A new class of microstructures which lead to transformation‐induced faulting in magnesium germanate
A new class of microstructures which lead to transformation‐induced faulting in magnesium germanate
复制标题
导致锗酸镁中相变诱发断层的一类新型微观结构
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
H. Green
中科院分区：
文献类型：
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作者：
E. Riggs;H. Green
[1]在过去的15年里，在天然橄榄石、冰和其他各种橄榄石类似系统中，转换诱导的断层作用得到了广泛的研究，并且仍然是引发深源地震的可能的候选机制。其机制包括从亚稳主体形成细粒致密材料的微观信息包，然后这些材料表现为I型特征，它们结合在一起，允许主体II型剪切破坏。我们提出了一类新的相变微结构的证据，这种微结构也允许在高压下剪切破坏，但不需要在剪切破坏之前形成广泛分布的I型特征。我们观察到粗晶(∼150μm)Mg2GeO4橄榄石中沿晶面形成的薄平面相变带，其温度低于允许显著发展抗裂的温度。这些区域的发展很快，只有在∼25%的整体应变后才会发生。不断增加的应变导致这些区域的逐渐发展，一旦细晶尖晶石连续形成穿过试件的路径，反过来又导致整体剪切破坏。透射电子显微镜分析表明，橄榄石中(011)和(010)位错堆积在滑移面上形成的滑移带优先转变为较致密的尖晶石相纳米晶聚集体，这得益于这些滑移带的高应变能。这种新的、部分应变驱动的机制补充了先前研究中所描述的抗裂剪切破坏，并为快速矿物学转变触发整体剪切破坏增加了新的可能性。
[1] Transformation-induced faulting has been studied extensively in natural olivine, ice, and a variety of other olivine analog systems over the last 15 years and remains a likely candidate mechanism for initiating deep focus earthquakes. The mechanism involves the formation of microscopic packets of fine-grained denser materials from a metastable host, which then behave as mode I features that coalesce to allow bulk mode II shear failure. We present evidence for a new class of transformation microstructures that also allows shear failure at high pressures but which does not require the formation of widely distributed mode I features prior to shear failure. We have observed thin planar zones of transformation in coarse-grained (∼150 μm) Mg2GeO4 olivine that form along crystallographic planes in deformed grains at temperatures cooler than those that allow significant development of anticracks. The development of these zones is rapid and only occurs after ∼25% bulk strain. Increasing strain leads to progressive development of these zones, in turn leading to bulk shear failure once a continuous pathway of fine-grained spinel is formed that traverses the specimen. Transmission electron microscopy analysis shows that slip bands in olivine along (011) and (010) formed from dislocation pileups on these slip planes transform preferentially to a nanocrystalline aggregate of the denser spinel phase, aided by the high strain energy of these bands. This new, partially strain-driven mechanism compliments shear failure by anticracks as described in previous studies and adds new possibilities for the triggering of bulk shear failure by rapid mineralogical transformations.