17:15 〜 18:45
[SCG52-P04] 西太平洋海山群に存在する若いホットスポット海山列の探索
キーワード：ホットスポット、海山、アルカリ玄武岩、Sr-Nd-Pb同位体、小笠原海台、南鳥島
The West Pacific Seamount Province (WPSP) recognized as group of short-lived hotspot tracks erupted in the present French Polynesian region during the Early to Late Cretaceous. However, Hirano et al. (2021) unexpectedly found the Paleogene basalts on Ogasawara Plateaut (55.3 Ma), Uyeda Ridge (57.9 Ma), and submarine slope of Minamitorishima Island (40.2-33.2 Ma) which are on northern part of the WPSP area. Main edifice of the Ogasawara Plateau and the Minamitorishima Island formed during the mid-Cretaceous period revealed by some previous studies about reefal limestones. These two volcanic edifices clearly rejuvenated of Tertiary volcanic activity. Such hiatus could not be explained by simple theory of intraplate volcanism (hotspot hypothesis).
This study analyzed the Paleogene basalts and Cretaceous basalts of WPSP in order to test a Paleogene hotspot track besed on both geochemical and geometrical perspectives. The leached whole-rock Sr-Nd-Pb isotopic compositions both of the Cretaceous seamount and Paleogene rejuvenated lavas were measured by using MC-ICP-MS and TIMS. The original eruptive source regions were reconstructed on the basis of the Absolute Plate Motion model. The samples were totally classified into two groups, the Paleogene low 206Pb/204Pb and high 87Sr/86Sr group and the Cretaceous high 206Pb/204Pb and low 87Sr/86Sr group, the latter of which is totally belong the isotopic compositions of Early Cretaceous N-Wake seamounts owing to a larger contribution of HIMU components. In contrast, the Paleogene lavas are originated from compositionally different component (hotspot) from those of the Cretaceous samples which were erupted at present Mid-Pacific Mountains where no hotspot is observed. We have no data about seafloor observation such as multibeam and other geophysical surveys to recognize an active volcano yet, awaiting future exploring of this area.
This study analyzed the Paleogene basalts and Cretaceous basalts of WPSP in order to test a Paleogene hotspot track besed on both geochemical and geometrical perspectives. The leached whole-rock Sr-Nd-Pb isotopic compositions both of the Cretaceous seamount and Paleogene rejuvenated lavas were measured by using MC-ICP-MS and TIMS. The original eruptive source regions were reconstructed on the basis of the Absolute Plate Motion model. The samples were totally classified into two groups, the Paleogene low 206Pb/204Pb and high 87Sr/86Sr group and the Cretaceous high 206Pb/204Pb and low 87Sr/86Sr group, the latter of which is totally belong the isotopic compositions of Early Cretaceous N-Wake seamounts owing to a larger contribution of HIMU components. In contrast, the Paleogene lavas are originated from compositionally different component (hotspot) from those of the Cretaceous samples which were erupted at present Mid-Pacific Mountains where no hotspot is observed. We have no data about seafloor observation such as multibeam and other geophysical surveys to recognize an active volcano yet, awaiting future exploring of this area.