Lithospheric Magnetic Anomalies Research Articles

Lithospheric Magnetic Anomalies of the Polar Arctic According to CHAMP Satellite Data

Lithospheric Magnetic Anomalies of the Polar Arctic According to CHAMP Satellite Data

Volcanic thermal demagnetization of the Reiner Gamma magnetic anomaly

The age and formation mechanism of the Moon's lithospheric magnetic anomalies can give insight into the age and strength of the Moon's past global magnetic field. Here we focus on the magnetic anomaly Reiner Gamma, which is associated with a bright sinuous pattern on the surface known as a lunar swirl. We propose that portions of Reiner Gamma's magnetic source bodies were demagnetized by the heat from volcanic domes in the Marius Hills. We model one of the domes as an intrusive magma body and calculate its subsurface thermal evolution to constrain the volume and burial depth of the original magnetized source bodies. We infer that their burial depths do not exceed ~2 km, which is lower than the basalt thicknesses in this region (~3–4 km) and suggests that the source bodies were emplaced during the Moon's major episode of mare volcanism. The source depths and our inferred magnetization magnitudes are consistent with the magnetic source bodies being magnetized by a strong dynamo on the Moon for at least thousands of years at some point between ~3.5–3.9 Ga. In turn, the implied lack of a strong field during demagnetization implies the Moon's dynamo may have been merely episodically strong, or had permanently weakened at the time of dome formation between ~1.0–3.3 Ga.

The behavior of a lithospheric magnetization and magnetic field model

The Earth’s “lithosphere” is its outer shell, made up of the Earth’s crust and outermost mantle. The part of the Earth’s magnetic field that originates in the lithosphere consists of a superposition of magnetic anomalies with a broad spectrum of sizes and intensities, which arise from geological and tectonic features. The lithospheric magnetic field is known from surface observations, and on larger scales from above-surface measurements. The increase in recent decades of satellites dedicated to measuring the Earth’s magnetic field has improved significantly our models of the Earth’s magnetic environment. Based on these increasing observations, a number of comprehensive field models have been constructed, some of which focus solely on the lithosphere, such as the MF model series. We present a map of lithospheric magnetic anomalies at 400 km altitude, based on a vertically integrated magnetization model. This height was chosen because it is the expected orbital altitude of the Macau Science Satellite-1 (MSS-1) mission. The model presented herein indicates that the amplitude of the lithospheric anomalies at 400 km altitude is between −14.8 nT and 18.2 nT. This information is useful because it provides a reference for the lithospheric source of the Earth’s magnetic field that contributes to the magnetic measurements made from satellite instruments. The low inclination orbit of the MSS-1 mission will provide information that is sensitive to lateral variation within the lithosphere; these variations arise from plate tectonic features with longitudinal extent. In conclusion, the new MSS-1 mission will provide valuable information in detecting compositional variations in the lithosphere, and in delineating large-scale geological structures.

Lithospheric Magnetic Anomalies over Large Igneous Province Territories

Lithospheric Magnetic Anomalies over Large Igneous Province Territories

Observation and Study of Lithospheric Magnetic Anomalies on Profile SD in Mongolia

To understand the deep tectonic environment at the origin of strong earthquakes along the northern section of the North-South seismic belt and the central continental block of Mongolia, large-scale gravity and geomagnetic surveys and rock sample collection were carried out along the Suhbaatar-Ulaanbaatar-Dalandzadgad profile in Mongolia. The spatial distribution characteristics of the lithospheric magnetic field at 160 geomagnetic measuring points along the profile were then systematically analyzed and summarized. Based on the composition of the lithospheric magnetic field from different sources at different depths combined with the regional geological structure and collected rock sample lithology, the lithospheric magnetic field was further decomposed into different components—the basement, middle layer, and shallow surface—by the upward continuation method. The results show that these components have obvious zoning characteristics and that the lithospheric magnetic field distribution of the Suhbaatar-Ulaanbaatar-Dalandzadgad profile is related to the geological structure, rock lithology, seismic activity, natural remanent magnetization, and magnetic susceptibility. Many destructive earthquakes have occurred in the area where the lithospheric magnetic field changes dramatically, the lithologies are dominantly igneous, and the magnetic susceptibility and natural remanent magnetization are high. In contrast, the lithologies in the area with moderate variation in the lithospheric magnetic field are mostly sedimentary, the magnetic susceptibility and natural remanent magnetization are low, and destructive earthquakes are rare. Since the lithospheric magnetic field reflects the magnetic characteristics of the rocks above the Curie interface, its spatial distribution not only corresponds to the geological structure but also predicts the depth and location of faults. Therefore, it is significant to carry out geomagnetic surveys and rock sampling to analyze the characteristics of geological structures and research regional seismicity.

