辉绿岩裂缝对其磁组构的影响

磁组构是由岩石中磁性矿物定向分布而产生的组构特征，因此磁组构分析是研究岩石组构常用的技术手段，它具有 见效快、灵敏度高、无损样品等特点，近年来得到广泛应用。然而在磁组构研究工作中钻取定向样品或定向手标本时，常 常会遇到天然样品含有裂缝且裂缝中充填大量近地表沉积物和自生矿物。本文针对辉绿岩裂缝充填物对其磁组构结果的影 响程度做了详细研究，选用160个含裂缝的辉绿岩岩芯定向样品，通过对比去除裂缝充填物前后的磁组构变化，发现实验 前后所有样品磁化率大小变化率平均值<1%，磁组构方向变化平均值<1°，因此认为辉绿岩裂缝物质对其磁组构影响甚微。 矿物学和岩石磁学分析表明裂隙充填物主要为石英、长石，以及少量赤铁矿、黄铁矿和绿泥石等表生矿物。而辉绿岩的携 磁矿物主要是亚铁磁性的磁铁矿，其磁化率强度约为同等质量裂缝填充物的30倍，致使辉绿岩中的裂隙充填物对磁组构的 影响很小。

Effect of Diabase Crevices on AMS Fabrics

As a rapid and sensitive petrofabric tool, the anisotropy of magnetic susceptibility (AMS) has been extensively used in studying rock fabrics. Sometimes it is difficult to drill an intact oriented core sample without any crevice, in which various filling minerals can be found. To analyze the crevices’ effect on diabase magnetic fabrics, 160 diabase samples with crevices are selected to study the AMS data then remove the filling minerals in the crevices in order to compare magnetic fabric characteristics of the diabase before and after the treatment. The data analysis shows that the average difference in the AMS intensity of all the specimens is less than 1% and the difference in the average direction also falls in <1°. From the results, we conclude that crevices of diabase dykes hardly have much influence on the AMS features. Mineralogy and rock magnetic studies indicate that the main mineral constituents in the diabase crevices are quartz, feldspar, hematite, pyrite, and chlorite. The AMS intensity of these filling minerals is about one thirtieth of diabase that is dominanted by ferromagnetic mineral of magnetite, which makes crevices to have no much effect on the AMS results.