Magnetization of oceanic crustal layer 2—results and thoughts after DSDP Leg37

1977 ◽  
Vol 14 (4) ◽  
pp. 684-706 ◽  
Author(s):  
Patrick J. C. Ryall ◽  
James M. Hall ◽  
J. Clark ◽  
T. Milligan
Keyword(s):  
Magnetic Properties ◽  
Average Intensity ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Crustal Layer ◽  
Cation Deficiency ◽  
Layer 2 ◽  
Major Carrier ◽  
The Individual ◽  
High Degree

The detailed study of 455 basement samples from DSDP Leg 37 reveals magnetic properties, particularly inclinations and intensities, different from those commonly considered representative of Layer 2. Non-dipole inclinations are the most common. The deepest hole (582 m) has a vector average intensity of 24.3 × 10−4 emu cm−3 (24.3 × 10−1 A/m) and an inclination of only −14.5°. Induced magnetization never dominates and is usually much less than remanent magnetization, with Q ratio averaging 35 for basalts and 2.6 for plutonic rocks. Viscous magnetization acquisition constant, S, ranges widely from 0.001 to 1 × 10−4 emu cm−3 (0.001 to 1 × 10−1A/m), but is very rarely sufficient to cause VRM to dominate NRM.The major carrier of NRM is cation-deficient titanomagnetite produced by low-temperature oxidation of stoichiometric titantomagnetite. There is no trend of alteration with depth. All the magnetic properties are controlled by conditions within the individual basalt pillows or more massive units. A high degree of cation deficiency is associated with reduced NRM intensity, initial susceptibility, saturation magnetization, and VRM acquisition and increased MDF, Q ratio, and Curie point. Zones of low cation deficiency are presently found only in parts of massive units. With the exception of rare individual samples pillow sequences are highly oxidized throughout.A discussion is given of the kinds of ocean crust drilling and laboratory experiments required to solve the problems of the magnetic structure of Layer 2 as seen at the Leg 37 sites.

scholarly journals Synthesis and magnetic characterisation of Fe1−xMgxSb2O4 (x = 0.25, 0.50, 0.75) and their oxygen-excess derivatives, Fe1−xMgxSb2O4+y

2017 ◽  
Vol 5 (20) ◽  
pp. 4985-4995 ◽  
Author(s):  
Benjamin P. de Laune ◽  
Mariana J. Whitaker ◽  
Jose F. Marco ◽  
Michael F. Thomas ◽  
Frank J. Berry ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Low Temperature ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Oxygen Excess

The structures and magnetic properties of Fe1−xMgxSb2O4 and their products from low-temperature oxidation, Fe1−xMgxSb2O4+y, are described.

Theory of low-temperature deuteric oxidation with application to time evolution of ocean magnetic anomalies

2020 ◽  
Author(s):  
Valera Shcherbakov ◽  
Karl Fabian
Keyword(s):  
Low Temperature ◽  
Crack Formation ◽  
Vacancy Concentration ◽  
Ocean Floor ◽  
Stress Distributions ◽  
Low Temperature Oxidation ◽  
Russian Science ◽  
Temperature Oxidation ◽  
Wavelength Variation ◽  
High Degree

<p>The NRM of the ocean floor is carried by titanomagnetite grains that undergo low-temperature oxidation after initial cooling. Progressing oxidation is known to generate shrinkage cracks in   grains larger than approximately 5 mkm, and is suspected to   control the long wavelength variation of NRM-intensity across the ocean floor. Here we develop a quantitative theory of single-phase oxidation and crack formation by solving the vacancy-diffusion equation that describes the oxidation process for spherical titanomagnetite particles, where the diffusion coefficient strongly decreases with vacancy concentration. The latter dependence has been experimentally demonstrated and is essential to explain the peculiarities of the observed variations of oxidation-degree with ocean-floor age. The calculated diffusion profiles provide the exact stress distributions inside oxidized titanomagnetite spheres, and  predict a size limit for shrinkage-crack formation that agrees   with   microscopic observations of crack appearance in ocean-floor basalt samples. The new diffusion model provides a unified explanation of long-known experimental facts that 1) temperatures for the onset of low-temperature oxidation during laboratory heating are theoretically estimated as 200-400 °C, depending on grain size, and 2) that heating to 400-500 °C is required to obtain a sufficiently high degree of oxidation z about 0.8  for the development of  high-temperature exsolution lamellae. Calculations for ocean-floor conditions    quantitatively suggest that a rapid decrease of NRM intensity during the first 40 ka  results from  a deflection of magnetization by strong stresses that emerge in titanomagnetite grains of sub-critical sizes, and randomization of domain-state by crack formation in larger grains. This work was supported by Russian Science Foundation grant 19-47-04110401 (VS)<br><br></p>

