Semi-brittle and plastic deformation behaviors of mafic granulite are significant for evaluating characteristics of ductile zones in the lower crust region and the rheological strength of the lower crust. Axial compression experiments were carried out in this study with natural mafic granulite collected from the North China Craton, using a gas medium apparatus at 950–1,150°C and 300 MPa with strain up to 17%. The samples are composed of 57 vol.% Plagioclase, 19 vol.% Clinopyroxene, 20 vol.% Orthopyroxene, and 4 vol.% magnetite and ilmentite. The mean grain size is 300–700 μm. The bulk structural water content is 891 ± 399 wt ppm. At 950–1,000°C, the samples were brittly broken by scattered cracks and localized fault zones. At 1,050–1,075°C, the samples were deformed by ductile shear zones that broadened with increasing temperature, the deformation behavior is characterized by a steady-state semi-brittle creep; mechanic data yield a flow law of $\dot{\epsilon }={10}^{6.0\pm 0.3}{\text{MPa}}^{-5.8}{{\mathrm{s}}^{-1}\sigma }^{5.8\pm 0.1}\exp \left(-\frac{651\pm 68\text{kJ}/\text{mol}}{RT}\right)$. At 1,100–1,150°C, the samples plastically deformed with dislocation creep, and the deformation strength is reduced by recrystallization and partial melting; mechanical data yield a flow law of $\dot{\epsilon }={10}^{2.7\pm 0.8}{\text{MPa}}^{-4.1}{{\mathrm{s}}^{-1}\sigma }^{4.1\pm 0.2}\exp \left(-\frac{442\pm 13\text{kJ}/\text{mol}}{RT}\right)$. The strength profile based on our data implies that North China Craton has a wet and cold continental lower crust. Recrystallization and cataclastic flow involve grain size reduction that can lead to steady-state ductile behaviors of fault zones.

中文翻译：

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天然镁铁质花晶石脆性-韧性转变的实验研究


镁铁质花晶石的半脆性和塑性变形行为对于评价下部地壳区域韧性区的特性和下部地壳的流变强度具有重要意义。本研究使用从 North China Craton 收集的天然镁铁质花岗岩，使用 950–1,150°C、300 MPa 的气体介质装置进行轴向压缩实验，应变高达 17%。样品由 57 vol.% 斜长石、19 vol.% 斜辉石、20 vol.% 斜辉石和 4 vol.% 磁铁矿和辉石组成。平均晶粒尺寸为 300-700 μm。整体结构含水量为 891 ± 399 wt ppm。在 950–1,000°C 时，样品被分散的裂纹和局部断层带脆性破碎。在 1,050–1,075°C 时，样品被延性剪切区变形，该剪切区随着温度的升高而扩大，变形行为的特征是稳态半脆性蠕变;机械数据产生 的流定律为 $\dot{\epsilon }={10}^{6.0\pm 0.3}{\text{MPa}}^{-5.8}{{\mathrm{s}}^{-1}\sigma }^{5.8\pm 0.1}\exp \left(-\frac{651\pm 68\text{kJ}/\text{mol}}{RT}\right)$ 。在 1,100–1,150°C 时，样品发生位错蠕变的塑性变形，变形强度因再结晶和部分熔化而降低;机械数据产生 的流定律为 $\dot{\epsilon }={10}^{2.7\pm 0.8}{\text{MPa}}^{-4.1}{{\mathrm{s}}^{-1}\sigma }^{4.1\pm 0.2}\exp \left(-\frac{442\pm 13\text{kJ}/\text{mol}}{RT}\right)$ 。基于我们数据的强度剖面意味着华北克拉通具有潮湿和寒冷的大陆下地壳。再结晶和碎裂流涉及晶粒尺寸的减小，这可能导致断层带的稳态韧性行为。