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1

Numerical investigations of the spreading-rate dependence of anomalous skewness of marine magnetic anomalies due to seafloor spreading  

NASA Astrophysics Data System (ADS)

An improved understanding of the spreading-rate dependence of anomalous skewness from magnetic anomalies due to seafloor spreading will allow for better constraints on apparent polar wander paths, plate reconstructions, and the magnetic and thermal structure of oceanic lithosphere. Anomalous skewness, which is the difference between experimentally determined skewness and skewness expected from simple magnetization models with vertical reversal boundaries, has been observed to vary as a function of spreading rate, decreasing with increasing spreading rate and becoming negligible at spreading half-rates exceeding about 55 mm/a [Roest et al. 1992; Dyment et al. 1994]. In our analysis, we determine model-based estimates of anomalous skewness as a function of spreading rate for each anomaly. We do so by creating many synthetic profiles using the model of Dyment and Arkani-Hamed (1995), which was specifically constructed to produce anomalies with anomalous skewness consistent with observed anomalies. We experimentally determine the phase shift that causes the resulting synthetic magnetic anomaly to best match a profile produced from a "standard" model for anomalies due to seafloor spreading that assumes simple vertical reversal boundaries. We present results for those anomalies between 12r and 33r from which reliable paleomagnetic poles may potentially be determined. Differences in anomalous skewness for different anomalies determined at the same spreading rate can be attributed to the sequence effect, that is, the effect on the shape of a magnetic anomaly above seafloor of a single polarity chron of the magnetization of neighboring blocks of lithosphere magnetized during other chrons. We find that the sequence effect is smaller than we expected with the largest difference being between the results for anomaly 25r and those for anomaly 33r, for which the difference is 14 degrees at a 10 mm/a half-rate. Results for other anomalies lie between these two. We also infer a small outward displacement of the magnetic anomalies, which-like anomalous skewness-decreases with increasing spreading rate and vanishes at half rates exceeding 55 mm/a. We find that results obtained trying to find the best match to the synthetic magnetic anomaly profile are generally similar to results obtained when using the balanced-shoulder criterion for when an anomaly has been successfully deskewed. The values of chron-specific (or anomaly-specific) anomalous skewness that we have determined can be used to reduce the number of adjustable parameters in the determination of paleomagnetic poles from skewness data from three to two, to simply the latitude and longitude of the paleomagnetic pole. Implications for the northward motion of the Pacific Plate will be discussed.

Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

2011-12-01

2

Toward Quantifying the Spreading-Rate Dependence of Anomalous Skewness of Marine Magnetic Anomalies due to Seafloor Spreading  

NASA Astrophysics Data System (ADS)

In past work, reliable paleomagnetic poles have been determined from skewness data by solving for a single additional adjustable parameter, anomalous skewness, assumed to be independent of spreading rate [Petronotis et al. 1992, 1994; Petronotis & Gordon 1999]. Nonetheless, analysis of anomalies in several ocean basins indicate that anomalous skewness depends on spreading rate for spreading half rates less than ?50 mm/yr [Roest et al., 1992; Dyment et al. 1994]. To facilitate investigation of the influence of spreading-rate dependent anomalous skewness on the determination of paleomagnetic poles determined from skewness, we build on the model for marine magnetic anomalies due to seafloor spreading of Dyment and Arkani-Hamed [1995]. We use this model to estimate anomalous skewness as a function of spreading rate for many anomalies. Synthetic magnetic anomaly profiles for oceanic lithosphere with sloping curving reversal boundaries were produced by forward modeling. Anomalous skewness values for chrons 25n to 33r were visually determined at various spreading rates using two approaches: balancing the shoulders of an anomaly corresponding to a single chron and best matching an anomaly corresponding to a single chron to a synthetic anomaly determined assuming vertical reversal boundaries. The new results may facilitate the determination of paleomagnetic poles from less widely distributed crossings of a magnetic anomaly than were used before. Further implications for determination of paleomagnetic poles for the Pacific plate will be discussed.

Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

2010-12-01

3

A New Seafloor Spreading Model of the Red Sea: Magnetic Anomalies and Plate Kinematics  

NASA Astrophysics Data System (ADS)

A high resolution aeromagnetic survey over the Saudi Arabian side of the Red Sea confirms the existence of consistent magnetic anomaly patterns, continuous from 16 to 24°N, and episodic up to 28°N, typical of slow to ultraslow spreading centers. The older Saudi-Sudanese aeromagnetic survey shows that these anomalies are symmetrical between 18 and 23°N. The strong, short-wavelength anomalies over the central trough south of 24°N have long been identified as Chrons 1 to 3 (0-5 Ma). By contrast, the weaker, longer-wavelength anomalies over adjacent sediment-covered areas do not fit standard magnetic anomaly models. The abrupt basement deepening from ~ 1.5 km in the central trough to ~ 5 km beneath the sediments partly accounts for the lower amplitude but not for the lack of short wavelengths. Other spreading centers also lack short-wavelength, high-amplitude magnetic anomalies where covered by thick sediments (Andaman Basin, Juan de Fuca Ridge). We interpret this to reflect the absence of a well-defined layer of pillow lavas, whose emplacement is hampered by rapid, abundant sedimentation. The formation of dykes and sills instead of extrusive lavas results in weaker, less coherent magnetization, generating longer-wavelength anomalies. We test this inference by removing the extrusive basalt contribution from a slow spreading center crustal magnetization model. The computed magnetic anomalies fit well with the shape and amplitude of the anomalies observed in the Red Sea. Two major long-wavelength anomalies are dated at 10-11 Ma (Chron 5) and 14-15 Ma (Chron 5B), implying seafloor spreading back to at least 15 Ma and constraining plate-kinematic reconstructions. Beyond being a key to the geological evolution of the Red Sea, these results emphasize that oceanic crust may exist without clear, short wavelength magnetic anomalies, particularly at the onset of seafloor spreading, when abundant sedimentation may preclude the formation of pillow lavas. The location of many inferred ocean-continent boundaries, particularly beneath thick evaporite sequences, should therefore be revisited, alleviating the need for 'transitional' crust and allowing for a tighter fit of continents in initial reconstructions.

Dyment, J.; Tapponnier, P.; Afifi, A. M.; Zinger, M. A.; Franken, D.; Muzaiyen, E.

2013-12-01

4

Investigation of spreading center ecolution by joint inversion of seafloor magnetic anomaly and tectonic fabric data  

NASA Technical Reports Server (NTRS)

Spreading center segments that have experienced a complex tectonic history including rift propagation may have a complicated signature in bathymetric and magnetic anomaly data. To gain insight into the history of such regions, we have developed techniques in which both the magnetic anomaly patterns and seafloor fabric trends are predicted theoretically, and the combined predictions are compared numerically with the data to estimate best fitting parameters for the propagation history. Fitting functions are constructed to help determine which model best matches the digitized fabric and magnetic anomaly data. Such functions offer statistical criteria for choosing the best fit model. We use this approach to resolve the propagation history of the Cobb Offset along the Juan de Fuca ridge. In this example, the magnetic anomaly data prove more useful in defining the geometry of the propagation events, while the fabric, with its greater temporal resolution, is more useful for constraining the rate of propagation. It thus appears that joint inversion of magnetic and seafloor fabric data can be valuable in tectonic analyses.

Shoberg, Tom; Stein, Seth

1994-01-01

5

Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain  

E-print Network

Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However from Australia with Greater India during initial breakup at ~130 Ma, then rifted from India following

Granot, Roi

6

Magnetic anomalies  

NASA Astrophysics Data System (ADS)

The implications and accuracy of anomaly maps produced using Magsat data on the scalar and vector magnetic field of the earth are discussed. Comparisons have been made between the satellite maps and aeromagnetic survey maps, showing smoother data from the satellite maps and larger anomalies in the aircraft data. The maps are being applied to characterize the structure and tectonics of the underlying regions. Investigations are still needed regarding the directions of magnetization within the crust and to generate further correlations between anomaly features and large scale geological structures. Furthermore, an increased data base is recommended for the Pacific Ocean basin in order to develop a better starting model for Pacific tectonic movements. The Pacific basin was large farther backwards in time and subduction zones surround the basin, thereby causing difficulties for describing the complex break-up scenario for Gondwanaland.

Harrison, C. G. A.

1983-04-01

7

Updated interpretation of magnetic anomalies and seafloor spreading stages in the South China Sea - Implications for the Tertiary tectonics of Southeast Asia  

Microsoft Academic Search

An updated interpretation of the magnetic data of the South China Sea is presented, and its implications for the evolution of the South China Sea spreading ridge are discussed. A new identification of magnetic lineations in the basin is described. The kinematic parameters of spreading are then computed from the fit of the magnetic isochrons, and the characteristics of the

Anne Briais; Philippe Patriat; Paul Tapponnier

1993-01-01

8

Magnetic anomalies. [Magsat studies  

NASA Technical Reports Server (NTRS)

The implications and accuracy of anomaly maps produced using Magsat data on the scalar and vector magnetic field of the earth are discussed. Comparisons have been made between the satellite maps and aeromagnetic survey maps, showing smoother data from the satellite maps and larger anomalies in the aircraft data. The maps are being applied to characterize the structure and tectonics of the underlying regions. Investigations are still needed regarding the directions of magnetization within the crust and to generate further correlations between anomaly features and large scale geological structures. Furthermore, an increased data base is recommended for the Pacific Ocean basin in order to develop a better starting model for Pacific tectonic movements. The Pacific basin was large farther backwards in time and subduction zones surround the basin, thereby causing difficulties for describing the complex break-up scenario for Gondwanaland.

Harrison, C. G. A.

1983-01-01

9

MODMAG, a MATLAB program to model marine magnetic anomalies  

NASA Astrophysics Data System (ADS)

Identifying marine magnetic anomalies is the most common way to date the ocean floor. Although the technique of magnetic anomaly identification has not changed since the 1960s, a forward modeling software that is easy to use, fast and automatic, without abstruse parameters, was lacking. We present a user-friendly MATLAB-based interface, called MODMAG, which allows one to perform forward modeling of marine magnetic anomalies resulting from several successive spreading periods with different spreading rates and asymmetric spreading possibly alternating with axial jumps. The main advantage of our program is that the management of the magnetized bodies resulting from such successive spreading periods is not the user's responsibility. Spreading parameters can be set easily for the picking of the marine magnetic anomalies. Non-specialist geophysicists or geologists can therefore easily identify marine magnetic anomalies with the help of MODMAG.

Mendel, Véronique; Munschy, Marc; Sauter, Daniel

2005-06-01

10

Methods used to identify seafloor spreading magnetic anomalies and to establish their relationship with the top of the basement topography in the Argentine continental margin between 35° S and 48° S  

NASA Astrophysics Data System (ADS)

This paper discusses some methods for better identification of the spreading seafloor magnetic anomalies in the region between 35° S and 48° S at the outer edge of the continental margin of Argentina. In the area of Rio de la Plata craton and Patagonia Argentina, there is an extensional volcanic passive margin. This segment of the Atlantic continental margin is characterized by the existence of seismic reflectors sequences that lean toward the sea (seaward dipping reflectors - SDRs). These sequences of seismic reflectors, located in the transitional-continental basement wedge, are portrayed in seismic profiles as an interference pattern interpreted as basalt flows intercalated with sedimentary layers, and its origin is ascribed to volcanism occurred during the Early Cretaceous. The magnetic response of SDRs is in the area of the magnetic anomaly G (Rabinowitz and LaBrecque, 1979). Magnetic alignments are highlighted on a map by superimposing total field anomaly semitransparent layer of calculated numerical curvature. This method allows a regional identification of the most prominent alignments. It is convenient to calculate the curvature in the direction perpendicular to the magnetic alignments. The identification of seafloor spreading magnetic anomalies located in the eastern margin helps in the knowledge of the history of the Atlantic Ocean opening. M series magnetic alignments: M5n, M3n M0r (between 132 and 120 Ma) were identified in the analyzed area. The roughness of the top of the oceanic basement presents a contrast of amplitudes, in a wavelength range between about 4 km and 6 km, with the corresponding amplitudes in the area of the transitional crust. This contrast of amplitudes can be detected using spectral methods, especially short Fourier transform. The quantitative evaluation of the spectral energy density allowed the identification of wave numbers characterizing oceanic basement area and thus perform subsequent filtering of the signal with wavelengths found with the spectral method. The top of basement roughness was quantified using the root mean square (RMS), in sections of about 2 km, of residues between the depth of the basement top and first-degree polynomial that best fitted the sections. The spreading seafloor magnetic alignments are on oceanic crust area identified by the point of view of the roughness analysis. The combined use of the methods that we have developed on the magnetic surveys in the study area, allowed us to improve the layout of the magnetic alignments and identify the transition between oceanic and continental crust.

Abraham, D. A.; Ghidella, M. E.; Tassone, A.; Paterlini, M.; Ancarola, M.

2013-05-01

11

Magnetic Anomalies over Iceland.  

PubMed

An aeromagnetic survey of Iceland reveals broad anomalies of large amplitude over zones of recent volcanic activity. The source of the anomalies is ascribed to large masses of basalt that have been coherently remagnetized by intrusive heating. A simple correlation of the Icelandic anomalies with those of the ocean floor therefore appears unjustified. PMID:17836657

Serson, P H; Hannaford, W; Haines, G V

1968-10-18

12

Magnetic anomalies northeast of Shatsky Plateau  

E-print Network

trending Japanese lineations to form a magnetic bight north of Shatsky Plateau. The bight is interpreted to be evidence of a ridge-ridge-ridge (RRR) triple junction which ex1sted from about 124 MYBP (anomaly MlON time) into the Cretaceous Duiet Per1od.... A r1dge-fault-fault (RFF) triple junction existed at Shatsky Plateau for about 17 MY (anomalies Mlg-MlDN t1me). The plate boun- daries were: a Pacif1c-Farallon (P-F) transform fault, a Pacific-Kula (P-K) spreading ridge, and a Kula-Farallon (K...

Risch, David Lawrence

2012-06-07

13

Implications for the South Atlantic early breakup and seafloor spreading from joint interpretation of magnetic anomaly maps and seaward-dipping reflector sequences (SDRS) visible in conjugated reflection seismic sections  

NASA Astrophysics Data System (ADS)

The late history of the South Atlantic passive margin evolution is investigated in the view of interlaced magnetic anomalies related to seafloor spreading lineations and anomalies caused by seaward-dipping reflector sequences (SDRS). Our identification of previously unknown pre-M5n lineations in marine magnetic data offshore Argentina now makes the lineation pattern more complete and most importantly comparable and nearly symmetrical to the conjugated area offshore South Africa. Therefore, we can now compare several sets of published South Atlantic reconstruction poles to our new pre-M5n lineations off Argentina and their equivalents off South Africa. The analysis of the symmetry of SDRS and particularly of their along-margin extension further constrains the choice of possible reconstruction poles for the earliest opening phases. The interpretation of pre-M5n lineations also defines the exact time (M9r) of the termination of excess breakup related volcanic activity and the transition to "normal" seafloor spreading. This is compared to absolute radiometric ages from Parana/Etendeka flood basalts. The volcanic activity related to the southernmost volcanic margin segments falls approximately into the same time window as the continental flood basalt activity. Unfortunately, more detailed conclusions suffer seriously from an ongoing discussion about the absolute ages of the pre-M0r lineations in different versions of polarity timescales. New models for the magnetic response of SDRS reveal a high variability within the wedges on either side of the Atlantic and between the conjugated margins. Former identifications of anomaly M11r off Cape Town have already been questioned and can now be shown to be caused by structural or magnetization variations within SDRS.

Schreckenberger, Bernd; Koopmann, Hannes; Franke, Dieter; Schnabel, Michael

2013-04-01

14

Magnetic Anomalies in the Enderby Basin, the Southern Indian Ocean  

NASA Astrophysics Data System (ADS)

Magnetic anomalies in the Southern indian Ocean are vital to understanding initial breakup process of Gondwana. However, seafloor age estimated from magnetic anomalies still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the initial breakup process of Gondwana, vector magnetic anomaly data as well as total intensity magnetic anomaly data obtained by the R/V Hakuho-maru and the icebreaker Shirase in the Enderby Basin, Southern Indian Ocean, are used. The strikes of magnetic structures are deduced from the vector magnetic anomalies. Magnetic anomaly signals, most likely indicating Mesozoic magnetic anomaly sequence, are obtained almost parallel to the west of WNW-ESE trending lineaments just to the south of Conrad Rise inferred from satellite gravity anomalies. Most of the strikes of magnetic structures indicate NNE-SSW trends, and are almost perpendicular to the WNW-ESE trending lineaments. Mesozoic sequence magnetic anomalies with mostly WNW-ESE strikes are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and Gunnerus Ridge. Magnetic anomalies originated from Cretaceous normal polarity superchron are found in these profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. However Mesozoic sequence magnetic anomalies are only observed in the west side of the WNW-ESE trending lineaments just to the south of Conrad Rise and not detected to the east of Cretaceous normal superchron signals. These results show that counter part of Mesozoic sequence magnetic anomalies in the south of Conrad Rise would be found in the East Enderby Basin, off East Antarctica. NNE-SSW trending magnetic structures, which are similar to those obtained just to the south of Conrad Rise, are found off East Antarctica in the East Enderby Basin. However, some of the strikes show almost E-W orientations. These suggest complicated ridge reorganization occurred during initial breakup of Gondwana in the Enderby Basin.

Nogi, Y.; Sato, T.; Hanyu, T.

2013-12-01

15

Magnetic Anomaly Lineations in the Gulf of Aden  

NASA Astrophysics Data System (ADS)

We present the magnetic anomaly lineations in the Gulf of Aden to expose the seafloor spreading history. The Gulf of Aden is a young ocean basin formed by the rifting of Arabia Plate away from Somalia Plate. The Arabian plate moves away from Somalia Plate in an NE direction, at a rate of about 2 cm/yr. The rifting started from Oligocene (Bosworth et al., 2005). Seafloor spreading started at about 20 Ma in the eastern part of the Gulf of Aden (Fournier et al., 2010) and propagated westward into the Arabia-Africa continent (Manighetti et al., 1997). It reached the Afar hotspot area about 10 Ma (Audin et al., 2001). The spreading system continues to interact with the hotspot up to the present. Tamsett and Searle (1988) exposed that strike of segmentations of the spreading centers in the Gulf of Aden is NW-SE, although the trend of the spreading system is ENE. We examined magnetic anomaly data collected in the cruises by R/V L'Atalante in 1995 and R/V Hakuho-maru from 2000 to 2001 as well as those collected in other cruises. Elongated negative magnetic anomalies, which amplitude are more than 500 nT, are observed over the spreading centers. Most of the elongated anomalies are parallel with the spreading centers. The elongated magnetic anomalies west of 46 30'E have an E-W trend around the spreading centers. Several discontinuities in the magnetic anomaly contour map illustrate the position of the fracture zones concealed by sediments. Most of magnetic anomaly lineations east of 46 30'E have an N60-65 W strike. Our identification of magnetic anomaly lineations indicates a symmetric seafloor spreading with a spreading rate of about 1.0 cm/yr, although Leroy et al. (2004) showed an asymmetric seafloor spreading of the Sheba Ridge, east of our study area. The kinematics of the Arabia plate changed about 5 Ma, but our results did not show any coeval change in spreading rates of the spreading system in the Gulf of Aden.

Noguchi, Y.; Nakanishi, M.; Tamaki, K.; Fujimoto, H.; Huchon, P.; Leroy, S.; Styles, P.

2012-12-01

16

Spreading rate dependence of gravity anomalies along oceanic transform faults.  

PubMed

Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

2007-07-12

17

An Interpretation of the Seafloor Spreading History of the West Enderby Basin between Initial Breakup of Gondwana and Anomaly C34  

Microsoft Academic Search

The seafloor spreading evolution in the Southern Indian Ocean is key to understanding the initial breakup of Gondwana. We summarize the structural lineaments deduced from the GEOSAT 10?Hz sampled raw altimetry data as well as satellite derived gravity anomaly map and the magnetic anomaly lineation trends from vector magnetic anomalies in the West Enderby Basin, the Southern Indian Ocean. The

Yoshifumi Nogi; Kumiko Nishi; Nobukazu Seama; Yoichi Fukuda

2004-01-01

18

Satellite magnetic anomalies over subduction zones - The Aleutian Arc anomaly  

NASA Technical Reports Server (NTRS)

Positive magnetic anomalies seen in MAGSAT average scalar anomaly data overlying some subduction zones can be explained in terms of the magnetization contrast between the cold subducted oceanic slab and the surrounding hotter, nonmagnetic mantle. Three-dimensional modeling studies show that peak anomaly amplitude and location depend on slab length and dip. A model for the Aleutian Arc anomaly matches the general trend of the observed MAGSAT anomaly if a slab thickness of 7 km and a relatively high (induced plus viscous) magnetization contrast of 4 A/m are used. A second source body along the present day continental margin is required to match the observed anomaly in detail, and may be modeled as a relic slab from subduction prior to 60 m.y. ago.

Clark, S. C.; Frey, H.; Thomas, H. H.

1985-01-01

19

Crustal structure interpreted from magnetic anomalies  

NASA Technical Reports Server (NTRS)

This review, discusses publications during the last quadrennium (1987-1990) that used aeromagnetic data, marine magnetic data, satellite magnetic data, and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies. The publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies, particularly in deep crustal magnetization, exploration for hydrocarbons, and inversion of marine magnetic anomalies. Interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard.

Phillips, Jeffrey D.; Reynolds, Richard L.; Frey, Herbert

1991-01-01

20

New continental margin magnetic anomalies of East Antarctica  

NASA Astrophysics Data System (ADS)

Over the past decade, Australian, Norwegian and Russian marine surveys have collected integrated seismic, gravity and magnetic data in the southern Indian Ocean. The more than 350,000 line-km of new airborne and marine magnetic observations for the East Antarctic continental margin have been compiled into an improved definition of crustal magnetic anomaly patterns. This compilation provides important new constraints on the breakup processes and igneous activity related to the formation of the passive margin of East Antarctica. The eastern sector of the map from Bruce Rise in the west to the D'Urville Sea in the east is largely dominated by seafloor spreading magnetic anomalies. The 'Adélie Rift Block' of highly stretched and extensively faulted continental crust is associated with a smooth anomaly fabric. Abrupt magnetic anomaly changes along the oceanic-continent transition in the Cooperation Sea including the Enderby Basin Anomaly extend for more than 1680 km from the Kerguelen Plateau towards the Cosmonaut Sea. Three sectors of the East Antarctic continental margin exhibit pronounced disparities in the anomaly patterns that strongly suggest different modes of seafloor formation. Strong positive seafloor magnetic anomalies mark the southern margin of the Kerguelen Plateau, the Maud Rise and adjacent areas in the Riiser-Larsen Sea. The new compilation suggests that at least 300 km of the Enderby Basin and Shackleton Basin may be part of the Cretaceous Kerguelen Volcanic Province and possibly maps an abandoned 'fossil' spreading center in the central Enderby Basin. The majority of the published age models for the Enderby Basin and "Australian sector" of the East Antarctic margin are not in agreement with the structural grain of magnetic anomalies in the newly compiled map.

Golynsky, A. V.; Ivanov, S. V.; Kazankov, A. Ju.; Jokat, W.; Masolov, V. N.; von Frese, R. R. B.

2013-02-01

21

Regional magnetic anomaly constraints on continental rifting  

NASA Technical Reports Server (NTRS)

Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

1985-01-01

22

The source of marine magnetic anomalies  

NASA Technical Reports Server (NTRS)

The Vine-Matthews hypothesis (1963) is examined. This hypothesis suggests that oceanic rocks become polarized in the direction of the magnetic field at the time of their formation, thus recording the polarity history of the earth's magnetic field. This produces the lineated magnetic anomalies on either side of the midoceanic ridge crests. The strength of these magnetic anomalies is studied to determine the strength of magnetization. Indirect determinations of the magnetization intensity of the oceanic crust and direct observations of the oceanic crust are compared. It is found that the average magnetization of a 6-km thick oceanic crust is 1.18 A/m.

Harrison, Christopher G. A.

1987-01-01

23

Marine Magnetic Anomalies and the Reconstruction of the World  

NASA Technical Reports Server (NTRS)

Until the middle of the 20th century little was known about magnetic anomalies in the oceans. Then it was discovered that there are relatively large anomalies in most of the oceans and they were unrelated to any geological structure known at that time. In the early 1950's large anomalies had been found over the Mid-Atlantic Ridge, and linear anomalies over the eastern continental shelf of North America and, shortly after that, off the west coast. A survey of the ridge south of Iceland showed that the anomalies were linear, parallel to the ridge axis, and symmetrical about the axis. Using the theory that the anomalies were caused by geomagnetic field reversals and seafloor spreading it was possible to greatly extend the time scale of geomagnetic reversals, to determine the velocity of seafloor spreading and estimate the time of opening of the North Atlantic. Lamont had a world-wide collection of marine magnetic profiles. These were used, systematically, to determine the positions of most of the land masses of the world since the beginnings of the world's present oceans.

Heirtzler, James R.; Smith, David E. (Technical Monitor)

2000-01-01

24

The magnetic anomaly of the Ivreazone  

NASA Technical Reports Server (NTRS)

A magnetic field survey was made in the Ivreazone in 1969/70. The results were: significant anomaly of the vertical intensity is found. It follows the basic main part of the Ivrea-Verbano zone and continues to the south. The width of the anomaly is about 10 km, the maximum measures about +800 gamma. The model interpretation shows that possibly the anomaly belongs to an amphibolitic body, which in connection with the Ivrea-body was found by deep seismic sounding. Therefore, the magnetic anomaly provides further evidence for the conception that the Ivrea-body has to be regarded as a chip of earthmantle material pushed upward by tectonic processes.

Albert, G.

1979-01-01

25

US Aeromagnetic and Satellite Magnetic Anomaly Comparisons  

NASA Technical Reports Server (NTRS)

Scalar aeromagnetic data obtained by the U.S. Naval Oceanographic Office (NOO) Vector Magnetic Survey of the conterminous U.S. were screened for periods of intense diurnal magnetic activity and reduced to anomaly form, filtered, and continued upward. A number of correlations between the NOO, POGO and preliminary MAGSAT data are evident at satellite elevations, including a prominent transcontinental magnetic high which extends from the Anadarko Basin to the Cincinnati Arch. The transcontinental magnetic high is breached by negative anomalies located over the Rio Grande Rift and Mississippi River Aulacogen. Differentially reduced-to-pole NOO and POGO magnetic anomaly data show that the transcontinental magnetic high corresponds to a well-defined regional trend of negative free-air gravity and enhanced crustal thickness anomalies.

Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W. (principal investigators); Sexton, J. L.

1984-01-01

26

Reduction of satellite magnetic anomaly data  

NASA Technical Reports Server (NTRS)

Analysis of global magnetic anomaly maps derived from satellite data is facilitated by inversion to the equivalent magnetization in a constant thickness magnetic crust or, equivalently, by reduction to the pole. Previous inversions have proven unstable near the geomagnetic equator. The instability results from magnetic moment distributions which are admissible in the inversion solution but which make only small contribution to the computed values of anomaly field. Their admissibility in the solution could result from noisy or incomplete data or from small poorly resolved anomalies. The resulting magnetic moments are unrealistically large and oscillatory. Application of the method of principal components (e.g. eigenvalue decomposition and selective elimination of less significant eigenvectors) is proposed as a way of overcoming the instability and the method is demonstrated by applying it to the region around the Bangui anomaly in Central Africa.

Slud, E. V.; Smith, P. J.; Langel, R. A.

1984-01-01

27

Global magnetic anomaly and aurora of Neptune  

NASA Technical Reports Server (NTRS)

The large offset and tilt of Neptune's dipole magnetic field combine to create a global magnetic anomaly, analogous to but much more important than earth's South Atlantic Anomaly. Energetic particle precipitation loss within the Neptune anomaly creates 'atmospheric drift shadows' within which particle fluxes are greatly reduced. The energetic particle dropout observed by Voyager near closest approach occurred near the predicted times when Voyager passed within the atmospheric drift shadow. Extremely soft, structured bursts of ions and electrons within the drift shadow may result from plasma wave-induced pitch angle scattering of trapped particles confined near the magnetic equator. The dropout does not necessarily imply that Voyager passed through an earth-like discrete auroral zone, as earlier reported. The ion and electron fluxes observed within the dropout period correspond to particles that must precipitate to Neptune's atmosphere within the anomaly region. This anomaly precipitation can account for a major portion of the ultraviolet emissions previously identified as Neptune aurora.

Cheng, Andrew F.

1990-01-01

28

Global magnetic anomaly and aurora of Neptune  

SciTech Connect

The large offset and tilt of Neptune's dipole magnetic field combine to create a global magnetic anomaly, analogous to but much more important than Earth's South Atlantic Anomaly. Energetic particle precipitation loss within the Neptune anomaly creates atmospheric drift shadows within which particle fluxes are greatly reduced. The energetic particle dropout observed by Voyager near closest approach occurred near the predicted times when Voyager passed within the atmospheric drift shadow. Extremely soft, structured bursts of ions and electrons within the drift shadow may result from plasma wave-induced pitch angle scattering of trapped particles confined near the magnetic equator. The dropout does not necessarily imply that Voyager passed through an Earth-like discrete auroral zone, as earlier reported. The ion and electron fluxes observed within the dropout period correspond to particles that must precipitate to Neptune's atmosphere within the anomaly region. This anomaly precipitation can account for a major portion of the ultraviolet emissions previously identified as Neptune aurora.

Cheng, A.F. (Johns Hopkins Univ., Laurel, MD (USA))

1990-09-01

29

Satellite-altitude horizontal magnetic gradient anomalies used to define the Kursk Magnetic Anomaly  

NASA Astrophysics Data System (ADS)

The Kursk Magnetic Anomaly (KMA), Russia, is one of the world's largest magnetic anomalies. We used satellite altitude horizontal gradient magnetic anomaly data to study this feature. There are two main objectives of our research; the first, to determine if the technique of the horizontal magnetic anomaly gradient analysis can be applied to CHAMP satellite altitude data to define the outline of the source of the Kursk Magnetic Anomaly (KMA). Another objective is to use the ten years of CHAMP data to reproduce the horizontal magnetic anomaly gradient data that will be measured by the two lower orbiting ESA/Swarm mission. We will be able to evaluate the application of these newer satellite altitude data for studying large areas with significant crustal magnetization. While we have acquired sufficient CHAMP orbital data to compute a horizontal gradient anomaly map from these ten years of data; the future ESA/Swarm mission will, however, allow us to compute directly the horizontal magnetic anomaly without orbital altitude and/or magnetic secular variations; however the east-west gradient that the Swarm is measuring will minimize, but not eliminate, the difference in external fields between the two lower satellites. One will still need to use relatively quiet data (e.g., Kp < 1) for crustal field mapping. Our results, developed from interpreting the satellite horizontal magnetic anomaly data, indicate that the source of the KMA is bowl shaped body open to the northwest covering an area of approximately 190,000 km2.

Taylor, P. T.; Kis, K. I.; Wittmann, G.

2014-10-01

30

Inversion of marine magnetic anomalies by deconvolution  

E-print Network

large block size, it is demonstrated that the deconvolution technique can retrieve the equivalent source function when the anomaly due to each source block is clearly defined. The model profiles used were 115 samples in length, with a sample... magnetization structure. used to calculate the anomaly. 38 CHAPTER V RESOLUTION OF THE INVERSION TECHNIQUE The ability of the inversion procedure to recover short wavelength source blocks is limited by two factors; the sample interval of the magnetic...

Harry, Dennis Lee

2012-06-07

31

Regional magnetic anomaly constraints on continental breakup  

SciTech Connect

Continental lithosphere magnetic anomalies mapped by the Magsat satellite are related to tectonic features associated with regional compositional variations of the crust and upper mantle and crustal thickness and thermal perturbations. These continental-scale anomaly patterns when corrected for varying observation elevation and the global change in the direction and intensity of the geomagnetic field show remarkable correlation of regional lithospheric magnetic sources across rifted continental margins when plotted on a reconstruction of Pangea. Accordingly, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans.

von Frese, R.R.B.; Hinze, W.J.; Olivier, R.; Bentley, C.R.

1986-01-01

32

CHAMP Magnetic Anomalies of the Antarctic Crust  

NASA Technical Reports Server (NTRS)

Regional magnetic signals of the crust are strongly masked by the core field and its secular variations components and hence difficult to isolate in the satellite measurements. In particular, the un-modeled effects of the strong auroral external fields and the complicated- behavior of the core field near the geomagnetic poles conspire to greatly reduce the crustal magnetic signal-to-noise ratio in the polar regions relative to the rest of the Earth. We can, however, use spectral correlation theory to filter the static lithospheric and core field components from the dynamic external field effects. To help isolate regional lithospheric from core field components, the correlations between CHAMP magnetic anomalies and the pseudo magnetic effects inferred from gravity-derived crustal thickness variations can also be exploited.. Employing these procedures, we processed the CHAMP magnetic observations for an improved magnetic anomaly map of the Antarctic crust. Relative to the much higher altitude Orsted and noisier Magsat observations, the CHAMP magnetic anomalies at 400 km altitude reveal new details on the effects of intracrustal magnetic features and crustal thickness variations of the Antarctic.

Kim, Hyung Rae; Gaya-Pique, Luis R.; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo

2003-01-01

33

Geological reasons for change in intensity of linear magnetic anomalies of the Kursk magnetic anomaly  

NASA Technical Reports Server (NTRS)

The geological reasons for fluctuations in the anomalous field intensity along the polar axes were examined. The Kursk magnetic anomaly is used as the basis for the study. A geological-geophysical section was constructed which used the results of the interpretation of gravimagnetic anomalies.

Zhavoronkin, I. A.; Kopayev, V. V.

1985-01-01

34

Explanation of the nature of stripe magnetic anomalies without inversions  

NASA Astrophysics Data System (ADS)

Several scientists of different branches express doubts on the validity of the Earth's geomagnetic field inversions hypothesis [Vine F.J., Matthews D.H, 1963]. Presently a lot of information allows to link the appearance of stripe magnetic anomalies of both signs with the spreading fracture structure (horizontal segmentation of intrusions and sills, breaks in the strong crust, vertical movements of blocks), remagnetization near the borders of the blocks, hydrothermal activity. Non-inversion mechanism of origin of linear stripe magnetic anomalies in the oceans could be explained as follows. Ascending asthenospheric flows have been enrich with volatile components, become thinner, pressure on the walls of the lithospheric plates grows and part them. When it approaches the surface: - horizontal tensile pressure grows, - lithostatic pressure in the vertical column of rocks decreases, - crust strong upper layer flakes away and begins to move horizontally. It is important that thin magmatic and magnetic layers (further layers) of the newly formed strong upper crust move away from the ridge axis. The structure of such layers forms by horizontal stresses and so consist of the hills and depressions sequences or updiped and downdiped blocks heaped each other. This layer is the main source of the magnetic field and cannot be approximated by a horizontal homogeneous plate as it proved before. In the mid-ocean ridges (MOR) the folding periods of layer depend on its thickness and rigidity and horizontal velocity of spreading. The higher velocity - the longer periods of roughness are and contrary. Same pattern is observed for the stripe magnetic anomalies distribution. The magnetic field of the MOR forms there due to young lava flows which get thermoremanent magnetization according the current direction of geomagnetic field. Partial destruction of the relief, overlaying and creation of the new shapes occur when new magma penetrates the moved magnetic layer. The process entails partial flux reversal of rocks with the decrease of total magnetic field amplitude. The complicated magnetic field with alternating-sign linear anomalies appears. Taking into account limited vertical thickness of the oceanic magnetic layer, the false effect of negative magnetization would appear even with short shifts of the blocks. Conclusions. Theoretical calculations and analysis 'in situ' data prove that observation of magnetic anomalies of both signs in MOR areas are connected with fracturing tectonics, horizontal segmentation of sills, faults in the crust, vertical movements of blocks, self remagnetization near its margins. At the present time geological and geophysical facts lead to revision of some facts of tectonic theory and rejection of the old hypothesis connected with simplified ideas of the magnetic layer regularity and cyclical nature of magma flows. The main task of this work is to return scientists to the initial point of stripe magnetic anomalies discovery and general revision of the oceanic crust's structure without the limitations of Vine-Matthews-Morley hypothesis. Please fill in your abstract text.

Melikhov, Vjacheslav; Lygin, Ivan; Sokolova, Tatiana

2014-05-01

35

Equivalent magnetization over the World's Ocean and the World Digital Magnetic Anomaly Map  

NASA Astrophysics Data System (ADS)

As a by-product of our recent work to build a candidate model over the oceans for the second version of the World Digital Magnetic Anomaly Map (WDMAM), we derived global distributions of the equivalent magnetization in oceanic domains. In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface. We estimate magnetization vectors using the age map of the ocean floor, the relative plate motions, the apparent polar wander path for Africa, and a geomagnetic reversal time scale. We assume two possible magnetized source geometry, involving both a 1 km-thick layer bearing a 10 A/m magnetization either on a regular spherical shell with a constant, 5 km-deep, bathymetry (simple geometry) or following the topography of the oceanic basement as defined by the bathymetry and sedimentary thickness (realistic geometry). Adding a present-day geomagnetic field model allows the computation of our initial magnetic anomaly model. In a second step, we adjust this model to the existing marine magnetic anomaly data, in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies on 100, 200 or 400 km-long sliding windows (depending the spreading rate). Among the possible comparison criteria, we discard the maximal range - too dependent on local values - and the correlation and coherency - the geographical adjustment between model and data being not accurate enough - to favor the standard deviation around the mean value. The ratio between the standard deviations of data and model on each sliding window represent an estimate of the magnetization ratio causing the anomalies, which we interpolate to adjust the initial magnetic anomaly model to the data and therefore compute a final model to be included in our WDMAM candidate over the oceanic regions lacking data. The above ratio, after division by the magnetization of 10 A/m used in the model, represents an estimate of the equivalent magnetization under the considered magnetized source geometry. The resulting distributions of equivalent magnetization are further discussed in terms of mid-ocean ridges, presence of hotspots and oceanic plateaus, and the age of the oceanic lithosphere. Global marine magnetic data sets and models represent a useful tool to assess first order magnetic properties of the oceanic lithosphere.

Dyment, Jerome; Choi, Yujin; Hamoudi, Mohamed; Thébault, Erwan; Quesnel, Yoann; Roest, Walter; Lesur, Vincent

2014-05-01

36

Matching Martian Magnetic Anomalies and Snc Magnetic Properties  

Microsoft Academic Search

Understanding the origin of Martian magnetic anomalies is a major challenge for Martian studies, both in terms of planetary geodynamics and of magnetic petrology. Present models require a crustal magnetization of 15-30 A\\/m with a thickness of 20-50 km [e.g. 1]. SNC meteorites are the only material available to make a magnetominer- alogical model for this crustal magnetization. Here will

P. Rochette; V. Sautter; F. Brunet; V. Chevrier; J. P. Lorand

2002-01-01

37

Paleo-Pole Positions from Martian Magnetic Anomaly Data  

NASA Technical Reports Server (NTRS)

Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor s magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed four North and 3 South poles with two at approximately 60 degrees north latitude. These results suggest that during the existence of the Martian main magnetic field it experienced several reversals.

Taylor, Patrick T.; Frawley, James J.

2003-01-01

38

Paleo-Pole Positions from Martian Magnetic Anomaly Data  

NASA Technical Reports Server (NTRS)

Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor's magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed paleo-poles that were nearly equally divided between north, south and mid-latitudes. These results suggest that during the existence of the martian main magnetic field it experienced several reversals and excursions.

Frawley, James J.; Taylor, Patrick T.

2004-01-01

39

Remanent magnetizations of oceanic basalts on the back-arc spreading axis in the southern Mariana  

NASA Astrophysics Data System (ADS)

Magnetic anomaly high on a spreading axis has been a well-known character of the magnetic anomalies in the ocean, which is mainly related to magnetization intensity reduction with age due to low-temperature oxidation of titanomagnetite. Recently, a few deep-sea magnetic observations on the fast spreading axis showed that magnetization of the oceanic crust reflects relative paleointensity variation of the Brunhes Chron. These data suggest that the magnetization of oceanic basalt appears to reflect the geomagnetic intensity variation (i.e. the original thermoremanent magnetization (TRM) intensity variation) in spite of the alteration process (low-temperature oxidation of titanomagnetite). Previous studies discussed magnetization of oceanic crust on the basis of the natural remanent magnetization (NRM) itself. Therefore they cannot precisely estimate the alteration effect on magnetizations. In this study, we have reported progressive demagnetization results of NRM, anhysteretic remanent magnetization (ARM), and saturation isothermal remanent magnetization (SIRM) for the oceanic basalts on the back-arc spreading axis in the southern Mariana and discuss fundamental properties of magnetization of oceanic basalt.

Mochizuki, N.; Nogi, Y.; Asada, M.; Yoshikawa, S.; Okino, K.

2011-12-01

40

Crustal Magnetic Field Anomalies and Global Tectonics  

NASA Astrophysics Data System (ADS)

A wide variety of evidence suggests that the ruling isochron (geomagnetic polarity versus age) hypothesis of marine magnetic lineations has no merit - undermining therefore one of the central tenets of plate tectonics. Instead, variable induction by the ambient geomagnetic field is likely to be the principal agent for mega-scale crustal magnetic features - in both oceanic and continental settings. This revitalizes the fault-controlled susceptibility-contrast model of marine magnetic lineations, originally proposed in the late 1960s. Thus, the marine magnetic 'striping' may be ascribed to tectonic shearing and related, but variable, disintegration of the original iron-oxide mineralogy, having developed primarily along one of the two pan-global sets of orthogonal fractures and faults. In this way, fault zones (having the more advanced mineral alteration) would be characterized by relatively low susceptibility, while more moderately affected crustal sections (located between principal fault zones) would be likely to have less altered oxide mineralogy and therefore higher magnetic susceptibility. On this basis, induction by the present geomagnetic field is likely to produce oscillating magnetic field anomalies with axis along the principal shear grain. The modus operandi of the alternative magneto-tectonic interpretation is inertia-driven wrenching of the global Alpine age palaeo-lithosphere - triggered by changes in Earth's rotation. Increasing sub-crustal loss to the upper mantle during the Upper Mesozoic had left the ensuing Alpine Earth in a tectonically unstable state. Thus, sub-crustal eclogitization and associated gravity-driven delamination to the upper mantle led to a certain degree of planetary acceleration which in turn gave rise to latitude-dependent, westward inertial wrenching of the global palaeo-lithosphere. During this process, 1) the thin and mechanically fragile oceanic crust were deformed into a new type of broad fold belts, and 2) the continents were subjected to relative 'in situ' rotations (mostly moderate). Examples of marine magnetic lineations with landward continuation along prominent transcurrent fault zones, and the fact that striped marine magnetic anomalies may display orthogonal networks - concordant with the ubiquitous system of rectilinear fractures, faults and joints - corroborate the wrench tectonic interpretation of crustal field anomalies.

Storetvedt, Karsten

2014-05-01

41

Gravity and magnetic anomaly data analysis  

NASA Technical Reports Server (NTRS)

Progress on the analysis MAGSAT data is reported. The MAGSAT data from 40 deg S to 70 deg N latitude and 30 deg W to 60 E longitude was reduced to radial polarization. In addition, gravity anomaly data from this area were processed and a variety of filtered maps were prepared for combined interpretation of the gravity and magnetic data in conjunction with structural and tectonic maps of the area. The VERSATEC listings and cross-reference maps of variable and array names for the spherical Earth analysis programs NVERTSM, SMFLD, NVERTG, and GFLD were also prepared.

Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (principal investigators)

1982-01-01

42

A global magnetic anomaly map. [obtained from POGO satellite data  

NASA Technical Reports Server (NTRS)

A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin.

Regan, R. D.; Davis, W. M.; Cain, J. C.

1974-01-01

43

GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 17, PAGES 2765-2768, SEPTEMBER 1, 2000 Satellite magnetic anomalies related to seafloor  

E-print Network

magnetic anomalies related to seafloor spreading in the South Atlantic Ocean Michael E. Purucker Raytheon the treatment of satellite magnetic data, these signals are obscured in the South Atlantic Ocean because Atlantic Ocean al- lows us to 1) investigate the magnetic structure of the South Atlantic Ocean, 2

Dyment, Jérôme

44

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly1 , M., Quesnel2*  

E-print Network

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly1 2 Ouabego1,2 , M 44297159514 Email: quesnel@cerege.fr15 16 Abstract17 The Bangui Magnetic Anomaly (BMA) is the largest lithospheric magnetic field anomaly on18 Earth at low latitudes. Previous studies investigated its geological

Boyer, Edmond

45

New Magnetic Anomaly Compilation Illuminates the Formation of the Aleutian Basin  

NASA Astrophysics Data System (ADS)

Aleutian Basin crust is deeply buried beneath 2 to 5 km of sediment, so magnetic data provide valuable insights into its structure and origin. A new compilation of marine magnetic anomalies, derived from one recent cruise (2011) and re-analysis of dozens of legacy cruises (primarily 1970's to 1980's), provides both a refined view of the magnetic field in the Bering Sea area and insights into the formation of the deep-water Aleutian and Bowers Basins. In the Aleutian Basin, the magnetic fabric can be divided into two similar-sized areas of distinct types. Type 1 magnetic fabric is characterized by north-south-oriented lineations in the southern Aleutian Basin. The lineations have irregular spacing, reminiscent of seafloor spreading stripes, and the amplitudes of the anomalies are also consistent with a magnetic source formed at spreading centers. Seismic reflection data show that the strongest magnetic lineations in the Type 1 area are not associated with basement relief, supporting an origin from remanent magnetization variations and consistent with their formation by seafloor spreading. This interpretation is consistent with OBS refraction results indicating that this is mafic crust ~8 km thick. The pattern of anomalies does not show an obvious symmetry about a possible fossil spreading axis, and attempts to assign the sequence of lineaments to the geomagnetic polarity timescale are not definitive. Thus, we cannot rule out either of the two hypotheses for the formation of the Aleutian Basin, as a Paleogene back-arc basin or as captured (old) plate trapped by formation of the Aleutian subduction zone at ~50 Ma. Type 2 magnetic fabric is characterized by higher-amplitude and more heterogeneous magnetic anomalies than Type 1 fabric, and it is located around the margins of the Aleutian Basin, to the north and west of the lineated fabric. Some features of the basement (e.g. Sounder Ridge) have corresponding magnetic anomalies in Type 2 areas, but other anomalies with little basement topography imply significant variations in the magnetic properties (susceptibility, remnant strength, or both) of the igneous crust. Seismic imaging and dredging near the Beringian Margin indicate that significant extensional deformation and subsidence of the margin has occurred seaward into the deep-water Aleutian Basin, and the boundary between Type 2 and Type 1 magnetic fabric may indicate the boundary between modified-continental crust and oceanic crust.

Scheirer, D. S.; Barth, G. A.; Scholl, D. W.; Stern, R. J.

2013-12-01

46

Statistical analysis of the lithospheric magnetic anomaly data  

NASA Astrophysics Data System (ADS)

Different analyses carried out on the lithospheric magnetic anomaly data from GEODAS DVD v5.0.10 database (World Digital Magnetic Anomaly Map, WDMAM) show that the data distribution is not Gaussian, but Laplacian. Although this behaviour has been formerly pointed out in other works (e.g., Walker and Jackson, Geophys. J. Int, 143, 799-808, 2000), they have not given any explanation about this statistical property of the magnetic anomalies. In this work, we perform different statistical tests to confirm that the lithospheric magnetic anomaly data follow indeed a Laplacian distribution and we also give a possible interpretation of this behavior providing a model of magnetization which depends on the variation of the geomagnetic field and both induced and remanent magnetizations in the terrestrial lithosphere.

Pavon-Carrasco, Fco Javier; de Santis, Angelo; Ferraccioli, Fausto; Catalán, Manuel; Ishihara, Takemi

2013-04-01

47

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

NASA Astrophysics Data System (ADS)

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.

