The IDQ curve: A tool for evaluating the direction of remanent magnetization from magnetic anomalies

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. J85-J98
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Dalian Zhang ◽  
Bangshun Wei ◽  
Meixia Geng ◽  
...  
Keyword(s):  
Remanent Magnetization ◽  
Field Data ◽  
Eastern China ◽  
Synthetic Data ◽  
Magnetic Anomalies ◽  
Natural Remanent Magnetization ◽  
Magma Intrusion ◽  
Magnetization Direction ◽  
Ore Bodies ◽  
Using Data

Natural remanent magnetization acts as a record of the previous orientations of the earth’s magnetic field, and it is an important feature when studying geologic phenomena. The so-called IDQ curve is used to describe the relationship between the inclination ( I) and declination ( D) of remanent magnetization and the Köenigsberger ratio ( Q). Here, we construct the IDQ curve using data on ground and airborne magnetic anomalies. The curve is devised using modified approaches for estimating the total magnetization direction, e.g., identifying the maximal position of minimal reduced-to-the-pole fields or identifying correlations between total and vertical reduced-to-the-pole field gradients. The method is tested using synthetic data, and the results indicate that the IDQ curve can provide valuable information on the remanent magnetization direction based on available data on the Köenigsberger ratio. Then, the method is used to interpret field data from the Yeshan region in eastern China, where ground anomalies have been produced by igneous rocks, including diorite and basalt, which occur along with magnetite and hematite ore bodies. The IDQ curves for 24 subanomalies are constructed, and these curves indicate two main distribution clusters of remanent magnetization directions corresponding to different structural units of magma intrusion and help identify the lithologies of the magnetic sources in areas covered by Quaternary sediments. The estimated remanent magnetization directions for Cenozoic basalt are consistent with measurements made in paleomagnetism studies. The synthetic and field data indicate that the IDQ curve can be used to efficiently estimate the remanent magnetization direction from a magnetic anomaly, which could help with our understanding of geologic processes in an area.

scholarly journals Petrophysical Properties (Density and Magnetization) of Rocks from the Suhbaatar-Ulaanbaatar-Dalandzadgad Geophysical Profile in Mongolia and Their Implications

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Tao Yang ◽  
Jintian Gao ◽  
Zuowen Gu ◽  
Baatarkhuu Dagva ◽  
Batsaikhan Tserenpil
Keyword(s):  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Ground Surface ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Natural Remanent Magnetization ◽  
Petrophysical Properties ◽  
Geological History ◽  
Essential Information ◽  
Variable Gravity

Petrophysical properties of 585 rock samples from the Suhbaatar-Ulaanbaatar-Dalandzadgad geophysical profile in Mongolia are presented. Based on the rock classifications and tectonic units, petrophysical parameters (bulk density, magnetic susceptibility, intensity of natural remanent magnetization, and Köenigsberger ratio) of these rocks are summarized. Results indicate that (1) significant density contrast of different rocks would result in variable gravity anomalies along the profile; (2) magnetic susceptibility and natural remanent magnetization of all rocks are variable, covering 5-6 orders of magnitude, which would make a variable induced magnetization and further links to complex magnetic anomalies in ground surface; (3) the distribution of rocks with different lithologies controls the pattern of lithospheric magnetic anomaly along the profile. The petrophysical database thus provides not only one of the keys to understand the geological history and structure of the profile, but also essential information for analysis and interpretation of the geophysical (e.g., magnetic and gravity) survey data.

3D modeling and inversion of VLF and VLF-R electromagnetic data

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. WB219-WB231 ◽  
Author(s):  
P. Kaikkonen ◽  
S. P. Sharma ◽  
S. Mittal
Keyword(s):  
Field Data ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Low Frequency ◽  
Reliability And Validity ◽  
Physical Parameters ◽  
Model Parameters ◽  
Data Inversion ◽  
Inversion Procedure ◽  
Using Data