Reflection of Mantle-Plume Magmatism Processes in Lithospheric Magnetic Anomalies according to CHAMP Satellite Data

Reflection of Mantle-Plume Magmatism Processes in Lithospheric Magnetic Anomalies according to CHAMP Satellite Data

Lithospheric Magnetic Anomalies of the Eastern Part of the Arctic Ocean as Images of Tectonic Structures

Lithospheric Magnetic Anomalies of the Eastern Part of the Arctic Ocean as Images of Tectonic Structures

Possible Use of Satellite Geomagnetic Observations in Geological and Tectonic Studies of Lithosphere Structure

Features that reflect parameters of the geological and tectonic structure in lithospheric magnetic anomalies obtained using measurements by the CHAMP Earth satellite. A database on full vector module Ta and vertical component Za of the lithosphere’s magnetic field at satellite altitudes is created using a original technology for separating an anomaly magnetic field from measurements made by the CHAMP satellite. The positions of large-scale anomalies over the territories of the eastern Carpathians, the Tarim large igneous province, the Khatanga trap plume and the Kolyma–Omolon microcontinent was determined. Data analysis on the magnetization of the lower crust structures in conjunction with other geophysical means allows us to identify conditions of the origin and evolution of the mantle and the mantle–crust ore-forming systems that result in the formation of large and unique ore deposits. It is shown that quantitative geological information can be derived from magnetic data by clarification of the boundaries position of Precambrian provinces covered by Phanerozoic sediments. As a parameter reflecting the actual positions of structures of the lower crust and their physical properties, the lithospheric magnetic field can be used to distinguish, contour and correct them in addition to other geological and geophysical means.

Reflection of Large Tectonic Structures of the Eastern Part of the Arctic Ocean in the Lithospheric Magnetic Field

The article considers maps of the field of lithospheric magnetic anomalies—images of the deep structures of the Arctic Ocean—constructed from observations by the CHAMP satellite. The lithospheric magnetic anomalies corresponding to the most significant tectonic structures were revealed: Lomonosov Ridge, Mendeleev Ridge, Alpha Rise, and the Amundsen, Podvodnikov and Makarov basins. The distribution of the regional magnetic anomaly field, which is a complex set of positive and negative segments of various shapes and amplitudes, is discussed in light of the modern geological and geophysical views on the structure of the Arctic Ocean lithosphere. The constructed lithospheric magnetic field model indicates that in the region of conjugation with Eurasia the foot and the slope of Lomonosov Ridge are morphologically related to the continental margin, while the area of Mendeleev and Alpha elevations in central Arctic appears to be a single-block structure with a continental-type crust.

