Early phases of mountain building are usually poorly constrained although they may provide insights into both the wedge rheology and the role of inheritance. In the central Pyrenean Axial Zone, a main exhumation peak at 35–30 Ma is particularly well constrained but the previous exhumation stages are much less constrained. In this study, we present new low‐temperature thermochronological zircon fission‐track and (U‐Th)/He data and structural observations to constrain the thermal history of the Axial Zone and its shortening sequence during the whole Alpine collision. The dataset collected along the ECORS profile suggests two main collisional cooling phases. An early stage of Alpine shortening (from 70 to 40 Ma) is characterized by low rates of cooling/exhumation in the whole Axial Zone around 5–10°C/Myr and 200 ± 50 m/Myr. During this phase, deformation was distributed within the whole Axial Zone. This result questions the occurrence of a quiescence phase in the Axial Zone. Between 40 and 20 Ma, a more localized second phase with cooling rates around 30°C/Myr and high exhumation rates >800 m/Myr is only recorded in the Maladeta massif. During this second phase, much lower denudation rates are recorded further north and south, thus suggesting rather symmetrical exhumation in the Axial Zone, controlled by underplating of the youngest crustal ramp, the Rialp thrust. This sequence of shortening, from distributed to localized deformation, appears to be characteristic in other collisional wedges as well.

中文翻译：

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比利牛斯山中部建筑物：来自轴向带的新的LT热年代学数据的限制

尽管山区建筑的早期阶段可能提供有关楔形流变学和继承作用的见解，但它们通常受约束不大。在比利牛斯山脉中部轴向带，主要发掘高峰在35-30 Ma受到特别良好的约束，但以前的发掘阶段受的约束则少得多。在这项研究中，我们提出了新的低温热年代学锆石裂变径迹和（U-Th）/ He数据以及结构观察，以约束整个高山碰撞过程中轴带的热历史及其缩短序列。沿ECORS剖面收集的数据集提出了两个主要的碰撞冷却阶段。高山缩短的早期阶段（从70 Ma到40 Ma）的特征在于，整个轴向区域的冷却/回火率较低，约为5-10°C / Myr和200±50 m / Myr。在此阶段，变形分布在整个轴向区域内。该结果对轴向区域中静止阶段的发生提出了质疑。在40至20 Ma之间，仅在Maladeta断层中记录到了局部化程度更高的第二相，冷却速率大约为30°C / Myr，高发掘速率大于800 m / Myr。在第二阶段，南北方向记录的剥蚀率要低得多，这表明轴向区域的掘出是相当对称的，受最年轻的地壳斜坡Rialp逆冲作用的控制。从分布变形到局部变形的这种缩短顺序在其他碰撞楔形中也具有特征。仅在Maladeta断层中记录到了更局限的第二阶段，冷却速率约为30°C / Myr，高发掘速率> 800 m / Myr。在第二阶段，南北方向记录的剥蚀率要低得多，这表明轴向区域的掘出是相当对称的，受最年轻的地壳斜坡Rialp逆冲作用的控制。从分布变形到局部变形的这种缩短顺序在其他碰撞楔形中也具有特征。仅在Maladeta断层中记录到了更局限的第二阶段，冷却速率约为30°C / Myr，高发掘速率> 800 m / Myr。在第二阶段，南北方向记录的剥蚀率要低得多，这表明轴向区域的掘出是相当对称的，受最年轻的地壳斜坡Rialp逆冲作用的控制。从分布变形到局部变形的这种缩短顺序在其他碰撞楔形中也具有特征。