块-基质剪切带中的滑动和应力: 2. 蛇纹石填充扩张斜面的数值模拟

IF 2.6 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of Structural Geology Pub Date : 2024-08-19 DOI:10.1016/j.jsg.2024.105238
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引用次数: 0

摘要

我们利用二维数值模型,以新西兰敦山蛇绿岩的一个野外实例为基础,探讨了断层约束扩张性斜坡的滑动和应力动态。该锯齿位于一米尺度的块状蛇绿岩辉长岩中,该辉长岩辉长岩嵌于 "块-基质 "蠕动蛇绿岩剪切带中。模型显示了密封锯齿岩与主岩之间接触面拉伸强度的周期性超标如何导致新的裂缝密封带的偶发性打开和沉积,其厚度受限于阶跃边界断层尖端周围的应力释放。模型中的切向应力释放低于线性弹性断裂力学的预测值,这是因为边界断层在破坏后的蠕变作用下,会缓慢出现额外的裂缝开口。对于 10 km 厚的覆盖层和恒定的高流体压力,我们预测的事件应力释放量约为 16 MPa,锯齿两侧的总裂缝张开量为 ∼ 22 μm,与现场实例中的裂缝密封带宽度一致。由于我们的模型显示总裂缝宽度反映了初始开裂和随后的蠕变,因此我们建议在类似剪切带环境中使用裂缝密封带宽度直接推断应力释放时要谨慎。
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Slip and stress in block-in-matrix shear zones: 2. numerical modelling of a serpentine-filled dilational jog

We use 2-D numerical models to explore slip and stress dynamics in a fault-bound dilational jog, informed by a field example from the Dun Mountain Ophiolite in New Zealand. The jog is hosted in a metre-scale phacoid of massive serpentinite embedded in a “block-in-matrix” creeping serpentinite shear zone. The models show how periodic exceedance of the tensile strength of the contact between the sealed jog and host rock leads to episodic opening and deposition of a new crack-seal band, with a thickness limited by the release of stress around the tips of the stepover-bounding faults. Jog stress release in the model is lower than that predicted from linear elastic fracture mechanics because additional crack opening can occur slowly due to post-failure creep on the bounding faults. For 10 km overburden and constant high fluid pressure, we predict event stress release of ca. 16 MPa and total crack opening of ∼22 μm on either side of the jog, consistent with crack-seal band widths in the field example. Because our models show that total crack width reflects both initial cracking and subsequent creep, we suggest caution when using crack-seal band widths to directly infer stress release in similar shear zone settings.

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来源期刊
Journal of Structural Geology
Journal of Structural Geology 地学-地球科学综合
CiteScore
6.00
自引率
19.40%
发文量
192
审稿时长
15.7 weeks
期刊介绍: The Journal of Structural Geology publishes process-oriented investigations about structural geology using appropriate combinations of analog and digital field data, seismic reflection data, satellite-derived data, geometric analysis, kinematic analysis, laboratory experiments, computer visualizations, and analogue or numerical modelling on all scales. Contributions are encouraged to draw perspectives from rheology, rock mechanics, geophysics,metamorphism, sedimentology, petroleum geology, economic geology, geodynamics, planetary geology, tectonics and neotectonics to provide a more powerful understanding of deformation processes and systems. Given the visual nature of the discipline, supplementary materials that portray the data and analysis in 3-D or quasi 3-D manners, including the use of videos, and/or graphical abstracts can significantly strengthen the impact of contributions.
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