Open Access40 Ar/ 39 Ar ages and palaeomagnetism of transitionally magnetized volcanic rocks in the Society Islands, French Polynesia: Raiatea excursion in the upper‐Gauss Chron
Author(s) -
Yamamoto Y.,
Ishizuka O.,
Sudo M.,
Uto K.
Publication year - 2007
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2006.03277.x
Subject(s) - excursion , geology , paleomagnetism , earth's magnetic field , geomagnetic pole , paleontology , volcano , lava , geomagnetic secular variation , geomagnetic reversal , geophysics , seismology , magnetic field , physics , political science , law , quantum mechanics , geomagnetic storm
SUMMARY Volcanic rock samples from several sites in the Society Islands, French Polynesia were found to be transitionally magnetized. To better characterize these geomagnetic events, we performed laser‐heating 40 Ar/ 39 Ar dating and additional palaeomagnetic measurements on these samples. The measurements give virtual geomagnetic pole (VGP) latitudes of 0.7–52.4°N and virtual dipole moment (VDM) values of 0.433–0.682 × 10 22 A m 2 which are typical for the transitional geomagnetic field. These transitional events occurred at 2.77 ± 0.02 Ma (Raiatea), 3.20 ± 0.03 Ma (Tahaa) and 4.40 ± 0.01 Ma (Maupiti). Considering the reported radioisotopic ages for known geomagnetic events, it is suggested the first event is a previously unknown geomagnetic excursion (Raiatea excursion) while the latter two probably correspond to known polarity transitions (upper boundary ages of the Mammoth reversed subchron and the Nunivak normal subchron). The existence of the proposed Raiatea excursion is supported by the contemporaneous palaeointensity low recognized in the relative palaeointensity stack from the equatorial Pacific.