某些油气田地表土壤的磁性与烃运移相互关系研究

根据鄂尔多斯盆地靖边气田上方的ＭＩ０２线、江苏储家楼油田与江汉盆地花园油田地表十字剖面土壤磁性的测量结果，研究地表是否存在与深部油气藏中烃类垂向运移相关磁性蚀变带的可能性及其分布形式．结果表明，ＭＩ０２线样品显示了明显的高磁性异常特征，并与酸解烃之间呈很强的正相关．磁滞回线形态与参量显示出明显的亚铁磁性特征．电子探针分析结果表明，样品中主要磁性矿物（磁铁矿）中高温杂质元素含量很低．江汉盆地花园油田十字剖面磁滞回线参量（饱和磁化强度Ｊｓ与饱和等温剩磁Ｊｒ）的高异常位于油田周边，油田顶部土壤呈典型顺磁性特征．储家楼油田地表土壤的高磁性异常主要位于油田上方，它们均与盖层中的断裂构造对应，储家楼油田的高磁性样品中发现的典型球粒状磁铁矿为次生低温磁铁矿，它与烃运移之间存在成因关系．     

Internal structure of Ustica volcanic complex (Italy) based on a 3D inversion of magnetic data

A ground magnetic study of Ustica Island was performed to provide new insights into subsurface tectonic and volcanic structures. The total-intensity anomaly field, obtained after a data-reduction procedure, shows the presence of a W–E-striking magnetic anomaly in the middle of the island and another two intense anomalies, which seem to continue offshore, in the southwestern and the northeastern sides, respectively. The detected anomalies were analyzed by a quadratic programming (QP) algorithm to obtain a 3D subsurface magnetization distribution. The volcano magnetization model reveals the presence of intensely magnetized volumes, interpreted as the feeding systems of the main eruptive centers of the island, which roughly follow the trend of the main regional structural lineaments. These findings highlight how regional tectonics has strongly affected the structural and magmatic evolution of the Ustica volcanic complex producing preferential ways for magma ascent.     

Geophysical signatures of uranium mineralization and its subsurface validation at Beldih,Purulia District,West Bengal,India: a case study

The Beldih open cast mine of the South Purulia Shear Zone in Eastern India is well known for apatite deposits associated with Nb–rare‐earth‐element–uranium mineralization within steeply dipping, altered ferruginous kaolinite and quartz–magnetite–apatite rocks with E–W strikes at the contact of altered mafic–ultramafic and granite/quartzite rocks. A detailed geophysical study using gravity, magnetic, and gradient resistivity profiling surveys has been carried out over ～1 km² area surrounding the Beldih mine to investigate further the dip, depth, lateral extension, and associated geophysical signatures of the uranium mineralization in the environs of South Purulia Shear Zone. The high‐to‐low transition zone on the northern part and high‐to‐low anomaly patches on the southeastern and southwestern parts of the Bouguer, reduced‐to‐pole magnetic, and trend‐surface‐separated residual gravity–magnetic anomaly maps indicate the possibility of highly altered zone(s) on the northern, southeastern, and southwestern parts of the Beldih mine. The gradient resistivity survey on either side of the mine has also revealed the correlation of low‐resistivity anomalies with low‐gravity and moderately high magnetic anomalies. In particular, the anomalies and modeled subsurface features along profile P6 perfectly match with subsurface geology and uranium mineralization at depth. Two‐dimensional and three‐dimensional residual gravity models along P6 depict the presence of highly altered vertical sheet of low‐density material up to a depth of ～200 m. The drilling results along the same profile confirm the continuation of uranium mineralization zone for the low‐density material. This not only validates the findings of the gravity model but also establishes the geophysical signatures for uranium mineralization as low‐gravity, moderate‐to‐high magnetic, and low‐resistivity values in this region. This study enhances the scope of further integrated geophysical investigations along the South Purulia Shear Zone to delineate suitable target areas for uranium exploration.     

