Paleomagnetism of Line Islands Seamounts: Evidence for Late Cretaceous and Early Tertiary Volcanism

摘要

Seamount magnetic anomaly studies have been conducted on eight volcanoes in the Line Islands seamount chain. The magnetic anomalies of these seamounts were inverted to obtain paleomagnetic information. Four of these gave paleomagnetic pole positions consistent with other Pacific Cretaceous pole positions. Of these, three have reliable radiometric ages ranging from 72 to 85 Ma. The remaining four seamounts gave geomagnetic poles that agree with other Eocene-Early Oligocene Pacific paleomagnetic data, and one has a reliable radiometric age of 39 Ma. All of the apparently Eocene volcanoes occur in the central Line Islands between 8 deg N and 3 deg S. We suggest that the Eocene volcanic event was approximately coincident with the profound change in Pacific plate motion, recorded by the bend in the Hawaiian-Emperor seamount chain that occurred at approximately 43 Ma. This volcanism may have resulted from the large change in intraplate stress accompanying the change of plate motion. The change in stress might have pulled apart a zone of weakness caused by the original formation of the Line Islands. Detailed paleomagnetic modeling of the Line Islands seamounts was necessary to obtain good results, as seven of the eight seamounts appear to be inhomogeneously magnetized to some extent. Despite these inhomogeneities the high goodness-of-fit parameters and the excellent agreement of these results with other Pacific paleomagnetic data suggest that the paleopoles derived from these seamounts are reliably determined.