Magnetic Fabric and Its Significance in the 1400 Ma Mealy Diabase Dykes of Labrador, Canada
Magnetic Fabric and Its Significance in the 1400 Ma Mealy Diabase Dykes of Labrador, Canada
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加拿大拉布拉多1400 Ma粉状辉绿岩岩脉中的磁性织物及其意义
DOI：
10.1029/jb093ib11p13689
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发表时间：
1988
影响因子：
--
通讯作者：
A. Desbarats
中科院分区：
文献类型：
--
作者：
John K. Park;E. Tanczyk;A. Desbarats
相对较新的米利辉绿岩墙群的磁化率各向异性(AMS)研究表明，AMS与岩石中的变形效应之间存在相关性。在对211个在古地磁研究中加热到640°C的样品和22个在交替磁场中逐步处理的新鲜样品的实验工作中，发现了几个AMS组分。17个轻微变形或没有变形的地点具有由两个主要成分组成的磁性组构。稳定分量属于初级形状各向异性，具有最小和最大主磁化率方向，分别优先垂直和沿岩墙走向(≈N 60°E)定向。这种构型与侵位后应力场的起源是一致的，即水平伸展作用于部分结晶的岩浆垂直薄片。这一分量相对于现今水平方向的方向表明，岩墙自就位以来没有倾斜。这种不稳定成分被高达250mT的磁场移除，归因于格伦维尔造山运动期间温和的构造应力所产生的诱导(域)各向异性。用置换椭球法求出其主成分的近似方位，表明存在东西方向的最大应力。另外四个具有明显变形的地点具有无法可靠分析的磁性组构，但这些组构可能主要由格伦维尔造山运动期间形成的磁畴和应力诱导的各向异性组成。
An anistropy of magnetic susceptibility (AMS) study of the relatively fresh Mealy diabase dyke swarm indicates a correlation between the AMS and the deformational effects in the rocks. Several AMS components were revealed during experimental work on 211 samples that had been heated to 640°C during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields. Seventeen sites with slight or no deformation have a magnetic fabric composed of two major components. The stable component, attributed to a primary shape anisotropy, has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike (≈N 60°E), respectively. This configuration is consistent with an origin due to a post-emplacement stress field, whereby horizontal extension acted on a vertical sheet of partially crystallized magma. The orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement. The unstable component, removed by fields up to 250 mT, is attributed to induced (domain) anisotropy produced by mild tectonic stress during the Grenville Orogeny. The approximate orientation of its principal components, as found by the method of substitutional ellipsoids, suggests an east-west-directed maximum stress. Four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed, but which may be largely composed of domain and stress-induced anisotropies developed during the Grenville Orogeny.