Dissolution precipitation creep versus crystalline plasticity in high-pressure metamorphic serpentinites
Dissolution precipitation creep versus crystalline plasticity in high-pressure metamorphic serpentinites
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DOI：
10.1144/sp360.8
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
S. Wassmann;B. Stöckhert;C. Trepmann
中科院分区：
文献类型：
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作者：
S. Wassmann;B. Stöckhert;C. Trepmann
摘要蛇纹岩被广泛认为是俯冲带中的弱物质，对俯冲通道的发育起着重要作用。关于变形机制的信息和描述这些大规模流动过程的适当流变模型只能从古代俯冲带出土的天然蛇纹岩中获得。利用光学和扫描电子背散射衍射（EBSD）技术研究了西阿尔卑斯采尔马特-萨斯带hp变质蛇纹岩（pp . 2±0.5 GPa, tc . 550±50°c）的显微结构记录。片岩和组成层状岩石显示普遍存在的小尺度褶皱。没有证据表明位错蠕变造成了明显的变形。相反，微织构包括应变阴影和蠕变，表明高应变是通过溶解沉淀蠕变积累的。从流变学的角度来看，这表明在俯冲带的较深处，蛇纹岩具有牛顿行为和低粘度的长期流动。这并不排除位错蠕变和在较高应力水平下的幂律流变，正如在应力集中的局部位置和地震后蠕变的瞬态发作中所实现的那样。
Abstract Serpentinite is widely assumed to constitute weak material in subduction zones and to play an essential role for the development of a subduction channel. Information on deformation mechanisms and appropriate rheological models to describe these large-scale flow processes can only be obtained from natural serpentinites exhumed from ancient subduction zones. We examine the microstructural record of HP-metamorphic (P c. 2±0.5 GPa, T c. 550±50 °C) serpentinites exposed in the Zermatt–Saas zone, Western Alps, using optical and scanning electron microscopy with electron backscatter diffraction (EBSD). The schistose and compositionally layered rocks show pervasive small-scale folding. There is no evidence for any significant deformation by dislocation creep. Instead, the microfabrics including strain shadows and crenulation cleavage indicate that high strain is accumulated by dissolution precipitation creep. In terms of rheology, this suggests Newtonian behaviour and a low viscosity for the long-term flow of serpentinites in deeper levels of subduction zones. This does not preclude dislocation creep and a power law rheology at higher stress levels, as realized at local sites of stress concentration and transient episodes of post-seismic creep.