共查询到20条相似文献，搜索用时 15 毫秒
1.
介绍了高精度航磁调查在西天山东段的应用效果.在高精度航磁图上,展现出多个不同磁场背景及磁异常特征区,它们是不同构造、岩浆活动、地层及岩性分布的综合反映.该区不仅区域磁场特征明显,而且局部异常信息也极为丰富.在最新的高精度航磁图上,已知铁矿异常特征明显,为矿区外围勘探和同类地区寻找新的铁矿提供了依据.利用高精度航磁资料,新发现了五十余处铁矿异常,在2007年进行了地面查证的5处异常中,有4处见矿.这些新的铁矿异常的成功发现不仅带来了巨大的经济效益,也为今后利用高精度航磁测量在类似地区进行找矿积累了经验. 相似文献
2.
The intersection of the Juan de Fuca ridge and Blanco fracture zone is characterized by unusually high amplitude magnetic anomalies (over 1500 nT) which appear to be associated with a body roughly 50 km in length and 20 km in width aligned along the fracture zone. Simple three-dimensional magnetic models indicate that this anomaly is probably caused by a highly magnetized block of material situated in the western end of the Blanco fracture zone near its intersection with the Juan de Fuca ridge. Rock magnetization studies of tholeiitic basalts dredged from this area confirm the presence of highly magnetized basalts near the ridge crest/transform fault intersection. These tholeiitic basalts are enriched in iron and titanium relative to “normal” oceanic tholeiites, apparently the result of extensive shallow fractionation involving olivine, plagioclase, and clinopyroxene. Magnetic model studies indicate that an average thickness of no more than 500 m of these iron-rich basalts is necessary to produce the observed anomaly pattern. Comparison of these basalts with samples previously dredged from the Juan de Fuca ridge crest suggests that these Fe-rich, highly magnetized basalts probably “leaked” out of the southernmost portion of the Juan de Fuca ridge. 相似文献
3.
We propose that magnetic anomalies south of Australia and along the conjugate margin of Antarctica that were originally identified as anomalies 19 to 22 may be anomalies 20 to 34. The original anomaly identification has two troublesome aspects: (1) it does not account for an “extra” anomaly between anomalies 20 and 21, and (2) it provides no explanation for the rough topography comprising the Diamantina Zone. With our revised identification there is no “extra” anomaly and the Diamantina Zone is attributed to a period of very slow spreading (～4.5mm/yr half rate) between 90 and 43 m.y. The ages bounding the interval of slow spreading (90 and 43 m.y.) correspond to times of global plate reorganizations. Our revised identification opens up the possibility that part of the magnetic quiet zone south of Australia formed during the Cretaceous long normal polarity interval. Breakup of Australia and Antarctica probably occurred sometime between 110 and 90 m.y. B.P. The “breakup unconformity” identified by Falvey in the Otway Basin may correspond to a eustastic sea level change. 相似文献
4.
M.A. Mayhew 《Earth and Planetary Science Letters》1984,71(2):290-296
Long-wavelength anomalies in the total magnetic field measured by Magsat over the United States and adjacent areas are inverted to an equivalent surface layer magnetization distribution. The model is based on an equal-area dipole grid at the Earth's surface. Model resolution, defined as the closest dipole spacing giving a solution having physical significance, is about 220 km for Magsat data in the elevation range 300–550 km. The magnetization contours correlate well with large-scale tectonic provinces. A higher-resolution (200 km) model based on relatively noise-free synthetic “pseudodata” is also presented. An excellent inverse correlation between apparent magnetization and heat flow in the western U.S. is demonstrated. A new regional heat flow map derived indirectly from Magsat data shows nearly all the important thermal anomalies evidenced in previous published maps. Notably, the map predicts high heat flow in Nebraska and the Dakotas, suggesting the presence of a “blind” geothermal area of regional extent. 相似文献
5.
用欧亚大陆地面电离层垂测站资料考察1989年3月12～16日磁暴期间的电离层暴形态及其发展变化. 特强磁暴引发的电离层暴是全球性的,但自磁层沉降的高能粒子对热层低部的加热程度及区域分布不同,因而各经度链区域内电离层暴的特征也有所差异. 本文研究表明,与理论推断对照,欧洲地区内F2层最大电子密度NmaxF2(或f0F2)并不出现正暴现象,而负暴自高纬向低纬的发展则与典型的热层环流结果相符. 此外,此磁暴过程期间在中低纬区存在明显的波动过程. 在亚洲高纬地区,磁暴初期13日有约10 h的正暴,而负暴过程则与欧洲地区类似,但不太清晰;且无波动现象. 磁暴期间,同一经度链的中低纬地区,夜间常发生多站同时的h′F突增. 本文再次证实这是一般磁暴期间常出现的普遍现象. 相似文献
6.
