Boso TTT-Type Triple Junction: Formation of Miocene to Quaternary Accretionary Prisms and Present-Day Gravitational Collapse - Accretionary Prisms and Convergent Margin Tectonics in the Northwest Pacific Basin - page 71

Fig. 10 Geologic map of the subsea area from the Sagami trough to the Boso triple junction
(Adapted from Geological Survey of Japan ( 1990 )). The dark yellow rock unit Pg may correspond
to Paleogene to middle Miocene beds that are partly equivalent to the Kinone Formation on the
Boso Peninsula. Yellow units are middle to late Miocene age. The blue unit D, immediately west
of the triple junction, represents the present-day accretionary prism and the green unit R corre-
sponds to the Neogene accretionary prism at the landward toe of the Izu-Bonin trench (Copyright
permission from Geological Survey of Japan #60635500-A-20110119-002)
the Bonin Islands to the Boso Peninsula, and may be the Oligocene to lower Miocene
rock unit (Pg) shown on the submarine geologic map of Fig. 10 . We conclude that the
Boso triple junction area hosts a sequence of trench-fill sediments that has accumu-
lated 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.