Susceptibility and remanent magnetization inversion of magnetic data with a priori information of the Köenigsberger ratio

2020 ◽  
Vol 221 (2) ◽  
pp. 1090-1109
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Boxin Zuo ◽  
Henglei Zhang ◽  
Meixia Geng ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Magnetization Vector ◽  
Northwest China ◽  
Natural Remanent Magnetization ◽  
Gradient Algorithm ◽  
Magnetic Data ◽  
Preconditioned Conjugate Gradient ◽  
Data Set ◽  
Discrete Values

SUMMARY Magnetic susceptibility and natural remanent magnetization of rocks are useful parameters to study geological structures and geodynamic processes. Traditional widely used algorithms for the inversion of magnetic data can recover the distribution of the apparent susceptibility or total magnetization intensity, but do not provide information on the remanent magnetization. In this paper, we propose a framework to directly invert for the magnetic susceptibility and the natural remanent magnetization vector using surface or airborne magnetic data, assuming that the Köenigsberger ratio of the rock is known or approximately deducible. The susceptibility and remanence are computed using two different approaches: (1) the susceptibility, intensity, and direction of the remanent magnetization are continuously recovered for each discretized cell and (2) the remanence direction is assumed to be uniform in each subzone and is iteratively computed as discrete values. Both processes are implemented using the preconditioned conjugate gradient algorithm. The method is tested on three synthetic models and one field data set from the Zaohuohexi iron-ore deposit, Qinghai Province, northwest China. The results of the continuous inversion show the trend of the remanent magnetization directions, while the discrete inversion yields more specific values. This inversion framework can determine the source bodies’ geometry and position, and also provide superposed and comprehensive information on the natural remanent magnetization, which may be useful to investigate geological bodies bearing stable primary remanent magnetization.

A paradigm shift in magnetic data interpretation: Increased value through magnetization inversions

2021 ◽  
Vol 40 (2) ◽  
pp. 89-98
Author(s):  
Yaoguo Li ◽  
Jiajia Sun ◽  
Shu-Ling Li ◽  
Marcelo Leão-Santos
Keyword(s):  
Paradigm Shift ◽  
Remanent Magnetization ◽  
Mineral Content ◽  
Mineral Exploration ◽  
Magnetization Vector ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Data Set ◽  
Total Magnetization ◽  
Informational Value

Magnetic data are sensitive to both the induced magnetization in rock units caused by the present earth's magnetic field and the remanent magnetization acquired by rock units in past geologic time. Susceptibility is a direct indicator of the magnetic mineral content, whereas remanent magnetization carries information about the formation process and subsequent structural movement of geologic units. The ability to recover and use total magnetization, defined as the vectorial sum of the induced and remanent magnetization, therefore enables us to take full advantage of magnetic data. The exploration geophysics community has achieved significant advances in inverting magnetic data affected by remanent magnetization. It is now feasible to invert any magnetic data set for total magnetization. We provide an overview of the state of the art in magnetization inversion and demonstrate the informational value of inverted magnetization through a set of case studies from mineral exploration problems. We focus on the methods that recover either the magnitude of the total magnetization or the total magnetization vector itself.

Magnetization vector imaging for borehole magnetic data based on magnitude magnetic anomaly

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D429-D444 ◽  
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Tianyou Liu ◽  
Jie Feng ◽  
Wenli Gao ◽  
...  
Keyword(s):  
Conjugate Gradient Method ◽  
Conjugate Gradient ◽  
Gradient Method ◽  
Magnetization Vector ◽  
Real Data ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Preconditioned Conjugate Gradient ◽  
Magnetization Direction ◽  
Magnetization Intensity

Remanent magnetization and self-demagnetization change the magnitude and direction of the magnetization vector, which complicates the interpretation of magnetic data. To deal with this problem, we evaluated a method for inverting the distributions of 2D magnetization vector or effective susceptibility using 3C borehole magnetic data. The basis for this method is the fact that 2D magnitude magnetic anomalies are not sensitive to the magnetization direction. We calculated magnitude anomalies from the measured borehole magnetic data in a spatial domain. The vector distributions of magnetization were inverted methodically in two steps. The distributions of magnetization magnitude were initially solved based on magnitude magnetic anomalies using the preconditioned conjugate gradient method. The preconditioner determined by the distances between the cells and the borehole observation points greatly improved the quality of the magnetization magnitude imaging. With the calculated magnetization magnitude, the distributions of magnetization direction were computed by fitting the component anomalies secondly using the conjugate gradient method. The two-step approach made full use of the amplitude and phase anomalies of the borehole magnetic data. We studied the influence of remanence and demagnetization based on the recovered magnetization intensity and direction distributions. Finally, we tested our method using synthetic and real data from scenarios that involved high susceptibility and complicated remanence, and all tests returned favorable results.

