Vertical axis rotations in fold and thrust belts: Comparison of AMS and paleomagnetic data in the Western External Sierras (Southern Pyrenees)
Vertical axis rotations in fold and thrust belts: Comparison of AMS and paleomagnetic data in the Western External Sierras (Southern Pyrenees)
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DOI：
10.1016/j.tecto.2012.01.023
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发表时间：
2012-04
期刊：
影响因子：
2.9
通讯作者：
Ó. P. Anchuela;Emilio L. Pueyo;A. P. Juan;A. Imaz
中科院分区：
文献类型：
--
作者：
Ó. P. Anchuela;Emilio L. Pueyo;A. P. Juan;A. Imaz
当逆冲推覆过程中发生斜向构造和垂直轴旋转（VAR）时，褶皱-冲断带的几何学和运动学可能是复杂的环境。许多技术可以用来解开这种复杂的构造历史，从经典的应变分析和古水流变化，到更现代的方法，如古地磁和方解石双晶分析。在本文中，磁化率的各向异性进行了比较，推导出的古地磁数据沿着三个横截面在外部Sierras和哈卡盆地（西南比利牛斯山）的垂直轴旋转。这些数据表明：1）AMS代表了倾斜前的变形组构，磁线理在后期变形中表现为被动标志; 2）在该区可以找到古地磁场的原始记录。因此，与古地磁基准的差异是局部VAR。两个数据集的对比分析表明：（1）相邻地点的古地磁VAR和磁线理方向变化相似;（B）VAR与磁线理趋势变化之间存在显著的线性回归关系。磁线理相对于预期的局部磁线理允许垂直轴旋转的偏差，以量化使用AMS数据集。古地磁和AMS数据的综合分析使得：1）在具有类似AMS模式的区域中更快地比较运动学演化; 2）识别与VAR相关的磁性线理的异常方向;以及3）使用AMS分析作为从其他技术确定的VAR的均匀性测试。AMS被建议作为一个合适的初步技术，以选择进一步的网站，古地磁分析，因为古地磁实验室程序比AMS测量更耗时，AMS通常不修改样品剩磁，因此样品可以用于这两种类型的分析。
Geometry and kinematics of fold-and-thrust belts can be complex settings when oblique structures and vertical-axis rotations (VAR) take place during thrust emplacement. Many techniques can be used to unravel such complex tectonic histories, from classic ones like strain analysis and changes of paleocurrents, to more modern approaches such as paleomagnetism and calcite twin analysis. In this paper, anisotropy of magnetic susceptibility is compared to vertical axis rotations deduced from paleomagnetic data along three cross-sections in the External Sierras and the Jaca Basin (southwestern Pyrenees). These data enable us to state that: 1) AMS represents pre-tilting deformation fabrics and magnetic lineation behaves like a passive marker during later deformation; and 2) a primary record of the paleomagnetic field can be found in the area. Therefore, the difference with the paleomagnetic reference is the local VAR. The comparison of the two datasets allows us to draw the following conclusions: A) the changes in both paleomagnetic VAR and magnetic lineation orientation between neighbouring sites are similar; and B) there is a significant linear regression between VAR and trend changes in magnetic lineation. Deviations in magnetic lineation with respect to the expected local magnetic lineation permit vertical axis rotations to be quantified using the AMS dataset. The combined analysis of paleomagnetic and AMS data enables: 1) a quicker comparison of the kinematic evolution in areas with similar AMS patterns; 2) the identification of anomalous orientations of magnetic lineation linked to VARs; and 3) the use of AMS analysis as a homogeneity test for VARs determined from other techniques. AMS is proposed as a suitable preliminary technique to select further sites for paleomagnetic analysis since paleomagnetic laboratory procedures are much more time-consuming than AMS measurements, AMS does not usually modify sample remanence and hence samples can be used for both types of analysis.