Geoscience Reference
In-Depth Information
Although the geometric (Le Pichon and Huchon
1987
; Hamano
1987
; Huchon
and Labaume
1989
), geophysical (Seno et al.
1989
), and sedimentologic (Soh et al.
1988, 1990
) aspects of the Boso triple junction have been considered, a detailed
assessment of its geologic significance has yet to be done. Preliminary reports by
Ogawa et al. (
1989, 2008
) described the unstable topography of the Boso triple
junction area from analyses of multibeam echosounder data and single-channel
seismic profiles collected during the first phase of the French-Japanese KAIKO
project in 1984 (KAIKO I Research Group
1986
; Nakamura et al.
1987
; Renard
et al.
1987
; Pautot et al.
1987
). However, there remains an abundance of topo-
graphic and geologic data collected during the KAIKO project that have not been
fully evaluated.
The geology of subaerial exposures of accretionary complexes both on and
adjacent to the Honshu and Izu arcs has been well studied (Ogawa and Taniguchi
1988
; Geological Survey of Japan
1990
). Similarly, correlations among the suba-
erial and marine exposures of these complexes are well established (Geological
Survey of Japan
1990
; Ogawa et al.
2008
). Together, these geologic relationships
suggest that the NW-SE trending geologic units exposed on land on the Miura and
Boso peninsulas (Fig.
2
) can be extended from the Honshu arc subparallel to the
KkC
KuC
(Katsuura Basin)
Fig. 2
Bathymetric map of the area around the Sagami trough and Boso triple junction
(Hydrographic Department
1988
), showing the relation between the North America (
NAM
),
Philippine Sea (
PHS
), and Pacific (
PAC
) plates. Shaded and dotted areas indicate the present-day
depositional basins: from the northwest,
SB
(Sagami Basin),
MSTB
(Middle Sagami Trough
Basin),
NB
(Katsuura Basin), and
MF
(Mogi Fan in the Bando Deepsea Basin). Submarine troughs
and canyons are also shown:
SOT
(Soh-Oh Trough),
BC
(Boso Canyon),
KkC
(Katakai Canyon),
and
KuC
(Katsuura Canyon).
OBC
is the Okinoyama Bank Chain.
MP
and
BP
are the Miura and
Boso peninsulas, respectively (Modified from Ogawa et al.
1989
)
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