Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France
Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France
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法国东比利牛斯山脉早期造山作用的热年代学证据
作者：
S. Ternois;M. Odlum;M. Ford;R. Pik;D. Stockli;B. Tibari;A. Vacherat;Vincent Bernard
在碰撞造山带中，将早期造山作用的热特征与先前的裂谷作用或后续的热事件区分开来是一项重大挑战。我们对东比利牛斯山（法国）后楔中的古生代阿格利 - 萨尔韦齐内斯地块进行了综合地质和低温热年代学研究。北比利牛斯山保存了从裂谷到碰撞转变的最佳地质记录之一。阿格利 - 萨尔韦齐内斯地块代表了阿普特期 - 森诺曼期裂谷系的欧洲远端反转边缘。在整个外造山地块采集了17个样本，并进行了低温热年代学分析：锆石（U - Th）/He定年记录了比利牛斯汇聚起始和早期阶段地块的冷却历史，而磷灰石（U - Th）/He定年则完善了板块碰撞的记录。通过对新的低温热年代学数据进行反演和正演模拟，我们表明比利牛斯山后楔记录了两个明显的造山冷却阶段，即晚坎帕阶 - 马斯特里赫特阶和伊普雷斯阶 - 巴顿阶，我们分别将其与远端裂谷边缘的早期反转和主碰撞相关联。检测到更早的阿普特晚期 - 土伦期冷却历史，可能与裂谷作用和/或裂谷后作用有关。在古新世期间没有冷却的证据，在此期间相邻的阿基坦后前陆盆地记录到构造平静。利用我们的低温热年代学数据和地质约束条件，我们提出了一个地壳尺度的顺序恢复模型，用于解释东比利牛斯山从伸展到造山作用高峰期的构造和热转变，这表明逆冲和底侵过程都对阿普特期 - 森诺曼期裂谷系的早期反转有贡献。
In collisional orogens, distinguishing the thermal signature of early orogenesis from the preceding rift or from subsequent thermal events is a major challenge. We present an integrated geological and low‐temperature thermochronology study of the Paleozoic Agly‐Salvezines crustal block in the retrowedge of the eastern Pyrenees (France). The northern Pyrenees preserves one of the best geological records of a rift‐to‐collision transition. The Agly‐Salvezines block represents the inverted distal European margin of an Aptian–Cenomanian rift system. Seventeen samples were collected throughout the external orogenic massif and analyzed for low‐temperature thermochronology: zircon (U‐Th)/He dating documents the cooling history of the massif during the initiation and early phase of Pyrenean convergence, while apatite (U‐Th)/He dating completes the record of plate collision. Using inverse and forward modeling of new low‐temperature thermochronology data, we show that the Pyrenean retrowedge records two clear phases of orogenic cooling, Late Campanian–Maastrichtian and Ypresian–Bartonian, which we relate to early inversion of the distal rifted margin and main collision, respectively. An earlier, late Aptian–Turonian cooling history is detected, possibly related to rifting and/or postrift. No cooling is evidenced during the Paleocene during which tectonic quiescence is recorded in the adjacent Aquitaine retroforeland basin. Using our low‐temperature thermochronology data and geological constraints, we propose a crustal‐scale sequentially restored model for the tectonic and thermal transition from extension to peak orogenesis in the eastern Pyrenees, which suggests that both thrusting and underplating processes contributed to early inversion of the Aptian–Cenomanian rift system.