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The clay fabric of shales is a strain gauge
Journal of Structural Geology ( IF 3.1 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.jsg.2020.104130
Tiphaine Boiron , Charles Aubourg , Pierre-Alexandre Grignard , Jean-Paul Callot

Abstract Shales with their large clay fraction are prone to deform in an almost ductile way under tectonic loading. Here, we propose to monitor and quantify the evolution of strained shales clay fabric in the field of illite diagenesis by using magnetic fabric. In the footwall of a south Pyrenean thrust, 281 shales samples have been collected along a 2 km long exceptional exposure. The cleavage evolves from pencil structures at ~1 km of the thrust, to pencil cleavage at ~850 m and slaty cleavage at ~170 m. The average magnetic foliation of illite remains nearly parallel to bedding over a distance of ~600 m despite development of pencil cleavage. It is at ~600 m of the thrust that illite foliation shifts gradually from bedding to cleavage. By contrast, the magnetic fabric scalar data reflect a more continuous evolution of the deformation. The application of a rigid rotation model of the clays allows to quantify the strain magnitude using Eigen values of tensor. This strain magnitude is consistent with distance to the thrust and conforms favorably with a trishear modelling of this thrust damage. We demonstrate therefore that the magnetic fabric of illite-rich shales is a strain gauge.

中文翻译:

页岩的粘土织物是应变计

摘要 含有大量粘土的页岩在构造载荷作用下容易以几乎延展的方式变形。在这里,我们建议通过使用磁性织物来监测和量化伊利石成岩领域中应变页岩粘土织物的演化。在南比利牛斯山冲断层的下盘,沿着 2 公里长的异常暴露采集了 281 个页岩样本。解理从冲断层约 1 km 处的铅笔状结构演化到约 850 m 处的铅笔状解理和约 170 m 处的板状解理。尽管发展了铅笔解理,但伊利石的平均磁叶理在约 600 m 的距离内几乎与层理平行。伊利石叶理逐渐从层理向解理转变是在推力的~600 m处。相比之下,磁性织物标量数据反映了更连续的变形演变。粘土刚性旋转模型的应用允许使用张量的特征值来量化应变大小。该应变大小与到推力的距离一致,并且与这种推力损坏的三剪模型一致。因此,我们证明富含伊利石的页岩的磁性结构是应变仪。
更新日期:2020-09-01
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