The magnetization of the ocean floor: stress and fracturing of titanomagnetite particles by low-temperature oxidation

2020 ◽  
Vol 221 (3) ◽  
pp. 2104-2112 ◽  
Author(s):  
Karl Fabian ◽  
Valera P Shcherbakov
Keyword(s):  
Low Temperature ◽  
Crack Formation ◽  
Vacancy Concentration ◽  
Natural Remanent Magnetization ◽  
Ocean Floor ◽  
Stress Distributions ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Wavelength Variation ◽  
High Degree

SUMMARY The natural remanent magnetization (NRM) of the ocean floor is carried by titanomagnetite grains that undergo low-temperature oxidation after initial cooling. Progressing oxidation is known to generate shrinkage cracks in grains larger than approximately 5 μm, and is suspected to control the long wavelength variation of NRM-intensity across the ocean floor. Here we develop a quantitative theory of single-phase oxidation and crack formation by solving the vacancy-diffusion equation that describes the oxidation process for spherical titanomagnetite particles, where the diffusion coefficient strongly decreases with vacancy concentration. The latter dependence has been experimentally demonstrated and is essential to explain the peculiarities of the observed variations of oxidation-degree with ocean-floor age. The calculated diffusion profiles provide the exact stress distributions inside oxidized titanomagnetite spheres, and predict a size limit for shrinkage-crack formation that agrees with microscopic observations of crack appearance in ocean-floor basalt samples. The new diffusion model provides a unified explanation of long-known experimental facts that (1) temperatures for the onset of low-temperature oxidation during laboratory heating are theoretically estimated as 200–400 ○C, depending on grain size and (2) that heating to 400–500 ○C is required to obtain a sufficiently high degree of oxidation z ≈ 0.8 for the development of high-temperature exsolution lamellae. Calculations for ocean-floor conditions quantitatively suggest that a rapid decrease of NRM intensity during the first 40 ka results from a deflection of magnetization by strong stresses that emerge in titanomagnetite grains of subcritical sizes, and randomization of domain-state by crack formation in larger grains.

The Iceland Research Drilling Project crustal section: variation of magnetic properties with depth in Icelandic-type oceanic crust

1985 ◽  
Vol 22 (1) ◽  
pp. 85-101 ◽  
Author(s):  
James M. Hall
Keyword(s):  
Magnetic Properties ◽  
Low Temperature ◽  
Oceanic Crust ◽  
Hydrothermal Alteration ◽  
Vertical Section ◽  
Low Temperature Oxidation ◽  
Ocean Crust ◽  
Temperature Oxidation ◽  
Near Surface ◽  
Surface Magnetization

An attempt has been made to identify the processes that give rise to a number of depth trends in the magnetization of a 3.1 km vertical section of Icelandic-type oceanic crust and to assess the possibility that similar processes act, and depth trends occur, in typical oceanic crust. The depth trends in the Icelandic section consist of a general increase in saturation and induced magnetization to 2 km crustal depth, below which flow magnetization decreases while dike magnetization remains constant, and of large changes in flow magnetization that occur on a scale of a few hundred metres below 3 km crustal depth.Increase in saturation and induced magnetization with depth in the upper 2 km is thought to be the result of two processes: a decrease in low-temperature oxidation from the original lava surface to 700–800 m crustal depth, thence an increase in hydrothermal alteration with depth. This interpretation is based on oxide petrography and Curie temperatures, which show a weakly defined minimum in the 700–800 m interval, then an increase to ubiquitous "magnetite" values at just below 2 km crustal depth. Although the relationship between magnetic properties and oxide alteration is reasonably well known for the low-temperature oxidation process from laboratory studies and ophiolite and typical ocean-crust analogs, the change in magnetic properties during hydrothermal alteration is not generally known, nor are ophiolite or typical ocean-crust analogs presently available.Decrease in flow saturation and induced magnetization below 2 km is likely to be the result of alteration of magnetite (sensu lato) to nonmagnetic phases, either on a fine scale to hematite (s.l.) between 2 km and 3 km, or by leaching of iron, leaving anatase pseudomorphs after magnetite (s.l.) below 3 km. The relatively low porosity of the dikes is likely to have protected dike magnetite below 2 km from such oxidation and leaching processes.The study confirms that secondary magnetite in several forms is an important magnetic constituent of the flows in the lower part of the section, particularly where decomposition of primary magnetite is widespread. Secondary magnetite occurs as vermiform or bladelike masses, as rims associated with former silicates, or as fresh continuous magnetite occurring either as subhedral grains or as "reconstructed" primary grains in which relics of sphene-replaced ilmenite lamellae grids are seen.In conclusion, the possibility that the near-surface magnetization of typical ocean crust is commonly the minimum value for a layer extending downwards to the onset of an epidote-bearing facies deserves serious consideration, as does the possibility that strong, stable magnetization of secondary origin occurs in flows where dike density becomes significant.

