In the Quebec Appalachians, the St-Joseph fault is a major normal fault that mostly juxtaposes metamorphic remnants of the Laurentian margin in its footwall and the adjacent oceanic domain accreted during the Ordovician Taconian orogeny in the hanging wall. It locally merges into and overprints the Baie Verte-Brompton line (BBL). The existence of late Silurian extensional deformation is well known in the Appalachians, but the associated structures, like the St-Joseph fault, and their regional distribution have not previously been precisely described and characterized. We present a detailed description of the macroscopic fabrics and extensional fault structures observed along the St-Joseph fault for hundreds of kilometers in the Quebec Appalachians. A petrographic and numerical microstructural analysis is presented as a test to quantitatively evaluate the metamorphic and structural contrasts between the footwall and hanging wall sequences, as well as the shear strain and fault offset related to the St-Joseph fault. The main movement along this SE-dipping fault is normal and characterized by brittle-ductile fabrics and fault surfaces marked in places by tectonic slices of serpentinite and/or altered and sheared peridotite. Besides, a strong textural contrast between the rock units of its hanging wall and footwall imply a fault throw of several kilometers (4–8 km). The inferred timing of the maximum, normal-sense displacement activity along this structure is Late Silurian-Early Devonian and interpreted as genetically related to the sedimentation of the Gaspé Belt and exhumation of the Laurentian margin. It is attributed to a late Salinic tectonic period of large-scale crustal extension of ca. 10 Ma lasting while the internal parts of the orogen (Maritimes and New-Brunswick) were already experiencing collision with Avalonia. The down-dip normal fault movement features are overprinted by consistent curvilinear and low-plunging slickenlines indicating that fault movement has evolved into late dextral strike-slip. This suggests that during the early Devonian, crustal extension progressively transitioned into a compressional regime due to the approaching Avalonia, which was accommodated by a transtensionnal phase with a progressive rotation of fault movement toward a dextral component.

在魁北克阿巴拉契亚山脉，St-Joseph 断层是主要的正断层，主要并列其下盘劳伦边缘的变质残余物和上盘中奥陶纪 Taconian 造山运动期间增生的相邻洋域。它在本地合并到 Baie Verte-Brompton 线 (BBL) 并叠印。阿巴拉契亚山脉晚期志留纪伸展变形的存在是众所周知的，但相关的构造，如圣约瑟夫断层，及其区域分布，以前没有被精确描述和表征。我们详细描述了沿圣约瑟夫断层在魁北克阿巴拉契亚山脉数百公里处观察到的宏观结构和伸展断层结构。提出了岩相学和数值微观结构分析作为定量评估下盘和上盘序列之间的变质和构造对比以及与圣约瑟夫断层相关的剪切应变和断层偏移的测试。沿着这条 SE 倾斜断层的主要运动是正常的，其特征是脆性-韧性织物和断层表面以蛇纹岩和/或蚀变和剪切橄榄岩的构造切片为标志。此外，其上盘和下盘岩石单元之间强烈的纹理对比意味着几公里（4-8公里）的断层。推断的最大值的时间，沿着该结构的正常位移活动是晚志留世-早泥盆世，并被解释为与加斯佩带的沉积和劳伦边缘的挖掘在成因上有关。它归因于约 2000 年大规模地壳伸展的盐碱期晚期构造时期。10 Ma 持续，而造山带的内部（滨海和新不伦瑞克）已经与阿瓦隆尼亚发生碰撞。下倾的正断层运动特征被一致的曲线和低倾角的光滑线所覆盖，表明断层运动已演变为晚期右旋走滑。这表明在早泥盆世，由于阿瓦隆尼亚的逼近，地壳伸展逐渐转变为挤压状态，