A. G. Gubanov O. A. Bogatikov B. S. Karamurzov L. E. Tsukanova A. B. Leksin V. M. Gazeev A. V. Mokhov T. A. Gornostaeva A. V. Zharikov V. M. Shmonov A. Ya. Dokuchaev S. A. Gorbacheva A. V. Shevchenko 《Journal of Volcanology and Seismology》2011,5(4):223-240
In addition to traditional degassing of the melt in the subsurface magma chambers of the “dormant” El’brus volcano, alsodegassing through pores and microcracks that occur in the top of magma chambers has also been detected. It is proven by studies of compactness, porosity, and permeability of the rocks. The speeds at which gases (H, He, H2S, CO2, F, and Cl) pass through gneiss and volcanic rocks were estimated. Magma chambers on the ground surface are expressed in stable thermal anomalies revealed by night-time thermal sounding from an NOAA satellite. The presence of magma chambers at depths of 2–12 km was proven by magnetotelluric sounding [Sobisevich et al., 2003] and gravity studies. In addition to occasional “columns” of bright-white fluorescence above the thermal anomalies, aerosol “clouds” and hydrogen flows were detected by lidar and hydrogen surveying [Alekseev et al., 2007, 2009]. Observation at the same sites detected steam outbursts occurring periodically, the snow-ice cover thaws and the smell of hydrogen sulfide is felt. Geochemical characteristics of degassing were studied by snow sampling from up to 1 m deep pits. They were taken within contours of the thermal anomalies, above active fault zones, in the sites of bright-white fluorescence “columns,” and on a new fumarole locality. It is shown that the degassing of melt was accompanied by the gas transporting many elements (Li, B, Si, P, S, Ca, Zn, Pb, Mo, Ba, W, Hg, Ag, U, Th, I, Au, and Pt) in a fine-grained state (a few microns or possibly nanometers) with an active participation of F and Cl. Native platinum, chalcopyrite, halite, sylvite, barite, gypsum, zircon, opal, chlorinated organics, etc. were for the first time discovered in the Mt. El’brus area using electron microscope studies of solid residue from dehydrated snow samples. “Hidden” ore mineralization genetically related to degassing of melts enriched in ore elements may be supposedly found in paleo- and present-day areas of volcanic activity. 相似文献
7.
根据波茨坦地磁场模型(POMME6.2),研究喜马拉雅东构造结周围地区地壳磁异常的空间分布、磁异常随高度的衰减特征.利用二维小波变换方法对地表磁异常进行分解,分析小波细节组合和逼近信号的异常特点.讨论磁异常与地质构造的联系.结果表明,研究区内地壳磁异常分布相当不均匀.喜马拉雅—东构造结—龙门山—大巴山地区分布着较强的负磁异常;四川盆地为正磁异常,其他地区磁异常较弱.东构造结对周围地区磁异常有重要影响,它及其周围地区的地壳磁异常都是在负磁或弱磁异常背景上,叠加着中短波长的正负磁异常.这些中小尺度磁异常由中、上层地壳磁性物质产生,走向与地质构造基本一致.沿金沙江、红河断裂带分布着清晰的弱磁异常带.龙门山断裂带、丽江—小金河断裂带和红河断裂带是磁异常强弱过渡带.青蒇高原中部东西向的磁异常,在东构造结弧顶地区呈弧形分布.青藏高原中部和滇中地块带状、团状磁异常具有相同的衰减规律. 相似文献
8.
