Bottom Relief and Magnetic Anomaly of the Ninetyeast Ridge Near 5°

Abstract

The geophysical survey on cruise 42 of the R/V Akademik Boris Petrov (2017) in the survey area near site 758 ODP significantly refined knowscarp about the bottom topography of the northern segment of the Ninetyeast Ridge. It is crossed by E–W transversal linear troughs, which are apparently young tectonic fractures. The morphology of the narrow elevated block in the central part of the deep depression between neighboring large volcanic edifices has been characterized in detail. In addition to linear tectonic structures, the main features of this block are two volcanic seamounts. A detailed magnetic survey in this area identified for the first time the nature of sources of magnetic anomalies on the Ninetyeast Ridge. Intense local magnetic anomalies have been observed here, both confined to local structures of the bottom and basement relief, and clearly unrelated to them. These anomalies have a complex interfering nature caused by the superposition of fields from sources separated by magnetization, spatial position, and age. According to the results of paleomagnetic analysis of the anomalies, the age of the structures here is very wide: the youngest features formed about 20 Ma ago, and the oldest, over 80 Ma ago.