Tracing Earth’s tectono-volatile cycle using apatite inclusions in zircons

Subduction and recycling directly control the volatile budget and fluid fluxed reactions in the Earth’s mantle. As a consequence of mantle melting, the release of magmatic gases contributes to atmospheric cycles by powering redox reactions. Recycling is less important in mid-ocean ridges and hot-spots where mantle melting is driven by mantle upwelling and decompression. Although the contrasting nature between these two tectonic settings seems intuitive, a comparative discrimination between their volatile evolution has not been fully established.

Zircons and their apatite inclusions can offer a much-needed proxy to understand the evolution of magmas and the tectono-volatile cycles on Earth. Zircon can be reliably dated and provide important source information via U-Pb, Hf and O isotope analyses. Apatite inclusions shielded in zircons are carriers of primary geochemical signature and volatile content of magmas. S, Cl, F and OH fit its crystallographic lattice, revealing the primary water content, redox state, and volatile composition of their source magmas. 

This project uses cutting-edge in-situ techniques, including EPMA, LA-ICP-MS and synchrotron radiation to analyse samples from the Coast Mountains in Canada and Rhyolite Mountains in Iceland; prima facie cases of subduction and mid-ocean plume-driven tectonic settings, respectively. The results will be compared to Archaean samples of an uncertain tectonic setting to clarify the tectono-volatile cycle in the early Earth.