Detecting and Correcting for Paleomagnetic Inclination Shallowing of Sedimentary Rocks: A Review
Detecting and Correcting for Paleomagnetic Inclination Shallowing of Sedimentary Rocks: A Review
复制标题
DOI：
10.3389/feart.2016.00007
复制
发表时间：
2016-02
影响因子：
2.9
通讯作者：
Yong-Xiang Li;K. Kodama
中科院分区：
文献类型：
--
作者：
Yong-Xiang Li;K. Kodama
磁各向异性和伸长/倾斜(E-I)方法作为探测和校正沉积岩中古地磁倾角变浅的两种重要手段已越来越多地被使用，这是60年前首次发现的。这两种方法都是建立在一定的假设基础上的，因此在研究沉积岩中的浅倾角方面具有优势和固有的局限性。E-I方法相对容易使用，但由于地磁场的古分子变化，它需要大量的数据集来充分采样古地磁方向。此外，缓慢的沉积物堆积速率和局部构造可能导致使用E-I方法的校正不足或过高。对于磁各向异性技术，为了准确地确定剩磁颗粒的体磁各向异性和单个颗粒的磁各向异性，即样品的a因子，需要进行劳动密集型、复杂的实验室岩石磁学实验。我们的综述表明，尽管应用基于各向异性的倾斜度校正需要密集的实验室工作，但值得投入这一努力。此外，联合使用磁化率和剩磁各向异性测量以及详细的岩石磁测量来确定颗粒的各向异性“a”因子，具有检索倾斜变浅的直接证据并以高度可信的方式对其进行校正的优点。我们告诫不要在没有充分了解每种技术的基本假设和内在局限性的情况下使用这两种方法中的任何一种。这两种技术的使用和比较可以为沉积岩提供最稳健的倾斜浅校正。
Magnetic anisotropy and the elongation/inclination (E-I) approaches have been increasingly employed as two important means for detecting and correcting the paleomagnetic inclination shallowing in sedimentary rocks that was first recognized sixty years ago. Both approaches are based on certain assumptions, and thus have advantages and intrinsic limitations in investigating shallow inclinations in sedimentary rocks. The E-I approach is relatively easy to use, but it needs a large dataset to adequately sample paleomagnetic directions due to paleosecular variation of the geomagnetic field. Also, slow sediment accumulation rates and local tectonics could lead to under- or over-corrections using the E-I approach. For the magnetic anisotropy technique, labor-intensive, sophisticated laboratory rock magnetic experiments are required in order to accurately determine both bulk magnetic anisotropy of remanence-carrying grains and magnetic anisotropy of an individual particle, i.e., “a” factor, of samples. Our review shows that, despite the intensive laboratory work necessary for applying anisotropy-based inclination corrections, it is worth investing the effort. In addition, the joint use of magnetic susceptibility and remanence anisotropy measurements as well as detailed rock magnetic measurements for determining the particle anisotropy “a” factor have the advantage of retrieving direct evidence of inclination shallowing and correcting for it with high confidence. We caution against use of either of the two approaches without full appreciation of the underlying assumptions and intrinsic limitations of each technique. The use and comparison of both techniques could provide the most robust inclination shallowing correction for sedimentary rocks.