Changes of lithospheric magnetic anomalies with altitude (According to the CHAMP satellite)

Maps of the magnitude of the full vector and the vertical component of an anomalous lithospheric magnetic field over the Voronezh anticline (VA) for the three high-altitude observation levels were compiled based on geomagnetic measurements from the CHAMP satellite. The isometric positive anomaly centered at about 50° N and 37° E stands out. Its amplitude decreases with increasing observation altitude without changing the form. Comparison of the parameters of the detected anomaly with data obtained for this site by other methods confirms that it really exists and that its spatial position is accurately determined, which indicates the reliability of the values of the selected field of lithospheric anomalies. The change in the parameters of the magnetic anomaly with respect to the observation level over the Earth’s surface is consistent with the concepts of geological structural features of the lithosphere in the region. The anomaly offset to the south on the satellite altitudes apparently indicates an uplift of crystalline basement rocks and a more southern position of VA deep roots relative to that accepted in the global magnetization model. The use of satellite data obtained at different altitudes opens up additional possibilities for the application of gradient methods in the interpretation of the magnetic fields of lithospheric anomalies.     

磁总场异常垂直梯度三维相关成像

本文提出了磁总场异常垂直梯度三维相关成像方法,用于成像地下等效磁源分布.它首先将地下待成像空间划分为三维规则网格,然后直接计算每个网格节点磁偶板子在观测面理论磁总场异常垂直梯度与实测磁总场异常垂直梯度的互相关,其相关系数值表征等效磁偶极子分布(即磁偶极子发生的概率).理论长方体组合模型数据和实际某矿区磁测资料试验结果表明本文方法计算得到的相关系数值能基本反映地下的磁源分布,且分辨率明显高于磁总场异常三维相关成像的分辨率,也高于基于熵滤波分离异常的磁总场异常三维相关成像的分辨率.     

Possible extensions of the Narmada-Son lineament towards Murray Ridge (Arabian Sea) and the eastern syntaxial bend of the Himalayas

Geophysical data contiguous with the Narmada-Son lineament suggests its possible extension westward into the Arabian Sea and eastward up to the Shillong Plateau. The airborne magnetic anomaly map of the north Arabian Sea delineates a linear trend of magnetic anomalies in line with the Narmada-Son lineament. This group of magnetic anomalies, spreading over 20°N to 22°N, starts near the west coast of India at 21°N, 69°30′E and extends to the Murray Ridge. The tectonic feature represented by this group of magnetic anomalies is buried by a thick layer of sediments. This westward extension of the lineament is also reflected in the average Bouguer gravity anomaly map of the Indian Ocean. Towards the east, the gravity and magnetic data delineate a subsurface linear tectonic feature which extends in line with this lineament to the eastern syntaxial bend. These various geophysical signatures further suggest the lineament to be a typical rift-like structure. The tectonic implications of the lineament, which extends from the western to the eastern margins of the Indian plate, is discussed.     

渤海南部莱州湾Lz908孔沉积物的岩石磁学性质

亚洲大陆边缘海和陆表海在区域的物质和能量交换以及区域气候与环境演化过程中扮演了关键角色.磁性地层学和环境磁学方法是建立年代框架和环境演变序列的有效手段,但是,由于该地区边缘海和陆表海沉积物中磁性矿物来源十分复杂,磁性地层学和环境磁学研究的重要基础是要精细地解译沉积物的岩石磁学性质.为此,本文利用渤海南部莱州湾Lz908孔与钻孔附近的现代沉积物样品进行了详细的岩石磁学对比研究.结果显示,渤海南部沉积物中的磁性矿物主要是较粗颗粒(较大的准单畴至多畴)磁铁矿,还有少量磁赤铁矿,部分沉积物还含有赤铁矿和针铁矿,其中磁铁矿是特征剩磁的主要载体;莱州湾现代河流-海洋沉积物和钻孔样品之间的磁性特征无显著差异,说明莱州湾沉积物堆积之后尚未经历明显的沉积后期改造.     

Magnetic studies of basalt fragments recovered by deep drilling in Iceland,and the “magnetic layer” concept

The magnetic susceptibility of 1300 samples of igneous rock drill cuttings obtained from eight deep drill holes in Iceland has been measured, in order to directly provide limits on the thickness of the layer which is the source of the magnetic anomalies over Iceland. The remanent magnetism of some of the material has also been studied, and the variation of magnetic susceptibility in 740 lava flows from eastern Iceland has been analysed as a function of depth of burial.All the results indicate no systematic change of susceptibility with depth up to 2.0 km. The Curie point of all deeply buried basalts in Iceland appears to be close to that of magnetite, so that the magnetic layer may be 5 km or more in thickness when susceptibility contrasts are considered; lateral contrasts in primary remanence may reach to 3 km depth. Derivation of a magnetic layer thickness in Iceland from analyses of magnetic anomalies, using methods which have been conventionally applied to marine magnetic anomalies could, on the other hand, yield much lower apparent thickness values (less than 1 km).We therefore argue that estimates of the magnetic layer thickness in oceanic regions should be based on considerations of magnetite Curie point isotherm behaviour, rather than on anomaly analysis.     

