ABSTRACT

This work presents the structural evolution of a poorly studied key-area in the middle Ala Valley, Western Alps, where two tectono-metamorphic units are exposed. A geological map at the 1:10.000 scale, integrated with meso- and microstructural analysis, has been realised. We investigated the contact area between Gran Paradiso Massif in the footwall and Lower Piedmont Zone in the hanging wall. Both tectono-metamorphic units, with a different paleogeographic affinity, preserve similar polyphasic deformation histories, defined by four deformation phases. The Dp phase, strongly transposing previous structural relicts, is marked by a high-pressure assemblage associated with the Sp foliation. Dp controls the lithological boundary attitude. A mylonitic zone, developed during the Dp, showing kinematic indicators pointing to a top-to-the N-NW sense of shear, is responsible for the juxtaposition of the two units. Dp structural elements are deformed by Dp+1 and Dp+2 subsequent phases. A greenschist-facies overprinting was observed during the Dp+1 phase.

摘要

这项工作展示了西阿尔卑斯山阿拉河谷中部一个研究不足的关键区域的结构演化，该区域暴露了两个构造变质单元。已经实现了 1:10.000 比例尺的地质图，结合细观和微观结构分析。我们调查了下盘的 Gran Paradiso 地块和上盘的下皮埃蒙特区之间的接触面积。两个具有不同古地理亲和力的构造变质单元都保留了相似的多相变形历史，由四个变形阶段定义。Dp 阶段，强烈转置先前的结构遗迹，以与 Sp 叶理相关的高压组合为标志。Dp 控制岩性边界姿态。在 Dp 期间形成的糜棱带，显示指向顶部到 N-NW 剪切感的运动学指标，负责两个单元的并置。Dp 结构元素通过 Dp+1 和 Dp+2 后续阶段变形。在 Dp+1 相期间观察到绿片岩相叠印。