Six-minute grid mean values of free air gravity and magnetic anomalies in Marsden square 150

1976 ◽  
Author(s):  
K G Shih
Keyword(s):  
Magnetic Anomalies ◽  
Mean Values ◽  
Free Air ◽  
Gravity And Magnetic ◽  
Free Air Gravity

Gulf of Aden spreading does not conform to triple-junction formation

Geology ◽  
2021 ◽  
Author(s):  
Khalid A. Almalki ◽  
Peter G. Betts
Keyword(s):  
Triple Junction ◽  
Sensu Stricto ◽  
Magnetic Characteristics ◽  
Gulf Of Aden ◽  
Central Domain ◽  
Potential Field Data ◽  
Free Air ◽  
Gravity And Magnetic ◽  
Free Air Gravity ◽  
Transitional Crust

The Gulf of Aden represents an evolving example of a juvenile ocean system and is considered the most evolved rift arm of the Afar triple junction. We have undertaken analysis of recent coupled satellite and marine potential-field data to understand the first-order crustal architecture along the entire length of the gulf. Our interpretation suggests the Gulf of Aden has three domains with distinct free-air gravity and magnetic characteristics. These domains record a progression from active seafloor spreading in the eastern domain, through isolated and discontinuous spreading segments in the central domain, to active continental rifting in the western domain immediately adjacent to the Afar triple junction. Forward models suggest the presence of transitional crust, which displays linear magnetic stripe–like anomalies that bound oceanic stripes in the central domain and covering the majority of the western domain. Magnetic anomalies differ from magnetic stripes sensu stricto because they are discontinuous and cannot be correlated along the length of the gulf. Detection of northwest-southeast extension in the central domain based on magnetic stripe orientation is inconsistent with the regional northeast-southwest extension. Our observations reflect heterogeneous opening of the Gulf of Aden basins, in which spreading is migrating toward Afar as a series of isolated spreading segments, rather than initiating at the junction as proposed by classical platetectonic theory. This mechanism of ocean initiation is inconsistent with transtensional models that involve wholesale tearing of continental crust and contradicts conceptual models that rely on the Afar plume in initiating or driving the extension.

MID-ATLANTIC RIDGE NEAR 45° NORTH: I. THE MEDIAN VALLEY

1966 ◽  
Vol 3 (3) ◽  
pp. 327-349 ◽  
Author(s):  
B. D. Loncarevic ◽  
C. S. Mason ◽  
D. H. Matthews
Keyword(s):  
Gravity Anomaly ◽  
Bouguer Anomaly ◽  
Magnetic Anomalies ◽  
Two Dimensional ◽  
Total Field ◽  
Dimensional Model ◽  
Free Air ◽  
Mid Atlantic Ridge ◽  
Strong Resemblance ◽  
Free Air Gravity

Detailed maps of bathymetry, free air gravity anomaly, and total field magnetic anomaly are presented for an area approximately 50 × 20 mi along the crest of the ridge. The median valley and the associated belt of large positive magnetic anomalies are continuous and display a striking lineation in direction 019°. The free air gravity anomaly shows a strong resemblance to topography. This correlation disappears when the Bouguer anomaly is calculated, indicating that the intrusive body immediately underlying the median valley is not significantly different in density from those bodies beneath the elongated sea mounts which overlook the valley. Small variations in the Bouguer anomaly indicate that there is an increase in density in a northwest direction across the survey area. Magnetic anomalies within the surveyed area can be simulated by a two-dimensional model in which steeply dipping contacts separate blocks of rock having different magnetizations. These blocks could be entirely within the volcanic layer extending to a depth of 5 km below sea level, but the central block, underlying the median valley, must be much more strongly magnetized than those adjacent to it. The mechanism by which the valley was formed remains obscure.

A DIRECT COMPUTATION OF GRAVITY AND MAGNETIC ANOMALIES CAUSED BY 2- AND 3-DIMENSIONAL BODIES OF ARBITRARY SHAPE AND ARBITRARY MAGNETIC POLARIZATION BY EQUIVALENT‐POINT METHOD AND A SIMPLIFIED CUBIC SPLINE

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 610-622 ◽  
Author(s):  
Chao C. Ku
Keyword(s):  
Arbitrary Shape ◽  
Gaussian Quadrature ◽  
Magnetic Anomalies ◽  
Cubic Spline ◽  
The Body ◽  
Point Method ◽  
Magnetic Polarization ◽  
3 Dimensional ◽  
Equivalent Point ◽  
Gravity And Magnetic

A computational method, which combines the Gaussian quadrature formula for numerical integration and a cubic spline for interpolation in evaluating the limits of integration, is employed to compute directly the gravity and magnetic anomalies caused by 2-dimensional and 3-dimensional bodies of arbitrary shape and arbitrary magnetic polarization. The mathematics involved in this method is indeed old and well known. Furthermore, the physical concept of the Gaussian quadrature integration leads us back to the old concept of equivalent point masses or equivalent magnetic point dipoles: namely, the gravity or magnetic anomaly due to a body can be evaluated simply by a number of equivalent points which are distributed in the “Gaussian way” within the body. As an illustration, explicit formulas are given for dikes and prisms using 2 × 2 and 2 × 2 × 2 point Gaussian quadrature formulas. The basic limitation in the equivalent‐point method is that the distance between the point of observation and the equivalent points must be larger than the distance between the equivalent points within the body. By using a reasonable number of equivalent points or dividing the body into a number of smaller subbodies, the method might provide a useful alternative for computing in gravity and magnetic methods. The use of a simplified cubic spline enables us to compute the gravity and magnetic anomalies due to bodies of arbitrary shape and arbitrary magnetic polarization with ease and a certain degree of accuracy. This method also appears to be quite attractive for terrain corrections in gravity and possibly in magnetic surveys.

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