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

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

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

The Mid-Atlantic Ridge near 45° N. XIII. Magnetic properties of basalt bore-core

1970 ◽  
Vol 7 (6) ◽  
pp. 1515-1527 ◽  
Author(s):  
J. Brooke ◽  
E. Irving ◽  
J. K. Park
Keyword(s):  
Magnetic Properties ◽  
Coercive Force ◽  
Physical Properties ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
The Core ◽  
Mid Atlantic Ridge ◽  
Technical Interest

Three bore-cores containing basalts have been obtained from the Mid-Atlantic Ridge at 45° N. The material is fresh and ideal for the study of physical properties. The drilling record and the nature of the core itself suggest that much of the basalt is from detached boulders, although one core may be in situ. In one core, variations in coercivity by a factor 2 occur within a distance of 5 cm. The coercive force spectra of anhysteretic and natural remanent magnetization are similar, but there are small differences due to secondary components which are used to predict correctly the polarity of 11 out of 12 specimens studied. This result may be of technical interest only since there is no guarantee that the material is in situ.

scholarly journals Tracing of traffic-related pollution using magnetic properties of topsoils in Daejeon, Korea

2020 ◽  
Vol 79 (20) ◽  
Author(s):  
Seungwoo Lee ◽  
Seoyeon Kim ◽  
Hyeji Kim ◽  
Youlee Seo ◽  
Yeoncheol Ha ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Coarse Grained ◽  
Morphological Observation ◽  
Exhaust Emission ◽  
Thermal Demagnetization ◽  
Main Street ◽  
Traffic Related Pollution ◽  
The Difference

Abstract The present study was designed to explore the possibility of roadside pollution screening using magnetic properties of topsoil samples in Daejeon, South Korea. Low-field magnetic susceptibility, frequency dependence of magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRM were determined for roadside topsoil samples. Magnetic susceptibility measured on 238 samples from the upper 5 cm of the topsoils ranged from 8.6 to 82.5 × 10–5 SI with a mean of 28.3 ± 10.8 × 10–5 SI. The proximal zone, 55 m wide area situated on either side of the main street, exhibited an enhancement of magnetic susceptibility. In areas distant from the main street, low magnetic susceptibility (< 50 × 10–5 SI) was observed. The topsoil samples exhibited significant susceptibility contrasts, suggesting that two dimensional magnetic mapping was effective in identifying traffic-related pollution. A few magnetic hotspots with intensities of magnetic susceptibility near or over 50 × 10–5 SI might reflect the difference in topographic elevation and surface morphology. Among various IRM-related parameters, remanence of coercivity was most significant statistically. In most samples, IRM component analysis provided dual coercivity components. Thermal demagnetization of composite IRM and morphological observation of magnetic separates suggest angular magnetite produced by vehicle non-exhaust emissions spherical magnetite derived from exhaust emission to be the dominant contributors to the magnetic signal. It is likely that lower- and higher-coercivity components represent the presence of coarse-grained angular magnetite and fine-grained spherical magnetite, respectively.

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

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

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

Properties of Cryogenic Treated Cemented Carbides (WC-Co)

2020 ◽  
Vol 403 ◽  
pp. 75-89
Author(s):  
Vojtěch Průcha ◽  
David Bricín ◽  
Antonín Kříž ◽  
Zdeněk Jansa
Keyword(s):  
Fracture Toughness ◽  
Cryogenic Treatment ◽  
The Other ◽  
Coarse Grained ◽  
Cemented Carbides ◽  
Polished Surface ◽  
X Ray Diffraction ◽  
Deep Cryogenic Treatment ◽  
Fine Grained ◽  
Disk Test

The present paper explores the effects of deep cryogenic treatment (DCT) on the properties of WC-Co cemented carbides. The investigation involved four different cemented carbide (CC) grades. Two of them were coarse-grained WC with grain sizes larger than 6 μm and binder fractions of 10 and 15 wt. %. The other two were fine-grained with WC grains of 0.5-0.8 μm and the same binder fractions of 10 and 15 wt. %. Their specimens were ground and polished to prepare them for DCT. In each specimen, one half of this polished surface was used for testing the properties of the CC before cryogenic treatment. The post-DCT properties were then determined on the other half. Properties of the cemented carbides prior to and after DCT were studied using optical and scanning electron microscopy, X-ray diffraction, hardness testing according to Vickers scale followed by calculation of fracture toughness KIC and a ball-on-disk test of the wear resistance of the surface. One of the findings was that cryogenic treatment led to a decrease in residual stresses and to lower fracture toughness KIC in the CC.

