Testing determinations of absolute paleointensity from the 1955 and 1960 Hawaiian flows

摘要

A new exhaustive study of the flows erupted in 1955 and 1960 from the Kilauea volcano (Big Island of Hawaii) has been conducted in order to constrain the dispersion inherent to the data of absolute paleointensity reported so far and ultimately to determine what are the most critical parameters to obtain suitable determinations. The mean directions derived from both flows agree with the expected field within less than 2°. Paleointensity experiments have been performed using a double heating Thellier procedure completed by systematic pTRM checks. Almost all samples display a linear NRM-TRM straight line but only 20% of the samples have provided suitable results less than 10% away from the expected field. In the other cases, the deviation from the expected paleointensity is related to the quality of the pTRM checks, which thus provides a threshold value for acceptance of pTRM checks. All successful determinations less than 10% away from the expected value have a maximum DRAT (Selkin and Tauxe, 2000) that never exceeds 5% while the mean value of all deviations is lower than 3.5%. Another interesting feature is the existence of a link between the unblocking temperature spectra and the accuracy of the paleofield, which points out the origin of difficulties in the presence of a wide distribution of grain sizes and/or the existence of several magnetic phases. The results also indicate that magnetite with a narrow range of high unblocking temperatures and little variability in grain size is a favorable situation to obtain suitable determinations with a high success rate. These observations may well explain the dispersion inherent to the previous studies of the Hawaiian flows.