In salt-detached fold-and-thrust belts, contractional modification of salt structures may include decapitation by thrusting, but examples are not well known in the subsurface and undocumented in outcrop. Here we present a surface exposure of an intrasalt, sub-horizontal shear zone at the boundary between the Tarcău and Subcarpathian nappes in the Romanian Eastern Carpathians. The Mânzălești diapir forms the largest rock salt outcrop in Europe, with unique salt-karst geomorphology. Numerous wells show that the outcrop is above deep-seated salt of a precursor salt-cored anticline or passive diapir whose base is at >3,500 m. Multiscale observations using UAV-based digital outcrop models, fieldwork, and microstructure analysis show that the outcrop is characterized by sub-horizontal foliation with isoclinal folds, unlike the subvertical fabric of most Romanian diapirs. The halite is rich in clastic inclusions, with a power-law size distribution caused by tectonic reworking of originally impure salt. Microstructures show that the halite matrix is strongly deformed by dislocation creep, forming subgrains and dynamically recrystallized grains around large porphyroclasts with piezometry indicating relatively high differential stress of around 4 MPa, at pressures sufficient to suppress dilatancy. The observations are best explained by sub-horizontal shear generated by an overriding nappe, overprinting an original coarse-grained salt fabric during decapitation of the salt body.

中文翻译：

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罗马尼亚 Mânzălești Diapir 中的低角剪切力：东喀尔巴阡山脉褶皱冲断带中的盐分斩首

在脱离盐层的褶皱冲断带中，盐结构的收缩变形可能包括冲断造成的斩首，但在地下的例子并不为人所知，在露头中也没有记录。在这里，我们展示了在罗马尼亚东喀尔巴阡山脉的 Tarcău 和 Subcarpathian 推覆之间的边界处盐内、亚水平剪切带的表面暴露。Mânzălești底辟形成了欧洲最大的岩盐露头，具有独特的盐岩地貌。大量井表明，露头位于前体盐芯背斜或被动底辟的深层盐层之上，其基底>3,500 m。使用基于无人机的数字露头模型、实地工作和微观结构分析进行的多尺度观测表明，露头的特征是具有等斜褶皱的亚水平叶理，不像大多数罗马尼亚尿布的垂直结构。岩盐中含有丰富的碎屑包裹体，其大小分布呈幂律分布，这是由原始不纯盐的构造改造造成的。显微结构表明，岩盐基质因位错蠕变而发生强烈变形，在大斑岩碎屑周围形成亚晶粒和动态再结晶晶粒，测压法表明，在足以抑制膨胀的压力下，压力差值相对较高，约为 4 MPa。观察结果最好通过覆盖推顶产生的亚水平剪切来解释，在盐体斩首期间覆盖原始粗粒盐织物。显微结构表明，岩盐基质因位错蠕变而发生强烈变形，在大斑岩碎屑周围形成亚晶粒和动态再结晶晶粒，测压法表明，在足以抑制膨胀的压力下，压力差值相对较高，约为 4 MPa。观察结果最好通过覆盖推顶产生的亚水平剪切来解释，在盐体斩首期间覆盖原始粗粒盐织物。显微结构表明，岩盐基质因位错蠕变而发生强烈变形，在大斑岩碎屑周围形成亚晶粒和动态再结晶晶粒，测压法表明，在足以抑制膨胀的压力下，压力差值相对较高，约为 4 MPa。观察结果最好通过覆盖推顶产生的亚水平剪切来解释，在盐体斩首期间覆盖原始粗粒盐织物。