Correlation between lithospheric magnetic anomalies and tectonic structures in the Norwegian-Greenland region of the Arctic

The studies of the deep structure and tectonics of the Arctic are important for solving the fundamental problems of modern geodynamics and developing its natural resources. This region is also of interest from the geopolitical point of view, in particular, considering the boundaries of the marginal seas. Our study aims to investigate the lithospheric (anomalous) geomagnetic field in the Norwegian-Greenland region of the Arctic and to correlate the identified anomalies with tectonic structures located in the region under study. The database includes the CHAMP satellite measurements of the modulus of the total geomagnetic field vector (the satellite operated at the altitude of ~280 km). This article describes the satellite data processing method applied to distinguish between the lithospheric part and other components of the geomagnetic field. Map showing the total vector modulus of the lithospheric field has been constructed for the studied area. The article discusses the possible nature of the lithospheric magnetic anomalies and their relation to the processes that occur under the territory of Greenland. According to our interpretation of the maps, the geomagnetic field anomalies are related to the modern large-scale geological and tectonic structures located in the studied area. The obtained results can facilitate further comprehensive geological and geophysical studies and contribute to modeling of the evolution of the lithosphere.

Analysis of the lithospheric magnetic anomalies and tectonics in continental China and the adjacent regions using CHAMP satellite data

In this paper, the CHAMP satellite data from the last decade are used to map the lithospheric magnetic field in continental China at altitudes of 300 and 400 km using the spline function model technique. The results show that our model has higher amplitude than the spherical harmonic magnetic field model MF7. The resulting lithospheric anomaly distribution of continental China agrees with the geotectonic structure and crustal thermal structure. The magnetic anomaly distribution clearly indicates extrusion of the Tibetan Plateau towards the northeast and northwest directions. Northward movement is impeded by the relative rigid Tarim Basin featured with positive magnetic anomalies. The positive magnetic anomalies in Tarim basin extend to the northern Tibetan Plateau, suggesting that the southern part of Tarim Basin underthrusted the northern Tibetan Plateau.

Derivation and Error Analysis of the Earth Magnetic Anomaly Grid at 2 arc min Resolution Version 3 (EMAG2v3)

AbstractThe Earth Magnetic Anomaly Grid at 2 arc min resolution version 3, EMAG2v3, combines marine and airborne trackline observations, satellite data, and magnetic observatory data to map the location, intensity, and extent of lithospheric magnetic anomalies. EMAG2v3 includes over 50 million new data points added to NCEI's Geophysical Database System (GEODAS) in recent years. The new grid relies only on observed data, and does not utilize a priori geologic structure or ocean‐age information. Comparing this grid to other global magnetic anomaly compilations (e.g., EMAG2 and WDMAM), we can see that the inclusion of a priori ocean‐age patterns forces an artificial linear pattern to the grid; the data‐only approach allows for greater complexity in representing the evolution along oceanic spreading ridges and continental margins. EMAG2v3 also makes use of the satellite‐derived lithospheric field model MF7 in order to accurately represent anomalies with wavelengths greater than 300 km and to create smooth grid merging boundaries. The heterogeneous distribution of errors in the observations used in compiling the EMAG2v3 was explored, and is reported in the final distributed grid. This grid is delivered at both 4 km continuous altitude above WGS84, as well as at sea level for all oceanic and coastal regions.

Thermoremanence acquisition and demagnetization for titanomagnetite under lithospheric pressures

AbstractThe geological sources of large‐scale lithospheric magnetic field anomalies are poorly constrained. Understanding the magnetic behavior of rocks and minerals under the pressures and temperatures encountered at large crustal depths is particularly important in that task. The impact of lithospheric pressure is not well known and most of the time neglected in numerical models of the geological sources of magnetic anomalies. We present thermal remanent magnetization (TRM) acquisition and stepwise thermal demagnetization on synthetic titanomagnetite dispersed powder, within an amagnetic cell under hydrostatic pressure up to 1 GPa. TRM is measured after thermal cycling within a cryogenic magnetometer. Pressure‐dependent increase in the Curie temperature (initially in the 50–70°C range) is observed, mostly between 0.3 and 0.6 GPa, on the order of 20 K/GPa. TRM intensity also increases with pressure up to 200% at 675 MPa, although the pressure variation with temperature inside the cell complicates the interpretation.