MAURICE K. SEGUIN 《Geophysical Prospecting》1971,19(3):459-486
The deposits of the central sector of the Labrador Trough are magnetite-rich iron ores subjected to enrichment by the process of leaching. In spite of the fact that some ore types are porous and low in density, most of the ore zones have undergone a net increase in density brought about by enrichment. In the course of their formation, the magnetic characteristics of the rocks have changed and a great deal of the magnetite was altered to relatively non-magnetic iron oxides and hydrous iron oxides. Consequently, induced as well as remanent magnetization decreased, but the ratio of the latter with respect to the former increased substantially. All drift-covered areas underlain with iron-formation are potential ore producing areas. From measurements of the first two physical properties and determination of the thickness of overburden by means of a combined gravity-magnetic-seismic or resistivity survey, it is possible to detect and distinguish the iron formations and potential ore zones from the country rocks. In spite of the fact that the iron formations are a complex assemblage of rock types, each having different physical and chemical properties, a qualitative and semi-quantitative correlation between the results of the surveys and the geology as well as the structure of the area could be established. Consequently, in order to increase the chances of success, first a mathematical correlation of the amplitude of the gravity anomalies with the specific gravity, the iron content, the silica content, the porosity factors and the dimensions of the underlying orebodies, and secondly, a quantitative correlation of the ground magnetic intensity relative to the reference lithologie unit with the percentage of Fe3 O4 recovery and the volume magnetic susceptibility were done for many deposits. A few discoveries were made with this method. Finally, a fully quantitative interpretation of the geophysical data using a multimodeling analysis led to the discovery of additional direct-shipping iron ore deposits in the Schefferville mining district of Canada. 相似文献
9.
D. M. Pechersky 《Izvestiya Physics of the Solid Earth》2007,43(10):844-854
The data on the amplitude of variations in the direction and paleointensity of the geomagnetic field and the frequency of reversals throughout the last 50 Myr near the Paleozoic/Mesozoic and Mesozoic/Cenozoic boundaries, characterized by peaks of magmatic activity of Siberian and Deccan traps, and data on the amplitude of variations in the geomagnetic field direction relative to contemporary world magnetic anomalies are generalized. The boundaries of geological eras are not fixed in recorded paleointensity, polarity, reversal frequency, and variations in the geomagnetic field direction. Against the background of the “normal” field, nearly the same tendency of an increase in the amplitude of field direction variations is observed toward epicenters of contemporary lower mantle plumes; Greenland, Deccan, and Siberian superplumes; and world magnetic anomalies. This suggests a common origin of lower mantle plumes of various formation times, world magnetic anomalies, and the rise in the amplitude of geomagnetic field variations; i.e., all these phenomena are due to a local excitation in the upper part of the liquid core. Large plumes arise in intervals of the most significant changes in the paleointensity (drops or rises), while no correlation exists between the plume generation and the reversal frequency: times of plume formation correlate with the very diverse patterns of the frequency of reversals, from their total absence to maximum frequencies, implying that world magnetic anomalies, variations in the magnetic field direction and paleointensity, and plumes, on the one hand, and field reversals, on the other, have different sources. The time interval between magmatic activity of a plume at the Earth’s surface and its origination at the core-mantle boundary (the time of the plume rise toward the surface) amounts to 20–50 Myr in all cases considered. Different rise times are apparently associated with different paths of the plume rise, “delays” in the plume upward movement, and so on. The spread in “delay” times of each plume can be attributed to uncertainties in age determinations of paleomagnetic study objects and/or the natural remanent magnetization, but it is more probable that this is a result of the formation of a series of plumes (superplumes) in approximately the same region at the core-mantle boundary in the aforementioned time interval. Such an interpretation is supported by the existence of compact clusters of higher field direction amplitudes between 300 and 200 Ma that are possible regions of formation of world magnetic anomalies and plumes. 相似文献
10.
DSO(Direct Shipping Ore,直运块矿)是一种高品位的富铁矿.在加拿大拉布拉多(Labrador)地槽谢菲尔威利(Schefferville)铁矿成矿带,含铁建造苏克曼(Sokoman)组地层全铁含量低、具高密度、强磁性,能够引起高重力异常与高磁异常;而风化淋滤后富集的赤铁矿和针铁矿等(也称DSO)全铁含量高,具高密度、无磁性,仅能够引起高重力异常.采用一般的滤波方法不能提取DSO的重、磁异常.本文采用基于泊松(Poisson)公式的磁场换算磁源重力异常(pseudo-gravity anomaly)方法,由磁场换算磁源重力异常,再与实测重力异常对比,得到纯粹由高密度、无磁性的DSO产生的剩余重力异常,对剩余重力异常采用密度成像与2.5D反演方法解释DSO.泊松公式虽然提出时间很长,但迄今为止仅仅用在资料解释中的定性分析,本文推导并实现了密度磁性非均匀条件下经典泊松公式的形式与实现过程,提出了多尺度窗口滑动线性回归修正的磁场换算磁源重力异常方法,使该公式的数学原理能够对重、磁异常的反演解释定量化.最后本文将多尺度窗口滑动线性回归修正的换算磁源重力异常方法用于加拿大拉布拉多地槽谢菲尔威利铁矿成矿带铁矿勘探,较好地解决了寻找高密度、无磁性DSO的问题. 相似文献
11.
