The Brenner base tunnel (BBT) natural laboratory – From cross-section construction over fabric and elastic anisotropy analysis to 4D structural modeling

布伦纳山口地区的铁路隧道(布伦纳隧道，BBT)目前正在建设中，计划全长达公里，为东阿尔卑斯山提供了独特的地质景观。隧道断面横跨Tauern Window的非正式推覆体堆叠的西侧，包括奥斯特罗尔山、宾尼尼期和宾尼尼亚期单元以及南阿尔卑斯山的地下室。因此，该断面覆盖了东阿尔卑斯山的大部分主要构造单元，位于Transalp地震断面以西约25公里处。为了更好地了解构造构造和发展，并将上地壳结构与地球物理成像结果相关联，我们计划利用3D MOVE软件，结合地质地表信息、地震、岩石物理、显微构造和地质年代学数据，以及构造建模。BBT提供了获得非常长横断面的独特地下信息的可能性，包括仔细调查覆盖BBT断面大部分可用钻芯的机会。钻芯扫描和描述将与应用中子衍射织构分析和波速各向异性建模的显微组构研究相结合。构造数据提供了关于应变局部化以及断层和剪切带在这一长地壳剖面中形成的信息，这是任何近距离分辨率的地表调查都无法完成的。额外的地质测绘和隧道数据汇编允许以最详细的方式构建地质横断面。根据现有的西部陶恩窗折返构造模型，可以利用三维运动来检验该地区相关断裂带的活动性。对所有主要构造的详细分析、地表和隧道之间的相关性以及2D、3D建模可能有助于识别关键构造，这些构造可能指示也可能不指示由于俯冲极性变化而改变的构造输送方向。微观组构和岩石物理数据，特别是钻芯扫描和测井以及纹理建模和三轴实验所产生的弹性各向异性，将被包括在横截面构造和3D Move建模中。基于我们的模拟和我们的实验室数据以及现有的时间限制，我们最终打算在空间和时间上成像我们的地壳上部BBT剖面的结构、微结构和岩石物理参数的模式。此外，我们的弹性各向异性结果可以应用于处理地震数据和在SPP 4D-MB框架和整个AlpArray项目中收集的其他深度测深成像技术。在这一点上，我们还有助于解释更深层次的地壳调查，重点是岩石圈的解剖和西部陶恩地区俯冲极性逆转的任何迹象。

The railway tunnel in the Brenner pass area (Brenner Basistunnel, BBT), which is currently under construction and is planned to reach a total length of 64 km, provides a unique geological view into the Eastern Alps. The tunnel transect crosses the western side of the antiformal nappe stack of the Tauern window including Austroalpine, Penninic, and Sub-Penninic units as well as basement of the Southern Alps. Hence, this transect covers most of the major tectonic units of the Eastern Alps, approximately 25 km west of the TRANSALP seismic cross section. To better understand the tectonic architecture and development, and to correlate the upper crustal structure with geophysical imaging results, we plan to combine geological surface information, seismic, petrophysical, microstructural and geochronological data, as well as tectonic modeling, using the software 3D MOVE.The BBT offers the unique possibility to get subsurface information of a very long cross section, including the opportunity to investigate carefully the available drill cores that cover most of the BBT transect. Drill core scanning and description will be combined with microfabric studies that apply neutron diffraction texture analysis and Vp/Vs-anisotropy modeling. The structural data provide information about strain localization as well as fault and shear zone formation in this long crustal section, which cannot be done by surface investigation in any close by resolution. Additional geological mapping and tunnel data compilation allows to construct the geological cross-section in the highest detail. Based on current tectonic models of the exhumation of the Western Tauern window, the activity of related fault zones in the area can be tested using 3D MOVE. A detailed analysis of all the major structures, correlation between the surface and the tunnel, and 2D-, 3D-modeling may help to identify crucial structures that may or may not indicate changing tectonic transport directions due to a subduction polarity change. Microfabrics and petrophysical data and especially the elastic anisotropy results from the drill core scanning and logging as well as from the texture modeling and the triaxial experiments, will be included in the cross section construction and the modeling with 3D MOVE. Based on our modeling and our laboratory data and the available time constraints we finally intend to image the patterns of our structural, microstructural and petrophysical parameters of the upper crustal BBT section in both, space and time. Furthermore, our elastic anisotropy results can be implemented into the processing of the seismic data and other deep sounding imaging techniques collected in the framework of the SPP 4D-MB and the entire AlpArray project. In that we also contribute to the interpretation of the deeper crustal investigation that focus on the anatomy of the lithosphere and any indication of a reversal in subduction polarity in the western Tauern area.