Project: Deep volatiles cycle during subduction of the continental crust and crust-mantle interaction

Acronym: DeVol

This research is part of the project No. 2021/43/P/ST10/03202 co-funded by the National Science Centre and the European Union Framework Programme for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie grant agreement no. 945339.

Project location:

AGH University of Kraków, Kraków, Poland (https://www.agh.edu.pl/)

Faculty of Geology, Geophysics and Environmental Protection (https://www.wggios.agh.edu.pl/)

Department of Mineralogy, Petrography and Geochemistry (https://kmpg.agh.edu.pl/)

Orogen Dynamics Team (http://odt.agh.edu.pl/)

Project description:

Volatiles (e.g., H2O, CO2, Cl, F, Br, I) are known to move between the Earth’s biosphere and the atmosphere making a cycle. This cycle has also a deep component that is controlled by plate tectonics and it influences several global scale processes such as Earth’s evolution and chemical differentiation and most importantly the formation of oceans and atmosphere, climate changes and the presence of life on Earth. The deep portion of the cycle starts with the segregation of volatiles in oceanic and continental crust rocks within minerals, in pores between the grains and in microfossils and organic matter. In convergent margins, when two plates move toward each other, the denser plate continues to move under the lighter and toward the mantle in a process called subduction. During subduction, the crust transports volatiles from the surface to the mantle. The crust on its journey is subject to dehydration and partial melting that allow the release of volatiles and other incompatible elements in fluids and melts. These fluids and melts can interact with the overlying mantle enriching it in volatiles with a process called metasomatism. In the case of the subduction of the oceanic lithosphere, this interaction can trigger the partial melting of the mantle and thus the partial re-emission of volatiles to the atmosphere via volcanic eruptions above the mantle. Several studies over the last decade demonstrated that the continental crust can mobilize a significant amount of volatiles and other incompatible elements in melts and fluids. However, studies on quantification of the volatiles mobilized and the estimates of volatiles fluxes are still scarce.

In collisional settings, the subduction of the continental crust is followed by the collision of the two continents. In these settings, the volcanic arc does not form and thus volatiles in fluids and melts are then ultimately stored in the mantle overlaying the subducted continental crust rather than partially re-emitted in atmosphere. The proposed project aims to better understand the contribution of the continental crust for the mobilization and storage of carbon and halogens (i.e., Cl, F, Br and I).

Objectives:

• Understanding the volatiles behavior in collisional settings during the subduction of the continental crust.
  
• Quantifing the amounts of volatiles that are released in fluids and melts.
  
• Determining volatiles fluxes and tracking those fluxes through the stage of the Earth’s evolution between 420 Ma and 90 Ma (Phanerozoic).
  

Target:

• Study of melt and fluid inclusions of crustal origin trapped in mantle and associated felsic rocks now part of the crustal package. The rocks specimen selected were deeply subducted at ~ 100-120 km (high pressure) and they come from three major European mountain belts formed at different times in the Phanerozoic. The target of high pressure rocks is especially important for carbon because it is more soluble in fluids and melts at higher pressure.
  

How?

• Geological filed work in Western Gneiss Region (Scandinavian Caledonides, Norway), Bohemian Massif (Variscan orogeny, central Europe) and the Alpine orogeny (Eastern Alps) to collect suitable samples.
  
• Detailed observation with the optical microscope.
• Geochemical analyses on minerals and melt/fluid inclusions to determine the volatiles distribution and concentration.
• Mass balance calculations to determine volatiles fluxes in the different orogens and quantification of amount of volatiles stored within the single orogenic event and throughout most of the Phanerozoic.
  

Publications:

• Ferrero, S., Borghini, A., et al., 2023. H2O and Cl in deep crustal melts: the message of melt inclusions in metamorphic rocks, European Journal of Mineralogy, 35, 1031-1049, https://doi.org/10.5194/ejm-35-1031-2023.
  

Fieldwork in Norway (August 2023):

Migmatitic gneiss hosting eclogite pods (indicated with white arrows) in Otrøya Island, Norway.

Migmatitic gneiss hosting a peridotite body (dashed white rectangle) in Svartberget, Norway.

Principal Investigator:

Dr. Alessia Borghini

Marie Curie Fellow