Mn2GeO4中从橄榄石到瓦斯利石结构的转变断层:对深焦距地震物理机制的影响

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Tectonophysics Pub Date : 2024-08-13 DOI:10.1016/j.tecto.2024.230467
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引用次数: 0

摘要

为了研究 Mn2GeO4橄榄石中的转化断层,我们进行了高压和温度变形实验,并结合声发射(AE)监测。可变质的 Mn2GeO4橄榄石在 800 至 1100 K 的温度范围内表现出明显的脆化行为,并发出许多 AE。在每个温度下,脆性形变的特点是分为两个阶段:(1) "准备 "阶段,出现大量弥散分布的低强度 AE 和较大的 b 值 (>2);(2) 失效阶段,较大强度的 AE 形成平面分布,b 值约为 1。典型厚度为 100 nm 的扭结带边界(KBB)充满了纳米级的β-Mn2GeO4 "刨痕"。扭结带内通常存在密集的二次剪切定位阵列,表明其中存在显著的剪切变形。综合观察结果表明,从晶粒尺度到样品尺度,可变质 Mn2GeO4 橄榄石中的断层是一个自相似过程。观察到的脆化行为和可变质 Mn2GeO4 橄榄石的微观结构与我们以前报告过的 Mg2GeO4 橄榄石中的脆化行为和微观结构基本相同,这表明可变质橄榄石中断层的物理机制对高压相的特定晶体结构并不敏感。我们在实验中观察到的断层过程中的低 b 值(约 1)与冷俯冲带的深焦点地震相似。只要自相似性假设在地质尺度上成立,我们观察到的机制就能解释冷变质地幔楔中的深焦点地震。
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Transformational faulting in Mn2GeO4 from olivine to wadsleyite structure: Implications for physical mechanism of deep-focus earthquakes

High-pressure and temperature deformation experiments interfaced with acoustic emission (AE) monitoring have been conducted to study transformational faulting in Mn2GeO4 olivine, which transforms to the β phase, isostructural to wadsleyite. Metastable Mn2GeO4 olivine exhibits a marked embrittlement behavior at temperatures between 800 and 1100 K, emitting numerous AEs. At each temperature, brittle deformation is characterized by a two-stage process: (1) a “preparation” stage with numerous diffusedly located low-magnitude AEs and large b values (>2), and (2) a failure stage where larger-magnitude AEs form a planar distribution with b values about 1. Microstructure analysis reveals extensive kink band development in olivine grains in the recovered samples. Kink band boundaries (KBBs), with a typical thickness of ∼100 nm, are filled with a nanometric β-Mn2GeO4 “gouge”. A dense array of secondary shear localizations is often present within the kink bands, suggesting significant shear deformation therein. The combined observations suggest that faulting in metastable Mn2GeO4 olivine is a self-similar process, from grain-scale to the sample-scale. Both observed embrittlement behavior and the microstructure of metastable Mn2GeO4 olivine are essentially identical to those in Mg2GeO4 olivine we have reported previously, indicating that the physical mechanism of faulting in metastable olivine is insensitive to the specific crystallographic structure of the high-pressure phase. The low b values (about 1) observed in the faulting process in our experiments are similar to those of deep focus earthquakes in cold subduction zones. Our observed mechanism explains deep focus seismicity in cold metastable mantle wedges, provided that the self-similarity assumption holds to geological scales.

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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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