Three-dimensional linearized nonlinear electromagnetic inversion is developed for revealing the subsurface conductivity structure using isolated very low frequency (VLF) and VLF-resistivity anomalies due to conductors that may be arbitrarily directed towards the measuring profiles and the VLF transmitter. We described the 3D model using a set of variables in terms of geometric and physical parameters. These model parameters were then optimized (parametric inversion) to obtain their best estimates to fit the observations. Two VLF transmitters, i.e., the [Formula: see text], [Formula: see text] (“E”) and the [Formula: see text], [Formula: see text] (“H”) polarizations, respectively, can be considered jointly in inversion. After inverting several noise-free and noisy synthetic data, the results revealed that the estimated model parameters and the functionality of the approach were very good and reliable. The inversion procedure also worked well for the field data. The reliability and validity of the results after the field data inversion have been checked using data from a shear zone associated with uranium mineralization.

New constraints on the role of late Variscan extension in the origin of the Eastern Galicia Magnetic Anomaly (NW Spain)

2020 ◽  
Author(s):  
Puy Ayarza ◽  
Juan José Villalaín ◽  
Jose Ramón Martínez Catalán ◽  
Fernando Alvarez Lobato ◽  
Manuela Durán Oreja ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Remanent Magnetization ◽  
Magnetic Anomalies ◽  
Natural Remanent Magnetization ◽  
Source Rocks ◽  
Magmatic Rocks ◽  
Extensional Tectonic ◽  
Tectonic Window ◽  
Central Iberian Arc

<p><span lang="EN-US">The Eastern Galicia Magnetic Anomaly (EGMA) is one of the most conspicuous and, definitively, the best studied of all the magnetic anomalies in the Central Iberian Arc (CIA). This is probably due to its location, on the thoroughly researched Lugo-Sanabria gneiss dome and to the unique fact that its source rocks crop out in the Xistral Tectonic Window. Multiple studies and models of this anomaly have been carried out in the last 25 years and still, new results keep on shedding more light on its understanding. Rock magnetic analyses, natural remanent magnetization, anisotropy of the magnetic susceptibility and stable isotopes geochemistry carried out on the rocks that produce this anomaly have provided new insights on the processes that led to magnetization and on its age. Results suggest that magnetization of source rocks is a consequence of the increase in oxygen fugacity underwent by metamorphic and magmatic rocks affected by late-Variscan extensional tectonics. Extensional detachments were the pathways that allowed the entrance of fluids that led to syn-tectonic crystallization of magnetite and hematite in S-Type granites. Accordingly, magnetization is not really linked to primary lithologies but mostly to extensional structures. This process took place in the late Carboniferous to earliest Permian, during the Kiaman reverse superchron. Natural remanent magnetization exhibited by hematite-bearing samples confirms the age of the magnetization and adds complexity to the interpretation of the EGMA, where remanence has been often largely ignored or underestimated. Understanding the origin of the EGMA contributes to the interpretation of other anomalies existing in the CIA, also located on thermal domes. Furthermore, it provides new hints to interpret magnetic anomalies located in extensional tectonic contexts worldwide</span></p>

Estimating the Magnetization Direction of Sources through Correlation between Reduced-to-Pole Anomaly and Normalized Source Strength

2014 ◽  
Vol 644-650 ◽  
pp. 3793-3796
Author(s):  
Liang Hui Guo ◽  
Rui Gao ◽  
Guo Li Zhang
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Cross Correlation ◽  
Synthetic Data ◽  
Field Direction ◽  
Magnetic Data ◽  
Source Strength ◽  
Magnetization Direction ◽  
New Approach ◽  
Total Magnetization

Under the effects of remanent magnetization, total magnetization direction is different from geomagnetic field direction, which makes magnetic data processing and interpretation complexity. In this paper, we present a new approach for estimating the total magnetization direction of sources via cross-correlation between the reduced-to-pole anomaly and the normalized source strength (who is less sensitive to remanent magnetization). The geomagnetic field direction is used to calculated the normalized source strength, while various assumed total magnetization directions are used to calculated the RTP anomalies. The maximum correlation between the RTP anomalies and the normalized corresponds to the estimated total magnetization direction. Test on synthetic data showed that the new approach is simple and effective.

