Interpretation of Magnetic Anomalies at Low Latitudes: Potential Pitfalls
D. E. Bird, S. A. Hall, J, F. Casey, P. S. Millegan, 1998. "Interpretation of Magnetic Anomalies at Low Latitudes: Potential Pitfalls", Geologic Applications of Gravity and Magnetics: Case Histories, Richard I. Gibson, Patrick S. Millegan
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The vector nature of the Earth's magnetic field dictates that interpreters must take care to understand pitfalls related to the orientation of the field (i.e., magnetic inclination and declination), and the relationship of the magnetic field to a region's geology. The case history presented here demonstrates one such pitfall. Present models for the formation of the Grenada Basin vary from north-south extension to northeast-southwest extension to east-west extension. Gridded magnetic anomalies over the basin provide a picture of the Earth's field that contributes to this spectrum of possible extensional origins.
The Grenada Basin is a back-arc basin located near the eastern edge of the Caribbean Plate. The basin is bounded on the east and west by the roughly north-south-trending active Lesser Antilles and remnant Aves Ridge Island Arcs, respectively. Although this physiography, as well as gravity data, supports formation by near east-west extension, magnetic anomalies over the basin exhibit predominantly east-west trends. The crust of the Grenada Basin and of other back-arc basins forms similarly to the crusts of ocean basins. If the observed magnetic anomalies over the basin are produced by sea-floor spreading, then the orientation of extension may be complex. Extension in most back-arc basins is roughly normal to their trenches and subduction zones, but some basins appear to exhibit oblique extension. A careful interpretation of magnetic profiles reveals low-amplitude magnetic anomaly trends, oriented subparallel to the island arc, over the southern part of the Grenada Basin, which supports a model for basin development by near east-west extension.