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Boso TTT-Type Triple Junction: Formation of Miocene to Quaternary Accretionary Prisms and Present-Day Gravitational Collapse

2011; Springer Nature (Netherlands); Linguagem: Inglês

10.1007/978-90-481-8885-7_3

1876-1690

Yujiro Ogawa, Yukio Yanagisawa,

Methane Hydrates and Related Phenomena

The Boso triple junction, the only known trench-trench-trench type triple junction, was surveyed by the ROV KAIKO-10K after the French–Japanese KAIKO project and related R/V Hakuho-Maru cruises. This paper summarizes the bathymetry and geologic structure, and the types and ages of rocks and sediments observed in the Boso triple junction area during these studies. We used diatom biostratigraphy to elucidate the evolution of Miocene accretionary prism units exposed in the Izu-Bonin forearc and in subaerial exposures on the Boso Peninsula. The instability of the Boso triple junction system since the Miocene is attributed to repeated trench sediment accretion and collapse. We conclude that the Boso triple junction area hosts a sequence of trench-fill sediments that has accumulated between the easternmost margin of the Izu forearc and the easternmost Nankai trough since the Miocene. However, recent instability at the Boso triple junction is characterized by repetitive episodes of development and subsequent collapse of a ponded basin close to the accretionary prism that are intimately associated with the development of the Boso triple junction system.