Paleointensities of the Hawaii 1955 and 1960 Lava Flows: Further Validation of the Multi-specimen Method

Abstract

The Kilauea 1955 and 1960 lava flows (Big Island of Hawaii, USA), both emplaced in a field of ∼36 μT, were studied using the multi-specimen parallel differential partial thermoremanent magnetization (pTRM) paleointensity (PI) method. In nineteen specimens from an upper cooling unit of the 1955 flow, the pTRMs were acquired at a temperature of 450°C and a PI of 34.3 ± 1.5/1.6 μT was obtained, while 13 specimens of the lower cooling unit heated to 230°C resulted in a PI of 38.5 ± 3.3 μT. The 1960 flow was studied at various temperatures of 400, 440, 480, 500 and 550°C. At 400 and 550°C overestimates of the PI were obtained: 47.3 μT and 41.5 μT respectively. The other temperatures yielded PI values ranging from 32.2 to 34.2 μT, just 6–11% lower than the expected field and similar to the 1955 flow results. The 550°C PI result is biased because of mineral alteration as indicated by an 18% susceptibility decrease which reduces the pTRM capacity leading to an overestimate of the PI. The overestimate of the PI at 400°C may be due to the comparatively small pTRM acquired and thus to larger high-temperature pTRM tails. Results obtained with the multi-specimen method for both flows compare favorably with the best other PIs obtained by the Thellier–Coe, Thellier–Thellier and microwave methods. The success rate is high with more than 90% of specimens contributing to a PI. Only the Thellier–Coe method used on single plagioclase crystals and the microwave method have similar success rates.