Cordani, Renato; Shukowsky, Wladimir

2009-10-01

48

Rapid interactive modeling of 3D magnetic anomalies  

NASA Astrophysics Data System (ADS)

I implement a MATLAB® function (for_3DFFT_mag) for calculating magnetic anomalies from a 3D distribution of magnetization, which can be loaded interactively through an user-friendly graphic interface. The forward calculation engine is based on a 3D Fast Fourier Transform computation, that gives accurate results in a very short computing time, making the use of this program particularly suitable for 3D interactive modeling of observed magnetic anomalies.

Caratori Tontini, Fabio

2012-11-01

49

Magnetic and Bathymetrie Data Bearing on Sea-Floor Spreading North of Iceland  

Microsoft Academic Search

rates of 1.0 cm\\/yr normal to the ridge crests between Iceland and the Jan Mayen fracture zone and on Mohns ridge. The trans-Arctic extension of the ridge is characterized by anomalously great water depths and spreading rates probably I cm\\/yr or less. The magnetic anomaly signatures reveal exceptionally low amplitudes compared to other ridges, even when these factors are taken

Peter R. Vogt; Ned A. Ostenso; G. Leonard Johnson

1970-01-01

50

Study of gravity and magnetic anomalies using MAGSAT data  

NASA Technical Reports Server (NTRS)

The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.

Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (principal investigators)

1981-01-01

51

Do Satellite Magnetic Anomaly Data Accurately Portray the Crustal Component?  

NASA Technical Reports Server (NTRS)

Scalar aeromagnetic data obtained during the U.S. Naval Oceanographic Office (NOO)-Vector Magnetic Survey of the conterminous United States were upward continued by equivalent point source inversion and compared with POGO satellite magnetic anomaly and preliminary scalar MAGSAT data. Initial comparisons indicate that the upward continued NOO data is dominated by long wavelength (approximately equal to 1000 to 3000 km) anomalies which are not present in the satellite anomaly data. Thus, the comparison of the data sets is poor. Several possible sources for these differences are present in the data analysis chain. However, upon removal of these long wavelengths from the upward continued NOO data, a close comparison observed between the anomalies verifies that satellite magnetic anomaly data do portray the crustal component within a range of wavelengths from roughly 1000 km down to the resolution limit of the observations.

Vonfrese, R. R. B.; Hinze, W. J. (principal investigators)

1984-01-01

52

Magnetic resonance images of neuronal migration anomalies.  

PubMed

Neuronal migration anomalies are a spectrum of brain malformations caused by insults to migrating neuroblasts during the sixth week to fifth month of gestation. To study the characteristics of MRI findings in migration anomalies, MR images of 36 patients (28 children and 8 adults) with migration anomalies were evaluated. Five patients had lissencephaly, eight had pachygyria, twelve had schizencephaly, six had heterotopias of gray matter, three had hemimegalencephaly, and two had polymicrogyria. The frequency of migration anomalies was 0.51% of all cranial MRI studies and 1.21% of pediatric cranial MRI studies at our hospital. The major clinical presentations of these patients were seizure (64%), development delay (42%), motor deficits (42%) and mental retardation (25%). Twenty-five patients (69%) associated with other brain anomalies, including: other migration anomalies in 12 cases (33%), absence of the septum pellucidum in 10 cases (28%), Dandy-Walker malformation/variant in 5 cases, arachnoid cyst in 4 cases, agenesis of the corpus callosum in 3 cases, holoprosencephaly in 2 cases, mega cisterna magna in 1 case and cephalocele in 1 case. Some of them presented with multiple complicated anomalies. As MR imaging provides superb gray-white matter distinction, details of cortical anatomy and multiplanar capability, it can clearly delineate the detail morphologic changes of the brain caused by neuronal migration disorders as well as the associated anomalies. PMID:9780601

Jaw, T S; Sheu, R S; Liu, G C; Chou, M S

1998-08-01

53

Distribution of Narrow-Width Magnetic Anomalies in Antarctica.  

PubMed

Data for aeromagnetic profiles obtained in Antarctica during the 1963-64 austral summer were used together with earlier results to construct a map showing the areal distribution of narrow-width magnetic anomalies. Numerous anomalies are associated with known volcanic mountains in western Antarctica. A large area of few anomalies is probably a result of an extension of the thick metasedimentary section observed in the Ellsworth Mountains. Portions of the Trans-Antarctic Mountains have associated anomalies which are probably caused by late Cenozoic volcanic rocks. PMID:17811603

Behrendt, J C

1964-05-22

54

Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?  

NASA Technical Reports Server (NTRS)

Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.

Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.

1999-01-01

55

Deflection of solar wind protons from the Lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

The first measurements, which was made on the lunar orbits, has shown that Moon has no its intrinsic dipolar magnetic field. However the residual magnetization in returned lunar samples and also the anomalous magnetization of lunar surface (till several hundred nT) was found even in Apollo missions. Observations of Kaguya and Chandrayaan reveal the significant solar wind protons deflection from the lunar surface in particular from the magnetic anomalies regions. Such deflection implies that the magnetic anomalies may act as magnetosphere-like obstacles (mini-magnetospheres), modifying the upstream plasma. We examined the conditions in solar wind and estimated plasma parameters in solar wind and in crustal magnetic field. Then we made the estimation of the possibility of mini-magnetosphere and shock-like structure formation. Also we applied our calculations to the case of big anomaly.

Sadovski, Andrei M.; Skalsky, Alexander A.

2014-05-01

56

Study of magnetic anomalies over archaeological targets in urban environments  

NASA Astrophysics Data System (ADS)

Magnetic prospecting is one of the most widely used methods for investigating archaeological sites in the world. It is often applied before and during various types of industrial development and in agricultural areas. In Israel, most potential archaeological targets are located in urban settings, which substantially complicate their geophysical signatures. Noise from natural factors such as the inclined magnetization (about 44°) complex geological structure of the sites, and uneven terrain relief as well as artificial sources such as modern iron-containing objects, power lines and underground communications can confound the interpretation of magnetic anomalies. For the quantitative analysis of magnetic anomalies from ancient targets in Israel nonconventional procedures ( Khesin et al., 1996; Eppelbaum and Khesin, 2001) were applied. In this paper the effects of power lines on the quantitative analysis of magnetic anomalies indicative of archaeological objects are investigated. The method was tested on two typical models of physical-archaeological ancient remains by using different distances to the power line.

Eppelbaum, Lev V.

57

APPLICATION OF SATELLITE MAGNETIC ANOMALY DATA TO CURIE ISOTHERM MAPPING  

Microsoft Academic Search

A boundary condition on temperature the Curie temperature is restricted to a narrow at depth in the continental crust can in principle range (aboUt 520ø-560øC). be obtained by mapping of the Curie isotherm where it forms the base of the magnetic crust. An approach to mapping magnetic crustal thickness using satellite magnetic anomaly data is describ- ed. Because magnetic crustal

M. A. Mayhew

1982-01-01

58

The Origin of the Jurassic Quiet Zone -new insights from Hawaiian Jurassic magnetic anomalies (Invited)  

NASA Astrophysics Data System (ADS)

Marine magnetic anomalies recorded in oceanic crust, have played a central role in documenting Earth's magnetic field history as compiled in the geomagnetic polarity timescale (GPTS). The oldest part of the marine record is the Jurassic Quiet Zone (JQZ) (pre-M29 chrons) which is known to be a period when field intensity was low, while reversal rate was high. The origin and character of the JQZ has been the subject of marine magnetic studies over past 20 years in the western Pacific where the oldest and arguably best preserved Jurassic magnetic anomalies create three Jurassic lineation sets (Japanese, Hawaiian, and Phoenix). The Japanese JQZ sequence was extensively investigated by an aeromagnetic and 2 deeptow magnetometer surveys, revealing (i) the presence of lineated anomalies older than M29; (ii) a GPTS record extending from M29 to M44 with a tie to ODP Hole 801C and (iii) remarkably fast reversals that decrease in intensity back in time until M38. Prior to M38 there is a low amplitude zone (LAZ) in anomalies lasting until M42, when both anomaly amplitude and a lineated character reappears around Hole 801C. Recently collected (2011) high quality seasurface marine magnetic anomaly data from the Hawaiian lineations show changes in magnetic anomaly shape and amplitude that are similar in to the Japanese lineations, suggesting that the anomalies record globally coherent geomagnetic field behavior for the Jurassic. Specifically, the strong similarity of anomaly patterns between the Japanese and Hawaiian sequences from M19 to M38 supports the remarkably dynamic geomagnetic field behavior of fast reversals and changing intensity, confirming a proposed record of the GPTS sequence for M29 to M38. While the LAZ in the Hawaiian sequence is not as clear as in the Japanese lineations, we believe we can correlate the earlier M42-M44 sequence between the two sets of lineations. The slower spreading rate in the Hawaiian lineations may contribute to this lack of resolution of the LAZ and result in a less clear recording of anomalies. We present models to investigate if this is simply a lack of spatial resolution or if there are indeed different processes active within the Hawaiian sequence such as seamount/plateau formation and crustal construction.

Tominaga, M.; Tivey, M.; Sager, W. W.

2013-12-01

59

Upper Lithospheric Sources of Magnetic and Gravity Anomalies of The Fennoscandian Shield  

Microsoft Academic Search

Magnetic total intensity anomalies (DGRF-65), Bouguer anomalies (d=2670 kg\\/m3) and geological units from 3400 Ma to present of the Fennoscandian Shield have been digitally compiled and printed as maps 1:2 000 000. Insert maps 1:15,000,000 com- pare anomaly components in different source scales: pseudogravimetric anomaly ver- sus Bouguer anomaly, DGRF-65 anomaly versus pseudomagnetic anomaly, magnetic vertical derivative versus second derivative

J. V. Korhonen; T. Koistinen

2002-01-01

60

A method of inversion of satellite magnetic anomaly data  

NASA Technical Reports Server (NTRS)

A method of finding a first approximation to a crustal magnetization distribution from inversion of satellite magnetic anomaly data is described. Magnetization is expressed as a Fourier Series in a segment of spherical shell. Input to this procedure is an equivalent source representation of the observed anomaly field. Instability of the inversion occurs when high frequency noise is present in the input data, or when the series is carried to an excessively high wave number. Preliminary results are given for the United States and adjacent areas.

Mayhew, M. A.

1977-01-01

61

Google Earth Community: Magnetic Anomalies of the Earth  

NSDL National Science Digital Library

This is a Google Earth image overlay map of magnetic anomaly information derived from more than 50 years of aeromagnetic surveys over land areas, research vessel magnetometer traverses at sea, and observations from earth-orbiting satellites, supplemented by anomaly values derived from oceanic crustal ages. The objective is to provide an interpretive dimension to surface observations of the Earth's composition and geologic structure. This is a good means of demonstrating how data from minerals contributes to our knowledge of plate tectonics.

Community, Google E.

62

SEISMIC DISCRIMINATION OF THERMAL AND MAGNETIC ANOMALIES IN SUNSPOT UMBRAE  

SciTech Connect

Efforts to model sunspots based on helioseismic signatures need to discriminate between the effects of (1) a strong magnetic field that introduces time-irreversible, vantage-dependent phase shifts, apparently connected to fast- and slow-mode coupling and wave absorption and (2) a thermal anomaly that includes cool gas extending an indefinite depth beneath the photosphere. Helioseismic observations of sunspots show travel times considerably reduced with respect to equivalent quiet-Sun signatures. Simulations by Moradi and Cally of waves skipping across sunspots with photospheric magnetic fields of order 3 kG show travel times that respond strongly to the magnetic field and relatively weakly to the thermal anomaly by itself. We note that waves propagating vertically in a vertical magnetic field are relatively insensitive to the magnetic field, while remaining highly responsive to the attendant thermal anomaly. Travel-time measurements for waves with large skip distances into the centers of axially symmetric sunspots are therefore a crucial resource for discrimination of the thermal anomaly beneath sunspot umbrae from the magnetic anomaly. One-dimensional models of sunspot umbrae based on compressible-radiative-magnetic-convective simulations such as by Rempel et al. can be fashioned to fit observed helioseismic travel-time spectra in the centers of sunspot umbrae. These models are based on cooling of the upper 2-4 Mm of the umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The travel-time reductions characteristic of these models are primarily a consequence of a Wilson depression resulting from a strong downward buoyancy of the cooled umbral medium.

Lindsey, C. [NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301 (United States); Cally, P. S. [School of Mathematical Sciences, Monash University, Victoria (Australia); Rempel, M. [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green Drive CG1, Boulder, CO 80301 (United States)

2010-08-20

63

Seismic Discrimination of Thermal and Magnetic Anomalies in Sunspot Umbrae  

NASA Astrophysics Data System (ADS)

Efforts to model sunspots based on helioseismic signatures need to discriminate between the effects of (1) a strong magnetic field that introduces time-irreversible, vantage-dependent phase shifts, apparently connected to fast- and slow-mode coupling and wave absorption and (2) a thermal anomaly that includes cool gas extending an indefinite depth beneath the photosphere. Helioseismic observations of sunspots show travel times considerably reduced with respect to equivalent quiet-Sun signatures. Simulations by Moradi & Cally of waves skipping across sunspots with photospheric magnetic fields of order 3 kG show travel times that respond strongly to the magnetic field and relatively weakly to the thermal anomaly by itself. We note that waves propagating vertically in a vertical magnetic field are relatively insensitive to the magnetic field, while remaining highly responsive to the attendant thermal anomaly. Travel-time measurements for waves with large skip distances into the centers of axially symmetric sunspots are therefore a crucial resource for discrimination of the thermal anomaly beneath sunspot umbrae from the magnetic anomaly. One-dimensional models of sunspot umbrae based on compressible-radiative-magnetic-convective simulations such as by Rempel et al. can be fashioned to fit observed helioseismic travel-time spectra in the centers of sunspot umbrae. These models are based on cooling of the upper 2-4 Mm of the umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The travel-time reductions characteristic of these models are primarily a consequence of a Wilson depression resulting from a strong downward buoyancy of the cooled umbral medium.

Lindsey, C.; Cally, P. S.; Rempel, M.

2010-08-01

64

Lunar magnetic anomaly concentrations at the antipodal regions  

NASA Astrophysics Data System (ADS)

The high resolution lunar-wide magnetic anomaly map derived from Lunar Prospector (LP) vector magnetometer data has revealed weak anomalies over the nearside large impact basins flooded by mare basalts. Stronger anomaly features are observed over many of the Nectarian and Pre-Nectarian aged lunar highlands. In particular, regions antipodal to some of the largest basin-forming impact craters show strong magnetic anomaly concentrations. Of the 43 basins investigated here, antipodal regions of 9 basins show these anomalous features with strengths in excess of 1-18 nT at LP's mapping altitude (30 km). These distinct anomalous concentrations were previously known to occur only at the antipodes of Imbrium, Orientale, Serenitatis, Crisium and Nectaris basins. The mean magnetic anomaly strength within each antipodal region, when plotted against increasing age of the antipodes, shows two age groupings with similar magnetic behavior. The first age grouping - (Imbrium, Orientale, Serenitatis, Crisium and Nectaris) is of Imbrium to Nectarian in age. This grouping is correlative with peak magnetic field enhancements between 3.6 and 3.9 Gyr, inferred from paleomagnetic data from the returned Apollo samples. The second age grouping (Lorentz, Coulomb-Sarton, Tranquillitatis and Cognitum) is of Mid to Early Pre-Nectarian age. This grouping has not been correlated to any known global magnetic field enhancement event, and needs further investigation to ascertain the origin of the anomalies. Although spatially adjacent, the magnetic field signatures of the Serenitatis and Imbrium antipodes exhibit distinct features, supporting the antipodal hypothesis. The absence of appreciable field enhancements at 34 other antipodes, however, indicates the importance of other processes, and superposition effects, that have operated on the Moon during its history.

Hemant Singh, Kumar; Kuang, Weijia; Singh, Raghav

2014-05-01

65

The early break-up phase of the South Atlantic - magnetic anomalies, volcanism and kinematics  

NASA Astrophysics Data System (ADS)

The South Atlantic has been generally recognized as a prime example for continental break-up with accompanying volcanic activity reflected today in massive seaward dipping reflector sequences (SDRS) in reflection as well as high velocity lower crust in refraction seismic data. The early history of the South Atlantic passive margin evolution is investigated in the view of interlaced magnetic anomalies related to seafloor spreading lineations and anomalies caused by seaward-dipping reflector sequences (SDRS). As the Atlantic opened from South to North, the magma-poor segments of the southernmost South Atlantic are also the oldest segments of the Ocean. Therefore, the magma-poor segments on the conjugated margins must be considered crucial in the understanding of the initial phase of spreading and rifting concluding in the opening of the South Atlantic. The interpretation of pre-M5n lineations define timing of the termination of excess breakup related volcanic activity and the transition to 'normal' seafloor spreading. Termination of magnetic anomalies within SDR wedges point towards a scissor-like succession in volcanic activity from south to north, following the opening of the South Atlantic. Reflection, refraction seismic and potential field data show that while the two conjugated margins share much of their structural features such as segmentation and abundant volcanism, they are by no means perfectly symmetrical. This is for example shown in shelf width, strength of the magnetic anomalies or orientation of break-up related sedimentary basins. From our data, we suggest changes in spreading and later rifting direction to be the cause of for these asymmetries. This directional change is also suggested to be responsible for the change in margin character from magma-poor to volcanic rather than solely a spontaneous change in crustal melt-generation. New models for the magnetic response of SDRS reveal a high variability within the wedges on either side of the Atlantic and between the conjugated margins. Former identifications of anomaly M11r off Cape Town have already been questioned and can now be shown to be caused by structural or magnetization variations within SDRS.

Koopmann, H.; Schreckenberger, B.; Franke, D.; Becker, K.; Schnabel, M.

2013-12-01

66

First high-resolution near-seafloor survey of magnetic anomalies of the South China Sea  

NASA Astrophysics Data System (ADS)

We successfully conducted the first high-resolution near-seafloor magnetic survey of the Central, Southwest, and Northern Central Basins of the South China Sea (SCS) during two cruises on board Chinese R/V HaiYangLiuHao in October-November 2012 and March-April 2013, respectively. Measurements of magnetic field were made along four long survey lines, including (1) a NW-SE across-isochron profile transecting the Southwest Basin and covering all ages of the oceanic crust (Line CD); (2) a N-S across-isochron profile transecting the Central Basin (Line AB); and (3) two sub-parallel NE-SW across-isochron profiles transecting the Northern Central Basin of the SCS (Lines D and E). A three-axis magnetometer was mounted on a deep-tow vehicle, flying within 0.6 km above the seafloor. The position of the tow vehicle was provided by an ultra-short baseline navigation system along Lines D and E, while was estimated using shipboard GPS along Lines AB and CD. To investigate crustal magnetization, we first removed the International Geomagnetic Reference Field (IGRF) of 2010 from the measured magnetic data, and then downward continued the resultant magnetic field data to a horizontal plane at a water depth of 4.5 km to correct for variation due to the fishing depth of the deep-tow vehicle. Finally, we calculated magnetic anomalies at various water depths after reduction-to-the-pole corrections. We also constructed polarity reversal block (PRB) models of crustal magnetization by matching peaks and troughs of the observed magnetic field anomaly. Our analysis yielded the following results: (1) The near-bottom magnetic anomaly showed peak-to-trough amplitudes of more than 2,500 nT, which are several times of the anomaly amplitudes at the sea surface, illustrating that deep-tow measurements acquired much higher spatial resolutions. (2) The deep-tow data revealed several distinctive magnetic anomalies with wavelengths of 5-15 km and amplitudes of several hundred nT. These short-wavelength anomalies were unrecognized in sea surface measurements. (3) Preliminary results showed that the study regions might have experienced several episodes of magnetic reversal events that were not recognized in existing models. (4) We are currently investigating the geomagnetic timing of these relatively short-duration events to determine the detailed spreading history of the sub-basins of the SCS. These high-resolution near-seafloor magnetic survey lines are located close to the planned drilling sites of IODP Expedition 349 scheduled for January-March 2014.

Lin, J.; Xu, X.; Li, C.; Sun, Z.; Zhu, J.; Zhou, Z.; Qiu, N.

2013-12-01

67

Understanding the Tectonic Features in the South China Sea By Analyzing Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

The South China Sea (SCS) is surrounded by the Eurasia, Pacific and India-Australia plates. It formed during Late Oligocene-Early Miocene, and is one of the largest marginal seas in the Western Pacific. The collision of Indian subcontinent and Eurasian plate in the northwest, back-arc spreading in the centre and subduction beneath the Philippine plate along Manila trench in the east and along Palawan trough in the south had produced the complex tectonic features in the SCS that we can see today. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of the SCS. Here, we analyzed the magnetic data of this area using new data enhancement techniques to understand the regional tectonic features. We assembled the magnetic anomalies data with a resolution of two arc-minute from the World Digital Magnetic Anomaly Map, and then gridded the data on a regular grid. Then we used the method of reduction to the pole at low latitude with varying magnetic inclinations to stably reduce the magnetic anomalies. Then we used the preferential continuation method based on Wiener filtering and Green's equivalence principle to separate the reduced-to-pole (RTP) magnetic anomalies, and subsequently analyze the regional and residual anomalies. We also calculated the directional horizontal derivatives and the tilt-angle derivative of the data to derive clearer geological structures with more details. Then we calculated the depth of the magnetic basement surface in the area by 3D interface inversion. From the results of the preliminary processing, we analyzed the main faults, geological structures, magma distribution and tectonic features in the SCS. In the future, the integrated interpretation of the RTP magnetic anomalies, Bouguer gravity anomalies and other geophysical methods will be performed for better understanding the deep structure , the tectonic features and evolution of the South China Sea. Acknowledgment: We acknowledge the financial support of the SinoProbe project (201011039), the Fundamental Research Funds for the Central Universities (2010ZY26, 2011PY0184), and the National Natural Science Foundation of China (40904033, 41074095).

Guo, L.; Meng, X.; Shi, L.; Yao, C.

2011-12-01

68

The next generation Antarctic digital magnetic anomaly map  

USGS Publications Warehouse

S (Golynsky et al., 2001). This map synthesized over 7.1 million line-kms of survey data available up through 1999 from marine, airborne and Magsat satellite observations. Since the production of the initial map, a large number of new marine and airborne surveys and improved magnetic observations from the Ørsted and CHAMP satellite missions have become available. In addition, an improved core field model for the Antarctic has been developed to better isolate crustal anomalies in these data. The next generation compilation also will likely represent the magnetic survey observations of the region in terms of a high-resolution spherical cap harmonic model. In this paper, we review the progress and problems of developing an improved magnetic anomaly map to facilitate studies of the Antarctic crustal magnetic field

von Frese, R.R.B; Golynsky, A.V.; Kim, H.R.; Gaya-Piqué, L.; Thébault, E.; Chiappinii, M.; Ghidella, M.; Grunow, A.; ADMAP Working Group

2007-01-01

69

New magnetic anomaly map of East Antarctica and surrounding regions  

USGS Publications Warehouse

community over East Antarctica and surrounding regions, significantly upgrade the Antarctic Digital Magnetic Anomaly Project (ADMAP) compilation and lead to substantial improvements in magnetic anomaly pattern recognition. New data have been matched in one inverse operation by minimizing the data differences for the areas of overlap. The aeromagnetic data show many previously unknown magnetic patterns, lineaments and trends, defining the spatial extent of Ferrar volcanics and plutonic Granite Harbour Intrusives in the Transantarctic Mountains and previously unknown tectonic trends of the East Antarctic craton. Regional aeromagnetic investigations have successfully delineated Early Paleozoic inherited crustal features along the flanks of the West Antarctic Rift System and the southern boundary of the Archean Ruker Terrane in the Prince Charles Mountains. Magnetic records along the East Antarctic continental margin provide new constraints on the breakup of Gondwana.

Golynsky, A.; Blankenship, D.; Chiappini, M.; Damaske, D.; Ferraccioli, F.; Finn, C.; Golynsky, D.; Goncharov, A.; Ishihara, T.; Ivanov, S.; Jokat, W.; Kim, H.R.; König, M.; Masolov, V.; Nogi, Y.; Sand, M.; Studing, M.; ADMAP Working Group

2007-01-01

70

Approximating edges of source bodies from magnetic or gravity anomalies.  

USGS Publications Warehouse

Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors

Blakely, R.J.; Simpson, R.W.

1986-01-01

71

New digital magnetic anomaly database for North America  

USGS Publications Warehouse

The Geological Survey of Canada (GSC), U.S. Geological Survey (USGS), and Consejo de Recursos Minerales of Mexico (CRM) are compiling an upgraded digital magnetic anomaly database and map for North America. This trinational project is expected to be completed by late 2002.

Finn, C. A.; Pilkington, M.; Cuevas, A.; Hernandez, I.; Urrutia, J.

2001-01-01

72

Interpretation of magnetic anomalies over the Grenada Basin  

Microsoft Academic Search

The Grenada Basin is a back arc basin located near the eastern border of the Caribbean Plate. The basin is bounded on the west by the north-south trending Aves Ridge (a remnant island arc) and on the east by the active Lesser Antilles island arc. Although this physiography suggests that east-west extension formed the basin, magnetic anomalies over the basins

Dale E. Bird; Stuart A. Hall; John F. Casey; Patrick S. Millegan

1993-01-01

73

Interpretation of magnetic anomalies over the Grenada Basin  

Microsoft Academic Search

The Grenada Basin is a back arc basin located near the eastern border of the Caribbean Plate. The basin is bounded on the west by the north-south trending Aves Ridge (a remnant island arc) and on the east by the active Lesser Antilles island arc. Although this physiography suggests that east-west extension formed the basin, magnetic anomalies over the basin

Dale E. Bird; Stuart A. Hall; John F. Casey; Patrick S. Millegan

1993-01-01

74

Robotic mapping assisted by local magnetic field anomalies  

Microsoft Academic Search

This paper presents a method to incorporate measurement of local magnetic field anomalies into the SLAM (Simultaneous Localization And Mapping) algorithm. One of the key problems of SLAM is loop closure, which means to map the same place into the same location on the generated map when the place is revisited by the robot. It is particularly important for large

Haiyang Zhang; Fred Martin

2011-01-01

75

Estimation of lower crust magnetization form satellite derived anomaly field  

NASA Technical Reports Server (NTRS)

Various lines of evidence point to the lower crust as the source of the long-wavelength magnetic anomaly field measured by the POGO and Magsat satellites. Using seismically determined lower crust thicknesses and equivalent source inversion of the satellite anomaly data, magnetization for the lower crust for much of the United States has been calculated. The average magnetization for two hundred sixty-six 150 x 150 km areas is 3.5 A/m with a standard deviation of 1.1 A/m. These values are consistent with laboratory measurements of mafic-ultramafic rocks expected in the lower crust, and in agreement with previous estimates of lower crust magnetization based on long-wavelength aeromagnetic data. Average lower crust thickness for the same areas is 18.2 km (sigma = 6.4). Thus, over large regions, it appears that variation in magnetization and variation in magnetic layer thickness contribute almost equally in causing the anomaly field variation at satellite altitude.

Schnetzler, C. C.; Allenby, R. J.

1983-01-01

76

Low energy spread ion source with a coaxial magnetic filter  

DOEpatents

Multicusp ion sources are capable of producing ions with low axial energy spread which are necessary in applications such as ion projection lithography (IPL) and radioactive ion beam production. The addition of a radially extending magnetic filter consisting of a pair of permanent magnets to the multicusp source reduces the energy spread considerably due to the improvement in the uniformity of the axial plasma potential distribution in the discharge region. A coaxial multicusp ion source designed to further reduce the energy spread utilizes a cylindrical magnetic filter to achieve a more uniform axial plasma potential distribution. The coaxial magnetic filter divides the source chamber into an outer annular discharge region in which the plasma is produced and a coaxial inner ion extraction region into which the ions radially diffuse but from which ionizing electrons are excluded. The energy spread in the coaxial source has been measured to be 0.6 eV. Unlike other ion sources, the coaxial source has the capability of adjusting the radial plasma potential distribution and therefore the transverse ion temperature (or beam emittance).

Leung, Ka-Ngo (Hercules, CA); Lee, Yung-Hee Yvette (Berkeley, CA)

2000-01-01

77

Lunar magnetic anomalies detected by the Apollo substatellite magnetometers  

USGS Publications Warehouse

Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate presently available magnetic anomaly maps - one covering a portion of the lunar near side and the other a part of the far side. The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous, light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. An age for Cavalerius (and, by implication, for Reiner Gamma) of 3.2 ?? 0.2 ?? 109 y is estimated. The main (30 ?? 60 km) Reiner Gamma deposit is nearly uniformly magnetized in a single direction, with a minimum mean magnetization intensity of ???7 ?? 10-2 G cm3/g (assuming a density of 3 g/cm3), or about 700 times the stable magnetization component of the most magnetic returned samples. Additional medium-amplitude anomalies exist over the Fra Mauro Formation (Imbrium basin ejecta emplaced ???3.9 ?? 109 y ago) where it has not been flooded by mare basalt flows, but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The mean altitude of the far-side anomaly gap is much higher than that of the near-side map and the surface geology is more complex, so individual anomaly sources have not yet been identified. However, it is clear that a concentration of especially strong sources exists in the vicinity of the craters Van de Graaff and Aitken. Numerical modeling of the associated fields reveals that the source locations do not correspond with the larger primary impact craters of the region and, by analogy with Reiner Gamma, may be less conspicuous secondary crater ejecta deposits. The reason for a special concentration of strong sources in the Van de Graaff-Aitken region is unknown, but may be indirectly related to the existence of strongly modified crustal terrain which also occurs in the same region. The inferred directions of magnetization for the several sources of the largest anomalies are highly inclined with respect to one another, but are generally depleted in the north-south direction. The north-south depletion of magnetization intensity appears to continue across the far-side within the region of coverage. The mechanism of magnetization and the origin of the magnetizing field remain unresolved, but the uniformity with which the Reiner Gamma deposit is apparently magnetized, and the north-south depletion of magnetization intensity across a substantial portion of the far side, seem to require the existence of an ambient field, perhaps of global or larger extent. The very different inferred directions of magnetization possessed by nearly adjacent sources of the Van de Graaff-Aitken anomalies, and the depletion in their north-south component of magnetization, do not favor an internally generated dipolar field oriented parallel to the present spin axis. A variably oriented interplanetary magnetizing field that was intrinsically strong or locally amplified by unknown surface processes is least inconsistent with the data. ?? 1979.

Hood, L. L.; Coleman, Jr. , P. J.; Russell, C. T.; Wilhelms, D. E.

1979-01-01

78

Manifestation of the petrogeneration zones of Northern and the Bering seas in ground magnetic anomalies and anomalies of satellite Champ  

NASA Astrophysics Data System (ADS)

The purpose of this paper are showed results of studying of specificity of a deep structure of zones of petrogeneration Northern and the Bering seas on aeromagnetic and satellite magnetometric datas. Research lateral and vertical heterogeneitys an earth's crust of Northern sea is carried out on the basis of the analysis of measurements of satellite Champ at height of 100 km and the digital database created on materials of sea shooting of a geomagnetic field, executed on non-magnetic schooner "Zarya". On sea measurements in Northern sea through large oil fields and gas ( Frigg, Ekofisk, Forties trough, Leman, etc.). Geomagnetic sections for an interval of depths from 1 up to 30 km are constructed. It has allowed to study character of distribution of magnetization of breeds of a cover, horizontal lamination intracore layers of an earth's crust and to allocate in zones petrogeneration synvertical fluidoconduct zones the channels described by alternation of not magnetic and low-magnetic layers. They were showed on geomagnetic sections as permeable zones quasi- laminated structures with the lowered magnetic properties in an interval of depths from 8 up to 28 km. Comparison to a map of the magnetic anomalies measured at height of 100 km by satellite Champ, has shown, that areas of the greatest petrocongestions North Sea ????? at height of 100 km are dated for a zone of gradients and a minimum of northeast displacement of regional anomalies of western and east blocks of Northern sea. It corresponds to representations about an orientation of a fissuring zone and the increased size of a geothermal gradient North Sea rift and is corresponded position allocated on hydromagnetic structures deep fluidoconduct channels. Thus, distribution to water areas of deposits of deposits is emphasized not only low-magnetic areas in a thickness of a sedimentary cover where they are directly located, but also by not magnetic lenses in breeds of the base spreading it in intervals of depths of 8-11 km and 15-18 km. The oil-gas-bearing province of the Bering Sea occupies uniform sedimentary megabasin. On aeromagnetic measurements at height of 300 m are constructed geomagnetic sections in an interval of depths from 0.5 km up to 25 km crossing the basic zones possible petrocongestions with traps structural and of structural - stratigraphic types. Distribution of magnetization in an interval of development of potentially productive sandy layers on depths from 1 up to 5 km is received. The most perspective zones possible petrocongestions are allocated in Ilpinsky, Olutorsky and Olutorsko-Komandorsky sedimentary basins. The deep permeable zone with system of low-magnetic lenses in intervals of depths 8-10, 12, 18-20 km, dated to Pilgin zone possible petrocongestions was most brightly showed. Comparison of ground supervision to the data received by results of measurements from satellite Champ at height of 100 km, shows, that large oil-gas-bearing Vertuhovskaya, Karaginskaya, Pahachiskaya and Pilginskaya zones are dated for a minimum isometric satellite magnetic anomaly. At height of 400 km this minimum keeps the form that speaks about stability of a condition of the permeable zones supervising oil-gas-bearing.

Litvinova, Tamara; Krasinsky, Egor; Petrova, Alevtina; Demina, Irina

2010-05-01

79

Effects of Exsolution Lamellae on Magnetic Properties of Crustal Rocks and Contributions to Remanent Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

Magnetic anomalies from crustal sources are measured over a wide range of scales and elevations, from near-surface to satellites. They reflect magnetic minerals in rocks, which respond to the changing planetary magnetic field. Anomalies are influenced by the geometry of the geological bodies, and magnetic properties of the minerals. Commonly, magnetism of continental crust has been described in terms of bulk ferrimagnetism of minerals, and much attributed to induced magnetization. Though remanent magnetization was crucial for dating the ocean floor, and is important in mineral exploration, its contribution to continental magnetic anomalies is commonly ignored. Over the last decade studying remanent anomalies in crustal rocks, we discovered a new type of remanence, 'lamellar magnetism'. This is due to layers of mixed Fe2+/Fe3+ valence at (001) contacts between exsolution lamellae and hosts of ilmenite and hematite. The mixed-valence contact layers are placed by chemistry between hematite Fe3+ layers and ilmenite Ti4+ layers, where they provide reduction of ionic charge imbalance. Placement requires that the uncompensated spin of contact layers on opposite sides of a lamella be in-phase magnetically. This produces a net ferrimagnetic moment per lamella of ~4 uB per formula unit, regardless of lamella thickness, thus net moment is greatest with the greatest density of magnetically in-phase fine lamellae created during slow cooling. We can show that in-phase magnetization of lamellae is greatly enhanced in foliated samples, where the statistical (001) plane is parallel to the Earth field at the time of exsolution. Strictly speaking, the resulting magnetization is a chemical remanence with very high stability. Lamellar magnetism is responsible for numerous remanent magnetic anomalies in continental rocks we present here. We highlight some bodies with NRMs > 20 A/m which are possible analogs for sources of remanent anomalies on Mars.

McEnroe, S. A.; Robinson, P.; Fabian, K.; Brown, L. L.; Harrison, R. J.

2011-12-01

80

Tracking pigeons in a magnetic anomaly and in magnetically "quiet" terrain  

NASA Astrophysics Data System (ADS)

Pigeons were released at two sites of equal distance from the loft, one within a magnetic anomaly, the other in magnetically quiet terrain, and their tracks were recorded with the help of GPS receivers. A comparison of the beginning of the tracks revealed striking differences: within the anomaly, the initial phase lasted longer, and the distance flown was longer, with the pigeons' headings considerably farther from the home direction. During the following departure phase, the birds were well homeward oriented at the magnetically quiet site, whereas they continued to be disoriented within the anomaly. Comparing the tracks in the anomaly with the underlying magnetic contours shows considerable differences between individuals, without a common pattern emerging. The differences in magnetic intensity along the pigeons' path do not differ from a random distribution of intensity differences around the release site, indicating that the magnetic contours do not directly affect the pigeons' routes. Within the anomaly, pigeons take longer until their flights are oriented, but 5 km from the release point, the birds, still within the anomaly, are also significantly oriented in the home direction. These findings support the assumption that magnetically anomalous conditions initially interfere with the pigeons' navigational processes, with birds showing rather individual responses in their attempts to overcome these problems.

Schiffner, Ingo; Fuhrmann, Patrick; Wiltschko, Roswitha

2011-07-01

81

Interpretation of long- and short-wavelength magnetic anomalies  

USGS Publications Warehouse

Magset was launched on October 30, 1979. More than a decade of examining existing data, devising appropriate models of the global magnetic field, and extending methods for interpreting long-wavelength magnetic anomalies preceded this launch Magnetic data collected by satellite can be interrupted by using a method of analysis that quantitively describes the magnetic field resulting from three-dimensional geologic structures that are bounded by an arbitrary number of polygonal faces, Each face my have any orientation and three or more sides. At each point of the external field, the component normal to each face is obtained by using an expression for the solid angle subtended by a generalized polygon. The "cross" of tangential components are relatively easy to obtain for the same polygons. No approximations have been made related to orbit height that restrict the dimensions of the polygons relative to the distance from the external field points. This permits the method to be used to model shorter wavelength anomalies obtained from aircraft or ground surveys. The magnetic fields for all the structures considered are determine in the same rectangular coordinate system. The coordinate system is in depended from the orientation of geologic trends and permits multiple structures or bodies to be included in the same magnetic field calculations. This single reference system also simplified adjustments in position and direction to account for earth curvature in regional interpretation.

DeNoyer, John M.

1980-01-01

82

Spreading of Magnetic Reconnection X-lines in Three Dimensions  

NASA Astrophysics Data System (ADS)

Naturally occurring magnetic reconnection often begins in a spatially localized region and spreads in the out-of-plane direction in time. A number of authors have studied this problem for magnetotail applications such as substorms and bursty bulk flows, for which the out-of-plane (guide) field is typically small. However, spreading also occurs in laboratory experiments and two-ribbon solar flares (such as the Bastille Day flare), and is inferred to occur at the dayside magnetopause. The reconnection site in each of these settings is known or thought to have a significant guide field. With no guide field, it was shown that the reconnection spreading is controlled by the species that carries the current. However, laboratory experiments with a large guide field (Katz et al., Phys. Rev. Lett., 104, 255004, 2010) revealed that spreading takes place in both directions at the Alfven speed based on the guide field. This implies a qualitative change of behavior as the guide field varies. We present a scaling argument for the condition on the guide field at which the nature of the spreading switches from being caused by current carriers to Alfven waves. Further, we show results of three-dimensional two-fluid simulations that agree with the theory. We discuss applications to observations.

Cassak, Paul; Shepherd, Lucas

2012-03-01

83

Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)  

NASA Astrophysics Data System (ADS)

The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We speculate that intensive magma intrusion occurred beneath the caldera wall and has provided the heat to generate hydrothermal fluid, which has been spouting out through the caldera wall faults. The surface expression of the vent field extends beyond the alteration zone inferred from the magnetization distribution, spreading upwards in the caldera wall. High-resolution topography around the Hakurei site indicates that the hydrothermal vents are generally distributed over a landform of slope failure. These observations would imply that hydrothermal fluid rising up in the up-flow zone moves laterally as well when it comes near the seafloor, probably along numerous fractures and fissures in the caldera wall. The distribution of pre-existing faults and fractures may rather control the fluid flow pathways in the shallow part and condition the surface extent of the vent field.

Honsho, C.; Ura, T.; Kim, K.

2013-12-01

84

1414 IEEE TRANSACTIONS ON MAGNETICS, VOL. 47, NO. 5, MAY 2011 Ships Magnetic Anomaly Computation With Integral Equation and Fast  

E-print Network

1414 IEEE TRANSACTIONS ON MAGNETICS, VOL. 47, NO. 5, MAY 2011 Ships Magnetic Anomaly Computation) and a fast multipole algorithm (FMM) in order to model ships magnetic anomaly. complex geometries of real, magnetostatics, marine technology. I. INTRODUCTION ANAVAL vessel, magnetized in the earth's magnetic field

Paris-Sud XI, Université de

85

A magnetic anomaly of possible economic significance in southeastern Minnesota  

USGS Publications Warehouse

An aeromagnetic survey in southeastern Minnesota by the U. S. Geological Survey in cooperation with the State of Minnesota has revealed a high-amplitude, linear, and narrow magnetic feature that suggests a possible source of Precambrian iron-formation of economic value. For the past few years the U. S. Geological Survey has been conducting detailed geophysical studies of the midcontinent gravity anomaly--a broad, high-amplitude feature that extends from Lake Superior through the States of Minnesota, Iowa, Nebraska, and part of Kansas. As part of this study an aeromagnetic survey of the southern part of the State was made in cooperation with the State of Minnesota during the summer of 1963, in which a linear high-amplitude anomaly of the order of 4,000 gammas was discovered. Because of the high amplitude, the linearity, and the narrowness of the magnetic feature, it is believed the source may be Precambrian iron-formation of possible economic value. The anomalous area is in Fillmore County, approximately between the towns of Lanesboro and Peterson in the extreme southeastern part of the State. (See figures 1 and 2.) At the site of the anomaly, Cambrian sedimentary rocks occur in the valley of the Root River, and Ordovician rocks (nearly flat lying) mantle the upland areas. The uplands are largely covered by glacial deposits, which are relatively thin (Paul K. Sims, written communication, 1964). Depths to the Precambrian are estimated to range from 500 feet to 1,000 feet below the surface. The aeromagnetic map shown in figure 2 was compiled from continuous magnetic profiles made along east-west flight lines 1,000 feet above ground, and spaced approximately 1 mile apart. Contour intervals of 20, 100, and 500 gammas were used depending on the intensity. The instrument for the survey was a flux-gate type magnetometer (AN/ASQ-3A) which measures total-field variations. The contour map displays variations in magnetic pattern which are typical of shallow Precambrian rocks. Anomalies of the order of 1,000 gammas are shown along the east and west edges of the map. The outstanding feature is the previously mentioned linear positive anomaly that trends northeast and reaches a peak of 3,960 gammas. The positive anomaly is contoured from data on four consecutive profiles, but only two show high amplitudes. The high-amplitude anomalies along traverses 1 and 2 are shown in figure 3. Depth calculations suggest that the source of the anomaly lies about 1,000 feet below the surface. Assuming a dikelike source and magnetization resulting entirely from induction in the earth's field, several calculations were made in an attempt to fit the magnetic profile taken along the line AA' (see figs. 2 and 4), considered to be a typical cross-section of the magnetic anomaly. Comparisons are shown between observed and computed profiles. The fixed parameters used were (a) distance from detector to source of 2,000 ft; width of dike of 5,000 ft; dip of dike of 75?, 90?, 105? , and 120? , as shown. The best fit occurs when the dike is vertical or dips 75? to the southwest. For these cases, the susceptibility, k, is computed to be 0.016 c.g.s, units, and is comparable to k = 0.02+ calculated by Bath (1962) for the relatively unmetamorphosed iron-formation of the Main Megabi district in Minnesota where the induced magnetization was most likely the dominant magnetization. If the dominant magnetization for the anomaly in Fillmore County were remanent rather than induced, the economic importance of the anomaly would be greatly reduced. This anomaly seems sufficiently promising to warrant further geologic and geophysical investigation. Detailed ground magnetic and electrical studies would be useful to delineate the feature. In the final analysis, however, the presence of iron-formation can be determined only by the drill.

Zietz, Isidore

1964-01-01

86

Thermal Sensitivity of MD Hematite: Implication for Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Magnetic remanence of crustal rocks can reside in three common rock-forming magnetic minerals: magnetite, pyrrhotite, and hematite. Thermoremanent magnetization (TRM) of magnetite and pyrrhotite is carried mostly by single domain (SD) grains. The TRM of hematite grains, however, is carried mostly by multidomain (NM) grains. This characteristic is illustrated by TRM acquisition curves for hematite of variable grainsizes. The transition between truly NM behavior and tendency towards SD behavior his been established between hematite grainsizes of 0. 1 and 0.05 mm. Coarse grainsize of lower crustal rocks and the large sensitivity of MD hematite grains to acquire TRM indicates that hematite could be a significant contributor to long-wavelength magnetic anomalies.

Kletetschka, Gunther; Wasilewski, Peter J.; Taylor, Patrick T.

1999-01-01

87

Automatic Detection of UXO Magnetic Anomalies Using Extended Euler Deconvolution Kristofer Davis*  

E-print Network

anomalies in total-field magnetic data based on the concept of structural index (SI) of a magnetic anomaly and cost-effective methods for discriminating UXO targets. Recent work by Billings et al. (2002) has-based discrimination algorithms depends on the ability to automatically detect targets by picking the anomalies

88

Regional gravity and magnetic anomalies in the eastern Snake River Plain, Idaho  

Microsoft Academic Search

Over the eastern Snake River Plain, the Bouguer gravity anomaly and the magnetic intensity are, in general, high. In detail, both the gravity and the magnetic anomalies are a complex of highs and lows, in contrast to the simpler anomalies over the western Snake River Plain. The broad gravity high associated with the eastern Snake River Plain cannot be produced

D. R. Mabey

1978-01-01

89

Improving the geological interpretation of magnetic and gravity satellite anomalies  

NASA Technical Reports Server (NTRS)

Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication.

Hinze, William J.; Braile, Lawrence W.; Vonfrese, Ralph R. B.

1987-01-01

90

Numerical Simulations on Origin of Galilean Moons' Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B(sub 0) with a fixed orientation but varying field strength. Our results show that a finite B(sub 0) can substantially alter the dynamo processes inside the core. When the ambient field strength B(sub 0) increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B(sub 0). Furthermore, the generated field tends to be temporally more stable.

Jiao, LiQuo; Kuang, WeiJia; Ma, ShiZhuang

2011-01-01

91

Preliminary interpretation of satellite gravity and magnetic anomalies in the region of the Philippine Sea Plate  

NASA Astrophysics Data System (ADS)

The Philippine Sea, situated in the northwestern Pacific, is one of the largest marginal seas on the Earth. Analysis of the Philippine Sea's intraplate fault tectonic systems and lithosphere's density and magnetism structures has a significant contribution to understanding not only the dynamic principles of subduction and convergence zones but also effect of plate subduction on back-arc area. It is also important to have cognizance for structure evolution of the ocean crust, the tension and extending progress of marginal sea basins and the mechanisms of geodynamics. Meanwhile, it can be a significant approach for researching the evolution of the East China Sea and the South China Sea. Using high-precision gravity forwarding method based on spatial domain in spherical coordinate, we have calculated the Bouguer gravity disturbance (BGD) in the Philippine Sea based on the ETOPO1 1 arc-minute topography & bathymetry data and the gravity field model EIGEN-6C. After removing the gravity effect of the sediments and deep abnormal materials, we make spherical cap harmonic analysis of the residual anomaly and obtain the topography of Moho and apparent-density's distribution of our study area by alternate iteration inversion method. Then, we calculate the distributions of the study area's magnetic anomalies based on the Earth magnetic model NGDC720, reduce to the pole of the study area's magnetic anomalies by the equivalent source method based on spherical prism magnetic forwarding, inverse the processed magnetic anomalies with spherical cap harmonic analysis to obtain the topography of Curie surface and the apparent magnetic susceptibility distribution. Finally, we divide the Philippine Sea block into tectonic units and derive the faults distributions through the analysis of gravity magnetic anomalies' linear characteristics. The results show that West Philippine Basin is divided by Central Basin Ridge into two block units, the tectonic trend of the north block is south-east, but there is a trend migration to the south for the south tectonic block which may be related to the southeast rift of the Eurasian plate and the northwest spread of the Pacific plate. We find that there are faults of about south-north direction between the north block of West Philippine Basin and Urdaneta Plateau. Moreover, the tectonic is complicated in the south block of West Philippine Basin and there are no apparent tectonic trends. The Shikoku Basin and Parece Vela Basin have lower Bouguer gravity than in West Philippine Basin indicating that the West Philippine Basin has lower thickness crust and becomes thicker from north to south. The density distribution of Philippine plate is not homogeneous, which presents that it is higher in the west plate than the east and shows a low density and low magnetism at Central Basin Ridge. And there are many clear and strong striped magnetic anomalies in the West Philippine Basin having the direction of NWW-SEE, but in Shikoku Basin and Parece Vela Basin the magnetic anomaly is very weak. This study is supported by the National Science Foundation of China (Grant No.: 40730317 and 40774060 ) and International Cooperation Projection in Science and Technology (Grant No.: 2010DFA24580).

