南京下蜀土的岩石磁学特征   总被引：5，自引：0，他引：5  

许峰宇  李立文 《岩石学报》1996,12(3):491-497

对南京附近的下蜀土进行了岩石磁学测定，通过磁化率各向异性测量研究了它的沉积磁性组构特征，下蜀土的各异向性很不明显，各向异性废Ｐ小于水成岩的Ｐ值（＞１．０２），且与困面理度Ｆ高度相关，与磁线理度Ｌ相关不明显，这种特征与中国中部风成黄土极相似。对新生圩剖面进行的磁化率测量发现用化率曲线上有７个旋回的波峰、波谷变化，这与剖面中的古土壤－黄土系列相一致，说明下蜀土的剖面磁化率同样可以作为地层划分与对比，反映古气候冷暧变化的物理参数。对典型下蜀土样品进行的低温磁化率测量揭示出古土壤和黄土的成颗粒的构成不同，古土壤以超顺磁质为主，黄土以顺磁质为主。细小磁颗粒在古土壤中的积聚可能与古土壤的发育及古气候的暧湿程度有关。  相似文献   

闽西北地区隐爆作用与火山岩型铀矿化   总被引：1，自引：0，他引：1  

黄伟良 《铀矿地质》1997,13(5):285-289

隐爆角砾岩体对火山岩型铀矿化的控制作用已为实践所证明，并引起高度重视。本文阐述了闽西北地区隐爆角砾岩形成的时空条件、与围岩的关系、分带性及其鉴别要素。以实例说明隐爆角砾岩体对铀矿化起控制作用的３种主要形式，指出了寻找隐爆角砾岩体的方法。  相似文献   

我国磁法勘探的研究与进展   总被引：7，自引：2，他引：7       下载免费PDF全文

管志宁 《地球物理学报》1997,40(Z1):299-307

简要概述了我国磁法勘探50年来的研究与进展，主要包括：地面、航空与海洋磁测工作，磁力仪研制与生产，磁异常处理与转换技术，磁异常解释理论与方法，岩石磁性研究，磁法勘探在基础地质研究、固体矿产勘查、油气勘查和其他领域中的应用．  相似文献   

应用Winsurf软件绘制磁场分布等值线图     

赖加成 《福建地震》2004,(3)

观测场地磁场梯度测量结果最直观的表述方式就是利用ΔF值绘制出的场地地磁场分布等值线图。Winsurf软件是Golden公司开发的一个三维绘图软件包 ,可以绘制各种等值线图和三维立体图。目前最高版本为 8.0。本文较为详细地介绍了利用这个软件的应用方法、步骤。  相似文献   

磁学方法在环境污染研究中的应用   总被引：12，自引：0，他引：12  

闫海涛  胡守云  朱育新 《地球科学进展》2004,19(2):230-236

环境磁学方法问世20多年来，因其快速、灵敏、经济、无破坏性和信息量大的特点，在环境研究中得到广泛的应用。磁学方法可用于传统的污染分析技术（化学）之前的预研究，而后者一般耗费大量人力、物力和时间；它也可以作为环境污染评估的代用指标。近年来，随着世界环境污染问题的日益严重和倍受关注，磁学方法被广泛地应用于环境污染研究。欧洲环境磁学专家在重建污染历史、监测现代环境污染、追踪与分离污染源等方面，开展了大量的工作，并积累了一定的经验。介绍了磁学方法用于污染研究的显著特点、主要用途、野外工作方法以及相关仪器；展示了在大气、土壤、潮滩、河流、湖泊以及海洋等不同环境系统中，利用磁手段研究污染的成果和最新进展；对 于一些难点、热点问题，如磁性机理的研究、多源污染的分离、强烈多变的人类活动对获取有意义磁讯号的影响等，做了相应的分析和总结。  相似文献   

Magnetic domain structures and stray fields of individual elongated magnetite grains revealed by magnetic force microscopy (MFM)     

C. Frandsen  S.L.S. Stipp 《Physics of the Earth and Planetary Interiors》2004,141(2):121-129

In order to clarify the relationship between microscopic and macroscopic magnetic features of a rock, we applied magnetic force microscopy (MFM) as a local probe on a sample with an intense natural remanent magnetisation, a norite from Heskestad, Norway. We studied in detail seven magnetite (Fe₃O₄) exsolution lamellae, five of them were about 30 μm long and a few micrometers wide, two were significantly shorter; all were located in their natural host, a grain of clinopyroxene. By combining MFM images of surface magnetisation with information about shape observed with optical microscopy (OM), the internal domain structure was determined for individual grains. In general, the lamellae were pseudo-single-domain grains with open-flux domain magnetisations parallel to their long axes. The domain sizes were, in cross-section, on the order of a micrometer for the longer lamellae and about 300 nm for the short lamellae. By increasing the separation between the MFM probe and the exposed end of the lamellae, information could be obtained about the decrease in stray fields for the individual grains. Close to the lamellae, stray fields were significant even for grains with multiple domains. The largest fields were found above the largest domains. A separation of approximately one domain width was found to be a characteristic distance, where stray fields from adjacent domains begin to cancel one another.  相似文献   

