We are pleased to welcome George Zellmer to speak at a Petrology Lunch on: Plutonic nature of transcrustal magmatic systems revealed by submicron Sr disequilibria in plagioclase.

Abstract:

The new paradigm of transcrustal magmatic systems envisages remobilization of voluminous mush zones close to their solidus temperature with small amounts of interstitial melt. To test this paradigm, diffusion of major or trace elements across sharp compositional boundaries may be employed to obtain crystal residence times at magmatic temperatures. Plagioclase crystals are common crustal minerals yet reading the chronology of their zonation is hampered by complex high-frequency major element zonation, which determines trace element partitioning and diffusion behaviour. Here we present stacked CMOS-type active pixel sensor (SCAPS) isotopographic images yielding submicron-resolution Sr and major element zonation in volcanic plagioclase microantecrysts from the Southern Taupo Volcanic Zone (STVZ). Fourier-transform spatial frequency analysis of intracrystalline Sr disequilibrium during forward diffusion enabled parameterization of the decay of individual spatial frequencies and approximation of pre-eruptive zoning profiles. Pre-eruptive crystal residence times at magmatic temperatures are of the order of days to weeks for STVZ microantecrysts, timescales inconsistent with long residence at elevated temperatures. Our approach is applicable to volcanic systems globally. STVZ magmatism is characterized by ephemeral temperature spikes from small magma batches and remobilisation of small volumes of rapidly cooled antecrysts, characterizing the cool plutonic nature of this transcrustal magmatic system.

 

For the Zoom link:

Meeting ID: 921 4453 5423

Passcode: 142037