Paleomagnetism reveals emplacement age of tsunamigenic coral boulders in Ishigaki Island, Japan
Paleomagnetism reveals emplacement age of tsunamigenic coral boulders in Ishigaki Island, Japan
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古地磁学揭示了日本石垣岛引发海啸的珊瑚巨石的侵位年龄
DOI：
10.1130/g35366.1
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发表时间：
2014
期刊：
影响因子：
5.8
通讯作者：
H. Nagahama and K. Minoura
中科院分区：
文献类型：
--
作者：
Sato;T.;Nakamura,N.;K. Goto;Y. Kumagai;H. Nagahama and K. Minoura
我们使用与温度相关的粘性剩余磁化来估计日本石垣岛海岸线上引发海啸的珊瑚巨石的侵位年龄。这些巨石由纹状珊瑚岩组成，它们被海啸沉积的时间是通过放射性碳测年确定的。最近在石垣岛周围珊瑚礁边缘死亡的珊瑚记录了地球的电流磁场(现代地球磁场，PEF)，它是与骨骼中的磁场平行的剩磁。自从珊瑚骨骼被破坏性的海啸波作为巨石部署在海岸线上以来，与PEF平行的巨石上部分叠加了新的粘性磁化作用。热退磁结果表明，这些巨石至少旋转了一次，用L·Néel的单畴磁铁矿驰豫理论确定的侵位年龄与放射性碳年龄吻合较好，但也有多磁铁矿的痕迹。Néel理论在海啸珊瑚巨石中的新应用使我们有机会确定该地区个别海啸珊瑚巨石的年龄和运输方式。
We use temperature-dependent viscous remanent magnetization to estimate the emplacement age of tsunamigenic coral boulders along the shorelines of Ishigaki Island, Japan. The boulders consist of the hermatypic coralPorites, and the time of their deposition by tsunamis has been established using radiocarbon dating. Recently deceased corals at reef edges around Ishigaki Island record the Earth’s current magnetic field (present Earth field, PEF) as a remanence parallel to the field in the skeleton. Since the time when the coral skeletons were emplaced on the shorelines as boulders by destructive tsunami waves, a new viscous magnetization was partially overprinted in the boulder parallel to the PEF. The results of thermal demagnetization indicated that the boulders were rotated at least once, and their emplacement ages determined from L. Néel’s relaxation theory for single-domain magnetite agree well with the radiocarbon ages, although there are traces of multidomain magnetites. New application of Néel’s theory to tsunamigenic coral boulders gives us an opportunity to ascertain the age and transportation mode of individual tsunamigenic coral boulders in this area.