Abstract The deformation of eclogites and the driving forces for their fabric development are an important topic, potentially allowing to determine deformation rates and stresses in subduction zones, where the greatest number of large earthquakes occurs. Here, fabric studies of grain size and shape, texture, and chemical composition from two locations of Variscan and Alpine eclogites are presented. All samples show a well-developed crystallographic preferred orientation (CPO) of omphacite with a strong maximum of [001] in the lineation direction and a weaker maximum of poles to (010) normal to foliation. Garnet shows no systematic CPO. Anisotropic chemical zoning developed in omphacite and garnet during growth together with elongated grain shapes and can be related to a prograde (in terms of pressure change) P,T-path. The individual chemically zoned and elongated grains orientated in the stretching direction are single crystals without major internal misorientations. Chemical, microstructural, and CPO data indicate that the deformation microstructure and texture were produced by preferential crystal growth of garnet and omphacite grains in the extension direction. Dislocation creep can be excluded as a possible fabric formation process by the systematic and oriented chemical zonation of single crystals and absence of dynamic recrystallization microstructures. The dominant deformation is inferred to be diffusion creep, where dissolution of material took place in reacting mafic phases (plagioclase, pyroxene) and precipitation took place in the form of new eclogite facies minerals (omphacite, garnet, zoisite). This type of diffusion creep deformation represents a transformation process involving both, deformation and metamorphic reactions. It is emphasized that the weakening is directly connected to the transformation and therefore transient. The weakening facilitates diffusion creep deformation of otherwise strong minerals (pyroxene, garnet, zoisite) at far lower stresses than dislocation creep. The results imply low stresses during the deformation of eclogite blocks in subduction zones. These results can be applied to other rock types, too.

中文翻译：

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配合减弱：榴辉岩中由于矿物反应和变形相互作用而导致的扩散蠕变

摘要 榴辉岩的变形及其构造发展的驱动力是一个重要的课题，有可能确定俯冲带的变形率和应力，在那里发生大地震的次数最多。在这里，介绍了 Variscan 和高山榴辉岩两个位置的晶粒大小和形状、质地和化学成分的织物研究。所有样品都显示出绿铁矿的结晶择优取向 (CPO)，在排列方向上具有很强的最大值 [001]，而垂直于叶理的 (010) 极点的最大值较弱。Garnet 没有显示出系统的 CPO。绿辉石和石榴石在生长过程中形成的各向异性化学分带以及细长的晶粒形状，可能与顺行（在压力变化方面）P、T 路径有关。沿拉伸方向取向的单个化学分区和拉长晶粒是单晶，没有主要的内部错误取向。化学、微观结构和 CPO 数据表明，变形微观结构和织构是由石榴石和绿辉石晶粒在延伸方向上的优先晶体生长产生的。通过单晶的系统化和定向化学分带以及没有动态再结晶微结构，可以排除位错蠕变作为可能的结构形成过程。主要变形被推断为扩散蠕变，其中材料在反应性镁铁质相（斜长石、辉石）中发生溶解，并以新榴辉岩相矿物（绿辉石、石榴石、沸石）的形式发生沉淀。这种类型的扩散蠕变变形代表了涉及变形和变质反应的转变过程。需要强调的是，弱化与转变直接相关，因此是瞬态的。弱化促进了其他强矿物（辉石、石榴石、黝帘石）在远低于位错蠕变的应力下的扩散蠕变变形。结果表明俯冲带榴辉岩块体变形过程中应力较低。这些结果也可以应用于其他岩石类型。zoisite）的应力远低于位错蠕变。结果表明俯冲带榴辉岩块体变形过程中应力较低。这些结果也可以应用于其他岩石类型。zoisite）的应力远低于位错蠕变。结果表明俯冲带榴辉岩块体变形过程中应力较低。这些结果也可以应用于其他岩石类型。