Understanding the rheology of orogenic wedges requires the knowledge of the structural and thermal evolution of collisional units. In this study, we document the maximum temperature reached by the sedimentary cover nappes of the External Crystalline Massif (Western and central Alps) by Raman spectroscopy of carbonaceous material, between the Belledonne (France) and the Aar (Switzerland) Massifs. These cover units form the Helvetic/Dauphinois nappe complex. Maximum temperatures reached by the Upper Helvetic nappes lie in a range spanning from below 220 and 350 °C ± 50 °C. For the Lower Helvetic nappes, the temperatures spread between 226 and 358 °C ± 50 °C. These temperatures were projected on two structural cross sections in order to constrain the 3‐D thermal structure. From these data, we propose that the Helvetic nappes were deformed and emplaced before and/or during the thermal peak, which supports recent findings that shortening in the External Crystalline Massif was mainly accommodated during a 5‐ to 10‐Myr‐long thermal peak before deformation localized along crustal thrusts, which exhumed and cooled down the wedge. During this late exhumation, the isotherms corresponding to the thermal peak were passively folded.

中文翻译：

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欧洲阿尔卑斯山的轻型尿布的3-D热结构：对碰撞过程的影响

了解造山楔的流变学要求了解碰撞单元的结构和热演化。在这项研究中，我们通过贝勒多讷（法国）和Aar（瑞士）地块之间的碳质物质的拉曼光谱记录了外部晶体地块（西部和中部阿尔卑斯山）的沉积物覆盖物达到的最高温度。这些掩护单元形成了Helvetic / Dauphinois尿布复合体。上层助推尿布达到的最高温度在220至350°C±50°C以下。对于下Helvetic尿布，温度分布在226至358°C±50°C之间。将这些温度投影在两个结构横截面上，以约束3D热结构。根据这些数据，我们建议在热峰之前和/或期间对Helvetic尿布进行变形和定位，这支持了最近的发现，即外部结晶质块的缩短主要是在5至10米尔长的热峰中发生的，然后才沿着地壳发生了局部变形。推力，挖出并冷却了楔子。在此晚期发掘期间，对应于热峰的等温线被被动折叠。