Deformation at low and high stress-loading rates
Deformation at low and high stress-loading rates
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低应力加载率和高应力加载率下的变形
DOI：
10.1016/j.gsf.2018.05.002
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发表时间：
2019
影响因子：
8.9
通讯作者：
Seybold
中科院分区：
文献类型：
--
作者：
Trepmann;C. A. ;Seybold
在克里特岛塔雷奥里的伸展剪切带中，高压低温变质沉积物中的石英脉沿剪切带边界、扭结带边界和布丁颈部发生膨胀。从围岩中外延生长的弯曲细长颗粒具有丰富的平行于脉壁的流体包裹体轨迹，表明在围岩的溶解-沉淀蠕变过程中，裂隙封闭增量形成了矿脉。缝合的高角度晶界和亚晶的存在表明，回复和应变诱导晶界迁移的温度足够高，即高于300-350℃，接近峰值变质条件。围岩和大多数矿脉的石英中位错蠕变累积的应变量普遍较低，表明长期处于几十兆帕的低体应力条件。假定应力加载引起循环破裂和封闭的时间尺度小于在高应变率(10−10S−1到10−9S−1)下经历溶解-析出蠕变的变质介质的麦克斯韦松弛时间，该时间约为百年。相反，一些与面理不一致或不整合的脉体显示出不均匀的石英显微结构，具有微剪切带、亚基底变形片层、短波波动消光和局限于高应变区的重结晶颗粒。这些微观结构表明，在数百兆帕的瞬时高应力下，位错滑动控制的晶体塑性变形(低温塑性)，在松弛应力和至少300-350℃的温度下，随后发生恢复和应变诱导的晶界迁移。在绿片岩相条件下，岩石中的高差应力长期通过蠕变释放应力，需要快速的应力加载速率，可能是由于上覆地壳的地震活动。应力加载的时间尺度由沿断层的滑动事件的持续时间控制，即几秒到几分钟。这项研究表明，微观结构可以区分内部低应力加载速率下的变形(在百年时间尺度上为数十兆帕)和高(同震)应力加载速率下的变形(在分钟时间尺度上)。
In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. Bent elongate grains grown epitactically from the host rock with abundant fluid inclusion trails parallel to the vein wall indicate vein formation by crack-seal increments during dissolution-precipitation creep of the host rock. The presence of sutured high-angle grain boundaries and subgrains shows that temperatures were sufficiently high for recovery and strain-induced grain boundary migration, i.e. higher than 300–350 °C, close to peak metamorphic conditions. The generally low amount of strain accumulated by dislocation creep in quartz of the host rock and most veins indicates low bulk stress conditions of a few tens of MPa on a long term. The time scale of stress-loading to cause cyclic cracking and sealing is assumed to be lower than the Maxwell relaxation time of the metasediments undergoing dissolution-precipitation creep at high strain rates (10−10s−1to 10−9s−1), which is on the order of hundred years. In contrast, some veins discordant or concordant to the foliation show heterogeneous quartz microstructures with micro-shear zones, sub-basal deformation lamellae, short-wavelength undulatory extinction and recrystallized grains restricted to high strain zones. These microstructures indicate dislocation glide-controlled crystal-plastic deformation (low-temperature plasticity) at transient high stresses of a few hundred MPa with subsequent recovery and strain-induced grain boundary migration at relaxing stresses and temperatures of at least 300–350 °C. High differential stresses in rocks at greenschist-facies conditions that relieve stress by creep on the long term, requires fast stress-loading rates, presumably by seismic activity in the overlying upper crust. The time scale for stress loading is controlled by the duration of the slip event along a fault, i.e. a few seconds to minutes. This study demonstrates that microstructures can distinguish between deformation at internal low stress-loading rates (to tens of MPa on a time scale of hundred years) and high (coseismic) stress-loading rates to a few hundred MPa on a time scale of minutes.
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