地磁気逆転開始期の地球磁場変動

概要

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We report the paleomagnetic behaviors at the beginning of the latest geomagnetic polarity reversal (Brunhes-Matuyama reversal of 0.78 Ma age) recorded in Tahitian lava flows. We applied an improved paleointensity determination method (double heating technique of the Shaw method with low-temperature demagnetization, LTD-DHT Shaw method), and detected oscillation-like changes in virtual dipole moments (VDMs) with a large amplitude ranging from 1.5 × 1022 to 10.9 × 1022 AM2 just prior to the directional reversal. The VDM changes are almost linearly correlated with the virtual geomagnetic pole (VGP) latitudes (60-90°S). We call this VDM-VGP latitude trend “reversal line”. Although the Thellier data reported for the Brunhes-Matuyama reversal are more scattered than our data, they also show a weak trend in the VDM-VGP latitude diagram, supporting the reversal line from a different locality. The scatter in the Thellier data may be caused by overestimated paleointensities due to methodological problems which are indicated in the recent studies of historical lavas. Therefore it appears that the reversal line from the Tahitian lavas in this study does not show a local change but represents a global-scale phenomenon in the geomagnetic reversal process.
社団法人東京地学協会の論文
2005-04-25