T139 State-of-the-Art and Future Directions in Petrology and Petrochronology II: A Session in Honor of Chris Yakymchuk, University of Waterloo, GSA MGPV Early Geological Career Awardee for 2024

Monday, 23 September 2024
1:30 PM - 5:30 PM
206B

READING BETWEEN THE LINES: MODELLING MINERAL ZONING VIA DISEQUILIBRIUM ACCESSORY MINERAL GROWTH

Paper number: T139-3
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

The growth rings of mineral crystals provide snapshots of geologic systems—but when were those photos taken? Analysing discrete zones of crystals provides great details of evolving crustal processes unavailable for direct observation. Therefore, understanding the dissolution and growth of these crystals is critical in their use as proxies for temperature-pressure-composition conditions in magmatic and metamorphic systems. Attempts at accessory mineral modelling using the saturation of essential structural components in the melt paired with phase equilibrium modelling has tried to provide context for these data. However, these models are calculated assuming equilibrium between the entire accessory mineral and the rest of the system—conditions in which trace element zoning would be absent.

We pair thermodynamic phase equilibrium modelling with trace element and accessory mineral modelling to simulate equilibrium and disequilibrium growth of zircon. Using metasedimentary and igneous compositions to model the growth of zircon during crustal anatexis and magma emplacement respectively and better predict the zoning observed in the rock record. Our models indicate disequilibrium growth is a critical aspect in the formation and preservation of the zoning in accessory mineral crystals. Additionally, the trace element concentrations and ratios (e.g. Ti, Th/U, Gd/Yb) of accessory mineral grains are transient during crystal growth and may not be diagnostic indicators for petrochronology and tectonic reconstructions. Further, the relationship between cross-sectional area and volume is another important aspect of decoding accessory mineral data as relative thin rims can represent significant crystal growth. Temporally linking crystal growth and trace element data will lead to a better understanding of how system conditions evolve, geologic timescales, and ultimately enable more precise reconstructions of the Earth’s processes.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403576

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.