Open AccessMagnetic properties and paleointensities as function of depth in a Hawaiian lava flow
Author(s) -
de Groot Lennart V.,
Dekkers Mark J.,
Visscher Martijn,
ter Maat Geertje W.
Publication year - 2014
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2013gc005094
Subject(s) - geology , remanence , lava , magnetite , magnetic mineralogy , rock magnetism , petrology , mineralogy , volcano , flow (mathematics) , magnetic anomaly , thermoremanent magnetization , geophysics , geochemistry , magnetization , magnetic field , paleontology , geometry , mathematics , physics , quantum mechanics
Abstract 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 distance from the flow top; 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 ülvospinel 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 μT. This is in good agreement with the paleointensity results obtained using the thermal IZZI‐Thellier technique (41.6 ± 7.4 μT) 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.