老挝万象省爬立山铁矿床位于长山褶皱带北西端,是长山成矿带内与岩浆作用有关的一个大型铁矿床.矿床类型以矽卡岩型为主,其次为热液型,成矿作用与花岗岩类侵入作用有关,矿区内发育致密块状磁铁矿、孔洞状赤铁矿、砂砾土状铁矿.该区地球物理工作研究程度较低,仅有部分航磁资料,难以准确控制矿化异常;老挝热带雨林气候植被覆盖严重,地表露头难寻,圈定矿体规模和划分地层界线难度较大.为了获得该区铁矿体地表规模及深部延展,笔者在该区开展了1∶10000地面高精度磁法测量,运用解析延拓、水平总梯度模、垂向导数、2.5D人机交互反演等方法有效克服了低纬度地区磁异常化极不稳定形成假异常的问题,解译了爬立山矿区磁异常特征,提高了磁异常的解译分辨率,更加准确的控制了爬立山铁矿区铁矿体的范围、深部延展.后期钻探验证结果表明,在老挝地质勘查程度低、覆盖严重的爬立山地区开展高精度磁法是控制该地区铁矿的有效地球物理方法. 相似文献
12.
13.
E.S.W. Simpson J.G. Sclater B. Parsons I. Norton L. Meinke 《Earth and Planetary Science Letters》1979,43(2):260-264
East-west-trending Mesozoic magnetic anomalies M2 through M22 have been identified in the northern Mozambique Basin. These anomalies are best matched by sea floor created at 50°S trending N120°E and spreading at a rate of around 1.5 cm/yr. The northward increase in age inferred from the identifications of these anomalies are compatible with observed decrease in the “reliable” heat flow values from 1.4 to 1.1 μcal/cm2 s to the north in the basin. The anomalies terminate in the southern part of the Mozambique Channel against a magnetic quiet zone to the north. Both the Mozambique Basin anomalies and those recently observed off Antarctica are strong evidence in favour of a Gondwanaland reconstruction that places Dronning Maud Land against southern Mozambique, and a late Jurassic or older separation between Africa and Antarctica. 相似文献
14.
A method is proposed to detect buried magnetite concentrations within river sediments. Model studies show that relatively small (thickness 1 m, width 10 m) plate-shaped volumes with magnetite contents of 0.5% within a non-magnetic matrix can be detected by a detailed ground magnetic survey using a sensitive (0.1 nT) magnetometer. Tests along lines perpendicular to the river but at a different angle to the bedrock trend (or the aeromagnetic anomaly trend) reveal that essentially all total field and vertical’gradient’anomalies detected in the profiles are elongated in the river and/or valley direction. This shows that the anomaly sources are (buried) volumes of higher magnetite content within the river sediments. Further evidence for this is (1) that higher intensity total field and vertical’gradient’anomalies occur in an area where the river cuts through strongly magnetic serpentinites, (2) the absence of high frequency anomalies over unsorted glacial till, and (3) some features on power spectra. Relatively large volumes of high magnetite concentrations within the river sediments may well contain the highest concentration of heavy economic minerals such as gold. Consequently, the areas of greatest interest in the exploitation of buried placers may be selected from maps obtained by detailed magnetic surveys either on the ground or at low altitude by helicopter. 相似文献
15.
The results of palaeomagnetic surveys of Mesozoic and Tertiary rocks from Gondwanaland can be reconciled with the results of modelling the evolution of oceanic floors from analyses of marine magnetic anomalies. Previous inconsistencies were mainly due to errors apparent in the Australian Cenozoic palaeomagnetic data. An alternative Tertiary apparent polar wander path (APWP) has been constructed from an analysis of all published laterite and weathered profile data. Palaeomagnetic results for Africa, Antarctica, Australia, India, Madagascar and South America are compared for rotations corresponding to marine magnetic anomalies 16, 22, 28, 34 and M1 and for “fit”. India has been selected as the reference continent since it provides the most detailed APWP having drifted about 50° of latitude since breakup. 相似文献
16.
