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1.
Abstract— The magnetometer experiment (MAG) onboard the Near‐Earth Asteroid Rendezvous (NEAR)‐Shoemaker spacecraft detected no global scale magnetization and established a maximum magnetization of 2.1 times 10?6 Am2 kg?1 for asteroid 433 Eros. This is in sharp contrast with the estimated magnetization of other S‐class asteroids (Gaspra, ?2.4 times 10?2 Am2 kg?1; Braille, ?2.8 times 10?2 Am2 kg?1) and is below published values for all types of ordinary chondrites. This includes the L/LL types considered to most closely match 433 Eros based on preliminary interpretations of NEAR remote geochemical experiments. The ordinary chondrite meteorite magnetization intensity data was reviewed in order to assess the reasonableness of an asteroid‐meteorite match based on magnetic property measurements. Natural remanent magnetization (NRM) intensities for the ordinary chondrite meteorites show at least a 2 order of magnitude range within each of the H, L, and LL groups, all well above the 2.1 times 10?6 Am2 kg?1 level for 433 Eros. The REM values (ratio of the NRM to the SIRM (saturation remanent magnetization)) range over 3 orders of magnitude for all chondrite groups indicating no clear relationship between NRM and the amount of magnetic material. Levels of magnetic noise in chondrite meteorites can be as much as 70% or more of the NRM. Consequently, published values of the NRM should be considered suspect unless careful evaluation of the noise sources is done. NASA Goddard SFC studies of per unit mass intensities in large (>10 000 g) and small (down to <1 g) samples from the same meteorite demonstrate magnetic intensity decreases as size increases. This would appear to be explained by demagnetization due to magnetic vector randomness at unknown scale sizes in the larger samples. This would then argue for some level of demagnetization of large objects such as an asteroid. The possibility that 433 Eros is an LL chondrite cannot be discounted. 相似文献
2.
Ladislav Nabelek Martin Mazanec Simon Kdyr Gunther Kletetschka 《Meteoritics & planetary science》2015,50(6):1112-1121
Magnetic images of Chelyabinsk meteorite's (fragment F1 removed from Chebarkul lake) thin section have been unraveled by a magnetic scanning system from Youngwood Science and Engineering (YSE) capable of resolving magnetic anomalies down to 10?3 mT range from about 0.3 mm distance between the probe and meteorite surface (resolution about 0.15 mm). Anomalies were produced repeatedly, each time after application of magnetic field pulse of varying amplitude and constant, normal or reversed, direction. This process resulted in both magnetizing and demagnetizing of the meteorite thin section, while keeping the magnetization vector in the plane of the thin section. Analysis of the magnetic data allows determination of coercivity of remanence (Bcr) for the magnetic sources in situ. Value of Bcr is critical for calculating magnetic forces applicable during missions to asteroids where gravity is compromised. Bcr was estimated by two methods. First method measured varying dipole magnetic field strength produced by each anomaly in the direction of magnetic pulses. Second method measured deflections of the dipole direction from the direction of magnetic pulses. Bcr of magnetic sources in Chelyabinsk meteorite ranges between 4 and 7 mT. These magnetic sources enter their saturation states when applying 40 mT external magnetic field pulse. 相似文献
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4.
Gunther Kletetschka Petr Pruner Daniela Venhodova Jaroslav Kadlec 《Geochemical transactions》2007,8(1):2
A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree,
located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured
low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization
(SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long
sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because
it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age
(1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density.
The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity
and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little
Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis
of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component
in this tree may be thermal in origin and was controlled by local thermal condition. 相似文献
5.
Effect of citrate-bicarbonate-dithionite treatment on fine-grained magnetite and maghemite 总被引：8，自引：0，他引：8
Christopher P. Hunt Michael J. Singer Gunther Kletetschka Jeff TenPas Kenneth L. Verosub 《Earth and Planetary Science Letters》1995,130(1-4):87-94
Mineral magnetic properties of soils and parent materials have been interpreted in terms of paleoclimate and rates of soil formation but it is important to understand which minerals contribute to the mineral magnetic signal. Citrate-bicarbonate-dithionite (CBD) treatment has been used to determine the amounts of fine-grained, often pedogenic, ferrimagnetic minerals relative to coarse-grained, often inherited, magnetic minerals. However, questions have been raised about the effect of particle size on the efficacy of CBD in dissolving magnetite and maghemite grains. In this paper we use magnetic susceptibility and its frequency dependence, and the low-temperature behavior of a saturation isothermal remanent magnetization, to track the dissolution of carefully sized magnetite grains. We found that the standard CBD procedure dissolves fine magnetite particles (ca. < 1 μm) but leaves larger particles (ca. > 1 μm) essentially intact. Thin oxidized coatings, presumably maghemite, are also dissolved by the CBD procedure. These results support previous interpretations that the CBD procedure can be used to distinguish between pedogenic and lithogenic magnetic grains, assuming that most pedogenic magnetic grains are sufficiently small (ca. < 1 μm) and most lithogenic magnetic grains are sufficiently large (ca. > 1 μm). These results also show that the standard procedure is too harsh to differentiate between 1 μm grains of magnetite and maghemite. A modified CBD extraction that uses half as much dithionite reduces the magnetic susceptibility of 1 μm magnetite grains by only 10%. This method may be useful in distinguishing between magnetite and maghemite grains in this size range. 相似文献
6.
T.?KohoutEmail author G.?Kletetschka F.?Donadini M.?Fuller E.?Herrero-Bervera 《Studia Geophysica et Geodaetica》2008,52(2):225-235
The REM(AF) method is a new tool for the analysis of the origin and alternating field demagnetization coercivity spectra of
the remanent magnetization. We applied this method on precambrian Gila diabase sheets from Arizona in order to identify the
high coercivity magnetic carrier, and on artificially shocked Rowley Regis basalt from UK in order to analyze the effect of
the shock on the natural remanent magnetization.
In the Gila diabase the high coercivity magnetic component was identified to be most likely represented by the acicular magnetite
(increase in the efficiency ratio in the high coercivity region).
In the Rowley Regis basalt, the REM(AF) analysis revealed that comparing to NRM, the shock produced a different distribution
of the AF demagnetization coercivity spectra due to the occurrence of the Shock Remanent Magnetization. 相似文献
7.
Gunther Kletetschka Petr Schnabl Kristýna Šifnerová Zuzana Tasáryová Štěpán Manda Petr Pruner 《Studia Geophysica et Geodaetica》2013,57(1):103-117
Magnetic images have been produced at the distance of 0.1 mm from the polished basaltic thin sections of rocks from Prague Synform in Barrandian area. Three different magnetic textures were seen and when combined with optical imaging could be related to petrological features. The first magnetic texture revealed that most of the magnetic signature is localized within the amygdales formed later after the basalts became part of the sedimentary sequence. The second texture showed that the basaltic body contains large grain size distribution of magnetic carriers possibly with variable viscous magnetizations. The third texture suggested a presence of magnetic anisotropy of igneous origin. Such textural magnetic information along with the paleomagnetic characteristics of the basaltic rocks of Silurian age constrained the overall geological interpretation. 相似文献
8.
Günther Kletetschka 《Studia Geophysica et Geodaetica》1992,36(3):230-239
Summary The paper deals with the statistical approach to processing the polarity durations of the Earth's magnetic dipole over the past 170 million years. Partial elimination of the random component enables the mutual relation between normal and reversed polarities to be determined. The polarity time sequence has further been divided into several intervals. The frequency distributions for normal and reversed polarities have been established for each of these intervals. It has been found that the random component of the reversal triggering mechanism hides a pattern of behaviour which displays a certain amount of logic. 相似文献
9.
Remanent magnetization (RM) of rocks with hematite–ilmenite solid solution (HISS) minerals, at all crustal levels, may be an important contribution to magnetic anomalies measured by ground and satellite altitude surveys. The possibility that lower thermal gradient relatively deep in the crust can result in exsolution of HISS compositions with strong remanent magnetizations (RM) was studied for two bulk compositions within the HISS system. Samples from granulite-terrane around Wilson Lake, Labrador, Canada contains titanohematite with exsolved ferrian ilmenite lamellae. Other samples from the anorthosite-terrane of Allard Lake, Quebec, Canada contain ferrian ilmenite with exsolved titanohematite lamellae. In both cases, the final exsolved titanohematite has similar Ti content and carries dominant magnetic remanence with REM (=NRM/SIRM, where NRM is the natural remanent magnetization and SIRM is the saturation isothermal remanent magnetization) that is comparable to the Ti-free end member. The RM was acquired prior to exsolution and the ilmeno-hematite-rich rock possesses thermal remanent magnetization (TRM), whereas rocks with hemo-ilmenite possess chemical remanent magnetization (CRM). In both cases, we found fairly large homogeneous grains with low demagnetizing energy that acquired intense RM. The magnetism of the ilmeno-hematite solid solution phases is not significantly perturbed by the continuous reaction: ilmeno-hematitetitanohematite solid solution. Hence, the occurrence of HISS in rocks that cooled slowly in a low intensity magnetic field will have an intense magnetic signature characterized by a large REM. 相似文献
10.
Magnetic Anomalies on the Tree Trunks 总被引：2，自引：0，他引：2
Kletetschka Gunther Žila Vojtěch Wasilewski Peter J. 《Studia Geophysica et Geodaetica》2003,47(2):371-379
Magnetic measurements of soil and tree bark adjacent to a busy highway revealed a significant variation in the concentration of magnetic particles with distance from the highway. Further more, forest-facing tree-bark contains significantly more magnetic particles than road-facing tree-bark. Magnetic particles were detected both on the bark of the maple trees and in the first centimeter of the soil cover (O/A horizon). Stability of saturation isothermal magnetization (SIRM) and hysteresis parameters of the soil indicates the presence of single domain (SD/PSD) magnetic carriers. Measurements of the tree bark hysteresis parameters and SIRM detect a significant lower coercivity component that we interpret to be an indication of more abundant pseudo-single domain (PSD) type magnetic grains. Magnetic measurements around the perimeters of eight tree trunks reveal magnetic carriers whose distribution is antipodal to the source direction (highway). We interpret our observation by adopting an air circulation model, where suspended PSD/SD particles are carried in the air stream. The air stream from the heavy traffic lowers the amount of moisture on the tree trunk surfaces facing the highway and thus reduces an adhesive potential on this side. Therefore, more particles can stay on the moist side of the trunk protected from the direct airflow. 相似文献