The Mid-Atlantic ridge near 45° N. VII. Magnetic properties and opaque mineralogy of dredged samples

1970 ◽  
Vol 7 (2) ◽  
pp. 239-256 ◽  
Author(s):  
C. M. Carmichael
Keyword(s):  
Magnetic Properties ◽  
Remanent Magnetization ◽  
Complex Structure ◽  
Magnetic Anomalies ◽  
Natural Remanent Magnetization ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
Field Polarity ◽  
Fine Grained ◽  
Mid Atlantic Ridge

Measurements of the magnetic properties, paleomagnetic field intensity, and the inferred paleomagnetic field polarity have been made using fine grained basalt and coarser grained rock samples dredged from the mid-Atlantic ridge near 45° N and supplied by the Geological Survey of Canada. The opaque mineralogy of the samples was studied by microscope, Curie point, and X-ray diffraction techniques. The natural remanent magnetization of the basalt is of the order of 5 to 10 × 10−3 e.m.u./cm3 with some values from the center of the median valley reaching 10−1 e.m.u./cm3. Magnetic anomalies over the ridge can be accounted for by the remanent magnetization of a few hundred meters of this basalt. The coarse grained rocks were relatively weakly magnetized, and while they contribute little to the magnetic anomalies, their diverse character suggests that the major portion of the oceanic crust, below a thin veneer of fine grained basalt, has differentiated into a complex structure.

Identifying remanent magnetization effects in magnetic data

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 653-659 ◽  
Author(s):  
Walter R. Roest ◽  
Mark Pilkington
Keyword(s):  
Magnetic Anomaly ◽  
Remanent Magnetization ◽  
Close Agreement ◽  
Magnetic Anomalies ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Impact Structure ◽  
Magnetization Direction ◽  
Additional Constraints

Remanent magnetization can have a significant influence on the shape of magnetic anomalies in areas that are generally characterized by induced magnetization. Since modeling of magnetic anomalies is nonunique, additional constraints on the direction of magnetization are useful. A method is proposed here to study the possible contribution of remanent magnetization to a particular anomaly, by comparing two functions that are calculated directly from the observations: (1) the amplitude of the analytic signal, and (2) the horizontal gradient of pseudogravity. From the amplitude and relative position of maxima in these derived quantities, we infer the deviation of the magnetization direction from that of the ambient field. The approach is applied to the magnetic anomaly in the center of the Manicouagan impact structure (Canada). Our results, based only on the magnetic anomaly observations, are in close agreement with constraints on the direction of remanent magnetization from rock samples.

MAGNETIC PROSPECTING FOR IRON ORES IN JAMAICA

Geophysics ◽  
1955 ◽  
Vol 20 (3) ◽  
pp. 593-614 ◽  
Author(s):  
S. A. Vincenz
Keyword(s):  
Remanent Magnetization ◽  
Iron Ore ◽  
Ground Surface ◽  
Natural Remanent Magnetization ◽  
Ore Deposits ◽  
Small Scale ◽  
Rough Terrain ◽  
Near Surface ◽  
Ore Bodies ◽  
Iron Ore Deposits

Two ground magnetometer surveys over iron ore deposits in Jamaica are described and the results of the observations interpreted. An improvised but economical technique is used to measure the main magnetic properties of ore samples obtained from surface exposures, and a suitable statistical analysis is applied to determine the significance of these observations. The interpretation of the magnetic profiles, carried out on the basis of these observations, is complicated by the non‐uniformity of the natural remanent magnetization of the ores and the roughness of Jamaican topography. The ambiguities due to the latter factor are diminished by taking into account in the computations the changes in the elevation of the ground surface. The results of the interpretation are on the whole successful and give the approximate sizes and positions of the main ore bodies. A conclusion is reached that, in the case of small‐scale near‐surface deposits whose approximate position is already known, ground magnetometer surveys can be superior to those made from the air because of their smaller cost and greater power of resolution in rough terrain.

