Long‐wavelength magnetic anomalies in the Caribbean: Plate boundaries and allochthonous continental blocks

Abstract

Vector magnetic anomaly maps are derived at satellite altitude from Magsat data over the Caribbean and Middle America. To minimize smoothing of the anomaly field caused by averaging the data over the whole altitude range of Magsat measurements, two maps are derived in two nonoverlapping altitude ranges: 350–420 and 420–550 km. A composite map of the vertical component of the anomaly field is then computed at ground level. This map displays large positive anomalies associated with fast subduction zones. These anomalies define discontinuities in the downgoing slab associated with seismic gaps. Positive anomalies are also consistently observed above allochthonous blocks of continental origin in the Caribbean area and suggest that the average magnetization is larger in the continental lithosphere. Elongated magnetic lows are observed above transform boundaries of the Caribbean plate. The Cayman Trough anomaly is consistent with magnetization of the order of 1 A/m in the upper mantle. Demagnetization of the lithosphere along the Bocono‐El Pilar fault system which bounds the Caribbean plate to the south may be accounted for by frictional heating along shear zones. The pattern of anomalies along the southern margin of the United States is related to its accretionary tectonic history. Various estimates of the vertically integrated magnetization of both oceanic and continental lithospheres are computed using these anomalies and provide constraints on the vertical distribution of lithospheric sources of Magsat anomalies.

Depths to the magnetic layer bottom in the South China Sea area and their tectonic implications

“…However for the oceanic lithosphere it could be quite a different scenario, and it has been observed that the uppermost part of the mantle has magnetization in some oceanic regions (e.g. Counil et al 1989; Chiozzi et al 2005). Based on the traditional Parker–Oldenburg algorithm (Parker 1973; Oldenburg 1974), we also estimate the Moho depths in the area (Fig.…”

The seafloor spreading rate dependence of the anomalous skewness of marine magnetic anomalies

“…MAGSAT observations (Arkani-Hamed 1989;Counil, Achacha & Galdeano 1989) and studies of long-wavelength magnetic anomalies (Harrison & Carle 1981) suggest that the lower crust and possibly the upper mantle are magnetic and dominant sources of the anomalous skewness. The different models differ in their predictions of the effects of spreading rate and age of the polarity interval on the anomalous skewness.…”

An integrated geodynamic model of the Nankai subduction zone and neighboring regions from geophysical inversion and modeling

“…It is found that, in the oceanic basins studied in this paper, the Curie depths are consistently deeper than the Moho depths, indicating that about 10 km of the uppermost oceanic mantle is also magnetized. Magnetized mantle or Curie depth deeper than Moho has been previously suggested in various ocean basins by a number of scientists (Arkani-Hamed, 1988;Counil et al, 1989;Okubo et al, 1991;Hayling, 1991;Chiozzi et al, 2005;Li et al, 2010). Beneath the island arc and the forearc region, Curie depths tend to be closer to the Moho depths.…”