Perturbation of isotherms below topography: constraints from tunnel transects through the Alps

..。相反，这项研究的目的是在给定的剥蚀率、地形波长、起伏幅度和地温梯度的框架下，直接测量地形起伏下的等温线位置。我们的研究区域是穿越中西部阿尔卑斯山的三个隧道横断面：哥特哈德隧道、L隧道和勃朗峰隧道。这三个剖面都位于地貌起伏1500~2800米的快速剥离区，地形波长约10公里，具有典型的活动造山带地貌特征。隧道剖面和相应表面剖面的样品将通过锆石裂变径迹、磷灰石裂变径迹和磷灰石(U-Th)/He分析来确定年龄。这些年龄的分布将产生二维轮廓，显示地形下等温线的位置。二维剖面可以至少部分地与三维图像相关，显示不同热年代学测年技术对扰动效应的敏感性，并给出不同测年技术固有的扰动引起的对折返速率的高估的度量。结果将用于测试现有的模型，并为未来的模型概念提供基准。

... This study, in contrast, aims to directly measure the position of isotherms below topographic relief under a given framework of denudation rate, topographic wavelengths, relief amplitued, and geothermal gradient. Our study areas are three tunnel transects through the Central and Western Alps; the Gotthard, Lötschberg, and Mont Blanc tunnels. All three profiles are situated in rapidly exhuming areas with relief between 1500 and 2800 m and topographic wavelength of about 10 km, thus representing typical geomorphic features of active orogens. Samples from the tunnel profiles and their corresponding surface profile will be dated by zircon fission track, apatite fission track, and apatite (U-Th)/He analysis. Distributions of these ages will yield two-dimensional profiles showing the positions of isotherms below topography. The two-dimensional profiles may at least partly be correlated to three-dimensional images, show the sensitivity of the different thermochronologic dating techniques to the perturbation effect, and give a measure of the perturbation-induced overestimation of exhumation rates inherent to the different dating techniques. The results will be used to test existing models and to provide benchmarks for future model concepts.