中国及邻近地区CHAMP卫星磁异常的分布特征

本文利用CHAMP卫星磁测资料建立的新一代高阶地磁场模型POMME-4.2S,计算中国及邻区400 km高度的卫星磁异常及其垂直梯度,给出7个磁场分量的分布图,比较了截断水平对磁异常分布的影响,初步分析了磁异常与岩石圈构造的关系.主要结果表明,在四川盆地、塔里木盆地和松辽盆地等主要磁异常区,ΔZ异常中心的南北两边出现ΔX的异常中心,东西两边出现ΔY的异常中心.在球谐模型为90阶时,磁异常分布的基本形态已经确定,更高的模型阶数对磁异常只有微小调整.在磁异常较强的地区,磁异常及其垂直梯度同步变化.卫星磁异常与地形变化、断裂带分布、莫霍面深度和岩石圈厚度没有直接的对应关系,而与居里等温面深度、磁性层厚度有明显的相关性.居里等温面深、磁性层较厚的地区显示正磁异常,居里等温面浅、磁性层较薄的地区显示负磁异常.     

Geophysical investigation of buried Pleistocene subglacial valleys in Northern Germany

Buried Pleistocene subglacial valleys are extensively used as groundwater reservoirs by waterworks in northern Germany, although little is known about the locations and size of these valleys and the internal structure of the sediment fill. This lack of knowledge about important groundwater reservoirs is a challenge for geophysics.This paper summarizes the geophysical investigation of two buried Pleistocene subglacial valleys in northern Germany—the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne—including seismic, gravity, and airborne electromagnetic (AEM) surveys. Seismic sections show the detailed structure of the paleovalleys. The reliability of interpretation is enhanced by vertical seismic profiles in wells. The maximum depths of the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne were found to be 360 and about 400 m, respectively. Gravity survey revealed Bouguer anomalies above the sediment fill of both buried valleys. The Ellerbeker Rinne produces a negative residual anomaly of −0.5 mGal, whereas the sediments of the Bremerhaven–Cuxhavener Rinne produce a positive anomaly. The latter one is superimposed by negative gravity anomalies due to near-surface structures. The Bremerhaven–Cuxhavener Rinne can be mapped by airborne electromagnetics at locations without saltwater intrusion, which would affect the measurements. The electrical conductivity of the clay layer at the top of the valley fill differs significantly from that of the surrounding sand. The combined use of these three geophysical methods, which measure different physical parameters, leads to a better understanding of the subsurface geology and the hydrogeology of the Pleistocene subglacial valleys.     

九寨沟MS7.0地震前地磁异常

分析距离九寨沟M_S7.0地震震中分别为65 km、254 km和238 km的松潘地磁台、成都地磁台和天水地磁台2017年连续观测结果,发现九寨沟地震前,松潘地磁台出现异常变化,主要表现为2017年5月开始,松潘地磁台长时间垂直分量累积变化量达40 nT。短时间内也存在地磁场突变,最高可达10 nT,而成都地磁台和天水地磁台地磁场无明显异常。通过对观测数据的详细检查发现松潘地磁台很多观测日的最后一个观测值与后一观测日的第一个观测值相差超过1 nT,因此认为九寨沟地震前观测数据的异常是由观测系统异常导致。对三个台站地磁场垂直分量日变化的统计分析发现垂直分量在不同时段相关性保持一致,说明地震前短时间内不存在地磁垂直分量的明显异常变化,三个台站地磁场日变化的差异是由地下介质性质不同导致。岩石圈磁场在震中西侧区域出现正负异常交替现象,这可能与九寨沟地震的孕育有关。     

MEASUREMENTS OF THE VERTICAL GEOMAGNETIC FIELD GRADIENT BENEATH THE SURFACE OF THE ARCTIC OCEAN*

Simultaneous measurements made on an ice island and about 1000 ft. below show that magnetic anomalies can be detected in the presence of large time variations of the magnetic field. Attenuation and phase lag of time variations at depth are measurable but do not limit the utilization of the vertical gradient of geomagnetic total intensity for defining crustal anomalies.     