根据美国地球物理数据中心的地磁场模型(NGDC-720),研究云南地区地壳磁异常的空间变化,包括磁异常及其梯度的分布、磁异常随高度的衰减、不同波长成分对总体磁异常的贡献.比较磁异常与重力异常、大地热流、地震活动等地球物理信息的异同特征,探讨地壳磁异常与地质构造的关系.研究结果表明:丽江—小金河、红河断裂带以西的三江、滇西造山带的异常较弱,菱形地块的异常相对较强.研究区域的地壳磁异常主要是弱磁性基底背景下叠加的浅源磁性体产生.卫星磁异常显示滇中坳陷区具有清晰的偶极场特征.沿红河断裂带分布的正负磁异常带与断裂构造走向一致.围限菱形地块的丽江—小金河断裂、红河断裂、康定—奕良—水城断裂和弥勒—师宗—水城断裂带是磁异常的强弱过渡带.强烈地震发生的地点、大地热流值高的地区,地壳磁异常为负值或相对较弱. 相似文献
17.
Eugen Vujić Giuliana Verbanac Stanislav Francisković-Bilinski Vladis Vujnović Antun Marki 《Studia Geophysica et Geodaetica》2011,55(1):175-190
Based on the ground survey of total-field magnetic data at 53 sites, which recorded a time-series over the interval 2003–2005,
the core field + long wavelength lithospheric field over the middle-northern Croatia region was calculated. The area of the
survey was 18900 km2, an average distance between the neighbouring sites being 12 km. The results were reduced to 2004.5 epoch. This “normal”
total-field was estimated using the firstorder Taylor polynomial as a function of geographic coordinates, and the polynomial
coefficients were calculated with three methods of adjustment: simple and weighted least squares fits and adjustment according
to the most frequent value. The stability of the normal field was tested using the Monte Carlo-type test, by decreasing the
input data set in each adjustment (up to 90%). All obtained field residuals (measured-“normal”) were mutually compared, as
well as fit coefficients of the Taylor polynomials. The residual values indicate the presence of shorter-wavelength anomalies,
specifically three major residual anomalies were found (−106 nT, 74 nT and 57 nT). The geostatistical analysis of the ground
survey data and the normal field residuals (respectively), using the median absolute deviation method, was further conducted
in order to evaluate the calculated anomalies. The geological situation around the anomalies derived by the median absolute
deviation method, and around the normal field residual anomalies, is given. The correlation was found between higher value
anomalies of the normal field residuals, and shallow volcanic rocks and oil field, respectively. 相似文献
18.
A survey of the southern part of the Balearic Basin was flown in 1971 at a height of 600 m. The results of a survey of the northern part, flown at a height of 3000 m, which was previously published, have been downward continued to a height of 600 m. The resulting composite map shows well defined low amplitude (100 gammas) magnetic lineations of the Vine et Matthews' type offset by fracture zones. The lineated zones are bounded by large quasi-circular anomalies on the edge of possibly “continental” non magnetic zones. The results define a complex kinematic pattern of the opening of the Balearic Basin, in terms of plate tectonics. 相似文献
19.
Pauline Le Maire Lionel Bertrand Marc Munschy Marc Diraison Yves Géraud 《Geophysical Prospecting》2020,68(7):2307-2319
Magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three-component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales. 相似文献
20.
Michael Gadsden 《Physics of the Earth and Planetary Interiors》1983,33(1):65-67
A model mechanism has been derived for the evolution of the cation distribution in titanomaghemites, which have formed by the progressive removal of iron from the spinel lattice. According to the model, the cation distribution of a titanomaghemite is not a unique function of composition but depends on the path by which maghemitization has taken place. Cation distributions (and consequent magnetic properties) have been calculated and compared for titanomaghemite produced by the “removal of iron” and “addition of oxygen” mechanisms. For a given composition, the Curie point temperature is almost invariant, being, according to molecular field theory, more sensitive to composition than cation distribution. Therefore, the model cannot explain the variations observed in synthetic titanomaghemite of different provenances. According to the model, the spontaneous magnetization is significantly lower for the removal of iron mechanism, which may be helpful in explaining a decrease in the remanence of submarine basalts with age.Structurally metastable titanomaghemites invert to an intergrowth of phases on heating above approximately 350°C and it is expected that the inversion product would be independent of the mechanism by which maghemitization had previously taken place. Available X-ray, and other data, have been used to produce a simple model of the inversion process, and values of the Curie point of the inversion product and the ratio of the magnetization before and after the inversion derived. These model values compare favourably with experimental values for a synthetic titanomaghemite in which inversion was induced by progressive slow heating to approximately 600°C. The inversion process therefore has potential in determining the compositions of naturally occurring titanomaghemites. 相似文献