Chen, C.; Hu, Z.; Du, J.; Wang, Q.

2011-12-01

92

Evaluation of Magnetic Anomalies Located in Lower Bayou Teche, St. Mary Parish, Louisiana.  

National Technical Information Service (NTIS)

This report presents results of testing and assessment of eleven previously recorded magnetic anomalies located in Lower Bayou Teche, St. Mary Parish, Louisiana. Maintenance dredging of Lower Bayou Teche may impact several of the eight anomalies evaluated...

A. R. Saltus, R. C. Goodwin, W. P. Athens

1991-01-01

93

The Stand Locations of Ancient People Depending On The Intensity of Local Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

For analysis 235 ancient people stands in the region of Kursk magnetic anomaly (one of the strongest anomaly all over the world) were chosen. All stands were dated by radiocarbon method and are placed in the State List of Archaeological Monuments of Belgorod Region. The oldest stands were radiocarbon dated to 70,000-50,000 years before present (kyr BP). All stands are located along the 300 km valley of Oskol river, having got a homogeneous climatic conditions. At the half of the valley the intensity of local magnetic field is rather low (0-1000 nT), so the region should be considered as the most comfort area for human occupation. The distribution of human occupation at this site looks as follows: 100% at 50-10 kyr BP, 94% at 6-4 kyr BP, 87% at 4-2 kyr BP, 83% at 3-2 kyr BP and 64% at 2-1 kyr BP. At ancient time humans preferred to occupy the sites with low magnetic field intensity. The spreading of human occupation outside of the comfort zone (more than 34%) began at Iron Age (2-1 kyr BP). Thus it may be concluded that in Palaeolithic age (50-10 kyr BP) humans avoided the area with enhanced level of local magnetic field. This seems to be connected to bad influence of the factor on human health, lower level of orientation on the surface, may be to different plant distribution features, and state of ancient people anxiety. The spreading of human occupation out of the comfort zone at rather recent time seems to be caused by social-economic activity.

Shatokhin, I. T.; Khramov, A. V.; Shumilov, O. I.; Kasatkina, E. A.; Raspopov, O. M.

94

Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly  

NASA Astrophysics Data System (ADS)

An atypical nighttime spread-F structure is observed at or above the F-layer, near the crest of the ionospheric equatorial ionization anomaly region (EIA). This ionospheric atypical spread-F phenomenon was observed using two closed spaced (~115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21 S, 45.97 W) and Cachoeira Paulista (22.70 S, 45.01W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below to the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary GPS data were used to investigate the ionosphere environment conditions, during both events. The 6 GPS stations used in this study are distributed from near the equatorial region to low latitudes.

Fagundes, Paulo Roberto

2012-07-01

95

Comparison between the recent U.S. composite magnetic anomaly map and Magsat anomaly data  

NASA Technical Reports Server (NTRS)

The present investigation is concerned with a comparison of Magsat data with a Composite Magnetic Anomaly Map (CMAM) of the conterminous U.S. reported by Zietz (1982). The investigation was initiated to test the validity of the satellite measurements, and to provide insights into error or problems in either data set. It is found that upward continuation of the digital CMAM data is not in qualitative agreement with the Magsat map. However, if a least squares fit polynomial surface is taken out prior to upward continuation, there is improved quantitative agreement between a residual CMAM and Magsat. Causes for the remaining differences between the residual, upward continued CMAM and the Magsat map are also considered.

Schnetzler, C. C.; Taylor, P. T.; Langel, R. A.; Hinze, W. J.; Phillips, J. D.

1985-01-01

96

The Chiral Magnetic Effect and Anomaly-Induced Transport  

E-print Network

The Chiral Magnetic Effect (CME) is the phenomenon of electric charge separation along the external magnetic field that is induced by the chirality imbalance. The CME is a macroscopic quantum effect - it is a manifestation of the chiral anomaly creating a collective motion in Dirac sea. Because the chirality imbalance is related to the global topology of gauge fields, the CME current is topologically protected and hence non-dissipative even in the presence of strong interactions. As a result, the CME and related quantum phenomena affect the hydrodynamical and transport behavior of systems possessing chiral fermions, from the quark-gluon plasma to chiral materials. The goal of the present review is to provide an elementary introduction into the main ideas underlying the physics of CME, a historical perspective, and a guide to the rapidly growing literature on this topic.

Dmitri E. Kharzeev

2013-12-11

97

Current disruption and its spreading in collisionless magnetic reconnection  

SciTech Connect

Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2013)] have disclosed current disruption in the absence of an externally imposed guide field. During current disruption in MRX, both the current density and the total observed out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here, we show that current disruption is an intrinsic property of the dynamic formation of an X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of the dimensionality (2D or 3D) of reconnection. An analytic expression for the current drop is derived from Ampere's Law. Its predictions are verified by 2D and 3D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized magnetic reconnection spreads along the direction of the electron drift velocity with a speed which depends on the wave number of the perturbation. The implications of these results for MRX are discussed.

Jain, Neeraj; Büchner, Jörg [Max-Planck/Princeton Center for Plasma Physics, Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau (Germany)] [Max-Planck/Princeton Center for Plasma Physics, Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau (Germany); Dorfman, Seth [University of California Los Angeles, Los Angeles, California 90095 (United States)] [University of California Los Angeles, Los Angeles, California 90095 (United States); Ji, Hantao [Max-Planck/Princeton Center for Plasma Physics, Deparment of Astrophysica Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08540 (United States)] [Max-Planck/Princeton Center for Plasma Physics, Deparment of Astrophysica Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08540 (United States); Surjalal Sharma, A. [Department of Astronomy, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Astronomy, University of Maryland, College Park, Maryland 20742 (United States)

2013-11-15

98

Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly  

NASA Astrophysics Data System (ADS)

An atypical nighttime spread-F structure is observed on ionograms at or above the F2 trace, near the crest of the ionospheric equatorial ionization anomaly (EIA) region. This ionospheric atypical spread-F phenomenon was observed using two closed spaced (˜115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21°S, 45.97°W) and Cachoeira Paulista (22.70°S, 45.01°W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears in the ionogram as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary data from six GPS station were used to investigate the ionosphere environment conditions, during both events. The six GPS stations used in this study are distributed from near the equatorial region to low latitudes and provide evidence that the atypical nighttime spread-F structures are not related with large scale equatorial irregularities (plasma bubbles).

Fagundes, P. R.; Bittencourt, J. A.; de Abreu, A. J.; Moor, L. P.; Muella, M. T. A. H.; Sahai, Y.; Abalde, J. R.; Pezzopane, M.; Sobral, J. H. A.; Abdu, M. A.; Pimenta, A. A.; Amorim, D. C. M.

2012-04-01

99

Initial mapping and interpretation of lunar crustal magnetic anomalies using Lunar Prospector magnetometer data  

Microsoft Academic Search

Maps of relatively strong crustal magnetic field anomalies detected at low altitudes with the magnetometer instrument on Lunar Prospector are presented. On the lunar nearside, relatively strong anomalies are mapped over the Reiner Gamma Formation on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Oceanus Procellarum. The main Rima Sirsalis anomaly does not correlate

L. L. Hood; A. Zakharian; J. Halekas; D. L. Mitchell; R. P. Lin; M. H. Acuña; A. B. Binder

2001-01-01

100

Absolute Magnetization Distribution on Back-arc Spreading Axis Hosting Hydrothermal Vents; Insight from Shinkai 6500 Magnetic Survey  

NASA Astrophysics Data System (ADS)

Near-bottom magnetic profiling using submersible, deep-tow, Remotely Operated Vehicle (ROV) and Autonomous Underwater Vehicle (AUV) make possible to conduct high-resolution surveys and depict detailed magnetic features reflecting, for instance, the presence of fresh lavas or hydrothermal alteration, or geomagnetic paleo-intensity variations. We conducted near-bottom three component magnetic measurements onboard submersible Shinkai 6500 in the Southern Mariana Trough, where five active hydrothermal vent fields (Snail, Yamanaka, Archean, Pica, and Urashima sites) have been found in both on- and off-axis areas of the active back-arc spreading center, to detect signals from hydrothermally altered rock and to distinguish old and new submarine lava flows. Fourteen dives were carried out at an altitude of 1-40 m during the R/V Yokosuka YK10-10 and YK10-11 cruises in 2010. We carefully corrected the effect of the induced and permanent magnetizations of the submersible by applying the correction method for the shipboard three-component magnetometer measurement modified for deep-sea measurement, and subtracted the IGRF values from the corrected data to obtain geomagnetic vector anomalies along the dive tracks. We then calculated the synthetic magnetic vector field produced by seafloor, assumed to be uniformly magnetized, using three dimensional forward modeling. Finally, values of the absolute magnetizations were estimated by using a linear transfer function in the Fourier domain from the observed and synthetic magnetic anomalies. The distribution of estimated absolute magnetization generally shows low values around the five hydrothermal vent sites. This result is consistent with the equivalent magnetization distribution obtained from previous AUV survey data. The areas of low magnetization are also consistent with hydrothermal deposits identified in video records. These results suggest that low magnetic signals are due to hydrothermal alteration zones where host rocks are demagnetized by hydrothermal circulation. The low magnetization zones around the off-axis vent sites are about ten times wider than those surrounding the on-axis sites, possibly reflecting the longer duration of hydrothermal circulation at these sites. Another interesting result is that the absolute magnetization shows extremely high intensities (>80 A/m) at the neo volcanic zones (NVZ) and relatively low intensities (<10 A/m) two to five kilometers away from the NVZ. These variations are quite consistent with those of the Natural Remanent Magnetization measured on basalt samples, suggesting that the low-temperature oxidation of host rock due to the reaction with seawater has completed within a few kilometers distance from the spreading axis. We conclude that the magnetization of the uppermost oceanic crust decreases with age due to the combination of the both hydrothermal rapid alteration and the low-temperature gradual alteration processes.

Fujii, M.; Okino, K.; Honsho, C.; Mochizuki, N.; Szitkar, F.; Dyment, J.

2013-12-01

101

On long-wavelength magnetic anomalies over Indian region  

NASA Technical Reports Server (NTRS)

A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data.

Srinivasan, S.; Carlo, L.; Rastogi, R. G.; Singh, B. P. (principal investigators)

1983-01-01

102

Regional mapping of the lunar magnetic anomalies at the surface: Method and its application to strong and weak magnetic anomaly regions  

NASA Astrophysics Data System (ADS)

We have developed a new method for regional mapping of the lunar magnetic anomalies as the vector field at the surface using the satellite observation, that is the surface vector mapping (SVM). The SVM is based on the inverse boundary value problem with a spherical boundary surface. There are two main procedures for reducing effects of bias and noise on mapping: (1) preprocessing the data to provide first derivatives along the pass, and (2) the Bayesian statistical procedure in the inversion using Akaike's Bayesian Information Criterion. The SVM was applied to two regions: the northwest region of the South Pole-Aitken basin as a strong magnetic anomaly region, and the southeast region of the lunar near side as a weak magnetic anomaly region. Since the results from the different datasets of the Kaguya and Lunar Prospector observations show good consistency, characteristic features of the lunar magnetic anomalies at the surface are considered to be well estimated except for components of wavelength shorter than about 1°. From the results by the SVM, both of the regions show elongation patterns of the lunar magnetic anomalies, suggesting lineated structures of the magnetic anomaly sources.

Tsunakawa, Hideo; Takahashi, Futoshi; Shimizu, Hisayoshi; Shibuya, Hidetoshi; Matsushima, Masaki

2014-01-01

103

Optical effects of space weathering in lunar crustal magnetic anomaly regions based on CE-1 observations  

NASA Astrophysics Data System (ADS)

The discovery of mini-magnetospheres above the lunar surface suggests that magnetic shielding could have led to anomalous space weathering (little darkening with limited reddening) in magnetic anomaly regions. Using spectral data from Chang'E 1 Imaging Interferometer (IIM) and data from Lunar Prospector's magnetometer, we instigate the relationship between lunar crustal magnetic anomalies and the optical effects in those areas in association with space weathering. The IIM onboard China's Chang'E 1 (CE-1) spacecraft is a Fourier transform Sagnac imaging spectrometer operating in the visible to near infrared (0.48-0.96 ?m) spectral range, with 32 channels at spectral intervals of 325.5 cm-1. We selected four regions with crustal magnetic anomalies to study their albedo properties: three lunar swirls (Gerasimovich, Mare Marginis, and Reiner Gamma) and the area antipodal to Herzsprung. We found that all three of the anomalous albedo areas are associated with magnetic anomalies, however, no anomalous albedo feature is found in the last magnetic anomaly area. In addition, we also studied the correlation between magnetic anomaly strength and albedo anomaly on a global scale. Our initial analysis suggests an overall tread of less darkening with increased magnetic anomaly.

Li, H.; Wang, X.; Cui, J.; Fu, X.; Zhang, G.; Yao, M.; Liu, B.; Liu, J.; Li, C.; Ouyang, Z.

2013-12-01

104

Deep-tow study of magnetic anomalies in the Pacific Jurassic Quiet Zone  

E-print Network

The Jurassic Quiet Zone (JQZ) is a region of low amplitude, difficult-to-correlate magnetic anomalies located over Jurassic oceanic crust. We collected 1200 km of new deep-tow magnetic anomaly profiles over the Pacific JQZ that complement 2 deep...

Tominaga, Masako

2006-10-30

105

Estimating Antarctic Near-Surface Magnetic Anomalies from Oersted and CHAMP Satellite Magnetometer Observations  

NASA Technical Reports Server (NTRS)

Significant improvement in predicting near-surface magnetic anomalies can result from the highly accurate magnetic observations of the CHAMP satellite that is orbiting at about 400 km altitude. In general, regional magnetic signals of the crust are strongly masked by the core field and its secular variations due to wavelength coupling in the spherical harmonic representation and thus are difficult to isolate in the satellite measurements. However, efforts to isolate the regional lithospheric from core field components can exploit the correlations between the CHAMP magnetic anomalies and the pseudo magnetic effects inferred from gravity-derived crustal thickness variations. In addition, we can use spectral correlation theory to filter the static lithospheric field components from the dynamic external field effects. Employing these procedures, we processed the CHAMP magnetic conservations for an improved magnetic anomaly map of the Antarctic crust. Relative to the much higher altitude Oersted and noisier Magsat observations, CHAMP magnetic anomalies at 400 km altitude reveal new details on the effects of intra-crustal magnetic features and crustal thickness variations of the Antarctic. Moreover, these results greatly facilitate predicting magnetic anomalies in the regional coverage gaps of the ADMAP compilation of Antarctic magnetic anomalies from shipborne, airborne and ground surveys. Our analysis suggests that considerable new insights on the magnetic properties of the lithosphere may be revealed by a further order-of-magnitude improvement in the accuracy of the magnetometer.

vonFrese, Ralph R. B.; Kim, Hyung Rae; Gaya-Pique, Luis R.; Taylor, Patrick T.; Golynsky, Alexander V.; Kim, Jeong Woo

2004-01-01

106

Magnetic Structure of Backarc Spreading Axis with Hydrothermal Vents; the Southern Mariana Trough  

NASA Astrophysics Data System (ADS)

Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as habitat of microbial communities. The substantial variation of hydrothermal systems in various tectonic settings has important implications for the magnetic structure of oceanic crust. It has been very difficult to detect the geophysical signature of hydrothermal systems from sea-surface data because the small scale of hydrothermal systems is below the limit of resolution. The advance of near-bottom survey methods using a submersible, deep-tow, ROV and AUV has made possible high-resolution geophysical mapping around hydrothermal areas. Near-bottom magnetic surveys can provide direct information on the magnetization of the shallower oceanic crust, implying hydrothermal alteration both in active and fossil vent sites. Near-bottom three component magnetic measurements on submersible Shinkai 6500 were carried out at hydrothermal fields in the Southern Mariana Trough, a slow spreading backarc basin. Fourteen dive surveys were conducted during cruises YK11-10 and YK10-11. We investigated the magnetic structure of four hydrothermal systems located at on- and off-axis to clarify how the geophysical and geological setting controls the fluid circulation at small scale. Recent researches at slow spreading ridges showed a relationship between crustal magnetic structure and host rock around hydrothermal vents (e.g. Tivey and Dyment, 2010), but no observation at backarc spreading axis has been reported so far. We carefully corrected the effects of induced and permanent magnetizations of the submersible by applying the method of Isezaki [1986] with dumped least-square method (Honsho et al., 2009). After subtracting the IGRF from the corrected observed data, we obtained geomagnetic vector anomalies in geographical coordinate. For three transects of the axis, we applied three methods; 2D inversion technique (Parker and Huestis, 1972), 2D forward modeling technique (Honsho et al, 2009) and 2D direct inversion technique (Hussenoeder et al., 1995). Transect 1 (T1) and transect 2 (T2) are parallel and very closely located, crossing the neo-volcanic zone near an on-axis hydrothermal site (Snail Site) at different altitude, 2m and 30m. Transect 3 (T3) also crosses a large on-axis volcanic mound on which another hydrothermal site (Yamanaka Site) is located. The equivalent magnetization calculated on T1 and T2 are similar although their resolutions are different. The one along T3 shows high values around the large volcanic mound and an area of low magnetization near a hydrothermal field recognized from high-resolution bathymetry (Yoshikawa et al., 2012). A similar reduction of magnetization above hydrothermal fields was also reported in basalt-hosted sites along the Mid Atlantic Ridge. The detailed bathymetry (2m grid) collected by AUV Urashima in the study area allows us to investigate the effect of three dimensional structure. We estimate magnetization using a new technique based on 3D forward modeling (Szitkar et al, this meeting). A preliminary result shows a similar but more detailed magnetic structure around the Yamanaka Site compared to results of the 2D methods.

Fujii, M.; Okino, K.; Mochizuki, N.; Honsho, C.; Szitkar, F.; Dyment, J.; Nakamura, K.

2012-12-01

107

Paleomagnetic and rock magnetic characterization of magnetic anomalies in the Central Iberian Arc (Iberian Peninsula)  

NASA Astrophysics Data System (ADS)

The Central Iberian Arc is one of the four oroclines delineated by the European Variscan Belt. It is located in NW and Central Iberia and characterized by a conspicuous magnetic response. The most intense magnetic anomaly within this arc is the so called Eastern Galicia Magnetic Anomaly (EGMA; Aller et al., 1994), located in the northern part of Spain and associated to the Lugo-Sanabria dome, an extensional structure in the inner part of arc. The aeromagnetic map of the Iberian Peninsula (Ardizone et al., 1989; Miranda et al., 1989) shows that the EGMA continues to Central Spain and turns back to the Atlantic Ocean, as a broad positive anomaly, delineating a tight fold at the core of the Central Iberian Arc. The source of the EGMA seems to be magnetite-bearing migmatites and inhomogeneous granites formed during an extensive late Carboniferous thermal event triggered by Variscan crustal thickening. These rocks were modeled as a lens-shaped body up to 12 km thick with magnetic susceptibility values between 0.02and 0.03 SI units, that underlie the whole dome extension and continues toward the west of it (Ayarza and Martínez Catalán, 2007). However, this body crops out only in the deepest and northernmost part of the dome, in the Xistral Tectonic Window, and there, only its upper part is accessible. Migmatites and granitoids are abundant along the rest of the anomaly, but their magnetic susceptibility is low. Thus, the source of the magnetic anomaly should be buried there and its nature is unknown. Paleomagnetic and rock magnetic studies in the outcropping rocks responsible for the EGMA have been carried out, adding new constraints to the origin of this anomaly. Rock magnetic analysis as progressive acquisition of IRM, hysteresis loops, thermomagnetic experiments and X-ray indicate that the ferromagnetic fraction is dominated by multidomain magnetite and titanohematite. It is remarkable the unusual high anisotropy of magnetic susceptibility of these rocks, showing degree of anisotropy values 1.2magnetic fabric shows Variscan affinity, related to an extensional ductile detachment that bounds the Lugo-Sanabria dome to the west. The paleomagnetic analysis consisting in thermal and alternating field demagnetization allows isolating a stable paleomagnetic component with high coercivity and maximum unblocking temperatures of about 630°C, that systematically shows reversed polarity. This component has been interpreted as a remagnetization because its mean direction match those of the Iberian Peninsula after anticlockwise rotation related to the opening of the Bay of Biscay during the Early Cretaceous. All these data must be included in the models in order to place new constraints on the origin, position, and shape of the source and to asses whether all the broad magnetic anomaly at the core of the Central Iberian Arc has the same origin as the EGMA, or a deeper source contributes to it and to the rest of the anomaly.

Villalain, J.; Ayarza, P.; Martinez-Catalan, J. R.; Álvarez-Lobato, F.; Gómez-Barreiro, J.; Suárez Barrios, M.; Torres-López, S.

2013-12-01

108

Surveying the South Pole-Aitken basin magnetic anomaly for remnant impactor metallic iron  

NASA Astrophysics Data System (ADS)

The Moon has areas of magnetized crust (“magnetic anomalies”), the origins of which are poorly constrained. A magnetic anomaly near the northern rim of South Pole-Aitken (SPA) basin was recently postulated to originate from remnant metallic iron emplaced by the SPA basin-forming impactor. Here, we remotely examine the regolith of this SPA magnetic anomaly with a combination of Clementine and Lunar Prospector derived iron maps for any evidence of enhanced metallic iron content. We find that these data sets do not definitively detect the hypothesized remnant metallic iron within the upper tens of centimeters of the lunar regolith.

Cahill, Joshua T. S.; Hagerty, Justin J.; Lawrence, David J.; Klima, Rachel L.; Blewett, David T.

2014-11-01

109

Anomaly induced chiral magnetic current in a Weyl semimetal: Chiral electronics  

NASA Astrophysics Data System (ADS)

Electric circuits involving Weyl semimetals possess unusual properties induced by the quantum anomaly. The chiral magnetic current in a Weyl semimetal subjected to magnetic field modifies the behavior of such circuits in a drastic way. We consider two explicit examples: (i) a circuit involving the “chiral battery” and (ii) a circuit that can be used as a “quantum amplifier” of magnetic field. The unique properties of these circuits stem from the chiral anomaly and may be utilized for creating “chiral electronic” devices.

Kharzeev, Dmitri E.; Yee, Ho-Ung

2013-09-01

110

New frontiers in magnetic field interpretation and modeling: Examples from the World Digital Magnetic Anomaly Map  

NASA Astrophysics Data System (ADS)

The World Digital Magnetic Anomaly Map is a joint effort on the part of the marine, airborne, and satellite magnetic communities to stitch together a unified map of the earth's lithospheric magnetic field. Several preliminary versions of this map will be exhibited during AGU, and this presentation will highlight interpretations of data that have gone into making this map. Examples to be discussed include 1) the Chicxulub impact structure, 2) geodynamical interpretations of dike swarms, 3) structural and tectonic interpretations of aeromagnetic maps over forearc basins with Cenozoic to Recent faulting, 4) heat flux beneath the Antarctic ice sheet, 5) the role of magnetic interpretations in identifying diamond-bearing kimberlites, and 6) structural inferences drawn from magnetic surveys over the West Siberian basin, and the Urengoy gas field.

Purucker, M.

2006-12-01

111

Contributions of cretaceus quiet zone natural remanent magnetization to Magsat anomalies in the Southwest Indian Ocean  

NASA Technical Reports Server (NTRS)

The Magsat magnetic anomalies over the Southwest Indian Ocean are modeled using a combination of induced plus viscous remanent magnetization (IM/VRM) and natural remanent magnetization (NRM). Two broad, roughly parallel, SW to NE trending triple-peaked positive anomalies dominate the region, one lying south of Africa and the other north of Antarctica. Although these anomaly peaks generally correspond with the Agulhas Plateau/Maud Rise, Mozambique Plateau/Astrid Ridge, and Madagascar Ridge/Conrad Rise conjugate pairs, the IM/VRM contribution from structural characteristics (i.e., crustal thickness) accounts for only about 20% of the anomaly amplitudes. A spatially variable but observationally constrained NRM contribution in Cretaceous Quiet Zone (KQZ) crust is required to account for the location, shape, and amplitude contrast of these anomalies. Many crustal features in the Southwest Indian Ocean near Antarctica have little geophysical data to constrain their structure but do hagve tectonic conjugates near Africa for which much more geophysical data are generally available. Using geophysical and geological constraints from one member to model the magnetization structure of its conjugate reproduces the observed Magsat reduced-to-pole anomalies over both structures very well. This suggests that no significant alteration in their magnetization structure has occurred since the features split. Models of these conjugate structures show that IM/VRM reproduces the Magsat anomalies associated with non-KQZ crust but that both IM/VRM and a dominant NRM component are required to explain the anomalies associated with KQZ crust.

Fullerton, Lawrence G.; Frey, Herbert V.; Roark, James H.; Thomas, Herman H.

1994-01-01

112

Analyzing and modeling gravity and magnetic anomalies using the SPHERE program and Magsat data  

NASA Technical Reports Server (NTRS)

Computer codes were completed, tested, and documented for analyzing magnetic anomaly vector components by equivalent point dipole inversion. The codes are intended for use in inverting the magnetic anomaly due to a spherical prism in a horizontal geomagnetic field and for recomputing the anomaly in a vertical geomagnetic field. Modeling of potential fields at satellite elevations that are derived from three dimensional sources by program SPHERE was made significantly more efficient by improving the input routines. A preliminary model of the Andean subduction zone was used to compute the anomaly at satellite elevations using both actual geomagnetic parameters and vertical polarization. Program SPHERE is also being used to calculate satellite level magnetic and gravity anomalies from the Amazon River Aulacogen.

Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (principal investigators)

1981-01-01

113

The Stand Locations of Ancient People Depending On The Intensity of Local Magnetic Anomalies  

Microsoft Academic Search

For analysis 235 ancient people stands in the region of Kursk magnetic anomaly (one of the strongest anomaly all over the world) were chosen. All stands were dated by radiocarbon method and are placed in the State List of Archaeological Monuments of Belgorod Region. The oldest stands were radiocarbon dated to 70,000-50,000 years before present (kyr BP). All stands are

I. T. Shatokhin; A. V. Khramov; O. I. Shumilov; E. A. Kasatkina; O. M. Raspopov

2002-01-01

114

Magnetic Anomalies of the Fennoscandian Shield on a 2km resolution grid  

NASA Astrophysics Data System (ADS)

Joint magnetic anomaly grid of the Fennoscandian Shield was released 2002, smoothed and used as data for the WDMAM2007. In comparison with MF5 this grid showed superior characteristics to other sets. The data will be released as a 2 km resolution grid for the WDMAM2011 with eventual updates of anomaly levels.

Korhonen, Juha V.; Aaro, Sven; Reidar Skilbrei, Jan; All, Tarmo

2010-05-01

115

Crustal Structure of the Mid-Ocean Ridges 3. Magnetic Anomalies over the Mid-Atlantic Ridge  

Microsoft Academic Search

Fifty-eight magnetic profiles, of varying length, were used in a study of the magnetic anomaly pattern over the mid-Atlantic ridge between 60øN and 42øS. It was found that there is a basic pattern to the magnetic anomalies. A large anomaly is everywhere asso- ciated with the axis of the ridge. This anomaly is continuous over all latitudes except for off-

James R. Heirtzler; Xavier Le Pichon

1965-01-01

116

Curie point depth based on spectrum analysis of the magnetic anomaly data in East and Southeast Asia  

Microsoft Academic Search

The bottom of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. A method to estimate the depth extent of magnetic sources (Curie point depth analysis) was applied to the magnetic anomalies of East and Southeast Asia. Although the geologic and physiographic complexities of this area

A. Tanaka; Y Okubo; O Matsubayashi

1999-01-01

117

Magnetic Anomalies Within Lunar Impact Basins: Constraints on the History of the Lunar Dynamo  

NASA Astrophysics Data System (ADS)

Previous work has shown that lunar crustal magnetization has a combination of origins including shock remanent magnetization in transient magnetic fields and thermoremanent magnetization in a steady core dynamo magnetic field (e.g., Hood and Artemieva, Icarus, 2008; Richmond and Hood, JGR, 2008; Garrick-Bethell et al., Science, 2009; Hood, Icarus, 2011). In particular, magnetic anomalies within the interiors of lunar impact basins and large craters provide a potentially valuable means of constraining the history of the former dynamo (Halekas et al., MAPS, 2003; Hood, 2011). These anomalies likely have a thermoremanent origin owing to high subsurface temperatures reached at the time of impact and therefore require a long-lived, steady magnetic field to explain their magnetization. Central anomalies have previously been confirmed to be present using Lunar Prospector magnetometer (LP MAG) data within several Nectarian-aged basins (Moscoviense, Mendel-Rydberg, Crisium, and Humboldtianum), implying that a dynamo existed during this lunar epoch (Hood, 2011). Here, we further analyze low altitude LP MAG data for several additional basins, ranging in age from Nectarian to Imbrian. Results indicate that magnetic anomalies with a probable basin-related origin are present within at least two additional Nectarian-aged basins (Serenitatis and Humorum) and one Imbrian-aged basin (Schrodinger). No discernible anomalies are present within the largest Imbrian-aged basins, Imbrium and Orientale. While there is uncertainty regarding the age of the Schrodinger basin, it has been reported to be slightly more recent than Imbrium (Wilhelms, 1984). Our initial interpretation is therefore that a dynamo likely existed during the Imbrian epoch. The absence of anomalies within Imbrium and Orientale can be explained by insufficient conditions for acquisition of strong magnetization (e.g., inadequate concentrations of efficient remanence carriers) following these relatively large impacts.

Richmond, N. C.; Hood, L. L.

2011-12-01

118

Direct Observations of Magnetic Anomalies on the Lunar Surface under Varying Solar Wind Conditions  

NASA Astrophysics Data System (ADS)

In contrast to Earth, the Moon does not have a global dipolar magnetic field. Since the first lunar landing with Apollo 11, we know, though, that localised magnetic fields exist on the lunar surface. Measurements conducted by the Lunar Prospector magnetometer and electron reflectometer suggested that these localised magnetic fields are able to deflect the impinging solar wind in favourable cases (Lin et al., Science 1998). Magnetohydrodynamic simulations support the implication that mini-magnetospheres are formed above the locations of strong localised magnetic fields and can hold off the impinging solar wind (Harnett and Winglee, JGR 2002). Analysis of magnetic field data from Lunar Prospector of the Reiner Gamma anomaly region showed that the distortion of the magnetic field of this anomaly strongly depends on the impinging solar wind parameters, which was interpreted that the size and shape of the mini-magnetosphere changed with the solar wind parametes (Kurata et al., GRL 2005). Wieser et al., GRL 2010 showed that SARA, the Sub-KeV Atom Analyzer on board Chandrayaan-1, is able to detect an ENA image of the mini-magnetosphere in the measured energetic neutral atom flux. Here we analysed all orbits where CENA, the Chandrayaan-1 Energetic Neutral Analyzer, recorded data when a magnetic anomaly was in CENA's field-of-view. Our goal was to determine if 1) a signature of the magnetic anomaly is always visible in the ENA signal and if 2) there is a correlation between the solar wind dynamic pressure, the solar wind magnetic field, the local magnetic field strength and the reduction in the reflected ENA flux. Our results show that for the simplest case, i.e., the Gerasimovich anomaly, there is indeed a clear correlation between the shielding efficiency, the magnetic field strength and the solar wind dynamic pressure. For the other observed magnetic anomalies, for which the magnetic fields are not only weaker but also spatially more variable than that of the Gerasimovich anomaly, only in about half of the cases such a correlation was found. We therefore conclude that the magnetic anomaly interaction is in general quite complex and that data with higher spatial resolution and more detailed modelling is required to understand this process better.

Vorburger, A.; Wurz, P.; Barabash, S.; Wieser, M.; Futaana, Y.; Holmström, M.; Bhardwaj, A.; Dhanya, M. B.; Sridharan, R.; Asamura, K.

2012-04-01

119

Characterization of CHAMP magnetic data anomalies: magnetic contamination and measurement timing  

NASA Astrophysics Data System (ADS)

The CHAMP (CHAllenging Minisatellite Payload) mission ended after more than ten years in space on 19 September 2010. For achieving a high measurement accuracy of the magnetometers on CHAMP, detailed analyses of spacecraft magnetic characteristics in orbit are required. A decade of continuous magnetometer and housekeeping data are a good basis for evaluating some of the effects of variable spacecraft magnetic fields on the ambient field determination. It was found that some perturbations of FGM (FluxGate vector Magnetometer) or OVM (OVerhauser scalar Magnetometer) measurements are caused by stray fields induced by the power system, the ASC (advanced stellar compass) instrument or magneto-torquer currents. The magnetic effect of solar currents on FGM measurements varies with the local time of the orbit and amounts to 0.2 nT. In cases when one head of the ASC instrument was blinded by the sun, sometimes transient drops in instrument current strength occur, which were accompanied by magnetic disturbance signals (?0.3 nT) in FGM measurements. The magnetic residual contamination of OVM data by the torquer currents was of order 0.1 nT but still detectable. An improved torquer correction matrix is derived which eliminates this effect. In-flight scalar calibration parameters revealed some of the effects of timing anomalies. Time lags between FGM and OVM readings are misinterpreted by the scalar calibration as variations of the angles between some of the sensor axes. The resulting amplitudes of the anomalies presented here lie in the range of some 0.1 nT, but they are systematic in nature.

Yin, Fan; Lühr, Hermann; Rauberg, Jan; Michaelis, Ingo; Cai, Hongtao

2013-07-01

120

East west trending magnetic anomalies in the Southern Hemisphere of Mars: Modeling analysis and interpretation  

NASA Astrophysics Data System (ADS)

Maps of the vector components of the martian crustal magnetic field over the strongly magnetized Terra Cimmeria/Sirenum region are constructed using Mars Global Surveyor magnetometer data. Although pronounced east-west trending anomalies are present on the radial and north field component maps at the mapping altitude (˜360-380 km), these trends are much less prominent at the lower aerobraking altitude (˜90-150 km). Comparisons with similar maps produced using artificial data at the aerobraking altitude indicate that elongated sources in this region may have maximum lengths along the martian surface of ˜500 km and maximum aspect ratios of ˜2. Iterative forward modeling of several relatively isolated anomalies in the mapped region yields paleomagnetic pole positions consistent with those estimated in previous studies of other anomalies using mapping phase and science phasing orbit data. On this basis, it is inferred that sources in the studied region are most probably magnetized primarily in northward or southward directions. Using this additional constraint, iterative forward modeling is then applied to determine a magnetization distribution that is consistent with data at both the aerobraking altitude and the mapping altitude. The model magnetization distribution, which includes 41 discrete sources, again indicates no highly elongated sources. An examination of surface geology in the region as well as a consideration of the global distribution of anomalies suggests that magmatic intrusions (e.g., subsurface dike swarms), cooling in the presence of water, are the most likely sources of the magnetic anomalies.

Hood, Lon L.; Richmond, Nicola C.; Harrison, Keith P.; Lillis, Robert J.

2007-11-01

121

Reduced to Pole Long-wavelength Magnetic Anomalies of Africa and Europe  

NASA Technical Reports Server (NTRS)

To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alpine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

Hinze, W. J.; Vonfrese, R. R. B. (principal investigators); Olivier, R.

1984-01-01

122

Reduced to pole long-wavelength magnetic anomalies of Africa and Europe  

NASA Technical Reports Server (NTRS)

To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alphine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

Olivier, R.; Hinze, W. J.; Vonfrese, R. R. B.

1985-01-01

123

Satellite-Altitude Geopotential Study of the Kursk Magnetic Anomaly (KMA)  

NASA Technical Reports Server (NTRS)

With the successful launch of the Orsted, SAC-C and CHAMP satellites we are able to make both magnetic and gravity anomaly maps of the Earth's crust; magnetic from all three missions and gravity with CHAMP. We have used these data to study the KMA area of Russia. This is an important region for several reasons: (1) we have already made satellite magnetic anomaly maps of this region and they can be integrated with the gravity data from CHAMP for a comprehensive interpretation; (2) KMA contains the largest know reserves of iron-ore in the world; and (3) there are significant ground truth data available for this region from aeromagnetic, balloon surveys and geophysical mapping, including extensive rock magnetic/paleo-magnetic and geologic studies. Utilizing the gravity observations, collocated with the magnetic data enabled us to make a joint interpretation. While there is a high amplitude magnetic anomaly recorded over the KMA the gravity anomaly at satellite altitude revealed by CHAMP is only around 3-6 mGal but is not centered on the magnetic high. This would indicate that despite the fact that in the region of the KMA the rocks have a higher percentage of iron than in the surrounding formations the entire area is Archean-Proterozoic in age and therefore very dense.

Taylor, Patrick T.; Kim, Hyung Rae; vonFrese, Ralph R. B.; Potts, Laramie V.; Frawley, James J.

2003-01-01

124

Application of Magsat lithospheric modeling in South America. Part 1: Processing and interpretation of magnetic and gravity anomaly data  

NASA Technical Reports Server (NTRS)

Scalar magnetic anomaly data from MAGSAT, reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of South America and the Caribbean are compared to major crustal features. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative anomalies. Spherical earth magnetic modeling of the Amazon River and Takatu aulacogens in northeastern South America indicates a less magnetic crust associated with the aulacogens. Spherical earth modeling of both positive gravity and negative magnetic anomalies observed over the Mississippi Embayment indicate the presence of a nonmagnetic zone of high density material within the lower crust associated with the aulacogen. The MAGSAT scalar magnetic anomaly data and available free air gravity anomalies over Euro-Africa indicate several similar relationships.

Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (principal investigators); Keller, G. R.; Lidiak, E. G.

1984-01-01

125

Weak extremely-low-frequency magnetic field-induced regeneration anomalies in the planarian, Dugesia tigrina  

SciTech Connect

The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.

Jenrow, K.A.; Smith, C.H.; Liboff, A.R. [Oakland Univ., Rochester, MI (United States). Dept. of Physics] [Oakland Univ., Rochester, MI (United States). Dept. of Physics

1996-12-31

126

The intermediate wavelength magnetic anomaly field of the north Pacific and possible source distributions  

NASA Technical Reports Server (NTRS)

A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the MAGSAT field although a directional sensitivity in the MAGSAT field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.

Labrecque, J. L.; Cande, S. C.; Jarrard, R. D. (principal investigators)

1983-01-01

127

Intermediate-wavelength magnetic anomaly field of the North Pacific and posible source distributions  

NASA Technical Reports Server (NTRS)

A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the Magsat field although a directional sensitivity in the Magsat field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.

Labrecque, J. L.; Cande, S. C.; Jarrard, R. D.

1985-01-01

128

Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data  

NASA Technical Reports Server (NTRS)

A new Polar Orbit Geophysical Observatory (POGO) scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15-60. On the basis of the common features of this map with two new Magsat anomaly maps, dawn and dusk, two scalar magnetic anomaly maps of the Earth are presented using two selection criteria with different levels of stringency. These selection criteria suppress the noncrustal components of the original maps by different amounts. The more stringent selection criteria seek to eliminate as much contamination as possible, at the expense of suppressing some anomaly signal. This map is represented by spherical harmonics of degree 15-60. The less stringent selection criteria seek to retain as much crustal signal as possible, at the expense of also retaining some contaminating fields. This map is represented by spherical harmonics of degree 15-65. The resulting two maps are highly correlated with degree correlation coefficients greater than 0.8.

Arkani-Hamed, Jafar; Langel, Robert A.; Purucker, Mike

1994-01-01

129

Interactive Animation of Seafloor Spreading and Magnetic Field Reversals  

NSDL National Science Digital Library

This site from the University Corporation for Atmospheric Research (UCAR) offers an interactive simulation that shows how magnetic stripes on the ocean bottom can reveal the age of the material and reveal plate motion. An applet shows the magnetic polarities change as the user moves a compass across the ocean bottom on the screen.

2008-08-06

130

A Tale of Two Anomalies: Depletion, Dispersion, and the Connection between the Stellar Lithium Spread and Inflated Radii on the Pre-main Sequence  

NASA Astrophysics Data System (ADS)

We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T eff is nearly universal, and sets in by ~200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

Somers, Garrett; Pinsonneault, Marc H.

2014-07-01

131

The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa  

NASA Technical Reports Server (NTRS)

Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

Haggerty, S. E. (principal investigator)

1982-01-01

132

MAGSAT investigation of crustal magnetic anomalies in the eastern Indian Ocean  

NASA Technical Reports Server (NTRS)

Crustal magnetic anomalies in a region of the eastern Indian Ocean were studied using data from NASA's MAGSAT mission. The investigation region (0 deg to 50 deg South, 75 to 125 deg East) contains several important tectonic features, including the Broken Ridge, Java Trench, Ninetyeast Ridge, and Southeast Indian Ridge. A large positive magnetic anomaly is associated with the Broken Ridge and smaller positive anomalies correlate with the Ninetyeast Ridge and western Australia. Individual profiles of scalar data (computed from vector components) were considered to determine the overall data quality and resolution capability. A set of MAGSAT ""Quiet-Time'' data was used to compute an equivalent source crustal magnetic anomaly map of the study region. Maps of crustal magnetization and magnetic susceptibility were computed from the equivalent source dipoles. Gravity data were used to help interpretation, and a map of the ratio of magnetization to density contrasts was computed using Poisson's relation. The results are consistent with the hypothesis of induced magnetization of a crustal layer having varying thickness and composition.

Sailor, R. V.; Lazarewicz, A. R.

1983-01-01

133

Soil Magnetism and Magnetic Anomalies at the Marshall's Pen Archaeological Site, Mandeville, Jamaica  

NASA Astrophysics Data System (ADS)

Marshall's Pen, a 1000-acre parcel of land in Mandeville, Jamaica, underlain by limestone bedrock and bauxite soils, served as a coffee plantation in the early 19th century. Two to three hundred slaves of African descent worked the plantation from AD 1802 until slavery was abolished in Jamaica in 1838. The goal of the archaeological program at Marshall's Pen is to complement what little is known about Jamaican slave society from the historical record. Geophysical prospection was conducted at Marshall's Pen by ten undergraduate students as part of a Keck Geology Consortium project in the summer of 1999. In the slaves' village consisting of living and domestic labor areas, G858 cesium vapor magnetometer readings were taken every 0.1 seconds along 49 profiles, each 50 m long and spaced 1 meter apart, and magnetic susceptibility readings were taken at 1-meter intervals. Seven significant magnetic anomalies (up to 100 nT peak-to-peak) were detected in the village. Two of these were found to be caused by a buried machete and an iron woodworking tool. Three anomalies were associated with a large area of black, burned soil. Archaeological testing in this area produced partially carbonized seeds, charcoal, ceramics that were smudged after manufacture, and cutlery; this evidence suggests a domestic kitchen area. In situ susceptibility readings were zero on bedrock and low on the bauxite soils. Susceptibility readings generally correlated with the magnetics, to values as high as 50 (x 10-6, volume specific SI) in the ``kitchen'' area, suggesting a source in the susceptibility contrast for these magnetic anomalies. Soil samples were collected from the bauxite outside the village, and from the village area in the summer of 2001; ten village sites were sampled away from the kitchen area, and four from the kitchen area. Five samples from each site were boxed, weighed, and measured for laboratory susceptibility measurements. Eleven samples outide the village had a geometric mean susceptibility of 144 (x 10-8, mass-specific SI); forty-nine samples from the ten village off-kitchen sites had a mean susceptibility of 105; twenty samples from the four village on-kitchen sites had a mean susceptibility of 821. One sample from a village off-kitchen site had a susceptibility of 1894 due to the head of a roofing nail included in the sample. Isothermal remanent magnetization experiments were carried out on one sample from most sites. Three samples from outside the village had ratios of IRM(0.1T)/IRM(1.0T) of 0.76, 0.5, and 0.74; ratios for ten samples from the village away from the kitchen were between 0.72-0.77; ratios for two samples from the village in the kitchen were more easily saturated with values of 0.90 and 1.0. The susceptibility and IRM results are consistent with reduction of hematite from sites outside the kitchen to magnetite or maghemite at sites within the kitchen area. The resulting higher susceptibilities could generate the magnetic anomalies in this area.

Figueroa, E.; Sternberg, R. S.; Delle, J. A.; Lawrence, N. D.; McAdoo, B. G.; Savina, M. E.

2002-05-01

134

Why are There So Few Magnetic Anomalies in Martian Lowlands and Basins?  

NASA Technical Reports Server (NTRS)

The discovery of large areas of strongly magnetized crust on Mars [1,2] provides important information on the timing of both crustal and deeper interior processes on that planet. Critical to an understanding of that timing, as well as to the processes that have contributed to the magnetization and demagnetization of crustal materials, is the geographical distribution of magnetic anomalies discernible from spacecraft orbit. The paucity of resolved magnetic anomalies in the northern lowlands and within and surrounding the best-preserved major impact basins has been noted since the crustal field was first globally mapped [1], but no straightforward explanation of that full pattern has yet been offered. Here we suggest that ancient hydrothermal alteration of magnetic carriers in Martian lowlands and basins may have contributed to the magnetization distribution observed today.

Solomon, Sean C.; Aharonson, Oded; Banerdt, W. Bruce; Dombard, Andrew J.; Frey, Herbert V.; Golombek, Matthew P.; Hauck, Steven A., II; Head, James W., III; Johnson, Catherine L.; McGovern, Patrick J.

2003-01-01

135

Magnetic anomalies in east Pacific using MAGSAT data  

NASA Technical Reports Server (NTRS)

Methods for solving problems encountered in separating the core field from the crustal field are summarized as well as those methods developed for inverting total magnetic field data to obtain source functions for oceanic areas. Accounting for magnetization contrasts and the magnetization values measured in rocks of marine origin are also discussed.

Harrison, C. G. A. (principal investigator)

1983-01-01

136

Electric/magnetic duality for chiral gauge theories with anomaly cancellation  

E-print Network

We show that 4D gauge theories with Green-Schwarz anomaly cancellation and possible generalized Chern-Simons terms admit a formulation that is manifestly covariant with respect to electric/magnetic duality transformations. This generalizes previous work on the symplectically covariant formulation of anomaly-free gauge theories as they typically occur in extended supergravity, and now also includes general theories with (pseudo-)anomalous gauge interactions as they may occur in global or local N=1 supersymmetry. This generalization is achieved by relaxing the linear constraint on the embedding tensor so as to allow for a symmetric 3-tensor related to electric and/or magnetic quantum anomalies in these theories. Apart from electric and magnetic gauge fields, the resulting Lagrangians also feature two-form fields and can accommodate various unusual duality frames as they often appear, e.g., in string compactifications with background fluxes.