Combining CHAMP and Swarm Satellite Data to Invert the Lithospheric Magnetic Field in the Tibetan Plateau

CHAMP and Swarm satellite magnetic data are combined to establish the lithospheric magnetic field over the Tibetan Plateau at satellite altitude by using zonal revised spherical cap harmonic analysis (R-SCHA). These data are integrated with geological structures data to analyze the relationship between magnetic anomaly signals and large-scale geological tectonic over the Tibetan Plateau and to explore the active tectonic region based on the angle of the magnetic anomaly. Results show that the model fitting error is small for a layer 250–500 km high, and the RMSE of the horizontal and radial geomagnetic components is better than 0.3 nT. The proposed model can accurately describe medium- to long-scale lithospheric magnetic anomalies. Analysis indicates that a negative magnetic anomaly in the Tibetan Plateau significantly differs with a positive magnetic anomaly in the surrounding area, and the boundary of the positive and negative regions is generally consistent with the geological tectonic boundary in the plateau region. Significant differences exist between the basement structures of the hinterland of the plateau and the surrounding area. The magnetic anomaly in the Central and Western Tibetan Plateau shows an east–west trend, which is identical to the direction of the geological structures. The magnetic anomaly in the eastern part is arc-shaped and extends along the northeast direction. Its direction is significantly different from the trend of the geological structures. The strongest negative anomaly is located in the Himalaya block, with a central strength of up to −9 nT at a height of 300 km. The presence of a strong negative anomaly implies that the Curie isotherm in this area is relatively shallow and deep geological tectonic activity may exist.

Application of the data on the lithospheric magnetic anomalies in the problem of recognizing the earthquake prone areas

For the first time, an attempt is made to apply the data on the lithospheric magnetic anomalies of the Earth for determining the areas prone to strong earthquakes by means of the pattern recognition algorithms. The Caucasian region with the threshold magnitude of the strong earthquakes M 0 = 6 is considered. It is established that the data on the lithospheric magnetic anomalies are informative from the standpoint of recognizing the strong earthquake prone areas. Application of these data is promising for solving the similar problems for different seismically active regions.

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.

Lithospheric magnetic anomalies in the territory of Siberia (from measurements by the CHAMP satellite)

The position of lithospheric magnetic anomalies, detected in total magnetic intensity and the vertical component of the magnetic field, has been determined for Siberia using data from the CHAMP satellite. The paper describes the technique for the satellite data processing and the ways of recognition of regional lithospheric magnetic anomalies from satellite-measured values of the total geomagnetic field, which are obtained from several sources (external and internal with respect to the Earth’s surface). Maps of magnetic-field anomalies of different scales have been constructed for several regions of Siberia depending on the method of areal averaging. The possible geologic and physical nature of the magnetic anomalies and their relationship with deep-seated crustal structures are considered. Preliminary interpretation of the magnetic-field maps shows that the anomalies are connected with the present-day large geologic and geophysical elements of the basement. The features of the lithospheric magnetic field, as a parameter reflecting the present position of tectonic structures and their physical properties, can be used for their contouring in combination with other geological and geophysical methods.

ЛИТОСФЕРНЫЕ МАГНИТНЫЕ АНОМАЛИИ НА ТЕРРИТОРИИ СИБИРИ (по измерениям спутника СНАМР)

ЛИТОСФЕРНЫЕ МАГНИТНЫЕ АНОМАЛИИ НА ТЕРРИТОРИИ СИБИРИ (по измерениям спутника СНАМР)

Lithospheric magnetic anomalies in Southeast Asia from CHAMP data

New possibilities for the interpretation of long-period magnetic anomalies were opened up by the construction of their first satellite-based maps. The anomalies are due to lateral variations in the magnetic properties and thickness of the deep layers of magnetized rocks. The CHAMP orbital geometry is suitable for providing daily information on the magnetic field over the almost uniform grid above the Earth’s surface. These measurements favor calculation of the spherical harmonic model of the main magnetic field for each day separately. The distribution of regional lithospheric anomalies derived from the satellite measurements over the territory of Southeast Asia is analyzed. These lithospheric anomalies agree with the zonal-block crustal structure of this region revealed from geological assessments.