Change in the magnetic properties of bituminous coal intruded by an igneous dike, Dutch Creek Mine, Pitkin County, Colorado

Magnetization measurements have been made on natural coke–coal samples collected at various distances from a felsic porphyry dike in a coal seam in Dutch Creek Mine, Colorado to help characterize the nature and distribution of the iron-bearing phases. The magnetization passes through a maximum at the coke-to-coal transition about 31 cm from the dike contact. The magnetic measurements support the geochemical data indicating that magmatic fluids along with a high-temperature gas pulse moved into the coal bed. Interaction of the magmatic fluids with the coal diminished the reducing power of the thermal gas pulse from the dike to a point about 24 cm into the coal. The hot reducing gas penetrated further and produced a high temperature (400–525°C) zone (at about 31 cm) just ahead of the magmatic fluids. Metallic iron found in this zone is the principal cause of the observed high magnetization. Beyond this zone, the temperature was too low to alter the coal significantly.     

南海西北次海盆的磁条带重追踪及洋中脊分段性

由于缺少有效钻孔资料,对于南海扩张的时间一直存在较大的疑问.在南海三大海盆中,西北次海盆面积最小、磁条带特征不明显,因此对其扩张年代的争议最大.最新采集的高密度(小于10 km测线间距)船测地磁资料清晰地显示了西北次海盆磁条带的存在.在OBS和多道地震资料的约束下,利用船测地磁资料,本文对西北次海盆的地壳年龄进行了重追踪.根据定量的比较,西北次海盆的主体扩张始于35.8 Ma(C16n,2n),在34.7 Ma(C15)时其西南部开始扩张,扩张最终同时终止于33.2 Ma(C13n),整体的全扩张速率在40~50 mm/a之间.这表明南海的扩张可能首先起源于西北次海盆,在其结束扩张后,东部次海盆才开始打开(约30 Ma).得益于数据精度和密度的提高,利用化极后的磁力异常以及反演的磁化强度可以对西北次海盆进行二级中脊段的划分.我们共划分出六个中脊段和一个明确的转换断层.中脊的分段性与OBS反演的地壳厚度的变化相一致.转换断层东侧,中脊主体分为四个中脊段,每个中脊段长度均在30 km左右.转换断层西侧,存在一个长约50 km的中脊段和一个不确切的中脊段.中脊段上磁化强度的变化幅值和中脊段长度在整体上成正比.每个中脊段中央的磁化强度弱于中脊段两端的磁化强度,这与扩张速率相近的大西洋中脊的磁化强度特征一致.     

广义付里叶变换及其在磁共振成像中的应用

许多共振成像（ＭＲＩ）的应用,要求人体组织磁化强度的空间分布Ｆｏｕｒｉｅｒ变换的幅度和相位的精确分离,及利用正交双通道采集时间和空间高分辨图象序列。在传统的基于Ｆｏｕｒｉｅｒ变换的成象方法中,图象序列从一帧空间编码独立地重建得到,因此给定空间分辨率的情况下,每帧空间编码的数量限制了图象序列的时间分辨力;又常通过牺牲空间分辨率来提高图象序列的空间分辨录。由于传统Ｆｏｕｒｉｅｒ变换的核函数是线性相位,若变换ＭＲＩ技术必须很好地满足主磁场均匀性和梯度场线性的条件,因此传统Ｆｏｕｒｉｅｒ变换成象方法对临床应用中常出现ＭＲ信号相位失真极为敏感。本文提出：利用主磁场中组织的磁化强度不变,能很好消除图象的相位失真。     

唐山滦县震区视磁化强度分布与地震关系的研究

依据频率域磁化强度反演方法和程序，对唐山滦县震区航磁资料进行了数据处理，求取了该区视磁化强度的水平分布。反演结果反映了震区地壳内不同规模、不同物性的地壳岩体在平面上的投影。本文结合唐山滦县震区地震的时空分布及破裂方向，对该区地震的孕育及发生过程进行了探讨。     