给定观测精度下的点(线)源模型重力与磁力垂向识别能力研究

重、磁勘探具有效率高、成本低、工作范围广等优点,已在地球物理勘探中得到了广泛应用.前人大多在不考虑重、磁勘探观测精度的条件下进行了垂向识别能力的研究,但在考虑重、磁观测精度条件下,重力（重力异常、重力张量）与磁力（磁力异常、磁力三分量、磁力张量）对孤立异常的垂向识别能力如何则需要进行深入的理论研究.本文从重、磁场正演理论出发,以球体（点源模型）和无限延伸水平圆柱体（线源模型）为例,考虑给定观测精度条件下,以重力和磁力幅值大小与观测精度的关系来研究垂向识别能力,从而消除了背景场的影响,提高了研究结果的可靠度.通过研究表明,对于孤立异常,重力张量在浅部一定深度内比重力异常的垂向识别能力强,该深度与重力异常和重力张量观测精度的比值成正比;垂直磁化磁力张量在浅部一定深度内比化极磁力异常的垂向识别能力强,该深度与磁力异常与磁力张量观测精度的比值成正比;磁力在浅部一定深度内比重力的垂向识别能力强,该深度与地质体的磁化强度和剩余密度比值、重力观测精度和磁力观测精度比值成正比.通过重力和磁力垂向识别能力的研究将为重、磁勘探的实际应用起到指导作用.     

2022年青海门源6.9级地震前岩石圈磁场异常变化分析

基于青海及甘肃部分地区2020—2021年2期流动地磁测点的观测资料,获得该地区的岩石圈磁场异常变化,通过研究岩石圈磁场各个分量的变化特征,系统分析2022年1月8日青海门源6.9级地震前岩石圈磁场的异常变化特征。结果表明：(1)门源地震前,震中区域岩石圈磁场各个分量具有较为明显的异常显示。具体表现为：震中区域附近岩石圈磁场变化的水平矢量具有方向转向及幅值弱化的异常变化现象;垂直矢量方向出现明显的南向、北向对冲的异常现象;磁偏角在震中附近具有“0”变线和高梯级带分布;总强度和垂直分量在震中附近具有“0”变线分布,并发生弯曲。(2)依据压磁效应分析,冷龙岭断裂北部岩石圈磁场增大,应力变化主要以释放为主,应力变化应处于较低水平;冷龙岭断裂南部岩石圈磁场强度减小,应力变化主要以积累为主,应力变化应处于较高水平。门源地震前,冷龙岭断裂构造应力调整引起的压磁效应可能是造成震中区域岩石圈磁场异常变化的主要原因。     

Virtual Pole from Magnetic Anomaly (VPMA): A procedure to estimate the age of a rock from its magnetic anomaly only

Virtual Pole from Magnetic Anomaly (VPMA) is a new multi-disciplinary methodology that estimates the age of a source rock from its magnetic anomaly, taken directly from available aeromagnetic data. The idea is to use those anomalies in which a strong remanent magnetic component is likely to occur. Once the total magnetization of the anomaly is computed through any of the currently available methods, the line that connects all virtual paleogeographic poles is related with the position, on a paleogeographic projection, of the appropriate age fragment of the APWP curve. We applied this procedure to five (5) well-known magnetic anomalies of the South American plate in SE Brazil, all of them associated to alkaline complexes of Mesozoic age. The apparent ages obtained from VPMA on three of the anomalies where the radiometric age of the source rock is known – Tapira, Araxá and Juquiá – were inside the error interval of the published ages. The VPMA apparent ages of the other two, where the age of the source rock is not known (Registro and Pariqueraçu magnetic anomalies) were geologically coherent. We expect that the application of the VPMA methodology as a reconnaissance geochronological tool may contribute to geological knowledge over continental areas, especially when the source rocks of the magnetic anomalies are unknown or buried below superficial sediments.     

