[S-EM37_30AM1] 地磁気・古地磁気・岩石磁気

[SEM37-04] 溶結凝灰岩による絶対古地磁気強度測定：相対古地磁気強度と絶対古地磁気強度の対比

藤井 哲夢¹、*望月 伸竜²、長谷川 健³、岡田 誠³、渋谷 秀敏¹ (1.熊本大学自然科学研究科、2.熊本大学大学院先導機構、3.茨城大学理学部)

キーワード：絶対古地磁気強度, 相対古地磁気強度, テフラ, 酸素同位体比層序, 溶結凝灰岩

Absolute geomagnetic paleointensities (APIs) have been estimated from igneous rocks, while relative paleomagnetic intensities (RPIs) have been reported from sediment cores. These two datasets have been treated separately, as correlations between APIs and RPIs are difficult on account of age uncertainties. We present a procedure for directly correlating APIs with RPIs of a RPI stack. Correlations between APIs and RPIs were conducted with virtually no associated age errors using both tephrochronologic correlations and RPI minima. Using the stratigraphic positions of tephra layers in oxygen isotope stratigraphic records, we directly compared the RPIs and APIs reported from welded tuffs contemporaneously extruded with the tephra layers. In addition, RPI minima during geomagnetic reversals and excursions were compared with APIs corresponding to the reversals and excursions. The comparison of APIs and RPIs at these exact points allowed a reliable calibration of the RPI values. In this study, we applied the Tsunakawa-Shaw method to 21 welded tuffs to increase API dataset. We obtained mean paleointensities for 16 of the 21 welded tuffs. Since eight of the 16 welded tuff units were correlated with the oxygen isotope stratigraphy, they can be added to the API data used in the correlation procedure. Combining these API data with the reported data, we correlated API data with RPIs from the PISO-1500 stack and SINT-800 stack. For 13 correlation points, RPIs of the PISO-1500 stack showed a linear relationship with virtual axial dipole moments (VADMs) calculated from the APIs, indicating that the PISO-1500 stack has a linear relation to the axial dipole moment. On the other hand, PRIs from the SINT-800 stack has a tread with VADMs and the correlation coefficient is lower than that of the PISO-1500 stack. The correlation procedure with increased API data can contribute to constraining the relation between RPI of a RPI stack and API and calibrating a RPI stack to absolute values.