Many described subduction complexes (or mélanges) exhumed from seismogenic depths comprise thick, turbidite-dominated sequences with deformed zones containing clasts or boudins of more competent sandstone and/or basalt. In contrast, many active subduction zones have a relatively small thickness of sedimentary inputs (<2 km), turbidite sequences are commonly accreted rather than subducted, and the role of pelagic sediments and basalt (lavas and hyaloclastites) in the deforming zone near the plate interface at <20 km depth is poorly understood. Field investigation of Neoproterozoic oceanic sequences accreted in the Gwna Complex, Anglesey, UK, reveals repeated lenticular slices of variably sampled ocean plate stratigraphy (OPS) bounded by thin mélange-bearing shear zones. Mélange matrix material is derived from adjacent OPS lithologies and is either dominantly illitic, likely derived from altered siliciclastic sediment, or chloritic, likely derived from altered volcanics. In the illitic mélange, mutually cross-cutting phyllosilicate foliation and variably deformed chlorite-quartz-calcite veins suggest ductile creep was cyclically punctuated by transient, localized fluid pulses. Chlorite thermometry indicates the veins formed at 260 ± 10°C. In the chloritic mélange, recrystallized through-going calcite veins are deformed to shear strains of 4–5 within a foliated chlorite matrix, suggesting calcite veins in subducting volcanics may localize deformation in the seismogenic zone. Shear stress-strain rate curves constructed using existing empirical relationships in a simplified shear zone geometry predict that slip velocities varied depending on pore fluid pressure; models predict slow slip velocities preferentially by frictional sliding in chlorite, at pore fluid pressures greater than hydrostatic but less than lithostatic.

中文翻译：

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挖掘沉积物贫混杂岩中的非均质亚绿片岩变形

许多描述的从发震深度挖掘出的俯冲杂岩（或混杂岩）包括厚的、以浊积岩为主的层序，其变形带包含更合适的砂岩和/或玄武岩的碎屑或碎屑。相比之下，许多活动俯冲带的沉积输入厚度相对较小（<2 km），浊积岩层序通常是增生而不是俯冲，以及中上层沉积物和玄武岩（熔岩和透明质岩）在靠近板块的变形带中的作用<20 km 深度的界面知之甚少。对英国安格尔西 Gwna 复合体中新元古代海洋序列的实地调查揭示了可变采样的海洋板块地层学 (OPS) 的重复透镜状切片，这些切片以薄的混杂岩剪切带为界。混杂基质材料来源于相邻的 OPS 岩性，主要是伊利石，可能来源于蚀变的硅质碎屑沉积物，或者是绿泥石，可能来源于蚀变的火山岩。在伊利石混杂岩中，相互交叉的页硅酸盐叶理和变形的绿泥石-石英-方解石脉表明韧性蠕变周期性地被短暂的局部流体脉冲打断。绿泥石测温表明在 260 ± 10°C 时形成的脉。在绿泥石混杂岩中，再结晶贯穿的方解石脉在叶状绿泥石基质内变形为 4-5 的剪切应变，这表明俯冲火山中的方解石脉可能定位于发震带的变形。使用简化剪切带几何形状中的现有经验关系构建的剪切应力-应变率曲线预测滑动速度随孔隙流体压力而变化；模型优先通过绿泥石中的摩擦滑动来预测慢速滑移速度，在孔隙流体压力大于静水压力但小于岩石静力的情况下。