基于二阶导数的磁源边界与顶部深度快速反演

为实现磁异常反演,首先提出了磁异常非参数快速反演的概念,即无需提供先验信息.在Nabighian提出的磁场通用梯度公式的基础上,推导实现了基于磁异常垂向二阶导数的非参数快速反演(V2D_depth).它不仅可以获取场源的边界信息,同时可以反演场源的埋深.通过与Tilt_depth方法对比,本文方法计算的场源边界更清晰,反演的深度也更接近真实深度,同时较大程度上克服了Tilt_depth方法受叠加异常的影响.理论模型验证了方法的有效性,并通过准噶尔盆地某区块磁异常数据的处理,提取了受强大的区域背景场掩盖的石炭系火成岩产生的弱异常,突出了构造分区、断裂分布等信息,获取了火成岩的位置及埋深参数,为该区的火成岩油气藏勘探提供了有效的处理途径.     

A study of the vertical magnetic anomaly caused by magnetite deposits in Sua area of Palamau district,Bihar (India)

Summary A magnetic survey carried out in Sua area of the Palamau district, Bihar (India) has shown very interesting anomalies. The survey has been conducted specially to obtain the extension of the magnetite deposits which are being quarried at Sua. The interpretation of magnetic anomalies have clearly brought out the following facts: a) the magnetite is extending both sides of the quarry to a considerable distance, b) the nature of the anomaly indicates that the magnetite occurs in the form of veins. It has also been possible to find out the thickness of the veins and the depth at which they occur.     

磁赤道处化极方法

化向地磁极(化极)是最基本的磁测资料处理方法之一,化极能消除或减少斜磁化影响,提高对磁测资料的认识程度和解释水平,对研究地壳产生的磁异常具有重要意义.但低纬度地区特别是磁赤道处,化极处理很不稳定甚至奇异,一直是位场研究的难点.针对地磁纬度较低特别是磁赤道地区磁异常化极的困难,利用从磁北极处垂直磁化向低纬度地区水平磁化方向转换稳定的特点,提出"狭义化赤"概念,并将其与低纬度磁异常"倒相"解释方法结合,提出专门用于磁赤道处化极的方法.该方法扩展了现有的化极理论,实现了磁赤道处的稳定化极.区别于目前任何方法,专门用于(近)水平磁化条件下的化极计算,具有原理简单,实现方便,收敛速度快等特点.对理论模型和实际资料计算表明这种针对磁赤道地区磁异常的化极处理方法是稳定、可靠的.     

New magnetic data of the southern East China Sea and some geological interpretations

In September and October of 2011, a marine magnetic survey was conducted in the southern East China Sea between 120° and 126°E, 26° and 28°N with the research vessel Kexue-3. New magnetic maps with 5 × 5 km grid spacing were generated after meticulous data processing. Based on an analysis of magnetic anomaly features and further calculation results, including the total horizontal derivatives (THD), second order vertical derivatives (SVD) and analytic signal amplitude (ASA), several new tectonic insights on magnetic sources, basement structures and fault properties were obtained. The NE-SW or NNE-SSW oriented magnetic anomaly highs have different sources: (1) The high amplitude, short wavelength magnetic anomalies of the Zhemin Uplift are caused by shallow buried igneous rocks intruded along NE-NEE oriented faults. (2) The high amplitude, moderate wavelength magnetic anomalies of the Diaoyudao Uplift are caused by the metamorphic basement intruded by magmatic rocks. (3) The magnetic sources of the Yandang Uplift and Taibei Uplift in the shelf basin are shallow buried metamorphic basements and deep buried volcanic bodies, respectively. Several NW-SE or NWW-SEE oriented dextral strike-slip fault belts were identified as important tectonic boundaries. Each is composed of several en echelon and partly overlapping secondary faults. Initially formed in the Cretaceous, these fault belts have evolved through multiple periods, propagated seaward with the migration of the basement rifting and accommodated local stress fields in the Cenozoic.     

哈萨克斯坦MS6．1地震前新疆形变异常

研究2013年1月29日哈萨克斯坦6．1级地震前新疆境内形变资料异常。结果表明：震前乌什水管仪两分量、伸缩仪北南分量、体应变和克孜尔水准、基线存在趋势性转折异常;乌什水管倾斜仪北南分量、体应变、分量式应变与柯坪垂直摆倾斜仪北南分量、拜城地倾斜两分量和库车东风煤矿地倾斜北南分量存在不同程度的中短期异常,趋势异常和中短期异常显著。