Relating collisional kinematics to exhumation processes in the Eastern Alps
Relating collisional kinematics to exhumation processes in the Eastern Alps
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DOI：
10.1016/j.earscirev.2017.10.013
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发表时间：
2018
影响因子：
12.1
通讯作者：
C. Rosenberg;S. Schneider;A. Scharf;A. Bertrand;K. Hammerschmidt;A. Rabaute;J. Brun
中科院分区：
文献类型：
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作者：
C. Rosenberg;S. Schneider;A. Scharf;A. Bertrand;K. Hammerschmidt;A. Rabaute;J. Brun
通过对东阿尔卑斯地区表层和深部构造的回顾，将其时间和推断的位移场与碰撞过程中造山推覆体上、下地壳单元的发掘联系起来。讨论主要集中在陶恩窗口及其乡村岩石上，这是东阿尔卑斯山脉唯一一个造山楔从最上层的奥阿尔卑斯推覆体到最深处的欧洲基底推覆体持续暴露的地区。本文在综合构造和地质年代学资料，以及在剖面和地图视图上恢复碰撞位移的基础上，总结和讨论了长期以来关于该推覆体的挖掘机制的争议。我们得出结论，东阿尔卑斯西部的大量挖掘是由于大量的增厚和侵蚀造成的，而东阿尔卑斯东部没有观察到。推断主要增厚区和掘出区的侧向拉张断裂成核是为了适应西部压痕角附近的位移，以及为了减小东部地壳厚度和地表高程的大梯度。在前压痕阶段的恢复中，记录了大量向北增加的与造山带平行的伸展，范围从45公里到85公里不等，相当于伸展的15%，部分沿正断层进行。北钙质阿尔卑斯山脉和白云石山脉之间的南北缩短在西部达到75公里，在东部减少到30公里。这75公里中有55公里被安置在陶恩之窗地区。我们的运动学模型表明，沿共轭走滑断层的侧向挤压需要东阿尔卑斯西部大量的南北缩短。这种缩短与陶恩窗重建的直立折叠和侵蚀一致，从而解释了其发掘量最大的原因。相比之下，东阿尔卑斯山脉的东部终点代表了一个碰撞辐合几乎不被地壳增厚所容纳的地区。这种从主要受造山带垂直位移影响的西部高度缩短、增厚的楔体到以造山带平行位移为主要特征的东部几乎缩短和出土的楔体的转变，在空间上与欧洲板块深部构造的变化相吻合。事实上，推断出的大陆，欧洲板块，在西部的图像中消失在一个低速异常中，在东部没有检测到板块。欧洲被动边缘在地图上的一个继承步骤，导致其地壳比陶恩窗以东地区更早进入俯冲带，这可能解释了缩短和增厚的迅速减少，不同的同碰撞P-T梯度，以及Katschberg断裂以东大陆板块的消失。
Based on a review of the surface and deep structure of the Eastern Alps, we link the timing and the inferred displacement fields to exhumation of upper and lower crustal units of the orogenic nappe stack during collision. The discussion focuses mainly on the Tauern Window and its country rocks, the only area of the Eastern Alps where the orogenic wedge, from its uppermost Austroalpine nappes down to its deepest European basement nappes is continuously exposed. We summarize and discuss the long-standing controversy on the mechanisms of exhumation of this nappe stack on the base of a synthesis of structural and geochronological data, and restorations of collisional displacements, both in cross-sections and map views. We conclude that the large amounts of exhumation assessed for the western Eastern Alps resulted from large amounts of thickening and erosion, not observed in the eastern part of the Eastern Alps. Extensional faults, laterally bounding the area of major thickening and exhumation are inferred to nucleate in order to accommodate displacement around the indenter corner in the west, and in order to reduce a large gradient of crustal thickness and surface elevation in the East.Restorations to the pre-indentation stage, document an amount of northward increasing orogen-parallel extension, varying 45 km to 85 km, corresponding to 15% of extension, that is partly accommodated along normal faults. N-S shortening between the Northern Calcareous Alps and the Dolomites Indenter attained 75 km in the west and decreased to 30 km in the east. 55 km out of these 75 were accommodated in the area of the Tauern Window. Our kinematic model shows that lateral extrusion accommodated along conjugate strike-slip faults requires large amounts of north-south shortening in the western part of the Eastern Alps. Such shortening is consistent with the reconstructed upright folding and erosion of the Tauern Window, thus explaining the largest amount of its exhumation. In contrast, the eastern termination of the Eastern Alps represents an area where collisional convergence was barely accommodated by crustal thickening. This transition from a highly shortened, thickened and exhumed wedge in the west, mainly affected by orogen-perpendicular displacements, to a barely shortened and exhumed wedge in the east, mainly characterised by orogen-parallel displacements, spatially coincides with a change in the deep structure of the European slab. Indeed, the inferred continental, European Slab, imaged in the west disappears into a low velocity anomaly, where no slab is detected in the east. An inherited step in the geometry in map view of the European passive margin, causing its crust to enter the subduction zone earlier than the area east of the Tauern Window, may explain the rapid decrease of shortening, of thickening, the different syn-collisional P-T gradients, and the disappearance of the continental slab east of the Katschberg Fault.