Strain localisation in bimineralic rocks: Experimental deformation of synthetic calcite–anhydrite aggregates
Strain localisation in bimineralic rocks: Experimental deformation of synthetic calcite–anhydrite aggregates
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DOI：
10.1016/j.epsl.2005.09.014
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发表时间：
2005-12
影响因子：
5.3
通讯作者：
A. Barnhoorn;M. Bystricky;K. Kunze;L. Burlini;J. Burg
中科院分区：
文献类型：
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作者：
A. Barnhoorn;M. Bystricky;K. Kunze;L. Burlini;J. Burg
人造方解石-硬石膏聚集体在大剪切应变下的变形（在600 °C，300 MPa围压和对应于10−3s−1剪切应变速率的恒定角位移速率下，γ=12.4）导致了最初均质岩石应变局部化的首次实验观察。与纯方解石和硬石膏的实验相反，纯方解石和硬石膏均匀变形到大应变（γ≥5），方解石-硬石膏混合物的所有实验在γ>1时导致非均匀变形，在γ>4时在显微结构中形成窄的局部带。在这些带中，应变量至少是样品其余部分的两倍，并且相同相的单个颗粒聚集并对齐，从而形成类似于天然糜棱岩中的平面织物的微结构分层。硬石膏的变形机制从位错蠕变到扩散蠕变和/或晶界滑动的切换与应变局部化同时发生。它的结论是，变形引起的非均匀相分布引起的局部强度差异启动应变局部化的方解石-硬石膏混合物。该研究表明，在变形机制的变化相结合的两个阶段的存在下，可能是负责应变局部化在天然多矿物糜棱岩。
Deformation of synthetic calcite–anhydrite aggregates to large shear strains (up to γ=12.4 at 600 °C, 300 MPa confining pressure and a constant angular displacement rate corresponding to a shear strain rate of 10−3s−1) resulted in the first experimental observation of strain localisation from initially homogeneous rocks. In contrast to experiments on pure calcite and anhydrite, which deformed homogeneously to large strains (γ≥5), all experiments on calcite–anhydrite mixtures resulted in heterogeneous deformation at γ>1 and the formation of narrow localised bands in the microstructures at γ>4. In these bands, the amount of strain is at least twice as large as in the rest of the sample and individual grains of the same phase cluster and align, thereby forming microstructural layering similar to planar fabrics in natural mylonites. A switch in deformation mechanism in anhydrite from dislocation creep to diffusion creep and/or grain boundary sliding occurs simultaneously with strain localisation. It is concluded that deformation-induced heterogeneous phase distributions cause local strength differences initiating strain localisation in the calcite–anhydrite mixtures. The study suggests that the presence of two phases in combination with a change in deformation mechanism may be responsible for strain localisation in natural poly-mineralic mylonites.