Retrieving paleopoles using newly mapped lunar magnetic anomalies within basins

2020 ◽  
Author(s):  
Joana S. Oliveira ◽  
Lon L. Hood
Keyword(s):  
Magnetic Field ◽  
Dipole Moments ◽  
Magnetic Anomalies ◽  
Magnetization Direction ◽  
Global Models ◽  
Core Field ◽  
The North ◽  
Lunar Prospector ◽  
North Magnetic Pole ◽  
Using Data

<p>Orbital spacecraft magnetic field observations show that several isolated magnetic anomalies are found to be heterogeneously distributed over the lunar surface. The magnetic anomalies origin is still debated; however, it is largely accepted that an ambient core magnetic field was present during their formation. Contrary to previous studies, here we focus only on anomalies that are related to basins/craters, which correspond to the best possibility to hold ancient core field information. In particular, the basin rocks become thermoremanently magnetized as the melt sheet cools down slowly recording the ambient magnetic field that was present when the crater was formed.</p><p>We build regional magnetic field maps using data from quiet orbits of Lunar Prospector and Kaguya spacecraft. When comparing these regional maps to existing global models, several differences and details are discovered. Further investigation is required to understand why small scales are missing from global models. For each mapped crater, we perform inversions for the magnetization direction to estimate the corresponding paleopole position (defined as the north magnetic pole when the anomaly formed). In detail, a grid of dipoles is placed over the basin inner depression, where the melt sheet is believed to be. All dipoles have the same common direction, nonetheless different dipole moments.</p><p>Preliminary results show that paleopole positions of regionally mapped anomalies associated with craters are not in absolute agreement with previous paleopole studies. Also of significance is the distribution of dipoles obtained, which seem to be consistent with inferred impactor trajectories. We conclude that paleopole position results are highly dependent on the technique and choices we make to construct the magnetic field maps. Further studies of several other craters will be performed, but we expect large differences when using regionally mapped anomalies. Our results will help to better constrain the lunar ancient core field morphology.</p>

Inclinaison magnétique de roches basaltiques de la dorsale est-pacifique à 21°N et validité des critères de polarité

1983 ◽  
Vol 20 (2) ◽  
pp. 322-333 ◽  
Author(s):  
Brigitte Smith
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Mean Value ◽  
Magnetization Direction ◽  
Basaltic Rocks ◽  
Stable Direction ◽  
Normal Polarity ◽  
The Stability

Among the basaltic rocks sampled by submersible or dredged at the East-Pacific Rise axis around 21°N latitude (French–American–Mexican legs CYAMEX and RISE), 22 samples have been selected according to macroscopic, oriented criteria (elongation plane of feeder tubes in sheeted lavas, bubbles and gas cavities, stalactites, septa) from which the polarity of a sample, acquired in situ during its cooling, could be established.The natural remanent magnetization intensity of these generally voluminous samples (up to about 350 cm3) has a mean value of 11.35 ± 2.31 A∙m−1 (10−3 emu∙cm−3); the scatter of the values can be explained by the varying proportion of nonmagnetic material (glass, Mn) in the samples.The magnetic viscosity is always negligible and the stability of the remanent magnetization direction after alternating field demagnetization indicates that the stable direction determined is the direction of the original thermoremanence.Despite the relatively low latitude, which makes the occurrence of negative magnetic inclinations within a normal polarity period (Brunhes, in this case) more probable, no reverse polarity has been found. The mean inclination of the 22 samples is I = +41.8 ± 16.7° and becomes I = +42.2 ± 19.4° if the samples are grouped in 15 pin-point sampling sites; these values are not significantly different from those of the local dipole field, I = ±37.4°, or from those of the actual local field, I ~ +47°, which may be the result of effusions from the youngest lava flows.The scatter of the magnetic inclination values is more tightly bound to the quality of the polarity criteria than to the secular variation of the Earth ' s magnetic field, the latter interfering in only a few cases. It is obvious that the validity of the reorientation depends on (1) the morphological quality of the criteria used: those that are well developed, well represented in the sample, and apparently the most crystallized (glassy criterion has proved to be doubtful), permit a better reorientation of the sample; and (2) the principle of the criterion itself: criteria referring to vertical axes (stalactites) or vertical planes (septa) are more reliable than those based upon the determination of a horizontal plane (elongation plane of tubes in sheeted lavas).It appears from this study that macroscopic polarity criteria may be used in an almost systematic way to find the polarity of an in situ sample.

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