scholarly journals Behavior of oceanic crustal magnetization at high temperatures: Viscous magnetization and the marine magnetic anomaly source layer

1999 ◽  
Vol 26 (15) ◽  
pp. 2279-2282 ◽  
Author(s):  
Julie A. Bowles ◽  
H. Paul Johnson
Keyword(s):  
Magnetic Anomaly ◽  
High Temperatures ◽  
Crustal Magnetization

Magnetic exploration of ocean crust for craters of impact origin: Model results

Geophysics ◽  
1991 ◽  
Vol 56 (8) ◽  
pp. 1153-1157 ◽  
Author(s):  
Andrew R. Ochadlick
Keyword(s):  
Magnetic Anomaly ◽  
Deep Ocean ◽  
Point Of View ◽  
Ocean Floor ◽  
Magnetic Data ◽  
Data Sets ◽  
Ocean Crust ◽  
Crustal Magnetization ◽  
Simple Potential ◽  
The Impact

Magnetic data sets over deep ocean areas may contain clues to the existence of craters formed by the impact of an extraterrestrial body with the Earth’s ocean crust. To aid in the magnetic exploration of the ocean crust for oceanic impact craters, basic but effective computations from an impact model are studied from an aeromagnetic point of view. The main assumption of the analysis is that a sufficiently large impact can excavate large volumes of magnetized basalt, vaporize basalt, and raise basalt to temperatures above the Curie temperature (approximately 500°C) to alter the preimpact magnetization of the ocean floor and result in a magnetic anomaly being associated with an oceanic impact crater. In the absence of an existing theory on the influence of impacts on ocean crustal magnetization, the representation of a crater on the ocean floor by a simple potential provides, apparently for the first time, quantitative estimates of the crater’s magnetic anomaly along a horizontal surface. Numerical results from the model suggest that the detection of the anomaly of a Cretaceous‐Tertiary (K-T) type of impact is well within the capabilities of aeromagnetic technology.

Limitations of the long‐wavelength components of the North American magnetic anomaly map

Geophysics ◽  
1990 ◽  
Vol 55 (12) ◽  
pp. 1577-1588 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
W. J. Hinze
Keyword(s):  
Magnetic Anomaly ◽  
North American ◽  
Data Set ◽  
Long Wavelength ◽  
Related Data ◽  
The North ◽  
North American Data ◽  
Crustal Magnetization ◽  
Anomaly Map ◽  
Lateral Variations

The magnetic anomaly map of North America and its related data set provide the opportunity not only to view the obvious short‐wavelength anomalies (<300 km) in a continental context, but to isolate and analyze the longer wavelength anomalies. However, care must be used in analyzing the longer wavelengths because of the effects of noncrustal sources on these anomalies. Inversion of the anomalies into lateral variations of crustal magnetization suggests that the long‐wavelength anomalies (>2600 km) are strongly affected by core field components that have not been completely removed from the North American data set. Furthermore, the piecewise matching of the magnetic anomalies of adjacent survey areas in the map compilation has contaminated the intermediate wavelength anomalies (300–2600 km).

MAGNETIC ANOMALY EFFECTS DUE TO APPROXIMATING INFINITE RECTANGULAR PRISM SOURCES BY INFINITE LINE OR INFINITE SHEET SOURCES

Geophysics ◽  
1975 ◽  
Vol 40 (3) ◽  
pp. 530-537 ◽  
Author(s):  
J. N. Shapiro ◽  
G. Weynand ◽  
A. F. Gangi
Keyword(s):  
Magnetic Anomaly ◽  
Plate Tectonics ◽  
Rectangular Prism ◽  
Magnetization Distribution ◽  
The World ◽  
Simplifying Assumptions ◽  
Crustal Magnetization ◽  
Infinite Line ◽  
Ridge System

The inversion of oceanic magnetic anomaly data to obtain the crustal magnetization requires some assumptions regarding the magnetization distribution (Parker and Huestis, 1974). Two simplifying assumptions typically made for data near ridge systems are that the source magnetization is lineated parallel to the ridge system and that it is unidirectional. These assumptions follow directly from the theory of plate tectonics and have been used near the major ridge systems of the world. The presence of transform faulting can offset the lineations usually observed and render the first assumption invalid. In this note, only those cases in which both assumptions are valid will be considered.

In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

1991 ◽  
Vol 49 ◽  
pp. 660-661
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
High Temperatures ◽  
Image Resolution ◽  
Atomic Processes ◽  
Crystal Surfaces ◽  
Beam Radiation ◽  
Surface Areas ◽  
Transmission Electron ◽  
Reflection Electron Microscopy ◽  
Gas Reactions

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

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