Large rotation of the Easter microplate as evidenced by oriented paleomagnetic samples from the ocean floor

One of the goals of the Pito93 cruise along the perimeter of the Easter microplate was to obtain oriented rock samples from the ocean floor for paleomagnetic study. Using a new orienting device, the Geocompass, 14 oriented blocks were obtained during 6 dives conducted using the Ifremer DSRV Nautile. Paleomagnetic analysis shows that 13 of these 14 blocks give consistent results in thermal and AF demagnetizations, and reveals a mean Characteristic Remanent Magnetization (ChRM) direction within each block, with both normal and reverse polarities. After elimination of data from 5 blocks situated outside the microplate, and one block which bears an anomalous direction, we have computed a mean ChRM direction at Dm = 49.0°, Im = −39.0° (k = 10.2, α95 = 19.8 °, n = 7). Although the mean inclination is in agreement with the inclination of the recent dipole magnetic field (D = 0°, I = −43°), the average declination is significantly different from this direction, which we interpret as due to a bulk clockwise rotation of 48.5° ± 11° (after the bivariate average) of the Easter microplate over the past 2–3 Ma. This value is in excellent agreement with previous estimates based on remote geophysical measurements and models.