Abstract. Assessing the size of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont-Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean-Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modelling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e. ages of syn-rift sediments, rift-related fault activity and mafic rocks) and shows that the PL Basin opened in four stages: (1) Rifting of the proximal continental margin in Early Jurassic (200–180 Ma), (2) Hyper-extension of the distal margin in Early-Middle Jurassic (180–165 Ma), (3) Ocean-Continent Transition (OCT) formation with mantle exhumation and MORB-type magmatism in Middle-Late Jurassic (165–154 Ma), (4) Break-up and mature oceanic spreading mostly in Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm/yr, full rate) and decreased to ~ 5 mm/yr after 145 Ma while completely ceasing at about 130 Ma due to motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL Ocean reached a maximum of 250 km along a NW–SE transect between Europe and Adria (Ivrea). In the Cretaceous and Cenozoic, the amount of plate convergence between Adria (Ivrea) and Europe during Alpine subduction (84–35 Ma, 420 km) and collision (35–0 Ma, 260 km) largely exceeded the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys Ophiolites exhumed today derived from OCT zones. Our work highlights the importance of distal rifted continental margins during subduction and exhumation processes and provides quantitative estimates for future geodynamic modelling and a better understanding of the Alpine Orogeny.

中文翻译：

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皮埃蒙特-利古里亚盆地的运动学和范围–对阿尔卑斯俯冲过程的影响

摘要。评估以前海洋的大小是困难的，但是对于理解俯冲和掘尸过程至关重要，评估以前的海洋的大小在山脉地带中才是残留物。在这里，我们对皮埃蒙特－利古里亚（PL）海洋（称为高山特提斯）和瓦莱州盆地的开放和宽度提出了新的限制。我们使用西地中海-高山地区的区域构造重建，将其实现为具有岩石圈变形的全球板块运动模型，以及裂陷阶段的二维热力学建模，以测试我们的运动学重建在动力学方面的一致性。我们的模型与独立的数据集（即同裂谷沉积物的年龄，与裂谷有关的断层活动和镁铁质岩石的年龄）非常吻合，并显示了PL盆地的开放分为四个阶段：（1）侏罗纪早期（200） –180 Ma），成熟海洋性扩散主要发生在侏罗纪晚期（154-145 Ma）。传播速度从慢到极慢（最大22毫米/年，全速率），并在145 Ma之后降低至〜5 mm /年，而由于北部开放期间伊比利亚相对于欧洲的运动而在约130 Ma处完全停止大西洋。沿着欧洲和阿德里亚（伊夫雷亚）之间的西北-东南横断面，PL大洋的最终宽度最大为250 km。在白垩纪和新生代，在俯冲（84-35 Ma，420 km）和碰撞（35-0 Ma，260 km）期间，阿德里亚（Ivrea）和欧洲之间的板块汇聚量大大超过了海洋的宽度。我们建议，至少63％的俯冲和增生物质是高度变薄的大陆岩石圈，而今天挖掘出的大部分高山特提斯蛇绿岩都来自OCT区。