Low temperature magnetism and Mössbauer spectroscopy study from natural goethite

In this work a magnetic characterization was made of natural goethite from Burkina Faso, Africa, by using low temperature magnetization curves, hysteresis loops, Mössbauer spectroscopy at room temperature and 4.2 K, and AC susceptibility from 10 to 400 K. The samples are from two distinct geological sites that underwent different weathering processes. All measurements point to the occurrence of typical high coercivity goethite. Through Mössbauer spectroscopy sample BL44, from Gangaol, northeast Burkina Faso showed relaxation effects due to a wide distribution of grain size, including superparamagnetism threshold. AC susceptibility also supports this interpretation. The sample BL50 from Bonga in Burkina Faso is associated with lateritic Ni and in addition to goethite this sample also contained magnetite, as determined by Verwey transition in low temperature measurements as well as a small content of hematite identified by Mössbauer spectroscopy.     

磁化岩石层球面各向同性统计模型

磁化岩石层产生的磁场是利用磁场观测研究地球发电机过程的最主要障碍之一。基于对球面各向同性随机矢量场及其空间两点关联张量的认识,建立了球面各向同性磁化岩石层的统计模型。结果表明,如果岩石层的剩余磁化强度和磁化率均为球面各向同性,那么在地表观测到的岩石层磁场由球面各向同性和准各向同性两个部分组成。因此,即使统计性质最简单的磁化岩石层,其产生的磁场的统计性质也要复杂得多。     

Electric currents along earthquake faults and the magnetization of pseudotachylite veins

Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km³ of stressed igneous rocks adjacent to the fault plane can deliver 10³–10⁵ A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction.     

微磁模拟及在岩石磁学中的应用

岩石或沉积物的磁学性质受到所含矿物的种类、粒径、形状、相互作用以及环境等多种因素的作用,但是传统的岩石磁学实验很难定量解耦这些参数的影响.本文从微磁模拟与岩石磁学相结合的角度探讨了定量分析矿物磁学特征的研究进展.首先对微磁模拟的原理和发展历程进行了简要介绍.随后就矿物磁信息记录的物性影响和化学改造两个基本问题,总结了微磁模拟在岩石磁学领域的应用特色.最后对微磁模拟在岩石磁学中的研究前景提出了展望.以上讨论指出微磁模拟在地学中具有重要应用价值,加深了我们对地质过程中矿物磁学性质的理解.     

The Benedikt hydrothermal system (north-eastern Slovenia)

Records from magnetic signals in Buenos Aires loess–paleosol sequences have been published, but their relationship with environmental changes has been difficult to establish. Studies on the superparamagnetic (SP) population in present soils can help to understand these processes. Samples from present soils (Argiudolls) and a paleosol from the Buenos Aires Province (Argentina) were analyzed using low and room temperature magnetic measurements. They show that it is possible to support the hypothesis of a lognormal distribution of superparamagnetic particles, the median diameter near 15 nm. The presence of detritic pseudosingledomain (PSD) titanomagnetite, with low titanium content ranging between TM 28 and TM40, has been established. The linear correlation of SP content with ferrimagnetic susceptibility and with magnetization suggests that ferrimagnetic minerals drive the SP generation. Finally, it can be concluded that SP magnetic grains, in the Pampean plain, are generated by an inorganic process in adequate environmental pH and Eh of the soils.     

磁化强度矢量反演方程及二维模型正反演研究

导了磁化强度矢量层析成像方程,并与磁化强度标量层析成像方程进行了对比. 使该矢量层析成像方程既适用于三维的也适用于二维,既适用于使用磁场垂直分量资料,也适用于使用磁场总强度资料. 本文采用改进的高斯-赛德尔迭代求解磁化强度矢量层析成像方程,在求解方程中引进了与深度有关的权系数. 并对二维模型开展了正反演研究. 当模型层数为二层,且每层51个柱体时,采用零初始模型就能获得较好的磁化强度垂直分量和水平分量反演结果,除了异常体边部外,磁化方向比较可靠. 当模型层数为五层,且每层51个柱体时,采用零初始模型不能得到较好结果,改用接近背景值的均匀初始模型,反演的磁化强度垂直分量和水平分量大致接近真实,但不能刻划某些细节.