Abstract An intriguing example of chert–graywacke olistostrome is exceptionally well preserved within the late Neoproterozoic to early Cambrian Blovice accretionary wedge, Bohemian Massif. The olistostrome exhibits a block-in-matrix fabric defined by chert blocks isolated within the graywacke matrix. The major and trace element composition indicates two distinct types of cherts that formed either in a hydrothermal pelagic or hemipelagic environment supplied with a distal terrigenous material. The former is documented by elevated contents of Fe, Co, Zn, Ni, and Ti whereas the latter by high Al2O3 contents, relatively lower LaN/CeN ratios, and higher Eu/Eu* and Ce/Ce* values. Based on these geochemical data integrated with field observations and detrital zircon U–Pb ages of the host graywackes (determined using laser ablation ICP-MS), a new model for the origin of chert–graywacke association is proposed. The cherts are interpreted as representing pelagic and hemipelagic members of the Ocean Plate Stratigraphy (OPS) that formed in a sedimentary basin, carried on top of a subducting plate towards the trench. While moving over the outer swell (rise), the chert basin was intensely fractured and disrupted into large blocks or slabs. Subsequent motion of the plate brought the blocks onto an outer trench slope where they became gravitationally unstable to slide down and mix in the trench with distal, ca. 580–570 Ma turbidites derived from the overriding plate. Finally, this chert–graywacke olistostrome was covered by younger, ca. 560–547 Ma trench-fill turbidites (devoid of chert blocks) and accreted to the accretionary wedge toe, deformed, buried, and exhumed back to the wedge surface. We propose that such an olistostrome composed of pelagic/hemipelagic chert blocks and terrigenous, arc-derived graywacke matrix represents a rarely documented case of submarine, outer trench slope mass-wasting deposits and may be considered a new type of subduction-related melanges. We coin the term outer-trench-slope melange.

中文翻译：

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在波西米亚地块发现的一个巨大的晚前寒武纪含燧石的滑石：大洋板块地层 (OPS) 记录被沿外海沟斜坡的物质消耗所破坏

摘要 在新元古代晚期至早寒武纪布洛维采增生楔波希米亚地块中，燧石-格雷瓦克橄榄石的一个有趣例子保存得异常完好。olistostrome 表现出一种块状矩阵结构，由隔离在 Graywacke 矩阵内的燧石块定义。主要和微量元素组成表明两种不同类型的燧石形成于热液远洋或半远洋环境中，并提供远端陆源物质。前者表现为 Fe、Co、Zn、Ni 和 Ti 含量升高，而后者表现为 Al2O3 含量高、LaN/CeN 比率相对较低以及 Eu/Eu* 和 Ce/Ce* 值较高。基于这些地球化学数据，结合实地观测和寄主灰岩的碎屑锆石 U-Pb 年龄（使用激光烧蚀 ICP-MS 确定），提出了一种新的 chert-graywacke 关联起源模型。燧石被解释为代表在沉积盆地中形成的海洋板块地层 (OPS) 的远洋和半远洋成员，被带入俯冲板块的顶部朝向海沟。在外隆起（上升）上移动时，燧石盆地剧烈破裂并破碎成大块或板片。随后板块的运动将石块带到外沟斜坡上，在那里它们变得重力不稳定，滑下并在沟中与远端混合，大约。来自上覆板块的 580-570 Ma 浊积岩。最后，这个燧石-graywacke olistostrome 被年轻的，约。560-547 Ma 沟渠填充浊积岩（没有燧石块）并吸积到增生楔形趾部，变形，埋藏，并挖掘回楔形表面。我们认为，这种由远洋/半远洋燧石块和陆源、弧形衍生的灰岩基质组成的橄榄石代表了一个罕见的海底、外海沟斜坡质量消耗沉积物的案例，可以被认为是一种新型的俯冲相关混杂岩。我们创造了术语外沟槽斜坡混杂物。