Variability of Sea‐Surface Magnetic Anomalies at Ultraslow Spreading Centers: Consequence of Detachment Faulting and Contrasted Magmatism?

Abstract

AbstractThe capacity of oceanic crust to record geomagnetic polarity reversals makes sea‐surface magnetic anomalies an essential tool to study plate tectonics. The anomalies are usually well‐defined at magmatic spreading centers, but are distorted and eventually disappear on magma‐poor mid‐ocean ridges such as the ultraslow Southwest Indian Ridge (SWIR), making their interpretation difficult. We attribute the variability of the SWIR sea‐surface magnetic anomalies to the alternance of magmatic spreading and detachment faulting. A three‐layer magnetic model is used to simulate the influence of such an alternance on the sea‐surface magnetic anomalies. Conversely, observed magnetic profiles at the SWIR are modeled to unravel their off‐axis crustal structure and past mode of spreading. The intruding gabbro bodies on the footwall of detachment faults play a major role in explaining the variability of sea‐surface magnetic anomalies at slow and ultraslow spreading ridges.