Oceanic crust next to passive margins: A structural origin for magnetic zones

Abstract

Sea-surface 3-D magnetic intensity and resolution threshold curves have been completed for various patterns of spreading-generated magnetic source blocks on the sea-floor. These curves confirm that the earliest magnetic anomaly source blocks to form between oblique-to-spreading continental margins are too small to be individually resolved at the sea surface. This result suggests that a magnetically bland area (quiet zone) will develop during the early stages of spreading between oblique margins, regardless of the behaviour of the Earth's magnetic field at the time that the sea-floor formed. Sea-surface 3-D magnetic anomaly patterns have been computed for a possible sea floor spreading pattern formed between oblique-to-spreading continental margins during a time when regular magnetic reversals were occurring. This computation not only generates both the slope anomalies and quiet zones that characterize such margins, but also generates a diagnostic set of notched and bifurcated anomaly pattern elements, which we have subsequently recognized in marginal magnetic quiet zones adjacent to eastern Canada.