S1: Dynamics of igneous processes (Special Session, Joint Session with The Volcanological Society of Japan) [Oral presentations are by invitation only; poster presentations are open to all.]

12:30 PM - 2:00 PM JST(3:30 AM - 5:00 AM UTC)

[S1P-01] The youngest HIMU ocean island basalts in the Cook-Austral Islands

*Morihisa HAMADA¹, Takeshi Hanyu¹, Maria Luisa G. Tejada¹, Takashi Sano², Shoka Shimizu³, Qing Chang^1,4, Takashi Miyazaki¹, Tomoki Sato¹, Bogdan S. Vaglarov¹, Osamu Ishizuka⁵ (1. Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2. National Museum of Natural Sciences, 3. Chiba Univ., Sci. & Eng., 4. Univ. Tokyo, Sci., 5. Geological Survey of Japan, AIST)

Keywords:

Cook-Austral Islands,HIMU,Raivavae,President Thiers bank

Ocean island basalts (OIBs) from the Cook-Austral Islands in the South Pacific are unique for their geochemical diversity derived from extreme geochemical end member mantle sources, such as high μ (=²³⁸U/²⁰⁴Pb) mantle (HIMU) and enriched mantle (EM). OIBs with HIMU signature occur along the volcanic chain from Mangaia (~20 Ma) to Raivavae (7–11 Ma; Rairua stage), whereas those from other ocean islands and seamounts in this archipelago show EM signature. The origin of the abrupt geochemical gap between Raivavae (HIMU) and Rapa (EM; ~5 Ma) has been debated. We obtained volcanic rocks by dredging from a seamount off-Raivavae and the President Thiers bank, the latter of which is a seamount located between Raivavae and Rapa. All the recovered volcanic rocks showed HIMU signature. ⁴⁰Ar-³⁹Ar dating of the volcanic rocks yielded ages of about 8 Ma and 6–7 Ma, respectively, which are consistent with the younging trend of the HIMU volcanic chain from Mangaia (~20 Ma) to Raivavae (7–11 Ma; Rairua stage). Volcanic rocks from the President Thiers bank (6–7 Ma) are the youngest HIMU OIBs in the Cook-Austral Islands. We strongly suggest that the HIMU- and EM-type mantle sources are paired, that waning of the HIMU-type volcanism was replaced by EM-type volcanism, and that the two types of volcanisms were coeval and overlapped between 6 Ma and 9 Ma at the Cook-Austral Islands.