Jan De Rydt; Torsten T. Schmidt; Mario Trigiante; Antoine Van Proeyen; Marco Zagermann

2008-08-15

137

Lineated Near Bottom Magnetic Anomalies Over an Oceanic Core Complex, Atlantis Massif (Mid-Atlantic Ridge at 30°N)  

Microsoft Academic Search

Despite significant effort during the four decades since the Vine-Matthews-Morley hypothesis was first advanced, the relative importance of lower crustal (and possibly upper mantle) sources in generating lineated marine magnetic anomalies remains uncertain. Remanence measurements from samples obtained by drilling or dredging provide the most direct evidence that these deeper layers can be significant anomaly sources. Near bottom anomaly measurements

J. Gee; D. Blackman

2004-01-01

138

Study of magnetic anomalies over archaeological targets in urban environments  

Microsoft Academic Search

Magnetic prospecting is one of the most widely used methods for investigating archaeological sites in the world. It is often applied before and during various types of industrial development and in agricultural areas. In Israel, most potential archaeological targets are located in urban settings, which substantially complicate their geophysical signatures. Noise from natural factors such as the inclined magnetization (about

Lev V. Eppelbaum

139

A FORTRAN-77 computer program for three-dimensional inversion of magnetic anomalies resulting from multiple prismatic bodies  

NASA Astrophysics Data System (ADS)

A computer program in FORTRAN 77 is presented for three-dimensional inversion of total field magnetic anomalies resulting from multiple prisms with arbitrary magnetizations and orientations. The program is based on the nonlinear optimization technique of the Marquardt algorithm. The equations for the anomalies and derivatives with respect to various parameters of the prismatic bodies are programmed to minimize computing time. The derivatives are computed by analytical methods as the computation time is smaller than that required by numerical methods. Approximate equations allow rapid calculation of the magnetic anomalies and derivatives. Efficient methods are developed for three-dimensional inversion of magnetic anomalies by an appropriate use of the exact and approximate equations. The method is applied for inversion of the total field aeromagnetic anomalies over Mahanadi Basin, Orissa, and aeromagnetic anomalies over the western part of Cuddapah Basin, Andhra Pradesh, India.

Bhaskara Rao, D.; Ramesh Babu, N.

1993-07-01

140

Magan: A new approach to the analysis and interpretation of marine magnetic anomalies  

NASA Astrophysics Data System (ADS)

The identification of marine magnetic anomalies is an important phase of plate tectonic modeling, but is limited by the lack of professional software, either free or commercial, which may help in the accomplishment of this task, and by the practice of performing approximations that may prevent in some instances a correct interpretation of the magnetic data. Although basic forward-modeling and inversion algorithms that may be incorporated in the core of gravity or magnetic application software have been published since the late 1950s, most research groups have implemented their own tools independently from each other, and apart from a few cases such computer programs are not publicly accessible. Here a new methodology of analysis of marine magnetic data is described, which allows a quantitative correlation of magnetic anomalies from different profiles and a statistical determination of relative plate velocities. The method is implemented through a new free software package, Magan, available for the MS Windows environment. The program is especially designed to work with NGDC GEODAS ship-track and aeromagnetic data, but allows the import of any ASCII text file containing magnetic anomaly data. The basic forward-modeling algorithms included in the Magan core are based on well-known techniques of potential field geophysics, modified to take into account specific requirements of marine magnetic data analysis and plate tectonic modeling. Such a kernel is flanked by a friendly graphical user interface (GUI), which helps and speeds up the interpretation of the ship-track data. In particular, the program allows one to (1) draw and edit flow lines where magnetic data can be projected, (2) calculate more accurately modeled anomalies through the use of apparent polar wander paths and single block parameters, (3) generate age-distance and time-velocity graphs, and (4) generate crossing point files that can be subsequently used to build magnetic isochrons.

Schettino, Antonio

2012-02-01

141

Plasma-surface interaction in magnetic dipole fields: Understanding the near surface electrical environment in magnetic anomaly regions  

NASA Astrophysics Data System (ADS)

The Moon has no global magnetic field, only localized crustal magnetic anomalies. In-situ measurements have shown evidence for complex solar wind plasma interaction with these local magnetic fields, and indicated a strong correlation with the high-albedo markers on the lunar surface, so-called the lunar swirls. Due to the limitations of existing in-orbit and surface measurements, laboratory studies and computer simulations play important roles in understanding the near-surface/surface electric field environment in the magnetic anomaly regions. In laboratory experiments, we investigate plasma-surface interaction in a magnetic dipole field with magnetized electrons but unmagnetized ions to emulate the interaction of the solar wind with the lunar surface in moderate magnetic anomalies. We have studied the electric potential distributions above an insulating surface in a dipole field with the dipole axis parallel (0 degree) to the surface in plasma [Wang et al., 2012]. Here, we report on a complementary new study with the dipole field axes at 90 and 45 degrees to the surface. The dipole field is created with a cylindrical permanent magnet. When the dipole axis is normal to the surface, the surface potential in the central cusp region rises to more positive values than outside the field, and a bump-like potential structure emerges in the sheath above the surface. These results indicate a significant population of reflected electrons due to the magnetic mirror effect in the cusp region. The potential-bump structure diminishes when the plasma density and neutral pressure increase. A different vertical dipole field is created with a smaller-sized cylindrical magnet, which has a similar strength peaked at the central surface but decreases faster with the height. Our data shows that the potential bump moves closer to the surface and the rise in surface potential in the central cusp region is less than that above the larger-sized magnet. Two-dimensional potential contours above the surface with the 45 degrees dipole field are measured as well. The results from different field configurations show self-consistency. The implications of the laboratory results for the electric environment in lunar magnetic anomaly regions will be discussed. Wang, X., M. Horányi, S. Robertson, "Characteristics of a plasma sheath in a magnetic dipole field: Implications to the solar wind interaction with the lunar magnetic anomalies", J. Geophys. Res., 117, A06226 (2012).

Wang, X.; Howes, C.; Horanyi, M.; Robertson, S. H.

2012-12-01

142

Weak extremely-low-frequency magnetic field-induced regeneration anomalies in the planarian, Dugesia tigrina  

Microsoft Academic Search

The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting

K. A. Jenrow; C. H. Smith; A. R. Liboff

1996-01-01

143

Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil  

E-print Network

Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil A. B. Watts and S. L. Fontes (Observatório Nacional, Rio de Janeiro, Brasil) Cratonic basins comprise profile across the Parnaiba cratonic basin in NorthEast Brazil. The purpose of this project is to acquire

Watts, A. B. "Tony"

144

Hydrology in the Durius Valles Region: Evaluation of Possible Correlation with Volcanism and Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

We envision the contribution of subglacial flows, hydrothermalism and sapping in the Durius Valles system and the consequences in term of climate on Mars in recent geological times. We evaluate the possible correlation of the hydrology with volcanism and magnetic anomalies.

Cabrol, Natalie A.; Marinangeli, Lucia; Grin, Edmond A.

2000-01-01

145

Instructions for use Observation of an Unusual Magnetic Anomaly in the Superconducting Mixed State  

E-print Network

magnetization measurements for a single crystal of UBe13 down to 0.14 K, up to 80 kOe. We observed a magnetic anisotropic SC gap structures, unusual upper-critical field Hc2 [6,7], a multi-SC diagram [8], and a manner with broken time-reversal symmetry such as a nonunitary state [19]. Kromer et al. found a line of anomaly TLðx

Tsunogai, Urumu

146

Exploring the strength of newly formed oceanic lithosphere and its correlation with spreading rate and ridge depth anomalies  

Microsoft Academic Search

We have developed a moving window admittance technique to determine the relationship between free-air gravity anomaly and bathymetry as a function of wavelength over the world's ocean basins and their margins. Preliminary results from the Western Pacific Ocean show that the technique resolves the effective elastic thickness (Te), a proxy for long-term (>106 yr) strength, of the oceanic lithosphere to

L. M. Kalnins; A. B. Watts

2010-01-01

147

New Clues on the Source of the Central Magnetic Anomaly at Haughton Impact Structure, Canada  

NASA Astrophysics Data System (ADS)

The 23 km-diameter Haughton impact structure, located on Devon Island, Nunavut, Canada, is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich carbonate impact melt rocks fill the crater and impact-generated hydrothermal activity took place, but since then no significant geological event has affected the area. A 900 nT-amplitude magnetic anomaly with a wavelength of about 3 km is observed at the center of the crater (Pohl et al., 1988). Using high-resolution ground magnetic survey and magnetic property measurements on rock samples from inside and outside the structure, Quesnel et al. (2013) concluded that the source for this anomaly may correspond to uplifted and hydrothermally-aletered basement rocks. Hydrothermal activity can increase rock magnetization intensity by crystallization of magnetic minerals, such as magnetite and/or pyrrhotite. Here, we present the results of a new ground magnetic survey and electrical resistivity soundings conducted around the maximum of the magnetic anomaly. Drilling, with depths ranging from 5 m to 13 m was also conducted at three locations in the same area to ground truth the interpretation of geophysical data. The maximum of the magnetic anomaly is characterized by a ~50 m2 area of strong vertical magnetic gradient and low electrical resistivity, while the surroundings show weak gradient and large resistivity. Two drill holes into this localized area show about 6 m of sandy material with some more magnetic layers at about 5 m depth overlying a greenish impact melt breccia with very abundant and large clasts. Recovery in the first 9 meters is very poor, but down hole magnetic gradient measurement confirms the near 6 meter magnetic layer. A third hole was drilled outside the local area with strong magnetic gradients and shows, starting at 2 m depth a porous gray clast-rich impact melt rock that is very similar to the impact melt rock extensively cropping out in the crater. Therefore, the three drill holes confirm that the geophysical contrast at the crater center corresponds to a geological contrast and suggest a link with hydrothermal activity. The results of laboratory measurements (magnetic properties in particular) made on the drill cores will also be presented. References : Osinski, G. R. et al. 2005. MPS, 40:1759-1776 ; Pohl, J. et al. 1988. Meteoritics, 23:235-238 ; Quesnel, Y. et al. 2013. EPSL, 367:116-122.

Quesnel, Y.; Rochette, P.; Gattacceca, J.; Osinski, G. R.

2013-12-01

148

Ocean crust formation processes at very slow spreading centers: A model for the Mohns Ridge, near 72 deg N, based on magnetic, gravity, and seismic data  

NASA Astrophysics Data System (ADS)

The Mohns Ridge, in the Norwegian Greenland Sea, is one of the slowest spreading centers of the mid-ocean ridge system (8 mm/yr half rate). Sea Beam data acquired with R/V Jean Charcot near 72 deg N show that its rift valley floor is characterized by en echelon volcanic ridges, oriented obliquely relatively to the average strike of the ridge axis. These ridges are regularly spaced along the axis, about every 40 km, and are separated by nontransform discontinuities. Sharp positive magnetic anomalies, centered over the topographic highs, suggest that they are eruptive centers, considered as the surficial expression of active spreading cells. Over the rift valley, Bouguer anomalies obtained by subtracting the predicted effects due to seafloor topography from the measured free-air gravity field are consistent with a low density body within the lower crust having its upper surface lying at about 2 km below the sea surface. This body, if it exists, probably corresponds to the zone of low viscosity that can be inferred from the model of Chen and Morgan (1990b), which predicts the existence of a decoupling region, between the upper crust and the asthenophere below. Its width varies rapidly along-strike, from less than about 5 km to more than 15 km. In plan view, it has a pinch and swell form, which defines a series of spreading cells, the center of one cell being where the Bouguer anomaly is widest. Short wavelength (less than 10 to 20 km) along-strike variations, such as Bouguer anomaly lows centered on the topographic highs, reflect local effects associated with the presence of the eruptive centers. Seismic tomography data from a 20 x 10 km active oblique volcanic ridge near 72 deg 22 min N tend to indicate that the links between the main, low-velocity body at depth, and the magma injections centers which lie within the rift valley inner floor are probably complex.

Geli, Louis; Renard, Vincent; Rommevaux, Celine

1994-02-01

149

Joint geophysical investigation of a small scale magnetic anomaly near Gotha, Germany  

NASA Astrophysics Data System (ADS)

In the framework of the multidisciplinary project INFLUINS (INtegrated FLUid Dynamics IN Sedimentary Basins) several airborne surveys using a full tensor magnetic gradiometer (FTMG) system were conducted in and around the Thuringian basin (central Germany). These sensors are based on highly sensitive superconducting quantum interference devices (SQUIDs) with a planar-type gradiometer setup. One of the main goals was to map magnetic anomalies along major fault zones in this sedimentary basin. In most survey areas low signal amplitudes were observed caused by very low magnetization of subsurface rocks. Due to the high lateral resolution of a magnetic gradiometer system and a flight line spacing of only 50m, however, we were able to detect even small magnetic lineaments. Especially close to Gotha a NW-SE striking strong magnetic anomaly with a length of 1.5 km was detected, which cannot be explained by the structure of the Eichenberg-Gotha-Saalfeld (EGS) fault zone and the rock-physical properties (low susceptibilities). Therefore, we hypothesize that the source of the anomaly must be related to an anomalous magnetization in the fault plane. To test this hypothesis, here we focus on the results of the 3D inversion of the airborne magnetic data set and compare them with existing structural geological models. In addition, we conducted several ground based measurements such as electrical resistivity tomography (ERT) and frequency domain electromagnetics (FDEM) to locate the fault. Especially, the geoelectrical measurements were able to image the fault zone. The result of the 2D electrical resistivity tomography shows a lower resistivity in the fault zone. Joint interpretation of airborne magnetics, geoelectrical and geological information let us propose that the source of the magnetization may be a fluid-flow induced impregnation with iron-oxide bearing minerals in the vicinity of the EGS fault plane.

Queitsch, Matthias; Schiffler, Markus; Goepel, Andreas; Stolz, Ronny; Guenther, Thomas; Malz, Alexander; Meyer, Matthias; Meyer, Hans-Georg; Kukowski, Nina

2014-05-01

150

Equatorial Spread F Development\\/Disruption under Disturbance Electric Fields during Some Recent Intense Magnetic Storms  

Microsoft Academic Search

Equatorial spread F (ESF) and associated plasma bubble irregularity development can be initiated or inhibited under disturbance electric fields associated with magnetic storms. Case studies of ESF intensification\\/inhibition under intense storm conditions are rare, however. We have addressed this question using the data collected from the Brazilian network of Digisondes, a VHF radar and GPS scintillation receivers, complemented by Digisonde

M. A. Abdu; E. R. Paula; I. S. Batista; B. W. Reinisch; C. M. Denardini; J. H. Sobral

2006-01-01

151

Central magnetic anomalies of Nectarian-aged lunar impact basins: Probable evidence for an early core dynamo  

NASA Astrophysics Data System (ADS)

A re-examination of all available low-altitude LP magnetometer data confirms that magnetic anomalies are present in at least four Nectarian-aged lunar basins: Moscoviense, Mendel-Rydberg, Humboldtianum, and Crisium. In three of the four cases, a single main anomaly is present near the basin center while, in the case of Crisium, anomalies are distributed in a semi-circular arc about the basin center. These distributions, together with a lack of other anomalies near the basins, indicate that the sources of the anomalies are genetically associated with the respective basin-forming events. These central basin anomalies are difficult to attribute to shock remanent magnetization of a shocked central uplift and most probably imply thermoremanent magnetization of impact melt rocks in a steady magnetizing field. Iterative forward modeling of the single strongest and most isolated anomaly, the northern Crisium anomaly, yields a paleomagnetic pole position at 81° ± 19°N, 143° ± 31°E, not far from the present rotational pole. Assuming no significant true polar wander since the Crisium impact, this position is consistent with that expected for a core dynamo magnetizing field. Further iterative forward modeling demonstrates that the remaining Crisium anomalies can be approximately simulated assuming a multiple source model with a single magnetization direction equal to that inferred for the northernmost anomaly. This result is most consistent with a steady, large-scale magnetizing field. The inferred mean magnetization intensity within the strongest basin sources is ˜1 A/m assuming a 1-km thickness for the source layer. Future low-altitude orbital and surface magnetometer measurements will more strongly constrain the depth and/or thicknesses of the sources.

Hood, Lon L.

2011-02-01

152

The satellite magnetic anomaly of Ahaggar - Evidence for African Plate motion  

NASA Technical Reports Server (NTRS)

The Ahaggar volcanic province of North Central Africa is considered a region of excess heat flow (hot spot) and hence elevated Curie isotherm. Using a modified version of the Parker FFT potential field representation, magnetic signals were calculated at Magsat altitudes for models in which the African Plate is both fixed and moving. The moving-plate model extends the Curie isotherm anomaly in the direction of plate motion and provides a satisfactory match to vertical component anomaly data when the magnitude of plate velocity is 0.75 cm/yr. Although the signal levels are marginal for the scalar component anomalies of this region, the same model provides an adequate match to this data set and is clearly preferable to a fixed-plate model.

Phillips, R. J.; Brown, C. R.

1985-01-01

153

Prenatal diagnosis of fetal hydrometrocolpos secondary to a cloacal anomaly by magnetic resonance imaging.  

PubMed

Fetal female urogenital anomalies are often difficult to evaluate by ultrasonography, especially in late gestation. We report a case of fetal hydrometrocolpos detected at 35 weeks of gestation. Ultrasonography revealed a large retrovesical septate hypoechogenic mass in the fetal abdomen, however the sonographic findings were inconclusive. Magnetic resonance imaging (MRI) confirmed that the abdominal mass was fluid-filled with a mid-plane septum in the midline posterior to the bladder, and showed a connection to the dilated uterus that was duplicated. These findings were consistent with a diagnosis of hydrometrocolpos with septate vagina and uterus didelphys. The neonate showed abdominal distension, ambiguous genitalia and anal atresia with a single perineal opening. Hydrometrocolpos was secondary to a urethral type of cloacal anomaly. Aspiration of the mass and a colostomy were performed on the first postnatal day, followed by anorectoplasty at 19 months of age. MRI is a useful complementary tool for assessing fetal urogenital anomalies when ultrasonography is inconclusive. PMID:16184505

Hayashi, S; Sago, H; Kashima, K; Kitano, Y; Kuroda, T; Honna, T; Nosaka, S; Nakamura, T; Ito, Y; Kitagawa, M; Natori, M

2005-10-01

154

Modeling of the Central Magnetic Anomaly at Haughton Impact Structure, Canada  

NASA Astrophysics Data System (ADS)

Located on Devon Island, Nunavut, Canada, the 23-km diameter Haughton impact structure is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich impact melt rocks line the crater and impact-induced hydrothermal activity took place, but since then no significant geological event has affected the area. In the 1980s, ground magnetic and gravity measurements were carried out within the central part of the crater (Pohl et al., 1988). A significant anomaly was discovered and coarsely modeled by a source body of simple geometry. More recently, an airborne magnetic survey delivered additional data that covered the whole crater but no modeling was done (Glass et al., 2002). Here, we present the results of a new ground magnetic survey accompanied by rock magnetic property measurements made on all samples of the crater. This has provided additional constraints to investigate the origin of this central magnetic anomaly. By conducting modeling, we have been able to reveal the geometry and volume of the source body as well as its magnetization properties. Our results suggest that the necessary magnetization intensity to account for this anomaly is too large to be associated with uplifted pre-impact target rocks. Therefore, we suggest that hydrothermal alteration could have enhanced the magnetization of the central part of this crater. References : Osinski, G. R. et al. 2005. MPS, 40:1759-1776 ; Pohl, J. et al. 1988. Meteoritics, 23:235-238 ; Glass, B. J. et al. 2002, Abstract #2008. 33th LPSC

Quesnel, Y.; Gattacceca, J.; Osinski, G. R.; Rochette, P.

2011-12-01

155

Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization  

NASA Technical Reports Server (NTRS)

The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

Ruder, M. E.; Alexander, S. S.

1986-01-01

156

Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization  

NASA Astrophysics Data System (ADS)

The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

Ruder, M. E.; Alexander, S. S.

1986-05-01

157

Magnetic Properties of Quaternary Deposits, Kenai Peninsula, Alaska -- Implications for Aeromagnetic Anomalies of Upper Cook Inlet  

USGS Publications Warehouse

We measured magnetic susceptibilities of exposed Quaternary deposits on several beach cliffs and river banks on the Kenai Peninsula near Soldotna, Alaska. Data, descriptions, and photos from nine sites are included in this report. The mean susceptibility for Quaternary materials in this region is approximately 2.5 x 10-3 SI units. This is sufficiently magnetic to produce subtle aeromagnetic anomalies such as those observed to correlate with topographic features in the region of the measurements. The highest susceptibilities measured (greater than 20 x 10-3 SI units) may help, at least in part, to explain moderate amplitude aeromagnetic anomalies observed elsewhere in Cook Inlet, particularly those relating to structures showing Quaternary movement. Comparison of measured beach cliff susceptibility and susceptibility predicted from idealized formulas and two-dimensional cliff models suggests that measured susceptibilies underestimate true bulk susceptibility by 20 percent to 50 percent in this region.

Saltus, R. W.; Haeussler, P. J.

2004-01-01

158

Circum-Arctic mapping project: new magnetic anomaly map of the Arctic (to 60 degrees N)  

NASA Astrophysics Data System (ADS)

An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC, Germany-BGR and Norway-NGU) since 2005. This project aims to produce an atlas that will comprise geological and geophysical digital maps at a scale of 1: 5 million scale for the Arctic region limited by the 60 degree North latitude. New published and classified magnetic anomaly gridded data from each participant group were gathered and converted to a common datum (WGS84) and format. The Greenland region magnetic anomaly grid (Verhoef et al., 1996) has been updated with new aeromagnetic surveys performed in West Greenland between 1992-2001 (Rasmussen, 2002), and in the Nares Strait area (Damaske & Oakey, 2006; Oakey & Damaske, 2006). The oceanic area east of Greenland (NE Atlantic) contains most of the aeromagnetic data used in the Verhoef et al., (1996)'s compilation (pre-1990) plus new aeromagnetic surveys over offshore Norway collected up to 2007 (Olesen et al., 1997; Olesen et al., 2007; Gernigon et al., 2008). The gridded data has been upward continued to 1 km above ground or sea-level and trimmed around the areas of major overlaps. The Alaska USGS aeromagnetic compilation has been used as the "master grid" for merging the major gridded data sets together and the downward continued lithospheric magnetic field model MF6 derived from satellite data (Maus et al., 2008) has been used as a regional reference surface. We have used a blending function over the area of overlap in order to smooth the transition from one grid to the other (GridKnit, GEOSOFT). The resulting grid has been re-sampled to a 2 km grid cell. In order to construct the final Circum-Arctic magnetic anomaly grid (CAMP-M) we have adopted the approach used by several research groups for compiling the World Digital Magnetic Anomaly Map (WDMAM) and used near-surface magnetic data for the short wavelength component of the compilation and the satellite derived magnetic anomalies for the long wavelength (Hemant et al., 2007; Maus et al., 2007). MF6 extends to spherical harmonics degree 120 (333 km wavelength) and therefore it is able to provide consistent long wavelength information between 300 and 400 km. This information is mainly related to regional deeper and/or thicker portions of the magnetic sources within the crust. We have prepared two versions for the CAMP-M magnetic anomaly grid. The first one combines short wavelength components of regional grids (less than 400 km) with long wavelengths (400 km) of the MF6 model. The second one combines short wavelengths of regional datasets (obtained by filtering with a cosine squared taper to remove the wavelengths in the waveband between 307 and 333 km and larger, with the MF6 model (to degree 120). We have selected Model 1 as the new Circum-Arctic Magnetic Anomaly Map.

Gaina, Carmen

2010-05-01

159

True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate  

NASA Astrophysics Data System (ADS)

Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ?50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate magnetic anomalies due to seafloor spreading with much greater clarity than do shipboard profiles in the same region [Horner-Johnson and Gordon, 2003]. The pole that we obtain has compact 95% confidence limits. We reduce the profiles to this pole and show that the appearance of the reduced-to-the-pole profiles is sensitive to the assumed pole position. The new pole shows that Pacific hotspots have moved significantly relative to the spin axis during the formation of the Hawaiian island and seamount chain, and is consistent with Pacific hotspots having moved in approximate unison with Indo-Atlantic hotspots relative to the spin axis since 32 Ma B.P.

Gordon, R. G.; Horner-Johnson, B. C.

2010-12-01

160

Remanent magnetization and 3-dimensional density model of the Kentucky anomaly region  

NASA Technical Reports Server (NTRS)

A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. It is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled first using prismatic model sources and then using dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is readily detectable, but by scalar data as readily as vector data.

Mayhew, M. A.; Estes, R. H.; Myers, D. M.

1984-01-01

161

The Spreading of X-lines in Three Dimensions during Magnetic Reconnection with a Guide Field  

NASA Astrophysics Data System (ADS)

Naturally occurring magnetic reconnection often begins in a spatially localized region and spreads in the out-of-plane direction as time progresses. This has been studied by a number of authors for magnetotail applications such as substorms and bursty bulk flows, for which the out-of-plane (guide) field is typically small. However, this same behavior has been observed in laboratory experiments, in two-ribbon solar flares (such as the Bastille Day flare), and at the dayside of the magnetopause. In each of these settings, a significant guide field is present. Without a guide field, it was shown that the reconnection spreading is controlled by the species that carries the current. However, laboratory experiments with a large guide field (Katz et al., Phys. Rev. Lett., 104, 255004, 2010) revealed that the spreading takes place in both directions at the Alfven speed based on the guide magnetic field. We present three-dimensional two-fluid numerical simulations to address the condition on the guide field at which the nature of the spreading switches from being caused by the current carriers to being caused by Alfven waves. Applications for the corona will be discussed.

Shepherd, L. S.; Cassak, P.

2011-12-01

162

Prenatal magnetic resonance imaging detection of temporal lobes and hippocampal anomalies in hypochondroplasia.  

PubMed

Hypochondroplasia (HCH) is a genetic skeletal dysplasia, inherited in an autosomal dominant fashion. About 50-70% of HCH patients have a mutation in FGFR3 gene and in the majority of cases it is a de novo mutation. Recent magnetic resonance imaging studies on relative large cohorts of HCH patients have showed a central nervous system involvement with a high incidence of characteristic temporal lobe and hippocampal abnormalities. To the best of our knowledge, this report shows the first magnetic resonance imaging prenatal detection of characteristic brain anomalies in a case of HCH, molecularly confirmed through postnatal FGFR3 analysis. © 2014 John Wiley & Sons, Ltd. PMID:24839128

Cesaretti, Claudia; Spaccini, Luigina; Rustico, Mariangela; Parazzini, Cecilia; Doneda, Chiara; Re, Thomas J; Righini, Andrea

2014-10-01

163

The magnetic-anomaly model of the Jovian magnetosphere - A post-Voyager assessment  

NASA Technical Reports Server (NTRS)

Predictions previously put forth (Dessler and Vasyliunas, 1979) as tests for the magnetic-anomaly model (in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes) are reexamined in the light of Voyager and other recent observations. With regard to the prediction of a restricted longitude range of enhanced interaction between Io and Jupiter's ionosphere, the longitudinal asymmetries seen both in ground-based observations of sulfur emissions from the Io torus and in Voyager observations of Jovian auroral emissions are found to agree well with the predicted asymmetries.

Vasyliunas, V. M.; Dessler, A. J.

1981-01-01

164

Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic  

USGS Publications Warehouse

New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

2011-01-01

165

Martian meteorites and Martian magnetic anomalies: a new perspective from NWA 7034 (Invited)  

NASA Astrophysics Data System (ADS)

The magnetic anomalies observed above the Martian Noachian crust [1] require strong crustal remanent magnetization in the 15-60 A/m range over a thickness of 20-50 km [2,3]. The Martian rocks available for study in the form of meteorites do contain magnetic minerals (magnetite and/or pyrrhotite) but in too small amount to account for such strong remanent magnetizations [4]. Even though this contradiction was easily explained by the fact that Martian meteorites (mostly nakhlites and shergottites) are not representative of the Noachian Martian crust, we were left with no satisfactory candidate lithology to account for the Martian magnetic anomalies. The discovery in the Sahara of a new type of Martian meteorite (NWA 7034 [5] and subsequent paired stones which are hydrothermalized volcanic breccia) shed a new light on this question as it contains a much larger amount of ferromagnetic minerals than any other Martian meteorite. We present here a study of the magnetic properties of NWA 7034, together with a review of the magnetic properties of thirty other Martian meteorites. Magnetic measurements (including high and low temperature behavior and Mössbauer spectroscopy) show that NWA 7034 contains about 15 wt.% of magnetite with various degrees of substitution and maghemitization up to pure maghemite, in the pseudo-single domain size range. Pyrrhotite, a common mineral in other Martian meteorites is not detected. Although it is superparamagnetic and cannot carry remanent magnetization, nanophase goethite is present in significant amounts confirming that NWA 7034 is the most oxidized Martian meteorite studied so far, as already indicated by the presence of maghemite (this study) and pyrite [5]. These magnetic properties show that a kilometric layer of a lithology similar to NWA 7034 magnetized in a dynamo field would be enough to account for the strongest Martian magnetic anomalies. Although the petrogenesis of NWA 7034 is still debated, as the brecciation could be either of volcanic or impact origin [5,6,7], it appears that pervasive (and possibly shock-induced) hydrothermalism affecting the uppermost crust in the presence of a dynamo field during the Noachian is a viable scenario to account for the observed magnetic anomalies. Such a scenario is supported by the Noachian or even pre-Noachian age of NWA 7034 [8,9] and its chemical and mineralogical compositions that match the ones of the inferred Noachian crust [5]. The natural remanent magnetization of the NWA 7034 samples studied so far had been obliterated by the strong magnets used by meteorite hunters, but work is underway to obtain samples that may have kept their original Martian magnetization. References [1] Acuña M.H. et al. 1999. Science 284:790-793 [2] Langlais B. et al. 2004. JGR 109, doi: 10.1029/2003JE002048 [3] Quesnel Y. et al. 2007. Planet. Space Sci. 55:258-269 [4] Rochette P. et al. 2005 MAPS 40:529-540 [5] Agee C.B. et al. 2013. Science 339:780-785 [6] Hewins R.H. et al. 2013. 44th LPSC, abstract#2385 [7] Wittmann et al. 2013. 76th MetSoc meeting, abstract#5272 [8] Humayun et al. 2013. 76th MetSoc meeting, abstract#5198 [9] Nyquist et al. 2013. 76th MetSoc meeting, abstract#5318.

Gattacceca, J.; Rochette, P.; Scozelli, R. B.; Munayco, P.; Agee, C. B.; Quesnel, Y.; Cournede, C.; Geissman, J. W.

2013-12-01

166

Central Anomaly Magnetization High documentation of crustal accretion along the East Pacific Rise (9°55?–9°25?N)  

Microsoft Academic Search

Near-bottom magnetic data collected along the crest of the East Pacific Rise between 9°55? and 9°25?N identify the Central Anomaly Magnetization High (CAMH), a geomagnetic anomaly modulated by crustal accretionary processes over timescales of ?104 years. A significant decrease in CAMH amplitude is observed along-axis from north to south, with the steepest gradient between 9°42? and 9°36?N. The source of

Clare M. Williams; Maurice A. Tivey; Hans Schouten; Daniel J. Fornari

2008-01-01

167

Magnetic Anomalies Near Apollinaris Patera and the Medusae Fossae Formation, Mars  

NASA Astrophysics Data System (ADS)

Mars Global Surveyor magnetometer measurements were obtained over limited areas during the aerobraking phase of the mission at ~ 90 - 200 km altitude and globally during the mapping phase at ~ 360 - 420 km altitude. A correlation of one martian crustal field anomaly with a volcanic construct, Apollinaris Patera (A.P.), has previously been reported (Langlais, B. and M. Purucker, Planet. Space Sci., v. 55, p. 270, 2007). Here, we report more detailed mapping and modeling of the available MGS data over this construct and nearby volcanic units along the hemispheric dichotomy boundary. A map of the magnetic field magnitude at the mapping altitude contains a broad anomaly that correlates approximately with a large-scale volcanic plateau that adjoins the A.P. construct on its southwestern side. The volcanic plateau is mapped as part of the Medusae Fossae Formation (Lucus Planum) and may consist of pyroclastic flow deposits up to several km thick originating at one or more now-buried vents. Modeling of the A.P. anomaly using a near-surface disk source indicates that the horizontal scale size of the source is about twice as large as the surface diameter of the construct. Preliminary modeling of the Lucus Planum anomaly is consistent with a broad (500 - 1000 km) near-surface source although sources consisting of a series of deeply buried magma chambers cannot be excluded. Possible implications for martian dynamo history will be discussed.

Hood, L.; Langlais, B.

2009-04-01

168

Computed tomography and magnetic resonance imaging of the coronary sinus: anatomic variants and congenital anomalies.  

PubMed

The coronary sinus (CS) is an important vascular structure that allows for access into the coronary veins in multiple interventional cardiology procedures, including catheter ablation of arrhythmias, pacemaker implantation and retrograde cardioplegia. The success of these procedures is facilitated by the knowledge of the CS anatomy, in particular the recognition of its variants and anomalies. This pictorial essay reviews the spectrum of CS anomalies, with particular attention to the distinction between clinically benign variants and life-threatening defects. Emphasis will be placed on the important role of cardiac CT and cardiovascular magnetic resonance in providing detailed anatomic and functional information of the CS and its relationship to surrounding cardiac structures. Teaching Points • Cardiac CT and cardiovascular magnetic resonance offer 3D high-resolution mapping of the coronary sinus in pre-surgical planning.• Congenital coronary sinus enlargement occurs in the presence or absence of a left-to-right shunt.• Lack of recognition of coronary sinus anomalies can lead to adverse outcomes in cardiac procedures.• In coronary sinus ostial atresia, coronary venous drainage to the atria occurs via Thebesian or septal veins.• Coronary sinus diverticulum is a congenital outpouching of the coronary sinus and may predispose to cardiac arrhythmias. PMID:25048808

Chen, Yingming Amy; Nguyen, Elsie T; Dennie, Carole; Wald, Rachel M; Crean, Andrew M; Yoo, Shi-Joon; Jimenez-Juan, Laura

2014-10-01

169

Magnetization models for the source of the 'Kentucky anomaly' observed by Magsat  

NASA Technical Reports Server (NTRS)

Both the aeromagnetic data and magnetic anomaly data obtained by Magsat indicate the presence of a very magnetic source region within the crust beneath Kentucky and Tennessee. A source model was previously developed to fit surface gravity and long-wavelength aeromagnetic data, using limited seismic constraint. For the present study the model was further developed, and it is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled using both prismatic model sources and dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is determinable, but by scalar data as readily as vector data. Magnetization magnitude for the extended source region is about 3 A/m if the vertical extent of the source includes the whole of the crust.

Mayhew, M. A.; Estes, R. H.; Myers, D. M.

1985-01-01

170

Petrographic and Rock Magnetic Study of the Central Magnetic Anomaly, Manicouagan Impact Structure, Canada  

NASA Astrophysics Data System (ADS)

Drill core from a localized magnetic high in the centre of the Manicouagan impact structure reveals highly altered granulite grade rocks rich in magnetic carriers. High magnetic susceptibilities and natural remanent magnetic intensities appear to be due to the formation of magnetic minerals by both shock decomposition and hydrothermal alteration. This contrasts with other processes that produce the magnetic low observed over the majority of impact structures.

Scott, R. G.; Grieve, R. A. F.; Pilkington, M.

1996-03-01

171

Analysis of vector magnetic anomalies over the Bayonnaise Knoll caldera obtained from a deep-sea magnetic exploration by AUV  

NASA Astrophysics Data System (ADS)

Geophysical surveys near the seafloor are very effective methods in order to investigate fine structures of the oceanic crust. Such surveys have increased in researches and developments of the seafloor, and will be more and more necessary in the future. For example, seabed resources like hydrothermal deposits have recently focused attention behind the international situation for natural resources like a competition of resources development. In order to estimate accurate abundance of those resources, the above detailed investigations should be needed because of low resolution of geophysical surveys on the sea and low efficiency of exploratory drilling. From such a viewpoint, we have been developing a measurement system for magnetic explorations using an AUV and a deep-tow system. The magnetic exploration system consists of two 3-axis flux-gate magnetometers, one/two Overhauser magnetometer(s), an optical fiber gyro, a main unit (control, communication, recording), and an onboard unit. These devices except for the onboard unit are installed in pressure cases (depth limit: 6000m). Thus this system can measure three components and total intensity of the geomagnetic field in the deep sea. In 2009, the first test of the magnetic exploration system was carried out in the Kumano Basin using AUV Urashima and towing vehicle Yokosuka Deep-Tow during the R/V Yokosuka YK09-09 cruise. In this test, we sank a small magnetic target to the seafloor, and examined how the system worked. As a result, we successfully detected magnetic anomaly of the target to confirm the expected performance of that in the sea. In 2010, the magnetic exploration system was further tested in the Bayonnaise Knoll area both using a titanium towing frame during the R/V Bosei-maru cruise and using AUV Urashima during the R/V Yokosuka YK10-17 cruise. The purpose of these tests was to evaluate the performance of the system in an actual hydrothermal deposit area for practical applications of that. The Bayonnaise Knoll is a submarine caldera with an outer rim of 2.5-3 km and a floor of 840-920 m, which is located in the Izu-Ogasawara arc. A large hydrothermal deposit, Hakurei deposit, lies in the southeast part of the caldera. In the R/V Bosei-maru cruise, we observed three components of magnetic anomalies at depths of 400-570 m along SE-NW and WE tracks across the caldera. In the R/V Yokosuka YK10-17 cruise, we observed three components and total intensity of magnetic anomalies at altitudes of 60-100 m around the Hakurei deposit and at depth of 500 m above the caldera. The analysis of these data is now energetically pushed forward. A 3D gridded data set of the vector magnetic anomaly in the latter cruise was made by solving the Laplace's equation in the areas where observation data were not available, which is the unique procedure for analysis of the vector anomalies. Several magnetization solutions have been so far obtained by successive approximation and inversion methods. We will here present the measurement of the geomagnetic field and analysis of magnetization structure in Bayonnaise Knoll caldera. Note that this study has been supported by the Ministry of Education, Culture, Sports, Science & Technology (MEXT).

Sayanagi, K.; Isezaki, N.; Matsuo, J.; Harada, M.; Kasaya, T.

2011-12-01

172

Investigations of medium wavelength magnetic anomalies in the eastern Pacific using Magsat data  

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. Three long total magnetic field profiles taken over ocean basins were analyzed. It is found that there is a significant signal in the wavelength range of 1500 to 150 km. This is too short a wavelength to be caused by the core field, which becomes insignificant at about a wavelength of 1500 km; this intermediate wavelength signal is not caused by a typical sea floor spreading process, which should give maximum power in the wavelength region about 50 km. It is shown that the external magnetic field contributes very little to this intermediate wavelength signal. Efforts to explain the cause of this signal have failed.

Harrison, C. G. A. (principal investigator)

1980-01-01

173

Magnetic anomalies near Apollinaris Patera and the Medusae Fossae Formation in Lucus Planum, Mars  

NASA Astrophysics Data System (ADS)

The nature of strong martian crustal field sources is investigated by mapping and modeling of Mars Global Surveyor magnetometer data near Apollinaris Patera, a previously proposed volcanic source, supplemented by large-scale correlative studies. Regional mapping yields evidence for positive correlations of orbital anomalies with both Apollinaris Patera and Lucus Planum, a nearby probable extrusive pyroclastic flow deposit that is mapped as part of the Medusae Fossae Formation. Iterative forward modeling of the Apollinaris Patera magnetic anomaly assuming a source model consisting of one or more uniformly magnetized near-surface disks indicates that the source is centered approximately on the construct with a scale size several times larger and comparable to that of the Apollinaris Patera free-air gravity anomaly. A significantly lower rms deviation is obtained using a two-disk model that favors a concentration of magnetization near the construct itself. Estimates for the dipole moment per unit area of the Lucus Planum source together with maximum thicknesses of ˜3 km based on topographic and radar sounding data lead to an estimated minimum magnetization intensity of ˜50 A/m within the pyroclastic deposits. Intensities of this magnitude are similar to those obtained experimentally for Fe-rich Mars analog basalts that cooled in an oxidizing (high fO 2) environment in the presence of a strong (?10 ?T) surface field. Further evidence for the need for an oxidizing environment is provided by a broad spatial correlation of the locations of phyllosilicate exposures identified to date using Mars Express OMEGA data with areas containing strong crustal magnetic fields and valley networks in the Noachian-aged southern highlands. This indicates that the presence of liquid water, which is a major crustal oxidant, was an important factor in the formation of strong magnetic sources. The evidence discussed here for magnetic sources associated with relatively young volcanic units suggests that a martian dynamo existed during the late Noachian/early Hesperian, after the last major basin-forming impacts and the formation of the northern lowlands.

Hood, Lon L.; Harrison, Keith P.; Langlais, Benoit; Lillis, Robert J.; Poulet, Francois; Williams, David A.

2010-07-01

174

Investigation of source location determination from Magsat magnetic anomalies: The Euler method approach  

NASA Technical Reports Server (NTRS)

The applicability of the Euler method of source location determination was investigated on several model situations pertinent to satellite-data scale situations as well as Magsat data of Europe. Our investigations enabled us to understand the end-member cases for which the Euler method will work with the present satellite magnetic data and also the cases for which the assumptions implicit in the Euler method will not be met by the present satellite magnetic data. These results have been presented in one invited lecture at the Indo-US workshop on Geomagnetism in Studies of the Earth's Interior in August 1994 in Pune, India, and at one presentation at the 21st General Assembly of the IUGG in July 1995 in Boulder, CO. A new method, called Anomaly Attenuation Rate (AAR) Method (based on the Euler method), was developed during this study. This method is scale-independent and is appropriate to locate centroids of semi-compact three dimensional sources of gravity and magnetic anomalies. The method was presented during 1996 Spring AGU meeting and a manuscript describing this method is being prepared for its submission to a high-ranking journal. The grant has resulted in 3 papers and presentations at national and international meetings and one manuscript of a paper (to be submitted shortly to a reputable journal).

Ravat, Dhananjay

1996-01-01

175

A Semiclassical Formulation of the Chiral Magnetic Effect and Chiral Anomaly in Even d+1 Dimensions  

E-print Network

In terms of the matrix valued Berry gauge field strength for the Weyl Hamiltonian in any even spacetime dimensions a symplectic form whose elements are matrices in spin indices is introduced. Definition of the volume form is modified appropriately. A simple method of finding the path integral measure and the chiral current in the presence of external electromagnetic fields is presented. It is shown that within this new approach the chiral magnetic effect as well as the chiral anomaly in even d+1 dimensions are accomplished straightforwardly.

Omer F. Dayi; Mahmut Elbistan

2014-02-19

176

Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties  

NASA Astrophysics Data System (ADS)

analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6°44.1' N, 91°56.1' W) on the Cocos Plate in ˜15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David

2014-08-01

177

Analysis and interpretation of Ibuji spring magnetic anomaly using the Mellin transform  

NASA Astrophysics Data System (ADS)

The Mellin transform is a mathematical tool which has been applied in many areas of Mathematics, Physics and Engineering. Its application in Geophysics is in the computation of solution of potential problems for the determination of the mass as well as the depth to the basement of some solid mineral deposits. In this study, the Mellin transform is used to determine the depth to the top ( h) and the depth to the bottom ( H) of the basement of a profile of an anomalous magnetic body. Ibuji, the study area is located in Ifedore Local Government area of Ondo state, Nigeria, underlain by Precambrian complex rocks and bounded by geographical co-ordinate of Easting 5°00t'00? to 5°4t'30? and Northing 7°24t'00? to 7°27t'36?. The magnetic anomaly profile due to a two- dimensional body(vertical thin sheet)over magnetic spring of the study area was digitised and the values of magnetic amplitude (nT) with respect to its horizontal distance (say interval of 5 m) obtained from the digitized profile was then used in the computation of Mellin transform using Matlab programs. In order to determine the depths H and h, the amplitudes were considered at three arbitrary point ( s = ¼, ½ and ¾) such that, (0 < s < 1), where s is a complex variable of real positive integer. The value obtained for H was 47.95 m, which compared favourably with the result obtained using other methods. Meanwhile, the value obtained for h has a convergence restriction, whereby, at lower values of s, there is divergence, while at higher values of s, (about 0.9), the result converges and h was obtained to be 32.56 m. The Ibuji magnetic anomaly was therefore analysed to have a depth to the bottom ( H) of 47.95 m and depth to the top of 32.56 m using this mathematical tool.

Ozebo, Vitalis C.; Ogunsanwo, Fidelis O.; Adebayo, Gboyega A.; Adeniran, Olusola J.

2013-03-01

178

The Effect of Dissipation Mechanism and Guide Field Strength on X-line Spreading in 3D Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

In two-ribbon flares, the fact that the ribbons separate in time is considered evidence of magnetic reconnection. However, in addition to the ribbons separating, they can also elongate (as seen in animations of, for example, the Bastille Day flare). The elongation is undoubtedly related to the reconnection spreading in the out-of-plane direction. Indeed, naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. For example, it was suggested that X-line spreading is necessary to explain the observation of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006), and has been seen in reconnection experiments. A sizeable out-of-plane (guide) magnetic field is present at flare sites and in the solar wind. Here, we study the effect of dissipation mechanism and the strength of the guide field has on X-line spreading. We present results from three-dimensional numerical simulations of magnetic reconnection, comparing spreading with the Hall term to spreading with anomalous resistivity. Applications to solar flares and magnetic reconnection in the solar wind will be discussed.

Shepherd, Lucas; Cassak, P.; Drake, J.; Gosling, J.; Phan, T.; Shay, M. A.

2013-07-01

179

Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and  

E-print Network

Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications 2008; published 26 July 2008. [1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic. Tivey, and S.-M. Lee (2008), Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone

180

Reduction and treatment of magnetic anomalies of crustal origin in satellite data  

NASA Technical Reports Server (NTRS)

The problem of proper reduction and treatment of the residual total magnetic field observed on satellite orbits is studied. The reduction procedure used for Pogo satellite data is reviewed, and a procedure is presented for reducing the residual total field observed on satellite orbits to a spherical surface. Several examples based on selected models are provided to demonstrate the accuracy of the formulas developed for continuation of the satellite data from an irregular to a spherical surface. This procedure is tested on a set of Pogo data covering the area that contains the Bangui magnetic anomaly in central Africa. A technique is also given for determining the field components on a spherical surface and calculating the total field in any fixed direction of the geomagnetic field.

Bhattacharyya, B. K.

1977-01-01

181

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

The I -V characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the I -V characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of I -V characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the I -V curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic I -V characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the I -V curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.

Ringer, S.; Vieth, M.; Bär, L.; Rührig, M.; Bayreuther, G.

2014-11-01

182

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications  

NASA Technical Reports Server (NTRS)

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

183

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications  

NASA Technical Reports Server (NTRS)

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

184

Observation of a lunar mini-magnetosphere above a magnetic anomaly using energetic neutral atoms  

NASA Astrophysics Data System (ADS)

The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. When solar wind hits the lunar surface, it is partly backscattered as energetic neutral atoms. The intensity of the backscattered energetic neutral atoms is a measure of the intensity of the solar wind reaching the surface. We report on the imaging of a lunar magnetic anomaly in backscattered neutral hydrogen atoms: The image shows the formation of a partial void of the solar wind, a mini-magnetosphere, above the strong magnetic anomaly near the Crisium antipode on the lunar farside. The mini-magnetosphere is 360 km across at the surface and surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. These observations demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms, and its application to a new class of objects, mini-magnetospheres.

Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmström, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi

2010-05-01

185

First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms  

NASA Astrophysics Data System (ADS)

The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft has produced for the first time an image of a lunar magnetic anomaly in backscattered hydrogen atoms. The image shows that a partial void of the solar wind, a mini-magnetosphere, is formed above the strong magnetic anomaly near the Crisium antipode. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. The mini-magnetosphere is visible only in hydrogen atoms with energy exceeding 150 eV. Fluxes with energies below 100 eV do not show corresponding spatial variations. While the high-energy atoms result from the backscattering process, the origin of the low-energy component is puzzling. These observations reveal a new class of objects, mini-magnetospheres, and demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms.

Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmström, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi

2010-03-01

186

Energy Detection Based on Undecimated Discrete Wavelet Transform and Its Application in Magnetic Anomaly Detection  

PubMed Central

Magnetic anomaly detection (MAD) is a passive approach for detection of a ferromagnetic target, and its performance is often limited by external noises. In consideration of one major noise source is the fractal noise (or called 1/f noise) with a power spectral density of 1/fa (0magnetic anomaly detection and UDWT are introduced in brief, while a possible detection system based on giant magneto-impedance (GMI) magnetic sensor is also given out. Then our proposed energy detection based on UDWT is described in detail, and the probabilities of false alarm and detection for given the detection threshold in theory are presented. It is noticeable that no a priori assumptions regarding the ferromagnetic target or the magnetic noise probability are necessary for our method, and different from the discrete wavelet transform (DWT), the UDWT is shift invariant. Finally, some simulations are performed and the results show that the detection performance of our proposed detector is better than that of the conventional energy detector even utilized in the Gaussian white noise, especially when the spectral parameter ? is less than 1.0. In addition, a real-world experiment was done to demonstrate the advantages of the proposed method. PMID:25343484

Nie, Xinhua; Pan, Zhongming; Zhang, Dasha; Zhou, Han; Chen, Min; Zhang, Wenna

2014-01-01

187

A permanent magnet electron beam spread system used for a low energy electron irradiation accelerator  

NASA Astrophysics Data System (ADS)

The development of irradiation processing industry brings about various types of irradiation objects and expands the irradiation requirements for better uniformity and larger areas. This paper proposes an innovative design of a permanent magnet electron beam spread system. By clarifying its operation principles, the author verifies the feasibility of its application in irradiation accelerators for industrial use with the examples of its application in electron accelerators with energy ranging from 300 keV to 1 MeV. Based on the finite element analyses of electromagnetic fields and the charged particle dynamics, the author also conducts a simulation of electron dynamics in magnetic field on a computer. The results indicate that compared with the traditional electron beam scanning system, this system boosts the advantages of a larger spread area, non-power supply, simple structure and low cost, etc., which means it is not only suitable for the irradiation of objects with the shape of tubes, strips and panels, but can also achieve a desirable irradiation performance on irregular constructed objects of large size.

Huang, Jiang; Xiong, Yong-Qian; Chen, De-Zhi; Liu, Kai-Feng; Yang, Jun; Li, Dong; Yu, Tiao-Qin; Fan, Ming-Wu; Yang, Bo

2014-10-01

188

Lineated Near Bottom Magnetic Anomalies Over an Oceanic Core Complex, Atlantis Massif (Mid-Atlantic Ridge at 30°N)  

NASA Astrophysics Data System (ADS)

Despite significant effort during the four decades since the Vine-Matthews-Morley hypothesis was first advanced, the relative importance of lower crustal (and possibly upper mantle) sources in generating lineated marine magnetic anomalies remains uncertain. Remanence measurements from samples obtained by drilling or dredging provide the most direct evidence that these deeper layers can be significant anomaly sources. Near bottom anomaly measurements over tectonic exposures of the lower crust/upper mantle can yield valuable complementary information (e.g., patterns of polarity boundaries) as well as provide constraints on the timing and uplift history of these exposures. Here we report results from a near bottom magnetic survey of the Atlantis Massif, an oceanic core complex that formed within the past 1.5-2 Myr at the intersection of the Mid-Atlantic Ridge (30°N) and the Atlantis transform fault. Geological and geophysical data indicate the presence of gabbro and peridotite over much of the corrugated central dome, inferred to be the footwall of a detachment fault. A vector magnetometer deployed 25m aft of the deeply towed side scan sonar system allowed measurement of both the total field and horizontal and vertical anomalous fields. Five profiles across the central dome reveal a lineated anomaly low that was not evident in earlier sea surface profiles. The presence of lineated anomalies over presumed gabbro and ultramafic exposures may record the acquisition of remanence as these rocks were exhumed by detachment faulting. Anomaly profiles over the Lost City hydrothermal vent field exhibit a pronounced magnetic low (reversed polarity), suggesting that active serpentinization is not responsible for the overall magnetization pattern. When combined with results from planned IODP drilling at the site, these data should provide significant insights into the importance of gabbro and peridotite lithologies as sources for lineated magnetic anomalies.

Gee, J.; Blackman, D.

2004-05-01

189

Spectral and Magnetic Studies of Lesser-Known Lunar Magnetic and Albedo Anomalies  

Microsoft Academic Search

The origin of the lunar swirls is an outstanding puzzle in lunar geoscience. In addition, the swirls lie at the intersection of broader issues in planetary science, including planetary magnetism (e.g., the origin of the magnetized crust via core dynamo versus impact processes) and the relative importance of solar wind exposure versus micrometeoroid bombardment in producing the optical effects of

B. R. Hawke; D. T. Blewett; E. I. Coman; M. E. Purucker; J. J. Gillis-Davis

2009-01-01

190

High-temperature magnetic anomalies in Sr-doped La manganite structures  

SciTech Connect

The temperature dependence of the magnetization M, susceptibility {chi}, and magnetoresistance MR for 3 perovskite-variant manganite structures were studied: monoclinic (x=0.075) and orthorhombic (x=0. 125) La{sub 1-x}Sr{sub x}MnO{sub 3}, and tetragonal layered La{sub 2- 2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} (x=0.4) with x also indicating the nominal fraction of Mn{sup 4+}. In each case, evidence is found for unusual magnetic states at temperatures T above their primary magnetic transitions. In the first case, the high-T {chi} deviates from Curie-Weiss expectations, in the second case the MR extends to high T, and in the last, M and {chi} exhibit short-range anomalies at high T. This suggests that a key feature of these systems is the existence of multiple magnetic energy scales, independent of structure, dimensionality, or doping levels.

Potter, C.D.; Swiatek, M.; Mitchell, J.F.; Hinks, D.G.; Jorgensen, J.D.; Bader, S.D. [Argonne National Lab., IL (United States). Materials Science Div.; Argyriou, D.N. [Argonne National Lab., IL (United States). Science and Technology Center for Superconductivity

1996-12-31

191

Magnetization anomaly of Nb3Al strands and instability of Nb3Al Rutherford cables  

SciTech Connect

Using a Cu stabilized Nb{sub 3}Al strand with Nb matrix, a 30 meter long Nb{sub 3}Al Rutherford cable was made by a collaboration of Fermilab and NIMS. Recently the strand and cable were tested. In both cases instability was observed at around 1.5 Tesla. The magnetization of this Nb{sub 3}Al strand was measured first using a balanced coil magnetometer at 4.2 K. Strands showed an anomalously large magnetization behavior around at 1.6 T, which is much higher than the usual B{sub c2} {approx} 0.5 Tesla (4.2 K) of Nb matrix. This result is compared with the magnetization data of short strand samples using a SQUID magnetometer, in which a flux-jump signal was observed at 0.5 Tesla, but not at higher field. As a possible explanation for this magnetization anomaly, the interfilament coupling through the thin Nb films in the strands is suggested. The instability problem observed in low field tests of the Nb{sub 3}Al Rutherford cables is attributed to this effect.

Yamada, Ryuji; /Fermilab; Kikuchi, Akihiro; /Tsukuba Magnet Lab; Wake, Masayoshi; /KEK, Tsukuba

2006-08-01

192

Deciphering tectonic phases of the Amundsen Sea Embayment shelf, West Antarctica, from a magnetic anomaly grid  

NASA Astrophysics Data System (ADS)

The Amundsen Sea Embayment (ASE), with Pine Island Bay (PIB) in the eastern embayment, is a key location to understanding tectonic processes of the Pacific margin of West Antarctica. PIB has for a long time been suggested to contain the crustal boundary between the Thurston Island block and the Marie Byrd Land block. Plate tectonic reconstructions have shown that the initial rifting and breakup of New Zealand from West Antarctica occurred between Chatham Rise and the eastern Marie Byrd Land at the ASE. Recent concepts have discussed the possibility of PIB being the site of one of the eastern branches of the West Antarctic Rift System (WARS). About 30,000 km of aeromagnetic data - collected opportunistically by ship-based helicopter flights - and tracks of ship-borne magnetics were recorded over the ASE shelf during two RV Polarstern expeditions in 2006 and 2010. Grid processing, Euler deconvolution and 2D modelling were applied for the analysis of magnetic anomaly patterns, identification of structural lineaments and characterisation of magnetic source bodies. The grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf. Distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from (1) magmatic emplacement zones of Cretaceous rifting and breakup (100-85 Ma), to (2) a southern distributed plate boundary zone of the Bellingshausen Plate (80-61 Ma) and (3) activities of the WARS indicated by NNE-SSW trending lineaments (55-30 Ma?). The analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf.

Gohl, Karsten; Denk, Astrid; Eagles, Graeme; Wobbe, Florian

2013-02-01

193

Circum-Arctic Magnetic Anomalies - Challenges of Compilation and the Value of Regional Interpretation in a Frontier Area  

NASA Astrophysics Data System (ADS)

Important societal issues are driving increased attention to polar regions. The arctic, in particular, is the focus of scientific studies relating to climate change as well as resource exploration and territorial claims. The news and entertainment media are picking up on polar themes and driving interest within popular culture. Part of the attraction and mystique of the ends of the Earth lies in their relative inaccessibility and harsh environment. These same attributes make it difficult to conduct even basic scientific investigation, and therefore, the arctic remains a scientific frontier in many respects. Delineation of a robust tectonic framework for the top of the world is an essential prerequisite to resource assessment. The difficulty of making direct geologic observations beneath ice and sea requires remote measurement. Regional magnetic anomaly mapping provides important constraining information for the development of tectonic models for this structurally complex region. In addition to the obvious logistical challenges to detailed magnetic field measurement in the high arctic, noise and instability in the magnetic field itself at high latitudes presents difficulties. Nevertheless, regional magnetic anomaly data have been collected over the past 50 years for much of the arctic. The available surveys are diverse in vintage and survey design; the amplitude and frequency content of measured anomalies are widely variable. Availability of metadata and other documentation are also inconsistent for these surveys. This leads to significant challenges in constructing accurate regional magnetic anomaly maps. Preliminary maps from a new international cooperation effort (CAMP-GM, under the direction of Carmen Gaina, Geological Survey of Norway) provide the most consistent view yet of magnetic anomalies for the tectonically complex arctic basins and surrounding continents. Careful attention to digital compilation details allows the new grids to be mathematically filtered to assist in the regional characterization of magnetic domains and boundaries. The frequency content, amplitudes, and patterns of regional magnetic anomalies provide a window into the tectonic character and structure of the crust. Continental, oceanic, and various types of transitional crust each have a distinctive magnetic anomaly signature that can be used to define a fundamental tectonic framework of the circum-arctic. Interpretation can be extended by including additional data such as regional bathymetry (an indicator of crustal buoyancy and isostatic equilibrium) and free air gravity (an independent indicator of crustal density balance and composition). Used together with magnetic domains these data reveal a composite geodynamic subdivision of the arctic. This subdivision provides a framework for investigations of mineral and energy resource potential, tectonic reconstruction, and long-term climate dynamics.

Saltus, R. W.; Gaina, C.; Brown, P. J.

2007-12-01

194

Investigation of the Crust of the Pannonian Basin, Hungary Using Low-Altitude CHAMP Horizontal Gradient Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

The Pannonian Basin is a deep intra-continental basin that formed as part of the Alpine orogeny. It is some 600 by 500 km in area and centered on Hungary. This area was chosen since it has one of the thinnest continental crusts in Europe and is the region of complex tectonic structures. In order to study the nature of the crustal basement we used the long-wavelength magnetic anomalies acquired by the CHAMP satellite. The SWARM constellation, scheduled to be launched next year, will have two lower altitude satellites flying abreast, with a separation of between ca. 150 to 200 km. to record the horizontal magnetic gradient. Since the CHAMP satellite has been in orbit for eight years and has obtained an extensive range of data, both vertically and horizontally there is a large enough data base to compute the horizontal magnetic gradients over the Pannonian Basin region using these many CHAMP orbits. We recomputed a satellite magnetic anomaly map, using the spherical-cap method of Haines (1985), the technique of Alsdorf et al. (1994) and from spherical harmonic coefficients of MF6 (Maus et aI., 2008) employing the latest and lowest altitude CHAMP data. We then computed the horizontal magnetic anomaly gradients (Kis and Puszta, 2006) in order to determine how these component data will improve our interpretation and to preview what the SW ARM mission will reveal with reference to the horizontal gradient anomalies. The gradient amplitude of an 1000 km northeast-southwest profile through our horizontal component anomaly map varied from 0 to 0.025 nT/km with twin positive anomalies (0.025 and 0.023 nT/km) separated by a sharp anomaly negative at o nT/km. Horizontal gradient indicate major magnetization boundaries in the crust (Dole and Jordan, 1978 and Cordell and Grauch, 1985). Our gradient anomaly was modeled with a twodimensional body and the anomaly, of some 200 km, correlates with a 200 km area of crustal thinning in the southwestern Pannonian Basin.

Taylor, Patrick T.; Kis, Karoly I.; Puszta, Sandor; Wittmann, Geza; Kim, Hyung Rae; Toronyi, B.

2011-01-01

195

Paleomagnetic determinations on Lanzarote from magnetic and gravity anomalies: Implications for the early history of the Canary Islands  

NASA Astrophysics Data System (ADS)

The Bouguer and aeromagnetic anomaly maps of Lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island, indicating one isolated source. Assuming that the structure responsible for both anomalies is the same, a methodology has been designed to estimate the total magnetization vector of the source, which is interpreted as a large intrusive body (mafic core) positioned as a result of magma rising to the surface during the early stages of growth of Lanzarote. Considering its geometry to be known from a previous three-dimensional (3-D) gravity model, the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced-to-the-pole anomaly map, comparison between the gravity and the pseudogravity anomalies, and 3-D forward magnetic modeling. The total magnetization vector obtained by this method is defined by a module of 4.5 A m-1 and a direction D = -20° and I = 30°. Comparing the paleomagnetic pole, obtained from this direction, with the apparent polar wander path of Africa for the last 160 Myr, it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization (NRM) which could have been acquired between 60 and 100 Ma. This result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in Lanzarote took place during the Upper Cretaceous, thus providing the first evidence of a timeline for the early formative stages of this volcanic island.

Blanco-Montenegro, I.; Montesinos, F. G.; GarcíA, A.; Vieira, R.; VillalaíN, J. J.

2005-12-01

196

Examples of Models Fit to Magnetic Anomalies Observed Over Subaerial, Submarine, and Subglacial Volcanoes in the West Antarctic Rift System  

NASA Astrophysics Data System (ADS)

Aeromagnetic and marine magnetic surveys over the volcanically active West Antarctic rift system, constrained by seismic reflection profiles over the Ross Sea continual shelf, and radar ice sounding surveys over the West Antarctic Ice Sheet (WAIS) allowed calculation of models fit to very high-amplitude anomalies. We present several examples: exposed 2700-m high, subaerial erupted volcano Mt Melbourne; the 750-m high source of anomaly D (Hamilton submarine volcano) in the Ross sea; and the 600-m high edifice of Mt. CASERTZ beneath the WAIS. The character of these anomalies and their sources varies greatly, and is inferred to be the result of subaerial, submarine and subglacial emplacement respectively. Mt. Melbourne erupted through the WAIS at a time when it was grounded over the Ross Sea continental shelf. Highly magnetic volcanic flows inferred to have high remanent (normal) magnetization in the present field direction produce the 600-nT positive anomaly. The flows protected the edifice above the ice from erosion. Negligible amounts of probably subglacially erupted, apparently non-magnetic hyaloclastite exist in association with Mt. Melbourne. Mt. CASERTZ is nonmagnetic and the edifice is interpreted as consisting of a transient mound of unconsolidated hyaloclastite injected into the WAIS. However Mt. CASERTZ, about 8-km diameter, overlies a 200-m high, 40-km wide highly magnetic residual edifice modeled as the top of the source (an active subglacial volcano) of a 400-nT high positive anomaly. Any former edifices comprising hyaloclastite, pillow breccia or other volcanic debris injected into the moving WAIS apparently have been removed. About 400 other high- amplitude anomalies associated with low relief (80 percent less than 200 m) edifices at the base of the ice (the tops of the sources of these steep gradient anomalies) beneath the WAIS defined by radar ice sounding have been interpreted as having former hyaloclastite edifices, which were removed by the moving ice. The source of the -1300-nT negative anomaly D projecting 600 m above the Ross Sea continental shelf is enigmatic. We interpret models as either the result of reversed magnetization (less than 780 Ka) at a time of deglaciation of the continental shelf, or a hydrothermally altered central core surrounded by highly magnetic flows erupted beneath the Ross sea since deglaciation in Holocene time.

Behrendt, J. C.; Finn, C. A.; Blankenship, D. D.

2006-12-01

197

Interpretations of magnetic anomalies at a potential repository site located in the Yucca Mountain area, Nevada test site  

NASA Astrophysics Data System (ADS)

In the Yucca Mountain area, studies of the relation of magnetic properties to geologic features provided structural information at and near a potential site for storage of radioactive waste. Interpreted features include a tabular mass of magnetized sedimentary rock beneath thick deposits of volcanic rock, and 11 major faults that displace magnetized volcanic rock. The basis for mapping traces of faults and identifying their upthrown sides was developed elsewhere at Yucca fault in the relatively simple volcanic terrains of Yucca Flat. In the site area, analyses of aeromagnetic anomalies from a low altitude, east-west aeromagnetic survey show the Topopah Spring Member of the Paintbrush Tuff as the primary source of anomalies from faulted sequences of volcanic rock. Faults related to belts of positive and negative anomalies surrounding the site were identified. The possibility that an east-west pattern of anomalies is related to structure crossing the site was investigated by an aeromagnetic survey. A significant reduction in amplitude of these anomalies resulted when effects of the deeply buried argillite were removed.

Bath, G. D.; Jahren, C. E.

198

Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, S. A.; Brown, L. L.; Robinson, P.

2013-12-01

199

Magnetic properties of rocks of the Kapuskasing uplift (Ontario, Canada) and origin of long-wavelength magnetic anomalies  

NASA Astrophysics Data System (ADS)

The sources of long wavelength magnetic anomalies (LWA) in the crust are poorly understood. We have measured remanent and induced magnetizations of 210 samples of anorthosite, tonalite and mafic gneiss from the Kapuskasing uplift, an exposed partial crustal cross-section in northwestern Ontario, Canada. Anorthosites have generally high Q ratios of remanent/induced magnetization, in the range 0.3-60, and their natural remanent magnetization (NRM) is resistant to both thermal and alternating-field (AF) demagnetization. However, anorthosite NRMs (0.001-0.3 A m-1) are too weak to explain LWA amplitudes. Mafic gneisses also have relatively high Q ratios, peaking in the range 1-10, and the NRM is resistant to thermal and AF demagnetization. NRM and induced magnetization (IM) intensities are in the ranges 0.01-2 and 0.01-0.6 A m-1, respectively. Tonalites have a bimodal distribution of magnetization. The more strongly magnetic group has both NRM and IM intensities in the range 0.1-5 A m-1 and wide-ranging Q values, from 0.1 to 10 approximately. Some tonalites could be an LWA source, although the long-term stability of their NRMs at high temperature in the crust is questionable because unblocking temperatures are broadly distributed from 100 to 600°C. In general, Q values measured at surface temperatures overestimate remanence at depth. In the deep crust, IM remains more or less constant but remanence decreases both reversibly and irreversibly, leading to Q ratios of <0.2-0.3 for multidomain grains and ~1-3 for single-domain grains near their blocking temperatures. Thermoviscous magnetization over the Brunhes chron could add substantially to the effective induced magnetization. Typically induced + thermoviscous magnetization in the direction of the present Earth's field will outweigh remanence in the direction of an ancient field as a source of LWA originating in the deepest crust. Remanence may play a larger role for mid-crustal sources where single-domain grains are well below their blocking temperatures.

Dunlop, David J.; Özdemir, Özden; Costanzo-Alvarez, Vincenzo

2010-11-01

200

Investigating tectonic and bathymetric features of the Indian Ocean using MAGSAT magnetic anomaly data  

NASA Technical Reports Server (NTRS)

MAGSAT Investigator-B tapes were preprocessed by (1) removing all data points with obvious erroneous values and location errors; (2) removing smaller spikes (typically 15 nT or more), and deleting data tracks with fewer than 20 points; and (3) removing a linear trend from each track. The remaining data were recorded on tape for use by the equivalent source mapping (ESMAP) program which uses a least squares algorithm to fit the magnetization parameter of the grid of equivalent source dipoles in the crust to satellite data acquired at different times and locations. ESMAP was implemented on the TASC computing system and modified to read preprocessed MAGSAT tapes and interface with TASC plotting software. Some verification of the software was accomplished. Gridded 1-degree mean values of gravity anomaly and sea surface undulation computed from SEASAT radar altimeter were obtained and brought on line.

Lazarewicz, A. R.; Sailor, R. V. (principal investigators)

1982-01-01

201

The role of magnetic resonance imaging in refining the diagnosis of suspected fetal renal anomalies  

PubMed Central

Objective: This prospective study was designed to detect the role of magnetic resonance imaging (MRI) in refining the diagnosis of suspected fetal renal anomalies detected during screening sonography. Material and Methods: 54 pregnant women, with suspected fetal renal anomalies detected during routine ultrasound screening, were rescanned by MRI to refine the diagnosis of the suspected renal anomalies. The pregnancy outcome was examined externally and by postnatal ultrasonography. Results: Fifty-four cases of suspected renal anomalies detected during screening sonography of 8400 pregnant women (0.6%), were res-canned by MRI in this study. The MRI gave a similar diagnosis to postnatal ultrasound in 46 cases (16 cases of hydronephrosis, 14 cases of Polycystic Kidney Disease (PCKD), 9 cases of Multicystic Kidney Disease (MCKD), 2 cases of Renal Agensis (RA), 3 cases of single renal cyst and 2 cases of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 6 cases (4 cases of hydronephrosis diagnosed by MRI confirmed to be PCKD by postnatal ultrasound, also, 1 case of MCKD diagnosed by MRI confirmed to be hydronephrosis by postnatal ultrasound and 1 case of RA diagnosed by MRI confirmed to be normal by postnatal ultrasound). The prenatal ultrasound gave a similar diagnosis to postnatal ultrasound in 43 cases (14 cases of hydronephrosis, 13 case of PCKD, 9 cases of MCKD, 2 cases of RA, 3 cases of single renal cyst and 2 case of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 9 cases; 4 cases of hydronephrosis diagnosed by prenatal sonography confirmed to be PCKD by postnatal ultrasound, one case of PCKD+one case of MCKD, and one case of megacystis+hydroureter confirmed to be hydronephrosis by postnatal ultrasound, while one case of MCKD diagnosed by prenatal sonography was confirmed to be PCKD by postnatal ultrasound and one case of RA diagnosed by prenatal ultrasound was confirmed to be normal by postnatal ultrasound. Conclusion: The MRI can be used as a complementary adjunctive modality with excellent tissue contrast, especially in equivocal cases or inconclusive sonographic findings. PMID:24592062

Abdelazim, Ibrahim Anwar; Belal, Maha Mohamed

2013-01-01

202

Controls on Martian Hydrothermal Systems: Application to Valley Network and Magnetic Anomaly Formation  

NASA Technical Reports Server (NTRS)

Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of approximately 0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10(exp -16) sq m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10(exp -15) sq m. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10(exp -17) sq m and intrusion volumes as low as 50 cu km, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.

Harrison, Keith P.; Grimm, Robert E.

2002-01-01

203

Opening of the Amerasian Basin: A model based on sea-floor morphology, magnetic anomalies and paleomagnetic data  

Microsoft Academic Search

There are numerous models for the origins of the Amerasia Basin. The model we present here is based on sea-floor morphology, magnetic anomaly signatures and evidence derived from dredge hauls which indicate that the Arctic Alaska block traveled to its present location from a location close to the Canadian and Lomonosov margins. This location is further east than is called

D. B. Stone; K. Brumley

2010-01-01

204

Research for Key Techniques of Geophysical Recognition System of Hydrocarbon-induced Magnetic Anomalies Based on Hydrocarbon Seepage Theory  

NASA Astrophysics Data System (ADS)

Hydrocarbon seepage effects can cause magnetic alteration zones in near surface, and the magnetic anomalies induced by the alteration zones can thus be used to locate oil-gas potential regions. In order to reduce the inaccuracy and multi-resolution of the hydrocarbon anomalies recognized only by magnetic data, and to meet the requirement of integrated management and sythetic analysis of multi-source geoscientfic data, it is necessary to construct a recognition system that integrates the functions of data management, real-time processing, synthetic evaluation, and geologic mapping. In this paper research for the key techniques of the system is discussed. Image processing methods can be applied to potential field images so as to make it easier for visual interpretation and geological understanding. For gravity or magnetic images, the anomalies with identical frequency-domain characteristics but different spatial distribution will reflect differently in texture and relevant textural statistics. Texture is a description of structural arrangements and spatial variation of a dataset or an image, and has been applied in many research fields. Textural analysis is a procedure that extracts textural features by image processing methods and thus obtains a quantitative or qualitative description of texture. When the two kinds of anomalies have no distinct difference in amplitude or overlap in frequency spectrum, they may be distinguishable due to their texture, which can be considered as textural contrast. Therefore, for the recognition system we propose a new “magnetic spots” recognition method based on image processing techniques. The method can be divided into 3 major steps: firstly, separate local anomalies caused by shallow, relatively small sources from the total magnetic field, and then pre-process the local magnetic anomaly data by image processing methods such that magnetic anomalies can be expressed as points, lines and polygons with spatial correlation, which includes histogram-equalization based image display, object recognition and extraction; then, mine the spatial characteristics and correlations of the magnetic anomalies using textural statistics and analysis, and study the features of known anomalous objects (closures, hydrocarbon-bearing structures, igneous rocks, etc.) in the same research area; finally, classify the anomalies, cluster them according to their similarity, and predict hydrocarbon induced “magnetic spots” combined with geologic, drilling and rock core data. The system uses the ArcGIS as the secondary development platform, inherits the basic functions of the ArcGIS, and develops two main sepecial functional modules, the module for conventional potential-field data processing methods and the module for feature extraction and enhancement based on image processing and analysis techniques. The system can be applied to realize the geophysical detection and recognition of near-surface hydrocarbon seepage anomalies, provide technical support for locating oil-gas potential regions, and promote geophysical data processing and interpretation to advance more efficiently.

Zhang, L.; Hao, T.; Zhao, B.

2009-12-01

205

Characterization of Lunar Swirls at Mare Ingenii: A Model for Space Weathering at Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Marc Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (l) Despite having spectral characteristics of immaturity, the lunar swirls arc not freshly exposed surfaces. (2) The swirl surfaces arc regions of retarded weathering, while immediately adjacent regions experience accelerated weathering, (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (greater than 40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminaty analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe(sup 0) particle sizes responsible for the spectral effects of space weathering.

Kramer, Georgianna Y.; Combe, Jean-Philippe; Harnett, Erika M.; Hawke, Bernard Ray; Noble, Sarah K.; Blewett, David T.; McCord, Thomas B.; Giguere, Thomas A.

2011-01-01

206

Inverse Dipolar Magnetic Anomaly Over the Volcanic Cone Linked to Reverse Polarity Magnetizations in Lavas and Tuffs - Implications for the Conduit System  

NASA Astrophysics Data System (ADS)

A combined magnetics and paleomagnetic study of Toluquilla monogenetic volcano and associated lavas and tuffs from Valsequillo basin in Central Mexico provides evidence on a magnetic link between lavas, ash tuffs and the underground volcanic conduit system. Paleomagnetic analyses show that lavas and ash tuffs carry reverse polarity magnetizations, which correlate with the inversely polarized dipolar magnetic anomaly over the volcano. The magnetizations in the lava and tuff show similar southward declinations and upward inclinations, supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement. Conduit geometry is one of the important controlling factors in eruptive dynamics of basaltic volcanoes. However volcanic conduits are often not, or only partly, exposed. Modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination, which correlates with the reverse polarity magnetizations in the lava and tuff. The study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano. Time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava, suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff. The reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of Toluquilla volcano at about 1.3 Ma during the Matuyama reverse polarity C1r.2r chron.

Fucugauchi, J. U.; Perez-Cruz, L. L.; Trigo-Huesca, A.

2012-12-01

207

Magnetic resonance imaging of retropharyngeal lymph node metastasis in nasopharyngeal carcinoma: Patterns of spread  

SciTech Connect

Purpose: To investigate the incidence, distribution, and spread pattern of retropharyngeal lymph node (RLN) involvement in patients with nasopharyngeal carcinoma (NPC) by using magnetic resonance imaging (MRI). Methods and Materials: The MR images of 275 patients with newly diagnosed NPC were reviewed retrospectively. Nodes were classified as metastatic based on size criteria, the presence of nodal necrosis, and extracapsular spread. Results: Retropharyngeal lymph node involvement was detected in 175 (63.6%) patients. Metastatic RLNs were seen at the following levels: occipital bone, 24 (9.6%) nodes; C1, 157 (62.5%) nodes; C1/2, 40 (15.9%) nodes; C2, 27 (10.8%) nodes; C2/3, 1 (0.4%) node; and C3, 2 (0.8%) nodes. The incidence of RLN involvement was equal to the incidence of cervical lymph node involvement (81.4% vs. 81.4%) in 215 patients with nodal metastases. A significantly higher incidence of metastatic RLNs was observed in the presence of oropharynx, prestyloid parapharyngeal space, post-styloid parapharyngeal space, longus colli muscle, medial pterygoid muscle, levator muscle of velum palatini, tensor muscle of velum palatini, Level II node, Level III node, and Level V node involvement. A significantly lower incidence of metastatic RLNs was found in T1, N0, and Stage I disease. Conversely, no significant difference in the incidence of metastatic RLNs was observed between T1, 2, and, 3; N2 and N3; or Stage II, III, and IV disease. Conclusions: There is an orderly decrease in the incidence of metastatic lateral RLNs from the C1 to C3 level. Metastatic RLNs associate well with involvement of certain structures in early stage primary tumors and lymph node metastases of the upper jugular chain (Level II, Level III nodes) and the posterior triangle (Level V nodes). Both RLNs and cervical Level II nodes appear to be the first-echelon nodes in NPC.

Liu Lizhi [Imaging Diagnosis and Interventional Center, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China); Zhang Guoyi [Department of Radiation Oncology, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China); Xie Chuangmiao [Imaging Diagnosis and Interventional Center, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China); Liu Xuewen [Imaging Diagnosis and Interventional Center, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China); Cui Chunyan [Imaging Diagnosis and Interventional Center, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China); Li Li [Imaging Diagnosis and Interventional Center, State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou (China)]. E-mail: lililixj@hotmail.com

2006-11-01

208

3D Electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons typically have gyroradii larger than the magnetic anomaly scale size) and magnetic field strength. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SWIFF (project 2633430, swiff.eu). Cut along the dipole axis of the lunar anomaly, showing the electron density structure.

Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.

2013-12-01

209

Negative magnetic anomaly over Mt. Resnik, a subaerially erupted volcanic peak beneath the West Antarctic Ice Sheet  

USGS Publications Warehouse

Mt. Resnik is one of the previously reported 18 subaerially erupted volcanoes (in the West Antarctic rift system), which have high elevation and high bed relief beneath the WAIS in the Central West Antarctica (CWA) aerogeophysical survey. Mt. Resnik lies 300 m below the surface of the West Antarctic Ice Sheet (WAIS); it has 1.6 km topographic relief, and a conical form defined by radar ice-sounding of bed topography. It has an associated complex negative magnetic anomaly revealed by the CWA survey. We calculated and interpreted magnetic models fit to the Mt. Resnik anomaly as a volcanic source comprising both reversely and normally magnetized (in the present field direction) volcanic flows, 0.5-2.5-km thick, erupted subaerially during a time of magnetic field reversal. The Mt. Resnik 305-nT anomaly is part of an approximately 50- by 40-km positive anomaly complex extending about 30 km to the west of the Mt. Resnik peak, associated with an underlying source complex of about the same area, whose top is at the bed of the WAIS. The bed relief of this shallow source complex has a maximum of only about 400 m, whereas the modeled source is >3 km thick. From the spatial relationship we interpret that this source and Mt Resnik are approximately contemporaneous. Any subglacially (older?) erupted edifices comprising hyaloclastite or other volcanic debris, which formerly overlaid the source to the west, were removed by the moving WAIS into which they were injected as is the general case for the ???1000 volcanic centers at the base of the WAIS. The presence of the magnetic field reversal modeled for Mt. Resnik may represent the Bruhnes-Matayama reversal at 780 ka (or an earlier reversal). There are ???100 short-wavelength, steep-gradient, negative magnetic anomalies observed over the West Antarctic Ice Sheet (WAIS), or about 10% of the approximately 1000 short-wavelength, shallow-source, high-amplitude (50- >1000 nT) "volcanic" magnetic anomalies in the CWA survey. These negative anomalies indicate volcanic activity during a period of magnetic reversal and therefore must also be at least 780 ka. The spatial extent and volume of volcanism can now be reassessed for the 1.2 ?? 106 km2 region of the WAIS characterized by magnetic anomalies defining interpreted volcanic centers associated with the West Antarctic rift system. The CWA covers an area of 3.54 ?? 105 km2; forty-four percent of that area exhibits short-wavelength, high-amplitude anomalies indicative of volcanic centers and subvolcanic intrusions. This equates to an area of 0.51 ?? 105 km2 and a volume of 106 km3 beneath the ice-covered West Antarctic rift system, of sufficient extent to be classified as a large igneous province interpreted to be of Oligocene to recent age.

Behrendt, J.C.; Finn, C.; Morse, D.L.; Blankenship, D.D.

2006-01-01

210

Rock magnetic properties of the Arunta Block, Central Australia, and their implication for the interpretation of long-wavelength magnetic anomalies  

NASA Technical Reports Server (NTRS)

Rock magnetic and petrologic studies of a suite of deep crustal rocks from the Arunta Block of Central Australia reveal that the granulite grade rocks are in general much more magnetic than the amphibolite grade samples irrespective of bulk rock composition. The dominant magnetic mineral in all samples is relatively pure magnetite as determined from thermomagnetic and electron microprobe analysis. The bulk magnetic properties are typical of pseudosingle-domain to multidomain size material. The samples from our study have very large remanences compared to previous crustal magnetic studies, with the granulites having a median natural remanent magnetization of 4.1 A/m and Koenigsberger ratio of 7.2. These remanences are relatively resistant to the thermal demagnetization, with nearly 50 percent of the magnetization remaining after 400 C demagnetization. Thus remanence may contribute significantly to the observed magnetic anomalies, including long-wavelength magnetic anomalies, the source of which resides at depth and therefore at elevated temperature, where a thermoviscous remanant magnetization along the present-day field is likely to dominate.

Kelso, Paul R.; Banerjee, Subir K.; Teyssier, Christian

1993-01-01

211

Regional magnetic anomalies, crustal strength, and the location of the northern Cordilleran fold-and-thrust belt  

USGS Publications Warehouse

The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of malic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. ?? 2007 The Geological Society of America.

Saltus, R. W.; Hudson, T. L.

2007-01-01

212

Middle atmospheric electrodynamic modification by particle precipitation at the South Atlantic magnetic anomaly  

NASA Technical Reports Server (NTRS)

Evidence for a localized middle atmospheric electrodynamic modification at low latitudes (southern Brazilian coast) of the South Atlantic Magnetic Anomaly (SAMA), in association with enhanced geomagnetic activity, are presented in a unified way combining recent observational efforts and related numerical studies. They involve a distortion effect in the fair weather electric field at balloon altitudes. This effect is attributed to a local intensification of energetic electron precipitation through a related middle atmospheric ionization enhancement and is elucidated by numeric simulation. From the electric field measurements and the numeric simulation, the intensification of precipitation is considered to occur in fairly narrow regions at the observed low L values (around L = 1.13) of the SAMA, with horizontal extensions of the order of a few hundred kilometers. A physical mechanism that could be responsible for this sort of intensification is suggested. Furthermore, a comparison of the phenomenon of middle atmospheric electrodynamic modification at the SAMA with a similar one at auroral latitudes, in response to enhanced solar and geomagnetic activity, is also given.

Gonzalez, W. D.; Dutra, S. L. G.; Pinto, O., Jr.

1987-01-01

213

Calibration of Pre-M25 Marine Magnetic Anomalies: Magnetic Polarity Composite of ýLate Callovian Through Kimmeridgian  

NASA Astrophysics Data System (ADS)

Ammonite-zoned successions have yielded a composite magnetic polarity pattern ýspanning latest Callovian (lamberti ammonite Zone) through Late Kimmeridgian ýý(acanthicum Zone) that confirms marine magnetic anomalies M37 through to M24 ýinterpreted by deep-tow and other magnetic surveys in the western Pacific. This pattern ýwas constructed after thermal demagnetization of over 1000 samples from over 30 ýsections in Poland, British Isles, France and Spain. Polish sections include thick ýammonite-zoned limestone formations of the Krakow-Czestochowa-Wielun Upland and ýHoly-Cross Mountains. British limestone and clay formations were investigated in ýEngland (Dorset and Yorkshire) and in Scotland (the Isle of Skye). The sections include ýcandidates for the global stratotypes for the Callovian-Oxfordian and Oxfordian-ýKimmeridgian stage boundaries. All British and most of the Polish-French-Spanish ýsections are calibrated to ammonite biostratigraphy at the subzone level (Boreal-ýSubboreal realm and Sub-Mediterranean realm, respectively) and to regional sequence ýstratigraphy. The independent Boreal-Subboreal and Sub-Mediterranean composites of ýmagnetic polarity are consistent, and the main features of the modeled pre-M25 marine ýmagnetics can be calibrated. ý The Callovian-Oxfordian boundary (base of Quenstedtoceras mariae Zone) occurs in a ýnarrow normal-polarity subzone correlated to polarity subchron M36a of the western ýPacific magnetic polarity pattern. The beginning of the Middle and the Late Oxfordian ýsubstages as defined in the Sub-Mediterranean province in Poland correspond ýapproximately to M33 and M29 of the Pacific M-sequence. The placement of the ýOxfordian- Kimmeridgian boundary in the Sub-Boreal ammonite zonation (base of ýPictonia baylei Zone) is at the beginning of the M27r polarity zone. This is significantly ýolder than the traditional placement of the Oxfordian-Kimmeridgian boundary in the ýSub-Mediterranean zonation (base of Sutneria platynota Zone) near the base of the M25r ýpolarity zone.ý This project is a collaboration with A. Wierzbowski, M. Lewandowski, E. Glowniak, J. ýGutowski, P. Ziolkowski, M. Sidorczuk, and Z. Zlonkiewicz (Poland); A. Coe and J. ýWright, (England); and N. Nowaczyk (Germany)ý

Przybylski, P. A.; Ogg, J. G.

2007-12-01

214

Energetic neutral atom imaging of the moon: Observation of a mini-magnetosphere above a lunar magnetic anomaly  

NASA Astrophysics Data System (ADS)

The Sub-keV Atom Reecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 space-craft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. When solar wind hits the lunar surface, it is partly backscattered as energetic neutral atoms. The intensity of the backscattered energetic neutral atoms is a measure of the intensity of the solar wind reaching the surface. We report on the imaging of a lunar magnetic anomalies in backscattered neutral hydrogen atoms. At the example of the strong magnetic anomaly near the Crisium antipode on the lunar farside we show that a partial void of the solar wind, a mini-magnetosphere, is formed above the magnetic anomaly. The mini-magnetosphere is 360 km across at the surface and surrounded by a 300-km-thick region of enhanced plasma ux that results from the solar wind owing around the mini-magnetosphere. These observations demonstrate a new observational technique to study airless bodies, imaging in ackscattered neutral atoms, and its application to a new class of objects, mini-magnetospheres.

Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmström, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi

215

Coorelation between VHF scintillation and spread F  

NASA Astrophysics Data System (ADS)

The VHF scintillation observed over Bhopal, a station near the northern crest of the equatorial anomaly region, using the 244 MHz radio signal from FLEETSAT (730). The data use to study the occurrence characteristics of scintillation are recorded from March to April 2001 and then September to October 2001. The occurrences of scintillation are compared with the occurrence of spread-F over Delhi as observed by the modern digital ionosonde. The scintillation events are closely associated with the range type spread-F. In this paper the parameters of geomagnetic activity like Kp and Ap are used to study the association of the amplitude scintillation and spread-F. It is observed that an increase in magnetic activity suppressed the occurrence of scintillation and spread-F.

Smita, S.; Rashmi, R.; Gwal, G.

2003-04-01

216

Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California  

USGS Publications Warehouse

Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between magnetic susceptibilities and concentration of Cr and Ni. Although the study focused on characterizing the geophysical properties of ultramafic rocks and associated soils, it has also yielded information on other rock types in addition to ultramafic rocks, which can also locally host naturally-occurring asbestos; specifically, gabbro and metavolcanic rocks.

McCafferty, A.E.; Van Gosen, B. S.

2009-01-01

217

Analysis of the nature of excessive cosmic radiation in the area of the Brazilian magnetic anomaly at altitudes 250-500km, from Kosmos-225 satellite data  

NASA Technical Reports Server (NTRS)

Results are presented from a study of the region of anomalous cosmic radiation in the area of the Brazilian magnetic anomaly at the altitudes 250-500 km, using data measurements taken on the Kosmos-225 satellite (14-29 June 1968). The existence of a stable intensity anomaly discovered in the experiments on the second and third Soviet spacecraft-satellites is confirmed. The total vector of the geomagnetic field at different altitudes was compared with isoline maps. An altitude profile of the South Atlantic anomaly of radiation intensity was obtained, using data from the same instrument. The nature of the anomalies in cosmic radiation intensity over the regions of negative magnetic anomalies is discussed.

Raychenko, L. V.

1974-01-01

218

Mesozoic Magnetic Lineations in the Bering Sea Marginal Basin  

Microsoft Academic Search

A compilation of marine magnetic profiles from the Bering Sea marginal basin has revealed the existence of north-south trending magnetic lineations over the deep abyssal basins. The anomalies in the Aleutian and Bowers basins have maximum peak to peak amplitudes of 350 3' and wavelengths characteristic of sea floor spreading anomalies (25-100 km). These lineations are as much as 600

Alan K. Cooper; Michael S. Marlow; David W. Scholl

1976-01-01

219

A closer look at remanence-dominated aeromagnetic anomalies: Rock magnetic properties and magnetic mineralogy of the Russell Belt microcline-sillimanite gneiss, northwest Adirondack Mountains, New York  

Microsoft Academic Search

A large, distinct negative aeromagnetic anomaly of over 2000 nT associated with microcline-sillimanite-quartz gneisses in the Russell area, northwest Adirondack Mountains, was previously shown to be remanence-dominated, although the carriers of remanence were not well documented. Russell Belt gneisses have a strong natural remanent magnetization with steep remanence directions, D=263°, I=-58°, an average intensity of 3.6 A\\/m, and typical susceptibilities

Suzanne A. McEnroe; Laurie L. Brown

2000-01-01

220

Pacific-North American plate motion from very long baseline interferometry compared with motion inferred from magnetic anomalies, transform faults, and earthquake slip vectors  

NASA Technical Reports Server (NTRS)

Geodetic VLBI measurements were used to test whether the Pacific-North American plate velocity averaged over several years of direct observation (1984-1987) equals that averaged over millions of years. It was also tested whether this velocity parallels the San Andreas fault, transform faults and earthquake slip vectors in the Gulf of California, and earthquake slip vectors along the Queen Charlotte fault, along the Alaskan peninsula, and along the Kamchatkan peninsula. The VLBI data provide an estimate of the direction of plate motion that is independent of estimates from fault azimuths and earthquake slip vectors. The Euler vector determined from VLBI was found to be nearly identical to the Euler vector of plate motion model NUVEL-1, which is based on the trends of transform faults, earthquake slip vectors, and spreading rates from marine magnetic anomalies that average motion since 3 Ma. The velocity between the Pacific and North American plates averaged over the past several years equals or nearly equals its velocity averaged over the past several million years, the difference along their boundary nowhere exceeding 4 + or - 7 mm/yr.

Argus, Donald F.; Gordon, Richard G.

1990-01-01

221

Solar and magnetic control on night-time enhancement in TEC near the crest of the Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

The ionospheric Total Electron Content (TECs), derived by dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Bhopal (23.2°N, 77.4°E, Geomagnetic 14.2°N) were analyzed for the period of January, 2005 to February, 2008. The work deals with monthly, diurnal, solar and magnetic activity variations on night-time enhancement in TEC. From a total of 157 night-time enhancements, 75 occur during pre-midnight and 82 post-midnight hours. The occurrence of night-time enhancement in TEC is utmost during summer months, followed by equinox and winter months. The occurrence of night-time enhancement in TEC decreases with increase in solar and magnetic activities. We observed that peak size and half amplitude duration are positively correlated, while time of occurrence of night-time enhancement in TEC and time of peak enhancement are negatively correlated with solar activity. The peak size, half amplitude duration, time of peak enhancement and time of occurrence of night-time enhancement in TEC shows negative correlation with magnetic activity. The results have been compared with the earlier ones and discussed in terms of possible source mechanism responsible for the enhancement at anomaly crest region.

Trivedi, Richa; Jain, Sudhir; Jain, Amit; Gwal, A. K.

2013-01-01

222

Congenital anomalies and variations of the bile and pancreatic ducts: magnetic resonance cholangiopancreatography findings, epidemiology and clinical significance  

Microsoft Academic Search

Purpose  The objective of this paper is to document the magnetic resonance cholangiopancreatography (MRCP) findings and the epidemiology\\u000a of congenital anomalies and variations of the bile and pancreatic ducts and to discuss their clinical significance.\\u000a \\u000a \\u000a \\u000a Materials and methods  Three-hundred and fifty patients of both sexes (150 females, 200 males, age range 0–76 years, average age 38 years) underwent\\u000a MRCP for clinically suspected

M. De Filippo; M. Calabrese; S. Quinto; A. Rastelli; A. Bertellini; R. Martora; N. Sverzellati; D. Corradi; M. Vitale; G. Crialesi; L. Sarli; L. Roncoroni; G. Garlaschi; M. Zompatori

2008-01-01

223

Paleomagnetic Pole Locations of Lunar Swirl Albedo Magnetic Anomalies: A possible Pre- existence of Ancient Lunar dynamo  

NASA Astrophysics Data System (ADS)

The nature and the origin of the magnetic fields responsible of lunar remanent magnetization are highly debated. There are two possible magnetization processes; either the crustal field was generated by an ancient lunar dynamo or it was generated by external transient fields impact. Here, we investigate the hypothesis that the lunar magnetic field was generated by a paleo lunar dynamo process. Magnetometer data obtained by Lunar Prospector showed high swirl albedo over certain regions were inverted to determine paleomagnetic pole locations. These selected formations seem to have an Imbrian age. The mostly lie antipodal to large impact basins such as Descartes Formation, Mare Marginis, Mare Ingenii and Gerasimovich. The Reiner Gamma and Airy crater have not previously associated with antipodal impact basins. The modeling of these anomalies shows a clustered paleomagnetic pole positions within a radius of 35 degrees centered at (30S, 225E). This result supports the hypothesis of a now extincted paleo lunar dynamo that may have probably magnetized rocks of lunar crust. The scattered positions of the other obtained paleomagnetic pole locations suggest that the lunar remanent magnetization were since modified by subsequent impact events.

Sherif, B. M.; Mohamed, H.; Yves, C.

2007-12-01

224

Characterization and removal of errors due to local magnetic anomalies in directional drilling Nathan Hancock*  

E-print Network

of the Earth's magnetic field are unavoidable when local magnetic sources are present. Several scenarios can to the direction of the local geomagnetic field is determined from the magnetic measurements. Assuming a known's magnetic field is measured. A measurement error of 50 nT in field strength is considered to be the upper

225

Rock magnetic characteristics of faulted sediments with magnetic anomalies: A case study from the Albuquerque Basin, Rio Grande Rift, New Mexico (Invited)  

NASA Astrophysics Data System (ADS)

High-resolution airborne surveys in the Rio Grande rift have documented abundant short-wavelength, low-amplitude magnetic anomalies generated at faults within basin sediments. We present a rock magnetic study bearing on the source of a10-20-nT linear anomaly over the San Ysidro normal fault, which is well exposed in outcrop in the northern part of the Albuquerque Basin. Magnetic susceptibility (MS) values (SI vol) from 310 sites distributed through a 1200-m-thick composite section of rift-filling sediments of Santa Fe Group and pre-rift sedimentary rocks juxtaposed by the San Ysidro fault have lognormal distributions with well-defined means. These averages generally increase up section through eight map units: from 1.7E-4 to 2.2E-4 in the pre-rift Cretaceous and Eocene rocks, from 9.9E-4 to 1.2E-3 in three units of the Miocene Zia and Cerro Conejo Formations of the Santa Fe Group, and from 1.5E-3 to 3.5E-3 in three units of the Miocene-Pliocene Arroyo Ojito and Ceja Formations of the Santa Fe Group. Remanent magnetization is not important; Koenigsberger ratios are less than 0.3 for Santa Fe Group samples. Rock magnetic parameters (e.g., ARM/MS and S ratios) and petrography indicate that detrital magnetite content and its variable oxidation to maghemite and hematite are the predominant controls of magnetic property variations within the Santa Fe Group sediments. Magnetite is present in rounded detrital grains (including both homogeneous and subdivided types) and as fine inclusions in volcanic rock fragments. Santa Fe Group sediments with highest magnetic susceptibility have greatest magnetic-grain size as indicated by lowest ARM/MS ratios. Magnetic susceptibility increases progressively with sediment grain size to pebbly sand within the fluvial Arroyo Ojito Formation. In contrast, MS reaches highest values in fine to medium sands in eolian Zia Formation. Partial oxidation of detrital magnetite and resultant lower MS is spatially associated with calcite cementation in the Santa Fe Group; both oxidation and cementation probably reflect past flow of ground water through permeable horizons. Magnetic models of geologic cross sections that incorporate mean MS for the different stratigraphic units successfully mimic the aeromagnetic profiles across the San Ysidro fault. These models demonstrate multiple levels of magnetic contrasts due to fault juxtaposition of stratigraphic units, with contributions to the magnetic anomaly that vary along strike due to uneven erosion and dip of strata. Sediment provenance, depositional facies, and post-depositional preservation and alteration of magnetic minerals are all factors that contribute to producing aeromagnetic anomalies in faulted basin sediments.

Hudson, M. R.; Grauch, V. J.

2009-12-01

226

Phase equilibria at alkali-rich early proterozoic banded iron formation, Kursk magnetic anomaly, Russia  

NASA Astrophysics Data System (ADS)

Banded iron formation (BIF) rocks of Kursk Magnetic anomaly (KMA) are distinguished from well known Precambrian BIF by the alkali enrichment and aluminum depletion and as a total absence of the aluminum bearing minerals. From layered silicates the maximum saturated potassium phases seladonite and tetraferribiotite are of widespread occurrence instead stilpnomelane, minnesotaite and greenalite commonplace for low grade BIF. It has been widely distribution of the seladonite with the assemblage of tetraferribiotite, magnetite, hematite, and quartz distinguish ferruginous quartzites Mikhailovsk iron deposit (KMA) from well known Precambrian BIF of the ancient shields. From Fe-Mg silicates the aegirine, ribeckite and aluminum-less chlorite are present. The hematite and magnetite stability in the ferruginous quartzites assemblages suggest the high values of the oxygen fugacity near magnetite-hematite buffer. This is confirmed by somewhat increasing XMg values for seladonite, tetraferribiotite, chlorite, and ribeckite. The minerals producing with large amounts of ferric iron (seladonite, tetraferribiotite) in the ferruginous quartzites of Mikhailovsk iron deposit is caused by the oxygen fugacity high values. For example the ferrichamosite (Fe_5Fe3+(Fe3+Si_3)O10(OH)_8) is produced in place of the commonplace for the low-grade BIF greenalite (Fe_6Si_4O10(OH)_8). As a whole chlorites are a rarity in BIFs (Laird, 1989) through low rocks aluminum content and represent by chamosite (Gole, 1981), clinochlore and ripidolite (Miyano, Beukes, 1997). Chlorite in studied ferruginous quartzites has a uncommon aluminumless composition with high Fe3+ content and corresponds hypothetical end-member of chamosite - "ferrichamosite" and "ferriclinochlore" - "ferrichamosite" series (Burt, 1989). Uncommon aluminumless chlorite composition assumes that it appears during low-grade metamorphism and possible catagenesis: Mag + Hem + Qtz rightarrow H_2O rightarrow Fe-Chm + O_2 Sid + Qtz + Mag + Hem + H_2O rightarrow Fe-Chm + CO_2 + O_2. The seladonite producing is caused by relationship of the enriched K^+ metamorphic fluid with the BIF rocks: Sid + Qtz + Mag + Hem + H_2O + ^+ rightarrow Sld + CO_2 + O_2. It seems likely that tetraferribiotite produced similar to ferroseladonite: Mag + Sid + Qtz + H_2O + ^+ rightarrow Fe-Ann + CO_2 + O_2. The chlorite and potassium micas producing through siderite decomposition is more realistic because they content detectable magnesium. The sequence of mineral assemblages change is observed for alkali-rich iron quartzites with increasing temperature and/or oxygen fugacity. Reaction structures suggest ferriannite producing as a result following reactions: (1) through partially ferriannite decomposition by fO_2 increasing: Sld + O_2 rightarrow Fe-Ann + Qtz + Mag, Fe-Chm + Sld + O_2 rightarrow Fe-Ann + Qtz + Mag + H_2O and (2) with increasing temperature and siderite with ferroseladonite decomposition in carbonate bearing iron quartzites: Sld + Sd + Qtz rightarrow Fe-Ann + CO_2. The ribeckite occurrences are caused by relationship of the enriched Na^+ metamorphic fluid with the BIF rocks and are controlled by the variables: fO_2, aNa+ T ^oC (Miyano, Klein, 1983). If together with ribeckite siderite and ankerite are present, the ribeckite stability field is enlarged with the CO_2 activity decreasing. The ribeckite stability is not clear indicator of the metamorphic temperatures without considering other factors. The ribeckite (more exactly, fibrous variety - crocidolite) may crystallize through Fe-oxides, carbonates, and quartz decomposition during the low-grade metamorphism or diagenesis from 130 ^oC by the relationships Fe-rocks with Na^+ bearing solutions. The relatively large crystals alternating phyllosilicates appear through more high-grade metamorphism: Chl + Sld (Fe-Ann) + Na^+ rightarrow Rbk + Qtz + K^+ + H_2O. As a result reaction Rbk + Hem = Aeg + Mag + Qtz + H_2O high-grade ribeckite decomposition with the aegirine producing is occurred at 510-520^oC (Miyano, Beukes, 1997). However

Sayko, K. A.; Gerasimov, V. Yu.; Poskryakova, M. V.

2003-04-01

227

Multiprobe in-situ measurement of magnetic field in a minefield via a distributed network of miniaturized low-power integrated sensor systems for detection of magnetic field anomalies  

Microsoft Academic Search

Based on technologies developed for the Jet Propulsion Laboratory (JPL) Free-Flying-Magnetometer (FFM) concept, we propose to modify the present design of FFMs for detection of mines and arsenals with large magnetic signature. The result will be an integrated miniature sensor system capable of identifying local magnetic field anomaly caused by a magnetic dipole moment. Proposed integrated sensor system is in

Hamid H. Javadi; David Bendrihem; B. Blaes; Kobe Boykins; John Cardone; C. Cruzan; J. Gibbs; W. Goodman; U. Lieneweg; H. Michalik; P. Narvaez; D. Perrone; Joel D. Rademacher; R. Snare; Howard Spencer; Miles Sue; J. Weese

1998-01-01

228

Low-energy electron fluxes in the region of the Brazil magnetic anomaly on the basis of data from the 25th and 28th Meteor satellites  

Microsoft Academic Search

Experimental data on the distribution of low-energy electrons in the inner radiation belt near the Brazil magnetic anomaly are presented, as are data on electron energy fluxes (0.1-20 keV). It is noted that the points of reflection of the fluxes upon drift from west to east through the region of the anomaly fall to an altitude of approximately 100 km.

V. A. Diachenko; V. A. Lipovetskii; B. V. Marin; V. M. Feigin

1980-01-01

229

An annular high-current electron beam with an energy spread in a coaxial magnetically insulated diode  

SciTech Connect

An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.

Grishkov, A. A., E-mail: grishkov@to.hcei.tsc.ru; Pegel, I. V. [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)] [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)

2013-11-15

230

Detailed bathymetry and magnetic anomaly in the Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after approximately 2.1 Ma  

NASA Astrophysics Data System (ADS)

Detailed bathymetry and magnetic anomalies in the southern part of the Central Ryukyu Arc reveal recent volcanic structures in a southwestward extension of the active volcanic front of the Ryukyu Arc. A line of bathymetric highs running subparallel to this recent volcanic front was observed approximately 20 km to the east. A set of small, sharply defined magnetic anomalies extends southward from this line of bathymetric highs to the islands Kume-jima and Aguni-jima, suggesting the former existence of an ancient volcanic front. The ages of volcanic rocks from these islands indicate that magmatic activity along the ancient volcanic front continued until at least approximately 2.1 Ma. The presence of magnetic anomalies between the two volcanic fronts suggests that the volcanic front has moved gradually westward. This shift can be explained by the termination of asthenospheric upwelling and/or the rapid retreat of the Ryukyu Trench after its change in subduction direction.

Sato, Taichi; Oda, Hirokuni; Ishizuka, Osamu; Arai, Kohsaku

2014-12-01

231

Investigations of medium wavelength magnetic anomalies in the Eastern Pacific using MAGSAT data  

NASA Technical Reports Server (NTRS)

A paper which discusses a problem in representing the core magnetic field of the Earth using spherical harmonics was revised and accepted for publications. Page proofs of a second paper concerning off center dipole modelling of the Earth's magnetic field are presented.

Harrison, C. G. A. (principal investigator)

1982-01-01

232

The detection of intermediate size magnetic anomalies in Cosmos-49 and OGO-2, 4, and 6 data  

NASA Technical Reports Server (NTRS)

Benkova, Dolginov, and Simonenko have recently reported the presence of intermediate size magnetic anomalies in the data from COSMOS-49 and hypothesized a crustal and/or upper mantle origin. The spherical harmonic models of the internal potential function were examined, based on the OGO-2, 4, and 6 data (POGO (10/68) and later models), and verified the locations and amplitudes of those anomalies whose wavelengths approximate 4000 km. The comparison was made by subtracting a field model developed with a truncated series of n* = 9 from one computed with n* = 11 and generating a residual map equivalent to the COSMOS-49 data. The patterns of delta F so computed from POGO were then compared with the IZMIRAN maps and also were analyzed statistically, in both the spatial and frequency domains, using residuals computed from the raw COSMOS-49 data with the n* = 9 COSMOS-49 field model as reference. The two sets of data were thus derived from completely independent sets of observations and field references. The two patterns are shown to agree very well over the whole earth surface up to the 50 deg latitude limit of COSMOS-49.

Regan, R. D.; Davis, W. M.; Cain, J. C.

1973-01-01

233

A closer look at remanence-dominated aeromagnetic anomalies: Rock magnetic properties and magnetic mineralogy of the Russell Belt microcline-sillimanite gneiss, northwest Adirondack Mountains, New York  

NASA Astrophysics Data System (ADS)

A large, distinct negative aeromagnetic anomaly of over 2000 nT associated with microcline-sillimanite-quartz gneisses in the Russell area, northwest Adirondack Mountains, was previously shown to be remanence-dominated, although the carriers of remanence were not well documented. Russell Belt gneisses have a strong natural remanent magnetization with steep remanence directions, D=263°, I=-58°, an average intensity of 3.6 A/m, and typical susceptibilities of 10-4SI. The remanence is thermochemical in origin, acquired during cooling from peak metamorphic conditions of 650°-750°C during the Ottawan Orogen (1050-1080 Ma). The reversed polarity of remanence reflects a reversed paleofield, rather than self-reversed, contrary to earlier suggestions. The gneisses contain up to 3% oxide, predominantly metamorphic titanohematite, which accounts for the low susceptibility values and highly stable remanence. Optical observations show titanohematite grains with multiple generations of ilmenite, pyrophanite, rutile, and spinel exsolution lamellae. Microprobe analyses confirm titanohematite compositions ranging from 72 to 97%Fe2O3, with hematite83 being most typical. In rare samples, inclusions of magnetite were identified. The ubiquitous presence of titanohematite, and the rare occurrence of magnetite, is supported by thermal and alternating field demagnetization studies, saturation magnetization measurements, hysteresis properties, temperature-hysteresis studies, and low-temperature remanence measurements. Numerous crustal granulites have titanohematite as part of the oxide assemblage, and this may contribute a strong remanent component to what have previously been considered to be solely induced anomalies.

McEnroe, Suzanne A.; Brown, Laurie L.

2000-07-01

234

GMinterp, A Matlab Based Toolkit for Gravity and Magnetic Data Analysis: Example Application to the Airborne Magnetic Anomalies of Biga Peninsula, NW Turkey  

NASA Astrophysics Data System (ADS)

The analysis of gravity and magnetic field methods is becoming increasingly significant for the earth sciences as a whole and these potential field methods efficiently assist in working out both shallow and deep geologic problems and play important role on modeling and interpretation procedures. The main advantage of some gravity and magnetic data processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. If the data quality permits, many analyzing techniques can be carried out that help to build a general understanding of the details and parameters of the shallower or deeper causative body distributions such as depth, thickness, lateral and vertical extensions. Gravity and magnetic field data are usually analyzed by means of analytic signal (via directional derivatives) methods, linear transformations, regional and residual anomaly separation techniques, spectral methods, filtering and forward and inverse modeling techniques. Some commercial software packages are commonly used for analyzing potential field data by employing some of the techniques specified above. Additionally, many freeware and open-source codes can be found in the literature, but unfortunately they are focused on special issues of the potential fields. In this study, a toolkit, that performs numerous interpretation and modeling techniques for potential field data, is presented. The toolkit, named GMinterp, is MATLAB-based consisting of a series of linked functions along with a graphical user interface (GUI). GMinterp allows performing complex processing such as transformations and filtering, editing, gridding, mapping, digitizing, extracting cross-sections, forward and inverse modeling and interpretation tasks. The toolkit enables to work with both profile and gridded data as an input file. Tests on the theoretically produced data showed the reliability of developed toolkit. Additionally some experiments on real data sets were performed to interpret the geological structure of Biga Peninsula, NW part of Anatolia, Turkey. Keywords: GMinterp, GUI, airborne magnetic data, geology, Biga Peninsula

Ekinci, Y. L.; Yi?itba?, E.

2012-04-01

235

True polar wander since 32 Ma B.P.: A paleomagnetic investigation of the skewness of magnetic anomaly 12r on the Pacific plate  

NASA Astrophysics Data System (ADS)

We test the fixed hot spot and fixed spin axis hypotheses through a paleomagnetic investigation of the skewness of crossings of magnetic anomaly 12r (32 Ma B.P.) between the Galapagos and Clarion fracture zones on the Pacific plate. We focus on this region for three reasons. First, numerical experiments show that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma B.P. paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal-to-noise ratios. Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm a-1) above which anomalous skewness is negligible. The new pole (83.5°N, 44.6°E) has compact 95% confidence limits (ellipse with major semiaxis length of 3.1° toward 84° clockwise from north and minor semiaxis length of 1.2°) and is not subject to the biases inherent in other methods for estimating Pacific plate paleomagnetic poles. The pole differs significantly by ?5° from the pole predicted if the Pacific hot spots have been fixed with respect to the spin axis, thus demonstrating, for the first time from paleomagnetic data, that Pacific hot spots have moved relative to the spin axis since the formation of the elbow in the Hawaiian-Emperor chain. The pole is consistent, however, with previously published paleomagnetic poles in a reference frame fixed relative to Indo-Atlantic hot spots. Thus, the new results require no motion between Pacific and Indo-Atlantic hot spots since 32 Ma B.P. Instead, superimposed on whatever motion occurs between hot spots, as expected for true polar wander.

Horner-Johnson, Benjamin C.; Gordon, Richard G.

2010-09-01

236

Anomalies in electron spin resonance spectra of Ge1?xMnxTe diluted magnetic semiconductors  

Microsoft Academic Search

We report on magnetic properties and X-band electron spin resonance (ESR) study (80–430 K) of diluted magnetic semiconductors Ge1?xMnxTe(x=0.07–0.44) revealing ferromagnetism with the Curie temperature achieving 90 K. Effective magnetic moment peff per Mn2+ ion estimated from the Curie constant in the range 0.15?x?0.26 increases from 2.27 to 2.95 ?B. The temperature evolution of ESR spectra was found to have

E. A. Zvereva; O. A. Savelieva; A. E. Primenko; S. A. Ibragimov; E. I. Slyn’ko; V. E. Slyn’ko

2010-01-01

237

Anomalies in electron spin resonance spectra of Ge1-xMnxTe diluted magnetic semiconductors  

Microsoft Academic Search

We report on magnetic properties and X-band electron spin resonance (ESR) study (80-430 K) of diluted magnetic semiconductors Ge1-xMnxTe (x=0.07-0.44) revealing ferromagnetism with the Curie temperature achieving 90 K. Effective magnetic moment peff per Mn2+ ion estimated from the Curie constant in the range 0.15<=x<=0.26 increases from 2.27 to 2.95 muB. The temperature evolution of ESR spectra was found to

E. A. Zvereva; O. A. Savelieva; A. E. Primenko; S. A. Ibragimov; E. I. Slyn'ko; V. E. Slyn'ko

2010-01-01

238

The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies  

NASA Astrophysics Data System (ADS)

The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.

2014-06-01

239

Surface plasmon assisted magnetic anomalies on room temperature gold films in high-intensity laser fields  

E-print Network

Supplementing our STM and electron emission studies, concluding in electron pairing in strong laser fields, further time-of-flight electron emission studies were carried out, changing the angle of polarization of incident light, exciting surface plasmon oscillations. It has been found, that those parts of the electron spectrum which have been attributed to electron pairing have a significantly different angular dependence around 80GW/cm2 where the pairing effect has been found than outside this region (e.g. 120 GW/cm2). These results have been interpreted as the stepping in of ideal or partly ideal diamagnetism on the one hand and as anomaly in the magneto-optical effect (rotation) on the other in the same laser intensity region where the pairing effect has been found.

Kroó, N; Varró, S

2014-01-01

240

Vaginal Anomalies: Cloacal Anomalies  

MedlinePLUS

... feces following the procedure? Your child's ability to control either the flow of her urine or elimination of her stool depends on the severity of the anomaly. In milder cases, more than 90 percent of patients have good sphincter control and a nearly normal pattern eliminating stools. Between ...

241

Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration  

NASA Technical Reports Server (NTRS)

The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (principal investigators)

1981-01-01

242

The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada-Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton  

USGS Publications Warehouse

We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300??m, 3.5??km and 400??km. The MRA is the largest amplitude (13??nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12??km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5??km) aeromagnetic data produces an average magnetization of 2.5??A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt. Crown Copyright ?? 2008.

Pilkington, M.; Saltus, R.W.

2009-01-01

243

Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.  

USGS Publications Warehouse

An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross?section and finite strike?length. The equation can be separated into the two?dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term “two?and?a?half dimensional” (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.

Cady, J.W.

1980-01-01

244

The point spread function of electrons in a magnetic field, and the decay of the free neutron  

NASA Astrophysics Data System (ADS)

Experiments in nuclear and particle physics often use magnetic fields to guide charged reaction products to a detector. Due to their gyration in the guide field, the particles hit the detector within an area that can be considerably larger than the diameter of the source where the particles are produced. This blurring of the image of the particle source on the detector surface is described by a suitable point spread function (PSF), which is defined as the image of a point source. We derive simple analytical expressions for such “magnetic” PSFs, valid for any angular distribution of the emitted particles that can be developed in Legendre polynomials. We investigate this rather general problem in the context of neutron ?-decay spectrometers and study the effect of limited detector size on measured neutron decay correlation parameters. To our surprise, insufficient detector size does not affect the accuracy of such measurements much, even for rather large radii of gyration. This finding can considerably simplify the layout of the respective spectrometers.

Dubbers, D.; Raffelt, L.; Märkisch, B.; Friedl, F.; Abele, H.

2014-11-01

245

Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time  

NASA Astrophysics Data System (ADS)

The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.

Rastogi, R. G.; Chandra, H.; Janardhan, P.; Hoang, Thai Lan; Condori, Louis; Pant, T. K.; Prasad, D. S. V. V. D.; Reinisch, B.

2014-08-01

246

Magnetic field anomalies from seismo-ionospheric effects of 2011 Tohoku earthquake  

NASA Astrophysics Data System (ADS)

Anomalous magnetic variations were observed by ground magnetometers in East Asia area after the 2011 Tohoku earthquake. Some earlier reports showed the seismo-magnetic variations have obvious amplitude around the epicenter, we emphasis here that the variations can still be notable at stations 2000 to 4000 km away from epicenter and we define it as teleseismic magnetic disturbances (TMDs). TMDs appear about 8 min later after the arrival of seismic Rayleigh waves at teleseismic distances, and propagate at a horizontal velocity of 3.9 km/s. The wave-like TMDs last for no longer than 10 minutes, and have a main period of 2.1-3.3 min. TMDs are not generated by direct effects of processes in focal area crust or tsunami waves, instead, their properties consist with the Rayleigh wave model of seismo-ionospheric disturbances. Hence we conclude that the TMDs are the magnetic manifestation of seismotraveling ionospheric disturbances (STIDs), generated by the interaction between the ionosphere and atmosphere through acoustic waves launched by travelling Rayleigh waves. This work was jointly supported by NSFC (40904036, 41274155), China NIBRP (2011CB811405) and Project Supported by the Specialized Research Fund for State Key Laboratories.

Hao, Yongqiang; Xiao, Zuo; Zhang, Donghe

2013-04-01

247

Rotor cage anomalies and unbalanced magnetic pull in single-phase induction motors  

Microsoft Academic Search

This paper consists of an experimental and theoretical investigation of the effect that rotor cage defects have on the unbalanced magnetic pull (UMP) present in a single-phase motor. The paper presents a detailed development of a mathematical model which can be used to examine both porosity and soldering defects in cage rotors. In the experimental investigation, the UMP developed by

Stephen Williamson; Russell C. Healey; Jerry D. Lloyd; Joseph L. Tevaarwerk

1997-01-01

248

Particle-In-Cell Simulations of the Solar Wind Interaction with Lunar Crustal Magnetic Anomalies: Magnetic Cusp Regions  

NASA Technical Reports Server (NTRS)

As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 1 1/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.

Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.

2012-01-01

249

VHF ionospheric scintillations near the equatorial anomaly crest: solar and magnetic activity effects  

NASA Astrophysics Data System (ADS)

20 dB) mainly occur in the pre-midnight period, and in the post-midnight period, the scintillations are generally moderate (5-10 dB) or weak (<5 dB). The nocturnal scintillation occurrence decreases with the decrease in solar activity from 1989 to 1992. Monthly mean scintillation occurrence changes according to solar activity during E- and D-months but not so during J-months. The effects of magnetic activity on scintillations vary with season and, in general, inhibit the scintillation occurrence in the pre-midnight period and enhance it a little in the post-midnight period, especially after 0300 hours IST (Indian Standard Time). For most of the severe magnetic storms in which Dst goes below -125 nT and the recovery phase starts in the post-midnight to dawn local time sector, strong post-midnight scintillations, which sometimes extend for several hours beyond the local sunrise, are observed.

Kumar, S.; Gwal, A. K.

2000-02-01

250

Positive holes in magnesium oxide - Correlation between magnetic, electric, and dielectric anomalies  

NASA Technical Reports Server (NTRS)

The present magnetic susceptibility investigation of high purity MgO single crystals notes an anomally at 800 K which is associated with increasing electrical conductivity, a rise in static dielectric constant from 9 to 150, and the appearance of a pronounced positive surface charge. These phenomena can be accounted for in terms of peroxy defects which represent self-trapped, spin-paired positive holes at Mg(2+) vacancy sites. The holes begin to decouple their spins above 600 K.

Batllo, F.; Leroy, R. C.; Parvin, K.; Freund, F.; Freund, M. M.

1991-01-01

251

Magnetic field dependent zero-bias diffusive anomaly in Pb-oxide- n-InAs structures: Coexistence of 2D and 3D states  

NASA Astrophysics Data System (ADS)

The results of experimental and theoretical studies of zero-bias anomaly (ZBA) in the Pb-oxide- n-InAs tunnel structures in magnetic field up to 6 T are presented. A specific feature of the structures is a coexistence of the 2D and 3D states at the Fermi energy near the semiconductor surface. Experimentally observed magnetic field dependence of the amplitude of ZBA for different orientations of the magnetic field is in agreement with the proposed theoretical model. According to this model, electrons tunnel into 2D states, and move diffusively in 2D layer, whereas the main contribution to the screening comes from 3D electrons.

Minkov, G. M.; Germanenko, A. V.; Negachev, S. A.; Rut, O. E.; Sukhorukov, Eugene V.

1998-12-01

252

Curie isotherm surfaces inferred from high-altitude magnetic anomaly data  

NASA Technical Reports Server (NTRS)

Two-dimensional Curie depth models along two sections across the western United States are derived using an equivalent layer magnetization model derived from Magsat data, and the results are used to constrain finite element thermal models developed by Mayhew and Majer (1980). Regional heat flow variations predicted by the models compare favorably with those inferred from direct measurements. The methodology is applied to upward-continued aeromagnetic data, and the results are found to be in good agreement with previous Curie depth estimates and average measured heat flow.

Mayhew, M. A.

1985-01-01

253

Concentration anomalies of the magnetization of HgSe:Fe crystals  

NASA Astrophysics Data System (ADS)

The field and temperature dependences of the magnetization of the semimagnetic semiconductor HgSe:Fe have been studied experimentally. The spin splitting of the Landau levels in the de Haas-van Alphen quantum oscillations has been recorded in the iron impurity concentration interval of 7 × 1018 cm-3 < N Fe < 2 × 1019 cm-3. The effective area of the extreme cross section of the Fermi surface has been determined from the obtained dependences of the oscillation period on the iron concentration, and the concentration of the collectivized electrons under conditions of the stabilization of the Fermi level on the iron donor level has been estimated. The critical impurity concentration at which the sharp increase in the Curie-Weiss temperature occurs owing to the spontaneous spin polarization of the system of hybridized electron states in iron-doped mercury selenide has been determined.

Popenko, N.; Bekirov, B.; Ivanchenko, I.; Bludov, A.; Pashchenko, V.

2014-10-01

254

Opening of the Amerasian Basin: A model based on sea-floor morphology, magnetic anomalies and paleomagnetic data  

NASA Astrophysics Data System (ADS)

There are numerous models for the origins of the Amerasia Basin. The model we present here is based on sea-floor morphology, magnetic anomaly signatures and evidence derived from dredge hauls which indicate that the Arctic Alaska block traveled to its present location from a location close to the Canadian and Lomonosov margins. This location is further east than is called for by the conventional “windshield wiper” model. The paleomagnetic database that relates directly to the origins of the Arctic Ocean consists of a study of Cretaceous sediments (135Ma) from the northern coastal region of Alaska (Kuparuk oil field drill core) and younger sediments (100Ma) from the west end of the Arctic coastal plain (Utukok River area) plus volcanic rocks from the Okhotsk-Chukotka volcanic belt (67-90Ma). The pole positions derived from the sedimentary sequences from Alaska require a model involving both rotation and translation. We have also incorporated paleomagnetic paleolatitudes derived from borehole cores (no declination control), and inferred paleolatitudes based on the pervasive magnetic overprint found throughout Arctic Alaska. These data sets are also consistent with the translation plus rotation model presented. In most models the location of Chukotka is depicted as being more or less fixed with respect to Arctic Alaska, but the paleomagnetic poles determined for the Okhotsk-Chukotka volcanic suites are hard to reconcile with the paleogeography proposed here if Chukotka remains firmly attached to Arctic Alaska. The Chukotka data require that the volcanic belt was erupted at more northerly latitudes than its present location, thus it appears to have moved somewhat independently from Alaska. Looking to the future it would seem that the Okhotsk-Chukotka volcanic belt should be a prime target for paleomagnetic work. It is relatively accessible, and in contrast to the bulk of the sedimentary sections sampled in Northern Alaska, these rocks have proven to be good paleomagnetic recorders.

Stone, D. B.; Brumley, K.

2010-12-01

255

Evaluation of seismo-electric anomalies using magnetic data in Taiwan  

NASA Astrophysics Data System (ADS)

The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ? 5.5) in Taiwan during a period of 2002-2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event.

Chen, C. H.; Hsu, H. L.; Wen, S.; Yeh, T. K.; Chang, F. Y.; Wang, C. H.; Liu, J. Y.; Sun, Y. Y.; Hattori, K.; Yen, H. Y.; Han, P.

2013-03-01

256

Hyperfine anomalies of 95Tc-96Tc and 106Agm- 110Agm using brute-force nuclear magnetic resonance on oriented nuclei  

NASA Astrophysics Data System (ADS)

Brute-force nuclear magnetic resonance on oriented nuclei (BF-NMRON) experiments have been performed with 12 T maximum field and at 10 mK. The resonances for 95,96TcNb, 106AgmAg, and 110AgmAg have been observed. The magnetic moment of 106Agm was determined to be 3.705(4) ?N. Comparing the resonance frequencies of BF-NMRON and those of the known NMR-ON results in Fe, the hyperfine anomalies in Fe were determined: 95?96(Tc)=-0.026(17)%, 106m?110m(Ag)=0.10(6)%. The measured hyperfine anomalies are interpreted in terms of a microscopic theory including core polarization and exchange current effects.

Ohya, S.; Sato, H.; Izumikawa, T.; Goto, J.; Muto, S.; Nishimura, K.

2001-04-01

257

Basement and crustal structure from magnetic and gravity anomalies in the Songpan-Garzê and adjacent areas, China  

NASA Astrophysics Data System (ADS)

The Songpan-Garzê orogenic belt is located in the eastern part of the Tibetan Plateau and west of the Sichuan basin. It is bounded by the South China, North China, Kunlun-Qaidam and Qiangtang (North Tibet) continental blocks. To the east, the Longmen Shan thrust-nappe belt separates the Songpan-Garzê fold belt from the Sichuan basin. The Songpan-Garzê basin and adjacent area are filled with a thick sequence of Triassic flyschoid sedimentary rocks. Within the Songpan-Garzê area, the Neoproterozoic basement only crops out in the southern part, in the Danba antiformal structure and to the east, along the Longmen-Shan belt, in the Xuelongbao metamorphic complex. To the north, below the Triassic sedimentary rocks, the nature of the basement (oceanic or continental) remains unknown. In order to research the range and the affinity of the basement of Songpan-Garzê orogenic belt, we ascertain the distribution range of the basement of Songpan-Garzê orogenic belt with aeromagnetic and seismic data, and discuss the affinity of the basement of the Songpan-Garzê orogenic belt with the geochemical data. Before identifying the boundaries of the basement we reduced the magnetic anomalies to pole and continued them upward. The results show that the basement in Songpan-Ganzi areas belongs to Yangzi block. The boundaries are Erdaogou-Yushu-Litang in the west-south, Qingchuan-Dujiangyan in the east, and the line of southern Kunlun to Xinghai-Xiahe-Xihe. Under the restrictions of deep seismic sounding and rock density characteristics, we calculate the density structure of the crust across the Songpan-Garzê orogenic belt and adjacent areas along the gravity profile A-A', which trends 400NE. The density model of the crust in this area is divided into two parts, upper and lower crust, vertically. The depth of the Moho is about 62 km in the southwest, and 54 km in the northeast. This model shows that gravity isostasy obeys the Airy theory approximately within the Songpan-Garzê orogenic belt although a buried load in the bottom of lower crust. While a buried load remain beneath the Moho to the north of Songpan-Garzê orogenic belt. During constructing these buried loads we computed local decompensative gravity anomalies on the condition that the depth of the lithospheric bottom is 120km. This work was supported by Crust Probe Project of China (SINOPROBE-02, SINOPROBE-08-02), the Natural Science Foundation of China (Nos. 40830316, 40774026, 40874045 ), China Geological Survey (Nos. 1212010611809, 1212010711813, 1212010811033), and scientific research project for public welfare from the Ministry of Land and Resources of China (No. 200811021,201011042).

Zhang, J.; Gao, R.; Li, Q.; Zhang, S.; Guan, Y.; Wang, H.

2011-12-01

258

Spreading rates, rift propagation, and fracture zone offset histories during the past 5 my on the Mid-Atlantic Ridge; 25°–27°30? S and 31°–34°30? S  

Microsoft Academic Search

The southern Mid-Atlantic Ridge (MAR) is spreading at rates (34–38 mm yr?1) that fall within a transitional range between those which characterize slow and intermediate spreading center morphology.\\u000a To further our understanding of crustal accretion at these transitional spreading rates, we have carried out analysis of magnetic\\u000a anomaly data from two detailed SeaBeam surveys of the MAR between 25°–27°30?S and

S. Carbotte; S. M. Welch; K. C. MacDonald

1991-01-01

259

Breakup of Australia and Antarctica estimated as mid-Cretaceous (95 +\\/- 5 Ma) from magnetic and seismic data at the continental margin  

Microsoft Academic Search

A positive magnetic anomaly marks the seaward edge of the magnetic quiet zone along the southern margin of Australia eastward between 114° and 131°E and along the conjugate Antarctic margin between 105° and 132°E. This anomaly was originally interpreted as the oldest seafloor-spreading anomaly-A22, revised by Cande and Mutter to A34-in the Southeast Indian Ocean, but is better modelled as

J. J. Veevers

1986-01-01

260

The association between cerebral developmental venous anomaly and concomitant cavernous malformation: an observational study using magnetic resonance imaging  

PubMed Central

Background Some studies reported that cerebral developmental venous anomaly (DVA) is often concurrent with cavernous malformation (CM). But there is lack of statistical evidence and study of bulk cases. The factors associated with concurrency are still unknown. The purpose of this study was to determine the prevalence of concomitant DVA and CM using observational data on Chinese patients and analyze the factors associated with the concurrency. Methods The records of all cranial magnetic resonance imaging (MRI) performed between January 2001 and December 2012 in Beijing Tiantan Hospital were reviewed retrospectively. The DVA and CM cases were selected according to imaging reports that met diagnostic criteria. Statistical analysis was performed using the Pearson chi-square statistic for binary variables and multivariable logistic regression analysis for predictors associated with the concurrent CM. Results We reviewed a total of 165,230 cranial MR images performed during the previous 12 year period, and identified 1,839 cases that met DVA radiographic criteria. There were 205 patients who presented concomitant CM among the 1,839 DVAs. The CM prevalence in DVA cases (11.1%) was significantly higher than that in the non-DVA cases (2.3%) (P<0.01). In the multivariate analysis, we found that DVAs with three or more medullary veins in the same MRI section (adjusted OR?=?2.37, 95% CI: 1.73-3.24), infratentorial DVAs (adjusted OR?=?1.71, 95% CI: 1.26-2.33) and multiple DVAs (adjusted OR?=?2.08, 95% CI: 1.04-4.16) have a higher likelihood of being concomitant with CM. Conclusions CM are prone to coexisting with DVA. There is a higher chance of concurrent CM with DVA when the DVA has three or more medullary veins in the same MRI scanning section, when the DVA is infratentorial, and when there are multiple DVAs. When diagnosing DVA cases, physicians should be alerted to the possibility of concurrent CM. PMID:24628866

2014-01-01

261

Gravity and magnetic anomalies of the western Arctic ocean and its margins provide an imperfect window to a complex, multi-stage tectonic history (Invited)  

NASA Astrophysics Data System (ADS)

Numerous scenarios are still in play for the tectonic development of the western Arctic. A wide range of kinematic models have been proposed for the opening of the Canadian basin. These models feature different combinations and geometries of extensional and transform motion and have informal descriptive names including the so-called ‘windshield wiper’, ‘railroad tracks’, ‘squeegee’, and ‘saloon door’ options. Another controversial issue is the timing and role of the gigantic Alpha-Mendeleev large igneous province relative to the tectonic stages. In our opinion, many current Arctic models have not adequately dealt with the mass and thermal fluxes implied by this huge province. Available data are extremely sparse for the circum-Arctic, although current political and economic interests are fueling accelerated data collection. Recent compilations of gravity and magnetic data are currently the best bets for synoptic imaging, however imprecise, of crustal composition and structure. Modeling and interpretation of regional geophysical anomalies provide some of the only available tests for scenario evaluation in the absence of more direct determinations of crustal structure and composition. Our goal in this talk is to review the key geophysical features of the western Arctic and relate these elements to the expectations of competing tectonic models. These key geophysical features include (1) contrasting Arctic domains of overall magnetic “thickness” and anomaly “fabric” (the domains correlate generally with broad tectonic categories); (2) cryptic sub-linear magnetic anomalies in the Canada basin (interpreted by some authors to be oceanic stripes); (3) a subtle but persistent gravity trough in the central Canada basin (inferred by some authors to represent an extensional trough); (4) spectacular “shelf edge” free-air gravity anomalies along the Canadian and Alaskan passive margins that show significant along-strike variation (which can be interpreted to reflect relative amount of magmatic activity); (5) complex and chaotic magnetic texture and fabric in the Alpha-Mendeleev large igneous province (perhaps reflecting pre-intrusive structural features and trends); and (6) large-amplitude, long-wavelength “deep magnetic highs” including well-studied examples in northern Alaska and north-western Canada (inferred to represent deep crustal elements that influence overall strength of the crust/upper mantle). The overall complexity of the Arctic geophysical anomaly fabric is indicative of significant variation in crustal composition and reflects a complicated, multi-stage tectonic development. It seems very likely that the best tectonic solutions for the circum-Arctic will include sub-elements of many current end-member models.

Saltus, R. W.; Miller, E. L.; Gaina, C.

2010-12-01

262

Manifestations of the vector anomaly in covariant and light-front calculations of the anomalous magnetic moment of W{sup {+-}} bosons  

SciTech Connect

In the calculation of the anomalous magnetic moment of W{sup {+-}} bosons, we discuss vector anomalies occurring in the fermion loop that spoil the predictive power of the theory. While the previous analyses were limited to using essentially the manifestly covariant dimensional regulation method, we extend the analysis using both the manifestly covariant formulation and the light-front Hamiltonian formulation with several different regularization methods. We find that the zero-mode contribution to the helicity zero-to-zero amplitude for the W{sup {+-}} gauge bosons is crucial for the correct light-front (LF) calculations. Further, we confirm that the anomaly-free condition found in the analysis of the axial anomaly can also get rid of the vector anomaly in light-front dynamics (LFD) as well as in the manifestly covariant calculations. Our findings in this work may provide a bottom-up fitness test not only to the LF calculations but also to the theory itself, whether it is any extension of the Standard Model or an effective field theoretic model for composite systems.

Bakker, Bernard L.G. [Department of Physics and Astrophysics, Vrije Universiteit, De Boelelaan 1081, NL-1081 HV Amsterdam (Netherlands); Ji, Chueng-Ryong [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202 (United States)

2005-03-01

263

Negative Magnetic Anomalies Observed in the Central West Antarctica (CWA) Aerogeophysical Survey Over the West Antarctic Ice Sheet (WAIS), Whose Sources are Volcanic Centers (e.g. Mt Resnik) at the Base of the ice >780 Ka  

NASA Astrophysics Data System (ADS)

Analysis of a block of coincident aeromagnetic and radar ice-sounding data (from the CWA aerogeophysical survey) over the WAIS reveals ~1000 50->1000-nT, shallow -source, ``volcanic" magnetic anomalies, interpreted as caused by late Cenozoic alkaline magmatism associated with the West Antarctic rift system (WR). About 400 of these anomalies (conservatively selected) have topographic expression at the bed of the WAIS; >80% of these topographic features have <200 m bed relief. There are ~100 short-wavelength, steep-gradient, negative magnetic anomalies observed in the CWA survey, or ~10% of the ~1000 ``volcanic" anomalies. These negative anomalies indicate volcanic activity during a time of magnetic field reversal from normal to reversed polarity at least as old as 780 Ka (the Brunes-Matuyama reversal). The sources of ~18 of the anomalies, half concentrated in the area of the WAIS divide, have high bed-elevation (above sea level after ice removal and glacial rebound), very magnetic topography of high bed relief, up to 2 km. Five of these peaks have associated negative magnetic anomalies. One of the high topographic features, Mt. Resnik, marked by a complex negative anomaly, is a conical peak 300 m below the surface of the WAIS, and has ~2 km topographic relief. We interpret a magnetic model fit to this anomaly as comprising reversely magnetized (in the present field direction), 0.5-2.5-km thick volcanic flows at the summit overlying normally magnetized flows. Published models (1996) reported for the Hut Point anomaly, at Ross Island, Antarctica, a similar anomaly to Mt. Resnik, also required both normal and reversed magnetizations correlated with drill holes into dated volcanic flows (also part of the late Cenozoic WR) crossing the Brunhes-Matuyama boundary (780 Ka). Because of their form similar to exposed volcanoes in the WAIS area with edifices primarily comprising subaerially-erupted, very magnetic volcanic flows, which have resisted glacial erosion, Behrendt et al. (2004) interpreted that these 18 high-topograpy, high-relief sources are subglacial volcanoes (including the five >780 Ka) erupted subaerially during a period when the WAIS was absent.

Behrendt, J. C.; Finn, C. A.; Morse, D. L.; Blankenship, D. D.

2005-12-01

264

Joint interpretation of gravity and magnetic data in the Kolárovo anomaly region by separation of sources and the inversion method of local corrections  

NASA Astrophysics Data System (ADS)

We present a new interpretation of the Kolárovo gravity and magnetic anomalies in the Danube Basin based on an inversion methodology that comprises the following numerical procedures: removal of regional trend, depth-wise separation of signal of sources, approximation of multiple sources by 3D line segments, non-linear inversion based on local corrections resulting in found sources specified as 3D star-convex homogenous bodies and/or 3D contrasting structural contact surfaces. This inversion methodology produces several admissible solutions from the viewpoint of potential field data. These solutions are then studied in terms of their feasibility taking into consideration all available tectono-geological information. By this inversion methodology we interpret here the Kolárovo gravity and magnetic anomalies jointly. Our inversion generates several admissible solutions in terms of the shape, size and location of a basic intrusion into the upper crust, or the shape and depth of the upper/lower crust interface, or an intrusion into the crystalline crust above a rise of the mafic lower crust. Our intrusive bodies lie at depths between 5 and 12 km. Our lower crust elevation rises to 12 km with and 8 km without the accompanying intrusion into the upper crust, respectively. Our solutions are in reasonable agreement with various previous interpretations of the Kolárovo anomaly, but yield a better and more realistic geometrical resolution for the source bodies. These admissible solutions are next discussed in the context of geological and tectonic considerations, mainly in relation to the fault systems.

Prutkin, Ilya; Vajda, Peter; Bielik, Miroslav; Bezák, Vladimír; Tenzer, Robert

2014-04-01

265

A source-depth separation filter: Using the Euler method on the derivatives of total intensity magnetic anomaly data  

USGS Publications Warehouse

An overview is given on the benefits of applying the Euler method on derivatives of anomalies to enhance the location of shallow and deep sources. Used properly, the method is suitable for characterizing sources from all potential-field data and/or their derivative, as long as the data can be regarded mathematically as "continuous". Furthermore, the reasons why the use of the Euler method on derivatives of anomalies is particularly helpful in the analysis and interpretation of shallow features are explained.

Ravat, D.; Kirkham, K.; Hildenbrand, T.G.

2002-01-01

266

MAGSAT scalar and vector anomaly data analysis  

NASA Technical Reports Server (NTRS)

Efforts on the analysis of MAGSAT scalar anomaly data, the application of the scalar analysis results to three component vector data, and the comparison of MAGSAT data with corresponding MAGNET aeromagnetic and free air gravity anomaly data are briefly described.

1982-01-01

267

Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.

Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.

2014-06-01

268

The reduction, verification and interpretation of MAGSAT magnetic data over Canada  

NASA Technical Reports Server (NTRS)

Correlations between the MAGSAT scalar anomaly map produced at the Earth Physics ranch and other geophysical and geological data reveal relationships between high magnetic field and some metamorphic grade shields, as well as between low magnetic field and shield regions of lower metamorphic grade. An intriguing contrast exists between the broad low anomaly field over the Nasen-Gakkel Ridge (a spreading plate margin) and the high anomaly field over Iceland (part of a spreading margin). Both regions have high heat flow, and presumably thin magnetic crust. This indicates that Iceland is quite anomalous in its magnetic character, and possible similarities with the Alpha Ridge are suggested. Interesting correlations exist between MAGSAT anomalies around the North Atlantic, after reconstructing the fit of continents into a prerifting configuration. These correlations suggest that several orogenies in that region have not completely destroyed an ancient magnetization formed in high grade Precambrian rocks.

Coles, R. L. (principal investigator); Haines, G. V.; Vanbeek, G. J.; Walker, J. K.; Newitt, L. R.; Nandi, A.

1982-01-01

269

Midface anomalies in children.  

PubMed

A variety of congenital midface anomalies occur in children. High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have proved helpful in determining the nature and extent of dysplasia, thereby facilitating treatment planning. A classification system has been developed that groups these anomalies into four categories based on embryogenesis and anatomic location. These categories comprise anomalies that are related to the nasal cavity, nasofrontal region, nasolacrimal apparatus, and craniofacial syndromes. CT is the imaging modality of choice in children with possible choanal atresia, pyriform aperture stenosis, or anomalies of the nasolacrimal duct (eg, nasolacrimal duct stenosis, dacryocystoceles). MR imaging is the modality of choice in patients with congenital midface masses (eg, dermoid and epidermoid cysts, nasal gliomas, encephaloceles) and craniofacial syndromes (eg, Apert syndrome, Crouzon syndrome, Treacher Collins syndrome). In many cases, however, both CT and MR imaging are required to adequately evaluate midface anomalies. Familiarity with the characteristic imaging features of these anomalies along with knowledge of midface embryogenesis and normal developmental anatomy is essential to prevent misinterpretation of anatomic variations that may simulate disease. PMID:10903683

Lowe, L H; Booth, T N; Joglar, J M; Rollins, N K

2000-01-01

270

Spill Spread  

NSDL National Science Digital Library

In this simulation, learners explore how ocean currents spread all kinds of pollutionâincluding oil spills, sewage, pesticides and factory wasteâfar beyond where the pollution originates. Learners create an experimental "ocean" (water in a tray) and "continents" (rocks), then add melting ice cubes to create temperature-driven currents in the water. Learners observe how "pollution," represented by food coloring, spreads through the model ocean affected by both "currents" and "continents." This activity can be used with lessons on ocean science or environmental hazards.

Science, Lawrence H.

2007-01-01

271

Gravitational anomaly and transport phenomena.  

PubMed

Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid. PMID:21797593

Landsteiner, Karl; Megías, Eugenio; Pena-Benitez, Francisco

2011-07-01

272

Reliability of CHAMP Anomaly Continuations  

NASA Technical Reports Server (NTRS)

CHAMP is recording state-of-the-art magnetic and gravity field observations at altitudes ranging over roughly 300 - 550 km. However, anomaly continuation is severely limited by the non-uniqueness of the process and satellite anomaly errors. Indeed, our numerical anomaly simulations from satellite to airborne altitudes show that effective downward continuations of the CHAMP data are restricted to within approximately 50 km of the observation altitudes while upward continuations can be effective over a somewhat larger altitude range. The great unreliability of downward continuation requires that the satellite geopotential observations must be analyzed at satellite altitudes if the anomaly details are to be exploited most fully. Given current anomaly error levels, joint inversion of satellite and near- surface anomalies is the best approach for implementing satellite geopotential observations for subsurface studies. We demonstrate the power of this approach using a crustal model constrained by joint inversions of near-surface and satellite magnetic and gravity observations for Maude Rise, Antarctica, in the southwestern Indian Ocean. Our modeling suggests that the dominant satellite altitude magnetic anomalies are produced by crustal thickness variations and remanent magnetization of the normal polarity Cretaceous Quiet Zone.

vonFrese, Ralph R. B.; Kim, Hyung Rae; Taylor, Patrick T.; Asgharzadeh, Mohammad F.

2003-01-01

273

Breakup and early seafloor spreading between India and Antarctica  

NASA Astrophysics Data System (ADS)

We present a tectonic interpretation of the breakup and early seafloor spreading between India and Antarctica based on improved coverage of potential field and seismic data off the east Antarctic margin between the Gunnerus Ridge and the Bruce Rise. We have identified a series of ENE trending Mesozoic magnetic anomalies from chron M9o (~130.2 Ma) to M2o (~124.1 Ma) in the Enderby Basin, and M9o to M4o (~126.7 Ma) in the Princess Elizabeth Trough and Davis Sea Basin, indicating that India-Antarctica and India-Australia breakups were roughly contemporaneous. We present evidence for an abandoned spreading centre south of the Elan Bank microcontinent; the estimated timing of its extinction corresponds to the early surface expression of the Kerguelen Plume at the Southern Kerguelen Plateau around 120 Ma. We observe an increase in spreading rate from west to east, between chron M9 and M4 (38-54 mm yr-1), along the Antarctic margin and suggest the tectono-magmatic segmentation of oceanic crust has been influenced by inherited crustal structure, the kinematics of Gondwanaland breakup and the proximity to the Kerguelen hotspot. A high-amplitude, E-W oriented magnetic lineation named the Mac Robertson Coast Anomaly (MCA), coinciding with a landwards step-down in basement observed in seismic reflection data, is tentatively interpreted as the boundary between continental/transitional zone and oceanic crust. The exposure of lower crustal rocks along the coast suggests that this margin formed in a metamorphic core complex extension mode with a high strength ratio between upper and lower crust, which typically occurs above anomalously hot mantle. Together with the existence of the MCA zone this observation suggests that a mantle temperature anomaly predated the early surface outpouring/steady state magmatic production of the Kerguelen LIP. An alternative model suggests that the northward ridge jump was limited to the Elan Bank region, whereas seafloor spreading continued in the West Enderby Basin and its Sri Lankan conjugate margin. In this case, the MCA magnetic anomaly could be interpreted as the southern arm of a ridge propagator that stopped around 120 Ma.

Gaina, Carmen; Müller, R. Dietmar; Brown, Belinda; Ishihara, Takemi; Ivanov, Sergey

2007-07-01

274

Extravasation into brain and subsequent spread beyond the ischemic core of a magnetic resonance contrast agent following a step-down infusion protocol in acute cerebral ischemia  

PubMed Central

Background Limiting expansion of the ischemic core lesion by reinstating blood flow and protecting the penumbral cells is a priority in acute stroke treatment. However, at present, methods are not available for effective drug delivery to the ischemic penumbra. To address these issues this study compared the extravasation and subsequent interstitial spread of a magnetic resonance contrast agent (MRCA) beyond the ischemic core into the surrounding brain in a rat model of ischemia-reperfusion for bolus injection and step-down infusion (SDI) protocols. Methods Male Wistar rats underwent middle cerebral artery (MCA) occlusion for 3 h followed by reperfusion. Perfusion-diffusion mismatched regions indicating the extent of spread were identified by measuring cerebral blood flow (CBF) deficits by arterial spin-labeled magnetic resonance imaging and the extent of the ischemic core by mapping the apparent diffusion coefficient (ADC) of water with diffusion-weighted imaging. Vascular injury was assessed via MRCA, gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) penetration, by Look-Locker T1-weighted MR imaging after either a bolus injection (n?=?8) or SDI (n?=?6). Spatial and temporal expansion of the MRCA front during a 25 min imaging period was measured from images obtained at 2.5 min intervals. Results The mean ADC lesion was 20?±?7% of the hemispheric area whereas the CBF deficit area was 60?±?16%, with the difference between the areas suggesting the possible presence of a penumbra. The bolus injection led to MRCA enhancement with an area that initially spread into the ischemic core and then diminished over time. The SDI produced a gradual increase in the area of MRCA enhancement that slowly enlarged to occupy the core, eventually expanded beyond it into the surrounding tissue and then plateaued. The integrated area from SDI extravasation was significantly larger than that for the bolus (p?=?0.03). The total number of pixels covered by the SDI at its maximum was significantly larger than the pixels covered by bolus maximum (p?=?0.05). Conclusions These results demonstrate that the SDI protocol resulted in a spread of the MRCA beyond the ischemic core. Whether plasma-borne acute stroke therapeutics can be delivered to the ischemic penumbra in a similar way needs to be investigated.

2014-01-01

275

Constraints of Sea Beam data on crustal fabrics and seafloor spreading in the South China Sea  

NASA Astrophysics Data System (ADS)

The South China Sea is a mid-late Tertiary marginal basin. The magnetic anomaly lineations in the eastern part of the basin trend approximately east-west [1,2], suggesting a north-south direction of spreading. In the spring of 1985, two cruises on the French research vessel "Jean Charcot" provided Sea Beam coverage, seismic reflection, magnetic and gravity profiles. The Sea Beam data exhibit two major structural trends: scarps striking N50°E± 15°, interpreted as normal faults, and scarps striking N140°E± 15°, interpreted as fracture zones. This fabric implies a northwest-southeast direction of spreading, up to about 100 km north and south of the inferred spreading axis [3]. Dense Sea Beam coverage of a roughly 1° square area northwest of the Scarborough Seamounts chain shows that the emplacement of these seamounts was, at least in its initial stage, controlled by faulting in two orthogonal directions, N50°E and N140°E. Magnetic and gravimetric maps of the same area also reveal anomalies trending roughly N50°E, which are disrupted by transform zones striking N140°E. This detailed study indicates that the fracture zones may be closely spaced (less than 20-30 km) east of Macclesfield Bank. Furthermore, magnetic anomalies identified as 6 and 6a (20 Myr) along two north-south profiles located at both edges to the north of this detailed study area may be correlated with the N80°E trend characteristic of such anomalies in the eastern part of the South China Sea. The east-west trend of magnetic anomalies 6 and 6a, south of Scarborough seamount chain, recognised by Taylor and Hayes (1983) [1] is incompatible with the trend of the fault scarps observed on Sea Beam data. We infer that progressive, right-lateral offsets of the ridge across closely spaced discontinuities may account for the nearly east-west average trend of some of the magnetic anomalies, and of the Scarborough seamount chain, which represents the location of the relict spreading axis, in spite of a N50°E spreading direction. The whole central part of the basin east of 115°E may have formed in this way, since N130-140°E striking fracture zones are observed on the Sea Beam swaths. This model may correspond to the second of two successive spreading phases, with N-S and NW-SE directions of extension respectively, as was presented by the authors in a previous paper (Pautot et al., 1986 [3]). Alternatively, we may assume that the direction of extension did not change radically during the opening history [3], implying that oblique spreading occurred along N80°E trending ridge segments, creating the N80°E trending scarps and magnetic anomalies observed to the north and to the south of the study area. Such a direction of extension is compatible with mid-late Tertiary left-lateral movements along large N130-150°E strike-slip faults, such as the Red River and Wang Chao faults in South China and Sundaland.

Briais, Anne; Tapponnier, Paul; Pautot, Guy

1989-11-01

276

Antipodal Magnetic Anomalies on the Moon, Contributions from Impact Induced Currents Due to Positive Holes and Flexoelectric Phenomina and Dynamo  

NASA Technical Reports Server (NTRS)

Large impacts on the Moon generate large pressure pulses that penetrate the whole body. Several of these large impacts may have generated antipodal structure with anomalous magnetic intensity.These regions can be more than a thousand km across, with fields of the order of tens to hundreds of nT. This is the case of Orientale, Imbrium, Serenitatis, Crisium, and Nectaris impact basins. The production of large-scale magnetic fields and associated crustal magnetization due to lunar basin-forming impacts was hypothesized to have an origin in fields external to the impact plasma cloud that are produced by the magnetohydrodynamic interaction of the cloud with ambient magnetic fields and plasmas. During the period of compressed antipodal field amplification, seismic compressional waves from the impact converge at the antipode resulting in transient shock pressures that reach 2 GPa (20 kbar). This can produce conditions for shock magnetic acquisition of the crust antipodal to impact basins.

Kletetschka, G.; Freund, F.; Wasilewski, P. J.; Mikula, V.; Kohout, Tomas

2005-01-01

277

DOWN'S ANOMALY.  

ERIC Educational Resources Information Center

BOTH CLINICAL AND PATHOLOGICAL ASPECTS AND MATHEMATICAL ELABORATIONS OF DOWN'S ANOMALY, KNOWN ALSO AS MONGOLISM, ARE PRESENTED IN THIS REFERENCE MANUAL FOR PROFESSIONAL PERSONNEL. INFORMATION PROVIDED CONCERNS (1) HISTORICAL STUDIES, (2) PHYSICAL SIGNS, (3) BONES AND MUSCLES, (4) MENTAL DEVELOPMENT, (5) DERMATOGLYPHS, (6) HEMATOLOGY, (7)…

PENROSE, L.S.; SMITH, G.F.

278

Evidence for True Polar Wander since mid-Cenozoic time: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma) Between the Galapagos and Clarion Fracture Zones on the Pacific Plate  

NASA Astrophysics Data System (ADS)

In recent years, some researchers have asserted that there has been no motion of the Pacific hotspots relative to the spin axis since the age (ca. 47 Ma) of the elbow in the Hawaiian-Emperor chain (e.g., Tarduno et al. 2003). In contrast, the apparent polar wander of the Indo-Atlantic hotspots shows distinct motion of the hotspots relative to the spin axis over the same time interval (e.g., Morgan 1981; Besse and Courtillot 2002). If this latter shift is due to true polar wander, one would expect to see a similar shift of Pacific hotspots relative to the spin axis. Here we present critical new data and analyses to test these distinctly different hypotheses. Specifically, we present results of an investigation of the skewness of magnetic anomaly crossings of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones on the Pacific plate. We chose to focus on these adjacent regions for three reasons. First, numerical experiments showed that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal to noise ratios (Horner-Johnson and Gordon, 2003). Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm/yr) above which no anomalous skewness occurs. Moreover, for the first time, we combine uncertainties in plate- hotspot rotations (Andrews et al. 2005) with paleomagnetic uncertainties to obtain the total uncertainties of our new paleomagnetic pole reconstructed into the Pacific hotspot frame of reference. The results show significant and unambiguous motion of Pacific hotspots relative to the spin axis since 32 Ma. Moreover, when the 32 Ma Pacific plate paleomagnetic pole is reconstructed into the Pacific hotspot reference frame, it is consistent with the paleomagnetic pole of the Indo-Atlantic hotspots. We conclude that the global set of hotspots have mainly moved in unison relative to the spin axis since 32 Ma, which is most simply interpreted as true polar wander.

Horner-Johnson, B. C.; Gordon, R. G.

2007-12-01

279

Enhancement of co-seismic piezomagnetic signals near the edges of magnetization anomalies in the Earth's crust  

NASA Astrophysics Data System (ADS)

A scheme is proposed for calculating the piezomagnetic fields that accompany the propagation of seismic waves through a non-uniformly magnetized crust. Examples of the calculations are provided. Generally, the calculation of the co-seismic piezomagnetic fields involves laborious three-dimensional volume integrals, even if the magnetization structure is two-dimensional. However, the calculation can be simplified by taking the Fourier transform of spatial distributions of the field into consideration. As an example, we have performed calculations for both the non-uniformly and uniformly magnetized crust with an intensity of 10 A/m. The incident seismic wave is considered to consist of Rayleigh waves with an amplitude of 5 cm. The amplitudes of the piezomagnetic signals arising from uniformly magnetized crust are up to 0.2 nT, whereas those arising from non-uniformly magnetized crust are as large as 0.5 nT. This result indicates that the piezomagnetic field may be a plausible mechanism of generating co-seismic changes in the magnetic field with detectable amplitudes for large earthquakes, provided that the observation site is located near the magnetization boundaries.

Yamazaki, K.

2011-02-01

280

Magnetization induced dielectric anomaly in multiferroic LaFeO3-PbTiO3 solid solution  

NASA Astrophysics Data System (ADS)

Coexistence of both typically ferroelectric (Tc1˜434 K) and frequency dependent broad transitions (650 K?Tc2?800 K) in ? versus T is demonstrated in a multiferroic candidate form="infix">[(Pb0.8La0.2)(Ti0.8Fe0.2)O3 form="infix">]. The sample shows spontaneous magnetization and enhancement of magnetization on electrical poling. We demonstrate clearly that although the frequency dependent broad transition has no origin in ferroelectricity and is instead driven by a corresponding magnetic ordering at ˜650 K, the solid solution shows magnetoelectric coupling due to its pure ferroelectric behavior at and below 434 K.

Singh, Anupinder; Chatterjee, Ratnamala

2008-11-01

281

Magnetization induced dielectric anomaly in multiferroic LaFeO3-PbTiO3 solid solution  

Microsoft Academic Search

Coexistence of both typically ferroelectric (Tc1~434 K) and frequency dependent broad transitions (650 K<=Tc2<=800 K) in ?´ versus T is demonstrated in a multiferroic candidate [(Pb0.8La0.2)(Ti0.8Fe0.2)O3]. The sample shows spontaneous magnetization and enhancement of magnetization on electrical poling. We demonstrate clearly that although the frequency dependent broad transition has no origin in ferroelectricity and is instead driven by a corresponding

Anupinder Singh; Ratnamala Chatterjee

2008-01-01

282

Deriving the Ginzburg-Landau parameter from heat-capacity data on magnetic superconductors with Schottky anomalies  

E-print Network

the superconducting parameters.6 Never- theless, specific-heat measurements on magnetic supercon- ductors terms, were calculated and then subtracted to improve determination of the Ginzburg- Landau parameter-temperature superconductors without advanced computation. The approximate equations allow simple calculation of the degeneracy

Hampshire, Damian

283

Rotor cage anomalies and unbalanced magnetic pull in single-phase induction motors. II. Experimental and theoretical studies  

Microsoft Academic Search

For pt. I see ibid., p.558-65, (1996). This paper consists of an experimental and theoretical investigation of the effect that rotor cage defects have on the unbalanced magnetic pull (UMP) present in a single phase motor. The model used in the theoretical studies is developed in a companion paper. In the experimental investigation, the UMP developed by a number of

STEPHEN WILLIAMSON; RUSSELL C. HEALEY; JOSEPH L. TEVAARWERK

1996-01-01

284

Aspects on the origin of the precursory magnetic anomalies of the Mw 6.4 Aquila earthquake  

NASA Astrophysics Data System (ADS)

An anomalous behaviour of the scaling exponent derived from the detrended fluctuation analysis (DFA) of the time series of low frequency variations of the horizontal and vertical magnetic field components has been recently reported as being observed 2 months prior to the Mw 6.3 earthquake on 6 April 2009, close to L'Aquila city, Italy. Here, we suggest a possible physical explanation of this effect based on the experience from similar measurements in Greece. In particular, for example, we compare these observations associated with Aquila earthquake with the ones of the Mw 6.6 earthquake on 13 May 1995 at Kozani-Grevena, Greece where both magnetic field variations and seismic electric signals (SES) were recorded. Almost 1 month before the latter earthquake, anomalous variations in both electric and magnetic field were detected, the time series of that were analysed by means of DFA and led to an exponent close to unity. Similarly, the calculated DFA exponent for the Aquila earthquake time series of the anomalous magnetic field variations 2 months before the main shock was also found close to unity. These results could imply that in the case of Aquila, according to the Maxwell's laws, one should expect to observe simultaneously with the magnetic signal an associated SES activity, provided that an appropriate station to monitoring the earth's electric field variations in the same area was available. Hence, it seems that similar underlying non-linear dynamic processes in mechanical and as well as electromagnetic sense, with features of criticality, dominated in both pre-focal areas.

Dologlou, Elizabeth

2014-03-01

285

Volcanic Eruptions along the Galápagos Spreading Center Revealed by Geologic Mapping Using Alvin, Sentry and TowCam and Geochemical and Magnetic Paleointensity Studies  

NASA Astrophysics Data System (ADS)

High-resolution geologic mapping and laboratory studies have identified and characterized volcanic eruptions in two areas of the Western Galápagos Spreading Center, one far from the Galápagos hotspot (~95°W), and one closer to the hotspot (~92°W) with ~40-50% greater overall magma supply. Geologic maps were prepared using observations from HOV Alvin, TowCam, and high-resolution (~1 m spatial) bathymetry data collected by AUV Sentry of field relationships, sediment thickness, and lava morphology, as well as sample mineralogy, geochemistry, and magnetic paleointensity. Lavas from eight eruptive events at the low magma supply area are commonly plagioclase- and/or olivine-phyric, and have limited compositional variation. Two of these units were fed by fissures up to 6.5 km long, but the others are steep-sided clusters of pillow mounds up to 2.5 km in diameter and 250 m tall. In contrast, all six eruptive units presently identified in the high magma supply area were fed by fissures up to 7 km in length; these lavas are predominantly aphyric, and sheet and lobate lavas are more common. There is greater compositional diversity of erupted lavas in the high magma supply area as a whole (Mg # ranges from 26-60, vs. 44-62 at low supply), and also within individual eruptive units (range in MgO content up to 1.5 wt. % MgO, vs. 0.7 wt. % MgO at low supply). Preliminary conclusions from this study are that with increasing magma supply along this intermediate-spreading rate (~52-56 mm/yr) ridge, individual eruptions tend to be smaller (largest in each study area ~0.2 vs. >2 km3), more chemically heterogeneous and erupted at significantly higher average effusion rates.

Colman, A.; Sinton, J. M.; White, S. M.; Bowles, J. A.; Rubin, K. H.; Gruvee Science Team

2010-12-01

286

Magnetization of the oceanic crust - Thermoremanent magnetization of chemical remanent magnetization?  

NASA Technical Reports Server (NTRS)

A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80 percent of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness dicrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.

Raymond, C. A.; Labrecque, J. L.

1987-01-01

287

Spread Supersymmetry  

NASA Astrophysics Data System (ADS)

In the multiverse the scale of supersymmetry breaking, widetilde{m} = {F_X}/{M_{ * }} ?, may scan and environmental constraints on the dark matter density may exclude a large range of m from the reheating temperature after inflation down to values that yield a lightest supersymmetric particle (LSP) mass of order a TeV. After selection effects, for example from the cosmological constant, the distribution for widetilde{m} in the region that gives a TeV LSP may prefer larger values. A single environmental constraint from dark matter can then lead to multi-component dark matter, including both axions and the LSP, giving a TeV-scale LSP somewhat lighter than the corresponding value for single-component LSP dark matter. If supersymmetry breaking is mediated to the Standard Model sector at order X † X and higher, only squarks, sleptons and one Higgs doublet acquire masses of order widetilde{m} . The gravitino mass is lighter by a factor of M ? /M Pl and the gaugino masses are suppressed by a further loop factor. This Spread Supersymmetry spectrum has two versions, one with Higgsino masses arising from supergravity effects of order the gravitino mass giving a wino LSP, and another with the Higgsino masses generated radiatively from gaugino masses giving a Higgsino LSP. The environmental restriction on dark matter fixes the LSP mass to the TeV domain, so that the squark and slepton masses are order 103 TeV and 106 TeV in these two schemes. We study the spectrum, dark matter and collider signals of these two versions of Spread Supersymmetry. The Higgs boson is Standard Model-like and predicted to lie in the range 110-145 GeV; monochromatic photons in cosmic rays arise from dark matter annihilations in the halo; exotic short charged tracks occur at the LHC, at least for the wino LSP; and there are the eventual possibilities of direct detection of dark matter and detailed exploration of the TeV-scale states at a future linear collider. Gauge coupling unification is at least as precise as in minimal supersymmetric theories. If supersymmetry breaking is also mediated at order X, a much less hierarchical spectrum results. The spectrum in this case is similar to that of the Minimal Supersymmetric Standard Model, but with the superpartner masses 1-2 orders of magnitude larger than those expected in natural theories.

Hall, Lawrence J.; Nomura, Yasunori

2012-01-01

288

Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada Basin, and the geometry and timing of rifting in the Amerasia Basin, Arctic Ocean  

USGS Publications Warehouse

Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulder and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cape of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining seafloor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield simular tectonic reconstructions. Together with the orientation and age of rift-marine structures, these data suggest that: 1) prior to opening of the Amerasia basin, both northern Alaska and continental ridges of the Chukchi borderland were part of North America, 2) the extension that created the Amerasia basin formed rift-margin graben beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the basis of the stratigraphy of Northwind Ridge and sea-floor magnetic anomalies in the Canada basin accounts in a general way for the major crustal elements of the Americasia basin, including the highstanding ridges of the Chukchi borderland, and supports S.W. Carye's hypothesis that the Amerasia basin is the product of anticlockwise rotational rifting of Arctic Alaska from North America.

Grantz, A.; Clark, D. L.; Phillips, R. L.; Srivastava, S. P.; Blome, C. D.; Gray, L. B.; Haga, H.; Mamet, B. L.; McIntyre, D. J.; McNeil, D. H.; Mickey, M. B.; Mullen, M. W.; Murchey, B. I.; Ross, C. A.; Stevens, C. H.; Silberling, N. J.; Wall, J. H.; Willard, D. A.

1998-01-01

289

6d, Coulomb branch anomaly matching  

NASA Astrophysics Data System (ADS)

6d QFTs are constrained by the analog of 't Hooft anomaly matching: all anomalies for global symmetries and metric backgrounds are constants of RG flows, and for all vacua in moduli spaces. We discuss an anomaly matching mechanism for 6d theories on their Coulomb branch. It is a global symmetry analog of Green-Schwarz-West-Sagnotti anomaly cancellation, and requires the apparent anomaly mismatch to be a perfect square, . Then ? I 8 is cancelled by making X 4 an electric/magnetic source for the tensor multiplet, so background gauge field instantons yield charged strings. This requires the coefficients in X 4 to be integrally quantized. We illustrate this for theories. We also consider the SCFTs from N small E8 instantons, verifying that the recent result for its anomaly polynomial fits with the anomaly matching mechanism.

Intriligator, Kenneth

2014-10-01

290

Dyonic Anomalies  

E-print Network

We consider the problem of coupling a dyonic p-brane in d = 2p+4 space-time dimensions to a prescribed (p+2)-form field strength. This is particularly subtle when p is odd. For the case p = 1, we explicitly construct a coupling functional, which is a sum of two terms: one which is linear in the prescribed field strength, and one which describes the coupling of the brane to its self-field and takes the form of a Wess-Zumino term depending only on the embedding of the brane world-volume into space-time. We then show that this functional is well-defined only modulo a certain anomaly, related to the Euler class of the normal bundle of the brane world-volume.

Mans Henningson; Erik P. G. Johansson

2005-08-15

291

Quantum Mechanical Simulation and X-Ray Scattering Applied to Pressure-Induced Invar Anomaly in Magnetic Iron Alloy  

NASA Astrophysics Data System (ADS)

The Invar effect has remained at the forefront of materials research since Charles-Edouard Guillaume discovered the vanishing thermal expansion of Fe-Ni alloys in 1897. More recently, a pressure-induced Invar effect was discovered in Fe-Ni alloys, and the relationship between classical and pressure-induced Invar phenomena has added complexity to the century-old struggle to comprehend the microscopic origins of Invar behavior. In this thesis I present our recent discovery of pressure-induced Invar behavior in Pd3Fe with the ordered L12 structure. Nuclear forward scattering measurements show that the ferromagnetic ground state in Pd3Fe is destabilized with pressure, collapsing around 10GPa (V/V 0=0.96) to a low-spin magnetic state. From high-pressure synchrotron x-ray diffraction measurements we find a large volume collapse at ambient temperature to accompany the collapse of ferromagnetism. After the volume collapse there is a significant increase in the bulk modulus. Using nuclear resonant inelastic x-ray scattering to study the 57Fe phonon partial density of states (PDOS) at high pressures, we find the pressure-induced magnetic transition to cause an anomalous relative softening of the average phonon frequency. Heating our sample to 650K in a furnace at a pressure of 7GPa, synchrotron x-ray diffraction measurements reveal negligible thermal expansion from 300 to 523 K, demonstrating pressure-induced Invar behavior in Pd3Fe. Density functional theory calculations identify a ferromagnetic ground state in Pd3Fe with large moments at the Fe sites. These calculations show that the application of pressure counteracts the band-filling effect of Pd. By tuning the position of the top of the 3d band with respect to the Fermi level, pressure-induced Invar behavior resembles classical Invar behavior that is controlled by chemical composition. This insight marks the first step towards a unification of our understanding of classical and pressure-induced Invar behavior. Pressure drives the majority-spin t2g antibonding electronic states closer to the Fermi level. The transition to the low-spin state occurs as these t2g states move across the Fermi level, transferring charge to the minority-spin eg nonbonding electronic states. This charge transfer reduces the internal electronic pressure in the material, giving a volume reduction in the low-spin state. The movement of the t 2g states with increasing pressure results in a greater number of states at the Fermi level, increasing screening efficiency and softening the first nearest-neighbor Fe-Pd longitudinal force constants in the low-spin state. The measured and calculated magnetic transition pressures differ significantly, despite sharing similar elastic properties in both the ferromagnetic and low-spin states. The magnitude of the disagreement between theoretical and experimental magnetic transition pressures suggests a spin-disordered state exists at high pressures in Pd3Fe. A shape discrepancy between the calculated and measured high-pressure Fe PDOS suggests significant short-range spin correlations exist in this spin-disordered state.

Winterrose, Michael L.

292

The Anatomy of the Pion Loop Hadronic Light by Light Scattering Contribution to the Muon Magnetic Anomaly  

E-print Network

This thesis investigates the Hadronic Light by Light (HLL) scattering contribution to the muon $g-2$, which is one of the most important low energy hadronic effects and consists mainly of the quark loop, the pion pole and the charged pion and kaon loops. In this work the charged pion loop has been investigated more closely. After reviewing the subject a preliminary introduction to Chiral Perturbation Theory (ChPT), Hidden Local Symmetry (HLS) model and the full Vector Meson Dominance (VMD) model is given, and they are used to calculate the pion loop HLL scattering contribution to the muon anomalous magnetic moment. The momentum regions where the contributions of the bare pion loop, the VMD model, and the HLS come from, have been studied, to understand why different models give very different results. The effects of pion polarizability and charge radius on the HLL scattering, which appear at order $p^4$ in ChPT, from $ L_9$ and $ L_{10}$ Lagrangian terms and their momentum regions have been studied.

Abyaneh, Mehran Zahiri

2012-01-01

293

The Anatomy of the Pion Loop Hadronic Light by Light Scattering Contribution to the Muon Magnetic Anomaly  

E-print Network

This thesis investigates the Hadronic Light by Light (HLL) scattering contribution to the muon $g-2$, which is one of the most important low energy hadronic effects and consists mainly of the quark loop, the pion pole and the charged pion and kaon loops. In this work the charged pion loop has been investigated more closely. After reviewing the subject a preliminary introduction to Chiral Perturbation Theory (ChPT), Hidden Local Symmetry (HLS) model and the full Vector Meson Dominance (VMD) model is given, and they are used to calculate the pion loop HLL scattering contribution to the muon anomalous magnetic moment. The momentum regions where the contributions of the bare pion loop, the VMD model, and the HLS come from, have been studied, to understand why different models give very different results. The effects of pion polarizability and charge radius on the HLL scattering, which appear at order $p^4$ in ChPT, from $ L_9$ and $ L_{10}$ Lagrangian terms and their momentum regions have been studied.

Mehran Zahiri Abyaneh

2012-08-13

294

Anomaly Structure of Supergravity and Anomaly Cancellation  

E-print Network

We display the full anomaly structure of supergravity, including new D-term contributions to the conformal anomaly. This expression has the super-Weyl and chiral U(1)_K transformation properties that are required for implementation of the Green-Schwarz mechanism for anomaly cancellation. We outline the procedure for full anomaly cancellation. Our results have implications for effective supergravity theories from the weakly coupled heterotic string theory.

Daniel Butter; Mary K. Gaillard

2009-06-18

295

Anomaly Structure of Supergravity and Anomaly Cancellation  

E-print Network

We display the full anomaly structure of supergravity, including new D-term contributions to the conformal anomaly. This expression has the super-Weyl and chiral U(1)_K transformation properties that are required for implementation of the Green-Schwarz mechanism for anomaly cancellation. We outline the procedure for full anomaly cancellation. Our results have implications for effective supergravity theories from the weakly coupled heterotic string theory.

Butter, Daniel

2009-01-01

296

ANOMALY STRUCTURE OF SUPERGRAVITY AND ANOMALY CANCELLATION  

SciTech Connect

We display the full anomaly structure of supergravity, including new D-term contributions to the conformal anomaly. This expression has the super-Weyl and chiral U(1){sub K} transformation properties that are required for implementation of the Green-Schwarz mechanism for anomaly cancellation. We outline the procedure for full anomaly cancellation. Our results have implications for effective supergravity theories from the weakly coupled heterotic string theory.

Butter, Daniel; Gaillard, Mary K.

2009-06-10

297

Anomaly structure of supergravity and anomaly cancellation  

Microsoft Academic Search

We display the full anomaly structure of supergravity, including new contributions to the conformal anomaly. Our result has the super-Weyl and Kähler U(1), transformation properties that are required for implementation of the Green–Schwarz mechanism for anomaly cancellation.

Daniel Butter; Mary K. Gaillard

2009-01-01

298

Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma  

NASA Astrophysics Data System (ADS)

We present improved rotations, complete with uncertainties, for the Pacific-Farallon Ridge (PFR) between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma). Despite substantial shortening since ˜55 Ma, this ridge system and its remnants (e.g. the East Pacific Rise) have produced as much as 45 per cent of all oceanic lithosphere created since the Late Cretaceous, but reconstructions face the twin challenges of extensive subduction of Farallon crust-which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone (FZ) traces-and asymmetric spreading behaviour for at least the past 51 Myr. We have calculated best-fit `half'-angle stage rotations between nine geomagnetic chron boundaries (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y) using combined anomaly and FZ data from both the northern and southern Pacific Plate. For rotations younger than chron 24.3o, estimates for spreading asymmetry, derived using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific, allow full stage rotations to be calculated. Between 50 and 83 Ma, where no direct constraints on spreading asymmetry are possible, a `best-fit' full stage rotation was calculated based on the net Nazca:Pacific spreading asymmetry (Pacific spreading fraction fPAC = 0.44) over the past 50 Myr, with conservative lower and upper bounds, based on variability in the degree of spreading asymmetry over periods of <15 Myr, assuming fPACs of 0.5 and 0.36, respectively. Synthetic flowlines generated from our new stage rotation produce a better match to Pacific FZ trends than previously published rotations. With the exception of the chron 18o-20o rotation, the six stage poles for rotations between chrons 33y and 13y (74-33 Ma) all cluster tightly at 60-75°E, 60-68°N, consistent with the relatively constant trend of the major Pacific FZs. This stability spans at least one episode of Farallon Plate fragmentation caused by subduction of PFR segments beneath the Americas, at 55-48 Ma, which appears to have greatly accelerated divergence on the surviving ridge without significantly affecting the location of the instantaneous rotation pole. Together with quasi-periodic 15-20 Myr variations in the degree of spreading asymmetry that also appear to correlate with changes in spreading rate, this indicates that forces other than slab pull may be a factor in determining Pacific-Farallon Plate motions.

Rowan, Christopher J.; Rowley, David B.

2014-06-01

299

Estimation of hydrothermal deposits location from magnetization distribution and magnetic properties in the North Fiji Basin  

NASA Astrophysics Data System (ADS)

The North Fiji Basin is belong to one of the youngest basins of back-arc basins in the southwest Pacific (from 12 Ma ago). We performed the marine magnetic and the bathymetry survey in the North Fiji Basin for finding the submarine hydrothermal deposits in April 2012. We acquired magnetic and bathymetry datasets by using Multi-Beam Echo Sounder EM120 (Kongsberg Co.) and Overhouser Proton Magnetometer SeaSPY (Marine Magnetics Co.). We conducted the data processing to obtain detailed seabed topography, magnetic anomaly, reduce to the pole(RTP), analytic signal and magnetization. The study areas composed of the two areas(KF-1(longitude : 173.5 ~ 173.7 and latitude : -16.2 ~ -16.5) and KF-3(longitude : 173.4 ~ 173.6 and latitude : -18.7 ~ -19.1)) in Central Spreading Ridge(CSR) and one area(KF-2(longitude : 173.7 ~ 174 and latitude : -16.8 ~ -17.2)) in Triple Junction(TJ). The seabed topography of KF-1 existed thin horst in two grabens that trends NW-SE direction. The magnetic properties of KF-1 showed high magnetic anomalies in center part and magnetic lineament structure of trending E-W direction. In the magnetization distribution of KF-1, the low magnetization zone matches well with a strong analytic signal in the northeastern part. KF-2 area has TJ. The seabed topography formed like Y-shape and showed a high feature in the center of TJ. The magnetic properties of KF-2 displayed high magnetic anomalies in N-S spreading ridge center and northwestern part. In the magnetization distribution of KF-2, the low magnetization zone matches well with a strong analytic signal in the northeastern part. The seabed topography of KF-3 presented a flat and high topography like dome structure at center axis and some seamounts scattered around the axis. The magnetic properties of KF-3 showed high magnetic anomalies in N-S spreading ridge center part. In the magnetization of KF-2, the low magnetization zone mismatches to strong analytic signal in this area. The difference of KF-3 between the low magnetization zones and the analytic signals is considered that the submarine magnetic strength of KF-3 is lower than that of KF-1 and KF-2. The spreading ridges of the study areas showed common Central Anomaly Magnetization Highs (CAMH). As a whole, the previous studies on the structure of this study area (Auzende et al, 1990) support our results of the magnetic properties (Magnetic Anomaly and RTP). We can expect to have the better results by comparing with the other study like geophysics (seismic), geology, and geochemistry in this area. Reference Auzende, J.M., and 29 others, Active Spreading and Hydrothermalism in North Fiji Basin(SW Pacific). Results of Japanese French Cruise Kaiyo 87, Marine Geophysical Researches., 12, 269-283, 1990.

Choi, S.; Kim, C.; Park, C.; Kim, H.

2013-12-01

300

A new theory for interface spreading  

E-print Network

A new theory for interface spreading during sedimentation of monodisperse suspensions of spheres has been developed. Employing no adjustable parameters, it compares well with new data obtained using magnetic resonance imaging....

Puthran, Hansraj Nagappa

2012-06-07

301

High Occurrence of Aberrant Lymph Node Spread on Magnetic Resonance Lymphography in Prostate Cancer Patients With a Biochemical Recurrence After Radical Prostatectomy  

SciTech Connect

Purpose: To investigate the pattern of lymph node spread in prostate cancer patients with a biochemical recurrence after radical prostatectomy, eligible for salvage radiotherapy; and to determine whether the clinical target volume (CTV) for elective pelvic irradiation in the primary setting can be applied in the salvage setting for patients with (a high risk of) lymph node metastases. Methods and Materials: The charts of 47 prostate cancer patients with PSA recurrence after prostatectomy who had positive lymph nodes on magnetic resonance lymphography (MRL) were reviewed. Positive lymph nodes were assigned to a lymph node region according to the guidelines of the Radiation Therapy Oncology Group (RTOG) for delineation of the CTV for pelvic irradiation (RTOG-CTV). We defined four lymph node regions for positive nodes outside this RTOG-CTV: the para-aortal, proximal common iliac, pararectal, and paravesical regions. They were referred to as aberrant lymph node regions. For each patient, clinical and pathologic features were recorded, and their association with aberrant lymph drainage was investigated. The distribution of positive lymph nodes was analyzed separately for patients with a prostate-specific antigen (PSA) <1.0 ng/mL. Results: MRL detected positive aberrant lymph nodes in 37 patients (79%). In 20 patients (43%) a positive lymph node was found in the pararectal region. Higher PSA at the time of MRL was associated with the presence of positive lymph nodes in the para-aortic region (2.49 vs. 0.82 ng/mL; p = 0.007) and in the proximal common iliac region (1.95 vs. 0.59 ng/mL; p = 0.009). There were 18 patients with a PSA <1.0 ng/mL. Ten of these patients (61%) had at least one aberrant positive lymph node. Conclusion: Seventy-nine percent of the PSA-recurrent patients had at least one aberrant positive lymph node. Application of the standard RTOG-CTV for pelvic irradiation in the salvage setting therefore seems to be inappropriate.

Meijer, Hanneke J.M., E-mail: H.Meijer@rther.umcn.nl [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Lin, Emile N. van [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Debats, Oscar A. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Witjes, J. Alfred [Department of Urology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Span, Paul N.; Kaanders, Johannes H.A.M. [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Barentsz, Jelle O. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands)

2012-03-15

302

Dynamic Diffusion Magnetic Resonance Imaging of Infarct Formation and Peri-infarct Spreading Depression after Middle Cerebral Artery Occlusion (MCAO) in macacca fasicularis  

PubMed Central

Dynamic diffusion MRI was used to visualize hyperacute stroke formation in the brain of a cynomolgus macaque. Under fluoroscopic guidance, a microcatheter was placed into the middle cerebral artery (MCA). The animal was immediately transferred to a 1.5T clinical scanner. Dynamic T2-weighted imaging during bolus injection of Oxygen-17 enriched water through the microcatheter mapped out the territory perfused by the MCA segment. Serial diffusion measurements were made using diffusion-weighted echo-planar imaging, with a temporal resolution of 15 seconds, during injection of a glue embolus into the microcatheter. The apparent diffusion coefficient declined within the lesion core. A wave of transient diffusion decline spread through peripheral uninvolved brain immediately following stroke induction. The propagation speed and pattern is consistent with spreading peri-infarct depolarizations (PID). The detection of PIDs following embolic stroke in a higher nonhuman primate brain supports the hypothesis that spreading depressions may occur following occlusive stroke in humans. PMID:22253657

D'Arceuil, Helen E; de Crespigny, Alex

2011-01-01

303

Seismicity and active tectonic processes in the ultra-slow spreading Lena Trough, Arctic Ocean  

NASA Astrophysics Data System (ADS)

With its remote location in the ice-covered Fram Strait, Lena Trough is a poorly known segment of the global mid-ocean ridge system. It is a prominent member of the ultra-slow spreading mid-ocean ridges but its spreading mechanisms are not well understood. We relocalized teleseismically recorded earthquakes from the past five decades to identify tectonic processes in Lena Trough and the adjacent Spitsbergen Fracture Zone (FZ). During two cruises with RV Polarstern in 2008 and 2009 we deployed seismic arrays on ice floes to record the local seismicity of Lena Trough. We could identify and localize microseismic events which we assume to be present in the entire rift valley. In contrast, our relocalization of teleseismically recorded earthquakes shows an asymmetric epicentre distribution along Lena Trough with earthquakes occurring predominately along the western valley flanks of Lena Trough. In 2009 February/March, several high-magnitude earthquakes peaking in an Mb 6.6 event occurred in an outside-corner setting of the Spitsbergen FZ. This is the strongest earthquake which has ever been recorded in Fram Strait and its location at the outside-corner high of the ultra-slow spreading ridge is exceptional. Comparing the seismicity with the magnetic anomalies and high-resolution multibeam bathymetry, we divide Lena Trough in a symmetrically spreading northern part and an asymmetrically spreading southern part south of the South Lena FZ. We propose that a complex interaction between the former De Geer Megashear zone, which separated Greenland from Svalbard starting at Late Mesozoic/Early Cenozoic times, and the developing rift in the southern Lena Trough resulted an increasing eastward dislocation towards the Spitsbergen FZ between older spreading axes and the recent active spreading axis which we believe to be located west of the bathymetric rift valley flanks in a wide extensional plain.

Läderach, C.; Schlindwein, V.; Schenke, H.-W.; Jokat, W.

2011-03-01

304

Cervical meningocele and associated spinal anomalies.  

PubMed

Simple meningoceles are infrequent forms of dysraphism and are often benign. They have been associated with other spinal anomalies. The uncommon cervical meningocele may have a higher propensity to be associated with other spinal anomalies. Four patients with cervical meningocele are presented with radiographic evaluation and clinical course. Multiple abnormalities were documented radiographically and operatively, including hydrocephalus, Chiari malformation, hydromyelia, lipomeningomyelocele, tethered cord, thickened filum terminale, diastematomyelia, Klippel-Feil syndrome, and thoracic hemivertebrae. Prior to the development of any late neurological abnormality from associated spinal anomalies, magnetic resonance imaging is recommended early in a child born with a simple meningocele. PMID:3652068

Delashaw, J B; Park, T S; Cail, W M; Vollmer, D G

1987-01-01

305

Analysis of spacecraft anomalies  

NASA Technical Reports Server (NTRS)

The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable.

Bloomquist, C. E.; Graham, W. C.

1976-01-01

306

Quantum Spread Spectrum Communication  

SciTech Connect

We show that communication of single-photon quantum states in a multi-user environment is improved by using spread spectrum communication techniques. We describe a framework for spreading, transmitting, despreading, and detecting single-photon spectral states that mimics conventional spread spectrum techniques. We show in the cases of inadvertent detection, unintentional interference, and multi-user management, that quantum spread spectrum communications may minimize receiver errors by managing quantum channel access.

Humble, Travis S [ORNL

2011-01-01

307

Anomaly detection using topology  

NASA Astrophysics Data System (ADS)

In this paper we present a new topology-based algorithm for anomaly detection in dimensionally large datasets. The motivating application is hyperspectral imaging where the dataset can be a collection of ~ 10 6 points in R k, representing the reflected (or radiometric) spectra of electromagnetic radiation. The algorithm begins by building a graph whose edges connect close pairs of points. The background points are the points in the largest components of this graph and all other points are designated as anomalies. The anomalies are ranked according to their distance to the background. The algorithm is termed Topological Anomaly Detection (TAD). The algorithm is tested on hyperspectral imagery collected with the HYDICE sensor which contains targets of known reflectance and spatial location. Anomaly maps are created and compared to results from the common anomaly detection algorithm RX. We show that the TAD algorithm performs better than RX by achieving greater separation of the anomalies from the background for this dataset.

Basener, Bill; Ientilucci, Emmett J.; Messinger, David W.

2007-04-01

308

Is the Accrual Anomaly a Global Anomaly?  

E-print Network

This paper investigates the subsequent return implications of accruals within a sample of large, developed, international equity markets and assesses whether similar institutional features account for the accrual anomaly ...

LaFond, Ryan

2005-09-23

309

Anomalies in the polariton dynamics of a one-dimensional magnetic photonic crystal with antiferromagnetic interlayer ordering in an external DC electric field  

SciTech Connect

The effect of an external dc electric field on the electrodynamic properties of a one-dimensional magnetic photonic crystal (MPC) with antiferromagnetic interlayer ordering is analyzed within the effective-medium method with regard to the quadratic magneto-optical interaction. The magnetizations of adjacent tangentially magnetized ferromagnetic layers are antiparallel. In particular, the effect of a magnetic compensation point on the character of polariton dynamics in this type of MPCs is revealed.

Kulagin, D. V.; Savchenko, A. S.; Tarasenko, S. V., E-mail: s.v.tarasenko@mail.r [National Academy of Sciences of Ukraine, Galkin Institute of Physics and Technology (Ukraine); Shavrov, V. G. [Russian Academy of Sciences, Kotel'nikov Institute of Radio Engineering and Electronics (Russian Federation)

2010-02-15

310

Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge - results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor  

NASA Astrophysics Data System (ADS)

We investigate the magnetic signature of ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myr, exhumed large areas of mantle-derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62° E and 65° E. We show that, despite an ultra-slow spreading rate, volcanic areas within robust magmatic segments are characterized by well-defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.

Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.

2014-05-01

311

Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge: results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor  

NASA Astrophysics Data System (ADS)

We investigate the magnetic signature of an ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myrs, exhumed large areas of mantle derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62° E and 65° E. We show that, despite an ultraslow spreading rate, volcanic areas within robust magmatic segments are characterized by well defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.

Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.

2013-12-01

312

Magnetization of the oceanic crust: TRM or CRM?  

NASA Technical Reports Server (NTRS)

A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.

Raymond, C. A.; Labrecque, J. L.

1987-01-01

313

Congenital Anomalies in Bulgaria  

Microsoft Academic Search

The paper presents data and analysis concerning congenital anomalies in Bulgaria. Assessment is based on statistical data\\u000a reported in the National Statistical Institute Yearbook: Health Protection and the Sofia registry of congenital anomalies\\u000a in the period 1996 – 1999. Forty subgroups of isolated congenital anomalies and congenital diseases, detectable at birth during\\u000a in the first year of life, have been

E. Terlemesian; S. Stoyanov

314

Spread spectrum goes commercial  

Microsoft Academic Search

The use of spread-spectrum techniques to achieve more efficient utilization of available frequency spectra is examined. The two main spread-spectrum techniques, direct sequence and frequency hopping, are explained. In frequency hopping, the transmitter repeatedly changes (hops) the carrier frequency from one frequency to another. Direct-sequence transmission spreads the spectrum not by periodically changing the frequency but by modulating the original

D. L. Schilling; R. L. Pickholtz; L. B. Milstein

1990-01-01

315

How Leaky Are Seafloor Spreading Center Axes?  

NASA Astrophysics Data System (ADS)

Some 500 active vent sites, both focused and diffuse, have now been located along spreading centers by either visual confirmation or instrumental detection of the discharging plume. Discovery of the large majority of these sites was made easier by high-volume discharge of particle-laden plumes. These observations led to estimates (as can be derived from the InterRidge Vents Database) of site frequency from ~0.5-5/100 km, generally increasing with spreading rate. Over the last decade, however, the increasing use of oxidation-reduction potential (ORP (mV)) (aka Eh) sensors capable of detecting minute concentrations of reduced hydrothermal chemicals (e.g., Fe+2, sulfides, Mn+2, H2, and others) suggests that these frequency estimates may be far too conservative. This hypothesis is consistent with earlier results from a few large-scale, high-resolution camera tows on some EPR segments. ORP data provide two important advantages for site identification not available with other commonly used continuously recording sensors: (1) detection of low-temperature, particle-scarce plumes, and (2) detection of reduced chemical species with very short residence times, thus increasing the location specificity of the discharge source. Here, we present high-resolution distributions of ORP anomalies observed in past plume surveys along the Eastern Lau Spreading Center (19.5°-22.5°S) in 2004 and 2008, the Galápagos Spreading Center (94.6°-86°W) in 2005/6 and 2011, as well as new data (2011) from the East Pacific Rise (9°-10°N). Except for the 2011 GSC data (a standard CTD tow-yo), all data were collected during continuous horizontal tows of ORP sensors at various depths <~120 m above the seafloor. We used two approaches to verify that ORP anomalies were authentic hydrothermal signals and not (especially in the case of small anomalies) produced by some other transient chemical anomaly. First, on the 2008 ELSC and 2011 EPR tows we compared temperature (?T) and ORP (?ORP) data from the two deepest sensors on each tow. Although temperature anomalies (?T°C) rarely exceeded 0.1°C, all sensors showed a positive correlation between ?ORP and ?T (ELSC, 1569 & 1493 mV/°C, r2~0.4; EPR, 1760 & 986 mV/°C, r2~0.6). Second, comparison of tows conducted days and years apart regularly detected anomalies at the same locations. While an exact enumeration of all sites is impossible from water column data alone, we estimate ~20 sites along 115 km of the EPR (17.5/100 km), ~40 sites along 425 km of the ELSC (9.4/100 km), and ~50 sites along 900 km of the GSC (5.5/100km). Anomalies <~1 km apart are considered as from the same source. For the EPR and ELSC surveys, these frequencies are considerably higher than expected for ridges of similar spreading rate. The higher frequencies reported here more closely match results from visual vent-mapping along 128 km of the EPR at 9°-10°N and 17°-18°S.The lower site frequency along the GSC is consistent with plume data on other ridges influenced by hotspot thermal anomalies. The aggregate mass flux of discharges from numerous small sites is unknown, and could be significant; in any case, these sites may be vital oases for hydrothermal biota.

