Paleointensity study of the Brunhes-Matuyama reversal recorded in lavas on Tahiti Island by the LTD-DHT Shaw method

We have been investigating the Brunhes-Matuyama (B-M) polarity reversal recorded in lavas of the northern side of the Punaruu Valley, Tahiti Island. The lavas were sampled successively as possible as we can and in total 34 sites were located. From the bottom to the top of the sampled lavas, the directional data show a reversed (R) polarity, intermediate-normal-reversed (I-N-R) change and subsequently normal (N) period. These directional changes suggest that these lavas are considered to record the paleomagnetic field variation from the Matuyama chron to the whole stage of the B-M reversal. Paleointensity determinations were made by the LTD-DHT Shaw method (Tsunakawa and Shaw, 1994; Yamamoto et al., 2003; Mochizuki et al., 2004). For the directionally unstable period (I-N-R), the paleomagnetic field intensity was weak (4.7 μT). For the Matuyama reversed period prior to the directional reversal, the paleointensity results suggest that the field intensity varied in oscillation-like manner between 2 and 43 μT. It is noted that the virtual dipole moments (VDMs) in the oscillation-like change show a clear correlation with the VGP latitudes change, suggesting one of the important processes in the geodynamo for the polarity reversal.