Interactions between deformation and dissolution-precipitation reactions in plagioclase feldspar at greenschist facies

Gardner, Joe ORCID: 0000-0002-8593-0201, Wheeler, John ORCID: 0000-0002-7576-4465 and Mariani, Elisabetta ORCID: 0000-0002-0585-5265
(2021) Interactions between deformation and dissolution-precipitation reactions in plagioclase feldspar at greenschist facies. Lithos, 396-39. p. 106241.

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Rocks often undergo deformation and metamorphism simultaneously. However, relatively little research has been carried out on the interactions between deformation, fluid influx and a recently identified type of metamorphic reaction, termed interface-coupled dissolution-precipitation. In this study, optical microscopy and electron backscatter diffraction (EBSD) were used to investigate the interactions between deformation and dissolution-precipitation reactions in feldspar from metagabbros deformed at mid-crustal conditions. Fracturing and fluid influx promoted two types of dissolution-precipitation reactions that worked in tandem to convert Ca-bearing plagioclase to pure albite. Conventional dissolution and precipitation, here defined as dissolution precipitation reactions involving a transport step, worked to heal fractures and produce fine-grained albite. In parts of original grains that were not fractured, interface-coupled dissolution-precipitation occurred to albitize mm-cm scale grain fragments. Because interface-coupled replacement displays fast kinetics, reaction fronts were not preserved, so coupled dissolution-precipitation was identified using the following microstructural criteria: a lack of preserved zoning, indicating a fast reaction mechanism; orientation inheritance during reaction indicating epitaxial nucleation/topotactic replacement; intracrystalline strain containing Burgers vectors that indicate distortion was not derived from crystal plasticity; intragranular microporosity and second phase inclusions which share orientations with twin and cleavage planes of their parent grains. These criteria could be applied to any system to identify interface-coupled replacement in the absence of preserved reaction fronts. Brittle fracturing and dissolution-precipitation resulted in an overall grain size reduction, and a transition from dominantly brittle to dominantly viscous deformation, producing mylonites at greenschist facies, and contributing to the development of a regional-scale shear zone.

Item Type: Article
Uncontrolled Keywords: Greenschist-facies deformation, Fluid-rock interaction, Dissolution-precipitation, Interface-coupled replacement reactions, Epitaxy, Electron backscatter diffraction
Divisions: Faculty of Science and Engineering > School of Environmental Sciences
Depositing User: Symplectic Admin
Date Deposited: 08 Jun 2021 14:48
Last Modified: 02 May 2023 10:47
DOI: 10.1016/j.lithos.2021.106241
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