Investigating melt inclusions: insights into elemental recycling and boron isotopic signature from the Italian post-collisional setting
Authors:   , Luciani Natascia 
Published: September 2024

This research investigates the role of melt inclusions in understanding elemental
recycling and boron isotopic signatures within the Italian post-collisional geological
context, particularly in continental subduction zones and their complex processes.
Subduction zones, where one tectonic plate is thrust beneath another, are crucial
for transporting surface materials into the mantle, affecting Earth's volatile and
elemental cycles. This process contributes to mantle heterogeneity and influences
the atmosphere through volcanic outgassing, which impacts global climate. Boron
isotopes serve as effective tracers for subduction recycling due to their high
fractionation at low temperatures and strong fluid mobility, providing significant
insights into the fate of subducted materials in both oceanic and continental
collision settings. Analysing melt inclusions (MIs) in minerals like olivine offers
direct estimates of pre-eruptive volatile concentrations, but interpreting primary
melt compositions is challenging due to the migration and mixing of melts and
fluids.
The study addresses two primary objectives. First, it explores crustal recycling
contributions, investigating the primary magmas responsible for compositional
diversity in Italy and the distribution of individual subducted components like fluids
and sediments within the subduction system. Second, it examines boron isotope
signatures, analysing their geographic and temporal variations and identifying the
impact and sources of boron within subduction dynamics. Methodologically, the
study employs carbon and oxygen stable isotope analysis using a continuous-flow
technique that releases CO2 from fluid and melt inclusions for isotope ratio mass
spectrometry (IRMS), which allows for precise isotope measurements and helps

identify CO2 sources in geological samples. The research focuses on high-
potassium magmatic provinces in Italy, using MIs in olivine to understand mantle

heterogeneity and the two-stage melting model for boron.
The findings reveal significant crustal contributions to elemental recycling in Italian
volcanic rocks, particularly those high in potassium, with variations linked to
mantle heterogeneity and past subduction events. Volatile components in volcanic
inclusions indicate the role of recycled materials in the generation of volcanic

7

gases, with implications for understanding past climate impacts. The mantle
beneath Italy shows heterogeneity influenced by both oceanic and continental
subductions, as evidenced by variations in major elements, trace elements, and
boron isotopic compositions in MIs. Future work should focus on refining
techniques for analysing CO2 in MIs and further exploring the dynamics of volatile
recycling, particularly in complex subduction settings like Italy. Recommendations
include improving methods for analysing small-volume inclusions to better capture
primary melt compositions, extending studies to other subduction zones to
compare elemental and volatile recycling on a global scale, and investigating the
long-term climate impacts of subduction-derived volcanic outgassing.