Semiology of the Pain Syndrome - Identifying the Ideal Methods of Locoregional Anesthesia Based on Their Rationale and Features

2017 ◽  
Vol 68 (10) ◽  
pp. 2373-2377
Author(s):  
Mihaela Monica Scutariu ◽  
Vlad Danila ◽  
Corina Ciupilan ◽  
Oana Elena Ciurcanu
Keyword(s):  
Maxillofacial Surgery ◽  
Essential Element ◽  
Pain Syndrome ◽  
Oral And Maxillofacial Surgery ◽  
Structuring Element ◽  
Technical Accuracy ◽  
Locoregional Anesthesia ◽  
Special Approach ◽  
The Individual ◽  
High Degree

Anesthesia and the degree of control over the perception of pain depends on the personality of the individual, the socio-economic conditions, potential previous painful experiences and, last but not least, on fatigue and fear of the dentist. The perception of pain in patients is closely connected to their mental state. Pain is defined as a sensation of discomfort, with wide variations, both in quality and intensity, for different people in seemingly identical conditions; an unpleasant sensitive and emotional phenomena connected to the threat of a wound or caused in the tissues or described in the terms of this disease. The essential element of any type of anesthesia is analgesia, an effect which in some cases cannot be achived, due to the patient�s particularities or the physician�s lack of experience in anesthesia. Locoregional anesthesia (LRA) represents the blocking of the nociceptive sensitive and sympathetic autonomic afferents as well as that of motor efferents at the level of peripheral nerves� axons, by means of local anesthetic. To achieve the set purpose, we carried out a study on a representative human sample comprised of 10.123 patients treated in the Oral and Maxillofacial Surgery Clinic (Ambulatory) from the County Clinic Emergency Hospital St. Spiridon Iasi, between 01.01.2015-31.12.2016. The reason for the exclusion of certain categories of patients in the reseach was: the patients with a special conditions background require individual pre-anesthesia schemes, personalised for the nature of the pre-existing general condition, which must be further approved by the attending specialist physician : cardiologist, internist, diabetologist; children under 18 years old, with a high degree of anxiety; a high precentage of elderly patients, over 60 years old, possess a combination of general issues, thus requiring a special approach. The thoroughness lying at the core of the anesthetic practice, most especially the safegurading of a technical accuracy in the performance of anesthesia [12,], instead of improvisations, the lack of anatomical and stomatological training in general and the resulting inefficiency as such, is the underlying in-depth structuring element of this paper.

scholarly journals Territories of state-led aquaculture risk management: Thailand’s Plang Yai program

2020 ◽  
pp. 239965442096524
Author(s):  
Mariska JM Bottema ◽  
Simon R Bush ◽  
Peter Oosterveer
Keyword(s):  
Risk Management ◽  
Policy Instruments ◽  
Spatially Explicit ◽  
Financial Risks ◽  
Shared Resources ◽  
Globalizing World ◽  
Farmer Behavior ◽  
Key Policy ◽  
The Individual ◽  
High Degree

The Thai aquaculture sector faces a range of production, market and financial risks that extend beyond the private space of farms to include public spaces and shared resources. The Thai state has attempted to manage these shared risks through its Plang Yai (or ‘Big Area’) agricultural extension program. Using the lens of territorialization, this paper investigates how, through the Plang Yai program, risk management is institutionalized through spatially explicit forms of collaboration amongst farmers and between farmers and (non-)state actors. We focus on how four key policy instruments brought together under Plang Yai delimited multiple territories of risk management over shrimp and tilapia production in Chantaburi and Chonburi provinces. Our findings demonstrate how these policy instruments address risks through dissimilar but overlapping territories that are selectively biased toward facilitating the individual management of production risks, whilst enabling both the individual and collective management of market and financial risks. This raises questions about the suitability of addressing aquaculture risks by controlling farmer behavior through state-led designation of singular, spatially explicit areas. The findings also indicate the multiple roles of the state in territorializing risk management, providing a high degree of flexibility, which is especially valuable in landscapes shared by many users, connected to (global) value chains and facing diverse risks. In doing so we demonstrate that understanding the territorialization of production landscapes in a globalizing world requires a dynamic approach recognizing the multiplicity of territories that emerge in risk management processes.

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