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Low temperature plasticity and dislocation creep of Fangshan dolomite
  • Jianfeng Li,
  • Tongbin Shao,
  • Mao-shuang Song
Jianfeng Li
Guangzhou Institute of Geochemistry (CAS)
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Tongbin Shao
Guangzhou Institute of Geochemistry (CAS)

Corresponding Author:tshao@gig.ac.cn

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Mao-shuang Song
Guangzhou Institute of Geochemistry
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In order to explore the cause behind a recently so-called inversion of activation energy between dislocation-diffusion creep, we compress Fangshan dolomite at effective pressures of 50-300 MPa, temperatures of 27-900 ℃, and strain rates of 10-2×10 s using a Paterson-type apparatus. Two end-member deformation regimes, each with respective diagnostic flow law and microstructure, are recognized. At T≤500 ℃, low temperature plasticity (LTP), expressed by an exponential constitutive equation with and , was determined with weakly strain rate dependence and thermal hardening of the strength, and microstructures of predominant undulatory extinctions or f-twinning (Regime 1). At T≥800 ℃, dislocation creep, described by a power law equation ( with , and ), was defined with significant strain rate and temperature sensitivities of strength, and microstructures dominated by smooth undulating extinction and new recrystallized grains (Regime 2). Regime 3, transition from LTP to dislocation creep, is also recognized from ~600 ℃ to 800 ℃ with strain rate dependence of strength changing with temperature and developing microstructures similar to those of regime 2. Overall the medium-grained Fangshan dolomites show similar rheology to coarse-grained Madoc dolomites but a beginning temperature of regime 2 about 50-100 ℃ than the latter, making the dislocation creep of Fangshan dolomite clearly recognized under the condition that dolomite decomposition has no obvious effect. Extrapolated to nature, dislocation creep is expected to occur in a relatively narrow space undergoing high temperatures and relatively high stresses, instead diffusion creep is expected to dominate the deformation of dolomite in low stress tectonic settings.
May 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 5. 10.1029/2020JB021439