000311029 001__ 311029 000311029 005__ 20250730111103.0 000311029 0247_ $$2doi$$a10.1093/petrology/egw044 000311029 0247_ $$2ISSN$$a0022-3530 000311029 0247_ $$2ISSN$$a1460-2415 000311029 0247_ $$2WOS$$aWOS:000383734100006 000311029 0247_ $$2datacite_doi$$a10.3204/PUBDB-2016-04578 000311029 0247_ $$2openalex$$aopenalex:W2511727492 000311029 037__ $$aPUBDB-2016-04578 000311029 041__ $$aEnglish 000311029 082__ $$a550 000311029 1001_ $$0P:(DE-H253)PIP1008346$$aGasc, Julien$$b0 000311029 245__ $$aEffect of Water Activity on Reaction Kinetics and Intergranular Transport: Insights from the $\mathrm{Ca(OH)_{2} + MgCO_{3} \to CaCO_{3} + Mg(OH)_{2}}$ Reaction at 1·8 GPa 000311029 260__ $$aOxford$$bOxford Univ. Press$$c2016 000311029 3367_ $$2DRIVER$$aarticle 000311029 3367_ $$2DataCite$$aOutput Types/Journal article 000311029 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1519201302_13252 000311029 3367_ $$2BibTeX$$aARTICLE 000311029 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000311029 3367_ $$00$$2EndNote$$aJournal Article 000311029 500__ $$a(c) The Author. Published by Oxford University Press 000311029 520__ $$aThe kinetics of the irreversible reaction Ca(OH) 2 + MgCO 3 → CaCO 3 + Mg(OH) 2 were investigated at high pressures and temperatures relevant to metamorphic petrology, using both in situ synchrotron X-ray diffraction and post-mortem analysis of reaction rim growth on recovered samples. Reaction kinetics are found to strongly depend on water content; comparable bulk-reaction kinetics are obtained under water-saturated (excess water, c. 10 wt %) and under intermediate (0·1–1 wt % water) conditions when temperature is increased by c. 300 K. In contrast, similar reaction kinetics were observed at ∼673 K and 823 K between intermediate and dry experiments, respectively, where dry refers to a set of experiments with water activity below 1·0 (no free water), as buffered by the CaO–Ca(OH) 2 assemblage. Given the activation energies at play, this gap—corresponding to the loss of no more than 1 wt % of water by the assemblage—leads to a difference of several orders of magnitude in reaction kinetics at a given temperature. Further analysis, at the microscopic scale, of the intermediate and dry condition samples, shows that intergranular transport of calcium controls the reaction progress. Grain boundary diffusivities could be retrieved from the classic treatment of reaction rim growth rate. In turn, once modeled, this rate was used to fit the bulk kinetic data derived from X-ray powder diffraction, offering an alternative means to derive calcium diffusivity data. Based on a comparison with effective grain boundary data for Ca and Mg from the literature, it is inferred that both dry and intermediate datasets are consistent with a water-saturated intergranular medium with different levels of connectivity. The very high diffusivity of Ca in the CaCO 3 + Mg(OH) 2 rims, in comparison with that of Mg in enstatite rims found by earlier workers, emphasizes the prominent role of the interactions between diffusing species and mineral surfaces in diffusion kinetics. Furthermore, we show that the addition of water is likely to change the relative diffusivity of Mg and Ca in carbonate aggregates. From a qualitative point of view, we confirm, in a carbonate-bearing system, that small water content variations within the 0–1 wt % range have tremendous effects on both intergranular transport mechanisms and kinetics. We also propose that the water content dependent diffusivity of major species (Mg, Ca) in low-porosity metamorphic rocks is strongly dependent on the interaction between diffusing species and mineral surfaces. This parameter, which will vary from one rock-type to another, needs also to considered when extrapolating ( P , T , t , x H 2 O) laboratory diffusion data to metamorphic processes. 000311029 536__ $$0G:(DE-HGF)POF3-899$$a899 - ohne Topic (POF3-899)$$cPOF3-899$$fPOF III$$x0 000311029 588__ $$aDataset connected to CrossRef 000311029 693__ $$0EXP:(DE-H253)D-F2.1-20150101$$1EXP:(DE-H253)DORISIII-20150101$$6EXP:(DE-H253)D-F2.1-20150101$$aDORIS III$$fDORIS Beamline F2.1$$x0 000311029 7001_ $$0P:(DE-H253)PIP1008342$$aBrunet, Fabrice$$b1$$eCorresponding author 000311029 7001_ $$0P:(DE-H253)PIP1009446$$aBrantut, Nicolas$$b2 000311029 7001_ $$aCorvisier, Jérôme$$b3 000311029 7001_ $$0P:(DE-H253)PIP1008345$$aFindling, Nathaniel$$b4 000311029 7001_ $$0P:(DE-H253)PIP1011314$$aVerlaguet, Anne$$b5 000311029 7001_ $$0P:(DE-H253)PIP1002121$$aLathe, Christian$$b6 000311029 773__ $$0PERI:(DE-600)1466724-1$$a10.1093/petrology/egw044$$gVol. 57, no. 7, p. 1389 - 1408$$n7$$p1389 - 1408$$tJournal of petrology$$v57$$x1460-2415$$y2016 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.pdf$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.gif?subformat=icon$$xicon$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.jpg?subformat=icon-1440$$xicon-1440$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.jpg?subformat=icon-180$$xicon-180$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.jpg?subformat=icon-640$$xicon-640$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/pdf%20from%20editor%20%28restricted%20access%29.pdf?subformat=pdfa$$xpdfa$$yRestricted 000311029 8564_ $$uhttps://bib-pubdb1.desy.de/record/311029/files/Gasc2016_JPET.pdf$$yPublished on 2016-08-09. 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