Baker, E. T.; Resing, J. A.; Martinez, F.; Haymon, R. M.; Nakamura, K.; Walker, S. L.; Ferrini, V.

2013-12-01

316

Hot Flow Anomalies at Venus  

NASA Technical Reports Server (NTRS)

We present a multi-instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.

Collinson, G. A.; Sibeck, David Gary; Boardsen, Scott A.; Moore, Tom; Barabash, S.; Masters, A.; Shane, N.; Slavin, J.A.; Coates, A.J.; Zhang, T. L.; Sarantos, M.

2012-01-01

317

PHYSICAL REVIEW B 86, 174104 (2012) Infrared phonon anomaly and magnetic excitations in single-crystal Cu3Bi(SeO3)2O2Cl  

E-print Network

responses.2,3 In addition, the ability to synthesize geometrically frustrated magnetic materials is a geometrically frustrated layered material possessing magnetic order. P. Millet et al.4 determined the room.1103/PhysRevB.86.174104 PACS number(s): 63.20.D- I. INTRODUCTION Geometrically frustrated materials

Tanner, David B.

318

Magnetic investigations  

SciTech Connect

Air and ground magnetic anomalies in the Climax stock area of the NTS help define the gross configuration of the stock and detailed configuration of magnetized rocks at the Boundary and Tippinip faults that border the stock. Magnetizations of geologic units were evaluated by measurements of magnetic properties of drill core, minimum estimates of magnetizations from ground magnetic anomalies for near surface rocks, and comparisons of measured anomalies with anomalies computed by a three-dimensional forward program. Alluvial deposits and most sedimentary rocks are nonmagnetic, but drill core measurements reveal large and irregular changes in magnetization for some quartzites and marbles. The magnetizations of quartz monzonite and granodiorite near the stock surface are weak, about 0.15 A/m, and increase at a rate of 0.00196 A/m/m to 1.55 A/m, at depths greater than 700 m (2300 ft). The volcanic rocks of the area are weakly magnetized. Aeromagnetic anomalies 850 m (2800 ft) above the stock are explained by a model consisting of five vertical prisms. Prisms 1, 2, and 3 represent the near surface outline of the stock, prism 4 is one of the models developed by Whitehill (1973), and prism 5 is modified from the model developed by Allingham and Zietz (1962). Most of the anomaly comes from unsampled and strongly-magnetized deep sources that could be either granite or metamorphosed sedimentary rocks. 48 refs., 23 figs., 3 tabs.

Bath, G.D.; Jahren, C.E.; Rosenbaum, J.G. [Geological Survey, Denver, CO (USA); Baldwin, M.J. [Fenix and Scisson, Inc., Mercury, NV (USA)

1983-12-31

319

Perspectives on spreading depression  

Microsoft Academic Search

Spreading depression (SD) consists of a transient suppression of all neuronal activity that spreads slowly across regions of gray matter. The paper is divided into three parts. Martins-Ferreira describes 30 years of research on SD in the isolated retina. Much of this work has relied on the prominent intrinsic optical signals that accompany SD in the retina. By inducing SD

Hiss Martins-Ferreira; Maiken Nedergaard; Charles Nicholson

2000-01-01

320

North Cascades Geology: Sea-Floor Spreading  

NSDL National Science Digital Library

This site contains information about discoveries made after World War II when ocean-going geologists adapted sensitive magnetometers developed for antisubmarine warfare for use in seafloor research. This modern technology gave geologists their greatest boost in more than a century of field work and led to the idea of sea floor spreading. This site has animations showing sea-floor spreading and a magnetometer discovering magnetic strips. There are also diagrams showing the magnetic pattern on the ocean floor at the Juan de Fuca Ridge, Benioff-Wadati zones at continental margins, and an idealized representation of divergent plates with a resulting subduction zone.

321

Table of hyperfine anomaly in atomic systems  

SciTech Connect

This table is a compilation of experimental values of magnetic hyperfine anomaly in atomic and ionic systems. The last extensive compilation was published in 1984 by Büttgenbach [S. Büttgenbach, Hyperfine Int. 20 (1984) 1] and the aim here is to make an up to date compilation. The literature search covers the period up to January 2011.

Persson, J.R., E-mail: jonas.persson@ntnu.no

2013-01-15

322

The anomaly data base of screwworm information  

NASA Technical Reports Server (NTRS)

Standard statistical processing of anomaly data in the screwworm eradication data system is possible from data compiled on magnetic tapes with the Univac 1108 computer. The format and organization of the data in the data base, which is also available on dedicated disc storage, are described.

Giddings, L. E.

1976-01-01

323

Table of hyperfine anomaly in atomic systems  

NASA Astrophysics Data System (ADS)

This table is a compilation of experimental values of magnetic hyperfine anomaly in atomic and ionic systems. The last extensive compilation was published in 1984 by Büttgenbach [S. Büttgenbach, Hyperfine Int. 20 (1984) 1] and the aim here is to make an up to date compilation. The literature search covers the period up to January 2011.

Persson, J. R.

2013-01-01

324

Table of hyperfine anomaly in atomic systems  

E-print Network

This table is a compilation of experimental values of magnetic hyperfine anomaly in atomic and ionic systems. The last extensive compilation was published in 1984 by Buttgenbach (Hyperfine Interactions 20, (1984) p 1) and the aim here is to make an up to date compilation. The literature search covers the period to January 2011.

Jonas R. Persson

2011-10-27

325

Flame Spread Across Liquids  

NASA Technical Reports Server (NTRS)

The principal goal of our recent research on flame spread across liquid pools is the detailed identification of the mechanisms that control the rate and nature of flame spread when the liquid pool is initially at an isothermal bulk temperature that is below the fuel's flash point temperature. In our project, we specialize the subject to highlight the roles of buoyancy-related processes regarding the mechanisms of flame spread, an area of research cited recently by Linan and Williams as one that needs further attention and which microgravity (micro-g) experiments could help to resolve. Toward resolving the effects of buoyancy on this flame spread problem, comparisons - between 1-g and micro-g experimental observations, and between model predictions and experimental data at each of these gravitational levels - are extensively utilized. The present experimental and computational foundation is presented to support identification of the mechanisms that control flame spread in the pulsating flame spread regime for which long-duration, micro-g flame spread experiments have been conducted aboard a sounding rocket.

Ross, Howard D.; Miller, Fletcher J.; Sirignano, William A.; Schiller, David

1997-01-01

326

Anomalies on orbifolds  

SciTech Connect

We discuss the form of the chiral anomaly on an S1/Z2 orbifold with chiral boundary conditions. We find that the 4-divergence of the higher-dimensional current evaluated at a given point in the extra dimension is proportional to the probability of finding the chiral zero mode there. Nevertheless the anomaly, appropriately defined as the five dimensional divergence of the current, lives entirely on the orbifold fixed planes and is independent of the shape of the zero mode. Therefore long distance four dimensional anomaly cancellation ensures the consistency of the higher dimensional orbifold theory.

Arkani-Hamed, Nima; Cohen, Andrew G.; Georgi, Howard

2001-03-16

327

History of rift propagation and magnetization intensity for the Cocos-Nazca sspreading Center  

NASA Astrophysics Data System (ADS)

Analysis of magnetic anomaly profiles collected nearly parallel to tectonic flow lines allows detailed interpretation of the complicated tectonic history of the Cocos-Nazca spreading center. Forward models of the magnetic anomalies accounting for spreading rate variations, ridge jumps, asymmetric spreading, magnetization intensity variations, and bathymetry show excellent agreement with observed anomalies. Spreading rates can be constrained to a common finite rotation history through anomaly 4A with three changes in rates. Rate changes at about 1.5 Ma and 4.1 Ma correspond to changes in rate gradients and occur during the well-calibrated part of the reversal timescale, so they can unquestionably be identified as true changes in plate motion. A ˜15% rate decrease at about 5.2 Ma could be interpreted either as a change in plate motion or as an artifact of poor calibration of the older part of the timescale. The change at 4.1 Ma is especially important because many timescales are based on the assumption of constant spreading rate for this plate pair for 0-6 Ma. Rift propagation has played a dominant role in the continuous reorganization of the geometry of the ridge axis. Propagation has been predominantly away from the hotspot, with jumps predominantly south-ward. Propagation rates have ranged from 30 to 120 mm/yr, commonly near 70 mm/yr. Origin of most propagation sequences is difficult to interpret, but many appear to involve discrete southward ridge jumps forming a new segment near the hotspot. Magnetic anomaly amplitude appears to be a reliable tracer of Fe content of lavas. Several generalizations can be drawn about along-axis variations in magnetization intensities since 8 Ma: high magnetizations are only observed at the far ends (relative to the Galapagos hotspot) of segments at least 150 km long; offset at the end of a high-magnetization segment is at least 15 km; and there are no offsets larger than 30-45 km between high-magnetization segments and the reconstructed position of the hotspot. We interpret these patterns to indicate that fractionated lavas erupt where gradients in magma supply cause along-axis flow of evolved magma. The gradients in supply result from subaxial flow of hotspot-derived asthenosphere in a narrow conduit. This flow is only partly obstructed by an offset of 20-30 km but entirely blocked by an offset of 50 km.

Wilson, Douglas S.; Hey, Richard N.

1995-06-01

328

Isotopic Anomalies in CP Stars: Helium, Mercury, Platinum, and Calcium  

E-print Network

We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, non-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.

Cowley, C R; Castelli, F

2007-01-01

329

Isotopic Anomalies in CP Stars: Helium, Mercury, Platinum, and Calcium  

E-print Network

We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, non-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.

C. R. Cowley; S. Hubrig; F. Castelli

2007-11-15

330

Deep crustal structure of the northeastern Gulf of Mexico: Implications for rift evolution and seafloor spreading  

NASA Astrophysics Data System (ADS)

image deep crustal structure using marine seismic refraction data recorded by a linear array of ocean-bottom seismometers in the Gulf of Mexico Basin Opening project (GUMBO Line 3) in order to provide new constraints on the nature of continental and oceanic crust in the northeastern Gulf of Mexico. GUMBO Line 3 extends ~524 km from the continental shelf offshore Pensacola, Florida, across the De Soto Canyon and into the central Gulf basin. Travel times from long offset, wide angle reflections and refractions resolve compressional seismic velocities and layer boundaries for sediment, crystalline crust, and upper mantle. We compare our results with coincident multichannel seismic reflection data. Our velocity model recovers shallow seismic velocities (~2.0-4.5 km/s) that we interpret as evaporites and clastic sediments. A Cretaceous carbonate platform is interpreted beneath the De Soto Canyon with seismic velocities >5.0 km/s. Crystalline continental crust thins seaward along GUMBO Line 3 from 23-10 km across the De Soto Canyon. High seismic velocity lower crust (>7.2 km/s) is interpreted as extensive syn-rift magmatism and possibly mafic underplating, common features at volcanic rift margins with high mantle potential temperatures. In the central Gulf basin we interpret thick oceanic crust (>8 km) emplaced at a slow full-spreading rate (~24 mm/yr). We suggest a sustained thermal anomaly during slow seafloor-spreading conditions led to voluminous basalt flows from a spreading ridge that overprinted seafloor magnetic anomalies in the northeastern Gulf of Mexico.

Eddy, Drew R.; Van Avendonk, Harm J. A.; Christeson, Gail L.; Norton, Ian O.; Karner, Garry D.; Johnson, Christopher A.; Snedden, John W.

2014-09-01

331

The QCD trace anomaly  

E-print Network

In this brief report we compare the predictions of a recent next-to-next-to-leading order hard-thermal-loop perturbation theory (HTLpt) calculation of the QCD trace anomaly to available lattice data. We focus on the trace anomaly scaled by T^2 in two cases: N_f=0 and N_f=3. When using the canonical value of mu = 2 pi T for the renormalization scale, we find that for Yang-Mills theory (N_f=0) agreement between HTLpt and lattice data for the T^2-scaled trace anomaly begins at temperatures on the order of 8 T_c while when including quarks (N_f=3) agreement begins already at temperatures above 2 T_c. In both cases we find that at very high temperatures the T^2-scaled trace anomaly increases with temperature in accordance with the predictions of HTLpt.

Jens O. Andersen; Lars E. Leganger; Michael Strickland; Nan Su

2011-06-02

332

How Is Mono Spread?  

MedlinePLUS

... this tool to play your goals. Hot Topics Ebola: The Facts How to Make Sense of Health News Anxiety Disorders Relaxation Exercises The Flu Vaccine How Is Mono Spread? KidsHealth > Teens > Q&A > Mononucleosis > How Is Mono ...

333

Sea Floor Spreading I  

NSDL National Science Digital Library

In this introductory Excel tutorial (Activity I) students use Excel to explore the geodynamics model equation for ocean depth around a sea-floor spreading center. For students with no prior Excel experience.

Activity And Starting Point Page By R.m. Mackay. Clark College, Physics A.

334

Was the Midcontinent Rift part of a successful seafloor-spreading episode?  

NASA Astrophysics Data System (ADS)

~1.1 Ga Midcontinent Rift (MCR), the 3000 km long largely buried feature causing the largest gravity and magnetic anomaly within the North American craton, is traditionally considered a failed rift formed by isolated midplate volcanism and extension. We propose instead that the MCR formed as part of the rifting of Amazonia (Precambrian northeast South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established. A cusp in Laurentia's apparent polar wander path near the onset of MCR volcanism, recorded by the MCR's volcanic rocks, likely reflects the rifting. This scenario is suggested by analogy with younger rifts elsewhere and consistent with the MCR's extension to northwest Alabama along the East Continent Gravity High, southern Appalachian rocks having Amazonian affinities, and recent identification of contemporaneous large igneous provinces in Amazonia.

Stein, Carol A.; Stein, Seth; Merino, Miguel; Randy Keller, G.; Flesch, Lucy M.; Jurdy, Donna M.

2014-03-01

335

Complex lymphatic anomalies.  

PubMed

Complex lymphatic anomalies include several diagnoses with overlapping patterns of clinical symptoms, anatomic location, imaging features, hematologic alterations, and complications. Lymphatic malformations likely arise through anomalous embryogenesis of the lymphatic system. Analysis of clinical, imaging, histologic, and hematologic features is often needed to reach a diagnosis. Aspiration of fluid collections can readily define fluid as chylous or not. The presence of chyle indicates dysfunction at the mesenteric or retroperitoneal level or above the cisterna chyli due to reflux. The imaging patterns of generalized lymphatic anomaly (GLA) and Gorham-Stout disease have been segregated with distinctive bone lesions and peri-osseous features. More aggressive histology (spindled lymphatic endothelial cells), clinical progression, hemorrhage, or moderate hematologic changes should raise suspicion for kaposiform lymphangiomatosis. Biopsy may be needed for diagnosis, though avoidance of rib biopsy is advised to prevent iatrogenic chronic pleural effusion. Lymphangiography can visualize the anatomy and function of the lymphatic system and may identify dysfunction of the thoracic duct in central conducting lymphatic anomalies. Local control and symptom relief are targeted by resection, laser therapy, and sclerotherapy. Emerging data suggest a role for medical therapies for complications of complex lymphatic anomalies. Outcomes include recurrent effusion, infection, pain, fracture, mortality, and rarely, malignancy. Complex lymphatic anomalies present significant diagnostic and therapeutic challenges. Results from a phase 2 study of sirolimus in these and other conditions are expected in 2014. Improved characterization of natural history, predictors of poor outcomes, responses to therapy, and further clinical trials are needed for complex lymphatic anomalies. PMID:25241096

Trenor, Cameron C; Chaudry, Gulraiz

2014-08-01

336

On isostatic geoid anomalies  

NASA Technical Reports Server (NTRS)

In regions of slowly varying lateral density changes, the gravity and geoid anomalies may be expressed as power series expansions in topography. Geoid anomalies in isostatically compensated regions can be directly related to the local dipole moment of the density-depth distribution. This relationship is used to obtain theoretical geoid anomalies for different models of isostatic compensation. The classical Pratt and Airy models give geoid height-elevation relationships differing in functional form but predicting geoid anomalies of comparable magnitude. The thermal cooling model explaining ocean floor subsidence away from mid-ocean ridges predicts a linear age-geoid height relationship of 0.16 m/m.y. Geos 3 altimetry profiles were examined to test these theoretical relationships. A profile over the mid-Atlantic ridge is closely matched by the geoid curve derived from the thermal cooling model. The observed geoid anomaly over the Atlantic margin of North America can be explained by Airy compensation. The relation between geoid anomaly and bathymetry across the Bermuda Swell is consistent with Pratt compensation with a 100-km depth of compensation.

Haxby, W. F.; Turcotte, D. L.

1978-01-01

337

Seafloor spreading in the North Fiji Basin (Southwest Pacific)  

NASA Astrophysics Data System (ADS)

The Seapso Leg 3 cruise (December, 1985) was carried out in the North Fiji Basin aboard the IFREMER R.V. "Jean Charcot". The main purpose of the cruise was to carry out a geophysical and geological study of the central part of the basin between 16° S and 22°S. To this end. bathymetric profiles (with the help of the Seabeam multichannel echosounder), single-channel seismic reflection profiles and magnetic and gravimetric profiles were made. Moreover, geological samples were taken (by dredging and piston coring) as well as water samples (with the help of a multiprobe). One of the aims of the cruise was to explore the present-day spreading axis of the North Fiji Basin. We were able to show that accretion (the rate of which is about 7 cm/yr) in the North Fiji Basin has been constrained in a N-S direction for 3 Ma. Very recently, between 0.6 and 0.7 Ma ago, the accretion process changed, resulting in the creation of a ridge-ridge-trench triple junction centered at 173°30'E and 16°40'S. Water samples taken in the vicinity of this triple junction show significant anomalies of methane and manganese, which are probably linked to hydrothermal events. In its morphological characteristics (transversal as well as longitudinal) the ridge of the North Fiji Basin shows striking similarities to the East Pacific Rise. It presents the same differences in level, the same sizes of structures and the same particular features (overlapping spreading centers, offsets, etc.). Another aim of the SEAPSO cruise was to study the complex deformation area located immediately to the west of the Fiji Islands, which we interpret as a distensive type deformation in a strike-slip system.

Auzende, J. M.; Rissen, J. P.; Lafoy, Y.; Gente, P.; Charlou, J. L.

1988-01-01

338

Magnetic order and lattice anomalies in the J{sub 1}-J{sub 2} model system VOMoO{sub 4}  

SciTech Connect

High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO{sub 4}. Below {approx_equal}40 K the system orders in a simple Neel antiferromagnetic state (propagation vector k-vector=0), indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 (1) {mu}{sub B}/V{sup 4+} at 2 K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations.

Bombardi, A. [Diamond Light Source Ltd., Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Chapon, L.C. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Margiolaki, I.; Mazzoli, C. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex 9 (France); Gonthier, S.; Duc, F. [Centre d'Elaboration des Materiaux et d'Etudes Structurales, CNRS, 31055 Toulouse Cedex (France); Radaelli, P.G. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

2005-06-01

339

Strictly anomaly mediated supersymmetry breaking  

NASA Astrophysics Data System (ADS)

We consider an extension of the minimal supersymmetric Standard Model with anomaly mediation as the only source of supersymmetry breaking, and the tachyonic slepton problem solved by a gauged U(1) symmetry. The extra gauge symmetry is broken at high energies in a manner preserving supersymmetry, while also introducing both the seesaw mechanism for neutrino masses, and the Higgs ?-term. We call the model strictly anomaly mediated supersymmetry breaking. We present typical spectra for the model and compare them with those from so-called minimal anomaly mediated supersymmetry breaking. We find a Standard Model-like Higgs of mass 125 GeV with a gravitino mass of 140 TeV and tan??=16. However, the muon anomalous magnetic moment is 3? away from the experimental value. The model naturally produces a period of hybrid inflation, which can exit to a false vacuum characterized by large Higgs vacuum expectation values, reaching the true ground state after a period of thermal inflation. The scalar spectral index is reduced to approximately 0.975, and the correct abundance of neutralino dark matter can be produced by decays of thermally produced gravitinos, provided the gravitino mass (and hence the Higgs mass) is high. Naturally light cosmic strings are produced, satisfying bounds from the cosmic microwave background. The complementary pulsar timing and cosmic ray bounds require that strings decay primarily via loops into gravitational waves. Unless the loops are extremely small, the next generation pulsar timing array will rule out or detect the string-derived gravitational radiation background in this model.

Hindmarsh, Mark; Jones, D. R. Timothy

2013-04-01

340

The spreading of disorder.  

PubMed

Imagine that the neighborhood you are living in is covered with graffiti, litter, and unreturned shopping carts. Would this reality cause you to litter more, trespass, or even steal? A thesis known as the broken windows theory suggests that signs of disorderly and petty criminal behavior trigger more disorderly and petty criminal behavior, thus causing the behavior to spread. This may cause neighborhoods to decay and the quality of life of its inhabitants to deteriorate. For a city government, this may be a vital policy issue. But does disorder really spread in neighborhoods? So far there has not been strong empirical support, and it is not clear what constitutes disorder and what may make it spread. We generated hypotheses about the spread of disorder and tested them in six field experiments. We found that, when people observe that others violated a certain social norm or legitimate rule, they are more likely to violate other norms or rules, which causes disorder to spread. PMID:19023045

Keizer, Kees; Lindenberg, Siegwart; Steg, Linda

2008-12-12

341

Clinical Features and Associated Abnormalities in Children and Adolescents With Corpus Callosal Anomalies  

PubMed Central

Callosal anomalies are frequently associated with other central nervous system (CNS) and/or somatic anomalies. We retrospectively analyzed the clinical features of corpus callosal agenesis/hypoplasia accompanying other CNS and/or somatic anomalies. We reviewed the imaging and clinical information of patients who underwent brain magnetic resonance imaging in our hospital, between 2005 and 2012. Callosal anomalies were isolated in 13 patients, accompanied by other CNS anomalies in 10 patients, associated with only non-CNS somatic anomalies in four patients, and with both CNS and non-CNS abnormalities in four patients. Out of 31 patients, four developed normally, without impairments in motor or cognitive functions. Five of nine patients with cerebral palsy were accompanied by other CNS and/or somatic anomalies, and showed worse Gross Motor Function Classification System scores, compared with the other four patients with isolated callosal anomaly. In addition, patients with other CNS anomalies also had a higher seizure risk. PMID:24639939

Kim, Young Uhk; Park, Eun Sook; Jung, Soojin; Suh, Miri; Choi, Hyo Seon

2014-01-01

342

Correlation of Tectonic Provinces of South America and the Caribbean Region with MAGSAT Anomalies  

NASA Technical Reports Server (NTRS)

Intensities of MAGSAT scalar magnetic anomaly data correlate with the main tectonic provinces of South America and the Caribbean region. Magnetic anomalies of the continents generally have higher amplitudes than oceanic anomalies. This is particularly evident in Central America and in the shield areas of South America. The Caribbean Sea and Gulf of Mexico are underlain by prominent magnetic minima. Within these oceanic areas, linear magnetic highs correlate with topographic ridges which separate the Gulf of Mexico, the Colombian Basin, and the Venezuelan Basin. The boundaries of the Caribbean plate occur along magnetic gradients which are particularly sharp along the northern and western margins of the plate, but gradational along the southern margin where they merge with the Andean Cordillera. The anomalies along the western margin of the South American plate are also distinct and appear to be separate from those of the adjacent ocean basin. Eastern South America is characterized by magnetic anomalies which commonly extend into the Atlantic Ocean.

Lidiak, E. G.; Hinze, W. J.; Keller, G. R. (principal investigators); Yuan, D. W.; Longacre, M. B.

1984-01-01

343

Spread spectrum for commercial communications  

Microsoft Academic Search

The authors describe how spread spectrum operates and explain why the FCC has allocated several spectral bands for spread spectrum. They examine what is wrong with the spectrum allocations the way they are now. They show who is using and will use spread spectrum and why. In particular, they discuss the use of spread spectrum for mobile cellular communications: the

D. L. Schilling; L. B. Milstein; R. L. Pickholtz; M. Kullback; F. Miller

1991-01-01

344

Spread spectrum image steganography  

Microsoft Academic Search

In this paper, we present a new method of digitalsteganography, entitled spread spectrum image steganography(SSIS). Steganography, which means "covered writing" in Greek,is the science of communicating in a hidden manner. Followinga discussion of steganographic communication theory and reviewof existing techniques, the new method, SSIS, is introduced. Thissystem hides and recovers a message of substantial length withindigital imagery while maintaining the

Lisa M. Marvel; Charles G. Boncelet Jr.; Charles T. Retter

1999-01-01

345

Equivalent magnetization over the World Ocean  

NASA Astrophysics Data System (ADS)

In another presentation (Hamoudi et al., this meeting), we present the construction of a new candidate for the World Digital Magnetic Anomaly Map (WDMAM) over oceanic areas. This map is based on: (a) a more realistic forward modeling of the marine magnetic anomalies which includes remanent magnetization vectors taking into account the age and motion of the oceanic lithosphere; (b) evaluation of the equivalent magnetization by comparison of the synthetic and observed anomalies along ship tracks; and (c) adjustment of the synthetic anomaly maps using this equivalent magnetization prior to merging with the observed anomalies. A by-product of this approach is a global distribution of equivalent magnetization over the World's Ocean. Note that, because no global basement map exists for the oceanic areas, we assume a uniform, 5 km-deep and 1 km-thick magnetized layer for the forward model. The resulting equivalent magnetization is therefore relative to this over-simplistic magnetic source. A first observation is that, within the hypotheses of the forward model, the average equivalent magnetization is about 3 A/m, a value which compares well with the Natural Remanent Magnetization (NRM) measured on ancient basalt samples. As expected, the mid-ocean ridges are marked by stronger equivalent magnetizations, an observation which reflects both the stronger NRM measured at ridge axes and their shallower bathymetry (not taken into account in our forward model). More interesting is the observation of significant along-axis variations. In the North Atlantic Ocean, the Kolbeinsey and Reykjanes ridges around Iceland are marked by a very strong equivalent magnetization and the Azores Plateau by a strong one as well.. Again this may reflect the combined effect of shallower seafloor, thicker and/or more magnetized basaltic layer at hotspots. In contrast, the areas between 45 and 55°N and between 0 and 10°N (Equatorial FZ) correspond to a weak equivalent magnetization. Further south, the Mid-Atlantic Ridge displays a more uniform signature, although off-axis variations seem associated to the Tristan and St Helena hotspots. In the Indian Ocean, a strong equivalent magnetization characterizes areas of hotspot-ridge interaction such as the Gulf of Aden, the Central Indian Ridge near Rodrigues Island, the Southwest Indian Ridge near Marion Island, and the Southeast Indian Ridge near St Paul and Amsterdam Islands. A weaker one is observed in colder area, at the Australian-Antarctic Discordance and around the Rodrigues Triple Junction. The Pacific Ocean is characterized by a generally stronger equivalent magnetization, both near ridges and in abyssal plains. Time variations, i.e. along seafloor spreading flowlines, are apparent across the Mid-Atlantic and Pacific-Antarctic ridges, with highs near the ridge axis (younger than 10 Ma) and between ~83 and 60 Ma, just after the Cretaceous Normal Superchron and lows between ~60 and 10 Ma. The Mesozoic basins of the Pacific and Atlantic oceans show a weaker equivalent magnetization before ~155 Ma and a stronger one after. Basins covered by thick sediments such as the Bengal Bay, Great Australian Bight, Nova Scotia Basin, and Western Somali Basin show a very weak equivalent magnetization, reflecting both a deeper basement and a possible thermal demagnetization. Some of these variations coincide with satellite magnetic anomalies.

Dyment, J.; Hamoudi, M.; Choi, Y.; Thebault, E.; Quesnel, Y.; Roest, W. R.; Lesur, V.

2012-12-01

346

Euro-African MAGSAT anomaly-tectonic observations  

NASA Technical Reports Server (NTRS)

Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

Hinze, W. J.; Olivier, R.; Vonfrese, R. R. B.

1985-01-01

347

Euro-african MAGSAT Anomaly-tectonic Observations  

NASA Technical Reports Server (NTRS)

Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

Hinze, W. J.; Vonfrese, R. R. B. (principal investigators); Olivier, R.

1984-01-01

348

Deep-tow magnetic survey above large exhumed mantle domains of the eastern Southwest Indian ridge  

NASA Astrophysics Data System (ADS)

The recent discovery of a new type of seafloor, the "smooth seafloor", formed with no or very little volcanic activity along the ultra-slow spreading Southwest Indian ridge (SWIR) shows an unexpected complexity in processes of generation of the oceanic lithosphere. There, detachment faulting is thought to be a mechanism for efficient exhumation of deep-seated mantle rocks. We present here a deep-tow geological-geophysical survey over smooth seafloor at the eastern SWIR (62-64°N) combining magnetic data, geology mapping from side-scan sonar images and results from dredge sampling. We introduce a new type of calibration approach for deep-tow fluxgate magnetometer. We show that magnetic data can be corrected from the magnetic effect of the vehicle with no recourse to its attitude (pitch, roll and heading) but only using the 3 components recorded by the magnetometer and an approximation of the scalar intensity of the Earth magnetic field. The collected dredge samples as well as the side-scan images confirm the presence of large areas of exhumed mantle-derived peridodites surrounded by a few volcanic constructions. This allows us to hypothesis that magnetic anomalies are caused by serpentinized peridotites or magmatic intrusions. We show that the magnetic signature of the smooth seafloor is clearly weaker than the surrounding volcanic areas. Moreover, the calculated magnetization of a source layer as well as the comparison between deep-tow and sea-surface magnetic data argue for strong East-West variability in the distribution of the magnetized sources. This variability may results from fluid-rocks interaction along the detachment faults as well as from the repartition of the volcanic material and thus questions the seafloor spreading origin of the corresponding magnetic anomalies. Finally, we provide magnetic arguments, as calculation of block rotation or spreading asymmetry in order to better constrain tectonic mechanisms that occur during the formation of this peculiar seafloor.

Bronner, A.; Munschy, M.; Carlut, J. H.; Searle, R. C.; Sauter, D.; Cannat, M.

2011-12-01

349

Aeromagnetic anomalies between Yule Bay and Mertz Glacier (East Antarctica)  

NASA Astrophysics Data System (ADS)

Within the framework of a joint German-Italian Antarctic expedition (1999/2000) an aeromagnetic survey was flown along a 1000 km long corridor between Yule Bay and Mertz Glacier. Our aim is to investigate magnetic anomalies over the Lillie Glacier, Oates Coast and George V Coast survey areas to provide new insight into the northernmost Transantarctic Mountains and into its "backside", over the Wilkes Subglacial Basin. The Lillie Glacier anomaly map reveals contrasting magnetic signatures over the Late Devonian-Early Carboniferous Admiralty Intrusives of the Everett Range and of Yule Bay. A near-circular anomaly overlies the enigmatic occurrences of volcanic rocks of Unger Island and Surgeon Island granite. The Oates Coast map displays a linear magnetic anomaly over the Matusevich Glacier. It reveals mostly buried Cambro-Ordovician(?) Granite Harbour Intrusives and ultramafic rocks, associated with a major fault zone or a suture within the Wilson Terrane. Magnetic anomalies along the George V Coast indicate that the Ferrar Large Igneous Province, of Jurassic age, may extend along the northernmost edge of the Wilkes Subglacial Basin. Finally, an anomaly break close to the northwestern flank of the Wilkes Subglacial Basin, could mark the unexposed boundary between the Precambrian East Antarctic Craton and the Ross Orogen.

Damaske, D.; Ferraccioli, F.; Bozzo, E.

2003-04-01

350

A fetal autopsy case of body stalk anomaly.  

PubMed

Body stalk anomaly (BSA) is a sporadic polymalformative syndrome incompatible with extrauterine life. In utero detection of BSA by two-dimensional and three-dimensional ultrasonography and magnetic resonance imaging has been well documented. We herein describe a case of body stalk anomaly diagnosed at autopsy. The fetus had a large anterior midline abdominal wall defect with eventration of the visceral organs into the amnio-peritoneal sac and a completely absent umbilical cord. The associated anomalies included club foot, absent diaphragm, genitourinary, and gastrointestinal defects. The observed congenital anomalies supported the theory of embryonic dysgenesis as the etiologic factor. One of the major objectives in the performance of fetal autopsy is to be able to detect abnormalities that can have implications in future pregnancies. Despite the negligible familial recurrence rate of the broad spectrum of anomalies associated with this abdominal wall defect, the present case of fetal autopsy indeed delights to serve the living. PMID:19643652

Mathai, Alka Mary; Menezes, Ritesh G; Kumar, Suneet; Pai, Muktha R; Bhandary, Amritha; Fitzhugh, Valerie A

2009-09-01

351

The NEAR Rendezvous Burn Anomaly  

E-print Network

The NEAR Rendezvous Burn Anomaly of December 1998 Final Report of the NEAR (Near Earth Asteroid Report of the NEAR (Near Earth Asteroid Rendezvous) Anomaly Review Board November 1999 ©1999 The Johns .................................................................................................................................................... 4 Reconstructed Timeline

Rhoads, James

352

Spread spectrum image steganography.  

PubMed

In this paper, we present a new method of digital steganography, entitled spread spectrum image steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a discussion of steganographic communication theory and review of existing techniques, the new method, SSIS, is introduced. This system hides and recovers a message of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden message can be recovered using appropriate keys without any knowledge of the original image. Image restoration, error-control coding, and techniques similar to spread spectrum are described, and the performance of the system is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such a data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking. PMID:18267522

Marvel, L M; Boncelet, C R; Retter, C T

1999-01-01

353

Analysis and interpretation of MAGSAT anomalies over north Africa  

NASA Technical Reports Server (NTRS)

Crustal anomaly detection with MAGSAT data is frustrated by inherent resolving power of the data and by contamination from external and core fields. Quality of the data might be tested by modeling specific tectonic features which produce anomalies that fall within proposed resolution and crustal amplitude capabilities of MAGSAT fields. To test this hypothesis, north African hotspots associated with Ahaggar, Tibesti and Darfur were modeled as magnetic induction anomalies. MAGSAT data were reduced by subtracting external and core fields to isolate scalar and vertical component crustal signals. Of the three volcanic areas, only the Ahaggar region had an associated anomaly of magnitude above error limits of the data. Hotspot hypothesis was tested for Ahaggar by seeing if predicted magnetic signal matched MAGSAT anomaly. Predicted model magnetic signal arising from surface topography of the uplift and the Curie isothermal surface was calculated at MAGSAT altitudes by Fourier transform technique modified to allow for variable magnetization. Curie isotherm surface was calculated using a method for temperature distribution in a moving plate above a fixed hotspot. Magnetic signal was calculated for a fixed plate as well as a number of plate velocities and directions.

Phillips, R. J.

1985-01-01

354

Global Climate Highlights and Anomalies  

NSDL National Science Digital Library

NOAA's Global Climate Highlights and Anomalies page offers weekly summaries of global climate highlights and anomalies (warm, cold, wet, dry). Areas experiencing climate anomalies are color-marked on a global map, followed by written summaries of each region's climate conditions. All weeks are posted for the year 2000 (to present), and a link points users to the complete 1999 archive.

1999-01-01

355

Orbital studies of lunar magnetism  

NASA Technical Reports Server (NTRS)

Limitations of present lunar magnetic maps are considered. Optimal processing of satellite derived magnetic anomaly data is also considered. Studies of coastal and core geomagnetism are discussed. Lunar remanent and induced lunar magnetization are included.

Mcleod, M. G.; Coleman, P. J., Jr.

1982-01-01

356

Mass Anomalies on Ganymede  

NASA Technical Reports Server (NTRS)

Radio Doppler data from two Ganymede encounters (G1 and G2) on the first two orbits in the Galileo mission have been analyzed previously for gravity information . For a satellite in hydrostatic equilibrium, its gravitational field can be modeled adequately by a truncated spherical harmonic series of degree two. However, a fourth degree field is required in order to fit the second Galileo flyby (G2). This need for a higher degree field strongly suggests that Ganymede s gravitational field is perturbed by a gravity anomaly near the G2 closest approach point (79.29 latitude, 123.68 west longitude). In fact, a plot of the Doppler residuals , after removal of the best-fit model for the zero degree term (GM) and the second degree moments (J2 and C22), suggests that if an anomaly exists, it is located downtrack of the closest approach point, closer to the equator.

Schubert, G.; Anderson, J. D.; Jacobson, R. A.; Lau, E. L.; Moore, W. B.; Palguta, J.

2004-01-01

357

Heat flux boundary anomalies and thermal winds  

NASA Astrophysics Data System (ADS)

Several studies have shown strong effects of outer boundary heat flux patterns on the dynamo mechanism in planets. For example, the hemispherical field of the ancient Martian dynamo can be explained by a large scale sinusoidal anomaly of the core mantle boundary heat flux triggered by large scale mantle convection or giant impacts. The magnetic fields show typically the desired effect - though dynamo action is locally stronger where the underneath heat flux is higher. However, it remains an open question if these effects still apply for more realistic planetary parameters, such as vigor of the convection (Rayleigh number) or the rotation rate (Ekman). The sinusoidal variation of the CMB heat flux along the colatitude with larger heat flux in the southern and smaller in the northern hemisphere as used for Mars can lead to a concentration of magnetic field in the south. The shape of such a hemispherical dynamo matches the crustal magnetization pattern at the surface and seems therefore an admissible mode for the ancient Martian dynamo. As the consequence of the emerging latitudinal temperature gradients convection and induction are dominated by thermal winds. These zonal flows were found to be equatorial antisymmetric, axisymmetric, ageostrophic, of strong amplitude and have therefore a severe effect on core convection and especially the induction process. We measure the underlying thermal anomalies as a function of Rayleigh and Ekman number and show that they are responsible for the thermal winds. Our results suggest that temperature anomalies decrease clearly with the supercriticality of the convection due to faster stirring and mixing, but show no additional dependence on the Ekman number. Interestingly, the decline of the latitudinal temperature anomaly follows a recently suggested scaling law for the thickness of thermal boundary layers. Even though the convective supercriticality of planetary cores is rather large and therefore only a minor effect of thermal boundary disturbances is expected, we suggest thermal winds can still significantly contribute to the total kinetic energy in real planetary core.

Dietrich, Wieland; Wicht, Johannes

2013-04-01

358

Yearly Arctic Temperature Anomaly  

NSDL National Science Digital Library

This animation shows the yearly temperature anomaly over the Arctic region from 1981-82 through 2002-03. Years run from August 1 through July 31. Blue hues indicate cooling regions; red hues depict warming. Light regions indicate less change while darker regions indicate more. The temperature scale used ranges from -7.0 to +7.0 degrees Celsius in increments of .25 degrees. (See color bar below)

Starr, Cindy; Comiso, Josefino

2003-10-23

359

PREDICTING ROOT SPREAD FROM TRUNK DIAMETER AND BRANCH SPREAD  

Microsoft Academic Search

Trunk diameter and branch crown spread were linearly correlated with root spread in honey locust (Gleditsia triancamhos var. inermis), green ash (Fraxinus pennsylvanica), poplar (Populus X generosa), red maple (Acer rubrum) and southern magnolia (Magnolia grandiflora) but not in live oak (Quercus virginiana). Maximum root spread (excluding live oak) ranged from 1.68 times the dripline forash to 3.77 for magnolia.

Edward F. Gilman

1989-01-01

360

Prevent the Spread of Norovirus  

MedlinePLUS

... Submit Button CDC Features Prevent the Spread of Norovirus Language: English Español (Spanish) Share Compartir Norovirus spreads ... cramping, nausea, vomiting, and diarrhea. Anyone Can Get Norovirus Anyone can be infected with noroviruses and get ...

361

Oppositely directed pairs of propagating rifts in back-arc basins: Double saloon door seafloor spreading during subduction rollback  

NASA Astrophysics Data System (ADS)

When a continent breaks up into two plates, which then separate from each other about a rotation pole, it can be shown that if initial movement is taken up by lithospheric extension, asthenospheric breakthrough and oceanic accretion propagate toward the pole of rotation. Such a propagating rift model is then applied to an embryonic centrally located rift which evolves into two rifts propagating in opposite directions. The resultant rhombic shape of the modeled basin, initially underlain entirely by thinned continental crust, is very similar to the Oligocene to Burdigalian back-arc evolution of the Valencia Trough and the Liguro-Provencal Basin in the western Mediterranean. Existing well and seismic stratigraphic data confirm that a rift did initiate in the Gulf of Lion and propagated southwest into the Valencia Trough. Similarly, seismic refraction, gravity, and heat flow data demonstrate that maximum extension within the Valencia Trough/Liguro-Provencal Basin occurred in an axial position close to the North Balearic Fracture Zone. The same model of oppositely propagating rifts, when applied to the Burdigalian/Langhian episode of back-arc oceanic accretion within the Liguro-Provencal and Algerian basins, predicts a number of features which are borne out by existing geological and geophysical, particularly magnetic data. These include the orientation of subparallel magnetic anomalies, presumed to be seafloor spreading isochrons, in both basins; concave-to-the-west fracture zones southwest of the North Balearic Fracture Zone, and concave-to-the-east fracture zones to its northeast; a spherical triangular area of NW oriented seafloor spreading isochrons southwest of Sardinia; the greater NW extension of the central (youngest?) magnetic anomaly within this triangular area, in agreement with the model-predicted northwestward propagation of a rift in this zone; successively more central (younger) magnetic anomalies abutting thinned continental crust nearer to the pole of rotation in the Liguro-Provencal Basin. The latter feature demonstrates that a rift also propagated northeast in the Liguro-Provencal Basin, at least in its oceanic accretion phase of development. An adaptation of an existing model for subduction slab detachment occurring along the North African margin in the late Burdigalian/Langhian, proposes propagation in opposite directions of the slab tear. The resultant rhombic slab detachment is closely associated in space and time with the rhombic form of the Algerian/Liguro-Provencal basins, suggesting a cause and effect relationship.

Martin, A. K.

2006-06-01

362

The Galapagos Spreading Center  

NSDL National Science Digital Library

In this lesson, with a focus on mid-ocean ridges, students will discover how new ocean floor is formed. They will study the processes involved in creating new seafloor at a mid-ocean ridge, investigate the Galapagos Spreading Center system, and understand the different types of plate motion associated with ridge segments and transform faults. This hands-on activity uses online data resources and includes: focus questions, learning objectives, teaching time, audio/visual materials needed, background information, learning procedures, evaluations, extensions, as well as resources and student handouts.

363

Epidemiology: Understanding Disease Spread  

NSDL National Science Digital Library

Factors that influence disease spread throughout populations can be explored with the program Epidemiology. Both population and disease characteristics can be modeled over different time periods. The Susceptible- Infected- Recovered (SIR) model enables us to make predictions based on significant variables such as the flow of new susceptibles in to the population, transmission rates, disease deaths, and the duration of the disease. Ebola is used as a model organism and epidemiology is presented from both a microbiological and social perspective. * build epidemiological models of different diseases, design strategies for disease control, and test the effectiveness of these strategies on virtual populations

Marion Fass (Beloit College;Biology)

2006-05-20

364

Spread of SARS  

NSDL National Science Digital Library

In this module, we develop a simplified model (SIR) of the spread of an infectious disease before considering a more involved model of SARS. For the former, after analyzing the system and formulating the model with appropriate differential equations, we create a model using the systems modeling tool STELLA. For the latter, we build on the earlier model to perform the analysis and much of the model formulation, but leave the completion of the model to the student. Projects involve various refinements of the models along with additional problems.

Shiflet, Angela B.; Shiflet, George W.

365

Mars Crustal Remanent Magnetism: An Extinct Dynamo Leaves a Record of Field Reversals in the Heavily Cratered Highlands  

NASA Technical Reports Server (NTRS)

The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit about Mars, obtained vector magnetic field measurements just above the surface of Mars (altitudes > 100 kilometers). Crustal magnetization, largely confined to the most ancient, heavily cratered Mars highlands, is frequently organized in east-west trending linear features, the largest of which extends over 2000 km. A representative set of survey passes are modeled using uniformly magnetized thin plates and a generalized inverse methodology. Crustal remanent magnetization exceeds that deduced for the largest terrestrial magnetic anomalies by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity are found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale.

Connerney, John E.; Acuna, Mario H.; Ness, Norman F.; Wasilewski, Peter J.

1999-01-01

366

An analysis of ridge axis gravity roughness and spreading rate  

NASA Technical Reports Server (NTRS)

Fast and slow spreading ridges have radically different morphologic and gravimetric characteristics. In this study, altimeter measurements from the Geosat Exact Repeat Mission are used to investigate spreading rate dependence of the ridge axis gravity field. Gravity roughness provides an estimate of the amplitude of the gravity anomaly and is robust to small errors in the location of the ridge axis. Gravity roughness as a weighted root mean square of the vertical deflection at 438 ridge crossings on the mid-ocean ridge system is computed. Ridge axis gravity anomalies show a decrease in amplitude with increasing spreading rate up to an intermediate rate of about 60-80 mm/yr and almost no change at higher rates; overall the roughness decreases by a factor of 10 between the lowest and highest rates. In addition to the amplitude decrease, the range of roughness values observed at a given spreading rate shows a similar order of magnitude decrease with transition between 60 and 80 mm/yr. The transition of ridge axis gravity is most apparent at three relatively unexplored locations on the Southeast Indian Ridge and the Pacific-Antarctic Rise; on these intermediate rate ridges the transition occurs abruptly across transform faults.

Small, Christopher; Sandwell, David T.

1992-01-01

367

Ferromagnetic neutron stars: axial anomaly, dense neutron matter, and pionic wall  

E-print Network

We show that a chiral nonlinear sigma model coupled to degenerate neutrons exhibits a ferromagnetic phase at high density. The magnetization is due to the axial anomaly acting on the parallel layers of neutral pion domain walls spontaneously formed at high density. The emergent magnetic field would reach the QCD scale ~ 10^19 [G], which suggests that the quantum anomaly can be a microscopic origin of the magnetars (highly magnetized neutron stars).

Minoru Eto; Koji Hashimoto; Tetsuo Hatsuda

2012-09-21

368

Ferromagnetic neutron stars: Axial anomaly, dense neutron matter, and pionic wall  

NASA Astrophysics Data System (ADS)

We show that a chiral nonlinear sigma model coupled to degenerate neutrons exhibits a ferromagnetic phase at high density. The magnetization is due to the axial anomaly acting on the parallel layers of neutral pion domain walls spontaneously formed at high density. The emergent magnetic field would reach the QCD scale ˜1019[G], which suggests that the quantum anomaly can be a microscopic origin of the magnetars (highly magnetized neutron stars).

Eto, Minoru; Hashimoto, Koji; Hatsuda, Tetsuo

2013-10-01

369

Homomorphic deconvolution of marine magnetic anomalies  

E-print Network

~ -512 -374 -256 -128 0 128 256 374 512 Sample Number Fig. 15. A plot of the upward continuation operator for z = 3 km and z = 5 km. 1 2 41 11. 0 Ch O 123 192 iiave 0 mber Fig. 16. The 1og amplitude spectrum oi the upuia. d conti nua ti on opera... ~ -512 -374 -256 -128 0 128 256 374 512 Sample Number Fig. 15. A plot of the upward continuation operator for z = 3 km and z = 5 km. 1 2 41 11. 0 Ch O 123 192 iiave 0 mber Fig. 16. The 1og amplitude spectrum oi the upuia. d conti nua ti on opera...

Jones, Leo David

2012-06-07

370