Magnetic fabrics and rock magnetism of Proterozoic dike swarm from the southern São Francisco Craton, Minas Gerais State, Brazil     

Maria Irene Bartolomeu Raposo  Alexandre O. Chaves  Paulo Lojkasek-Lima  Manoel Souza D'Agrella-Filho  Wilson Teixeira   《Tectonophysics》2004,378(1-2):43-63

Magnetic fabric and rock magnetism studies were performed on 32 mafic dikes of a Proterozoic dike swarm from the southern São Francisco Craton (SFC; Minas Gerais State, SE Brazil). Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of remanent magnetization (ARM). The latter was performed imposing both anhysteretic (total (AAR) and partial pAAR)) and isothermal remanence magnetizations (AIRM). Partial anhysteretic remanence anisotropy was performed based on remanent coercivity spectra from a pilot specimen of each site. In most sites, AMS is dominantly carried by ferromagnetic minerals, however, in some sites, the paramagnetic contribution exceeds 70% of bulk susceptibility. Rock magnetism and thin section analysis allow classifying the dikes as non-hydrothermalized and hydrothermalized. Magnetic measurement shows that the mean magnetic susceptibility is usually lower than 5×10⁻³ (SI). Ti-poor titanomagnetites up to pure magnetite pseudo-single-domain (PSD) grain sizes carry the majority of magnetic fabrics for non-hydrothermalized dikes whereas coarse to fine grained Ti-poor titanomagnetites carry the majority of magnetic fabrics for hydrothermalized dikes.Three primary AMS fabrics are recognized which are coaxial with ARM fabric, except for two dikes, from both non-hydrothermalized and hydrothermalized dikes. Normal AMS fabric surprisingly is not dominant (31%). The parallelism between AMS, pAAR_0–30, pAAR_30–60 and pAAR_60–90 fabrics in the hydrothermalized dikes indicates that magnetic grains formed due to late-stage crystallization or to remobilization of iron oxides due to hydrothermal alteration after dike emplacement have acquired a mimetic fabric coaxial with the primary fabric given by coarse-grained early crystallized Ti-poor titanomagnetites. This fabric is interpreted as magma flow in which the analysis of K_max inclination permitted the inference that the dikes were fed by horizontal or subhorizontal fluxes (K_max<30°). Intermediate AMS fabric is the most important (41%) in the investigated swarm. It is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike. ARM determinations for these sites also remained intermediate except for two dikes. In one of them, AIRM fabric resulted in normal AMS fabric while for the other AAR fabric resulted in inverse AMS fabric. A combination of AMS and ARM fabrics suggest that magmatic fabric for both dikes were overprinted by some late local event, probably related to Brasiliano orogenic processes after dike emplacement. InverseInverse AMS fabric is a minority (four dikes). ARM determinations also remained inverse suggesting a primary origin for inverse AMS fabric.  相似文献   

Analysis of geomagnetic field along seismic profile P4 of the International Project POLONAISE'97     

T. Grabowska  G. Bojdys 《Tectonophysics》2004,383(1-2):15-28

This paper presents relative secular variations of the total intensity of the geomagnetic field against a background of results of magnetic anomaly interpretation along seismic profile P4. Profile P4 crosses a Variscan folding zone in the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ), and the Polish part of the East European Craton (EEC). Secular geomagnetic field variations measured in 1966–2000 along a line adjacent to seismic profile P4 were analysed. The study of secular variations, reduced to the base recordings at the Belsk Magnetic Observatory, showed that the growth of geomagnetic field at the East European Craton was slower than in the Trans-European Suture Zone and the Paleozoic Platform.A 2D crustal magnetic model was interpreted as a result of magnetic modelling, in which seismic, geological and geothermal data were also used. The modelling showed that there were significant differences in the magnetic model for geotectonic units, which had been earlier determined based on deep seismic survey data. It should be noted that a fundamental change of trend of the relative secular variations was observed at the slope of the Precambrian Platform. After analysing the geomagnetic field observed along profile P4, the hypothesis that the contact between Phanerozoic and Precambrian Europe lies in Poland's territory can be proven.  相似文献   

Curie-point depth from spectral analysis of magnetic data in central-southern Europe   总被引：3，自引：0，他引：3  

P. Chiozzi  Y. Okubo  M. Verdoya 《Physics of the Earth and Planetary Interiors》2005,152(4):267-276

The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29-33 km deep in the stable areas (central Europe Variscan units, Corsica-Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea-Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C).  相似文献   

The Magnetospheric cusps: A Summary     

T. A. Fritz  Q. G. Zong 《Surveys in Geophysics》2005,26(1-3):409-414

The polar cusps of the magnetosphere are key regions for the transfer of mass, momentum, and energy from the solar wind into the magnetosphere. Understaning these key regions and the dynamical interactions that occur there are fundamentally important to determining the physical nature of the magnetosphere. In this paper we try to summarize many of the conclusions reached in the papers of this special issue emphasizing the present concepts and definition of the cusp, what variations could be temporal structures and what could be spatial structures. We address the need for further measurements and the role of present and planned projects to address these needs.  相似文献