Linking cave sediments and soil magnetism in the Urșilor cave (Romania)

2021 ◽  
Author(s):  
Cristian George Panaiotu ◽  
Cristian Necula ◽  
Relu D. Roban ◽  
Alexandru Petculescu ◽  
Ionut-Cornel Mirea ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Frequency Dependence ◽  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Magnetic Mineral ◽  
Magnetic Data ◽  
Sediment Samples ◽  
Superparamagnetic Particles ◽  
Susceptibility Data ◽  
Cave Sediments

<p>Cyclical changes in the magnetic mineral assemblages have been observed in numerous sedimentary records confirming the relationship between rock magnetism and past global change. Several studies have shown that the magnetic susceptibility data of cave sediments reflect both long- and short-term climatic oscillations. These magnetic susceptibility variations are attributed to changes in climate-controlled pedogenesis which influence the production of low coercivity magnetic mineral phases, magnetite, and maghemite outside the cave. These soils with climate-dependent magnetic properties are then washed, blown, or tracked into the cave where they accumulate, creating the changes observed in rock magnetic data. We present a rockmagnetism study of the sediments from the Urșilor cave and the soils above the cave. Our focus is the detailed characterization of the ferromagnetic mineralogy preserved in the cave sediments and its links with potential soil sources. In the cave, we sampled four sections (2-3 m high) consisting mainly of silts and clays, with some sand layers. The age of the sediments is older than 40 ka. At the surface, we sampled various types of soils from 9 sites. For all samples, we measured: variation of magnetic susceptibility with frequency (976 and 15616 Hz), the anisotropy of magnetic susceptibility, isothermal remanent magnetization, and anhysteretic remanent magnetization. Because soils are characterized by the presence of superparamagnetic magnetite produced by pedogenesis which can be detected by the frequency dependence of magnetic susceptibility, we also measured the frequency dependence of soils and selected cave sediment samples at 13 frequencies (between 128 and 512000 Hz). Multi-frequencies measurements of the magnetic susceptibility of recent soils show that all the sampled soils have a strong frequency dependence indicating the presence of superparamagnetic particles produced by pedogenesis. Most of the sediment samples have an important frequency dependence similar to the one observed in the recent soils. As a preliminary conclusion, we can state that most of the fine cave sediments contain superparamagnetic particles, which can be probably attributed to soils transported into the cave by erosion. These results suggest that during the deposition of high magnetic susceptibility sediments it was a climate favorable for intense pedogenesis. The interpretation of the intervals with lower values of magnetic susceptibility is still under investigation to decide if represents a climatic signal or a change in the dynamics of sediment transport. <strong>Acknowledgment:</strong> The research leading to these results has received funding from the EEA Grants 2014-2021, under Project contract no. EEA-RO-NO-2018-0126.</p>

Multi-proxy study of the Cretaceous-Paleogene (K-Pg) boundary in deep-sea turbiditic sediments in the Uzgruň section (Outer Flysch Carpathians, Czech Republic)

2021 ◽  
Author(s):  
Šimon Kdýr ◽  
Tiiu Elbra ◽  
Miroslav Bubík ◽  
Petr Schnabl ◽  
Lilian Švábenická
Keyword(s):  
Magnetic Susceptibility ◽  
Czech Republic ◽  
Detection Limit ◽  
Remanent Magnetization ◽  
Magnetic Particles ◽  
Principal Component ◽  
Natural Remanent Magnetization ◽  
Ongoing Research ◽  
Small Stream ◽  
Magnetic Methods

