Jean-Baptiste Jacob , Hugo van Schrojenstein Lantman , Benoît Cordonnier , Luca Menegon , Jonathan Wright , François Renard
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引用次数: 0
Abstract
High-pressure metamorphic rocks in subduction zones undergo extreme pressure-temperature changes during exhumation, triggering complex micromechanical responses at the grain-to-sub-grain scale. While mineralogical and thermodynamic aspects of these processes are well studied, the development and preservation of residual stress in exhumed rocks remain poorly understood, besides very localized effects in host-inclusion systems. Here, we apply synchrotron scanning three-dimensional X-ray diffraction (s3DXRD) to an ultra-high-pressure garnet–quartz rock from the Lago di Cignana unit (Western Alps), revealing intra-crystalline misorientation, residual strain, and stress distributions at the ten-micrometer scale. Results show long-range residual stresses reaching several hundred Megapascals (MPa) over 10–100 μm, despite negligible strain at the macroscopic scale and absence of an oriented rock fabric. Quartz displays intra-grain misorientation up to 5∘, reflecting very local crystal plastic deformation resulting from dislocation activity. Garnet shows lower misorientation below 0.8∘, likely reflecting elastic strain gradients. These residual stresses are interpreted to result from anisotropic decompression during exhumation, locally amplified by grain interactions such as indenting tips and multi-anvil geometries. Composition gradients in garnet may also contribute to lattice distortion and stress retention. These long-range stress heterogeneities may influence rock rheology, metamorphic reactions, and affect elastic barometry results, underscoring the importance of rock microstructures in macroscale processes. Finally, our study demonstrates the value of synchrotron-based diffraction microscopy techniques to investigate metamorphic rocks. Besides in situ characterization of residual strain and stress, these methods open new avenues for multi-scale, three-dimensional investigation of intra-crystalline deformation and metamorphic reactions.
俯冲带高压变质岩在挖掘过程中经历了极端的压力-温度变化,引发了复杂的颗粒-亚颗粒微观力学响应。虽然这些过程的矿物学和热力学方面已经得到了很好的研究,但除了在宿主包裹体系统中非常局部的影响外,对挖掘出的岩石中残余应力的发展和保存仍然知之甚少。本文采用同步加速器扫描三维x射线衍射(s3DXRD)对西阿尔卑斯Lago di Cignana单元的超高压石榴石石英岩进行了分析,揭示了晶体内部的取向偏差、残余应变和10微米尺度的应力分布。结果表明,在10-100 μm范围内,尽管在宏观尺度上应变可以忽略不计,且没有定向岩石组构,但远程残余应力达到数百兆帕斯卡(MPa)。石英的晶粒内取向偏差可达5°,反映出位错活动引起的晶体局部塑性变形。石榴石在0.8°以下表现出较小的取向偏差,可能反映了弹性应变梯度。这些残余应力被解释为挖掘过程中各向异性减压的结果,局部被颗粒相互作用放大,如压痕尖端和多砧几何形状。石榴石中的成分梯度也可能导致晶格畸变和应力保持。这些长程应力非均质性可能影响岩石流变学、变质反应和弹性气压测量结果,强调了岩石微观结构在宏观过程中的重要性。最后,我们的研究证明了基于同步加速器的衍射显微技术在研究变质岩中的价值。除了原位表征残余应变和应力外,这些方法还为晶体内变形和变质反应的多尺度、三维研究开辟了新的途径。
期刊介绍:
Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.