FluidNET Science Conference Abstract - Dating by crushing: The promise of histories of fluid migration
Creators: name: Jan R. Wijbrans
name: Intan Chalid
name: Akbar Huseynov
name: Bertram A. Uunk
name: Rosanne Huybens
name: Wim van der Plas
name: Onno Postma
name: Huaning Qiu
name: Klaudia F. Kuiper
Publisher: name: Zenodo
Year: 2024

description: Dating by crushing: The promise of histories of fluid migration

 

Jan R. Wijbrans1, Intan Chalid1, Akbar Huseynov1, Bertram A. Uunk1, Rosanne Huybens1, Wim van der Plas1, Onno Postma1, Huaning Qiu1,2, Klaudia F. Kuiper1

1Vrije Universiteit Amsterdam, Department of Earth Sciences, 

2China University of Geosciences, Wuhan, School of Earth Resources.

 

In noble gas geochemistry there are several approaches to liberate trapped gas from minerals or rock samples. Bulk heating, either stepwise or by single fusion will ultimately free all gas components, spread out ion several steps or in bulk. These approaches are most commonly used. Spatial distribution of gases within the crystal lattices can be resolved by laser ablation/spot fusion. Since the late 1980’s, crushing has been used to liberate the volatiles from the sample. Again, bulk crushing to access the helium in basalt phenocrysts, or stepwise crushing when it is suspected that multiple gas components need to be resolved1.

These volatiles reside in fluid inclusions (FIs), that represent voids in the crystal lattice originating either from entrapment of volatiles during primary crystal growth, or originating from entrapment later in the history of the mineral. Primary and secondary inclusions can be distinguished by petrographic description, where primary inclusions occur either randomly or along growth zones such as crystal facets. Secondary inclusions may form by crack annealing, resulting in planar arrangements of numerous inclusions. FIs may be as large as >100 micrometer, and smaller.

 

40Ar/39Ar geochronology is useful in particular in essentially K-free mineral lattices, when the hydrous volatile component entrapped in the FIs contains appreciable concentrations of potassium2. Over time the radiogenic 40Ar component in the fluid will increase by radioactive decay of the dissolved 40K. In its simplest form the results from stepwise crushing would reveal mixing of the radiogenic component with a background, commonly modern atmosphere. In practice we almost always have to deal with an ambient non-radiogenic component as well, and in the literature cases have been described where in addition to a primary potassic hydrous fluid a secondary potassium-bearing fluid can be inferred. 

Stepwise crushing have proven to be a viable approach to separate primary and secondary volatile sources from a background contaminant. This would work under the assumption that primary and secondary inclusions have different properties such as size, and strength, where larger or weaker FIs would contribute to the spectrum by crushing in the early stages, and stronger and smaller FIs would dominate the latter stages. Resistance to resetting would be a function of mechanical or chemical recrystallization of the host mineral, and ultimately the diffusivity of the gas in the crystal lattice at high temperature.

 

Pitfalls include incomplete resolution of the mixing endmembers (often as a function of potassium concentration in the FIs), contribution from solid inclusions, or for the case of zeolites contribution of gas from the crystal lattice has been documented in the literature3. Strategies to improve separation of endmember components require attention. 

 

References:

1: Turner G, Bannon MP., 1992, GCA, DOI10.1016/0016-7037(92)90128-6 

2: Xiao M., 2022, GCA, DOI10.1016/j.gca.2022.01.025

3: Kendrick, M.A., Phillips D. 2009, GCA, DOI10.1016/j.gca.2009.06.032

 

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 956127