Influence of grain size, water, and deformation on dolomite reaction rim formation

Helpa, Vanessa; Rybacki, E.; Morales, Luiz Fernando Grafuhla; Dresen, Georg

doi:10.2138/am-2016-5580

Cited by 2 publications

(4 citation statements)

References 35 publications

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“…The lattice parameters a and c of McCarty et al [39] (a = 4.8071 Å, c = 16.0032 Å), coincident with those calculated by Reeder and Sheppard [40], allow for Equation (2) to be rewritten as:…”

Section: Mgco 3 Molar Fraction a (å) C (å)mentioning

confidence: 62%

“…Along the calcite-magnesite compositional series, dolomite, as the intermediary mineral equivalent to the reaction CaCO 3 + MgCO 3 = CaMg(CO 3 ) 2 boasts a cell volume decrease [1] of up to 12%, as compared to calcite [2]. Besides end-members and the intermediary phase, the continuous exchange of cations produces magnesian calcite (Ca 1−x Mg x CO 3 ) and non-stoichiometric dolomite as the most important minerals.…”

Section: Introductionmentioning

confidence: 99%

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Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

2017

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Quantitative phase analyses of carbonate rocks containing Mg-rich calcite and non-stoichiometric dolomite by the Rietveld method yielded improved results when the substitutions are refined for either minerals. The refinement is constrained by the c-axis of the lattice for both minerals using the formula c = −1.8603 nMg + 17.061 for calcite, where nMg is the molar fraction of Mg replacing Ca, and c = 16.0032 + 0.8632∆n Ca for dolomite, with ∆n Ca being the excess Ca in its B site. The one-step procedure was implemented into the Topas software and tested on twenty-two carbonate rock samples from diverse geological settings, considered analogues to petroleum system lithotypes of the pre-evaporite deposits of Southeastern Brazil. The case study spans over a wide range of calcite and dolomite compositions: up to 0.287 apfu Mg in magnesian calcite, and Ca in excess of up to 0.25 apfu in non-stoichiometric dolomite, which are maximum substitutions the formulas support. The method overcomes the limitations for the quantification of minerals by stoichiometry based on whole-rock chemical analysis for complex mineralogy and can be employed for multiple generations of either carbonate. It returns the mineral quantification with unprecedented detailing of the carbonates' composition, which compares very well to spot analysis (both SEM-EDS and EMPA) if those cover the full range of compositions. The conciliation of the quantification results based on the XRD is also excellent against chemical analysis, thermogravimetry, and carbon elemental analysis.

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Section: Mgco 3 Molar Fraction a (å) C (å)mentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

2017

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“…This different sensitivity to differential stress under dry and wet condition may for example explain that the formation of myrmekite during deformation of metagranites occurs preferentially at high stress sides under relatively dry conditions, but not during fluid-assisted nucleation at high strain (Menegon et al 2006). On the other hand, other experimental data on the influence of non-isostatic stress on reaction rim growth in the systems MgO-Al2O3 and CaCO3-MgCO3 show that, with few exceptions, the stress effect is small compared to the impact of water, starting material microstructure, impurities, assembly geometry and loading history (Götze et al 2010;Keller et al, 2010;Jeřábek et al 2014;Helpa et al 2015Helpa et al , 2016.…”

Section: Conclusion and Geological Applicationmentioning

confidence: 94%

“…Quantitative studies on mineral reaction rates in the presence of differential stress are still rare. Few experimental studies are dealing with the formation of spinel between periclase and corundum (Keller et al 2010;Götze et al 2010;Jeřábek et al 2014) and with the growth of dolomite between calcite and magnesite (Helpa et al 2015(Helpa et al , 2016, showing a minor influence of stress on reaction progress in most cases. In this study, we examine the geologically important system MgO-SiO2, which was extensively investigated in isostatic reaction experiments in the past (Fisler et al 1997;Yund 1997;Milke et al 2001Milke et al , 2007Milke et al , 2009aMilke et al , 2009bAbart et al 2004;Gardés et al , 2012.…”

Section: Introductionmentioning

confidence: 99%

Influence of differential stress on the growth of wet enstatite and enstatite-forsterite reaction rims

Rybacki

Helpa

2019

Miner Petrol

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Reaction rim growth experiments provide insight into mass transport phenomena, which are important for metamorphic rock-forming processes and deformation mechanisms. We investigated the formation of enstatite single rims between quartz and forsterite and of enstatite-forsterite double rims between quartz and periclase using porous polycrystalline starting materials. About 3 wt% water was added, acting as a catalyst for reactions.Experiments of mainly 4 and 23 h duration were performed in a Paterson-type deformation apparatus at 1000°C temperature, 400 MPa confining pressure and differential stresses between 0 and 46 MPa. The resulting reaction rim width varied between <1 µm and ≈ 23 µm, depending on duration and type of reaction product. At isostatic pressure conditions, our data indicate that rim growth is proportional to time, controlled by dissolution-precipitation at interfaces of interconnected fluid-filled pores. In contrast, under non-isostatic stress conditions the reaction rim thickness increases non-linearly with time, implying diffusioncontrolled growth. The magnitude of differential stress has no systematic influence on the reaction rate. Microstructural observations suggest that deformation-induced reduction of interconnected porosity causes this change in rate-controlling mechanism. For a natural MgO-SiO2 system, the results infer that fast interface-controlled reaction in the presence of high amounts of water is easily suppressed by concurrent deformation. Keywords Water  Rim growth  Differential stress  Mineral reaction  Deformation

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Influence of grain size, water, and deformation on dolomite reaction rim formation

Cited by 2 publications

References 35 publications

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

Influence of differential stress on the growth of wet enstatite and enstatite-forsterite reaction rims

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