Influence of stress, temperature, and strain on calcite twins constrained by deformation experiments
Influence of stress, temperature, and strain on calcite twins constrained by deformation experiments
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DOI：
10.1016/j.tecto.2013.04.021
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发表时间：
2013-08
期刊：
影响因子：
2.9
通讯作者：
E. Rybacki;B. Evans;C. Janssen;R. Wirth;G. Dresen
中科院分区：
文献类型：
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作者：
E. Rybacki;B. Evans;C. Janssen;R. Wirth;G. Dresen
对大理石和石灰岩样品进行了一系列低应变三轴压缩和高应变扭转实验，以研究应力、温度和应变对孪晶密度、具有1、2或3个孪晶组的颗粒的百分比以及孪晶宽度的演变的影响。圆柱形和狗骨形样品在20° C和350° C之间的半脆性区域中变形，围压为50-400 MPa，应变速率为~ 10− 4-10− 6 s− 1。样品承受高达~ 280 MPa的剪切应力τ，当变形至剪切应变γ> 1时失效。方解石孪晶的平均宽度随着温度和应变的增加而增加，因此，孪晶宽度的测量仅提供对峰值温度的粗略估计，除非已知对变形的额外约束。在卡拉拉大理岩中，孪晶密度NL（孪晶数/mm）随岩石应变硬化而增加，并与峰值差应力σ（MPa）近似相关，关系式为σ= 19.5±9.8 NL。位错缠结发生沿着孪晶界，导致一个复杂的细胞结构，这也演变与应力。如前所述，淬火后观察到的位错密度的平方根也与峰值应力相关。显然，孪晶密度和位错胞结构都是描述这些岩石强度的重要状态变量。
A series of low-strain triaxial compression and high-strain torsion experiments were performed on marble and limestone samples to examine the influence of stress, temperature, and strain on the evolution of twin density, the percentage of grains with 1, 2, or 3 twin sets, and the twin width—all parameters that have been suggested as either paleopiezometers or paleothermometers. Cylindrical and dog-bone-shaped samples were deformed in the semibrittle regime between 20° C and 350° C, under confining pressures of 50–400 MPa, and at strain rates of~ 10− 4–10− 6 s− 1. The samples sustained shear stresses, τ, up to~ 280 MPa, failing when deformed to shear strains γ> 1. The mean width of calcite twins increased with both temperature and strain, and thus, measurement of twin width provides only a rough estimation of peak temperature, unless additional constraints on deformation are known. In Carrara marble, the twin density, N L (no of twins/mm), increased as the rock hardened with strain and was approximately related to the peak differential stress, σ (MPa), by the relation σ= 19.5±9.8 N L. Dislocation tangles occurred along twin boundaries, resulting in a complicated cell structure, which also evolved with stress. As previously established, the square root of dislocation density, observed after quench, also correlated with peak stress. Apparently, both twin density and dislocation cell structure are important state variables for describing the strength of these rocks.