The effect of Dauphiné twinning on the crystallographic preferred orientation and deformation mechanism in quartz
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P572; P578.4+94; P313

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    Abstract:

    Minerals are the most important component of the lithosphere, whose deformation behavior, properties and physical/chemical processes directly affect the mechanical strength and rheological property of the continental lithosphere. Quartz is one of the main minerals in the crust. Dauphiné twinning in quartz consists of a 60° rotation around the c-axis. Previous studies have shown that Dauphiné twinning is only formed in the transformation between the α-quartz and β-quartz, however, furthermore evidences reveal that mechanical Dauphiné twinning is related to the influence of temperature and stress. Combined with the previous studies, we present structure and EBSD analysis of the deformed quartzites in the Gaoligong shear zone and find that the presence of Dauphiné twins has a great influence in the deformation process in quartz. The compliance of positive rhomb <r> is greater than the compliance of negative rhomb <z> in α-quartz. Thus, the positive rhomb <r> direction is more compliant for the stress. Dauphiné twinning is driven by the anisotropy in the elastic compliance of quartz and results in a little-described quartz crystallographic preferred orientation, characterized by the alignment of the poles of the planes of the more compliant positive rhomb <r> nearly parallel to the compression direction. Dauphiné twinning also plays an important role in the distribution of the intracrystalline plastic deformation and the activation of different sets of slip systems in the plastic deformation of quartz. Dauphiné twinning is a specific weakening mechanism and has a great contribution to the processes of intracrystalline strain localization, which not only results in the recoverable structu- ral weakening, but control the grain size reduction by dynamic recrystallization and grain boundary sliding mechanism. In addition, Dauphiné twinning could be a potential palaeopiezometer in quartz-bearing rocks.

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占乐凡,曹淑云,2022,石英道芬双晶对晶格优选取向及变形机制的贡献和意义[J].岩石矿物学杂志,41(6):1135~1146. ZHAN Le-fan, CAO Shu-yun,2022,The effect of Dauphiné twinning on the crystallographic preferred orientation and deformation mechanism in quartz[J]. Acta Petrologica et Mineralogica,41(6):1135~1146.

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History
  • Received:June 06,2022
  • Revised:August 22,2022
  • Adopted:
  • Online: November 16,2022
  • Published: November 20,2022
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