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<p>Phyllosilicates are silicate minerals with a sheet structure. Phyllosilicates including antigorite, chlorite, mica, and talc, commonly have a perfect (001) basal cleavage and intrinsically elastically anisotropic crystal structures. Studies of the lattice-preferred orientations (LPOs) of phyllosilicates have reported two characteristic types of [001] axis orientations: type-1 and type-2. Type-1 LPOs are characterized by [001] axes aligned subnormal to the foliation or the shear plane, while type-2 LPOs are characterized by [001] axes that form a girdle subnormal to the lineation or the shear direction. The type-1 LPO of phyllosilicates can be interpreted as the alignment of the basal cleavage subparallel to the shear plane. However, the mechanism responsible for the development of the type-2 LPO of phyllosilicates remains unclear. A thickening/narrowing simple shear (transtension) regime for phyllosilicates is consistent with the results of experiments on the development of a type-2 LPO of chlorite, which occurs following an increase in shear strain. However, the experimental chlorite samples were deformed under a lengthening/thinning methodology. The activation of antigorite slip systems may enable type-2 LPOs to develop under simple shear regimes, including thickening/narrowing (transtension) and lengthening/thinning shear. Microstructure studies of serpentinized peridotite suggest that phase boundary sliding between olivine and antigorite contributes to the development of type-2 LPOs in antigorite. However, there is a lack of experimental proof on the development of different LPOs in antigorite under simple shear conditions. Studies on the development of LPOs in chlorite lack detailed microstructural analyses focusing on slip systems and deformation mechanisms. Future studies to clarify the development mechanisms of LPOs in phyllosilicates should prioritize detailed investigations of simple shear regimes and slip systems. In addition, the effects of variations in modal compositions and shear strain on grain rotation mechanisms should be considered.</p>

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A review of phyllosilicate LPOs: insights from antigorite and chlorite

  • 期刊论文

  • 发表日期：

    2025年8月13日

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  • Dohyun Kim,
  • Munjae Park

摘要

Phyllosilicates are silicate minerals with a sheet structure. Phyllosilicates including antigorite, chlorite, mica, and talc, commonly have a perfect (001) basal cleavage and intrinsically elastically anisotropic crystal structures. Studies of the lattice-preferred orientations (LPOs) of phyllosilicates have reported two characteristic types of [001] axis orientations: type-1 and type-2. Type-1 LPOs are characterized by [001] axes aligned subnormal to the foliation or the shear plane, while type-2 LPOs are characterized by [001] axes that form a girdle subnormal to the lineation or the shear direction. The type-1 LPO of phyllosilicates can be interpreted as the alignment of the basal cleavage subparallel to the shear plane. However, the mechanism responsible for the development of the type-2 LPO of phyllosilicates remains unclear. A thickening/narrowing simple shear (transtension) regime for phyllosilicates is consistent with the results of experiments on the development of a type-2 LPO of chlorite, which occurs following an increase in shear strain. However, the experimental chlorite samples were deformed under a lengthening/thinning methodology. The activation of antigorite slip systems may enable type-2 LPOs to develop under simple shear regimes, including thickening/narrowing (transtension) and lengthening/thinning shear. Microstructure studies of serpentinized peridotite suggest that phase boundary sliding between olivine and antigorite contributes to the development of type-2 LPOs in antigorite. However, there is a lack of experimental proof on the development of different LPOs in antigorite under simple shear conditions. Studies on the development of LPOs in chlorite lack detailed microstructural analyses focusing on slip systems and deformation mechanisms. Future studies to clarify the development mechanisms of LPOs in phyllosilicates should prioritize detailed investigations of simple shear regimes and slip systems. In addition, the effects of variations in modal compositions and shear strain on grain rotation mechanisms should be considered.