美国奥本大学Raphael Gottardi团队报道了层状硅酸盐对自然变形岩石中石英变形组构的影响。相关论文于2024年4月16日发表于国际顶尖学术期刊《地质学》杂志上。

石英变形组构能反映糜棱岩中的应力和应变条件，其解释已成为运动学和结构分析的支柱。颗粒大小和形状的量化以及反映变形机制的组构的解释可以用来估计流动应力、应变速率、运动涡度和变形温度。石英流动规律的经验校准和测定是基于纯样品的室内实验，然而，纯石英岩糜棱岩相对罕见。特别是层状硅酸盐可以局部化和分配应变，从而抑制或增强不同的变形机制。实验结果表明，即使少量的层状硅酸盐含量(<15vol%)也能显著改变石英的应变行为。然而，很少有实地研究在自然环境中证明这些影响。

为了研究层状硅酸盐对石英应变组构的作用，研究定量分析了中新世Raft河滑脱剪切带（美国犹他州西北部）石英岩糜棱岩中的层状硅酸盐含量和分布。研究人员通过显微结构分析和电子背散射衍射，来量化石英变形结构和白云母的空间分布，并通过X射线计算机断层扫描来量化样品中白云母的含量，其含量在整个滑脱剪切带中收集的数量不同。

层状硅酸盐含量对石英变形机制有直接的控制作用，压力计的应用和基于石英变形组构的流动规律产生的应变率，和流动应力在样品中变化高达两个数量级。这些发现对研究石英岩糜棱岩流动规律，和中地壳剪切带应变局部化机制的应用具有重要意义。

附：英文原文

Title: A little mica goes a long way: Impact of phyllosilicates on quartz deformation fabrics in naturally deformed rocks

Author: Raphael Gottardi, Gabriele Casale, John Economou, Kristen Morris

Issue&Volume: 2024-04-16

Abstract: Quartz deformation fabrics reflect stress and strain conditions in mylonites, and their interpretation has become a mainstay of kinematic and structural analysis. Quantification of grain size and shape and interpretation of textures reflecting deformation mechanisms can provide estimates of flow stress, strain rate, kinematic vorticity, and deformation temperatures. Empirical calibration and determination of quartz flow laws is based on laboratory experiments of pure samples; however, pure quartzite mylonites are relatively uncommon. In particular, phyllosilicates may localize and partition strain that can inhibit or enhance different deformation mechanisms. Experimental results demonstrate that even minor phyllosilicate content (<15 vol%) can dramatically alter the strain behavior of quartz; however, few field studies have demonstrated these effects in a natural setting.To investigate the role of phyllosilicates on quartz strain fabrics, we quantify phyllosilicate content and distribution in quartzite mylonites from the Miocene Raft River detachment shear zone (NW Utah, USA). We use microstructural analysis and electron backscatter diffraction to quantify quartz deformation fabrics and muscovite spatial distribution, and X-ray computed tomography to quantify muscovite content in samples with varying amounts of muscovite collected across the detachment shear zone. Phyllosilicate content has a direct control on quartz deformation mechanisms, and application of piezometers and flow laws based on quartz deformation fabrics yield strain rates and flow stresses that vary by up to two orders of magnitude across our samples. These findings have important implications for the application of flow laws in quartzite mylonites and strain localization mechanisms in mid-crustal shear zones.

DOI: 10.1130/G52053.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52053.1/638212/A-little-mica-goes-a-long-way-Impact-of