Magnetization gaps associated with tearing in the Central America Subduction Zone

Counil, J. L.; Achache, J.

doi:10.1029/gl014i011p01115

Cited by 17 publications

(7 citation statements)

References 15 publications

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“…However small, we believe that these differences are significant and that the present maps provide a more accurate image of the lithospheric anomaly field, particularly above oceanic areas and near the equator. Indeed, local studies in the Caribbean [Counil and Achache, 1987;Counil et al, 1989] and in Asia [Achache et al, , also manuscript preparation, 1990] have shown that even small variations of the anomaly field at very short wavelength obtained by our method are found to be correlated with the geology. In the Bay of Bengal, where a negative anomaly is observed, the lithosphere was also formed during the CLN near 50øS [Besse and Courtillot, 1988].…”

Section: Comparison With Earlier Global Magsat Anomaly Mapsmentioning

confidence: 69%

New global vector magnetic anomaly maps derived from Magsat data

Cohen¹,

Achache²

1990

J. Geophys. Res.

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New global maps of the vector magnetic anomaly field of Earth are derived from Magsat data. hnprovement on earlier published vector and scalar maps is achieved with the following procedure: (1) The noise level of vector measurements associated with the discontinuities of the in-flight sensor attitude determination is reduced by selecting the data. (2) A monthly model of the main field is computed to account for secular variation, using only quiet day data. (3) The time dependence of the ring current effect is taken into account using hourly values of the Dst index based on ground observations. (4) Sectorial indices based on ground observations are introduced to select profiles corresponding to low magnetic activity. These indices provide a better discrimination of quiet data than the global Kp index usually used for that purpose. (5) A time-and longitude-dependent dynamic model of the equatorial electrojet is derived and used to correct magnetic measurements at low latitudes. Anomaly maps of X and Z components are obtained using selected measurements within the reduced altitude range: 350425 km. These maps are compared with earlier Magsat anomaly maps, and their respective resolutions are discussed. These maps evidence large anomalies of lithospheric origin within the oceanic domain. In particular, the Z map displays a characteristic pattern of long-wavelength anomalies in these areas. It is first shown that some of these anomalies, particularly in the North Atlantic and Indian oceans, may be correlated with the age of the lithosphere. Then, a significant similarity between magnetic and geoid anomalies above ocean basins is evidenced. This suggests that long-wavelength oceanic magnetic anomalies may also be attributed to variations of the thickness of the magnetized layer associated with ocean floor topography. result, these maps have hardly been used to investigate the distribution of magnetic sources in the lithosphere or even to derive local surface magnetization models.Most previous studies of the anomaly field observed by Magsat (see, e.g., Magsat special sections of Geophysical Research Letters, 9, 1982, and Journal of Geophysical Research, 90, 1985) were based on scalar maps and focused on the interpretation and modeling of local short-wavelength anomalies. Indeed, since the main and surface anomaly fields are of comparable magnitude at wavelengths near 3000 km [Langel and Estes, 1982a], the anomaly field of lithospheric origin is poorly represented at these wavelengths by total field anomaly maps (i.e., maps of the projection of the vector anomaly field onto the direction of the main field).Yet the solution to many problems regarding the global distribution of magnetization in the lithosphere and its relations with other geophysical parameters would benefit from accurate global vector anomaly maps: Is the thickness of the magnetic layer related to the age (or the temperature) of the lithosphere or does the magnetization depend significantly on the composition of the crust? Is remanent magnetization a sign...

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Section: Comparison With Earlier Global Magsat Anomaly Mapsmentioning

confidence: 69%

New global vector magnetic anomaly maps derived from Magsat data

Cohen¹,

Achache²

1990

J. Geophys. Res.

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“…This misplacement can also be observed in the previous studies of the Aleutians (Clark et al, ) and Central America (Vasicek et al, ), where dipping slab models were used. Counil and Achache () matched the observed anomalies at the Central America subduction zone using a set of horizontal magnetized bodies, all centered landward of the trench. Our results for the UVIM case, which use more recent satellite observations and a magnetization model incorporating other crustal sources, support their finding and suggest that it can be generalized to most present subduction zones.…”

Section: Discussionmentioning

confidence: 85%

Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

Williams

Gubbins

2019

JGR Solid Earth

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Most subduction zones have associated long‐wavelength anomalies in the lithospheric magnetic field observed at satellite altitude. We model the 13 subduction zones defined by seismicity and seismic tomography using vertically integrated magnetizations that are increasing, level, or decreasing away from the trench. These mimic end members of a magnetized mantle wedge, a uniform layer, and a magnetized dipping lithospheric slab. They are added to a global model of vertically integrated magnetization based on continental and oceanic geology. We find the dipping slab places the anomaly too close to the trench, while the other two fit the data equally well and use the level model in the main part of the study. Anomalies at the Sunda, Aleutians, Cascadia, Central American, and Kamchatka‐Japan zones are well modeled by uniform magnetization of differing susceptibilities and spatial extents. We show the South American anomaly is weak because the magnetization lies mainly in the null space that produces no external potential magnetic field. There is no anomaly associated with the Ryukyu system, possibly because the present subduction started too recently for magnetization to have formed. The magnetic anomaly stretching down the Baja California peninsula is not present in the prediction because there is no seismicity on which to base a slab geometry, but recent tomography suggests a fossil slab there and we propose historic subduction as the origin of the Baja magnetic anomaly. Finally, we discuss the mineralogical origins of the magnetization and favor serpentinization of the region above the subducted plate.

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“…The predicted anomaly map is free of such contaminations and thus helps to distinguish anomaly features over the C-O boundary. There are also anomaly features over the oceans, flanked by Phanerozoic con- tinental regions, which are due to either, subduction zones, viz., Aleutian arc (Clark et al, 1985) in the northern Pacific region, and southwest coast of Mexico (Counil and Achache, 1987) or with oceanic plateaus, especially off the eastern coast of Australia and southern coast of Africa. The strong negative anomaly features over the Labrador Sea, situated between Greenland and the North American craton, could be a result of higher VIS value on both sides of the continents as compared to the smaller value of the Labrador Sea (Bradley and Frey, 1991).…”

Section: Preliminary Resultsmentioning

confidence: 99%