Magnetic properties and paleointensities as function of depth in a Hawaiian lava flow - de Groot - 2014 - Geochemistry, Geophysics, Geosystems -
Wiley Online Library
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The outcome of paleointensity experiments largely depends on the rock-magnetic properties of the samples. To assess the relation between volcanic emplacement processes and rock-magnetic properties, we sampled a vertical transect in a &6 m thick inflated lava flow at Hawaii, emplaced in &588 AD. Its rock-magnetic properties vary as function of distan the observations can be correlated to the typical cooling rate profile for such a flow. The top and to a lesser extent the bottom parts of the flow cooled faster and reveal a composition of &TM60 in which the magnetic remanence is carried by fine-grained titanomagnetites, relatively rich in titanium, with associated low Curie and unblocking temperatures. The titanomagnetite in the slower cooled central part of the flow is unmixed into the magnetite and &lvospinel end-members as evidenced by scanning electron microscope observation. The remanence is carried by coarse-grained magnetite lamella (&TM0) with high Curie and unblocking temperatures. The calibrated pseudo-Thellier results that can be accepted yield an average paleointensity of 44.1&&&2.4 &T. This is in good agreement with the paleointensity results obtained using the thermal IZZI-Thellier technique (41.6&&&7.4 &T) and a recently proposed record for Hawaii. We therefore suggest that the chance of obtaining a reliable paleointensity from a particular cooling unit can be increased by sampling lavas at multiple levels at different distances from the top of the flow combined with careful preliminary testing of the rock-magnetic properties.}