12.5 Backarc and Retroarc Basins
603
BACKARC AND MARGINAL BASINS, SW PACIFIC
210
286
VOLCANIC ASH
GRADED SILT AND CLAY
NANNOFOSSIL OOZE
CLAYEY SILT
OR SILTY CLAY
VOLCANOGENIC
SILT AND SAND
UNCONFORMITY
BASALT
a
a , aUATERNARY
P, PLIOCENE
M, MIOCENE
O, OLlGOCENE
E,EOCENE
Pa, PALEOCENE
Fig. 12.30. a Modem backare and small ocean basins
of the southwestem Pacific and results of the Deep
seeond teetonie and magrnatie phase in the middle Mioeene
led to differential, partly rapid subsidenee (pull-apart) in
some subbasins. Then, subsidenee and magrnatie aetivities
eeased, and finally the basin experieneed eompressional
uplift and deformation to the present-day borderland-style
topography.
The lower half of a 1000 m thiek Mioeene to Quatemary
hemipelagie sequenee (average sedimentation rate about 50
mlMa) eonsists of silieeous claystones and poreellanites
with minor proportions of ealcareous ooze and rhyolite
VOLCANOGENIC
CONGLOMERATE
CJ SMALL QCEAN BASIN
o 8IO
_
R~ANTARCS
= CONrt>ENTAL &
= OUASI-CONTIIENTAL CRUST
........... TRENCH
• 286 DsoP DRILL-HOLE LQCATIQN
o
100
200
300
400
500
m
203
Sea Drilling Project shown in simplified sections for
specific sites (numbers). (After Leitch 1984)
tuff. The organie earbon eontent of these sediments is
mostly around 1 %. The upper half of the seetion is dominated by diatom ooze with an upwardly inereasing proportion of clay and silty clay, including voleanie ash.
Okinawa Trough. This narrow baekare basin on eontinental erust is still in an early stage of evolution (~2Ma). It
developed sinee about 2 Ma between Japan and Taiwan
(Fig. 12.28) behind the Ryukyu island are (Sibuet et al.
1998). The water depth of the basin inereases from about
200 m in the north to 2300 m in the southwest. The basin is
603
BACKARC AND MARGINAL BASINS, SW PACIFIC
210
286
VOLCANIC ASH
GRADED SILT AND CLAY
NANNOFOSSIL OOZE
CLAYEY SILT
OR SILTY CLAY
VOLCANOGENIC
SILT AND SAND
UNCONFORMITY
BASALT
a
a , aUATERNARY
P, PLIOCENE
M, MIOCENE
O, OLlGOCENE
E,EOCENE
Pa, PALEOCENE
Fig. 12.30. a Modem backare and small ocean basins
of the southwestem Pacific and results of the Deep
seeond teetonie and magrnatie phase in the middle Mioeene
led to differential, partly rapid subsidenee (pull-apart) in
some subbasins. Then, subsidenee and magrnatie aetivities
eeased, and finally the basin experieneed eompressional
uplift and deformation to the present-day borderland-style
topography.
The lower half of a 1000 m thiek Mioeene to Quatemary
hemipelagie sequenee (average sedimentation rate about 50
mlMa) eonsists of silieeous claystones and poreellanites
with minor proportions of ealcareous ooze and rhyolite
VOLCANOGENIC
CONGLOMERATE
CJ SMALL QCEAN BASIN
o 8IO
_
R~ANTARCS
= CONrt>ENTAL &
= OUASI-CONTIIENTAL CRUST
........... TRENCH
• 286 DsoP DRILL-HOLE LQCATIQN
o
100
200
300
400
500
m
203
Sea Drilling Project shown in simplified sections for
specific sites (numbers). (After Leitch 1984)
tuff. The organie earbon eontent of these sediments is
mostly around 1 %. The upper half of the seetion is dominated by diatom ooze with an upwardly inereasing proportion of clay and silty clay, including voleanie ash.
Okinawa Trough. This narrow baekare basin on eontinental erust is still in an early stage of evolution (~2Ma). It
developed sinee about 2 Ma between Japan and Taiwan
(Fig. 12.28) behind the Ryukyu island are (Sibuet et al.
1998). The water depth of the basin inereases from about
200 m in the north to 2300 m in the southwest. The basin is