<p>The composite profile, with 4 studied sections, is located near the Uzgruň village (Czech Republic) next to a small stream. The profile is composed of Late Maastrichtian to Palaeocene flysch sediments and the K-Pg boundary is set in claystones within this turbiditic setting. Ongoing research of local paleoenvironment and stratigraphy is based on paleo- and rock-magnetic methods, micropaleontology and geochemistry to obtain more detailed view of the local situation during the K-Pg extinction event. Based on biostratigraphy, two dinocyst zones (Bubík et al., 2002): Palynodium grallator and Carpatella cornuta (first occurrence in the Danian), two calcareous nannofossil zones in the Upper Maastrichtian, and the agglutinated foraminifer zone Rzehakina fissistomata in the Paleogene were distinguished. Biostratigraphic data support the K-Pg boundary interval. The uppermost Maastrichtian is indicated by nannofossil species Micula prinsii, UC26d<sup>TP</sup> zone. Basal Paleogene non-calcareous strata contain dinocyst Carpatella cornuta and agglutinated foraminifers of Rzehakina fissistomata zone. The presence of low-latitude nannofossil taxa M. prinsii and Ceratolithoides kamptneri show input of warm waters during the uppermost Maastrichtian. Several rock-magnetic methods, such as acquisition of Isothermal remanent magnetization (IRM), acquisition of Anhysteretic remanent magnetization (ARM), Anisotropy of magnetic susceptibility (AMS), Field dependence of magnetic susceptibility (HD) and Frequency dependence of magnetic susceptibility (FD), were applied to estimate behaviour and origin of magnetic particles. Natural remanent magnetization (NRM) values of samples range from 0.09 to 2.48 mA/m. Volume normalized magnetic susceptibility (MS) show values from 130 up to 1197 SI*10-6. There is no increase observed in MS across stratigraphic boundary due to turbiditic evolution of sediment. Due to character of sediments, we applied alternating field (AF) demagnetization and used principal component analysis (PCA; Kirschvink, 1980) for estimation of characteristic remanent component. Most of the K/Pg sections worldwide have well documented Iridium anomaly. In Uzgruň, the preliminary results show that although the values are not as pronounced, the Ir at K-Pg boundary is still higher than in surrounding sediments. For tracing of Deccan traps effect we plan to apply mercury (Hg)/total organic carbon (TOC) stratigraphy. TOC content of 20 pilot samples is low, but not under detection limit of the instrumentation (mean value 0.92 wt%). One sample reached value 4.41 wt% of TOC. Sulphur contents are reaching 1 wt%, but several samples were under detection limit of the instrumentation. Sulphur concentrations suggest more reduction conditions of burial.</p><p>Current research is supported by Czech Science Foundation project no. 19-07516S and is in accordance with research plan no. RVO67985831.</p><p>Bubík, M., Adamová, M., Bąk, M., Franců, J., Gedl, P., Mikuláš, R., Švábenická, L., & Uchman, A. (2002). Výsledky výzkumu hranice křída/terciér v magurském flyši u Uzgruně. Geologické výzkumy na Moravě a ve Slezsku, 9, 18–22</p><p>L. Kirschvink (1980), The least-squares line and plane and the analysis of palaeomagnetic data, Geophysical Journal International, 62(3), 699–718, https://doi.org/10.1111/j.1365-246X.1980.tb02601.x</p>

scholarly journals A survey of the natural remanent magnetization and magnetic susceptibility of Apollo whole rocks

2019 ◽  
Vol 290 ◽  
pp. 36-43 ◽  
Author(s):  
Camille Lepaulard ◽  
Jérôme Gattacceca ◽  
Minoru Uehara ◽  
Pierre Rochette ◽  
Yoann Quesnel ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization

Concealed faults and intrusions identification based on multiscale edge detection and 3D inversion of gravity and magnetic data: A case study in Qiongheba area, Xinjiang, Northwest China

2019 ◽  
Vol 7 (2) ◽  
pp. T331-T345 ◽  
Author(s):  
Jiayong Yan ◽  
Xiangbin Chen ◽  
Guixiang Meng ◽  
Qingtian Lü ◽  
Zhen Deng ◽  
...  
Keyword(s):  
Edge Detection ◽  
Junggar Basin ◽  
Northwest China ◽  
Gold Deposits ◽  
Combination Method ◽  
Magnetic Data ◽  
3D Inversion ◽  
Data Set ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

