Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble

Barbara Etschmann, Joel Brugger, Mark Pearce, Christine Ta, David Brautigan, Michael Jung, Allan Pring

    Research output: Contribution to journalArticlepeer-review

    22 Citations (Scopus)

    Abstract

    Limestone dolomitization is an example of a fluid-induced mineralogical transformation that commonly affects extensive rock volumes. To understand the mechanisms enabling these efficient replacement reactions, we investigated experimentally the dolomitization of a fractured calcite marble under flow-through conditions at mild hydrothermal conditions. Contrary to most earlier studies of coupled dissolution reprecipitation reactions that were conducted using small, individual grains, in this study, the integrity of the rock was preserved, so that the experiment explored the links between flow in a fracture and fluid-rock interaction. In these experiments, grain boundaries acted as microreactors, in which a Mg-poor 'protodolomite' formed initially, and then transformed into dolomite. The difficulty in nucleating dolomite played a key role in controlling the evolution of the porosity, by allowing for (1) initial dissolution along grain boundaries, and (2) formation of coarse porosity at the reaction interface. This porosity evolution not only enabled the reaction to progress efficiently, but also controlled the mineralogy of the system, as shown by brucite replacing calcite near the fracture once the fluid along calcite grain boundaries became sufficiently connected to the fluid flowing through the fracture. This study illustrates the role of grain boundaries, porosity evolution and nucleation in controlling reaction progress as well as the nature and textures of the products in pervasive mineralogical transformations.

    Original languageEnglish
    Article number1045
    Pages (from-to)1-12
    Number of pages12
    JournalCONTRIBUTIONS TO MINERALOGY AND PETROLOGY
    Volume168
    Issue number2
    Early online date2014
    DOIs
    Publication statusPublished - Aug 2014

    Keywords

    • Coupled dissolution reprecipitation reactions
    • Dolomitization
    • Experimental petrology
    • Grain boundaries
    • Hydrothermal reactions
    • Reactive transport

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