must be
returned to the convecting mantle to balance the loss of volatiles from the mantle at mid ocean ridges.