[S-CG45] Ocean Floor Geoscience

[SCG45-05] Magmatic evolutions erupted on the Cretaceous seamount province, western Pacific Plate

*Naoto Hirano¹, Hirochika Sumino², Taisei Morishita³ (1.Center for Northeast Asian Studies, Tohoku University, 2.Graduate School of Arts and Sciences, The University of Tokyo, 3.Hydrographic and Oceanographic Department, Japan Coast Guard)

Keywords:seamount, Pacific, alkali-basalt, petit-spot, hotspot

Numerous seamounts on the western part of Pacific Plate, occur within a region called the western Pacific seamount province (WPSP) that occurred during the Early to Late Cretaceous, where a group of short-lived hotspot seamount chains has formed over the present southern Pacific superplume (Koppers et al., 2003). The majority of Early Cretaceous guyots on the northern part of WPSP were instantaneously submerged as a result of a contemporaneous eustatic sea level rise during the middle Cretaceous time (e.g., Larson, 1991).

Some of the seamount chains cannot be explained using a classical hotspot hypothesis, such as that outlined for the Hawaii–Emperor seamount chain. The seamount chains do not exhibit linear age progression due to, for example, overlapping a younger hotspot (Koppers et al., 1998), coeval volcanism along pre-existing lithospheric fractures (Davis et al., 2002), or the presence of recycled material within the upper mantle immediately after a continental breakup event (Taneja et al., 2016). Moreover, it should be theoretically impossible to identify the age of seamount formation using a single radiometric age because the evolutions of seamount take a long duration of time, exemplified by present Hawaiian shield volcano (a few m.y.; Macdonald and Katsura, 1964), the Aitutaki Island along the Cook–Austral hotspot (7-8 m.y.; Jackson et al., 2020), and the Early Cretaceous Quesada seamount at Mariana Trench oceanward slope (over 10 m.y.; Hirano et al., 2002).

Newly provided Ar-Ar ages for basaltic rocks from seamount, knoll, plateau, ridge, spur, and the Minamitorishima (Marcus) Island outline the evolution of hotspot and petit-spot volcanisms in the northern part of WPSP (Hirano et al., 2019; 2021). This study first reports the Eocene ages for basaltic rocks within the WPSP, an area that has only previously yielded Cretaceous ages. The Eocene basalts from the Chuo Seamount (Ogasawara Plateau) and Minamitorishima Island are thought to reflect volcanic events that overprinted the Cretaceous volcanic edifices in this region. Although some examples of rejuvenated seamounts were previously identified during Ocean Drilling Program Leg 144, no research has yet identified rejuvenating post-Cretaceous volcanic events on pre-existing Cretaceous seamounts within the WPSP. The Minamitorishima Island, moreover, records two stages of Eocene submarine volcanic eruption that generated older pillow lavas (~40 Ma) and younger hyaloclastites of highly vesicular lava (~37 Ma), implying shield-building and rejuvenated volcanoes, respectively. The Eocene volcanic overprints of Minamitorishima mean the island represents a unique part of the northern WPSP as the majority of the Early to middle Cretaceous seamounts within this province became submerged as a result of latest Early to Late Cretaceous sea-level rise. Finally, a petit-spot volcano (younger than 3 Ma) in this region erupted at the greater distance from the trench axis which could be equally explained by a wider outer rise than that at other subduction systems.

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Hirano et al. (2002) Marine Geology, 189, 371-379.
Hirano et al. (2019) Deep-Sea Research Part I, 154, 103142.
Hirano et al. (2021) Island Arc, in press. DOI: 10.1111/iar.12386
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