Effect Of Diabase Crevices On Its AMS Fabrics

In the study of magnetic fabrics, it is necessary to drill orientated samples. And Orientated drill samples or hand specimen easily contain crevices which are filling of the near-surface sediments and authigenic minerals. Whether the presence of crevices with fillings will affect the characteristics of magnetic fabrics?For the scientific problem whether the crevices will affect diabase magnetic fabrics, we selected 160 oriented drill cores of diabase with crevices from more than 2000 cores drilled from the coastal areas of Zhejiang and Fujian, to perform systematic analysis of mineralogy and rock magnetism.Polarizing microscope, SEM, XRD, LRS, IR, and TM analysis were performed to study filling minerals, which shows that the main mineral constituents in the diabase crevices are quartz and feldspar, with minor hematite, pyrite, goethite and clinochlorite minerals. Under room temperature condition, their magnetic susceptibility intensity is less than 1/30th that of the same quality diabase. The filling materials in the sample fracture is no more than 5% of the total quality. Susceptibility of filling materials is accounted for only one percent of the strength of diabase susceptibility, indicating little contribution to the sample magnetic susceptibility.By comparing the magnetic fabrics of original specimen with the magnetic fabrics removing crevices and evaluate the influence degree. It shows that, most of the samples before and after crevice fillings removed, the anisotropy of magnetic susceptibility variations is small, the overall average variation of the magnetic susceptibility value rates no more than 1%, the average magnetic fabric direction change is less than 1°, within the scope of random error. Only the diabase with serious weathering and very low magnetic susceptibility value will have obvious influence; Therefore, crevices existence of diabase almost no affect magnetic fabrics, suggesting that in the operation of the actual magnetic fabric study, the presence of crevices could be ignored.NRM directions are basically identical to those diabase specimen from the same site to before and after remove crevice filling materials as well as free of crevices specimen, suggesting that natural remanent magnetization is possibly influenced by viscous remanent magnetism. Diabase samples whether or not containing crevices, the lower temperature remanent magnetism components are scattered with a large confidential circle; The high temperature remanent magnetism is quite stable and concentrated, both for the samples with and removed crevice fillings as well as the samples without crevices. All the characteristic remanent magnetization directions of high temperature are identical within the confidence level.Therefore, diabase samples containing crevices could still be used in the study of primary characteristic remanent magnetization.