Eo-Oligocene normal faulting in the Alps: Orogen-perpendicular subduction channel reactivation or orogen-parallel collapse following slab breakoff?

地幔深度的板块动力学可以迫使造山带伸展，导致山带的部分破坏。在阿尔卑斯中部，一套前中新世的伸展构造是在~35 Ma时由欧洲板块的板块断裂形成的。结构相关性和横切关系表明，这一阶段结束于~31 Ma之前。相比之下，最近创建的详细的热年代学数据表明，延伸持续到29-18 Ma。与时间的争议类似，延期的性质也存在争议。基于构造观测的模型认为造山带平行造山带塌陷，而基于热年代学数据的模型认为造山带正伸展重新激活了以前的板块界面/俯冲通道，即australpine - pennine边界。本文提出的项目将通过填补构造观测中的空白和直接定年来研究阿尔卑斯中部的伸展构造。该项目首次结合了近年来取得重大进展的地质年代学方法：U-Pb方解石地质年代学、40Ar/39Ar云母原位分析和石英矿化流体包裹体40Ar/39Ar定年，将用于确定地壳变形的时间。结果将提供对延伸的几何形状和寿命的详细了解。拟议的项目将测试上述两种模型。此外，详细的年代学知识将使中阿尔卑斯山脉的伸展与高压岩石的出土时间和年代相似，火成岩活动的变化以及当时碰撞带的远场变形（例如伸展期间可能的前陆褶皱-冲断带传播）联系起来。将这些影响地壳不同层次的过程整合在一个绝对年表中，将为板块断裂的造山作用提供时间解决的见解。

Slab dynamics at mantle depth can force orogens into extension resulting in partial destruction of the mountain belt. In the Central Alps a set of pre-Miocene extensional structures are attributed to slab breakoff from the European plate at ~35 Ma. Structural correlations and cross-cutting relationships suggest this phase ended prior ~31 Ma. In contrast, a recently created detailed thermochronologic dataset suggests that extension continued until 29–18 Ma. Similar to the controversy about timing, the nature of extension is debated. The model based on structural observations suggests orogen-parallel orogenic collapse while the one mostly based on thermochronologic data postulates orogen-normal extension that reactivated the former plate interface/subduction channel, i.e. the Austroalpine-Pennine boundary.The herein proposed project will investigate extensional structures in the Central Alps by filling in gaps in the structural observations and directly dating extension. The proposed project combines - for the first time - geochronologic methods that experienced major improvements in recent years: U-Pb calcite geochronology, 40Ar/39Ar mica in situ analysis and 40Ar/39Ar dating of fluid inclusions in quartz mineralizations will be used to determine the timing of crustal deformation. The results will provide a detailed understanding of the geometry and longevity of extension. The proposed project will test the two described models. Furthermore, detailed knowledge of the chronology will allow contextualizing the extension in the Central Alps with the similar timed and well dated exhumation of high-pressure rocks, changes in igneous activity and far field deformation in the collision zone at the time (e.g. possible foreland fold-and-thrust belt propagation during extension). Integrating these processes affecting different levels of the crust in an absolute chronology will provide time resolved insights into the orogenic effects of slab breakoff.