Three-component borehole magnetics in the COSC-2 drill hole

大约4亿年前，在志留纪和下泥盆纪的地质时期，两个大陆的碰撞发生在现在的斯堪的纳维亚地区。古大陆劳伦大陆被波罗的海俯冲，卡尔多山脉形成。造山过程是地球科学的极大兴趣，由于几个相似的过程，目前正在发生在喜马拉雅地区。为了研究造山过程，两个钻孔，每个约。2.5公里深，计划在COSC（斯堪的纳维亚喀里多尼亚碰撞造山运动）项目内钻探到前大陆之间的缝合带。COSC-1于2014年钻探，COSC-2计划于2020年夏季钻探。COSC-2将通过几个单位的较低的外来岩向下钻到原地芬诺斯堪的亚基底。COSC-2项目的主要目标之一是确定绿片岩相冲断岩片、加里东期主要滑脱构造和前寒武纪基底的变形特征和时代。在拟议的研究中，我们将在COSC-2钻孔中进行三分量磁力计测量。将对数据进行处理，并根据地理参考框架重新定位。由此产生的磁场异常将结合航空磁测和地震数据（地面和有线数据），在一个大规模的三维模型解释。通过三维建模，我们将大大减少目前模型中的非唯一性。结果被纳入现有的模型，从而提高精度的区域结构model.The解释的主要重点将是在Caledonide滑脱，由明矾页岩托管之间的接触带，和Fennoscandian基底。利用从三分量钻孔磁测数据中得到的天然剩磁矢量信息，我们将能够检验关于钻孔附近（~ 200 m）地质环境的几个假设。在显著的剩磁磁化区域，例如在形成芬诺斯堪的纳维亚基底的Rätan花岗岩中，自然剩磁磁化将被用来导出重建变形过程和斯堪的纳维亚加里东构造历史的重要约束。因此，我们将有助于更好地了解造山过程，这是COSC项目的主要目标之一。

About 400 million years ago, in the Silurian and lower Devonian geological time periods, a collision of two continents took place in the region of what is now Scandinavia. The paleo-continent Laurentia was underthrusted by Baltica, and the Caldonian montains were formed. The mountain-building processes are of great interest for geosciences due to several similarities to the processes currently taking place in the Himalayan region. In order to study the mountain building processes, two boreholes, each approx. 2,5 km deep, were planned to be drilled within the COSC (Collisional Orogeny in the Scandinavian Caledonides) project into the suture zone between the former continents. COSC-1 was drilled in 2014, COSC-2 is scheduled for summer 2020. COSC-2 will be drilled through several units of the lower allochthon down to the autochthonous Fennoscandian basement. One of the main objectives of the COSC-2 project is to define the character and age of deformation of the greenschist facies thrust-sheets, the main Caledonian décollement and the Precambrian basement. In the proposed study, we will carry out three-component magnetometer measurements in the COSC-2 borehole. The data will be processed and reoriented to a geographical reference frame. The resulting magnetic field anomalies will be interpreted in combination with aeromagnetic and seismic data (both surface and wire-line data) in terms of a large-scale 3-D model. Through three-dimensional modelling, we will significantly reduce the non-uniqueness in present models. The results are incorporated into the existing models and thus increase accuracy of the regional structural model.The main focus of interpretation will be on the contact zone between the Caledonide décollement, hosted by Alum shale, and the Fennoscandian basement. Using the vector information of the natural remanent magnetization derived from the three-component borehole magnetic data we will be able the test several hypotheses about the geological setting in the vicinity (~ 200 m) of the drill hole. In regions of significant remanent magnetization, for example within the Rätan granite forming the Fennoscandian basement, the natural remanent magnetization will be used to derive important constraints for the reconstruction of deformation processes and the tectonic history of the Scandinavian Caledonides. Therefore, we will contribute to an improved understanding of mountain building processes, one of the major goals of the COSC project.