<abstract xmlns="http://www.w3.org/1999/xhtml">

<p>Fluid-driven reactions are common in the upper crust, leading to mineral replacement and element redistribution on a kilometer to a micron scale. One common fluid-induced reaction is the chloritization of biotite. Chloritization can lead to the production of multiple phases, such as K-feldspar, titanite, and rutile, depending on local chemistry and fluid composition. Here, we compare different approaches to mass balance calculations using an altered garnet-bearing metapelite collected from Ny Friesland, Svalbard Archipelago, Norway. In the outcrop, amphibolite facies schists are cut by joints that acted as fluid pathways that led to the development of a narrow (~5 cm) alteration zone. Alteration involved the replacement of biotite by chlorite + K-feldspar ± rutile ± titanite. Mass balance calculations based on whole-rock composition and assuming immobile Zr indicate the addition of H<sub>2</sub>O, Si, Ti, Fe, or Mg and the removal of K or Ca. In contrast, mass balance calculated for the pseudomorphic replacement of Bt by Chl + Kfs ± Rt ± Ttn using X-Ray maps for three focused areas indicates the removal of Si or Ti rather than addition. Moles of product phase and elements gained or lost during this reaction varies between individual areas. This variation suggests that fluid heterogeneity and local chemistry governed the progression of the replacement reaction. All the product phases involved in the biotite breakdown are geochronometers and/or geothermometers, providing new opportunities for the petrochronology of fluid-induced reactions.</p>
</abstract>

Fluid-driven reactions are common in the upper crust, leading to mineral replacement and element redistribution on a kilometer to a micron scale. One common fluid-induced reaction is the chloritization of biotite. Chloritization can lead to the production of multiple phases, such as K-feldspar, titanite, and rutile, depending on local chemistry and fluid composition. Here, we compare different approaches to mass balance calculations using an altered garnet-bearing metapelite collected from Ny Friesland, Svalbard Archipelago, Norway. In the outcrop, amphibolite facies schists are cut by joints that acted as fluid pathways that led to the development of a narrow (~5 cm) alteration zone. Alteration involved the replacement of biotite by chlorite + K-feldspar ± rutile ± titanite. Mass balance calculations based on whole-rock composition and assuming immobile Zr indicate the addition of H2O, Si, Ti, Fe, or Mg and the removal of K or Ca. In contrast, mass balance calculated for the pseudomorphic replacement of Bt by Chl + Kfs ± Rt ± Ttn using X-Ray maps for three focused areas indicates the removal of Si or Ti rather than addition. Moles of product phase and elements gained or lost during this reaction varies between individual areas. This variation suggests that fluid heterogeneity and local chemistry governed the progression of the replacement reaction. All the product phases involved in the biotite breakdown are geochronometers and/or geothermometers, providing new opportunities for the petrochronology of fluid-induced reactions.

Mass transfer and element redistribution during chloritization of metamorphic biotite in a metapelite: insights from compositional mapping

Mineralogia

This work is licensed under the Creative Commons Attribution 4.0 International License.

Fluid-driven reactions are common in the upper crust, leading to mineral replacement and element redistribution on a kilometer to a micron scale. One common...

Mass transfer and element redistribution during chloritization of metamorphic biotite in a metapelite: insights from compositional mapping

Article Category: Original Paper

Published Online: Nov 06, 2023

Page range: 43 - 57

Received: Sep 21, 2022

Accepted: Sep 04, 2023

DOI: https://doi.org/10.2478/mipo-2023-0005

Keywords
fluids, mass balance calculations, XMap Tools, biotite breakdown

© 2023 Karol Faehnrich et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

Mass transfer and element redistribution during chloritization of metamorphic biotite in a metapelite: insights from compositional mapping

Article Category: Original Paper

Published Online: Nov 06, 2023

Page range: 43 - 57

Received: Sep 21, 2022

Accepted: Sep 04, 2023

DOI: https://doi.org/10.2478/mipo-2023-0005

Keywordsfluids, mass balance calculations, XMap Tools, biotite breakdown

© 2023 Karol Faehnrich et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

Keywords
fluids, mass balance calculations, XMap Tools, biotite breakdown