Subduction zones: Zooming in on time, space and composition
From HelsinkiUniversity, Finland
Hosted by Carmen Gaina
The geochemical variability in active volcanic systems provides a unique view into the processes during magma formation and ascent. It is in subduction zone environments where the geochemical cycling of melting, modification, and recycling on Earth starts impacting the compositional heterogeneity of the Earth’s mantle and crust. The major and trace element, radiogenic and U-series isotope geochemistry of minerals, whole rocks, and volcanic glasses in subduction zones can be used to decipher individual processes and their timescales from the subducting slab through the mantle and crust to eruption – the key to our understanding of the evolution of subduction zones.
Here, I will show that geochemical glass and mineral data from the Tongan, Vanuatu, and New Britain island arcs and their associated backarc spreading centers can be used to constrain the sources, processes, and timescales of melting and ascent. Limited crustal storage of melts and the relatively fast ascent of melts are largely independent of crustal thickness but occur along different ascent paths masking much of the slab and mantle wedge-related geochemical signatures. Magmas ascending through thicker island arc crust preferentially use tectonically induced paths. The source heterogeneity of the subducting slab and overlying mantle wedge affects composition on ka to Ma timescales however, crustal assimilation and fractional crystallization may affect composition on millennial timescales or shorter. Thus, the diversity of geochemical signatures in subduction zones is of great importance contributing to our understanding of the evolution of subduction zones and ultimately continental crust formation.