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

地幔深处的板片动力学可以迫使造山带伸展，导致山带的部分破坏。在中央阿尔卑斯山，一套前中新世伸展构造可归因于约35 Ma时从欧洲板块剥离的板片。构造对比和横切关系表明，这一阶段在约31 Ma之前结束。相比之下，最近建立的一个详细的热年代学数据集表明，伸展一直持续到29-18 Ma。与关于时机的争议类似，延期的性质也存在争议。基于构造观察的模型认为造山带平行造山崩塌，而主要基于热年代学数据的模型假设造山带正常伸展，重新激活了以前的板块界面/俯冲通道，即奥斯特罗阿尔卑斯-彭宁边界。拟议的项目首次结合了近年来经历重大改进的地质年代学方法：将使用方解石U-Pb年代学、40Ar/39Ar云母原位分析和石英矿化中流体包裹体的40Ar/39Ar定年来确定地壳变形的时间。这些结果将提供对延伸的几何和寿命的详细了解。拟议的项目将测试所描述的两个模型。此外，对年代学的详细了解将使我们能够将中阿尔卑斯山的伸展与当时碰撞带中类似的高压岩石折返、火成岩活动和远场变形(例如，伸展期间可能的前陆褶皱和冲断带传播)联系起来。在绝对年表中综合这些影响地壳不同层次的过程，将提供对板片断裂造山效应的时间分辨的洞察。

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.