Geomagnetic paleointensities at Hawaii between 3.9 and 2.1 Ma: preliminary results

Thellier¯Thellier experiments have been conducted on 454 samples from different sequences of the Waianae and Koolau volcanoes in Oahu, Hawaii. The sampled interval, as determined by K/Ar dating, spans from 3.9 to 2.1 Ma. Results from 89 samples from 41 flows meet restrictive reliability criteria and provide the first paleointensity estimates from Hawaii for the sampled period with good temporal resolution. On this time interval, the VADM shows ample fluctuations from a minimum of 2.3×1022 Am2 to a maximum of 11.5×1022 Am2, about an average value of 7.0±2.3×1022 Am2, suggesting that fluctuations of the geomagnetic field strength comparable in amplitude to the time-averaged value may be a characteristic of the field. During both the reverse Mammoth chron and the normal chron between the Mammoth and the Kaena, the field strength appears to increase with time.