High-temperature shear zone formation in Carrara marble: The effect of loading conditions
High-temperature shear zone formation in Carrara marble: The effect of loading conditions
复制标题
卡拉拉大理石高温剪切带的形成：加载条件的影响
DOI：
10.1016/j.tecto.2018.10.022
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发表时间：
2018
期刊：
影响因子：
2.9
通讯作者：
Dresen
中科院分区：
文献类型：
--
作者：
Nardini;Rybacki;Döhmann;M.J.E.A;Morales;Dresen
地壳深部的岩石变形往往局限于不同岩性、不同尺度的高温剪切带中。材料非均质性的存在触发了剪切带的发展，但控制局部化形成和演化的机制还不完全清楚。为了研究加载条件对剪切带沿非均质形核的影响，我们在Paterson形变试验机上进行了恒扭率(CTR)和恒扭矩(CT)条件下的扭转实验。样品组合由圆柱形的卡拉拉大理石样品组成，其中包含一块薄板的Solnhofen石灰石，垂直于圆柱体的纵轴。在实验条件下(90 0 °C，4 0 0 Mpa)，样品发生塑性变形，石灰岩的强度约为大理岩的9倍，在较强的基质中充当弱包裹体。最大体剪应变率为2 ∗ 10−4s−1，峰值剪应力为20 Mpa。CT测试在~20 Mpa的剪应力下进行，体剪应变率为1~4 ∗ 10−4s−1。最大体剪应变为~0.3和1.0时，实验终止。应变集中在包裹体前面的卡拉拉大理岩中，处于强烈变形的颗粒和强烈的粒度减小区域。在局部，也观察到了脆性变形共存的证据，而不考虑施加的载荷条件。包裹体尖端的局部剪切应变高达围岩应变的30倍，在距离包裹体较远时迅速下降到5倍。在两种体应变下，微观结构和织构参数的演化与加载条件无关。我们的结果表明，加载条件对材料形核和过渡阶段的异质性应变局部化没有显著影响。
Rock deformation at depths in the Earth's crust is often localized in high temperature shear zones occurring at different scales in a variety of lithologies. The presence of material heterogeneities is known to trigger shear zone development, but the mechanisms controlling initiation and evolution of localization are not fully understood.To investigate the effect of loading conditions on shear zone nucleation along heterogeneities, we performed torsion experiments under constant twist rate (CTR) and constant torque (CT) conditions in a Paterson-type deformation apparatus. The sample assemblage consisted of cylindrical Carrara marble specimens containing a thin plate of Solnhofen limestone perpendicular to the cylinder's longitudinal axis. Under experimental conditions (900 °C, 400 MPa confining pressure), samples were plastically deformed and limestone is about 9 times weaker than marble, acting as a weak inclusion in a strong matrix. CTR experiments were performed at maximum bulk shear strain rates of ~2 ∗ 10−4s−1, yielding peak shear stresses of ~20 MPa. CT tests were conducted at shear stresses of ~20 MPa resulting in bulk shear strain rates of 1–4 ∗ 10−4s−1. Experiments were terminated at maximum bulk shear strains of ~0.3 and 1.0.Strain was localized within the Carrara marble in front of the inclusion in an area of strongly deformed grains and intense grain size reduction. Locally, evidences for coexisting brittle deformation are also observed regardless of the imposed loading conditions. The local shear strain at the inclusion tip is up to 30 times higher than the strain in the adjacent host rock, rapidly dropping to 5 times higher at larger distance from the inclusion. At both bulk strains, the evolution of microstructural and textural parameters is independent of loading conditions. Our results suggest that loading conditions do not significantly affect material heterogeneity-induced strain localization during its nucleation and transient stages.
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