Wed 23rd November 2022 @ 12:00 nn, 312.222 and online via Webex (meeting #: 2652 439 4990 and password: JGf36T2PPgx)

Abstract:

The volatile contents of silicic crustal magmas inform models for volcanism, degassing behaviour, and hydrothermal ore formation. Volatile saturation pressures of phenocryst-hosted melt inclusions are generally restricted to late-stage, shallow magmas that have typically undergone substantial, ascent-driven degassing of CO₂ and SO₂. As an alternative approach, we directly sample the volatile contents of rhyolitic melt inclusions in the accessory mineral zircon. Our results reveal that zircons grow over an exceptional crustal depth range, from Moho depths (>25 km; deepest melt inclusion 31 km) to the upper crust (~5 km). Significantly, melt inclusions from porphyry copper deposit-related magmas have high melt inclusion CO₂ contents (up to 3970 ppm), indicating CO₂-rich sources (equilibrium fluid molar fraction CO₂ up to 0.95). Deep crustal zircons are transported to shallow levels in silicic melts percolating through transcrustal mush systems and/or in rapidly ascending volatile-charged magmas.

Short bio:

Damaris received a Master’s degree in Geology from the University of Bristol, UK in 2017. Her dissertation focused on the formation of tourmaline orbicules in the Cornish Granites and associated pegmatites. She stayed at Bristol to pursue a Ph.D. on the microanalysis of zircon-hosted melt inclusions from barren and mineralised magmatic systems, which she completed in March 2022. She is now a postdoc at Bristol, undertaking brine-rock interaction experiments as part of the NERC CuBES project, to understand the formation of sediment-hosted Cu deposits. Damaris is currently a visiting research associate at Curtin, working on an IGO-funded trial study to develop geochemical proxies for LCT pegmatite formation.