First vertical derivative of magnetic anomalies map, Canada = Carte des anomalies de la dérivée première verticale du champ magnétique, Canada. : M183-2/7878-PDF

"The first vertical derivative of magnetic anomalies map of Canada shows small variations in the magnetic field. The derivative is calculated from the residual magnetic field and enhances the short wavelength component of the field. The magnetic character of a rock depends on its composition and its deformational and metamorphic history. To map these variations, the Geological Survey of Canada has been acquiring aeromagnetic data since 1947. Over the years, more than 500 surveys have been carried out, generally with a flight-line spacing of 800 m and an altitude of 305 m above the ground. These aeromagnetic surveys have been levelled to each other to correct for arbitrary datums, slow variations of Earth's magnetic field over time, and differing survey specifications. The dominant structural trends of geological provinces, truncation of those trends at structural boundaries, and the characteristic patterns of suture zones can be recognized on the magnetic anomaly map. The magnetic signature of Precambrian basement rocks can be seen through the Phanerozoic sedimentary basin cover. Major dyke swarms can be traced over hundreds of kilometres from their radiating linear magnetic pattern. Oceanic crust has a characteristic striped magnetic pattern that is due to changes in the polarity of Earth's magnetic field, which occur over intervals of millions of years"--Abstract.

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publications.gc.ca/pub?id=9.961034&sl=1

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