The Chainons Bearnais (CB, North Pyrenean Zone) resulted from the Cenozoic contractional reactivation of the salt tectonics-bearing, hyperextended margin that initiated at the Europe-Iberia transition during the Early Cretaceous. In this tectonic scenario, assessing the relative contribution of extension and contraction to the present-day structure is crucial to reconstruct the hyperextended margin geometry and to quantify the subsequent shortening. This study undertakes this issue by defining the relationship between folding and two bedding-independent references: peak temperature isotherms and paleomagnetic data. Isotherms were reconstructed from 76 new measurements of Raman spectroscopy on carbonaceous materials (RSCM) and indicate temperatures at the time of peak metamorphism in the CB (110-85 Ma, end of extension). They are shallowly to moderately northwards dipping and cut across most of the folds deforming the Mesozoic units. Paleomagnetic data from 29 sites evidence a widespread remagnetization carried by pyrrhotite that was probably blocked during the early Paleogene (before the onset of continental collision) and postdated folding in the CB. Abnormal inclinations in this remagnetization suggest syn-collision tilts up to 60°to the north in the back limb of the Axial Zone. Based on the presented data set, we propose that the folding of the cover above the evaporitic decollement was almost fully completed by the end of the Cretaceous extension, with~85-100% of the dip of fold limbs being acquired before the remagnetization time. Cenozoic contraction reactivated the extensional faults in the shallow basement as top-to-the-S thrusts, leading to the passive transport and northwards tilting of the folded cover.

中文翻译：

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倒超伸展边缘的造山前褶皱和同造山基底倾斜：比利牛斯山脉北部的案例研究

Chainons Bearnais（CB，北比利牛斯带）是由早白垩世欧洲-伊比利亚过渡期开始的含盐构造、超伸展边缘的新生代收缩再激活造成的。在这种构造情景中，评估伸展和收缩对当今结构的相对贡献对于重建超伸展边缘几何形状和量化随后的缩短至关重要。本研究通过定义折叠和两个独立于层理的参考文献之间的关系来解决这个问题：峰值温度等温线和古地磁数据。等温线是从对碳质材料 (RSCM) 的拉曼光谱的 76 次新测量结果重建的，并指示 CB 中峰值变质时的温度（110-85 Ma，延伸结束）。它们从浅到中度向北倾斜并穿过大多数使中生代单元变形的褶皱。来自 29 个地点的古地磁数据证明磁黄铁矿进行了广泛的再磁化，这可能在古近纪早期（大陆碰撞开始之前）和 CB 的后期折叠期间被阻止。这种再磁化的异常倾斜表明轴带后肢的同步碰撞向北倾斜了 60°。根据所提供的数据集，我们提出，在白垩纪伸展结束时，蒸发脱层上方覆盖层的折叠几乎完全完成，在再磁化时间之前获得了~85-100% 的褶皱肢倾角。新生代收缩使浅层基底中的伸展断层重新激活，成为从顶部到 S 的逆冲断层，