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

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

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

scholarly journals Crack-enhanced weathering in inscribed marble: a possible application in epigraphy

2021 ◽  
Vol 33 (2) ◽  
pp. 189-202
Author(s):  
Stylianos Aspiotis ◽  
Jochen Schlüter ◽  
Kaja Harter-Uibopuu ◽  
Boriana Mihailova
Keyword(s):  
Raman Spectroscopy ◽  
Penetration Depth ◽  
Environmental Conditions ◽  
Coarse Grained ◽  
Asia Minor ◽  
X Ray Diffraction ◽  
Western Turkey ◽  
Fine Grained ◽  
Rock Types ◽  
Micro Cracks

Abstract. Raman spectroscopy has been applied to check if there are detectible material differences beneath the inscribed and non-inscribed areas of marble-based written artefacts, which could be further used to visualize lost or hardly readable text via suitable mapping. As a case study, marble segments with ∼ 2000-year-old inscribed letters from Asia Minor (western Turkey) and marble gravestones with 66 ± 14-year-old inscriptions from the cemetery of Ohlsdorf (Hamburg, Germany) have been subjected to Raman spectroscopy, as well as to complementary X-ray diffraction, wavelength-dispersive electron probe microanalysis, and Fourier-transform infrared spectroscopy, to thoroughly study the effect of different environmental conditions, grain size, and inscription age on the nature and penetration depth of marble alteration. The results demonstrate that environmental conditions rule over the type of dominant weathering changes, which are carotenoid molecular inclusions produced by lichen and amorphous carbon for marbles from Hamburg and Asia Minor, respectively. The alteration is much stronger in medium- and coarse-grained than in fine-grained marble, but it is suppressed by letter colouring. In the absence of letter colouring, the weathering-related products in both ancient and modern engraved marbles are more abundant beneath than away from the engraved areas, and the penetration depth is larger due to the enhancement of fissures and micro-cracks around the inscribed areas. We show that the Raman intensity ratio between the strongest peak of the weathering-related product (ν(C=C) ∼ 1520 cm−1 for carotenoids or the G peak ∼ 1595 cm−1 for soot-like carbon) and the strongest peak of marble (CO3 stretching near 1087 cm−1) can serve as a quantitative marker to indirectly map the lateral distribution of cracks induced during the inscribing process and hence can potentially be used to trace lost text on vanished marble inscriptions. This approach can be applied to other rock types, but further studies are required to identify the corresponding autochthonous weathering-related products.

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

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

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

The identification of single-domain titanomagnetite particles by means of transmission electron microscopy

1979 ◽  
Vol 16 (2) ◽  
pp. 375-379 ◽  
Author(s):  
P. P. K. Smith
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Remanent Magnetization ◽  
Magnetic Domain ◽  
Natural Remanent Magnetization ◽  
Small Particles ◽  
Dispersed Particles ◽  
Transmission Electron ◽  
Mid Atlantic Ridge ◽  
Means Of Transmission

A basalt sample dredged from the axis of the Mid-Atlantic Ridge has been ion-thinned and examined by transmission electron microscopy. Finely dispersed particles as small as 0.04 μm in diameter, occurring in amorphous patches of the rock, have been identified as titanomagnetite by means of electron diffraction and microanalysis. These small particles have dimensions appropriate to single magnetic domain behaviour, and are considered to be largely responsible for the strong and very stable natural remanent magnetization of this rock.

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