VOLUMETRIC CHANGES DURING SERPENTINIZATION OF ULTRAMAFIC MINERALS USING MICROREACTORS

Serpentinization encompasses a series of chemical reactions that accompany the hydrothermal alteration of mantle rocks (peridotites) producing serpentine, brucite, talc, magnetite and other volatiles species like H₂ and CH₄. Despite the serpentinization process playing a key role in subduction-related volatile exchange and the rheology of mafic rocks at subduction zones, mid-ocean ridges, and magma-poor passive margins, the rate at which serpentinization occurs is broadly unconstrained. Moreover, serpentinization is a self-propagating reaction that continues as long as hydrothermal fluids of relatively low salinity (3.5wt%) are in contact with unaltered surfaces of ultramafic rocks. In nature, this process occurs along veins generated by the volumetric increase of ultramafic minerals associated with hydration. Under experimental conditions, synthetic fluid inclusions (SFI) in ultramafic minerals serve as ideal chemical reactors to monitor the reaction progress as well as the rates of reaction. In this study, we conduct micro-CT analyses of a select group of SFI in olivine and pyroxene before and after serpentinization to characterize the initial SFI reactive surface areas, to monitor the volumetric expansion (∆V) of the serpentinization reaction, and to use ∆V as a proxy for reaction progress. After initial characterization, samples were placed at serpentinization conditions (250°C for olivine and 350°C for pyroxene) and removed from the furnace every 2–5 days to measure changes in both salinity and volume. The results of this study will provide an in-depth understanding of volumetric changes during serpentinization as an analogue to the onset of serpentine vein formation in peridotites.