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

阿尔卑斯山始渐新世正断层：板片断裂后造山带垂直俯冲通道重新激活或造山带平行塌陷？

• 批准号: 421790087
• 负责人: Dr. Daniel Rutte
• 金额: --
• 依托单位: Arbeitsgruppe Strukturgeologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/421790087?language=en
• 关键词: Eo; Oligocene; normal; faulting; Alps

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.

地幔深部的板块动力学可以迫使造山带伸展，导致造山带的部分破坏。在阿尔卑斯山中部，一组前中新世伸展构造被归因于约35 Ma时欧洲板块的板片断裂。构造相关性和交叉关系表明，这一阶段结束前31马。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。与时间上的争议类似，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的崩塌，而基于热年代学数据的模型则认为造山带的正向伸展作用重新激活了前板块界面/俯冲通道，即Austroalpine-Pennine边界。本项目将通过填补构造观测的空白和直接测定伸展作用的年代来研究阿尔卑斯山脉中部的伸展构造。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：U-Pb方解石地质年代学、40 Ar/39 Ar云母原位分析和石英矿化中流体包裹体的40 Ar/39 Ar定年将用于确定地壳变形的时间。结果将提供一个详细的几何形状和延长寿命的理解。拟议的项目将测试所述的两个模型。此外，详细的年代学知识将允许在中央阿尔卑斯山的延伸与类似的定时和良好的日期折返的高压岩石，在当时的碰撞区的火成岩活动和远场变形的变化（例如，可能的前陆褶皱和冲断带扩展期间）。将这些影响地壳不同层次的过程整合在一个绝对的年代学中，将为板片断裂的造山作用提供时间分辨的见解。