GEOMAGNETIC-FIELD INTENSITY OVER THE LAST 42,000 YEARS FROM CORE SOH-4, BIG-ISLAND, HAWAII

A record of the absolute geomagnetic field intensity spanning the last 42 kyr has been obtained from 100 lava flows (187 successful Thellier experiments) recovered in the top 468 m of core from the SOH-4 well o n the Island of Hawaii. Assuming a linear extrusion rate between the p resent and the 42 kyr date obtained with a refined K/Ar technique, thi s corresponds to an average of one flow every 420 years. Rock magnetic analysis identifies low-Ti content and high-Ti content magnetites in 75% and 25% of the samples, respectively, as the main carriers of magn etization. The low-Ti magnetites are very stable while some transforma tions occur upon heating in the other samples, but both groups allow r eliable paleointensity determinations. The directional record document s inclinations consistent with a geocentric dipole field for the last 16 kyr and between 38 and 42 kyr, Between 16 and 38 kyr shallower and, in some cases, negative inclinations, were observed. Because of the h igh extrusion rate and the exceptional percentage of reliable intensit y determinations, the record of the geomagnetic field intensity over t he last 42 kyr has a resolution comparable to the best sedimentary rec ords. The geomagnetic field intensity at Hawaii appears to have varied between 18 and 79 mu T and is characterized by large fluctuation with peak-to-peak amplitudes of 20-25 mu T. The observed values are quite consistent with other values obtained from Hawaii for the last 31 kyr (Mankinen and Champion, 1993a, b; Tanaka and Kono, 1991; Coe et al., 1 978), The mean intensity over the explored time interval, 45 mu T, is slightly higher than the present value of the geomagnetic field in Haw aii.