4:00 PM - 4:15 PM
[SVC36-09] Significance of subaqueous volcanic rocks collected from the deep-sea area of the western slope of the Izu Peninsula, Japan.
Keywords:Izu-Peninsula, Subaqueous volcanic rocks
The Izu Peninsula, located at the northern part of the Izu-Ogasawara Arc, consists of the middle Miocene Nishina and Yugashima Group which as a basement, the upper part of the Late Miocene to Pliocene Shirahama Group, and the uppermost part of the Quaternary Atami Group. Except for the Atami Group, which constitutes the uppermost part, the Yugashima and Shirahama Formations, which make up the lower part, were formed by volcanic activity on the seafloor (Okamura et al.,1999).
In October 2024, the Scientific cruise 3 was conducted in the northern part of the Izu-Ogasawara Arc and Suruga Bay by the R/V Bosei-Maru (1,700 tons). During the dredge survey, rock sampling was conducted at depths of 2200 to 1600 m off the coast of Hagachi-zaki, Izu Peninsula. A large number of rocks (strongly to weakly altered tuffaceous conglomerate and various volcanic rock fragments of basalt to rhyolite) were collected off the coast of Hagachi-zaki, Izu Peninsula. In this report, we discuss the formation environment of volcaniclastic rocks based on the morphological characteristics and diversity of the collected rocks.
The volcanic activity estimated of the rock sample is as follows: 1) Basaltic pyroclastic rocks were collected at the bottom of the sampler and are inferred to comprise the lower part of the slope. 2) The andesitic volcaniclastic, however, is a homogeneous fragments pf matrix (yellowish color: paragonite alteration), with some rhyolitic rock fragments also observed. 3) In addition, rock fragments that are porous and red oxidized rock fragments were observed in the brecciated fragments. This suggests that the volcanic activity environment has shifted from deep water to shallow water. Thus, the deep-sea area off the western side of the Izu Peninsula has been exposed as a variety of volcaniclastic rocks, ranging from a single basaltic volcanic ejecta to a variety of andesitic to rhyolitic volcanic clastic rocks, indicating a transition from deep- to shallow-sea volcanism environments.Reference: Okamura et al. (1999) 1:200,000 scale submarine geological map of Suruga Bay. Submarine Geological Map of Suruga Bay, No.52, Geological Survey of Japan.
In October 2024, the Scientific cruise 3 was conducted in the northern part of the Izu-Ogasawara Arc and Suruga Bay by the R/V Bosei-Maru (1,700 tons). During the dredge survey, rock sampling was conducted at depths of 2200 to 1600 m off the coast of Hagachi-zaki, Izu Peninsula. A large number of rocks (strongly to weakly altered tuffaceous conglomerate and various volcanic rock fragments of basalt to rhyolite) were collected off the coast of Hagachi-zaki, Izu Peninsula. In this report, we discuss the formation environment of volcaniclastic rocks based on the morphological characteristics and diversity of the collected rocks.
The volcanic activity estimated of the rock sample is as follows: 1) Basaltic pyroclastic rocks were collected at the bottom of the sampler and are inferred to comprise the lower part of the slope. 2) The andesitic volcaniclastic, however, is a homogeneous fragments pf matrix (yellowish color: paragonite alteration), with some rhyolitic rock fragments also observed. 3) In addition, rock fragments that are porous and red oxidized rock fragments were observed in the brecciated fragments. This suggests that the volcanic activity environment has shifted from deep water to shallow water. Thus, the deep-sea area off the western side of the Izu Peninsula has been exposed as a variety of volcaniclastic rocks, ranging from a single basaltic volcanic ejecta to a variety of andesitic to rhyolitic volcanic clastic rocks, indicating a transition from deep- to shallow-sea volcanism environments.Reference: Okamura et al. (1999) 1:200,000 scale submarine geological map of Suruga Bay. Submarine Geological Map of Suruga Bay, No.52, Geological Survey of Japan.