Qiongheba is a polymetallic ore concentration area located in the east margin of the Junggar Basin in Xinjiang, Northwest China. Because all three main types of metal deposits (porphyry-type copper, skarn-type iron-copper, and structural altered rock-type gold deposits) in this area are controlled strictly by fault structures and intrusions buried under the Quaternary sediments, the detection of concealed faults and intrusions is of great significance for mineral prospecting. We aim to make clear the faults and intrusions based on the high-precision gravity and magnetic data set. First, multiscale edge detection of gravity and magnetic data is used to distinguish and divide the faults system. Second, 3D recognition of concealed intrusions combining with 3D inversion and multiscale edge detection of gravity and magnetic is carried out to construct the 3D formation of concealed intrusions. Last, seven prospecting targets are proposed based on our research and existed regional geologic and geochemical information, and two of them have been confirmed to be rich in polymetal (Cu-Fe-Mo-Au in the Layikeleke deposit and Cu in the Baxi deposit) by drilling. Our research results not only proved the effectiveness of the combination method of 3D inversion and multiscale edge detection of gravity and magnetic data in the prospecting of concealed faults and intrusions, but they also provide abundant information for mineral exploration prediction in the Qiongheba 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.

Mapping of apparent magnetic susceptibility and the identification of fractures: A case study from the Eye-Dashwa Lakes pluton, Atikokan, Ontario

Geophysics ◽  
2010 ◽  
Vol 75 (3) ◽  
pp. B147-B156 ◽  
Author(s):  
Madeline D. Lee ◽  
William A. Morris ◽  
Hernan A. Ugalde
Keyword(s):  
Magnetic Susceptibility ◽  
Forward Modeling ◽  
Local Scale ◽  
Magnetic Data ◽  
Susceptibility Map ◽  
Magnetic Minerals ◽  
Data Set ◽  
Susceptibility Data ◽  
Apparent Susceptibility

In situ magnetic-susceptibility measurements are only possible on outcrops, which are often limited by overburden and water bodies. An alternative approach is to derive an apparent susceptibility map from total-magnetic-intensity (TMI) surveys, which was done in this study for the Eye-Dashwa Lakes pluton near Atikokan, Ontario. Susceptibility logs of cores directly link alteration to systematic changes in the amount and composition of magnetic minerals. The surficial distribution of alteration zones was originally estimated from a limited number of in situ magnetic-susceptibility measurements. Here, through forward modeling of the TMI data set, susceptibility data are used to validate the apparent susceptibility data set. The modeling accounts for the bathymetric surface of all lakes that cover the area. A two-step process of bulk and local-scale modeling was used to estimate apparent susceptibility patterns. Bulk magnetic susceptibility is used as an indicator of overall alteration content, and local-scale apparent magnetic-susceptibility values are computed using a forward-modeling routine. The new apparent magnetic data set indicates northwest and northeast linears, which are the same as those seen in previous studies.

scholarly journals Application of the pseudo-Thellier technique to a paleomagnetic record from lake El Trébol (Patagonia, Argentina)

2008 ◽  
Vol 47 (4) ◽  
pp. 319-327
Author(s):  
C. S. G. Gogorza ◽  
S. Torcida ◽  
A. M. Sinito ◽  
M. A. E. Chaparro
Keyword(s):  
Magnetic Susceptibility ◽  
Error Estimates ◽  
Sediment Core ◽  
Standard Method ◽  
Remanent Magnetization ◽  
Reasonable Agreement ◽  
Natural Remanent Magnetization ◽  
Isothermal Remanent Magnetization ◽  
Low Field ◽  
Relative Paleointensity

The pseudo-Thellier technique was applied to obtain relative paleointensity determinations using a sediment core from Lake El Tre?bol (Patagonia, Argentina). Measurements of intensity of natural remanent magnetization left (NRMleft) after AF demagnetization versus intensity of anhysteric remanent magnetization gained (ARMgained) at the same peak were carried out on a set of samples. Two versions of a jackknife resampling scheme were used to get error estimates on the paleointensity. The pseudo-Thellier paleointensity records were compared with the authors previous results where the remanent magne- tization at 20mT (NRM20mT) has been normalized using the anhysteric remanent magnetization at 20mT (ARM20mT), the satu- ration of the isothermal remanent magnetization at 20mT (SIRM20mT) and the low field magnetic susceptibility (k) (Gogorza et al., 2006). The pseudo-Thellier record shows a reasonable agreement with the standard method of normalization (NRM20mT/ ARM20mT).

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