HR: 0830h
AN: GP11C-0272    [PDF]
TI: Paleomagnetism of a Long Sequence of Lavas Recorded on the Island of Lana'i, Hawai'i, USA
AU: * Herrero-Bervera, E
EM: herrero@soest.hawaii.edu
AF: SOEST-HIGP University of Hawaii, Paleomagnetics and Petrofabrics Laboratory, 1680 East West Rd., Honolulu, HI 96822 United States
AU: Valet, J
EM: valet@ipgp.jussieu.fr
AF: I.P.G.P. UMR 7577 Geomagnetisme et Paleomagnetisme, 4 Place Jussieu, Paris, 75252 France
AB: Previous published work on Lana'i indicated that the volcano was formed mainly during the Matuyama Chron (Herrero-Bervera et al., 2000). In order to constrain further the timing of the active phases of the Lana'i volcano, we conducted a paleomagnetic and rock magnetic study involving a 250 m thick sequence of at least 300 flows that were erupted between 0.76+/-0.66 Ma and 1.46 +/-0.25 Ma according to previous K/Ar dating. Low-field susceptibility versus temperature (k-T) and SIRM experiments performed on a dozen flows indicate that magnetite dominates the remament magnetization (575$^{o}$ C). In a few cases a low-temperature mineral phase (300-400$^{o}$ C) could reflect the presence of titanomagnetite with low Ti content but the presence of maghemite or pyrrhotite cannot be completely excluded. Additional investigations are in progress on this matter. All specimens were stepwise demagnetized by alternating fields from 5 to 100 mT. Companion specimens from the same samples were demagnetized at 15 temperature steps. The demagnetization diagrams obtained with each technique showed a stable direction of remanence. In all cases, the characteristic (ChRM) component was clearly defined from at least seven successive directions isolated during stepwise demagnetization. The succession of the mean directions caclulated for each lava flow reveals the existence of three polarity intervals. Based on radiometric dates they were assigned to the Cobb, Jaramillo and Kamikatsura Subchrons. Thus, the present results, along with the radiometric ages of the lavas indicate that the tholeiitic flows that formed the Lanai volcano were erupted over a short time period and only during the Matuyama Chron (0.780-2.58 Ma). No eruption occurred during the Brunhes Chron (0.78 Ma) as previously reported for the K-Ar dated lavas in the Maunalei Gulch.
DE: 1513 Geomagnetic excursions
DE: 1520 Magnetostratigraphy
DE: 1522 Paleomagnetic secular variation
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting