27. March 2019 - 15:00 till 18:00
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Geological Society March Public Lecture - Matinee | The Geological Society | Wednesday, 27. March 2019

Diamond windows into the deep Earth
Kate Kiseeva, University College Cork, Ireland; University of Oxford, UK
The carbon cycle is one of the most important of Earth’s cycles: it impacts such important layers of our planet as atmosphere, hydrosphere and biosphere that is responsible for life. Large amounts of carbon are transported into the deep mantle via subduction. Some of this carbon is returned back to the surface via arc magmatism, and some of it is transported, with the downgoing slab, into the transition zone and the lower mantle, generating local heterogeneities.  
Despite efforts to quantitatively estimate the forms in which carbon that is stored in the mantle, the volume of each carbon reservoir and the magnitude of fluxes between these reservoirs, the Earth’s carbon cycle is still not well constrained. The main difficulty in quantifying the carbon cycle is the lack of hand specimens from depths below ~150 km. This leads to large uncertainties in the carbon content of much of the deep mantle (and what phase it is stored in), making it difficult to estimate the magnitude and mechanisms by which carbon goes from the surface to the deep mantle. Due to the fact that most of our planet is inaccessible by direct sampling, researchers have turned toward experimental, geophysical or computational methods to address the deep carbon cycle.
Although we do not have hand-sized pieces of the deep mantle that are brought quickly to the surface, there is one source of samples that we do have: inclusions in diamonds. Diamonds, thought to form in the upper mantle and the mantle transition zone (410-660 km) often incorporate small pieces of their surrounding material when they formed. These inclusions provide a unique window in the deep mantle, giving researchers much-needed information about the composition of our planet as well as processes which took places millions and billions of years ago.
Some of the deepest inclusions that have been found, derive from the mantle transition zone and the lower mantle (>660 km). These inclusions are exceedingly rare, but they are the only natural samples from those depths, and thus they carry a wealth of potential knowledge. In this talk I will  give an overview of deep diamonds and their inclusions: how these diamonds form, what minerals they bring, what they tell us about the composition of the deep mantle, and how they relate to the deep carbon cycle.
 
14.30     Tea and coffee served in the lower library
15.00     Lecture 
15.45     Questions and answers
16.00     Lecture ends and guests depart

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