The effect of stress/strain-induced texture evolution and grain boundary mobility on reaction rim growth in the wet system MgO-SiO2

• Applicant: Dr. Erik Rybacki
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2010 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 22341081

• Final Report Year: 2016

Final Report Abstract

This experimental project addresses mineral reaction between calcite and magnesite under isostatic and non-isostatic stress conditions, forming dolomite and magnesio-calcite. Results of this project provide new quantitative insights into reaction kinetics within the carbonate system. From isostatic annealing experiments on natural single crystal starting materials we established a model for diffusion-controlled dolomite rim growth and determined the kinetic parameters. The presence of excess water has no effect on the measured growth rate. Remarkably and counterintuitive, growth is not achieved by simple cation exchange, but oxygen diffusion is obviously involved to maintain mass balance and charge neutrality. Under non-isostatic conditions, the dolomite reaction kinetics is not significantly influenced by deformation as suggested by the minor contribution of additional elastic and plastic strain energy to the total thermodynamic driving force. Also, deformation-induced textural changes of the newly formed minerals do not change the growth rates of dolomite. In contrast, application of differential stress slightly enhances the growth rate of magnesio-calcite by deformation-induced 2D and 3D structural defects. High strain torsion testing reveals a reduction of magnesio-calcite and dolomite reaction layer thickness with increasing strain (-rate), presumably caused by concurrent grain rotation and forced interface-parallel diffusion. Beside time and P,T conditions, the grain size of the reactant phases is the most important factor controlling the reaction kinetics between calcite and magnesite, indicating the need of polycrystalline educt phases to better constrain natural reaction kinetics from laboratory experiments. Diffusion along grain boundaries within the reactants determines the growth rate of dolomite and magnesio-calcite, resulting in enhanced product growth rate for small reactant grain size. Applied to natural carbonate systems, nonisostatic stress and deformation may enhance the reaction kinetics mainly by grain size reduction of the reactants, for example by cataclasis or dynamic recrystallization. Similar results are expected for silicate systems, which demands to be verified.

Publications

• 2012. “Reaction kinetics of dolomite rim growth”. 14th International Conference on Experimental Mineralogy Petrology Geochemistry, Kiel, Germany, held 4-7 March, Conference Abstract p.76
  Helpa, V., E. Rybacki, G. Dresen, and R. Abart
  
• 2012. “Reaction kinetics of dolomite rim growth”. 1st European Mineralogical Conference, Frankfurt/Main, Germany, Conference Abstract 1:EMC2012-518
  Helpa, V., E. Rybacki, R. Abart, W. Heinrich, G. Dresen, G.
  
• 2013. “Dolomite reaction rim growth under non-isostatic stress”. Mineralogical Magazine - Goldschmidt Conference Abstracts, 77, 5, p. 1283
  Helpa, V., E. Rybacki, G. Dresen, W. Heinrich, R. Abart, and L.F.G Morales
  
• 2013. “The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions”. American Geophysical Union, Fall Meeting, abstract MR41A-2359
  Helpa, V., E. Rybacki, L.F.G. Morales, R. Abart, and G. Dresen
  
• 2014. “Reaction Kinetics of Dolomite Rim Growth.” Contributions to Mineralogy and Petrology 167 (4): 1001
  Helpa, V., E. Rybacki, R. Abart, L. F. G. Morales, D. Rhede, P. Jeřábek, and G. Dresen
  
• . 2015. “Influence of Stress and Strain on Dolomite Rim Growth: A Comparative Study.” Contributions to Mineralogy and Petrology 170 (2): 16
  Helpa, V., E. Rybacki, L. F. G. Morales, and G. Dresen
  
• 2015. “Influence of deformation on dolomite rim growth kinetics.” EGU General Assembly, Vienna, Austria, held 12-17 April Conference Abstract id. 735
  Helpa, V., E. Rybacki, L.F.G. Morales, and G. Dresen
  
• 2015. “Influence of deformation on dolomite rim growth.” 20th International Conference on Deformation Mechanism, Rheology and Tectonics. Aachen, Germany, held 7-11 September, Conference Abstract 97:136
  Helpa, V., E. Rybacki, L.F.G. Morales, and G. Dresen
  
• 2015. “Interplay between mineral reaction and deformation via structural defects.” Dissertation, Universität Potsdam, pp. 104
  Helpa, V.
  
• 2016. “Influence of grain size, water and deformation on dolomite reaction rim formation.” American Mineralogist, Band 101, Heft 12, S. 2655–2665
  Helpa, V., E. Rybacki, L. F. G. Morales, and G. Dresen