Magnetic polarity structure of the lower oceanic crust

A newly developed rock drill was used to take the first fully oriented samples from in-situ gabbros exposed on Atlantis Bank, which formed 11 m.y. ago on the Southwest Indian Ridge (SWIR). These paleomagnetic data locate the seabed outcrop of a normal polarity magnetic lineation within an outcrop of lower crust that correlates with overlying deep-towed and sea-surface magnetic field measurements. A systematic lateral offset between the seabed boundary and measured anomalies implies that the reversal boundary dips similar to 25 degrees to the south, away from the ridge axis. Paleomagnetic results suggest that following magnetization acquisition, the platform tilted south by similar to 20 degrees (range: 33 south degrees to 7 degrees north), implying an original reversal boundary dip of only similar to5 degrees.