The Bottom Relief and the Anomalous Magnetic Field of the Ninetyeast Ridge in Near 5° N

Abstract

The geophysical survey in cruise# 42 of R/V Akademik Boris Petrov (2017) at the polygon near Site 758 ODP clarified significantly knowledge about the bottom topography of the northern segment of the Ninetyeast Ridge. It is crossed by E–W transversal linear troughs, apparently being young tectonic fractures. The morphology of the narrow elevated block in the central part of the deep depression between neighboring large volcanic edifices is characterized in detail. Along with linear tectonic structures, the main features of this block are two volcanic seamounts. The detail magnetic survey at the polygon identified for the first time the nature of the sources of magnetic anomalies on the Ninetyeast Ridge. Intense local magnetic anomalies are observed here, both confined to local structures of the bottom and basement relief, and clearly unrelated to them. These anomalies are of 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 were formed about 20 million years ago, the oldest ones–over 80 million years ago.