Absolute paleointensity between 60 and 400 ka from the Kohala Mountain (Hawaii)

Magnetic experiments including thermal demagnetization of the natural remanent magnetization (NRM), mineralogical studies and paleointensity measurements have been conducted on ten lava flows, with ages between 60 ka and 400 ka, from the Kohala Mountain, Hawaii. Of the samples, 62 were subjected to double heating paleointensity experiments under vacuum. In total, 35% of the specimens did not exhibit significant magnetomineralogical changes during heating and met all the criteria for successful determinations of absolute paleointensity. A technique of corrections [1] was attempted for samples that exhibited changes in their ability to acquire partial thermoremanent magnetization (pTRM) during heating but did not show acquisition of chemical remanence (CRM). This procedure doubled the rate of success, with consistent results between the uncorrected and the corrected data from within the same flows. The successful paleointensity estimates obtained for 8 lava flows are found to be in good agreement with previous absolute paleointensities obtained from other areas. The results are also consistent with the synthetic curve (Sint-200) of relative paleointensity obtained for the past 200,000 years from deep-sea sediment cores [2]. There is thus no reason to infer the presence of large non-dipole fields in the vicinity of Hawaii. Overall, the geomagnetic intensity appears to have the same variability for at least the past 200 ka.