EGU23-3045, updated on 22 Feb 2023
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Constraining fluid-rock alteration and temperature history using multi-mineral argon spectra and conjoint T–t-Δ inversion

Yoli Wu1,2, Marnie Forster1,2, Geoff Fraser3, David Kelsey4, and Gordon Lister1,5,6
Yoli Wu et al.
  • 1Mineral Exploration Cooperative Research Centre, School of Earth & Environmental Sciences, University of Adelaide
  • 2Argon Geochronology Group, Research School of Earth Sciences, Australian National University, Canberra, Australia
  • 3Geoscience Australia
  • 4Geological Survey of Western Australia
  • 5W.H. Bryan Mining and Geology Research Centre, Sustainable Minerals Institute, The University of Queensland, Brisbane 4068, Australia
  • 6MinEx CRC affiliate, The Virtual Explorer Pty Ltd, Clear Range, NSW 2620

Metamorphic rocks record the imprint of the tectonic processes that shaped the lithosphere and record the effects of their journey through time and space. The record can be interrogated by using a number of different geochronological techniques. The 40Ar/39Ar geochronology method is particular useful when it comes to extracting information from the major rock-forming minerals such as mica and feldspar, commonly filling the temporal gap between the ages obtained by U–Pb dating of accessory minerals and the application of low-temperature thermochronometers. Here we present a case study illustrating a novel and innovative way to investigate metamorphic processes across tectonic settings and geologic time, involving metamorphic petrology, geochronology, geochemistry, numerical modelling and tectonics.

The method involves quantitative modelling of 40Ar/39Ar age spectrum morphologies, constrained by conjointly using information from white mica, biotite and potassium feldspar from a single Proterozoic gneiss. Temperature-controlled step-heating diffusion experiments provide estimates of the relevant diffusion parameters using Multi-Domain Diffusion (MDD) models to invert Arrhenius data. Computer modelling and simulation then allows the production of admissible temperature-time paths for all three minerals used in this study, allowing the identification of previously unrecognised episodes of mineral growth and/or periods of cryptic metasomatism. In this way, 40Ar/39Ar geochronology enables estimates for the timing of a sequence of mineral growth events and the veriation of ambient temperature through time.

Two examples are provided from Palaeoproterozoic gneisses from northern Australia. Typically, the morphology of each age spectrum (for biotite, white mica, and potassium feldspar) required a minimal two-component microstructure to explain the mixing pattern. In each mineral, a MDD model is needed to explain the pattern of gas release during furnace step-heating. Estimates of the diffusion parameters using the Arrhenius data allow the inference that both phengite-poorer muscovite and phengite-richer muscovite existed in the white mica aliquot. Quantitative modelling of the age spectrum morphology allowed constraints to be placed on possible temperature-time-growth (T-t-Δ) paths followed by the rock sample in the natural environment, spanning a duration of more than a billion years.

How to cite: Wu, Y., Forster, M., Fraser, G., Kelsey, D., and Lister, G.: Constraining fluid-rock alteration and temperature history using multi-mineral argon spectra and conjoint T–t-Δ inversion, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3045,, 2023.